Tidal current energy is one of the competitive alternative energy resources. Vertical axis turbine is the technology to extract energy from tidal current with some unique advantages. As the energy efficiency of vertical axis turbine is still relatively low, a blade tip device named end-plate is studied to improve the turbine’s performance. The end-plate was intended to block the fluid from flowing across the tip and the shape of the end-plate was designed according to the influence area of the tip flow. The comparison of the turbine with and without end-plates was made by numerical and experimental methods. Good agreement was achieved, and the result showed that adding end-plates on the tip of the blade could increase the turbine’s output power. On the basis of the former study, two kinds of end-plate enhancement were presented as inward-half end-plates and outward-half end-plates. The numerical research showed that both inward-half end-plates and outward-half end-plates had better output than the original end-plates. The numerical results also indicated that the blade with outward-half end-plates had the minimum amplitude of the torque over one rotational cycle among the three kinds of end-plates, while the blade with inward-half end-plates had the maximum amplitude of the torque. To obtain better power output and prolong the service life of turbine, the outward-half end-plate is recommended.
This article proposes a nonlinear viscoelastic iceberg material model. A nonlinear Burgers’ model in which Kelvin and Maxwell units are strain rate- and stress-dependent is adopted for the iceberg material. The strain rate effect is considered in this model based on the experimental results. The stress of the iceberg model grows linearly (in log form) with increasing strain rate before reaching the transition strain rate, after which the stress remains rather constant. A damage function that reflects the microstructure changes and severe fractures in ice is adopted as the failure criterion. The iceberg model is implemented using implicit integration Crank–Nicolson method and is incorporated in the commercial software LS-DYNA by a user-defined material. Laboratory-scale experiments, creep experiments and constant strain rate experiments, and reality-scale experiment, iceberg–rigid steel plate collisions, are simulated to validate the proposed iceberg material model. Simulated time–strain curves are compared with the results of creep experiments. In the constant strain rate experiments, the strain–stress curves for brittle and ductile failure and ultimate triaxial strength of the ice model are analysed. Area–pressure curves and contact force–displacement relations are investigated for different impact speeds in iceberg–steel plate collisions. The contact force is also studied in view of the kinetic energy of icebergs. The numerical results show that the proposed iceberg material model yields reasonably good results.
There is an environmentally and economically motivated need to reduce the fuel consumption and air emissions of ships. To achieve a reduction in energy consumption, the energy flow in the entire energy system of a ship must be analysed in both the component, or subsystem, level as well as in a holistic way to capture the interactions between the components. Of the currently available energy consumption monitoring and prediction methods or models, no single model or method can be used to assess the energy efficiency of an arbitrary vessel in both the early design phase and during operation. This study presents a new generic ship energy systems model that can be used for this purpose. This new model has two parts: one for the assessment of a ship’s energy consumption based on an ordinary static power prediction and one for advanced operational analysis, considering hydrodynamic and machinery systems effects. A Panamax tanker vessel was used as the case study vessel to prove the versatility of the model for five example simulations for the design and operation of ships. The examples include variations of the main dimensions, propeller design, engine layout and the operational profile on a North Atlantic route. From the results, different areas with a potential for energy savings were identified.
Oscillations within a rectangular harbor of parabolic bottom induced by small-scale landslides are investigated numerically based on Boussinesq-type equations and the results are used to reveal the characteristics of the oscillations generated on this type of bottom profile. Relatively, local and small-scale landslides within the harbor may induce obvious transverse oscillations. The predominant transverse components are those with small mode numbers m and n when the solid slides start moving from the backwall. The augmentation of the velocity of the slides along the parabolic seafloor may shift the amplitudes of the oscillation components to larger values, which corresponds to the physical understandings of the waves generated by landslides. In comparing the oscillations induced by the slides of constant velocity and those accelerated by gravity force with bottom friction, it is observed that the movements accelerated by gravity force may facilitate the development of certain oscillation modes while those with constant velocity may be in favor of others. While the landslides may not act on an isolated point of the bottom but follow a certain trajectory along the harbor, the transverse oscillations induced by landslides are sensitive to their position of departure both in the cross-harbor direction and in the offshore direction. The numerical result of each transverse eigenfrequency is very close to the theoretical prediction and the spatial structure of each mode may also be well captured by the existing analytical solutions based on shallow water equations. Although longitudinal oscillations may not be steadily generated with landslide movements on a parabolic bottom within the harbor, some patterns of several low-mode ones occur and are also sensitive to the initial location and trajectory of the slides. Wavelet spectra are used to analyze their evolutions and comparisons are made with theoretical predictions.
Owing to new regulations starting from 2025, all commercial canal boats have to comply to zero local emission standards in Amsterdam. It is therefore vital that a clear emission indicator is made available for vessels with a varying operational profile, such as canal boats. In this paper, it is argued that current indicators, such as the Energy Efficiency Design Index, are not suitable for these (passenger) vessels. This paper proposes environmental performance indicators that can quantify emissions, (non-dimensional) energy and fuel usage based on an operational profile set in the design phase. This profile includes part load operation and auxiliary consumers and it can compare new designed concepts with current baseline vessels based on the ‘benefit for society’ of different vessel types. In the proposed environmental performance indicators, several operational modes can be defined, in contrast with the currently proposed Energy Efficiency Design Index, which is a point index at 75% of installed power. To gauge not only local emissions but also global emissions, the environmental performance indicator methodology is used to determine a minimum efficiency from any power generation method. This minimum efficiency follows from a comparison between baseline vessels and concepts that are more energy efficient and emission friendly. The proposed environmental performance indicators were validated using measurements on typical propulsion configurations of canal boats in Amsterdam. Three full electric concepts were designed and compared with the measured baseline vessels. As full electric concepts do not have local emissions, the method of power generation must satisfy the requirement to have less global emissions than the mechanical baseline. Furthermore, an energy efficiency of at least 33% is calculated from a fossil-fuelled land-based power plant (including transport) to the boundary from quay to boat to be required for newly designed electric concepts to be more energy efficient than the mechanical baseline.
The revised smooth particle hydrodynamics method based on the Riemann solution has been used to simulate the interaction process between waves and perforated caissons. In contrast to wave surfaces and opening boundaries of the flume under different wave conditions, the accuracy of the numerical wave flume is verified, and the numerical results are highly consistent with the linear regular wave theory. The reflection coefficient comparison between the values calculated from the smooth particle hydrodynamics method and the test data shows good agreement. The smooth particle hydrodynamics method adopted in this article can be employed to study the reflection coefficient of perforated caissons under conditions of non-overtopping, unbreaking waves. The effects of the related factors on the reflection coefficient are also investigated, including the relative dissipation chamber width B/L and the wave steepness H/L. The wave surface and velocity vector distribution of water particles surrounding the wave dissipation chamber are discussed, including the vortex flow and wave reflux caused by the wave dissipation chamber, which play a significant role in wave energy consumption. The results of this investigation can be used in the hydrodynamic design of perforated caissons and may provide a reference for offshore structural engineering structures.
Floating breakwaters are structures with large ratio of length to breadth. The profile of an floating breakwater is the key to the hydrodynamic properties of it. In this work, a new kind of an F-type floating breakwater is presented. Its profile is asymmetric and looks like the English letter "F." We present both numerical and experimental findings on this F-type floating breakwater. Based on linear potential-flow theory, first, the boundary-element method is presented to study the interaction problem of a two-dimensional floating body with waves. Following that, the two-dimensional experiments are conducted in a wave flume to measure the diffracted and radiated waves, the resulting transmission and reflection coefficients, and the motion responses of the F-type floating breakwater. It is shown that the experimental data are, in general, in good agreement with the numerical predictions. The transmission coefficients that are measured and calculated are under 0.5 when the ratio of B/ (the ratio of model breadth to wavelength), when the F-type floating breakwater is fixed, is larger than 0.18. The ratio of B/, when the F-type floating breakwater is allowed to slide vertically only, is larger than 0.2 and the ratio of B/, when the F-type floating breakwater is allowed to rotate and slide, is larger than 0.22. To understand how the profile geometry can affect the performance of the F-type floating breakwater, a parametric study of the F-type floating breakwater’s main dimensions, including its profile breadth, draft, and angle, is conducted on the wave transmission coefficient. It is found that the transmission coefficients are particularly sensitive to the change in draft for certain sea conditions. These results are important since seeking the optimal principal dimensions can ensure minimum volume of displacement, thereby using less material and reducing the cost of construction sharply.
This article focuses on the motion control of autonomous underwater vehicles in the ocean environment by a robust adaptive controller in which there is no regressor matrix. Due to the different atmospheric conditions in the ocean environment, the hydrodynamic coefficients of autonomous underwater vehicles cannot be exactly available and there are many uncertainties in the dynamic model. This prevents the traditional controllers to overcome these difficulties immediately. Hence, developing the adaptive controllers for the autonomous underwater vehicles encountered with uncertainties is required to provide appropriate performance. In the conventional adaptive control system, it is assumed that the autonomous underwater vehicle dynamic model can be linearly written into regressor form. Since the dynamics of the underwater vehicles is very complex, the derivation of the regressor matrix is very tedious. To overcome these problems, a regressor-free adaptive controller is proposed for the autonomous underwater vehicles in the general form of the equations of motion. In this approach, the controller is derived by the inverse dynamic method. Also, by utilizing known basis functions weighted by constant unknown coefficients, the uncertainties of the control law are estimated. The adaptation laws are derived based on Lyapunov stability theorem. The validity of the proposed method is verified by some simulation experiments. The simulation results show that the proposed approach can improve the robustness of adaptive controller to the dynamic model uncertainties and the external disturbance.
This article describes a series of model tests conducted to examine extreme wave events associated with tropical cyclonic conditions and their impacts on an offshore deck structure. Extreme waves of a representative cyclonic sea state were examined in a towing tank within long-crested irregular wave trains. Experimental results presented include global forces and localised slamming pressures acting on a rigidly mounted box-shaped deck, which represents a simplified topside structure of a tension leg platform. The effect of static set-down on the still-water air gap was investigated by applying an equivalent reduction for the deck clearance. It was found that a small reduction of 20 mm (2.5 m full scale) in the original deck clearance can lead to a doubling of the magnitude of the horizontal force and the vertical upward-directed force components, as well as significantly increased slamming pressures in many locations on the deck underside.
The existence of mass eccentricity will lead to the energy transfer between axial and flexural vibrations of a beam. To study the coupling properties of a double-Timoshenko beam system, a non-uniform coupled double-beam system is modeled in which the upper beam is typical and the lower beam is mass eccentric simulated by a non-uniform two-layer Timoshenko beam. By incorporating Hamilton’s principle and spectral element method, the axial–bending coupled governing equations of the system are derived and the approach can also be easily used to analyze the influences of the parameters and other coupled beam systems. Both the free and forced vibration results of a double-beam system by this method are consistent with the corresponding finite element model’s and thus this method is validated. The coupled properties and their mechanism are revealed. The influences of axial and transverse flexible connection on the coupling properties including free and forced vibration are investigated. A systematic matching principle of reducing the vibration of the coupled system is proposed.
A mobile satellite communication antenna is a device installed on a moving carrier for mobile satellite communication. Gimballed motorized pedestals are used to eliminate the effect of disturbance and maintain uninterrupted communication when the carrier is moving. Mobile satellite communication antennas are becoming increasingly more popular due many advantages of mobile satellite communication. In this paper, a three-axis ship-mounted antenna on a pedestal gimbal system is studied. We study the problem with a different perspective and method from the previous work for two-axis antenna pedestals. The former studies treat the subsystems to be isolated and design controllers separately, which neglect the coupling effects in the dynamics of two or three-axis antenna pedestal gimbals. We treat three sub-systems as a whole and derive the dynamic model of the system using the Newton–Euler method. Based on the dynamic model, linear PI controllers are designed to stabilize the antenna to keep its orientation towards the satellite. The design objective of the control system is to direct the on-board antenna toward a satellite and to keep its orientation unaltered despite the effect of sea waves disturbing the antenna. Simulation results are presented to show the stabilization performance of the system with the synthesized controllers.
Offshore wind power is more abundant and stronger than the onshore, and more and more research enthusiasms have been raised in recent years. However, there are still many issues in the utilization of the offshore wind power such as the cost of installations and maintenance and the ability to resist extreme weather conditions. In this article, an offshore hydraulic wind turbine generator with variable-diameter rotor is presented. The diameter of the rotor can be regulated according to the wind speeds to achieve the maximum power coefficient. The hydraulic energy working as the transmission medium can improve the output power quality. The high-speed gearbox is removed, and the generator is installed on the platform, which facilitates the installations and maintenance. Here, the power conversion principle of the wind turbine generator was introduced first. Then, the dynamics and performance of the wind turbine generator was obtained. The relationship between the diameter of the rotor and the wind speed was established according to the dynamics and the optimum tip-speed ratio. Relying on the specific parameters, the dynamic response was calculated in Simulink. The results show that the instantaneous output of the wind turbine generator is relatively stable. Based on the power recovery method, the test platform was built, and the efficiency of the energy conversion device was tested. The experimental results demonstrate that the efficiency of the energy conversion device can be 88%. Finally, the total efficiency of the offshore hydraulic wind turbine generator was predicted to be 33.7%.
Prediction of fuel consumption rate level of a vessel per voyage posed to be a challenge under uncertainties. In such uncertain conditions, revealing of fuel consumption rate levels of the fleet of vessels is deemed imperative to ensure effective and efficient operations of the vessels per voyage. Therefore, development of uncertainty treatment model is necessary in this research. A combined algorithm that is made up of fuzzy rule base and utility theory methods is incorporated in the investigation of the fuel consumption rate levels of marine vessels. The mechanism of the algorithm is used to capture and combine all the important parameters that determine the fuel consumption rate level of each marine vessel. The workability of the model is demonstrated. The produced results revealed that the combined algorithm can support estimation of the fuel consumption rate levels of marine vessels and show which vessel is better than the other. Based on the results of this article, the management and crew of a marine vessel are equipped with the necessary decision support tool to optimize, implement and manage improvements on the performance characteristics and fuel consumption rate of their marine vessels during voyages.
Liquefied natural gas–fuelled ships, beginning with small-sized ships produced in the 2000s to large merchant ships, are expected to show a rapid increase in number. According to Lloyd’s Register, liquefied natural gas shows great promise as fuel for new ships. In line with this trend, it is necessary to establish adequate infrastructure for liquefied natural gas fuelling systems. In the bunkering chain, bunkering shuttles retrieve fuel from the terminals to fuel liquefied natural gas–fuelled ships berthing at the ports. Many researches have dealt with the technical feasibility or the necessity of ship-to-ship bunkering considering the liquefied natural gas bunkering processes, but none has covered them at the same time. This study examines the liquefied natural gas ship-to-ship bunkering chain considering the technically feasible combinations of liquefied natural gas storage and boil off gas treatment system. The suggested method decomposes this large infrastructure problem into two steps, which are pre-processing to estimate port statistics and integer programming model. The model can represent any port as long as the port’s ship statistics and their data are provided. We select three major ports with high liquefied natural gas bunkering potential as case studies to verify the proposed model.
The phase jump, energy transfer, and the associated vortex shedding modes of a circular cylinder undergoing forced oscillation normal to the incoming uniform flow are investigated numerically at Reynolds number (Re) of 200. The dependence of the fluid forces on the non-dimensional oscillating amplitude A* = A/D [0.1, 0.6] and frequency f* = fe/fs [0.5, 2.0] is examined, where A is the oscillating amplitude, D is the cylinder diameter, fe is the cylinder oscillating frequency, and fs is the Strouhal frequency of fixed cylinder at the same Reynolds number, respectively. The lock-in region is identified by the combination of Fourier analysis and Lissajous phase diagram. The phase difference between displacement and lift fluctuation and the energy transfer between fluid and structure are discussed. Within the lock-in region, a jump in the phase difference is found to occur in the cases with A* = 0.5 and 0.55 without a wake mode transition. The numerical results reveal that the appearance of the phase jump is consistent with the reversal of the energy transfer direction. For the special cases of A* = 0.5 and 0.55, changes in the sign of energy transfer are observed, while no reversal of energy transfer is observed at other amplitudes. The energy transfer direction is either from fluid to cylinder when A* [0.1, 0.4] or from cylinder to fluid when A* ≥ 0.6. It is confirmed that the energy transfer between fluid and cylinder is not only dependent on cylinder oscillating frequency but also on cylinder oscillating amplitude.
In order to evaluate potential benefits of new green shipping concepts that utilize wind power as auxiliary propulsion in ships or of offshore wind energy harvest, it is essential to have reliable wind speed statistics. A new method to find parameters in the Weibull distribution is given. It can be used either at a fixed offshore position or along arbitrary ship routes. The method employs a spatio-temporal transformed Gaussian model for wind speed variability. The model was fitted to 10 years’ ERA-Interim reanalysis data of wind speed. The proposed method to derive Weibull distribution is validated using wind speeds measured on-board by vessels sailing in the North Atlantic and the west region of the Mediterranean Sea. For the westbound voyages in the North Atlantic, the proposed method gives a good approximation of the observed wind distribution along those ship routes. For the eastbound voyages, significant difference is found between the observed wind distribution and that approximated by the proposed method. The suspected reason is attributed to the ship routing decisions of masters and software. Hence, models that consider only the wind climate description need to be supplemented with a method to take into account the effect of wind-aware routing plan.
The arbitrary Lagrangian–Eulerian method is used to simulate solitary wave interacting with wave wall of a rubble mound breakwater. The Navier–Stokes equations in arbitrary Lagrangian–Eulerian description are solved using operator splitting technique. The penalty-based coupling method is introduced to analyze the coupling of structure and fluid. A piston-type wave maker generating the incident solitary wave is set up in the computational domain. In order to evaluate the numerical model’s performance, a set of experimental studies are carried out in a wave flume using solitary waves at a 1:25 scale. The accuracy of simulation of the solitary wave is verified by comparing with the theoretical value and testing data of the wave surface. Wave transformation, impact and overtopping on the breakwater are simulated in this numerical flume, and the time history of pressure on the wave wall is analyzed. The distributions of maximum impact pressure for solitary waves with different wave heights from the numerical simulations show a good agreement with the experimental results. Based on the dynamic response of the breakwater, the stress distribution and the deformation of the wave wall are discussed. The numerical model can be used as a complementary tool for the design of this kind of structures.
This article presents the experimental and numerical studies on the flow-induced vibration of propeller blades under periodic inflows. A total of two 7-bladed highly skewed model propellers of identical geometries but different elastic characteristics were operated in four-cycle and six-cycle inflows to study the blade vibratory strain response. A total of two kinds of wire mesh wake screens located 400 mm upstream of the propeller plane were used to generate four-cycle and six-cycle inflows. A laser Doppler velocimetry system located 100 mm downstream of the wake screen plane was used to measure the axial velocity distributions produced by the wake screens. Strain gauges were bonded onto the propeller blades in different positions. Data from strain gauges quantified vibratory strain amplitudes and excitation frequencies induced by the wake screens. The propellers were accelerated through the flexible propeller’s fundamental frequency to investigate the effect of resonance on vibratory strain response. The numerical work was conducted using large eddy simulation and moving mesh technique to predict the unsteady forces acting on the propeller blade when operating in a nonuniform inflow.
This article focuses on the navigational control of underwater mobile robot. Differential evolution approach has been used to navigate the underwater robot from source to destination while avoiding various types of obstacles. Differential evolution algorithm has been employed to find out the robot’s global best pose among a set of possible solutions based on the fitness value with respect to the current sensory data about obstacles and target. Such evolutionary computation scheme can provide desirable convergence, diversity and also robustness depending on proper selection and adaptive tuning of parameters. Self-learning ability of the parameters in the path planning algorithm is crucial to deal with nonlinearities and ambiguities of hydrodynamics as created by high-frequency oscillations during underwater motion. A sequence of intermediate positions chosen by proposed dynamic differential evolution algorithm between start and goal points can be defined as a near-optimum path for underwater robot. During navigation of the robot, the path smoothness and clearance from obstacles and computational time are also considered for performance evaluation of implemented algorithm. The feasibility of the proposed underwater motion planning approach has been authenticated through the simulation and experimental results.
To investigate the multidirectional wave run-up and forces on a large cylinder, a numerical model of multidirectional random wave loads on a large-scale cylinder is established based on the linear theory of wave interaction with a large-scale bottom-mounted vertical cylinder. The incident directional wave is specified using a discrete form of the Mitsuyasu-type spreading function. A wave basin experiment was carried out, and the numerical calculation results were verified by the results of the physical experiment. The results indicate that the wave directionality has significant effects on the distribution of the wave run-up around the cylinder. The transverse wave force occurs due to which the multidirectional waves at the two sides of the cylinder are totally different from each other at any time because of the wave directionality. Specially, for the multidirectional random wave with small directional spreading parameter (s = 5), the transverse force Fy is about 57% of the normal force Fx and cannot be neglected any more. Results can provide reference for the real engineering design.
Accurate and reliable numerical predictions of propeller performance are a fundamental aspect for any analysis and design of a modern propeller. Prediction of cavitation and of cavity extension is another important task, since cavitation is one of the crucial aspects that influences efficiency in addition to propagated noise and blade vibration and erosion. The validation of the numerical tools that support the design process, including open-source codes, is, consequently, essential. The public availability of measurements and observations which cover not only usual thrust and torque in open water conditions (including cavitation) but also unsteady functioning with pressure pulse measurements in the case of the Potsdam Propeller Test Case certainly represents an extremely useful source of information and an excellent chance for verification and validation purposes. In the present work, the prediction of the Potsdam Propeller Test Case propeller performance using the OpenFOAM computational fluid dynamics package is proposed. After a preliminary validation and calibration of the OpenFOAM native Schnerr–Sauer interphase mass transfer model for cavitating flow, based on the experimental results on a 2D NACA66Mod hydrofoil, open water propeller performance and cavitation predictions are carried out. The OpenFOAM results are finally compared both with the available experimental measurements and with calculations carried out with StarCCM+ and with a proprietary boundary element method code, in order to assess the accuracy and the overall capabilities of the open-source tools (from meshing to post-processing) available in the OpenFOAM package. The comparison, in addition to assessing the accuracy of the open-source approach, is aimed to verify its advantages and drawbacks with respect to widely used solvers and to further verify the reliability of traditional boundary element method approaches that are still widely adopted for design and optimization (thanks to their extremely higher computational efficiency) in a very demanding test case.
This article addresses the main requirements and the process of creating the geometry of ship models that fulfil the highly demanding request for realism and performance of the virtual environments currently used in modern ship bridge simulators. It starts with a classification of the ships based on their role in the simulation and on the type of simulator used, and defines the main characteristics of the models. It also discusses the importance of a well-defined workflow and its impact on the modelling time and on the quality of the final product. The article provides contributions in the following areas: identification of the main requirements of polygonal models of ships for ship simulators; effective workflow for ship three-dimensional modelling and identification of most suitable modelling techniques for efficient creation of ship models. The study is supported by real examples of three-dimensional modelling of ships with different sizes and characteristics currently used by the ship manoeuvring simulator in the Centre for Marine Technology and Ocean Engineering of the University of Lisbon.
The effect of different bow shapes on the added resistance in waves was observed through a series of model tests. To this end, three different hull forms of KRISO Very Large Crude Carrier 2 were considered: an original hull form and two modified hulls with different bow shapes, called ax-bow and leadge-bow. The model tests were conducted for a wide range of wavelengths with two wave amplitudes in a regular head-sea condition at the design speed. Each test condition was imposed at least twice in order to check the repeatability of measurement, considering the uncertainties in model test and the nonlinear nature of the added resistance. This article introduces a preliminary study on the effects of surge motion, amplitude of incident wave, and green-water allowance around bow region. This article briefly includes the uncertainty analysis of recent study regarding the performance of the original hull. Based on the results of the experimental study for three different bow shapes, the parameters which influence the added resistance and motion responses are discussed.
The development of large medium-speed catamarans aims increasing economic viability and reducing the possible negative influence on the environment of fast sea transportation. These vessels are likely to operate at hump speed where wave-making can be the dominating component of the total resistance. Shallow water may considerably amplify the wave-making and hence the overall drag force. Computational fluid dynamics is used to predict the drag force of medium-speed catamarans at model and full scale in infinite and restricted water to study the impact on the resistance. Steady and unsteady shallow-water effects that occur in model testing or full-scale operation are taken into account using computational fluid dynamics as they are inherently included in the mathematical formulations. Unsteady effects in the ship-model response were recorded in model test experiments, computational fluid dynamics simulations and full-scale measurements and found to agree with each other. For a medium-speed catamaran in water that is restricted in width and depth, it was found that computational fluid dynamics is capable of accurately predicting the drag with a maximum deviation of no more than 6% when compared to experimental results in model scale. The influences of restricted depth and width were studied using computational fluid dynamics where steady finite width effects in shallow water and finite depth effects at finite width were quantified. Full-scale drag from computational fluid dynamics predictions in shallow water (h/L = 0.12 – 0.17) was found to be between full-scale measurements and extrapolated model test results. Finally, it is shown that current extrapolation procedures for shallow-water model tests over-estimate residuary resistance by up to 12% and underestimate frictional forces by up to 35% when compared to validated computational fluid dynamics results. This study concludes that computational fluid dynamics is a versatile tool to predict the full-scale ship resistance to a more accurate extent than extrapolation model test data and can also be utilised to estimate model sizes that keep finite-water effects to an agreed minimum.
Submarines have a safety operating envelope, the boundary of which is closely related to structural limits and the safety of crew. An envelope protection system guarantees that the submarine does not exceed the boundary, which reduces the frequency of operational accidents and mission time. In this article, an envelope protection system for the pitch angle is designed for a submarine. The envelope protection system consists of limit detection and limit avoidance. Limit detection is designed using a dynamic trim algorithm, and command limiting is used for the limit avoidance. An artificial neural network is adopted for on-line learning and modeling uncertainty compensation, and a linear quadratic regulator is employed to stabilize the error dynamics. A submarine maneuvering simulation program developed from the experimental data is used to validate the designed envelope protection system. The simulation results show the effectiveness of the envelope protection system.
Determination of high-speed crafts’ hydrodynamic coefficients will help to analyze the dynamics of these kinds of vessels and the factors affecting their dynamic stabilities. Also, it can be useful and effective in controlling the vessel instabilities. The main purpose of this study is to determine the coefficients of longitudinal motions of a planing catamaran with and without a hydrofoil using Reynolds-averaged Navier–Stokes method to evaluate the foil effects on them. Determination of hydrodynamic coefficients by experimental approach is costly and requires meticulous laboratory equipment; therefore, utilizing the numerical methods and developing a virtual laboratory seem highly efficient. In this study, the numerical results for hydrodynamic coefficients of a high-speed craft are verified against Troesch’s experimental results. In the following, after determination of hydrodynamic coefficients of a planing catamaran with and without foil, the foil effects on its hydrodynamic coefficients are evaluated. The results indicate that most of the coefficients are frequency-independent especially at high frequencies.
Based on the fact that jet formed in outer gill of sharks can reduce the wall friction during the breath process, a bionic jet surface model was established. The numerical simulations were carried out using shear stress transport k– model, and the simulation results accorded with that of experiments. First, in the case of fixed flow-velocity ratio, the drag reduction performance would be better with the smaller jet’s angle, and the impact that the angle has on the drag reduction would be greater with the increase in jet hole’s aperture. Second, in the case of fixed jet’s angle, the drag reduction had a nearly linear relationship with flow–velocity ratio. Namely, the drag reduction would be better as the flow–velocity ratio increased, and the larger the jet hole’s aperture, the better the drag reduction. In addition, compared with the case of smoothing surface, the flow structure in turbulent boundary layer was changed by jet, increasing the thickness of viscous bottom layer and decreasing the gradient of normal velocity perpendicular to wall. Finally, the drag reduction mechanism was proposed based on the increased velocity effect of turbulent core, isolation effect of wall and the increased turbulent damping effect.
Battle damage survivability is the prime design criterion of naval ships. Composites and hybrid structures such as polymer coating attract much attention to increase the ship survivability. Aiming to develop the parameter optimization design of the coating and to assess the underwater explosion shock environment and the blast-resistant effect of polymer coating efficiently, an approximate numerical method was performed in this preliminary study. An equivalent continuum model based on the homogenization theory was introduced to simulate the dynamic behavior of the coating. The test data of full-scale underwater explosion tests and the numerical simulation results were investigated. The blast-resistant property of the polymer coating was elaborated. The core strength had an important influence on the ship dynamic response: under low-intensity underwater explosion shock load, "soft" core had greater blast-resistant effect than the other ones, while under high-intensity underwater explosion shock load, "ordinary" core and "hard" core had better blast-resistant effect than the "soft" core.
Coiled tubing can be used for steel catenary riser pigging operations to remove wax and other debris attached on the interior of steel catenary riser to recover production and ensure safety. Due to its low rigidity, coiled tubing would deform which might finally damage coiled tubing and steel catenary riser. Thus, in order to ensure safety and reliability of the operation, this article proceeded experimental study on the axial load transfer behavior of a coiled tubing stuck in a steel catenary riser when the coiled tubing has not yet helical buckled. According to the experimental results, the inner pipe’s axial force transfer efficiency is always less than 1; the outer pipe of "unfixed steel catenary riser boundary" would elongate forced by the inner pipe within it, which makes the injected displacement of inner pipe within outer pipe of "unfixed steel catenary riser boundary" bigger than the injected displacement of inner pipe within outer pipe of "fixed steel catenary riser boundary" system at the same force-out; before the inner pipe helical buckles, inner pipe’s force transfer efficiency for unfixed and fixed system can be considered as the same. The research done above might provide important theoretical supports for the steel catenary riser pigging operation.
This article presents a simple mathematical model for predicting the running attitude of warped planing boats fixed in a heel angle and free to trim and sinkage. The proposed model is based on asymmetric 2D+T theory utilizing a pressure equation which is previously introduced in the literature to compute the hydrodynamic force acting on a heeled planing hull. Integration of pressure distribution on the asymmetric wedge sections enables the suggested model to compute trim angle, center of gravity rise, resistance, and heeling moment acting on the heeled planing boat in calm water. The hydrostatic force in addition to two drag forces acting on the pressure area and spray area are also taken into account. Finally, a computational algorithm is introduced to find the running attitude of the heeled planing boats. The validity of the proposed model is examined by comparing the obtained running attitudes for two planing hulls series with zero heel angle and computed lift force and heeling moment of a heeled planing boat against available experimental data. Based on the comparisons, favorable accuracy is observed for both symmetrical and asymmetrical conditions. Moreover, it is shown that existence of a heel angle can lead to a decrease in trim angle and resistance, while it intensifies the center of gravity rise of planing boats. It is also observed that as the beam Froude number increases, the heeling moment of the heeled boat reduces.
An efficient method for restraining the large vibration displacements and loads of offshore floating wind turbines under harsh marine environment is proposed by putting tuned mass dampers in the cabin. A dynamics model for a barge-type offshore floating wind turbine with a fore–aft tuned mass damper is established based on Lagrange’s equations; the nonlinear least squares Levenberg–Marquardt algorithm is employed to identify the parameters of the wind turbine; different parameter optimization methods are adopted to optimize tuned mass damper parameters by considering the standard deviation of the tower top longitudinal displacement as the objective function. Aiming at five typical combined wind and wave load cases under normal running state of the wind turbine, the dynamic responses of the wind turbine with/without tuned mass damper are simulated and the suppression effect of the tuned mass damper is investigated over the wide range of load cases. The results show that when the wind turbine vibrates in the state of damped free vibration, the standard deviation of the tower top longitudinal displacement is decreased approximately 60% in 100 s by the optimized tuned mass damper with the optimum tuned mass damper mass ratio 1.8%. The standard deviation suppression rates of the longitudinal displacements and loads in the tower and blades increase with the tuned mass damper mass ratio when the wind turbine vibrates under the combined wind and wave load cases. When the mass ratio changes from 0.5% to 2%, the maximum suppression rates vary from 20% to 50% correspondingly, which effectively reduce vibration responses of the offshore floating wind turbine. The results of this article preliminarily verify the feasibilities of using a tuned mass damper for restraining vibration of the barge-type offshore floating wind turbine.
Greenhouse gas emission and subsequent global warming have attracted more and more attention all over the world. As one of the biggest emission sources, shipping industry is suffering great emission reduction pressure from the public. Although shipping industry can improve the energy efficiency by exploring new strategies to reduce the fuel cost and the emission to air, some deficiencies may be discovered in practice due to lack of a comprehensive consideration of other significant factors, such as safety factors. Therefore, energy efficiency management strategies that consider both safety and economy factors have more practical significance for enhancing the ship energy efficiency. In this article, a power supply model considering economy, emission reduction and safety was established, and a multi-objective optimization problem to keep the system working at a high safety level, a low CO2 emission and a moderate fuel consumption was proposed. Furthermore, the particle swarm optimization algorithm was adopted to solve the multi-objective optimization problem, and the obtained non-inferior solutions could help officers on duty to select the optimum main engine speed by weighing the economy and the safety of the ship. The results show that the proposed method of energy efficiency management could reduce the greenhouse gas emission and the energy efficiency operation index (EEOI) of the ship effectively. The trade-off between ship economy, emission and robustness of the power supply system was studied, which is meaningful to the energy efficiency improvement and the CO2 emission reduction under the safety requirement of power supply.
Multi-bridge waterways of river can cause the navigational bottleneck phenomenon because of the decreased passing efficiency and the increased ship risk. The navigational capacity calculation not only makes benefits to deck officers in operating safely and efficiently but also assists supervisors in the maritime traffic organizing. An agent-based simulation is proposed to evaluate the navigational capacity of multi-bridge waterways in Wuhan. Automatic Identification System data are collected to characterize the maritime traffic of multi-bridge waterways. The Monte Carlo methods are used to generate agents, while the needed random numbers in terms of ship type, length, width, speed over ground and arrival time are generated according to the estimated parameters. Seven behaviour strategies of the agent are made based on the real operation requirements of multi-bridge waterways. The proposed agent-based simulation is validated by the real sectional maritime traffic volume data. Simulation results show that, under the current navigational conditions, the navigational capacity of the investigated multi-bridge waterways in middle season is approximately 1512 ships (597 upstream ships and 915 downstream ships) per day. In addition, the increase in speed over ground can improve the navigational capacity and facilitate the capacity utilization.
Hydrodynamic stress induced by marine currents subject subsea pipelines to failure vulnerability. Therefore, several methods have been established to protect such pipelines from hydrodynamic forces. The objective of this work is to investigate the performance of two different protection methods using computational fluid dynamics. A second-order accurate upwind finite volume computational fluid dynamics model was used to simulate isotropic turbulent flow around a subsea pipeline located on flat seabed. A comparison between four turbulence models revealed that both Menter’s shear stress transport k
In this article, the assumed mode method is applied to simplified dynamic analysis of stepped thickness rectangular Mindlin plates and stiffened panels with arbitrary boundary conditions. The natural and frequency responses of stepped thickness plate structures subjected to harmonic point excitation force and enforced acceleration at boundaries, respectively, are considered. Potential and kinetic energies of the system are formulated and used to derive eigenvalue problem utilizing Lagrange’s equation of motion, and mode superposition method is further used for forced response assessment. Characteristic orthogonal polynomials having the property of Timoshenko beam functions are used for the assumed modes. Numerical examples analysing vibration of stepped thickness plate structures with different topologies and various sets of boundary conditions are provided. Numerical results are compared with the results from the relevant literature and finite element solutions obtained by a general finite element tool, and a very good agreement is achieved. Hence, it is expected that stepped rectangular plate structures satisfying the prescribed criteria regarding natural and frequency responses can be efficiently designed based on the proposed method.
Fault tree analysis is a known methodology used for analysing engineering systems. The approach is usually conducted using known failure data. Given that most maritime operations are conducted in a challenging and uncertain environment, their failure data are usually unavailable requiring a flexible and yet robust algorithm for the analysis of the systems. This research therefore seeks to analyse hazards of ships during ship and port interface operations as a result of manoeuvring by incorporating fuzzy fault tree analysis method to optimise the performance effectiveness of the system. Fuzzy set theory provides the needed flexibility to represent vague information from the analysis process. The methodology is structured in such a manner that diverse sets of data can be integrated and synthesised for analysing the system. It is envisaged that the proposed method could avail safety specialist with a simple and a step-by-step framework for evaluating maritime hazards in seaport operations in a concise way.
Recent ship damages underline the importance of an accurate intact and damage stability analysis. The stability of ships is presently determined by applying quasi-static methods, neglecting dynamic effects; for flooding scenarios, flow calculations are not carried out either. In general, for damage cases, water dynamics inside the compartment affect ship motions. It has been observed that some kind of vessels could experience large roll motions due to the sudden water ingress after damage. In this article, a non-linear tool for damage stability evaluation is presented, including water dynamics in a flooded compartment. In particular the transient stage of flooding is investigated. The flooded water has been treated using the lumped mass approach. A new method has been developed and applied in this article in order to model the water motions: the freesurface is assumed to be no more horizontal but dependent on ship and flooded water accelerations. The developed method is intended to be an intermediate approach between the quasi-static method (uncoupled) and fully coupled method. In coupling the flooded water motions with ship motions, no more unknowns are introduced: only ship lateral acceleration is used to determine the freesurface inclination of the flooded water. A valuation is carried out, comparing the numerical result from the simulations with the experimental studies on a barge model. Additional applications are carried out on the free roll motion of the TNK tanker model.
This article considers key theoretical and practical issues that arise in the robust control synthesis for dynamic positioning. A dynamically positioned vessel maintains its position (fixed location or predetermined track) by means of active thrusters and propellers. The concise kinematics and vessel dynamics are presented using three degrees of freedom model for describing the horizontal motions. Then, the mixed H and µ-synthesis framework has been employed to deal with perturbed model under external disturbances as well as measurement noises. To avoid excessive control energy for dynamic positioning system, the high frequency waves have been filtered using simple weighting functions. Using optimal Hankel-norm model approximation, the resulting full-order controller has been significantly reduced to make it easy to implement the practical works. Next, the simulation results in both frequency and time domains are presented to demonstrate the effectiveness of the robust control algorithms using the appropriate weighting functions. Finally, it is found that the proposed dynamic positioning system provides good maneuverability and robustness over a wide range of operating conditions, even under parametric variations and sea disturbances with sensor noises.
The recovery of high temperature thermal energy released by propulsion engines in order to cover thermal loads is commonplace in contemporary ships. However, the medium- and low-temperature thermal energy is only partially exploited or not exploited at all. In the present work, an organic Rankine cycle system driving an electric generator is considered, in addition to the exhaust gas boiler, in order to recover available heat and produce electrical energy. The specifications of the system are determined by an optimization procedure taking economic criteria into consideration, apart from the technical criteria usually used in this kind of studies. More specifically, with the net present value as the objective function and by application of optimization algorithms, the optimal synthesis, design and operation of the organic Rankine cycle system are determined. For the particular vessel considered, the installation of the organic Rankine cycle is technically feasible and economically profitable, with a dynamic payback period of 4 years. The solution of the optimization problem is supplemented with a sensitivity analysis with respect to important parameters.
This article discusses the optimum hydrodynamic shape of the submarine stern based on the minimum resistance. Submarines consist of two major categories of hydrodynamic shape: the teardrop shape and the cylindrical middle-body shape. Due to the parallel middle-body shape in most of the naval submarines, those with cylindrical middle-body are studied here. The bare hull has three main parts: bow, cylinder and stern. This article proposes an optimum stern shape by the computational fluid dynamics method via Flow Vision software. In the hydrodynamic design point of view, the major parameters of the stern included the wake field (variation in fluid velocity) and resistance. The focus of this article is on the resistance at fully submerged mode without any regard for free surface effects. First, all the available equations for the stern shape of submarine are presented. Second, a computational fluid dynamics analysis has been performed according to the shape equations. For all the status, the following parameters are assumed to be constant: velocity, dimensions of domain, diameter, bow shape and total length (bow, middle and stern length).
This article describes the evaluation of the wave profile of submarine at surface condition and deck flooding which occurred by the wave making pattern at the bow. Movement of ships and submarines on the free surface of calm water creates the surface wave. Because of the difference in the bow shape and freeboard height, the wave making system in ships and submarines is different. Rounded or elliptical bow shape of submarines generates a high bow wave which causes deck and bow wetness. This is because of the fact that in submarines, this situation arises a small freeboard. In submarines, Deck wetness (because of deck flooding) is a very important subject that has some remarkable consequences, such as increase in resistance and added weigh. The focus of this article is on the added frictional resistance in the deck wetness condition. The bow wave profile, deck wetness and added resistance are studied in several Froude numbers by computational fluid dynamics method. This analysis is performed for a bare hull model at two different drafts by Flow Vision (V.2.3) software based on computational fluid dynamics method and solving the Reynolds-averaged Navier–Stokes equations.
This article examines the characteristics of transient voltage in long-distance cables in the subsea environment. The effects of changes in temperature and pressure (caused by changes in the ocean depth) on the transient voltage in cables were quantitatively analyzed. To interpret the characteristics of transient voltage, the transmission line was equalized as a -type circuit, and the effects of inductance, resistance, and capacitance (L, R, and C) according to the changes in temperature and pressure were mathematically modeled. Thus, we confirmed that the effect of temperature on transient voltage generated in cables is approximately 10-fold greater than the effect of pressure. Furthermore, using a fast Fourier transform analysis, we verified that the rate of change in the conducted noise caused by transient voltage generation is 0.001 dB/°C. Thus, through this study, we were able to quantitatively identify the effects of the subsea environment on conducted noise generation in cables.
The development of multi-country consolidation services has become a major feasible direction for major ocean freight forwarding firms in Taiwan. However, ocean freight forwarding firms must ponder which factors are most important when considering with the development of multi-country consolidation services. Therefore, the main purpose of this article was to apply the fuzzy analytic hierarchy process method to evaluate the key factors influencing the development of multi-country consolidation services for ocean freight forwarding firms in Taiwan. Based on the literature and experts’ opinions, a hierarchical structure with 4 assessment aspects and 16 assessment factors was first constructed, and the steps of fuzzy analytic hierarchy process method then proposed. Finally, based on the analytic hierarchy process experts’ questionnaires, we used the fuzzy analytic hierarchy process method to evaluate the key factors. The results showed that (1) "cost" is the most important aspect influencing the development of multi-country consolidation services for ocean freight forwarding firms in Taiwan; (2) in order of relative importance, the top eight key factors influencing the development of multi-country consolidation services for ocean freight forwarding firms in Taiwan are "cargo accuracy and tracking management,""consolidation cost,""deregulation of operations,""transport cost,""integrated logistics information management,""high frequency of ship sailings,""logistics-related operating costs," and "convenience of customs clearance," respectively. Furthermore, some discussions and recommendations concerning practical implications are provided for ocean freight forwarding firms operating in the multi-country consolidation market.
This article presents a procedure for how to relate fire performance of fibre-reinforced polymer composite structures to the fire safety regulations in Safety of Life at Sea II-2. It can be used as basis when performing a fire risk assessment to demonstrate that the degree of safety is at least equivalent to that provided by prescriptive requirements. A key issue is that requirements and test methods are based on the use of steel structures, which requires seeking the safety level implied by the regulations. This was demonstrated for the regulations and introduced hazards affecting the growth stage of a fire. The safety implied by regulations was related to fire performance of fibre-reinforced polymer composite by reference to fire tests involving typical materials and some relevant safety measures. Ignition was described as uncritical, while the fire growth on a fibre-reinforced polymer composite surface can be rapid. Flammability requirements are generally not achieved by an untreated panel but different means can be used for protection. A fire protective coating can be used to prevent ignition, and sprinkler is effective for both fire prevention and extinguishment on interior and external surfaces. For interior spaces, it can be relevant with a coating or thermal insulation also to hinder increased generation of smoke and toxic gases during fire evacuation. In all, it is shown that fire hazards during the fire growth stage are manageable, and a foundation is lain out for a well-structured fire risk assessment.
Circular plates with openings are used in many engineering structures, especially as swash bulkheads in cargo tanks of liquefied gas carriers. In this article, an approximate procedure is worked out for the vibration analysis of circular plates with different boundary conditions and a different number and size of openings with an arbitrary arrangement within the plate area. The assumed mode method, recently used in the vibration analysis of rectangular plates, is applied in this case. Following the basic idea, the effect of the openings is accounted for by subtracting the potential and kinetic energy of the cut-out plate parts corresponding to the total plate energies without openings. The procedure is illustrated with numerical examples related to the vibration analysis of annular plates and circular plates with openings. The results are evaluated through their comparison with an analytical and finite element method solution.
A good ship traffic scheduling mode can enhance traffic efficiency to a large degree, especially in restricted waterways such as approach channel of ports and straits. A ship scheduling model for restricted two-way waterways is proposed in this article. The assumption is made in the model that two-way transportation is not allowed for cases in which there is at least one large ship. Based on this assumption, a mathematical model is proposed to minimize the weighted average of the mean and the maximum waiting time given several safety restrictions. A sequential scheduling algorithm is proposed to solve such problem, in which the ships are divided into rounds. The ships in each round are scheduled simultaneously to enhance traffic efficiency by the trade-off between the priorities of small and large ships. Experiments are carried out by comparing sequential scheduling method with first-come-first-serve model. The results indicate that the proposed algorithm can reduce ships’ waiting time, whereas a lot of ships need to wait for long time with first come first serve. The distinctions are more evident with a higher proportion of large ships, and the proposed algorithm can keep ships’ waiting time to an acceptable level.
This article examines the distribution characteristics of the navigational environment in the Yangtze River trunk line using several information collection sensors installed on ships that navigate in this line. Through experiments on these ships, data of energy consumption and the navigational environment are collected. Water flow and waterway depth are proved to be the main influencing factors on the ship energy consumption via Spearman’s correlation analysis. Next, data of water velocity and waterway depth that cover the entire trunk line are graded using the k-means clustering algorithm. To build an evaluation matrix of navigational environment, the frequency distribution of each grade in different Yangtze River legs is counted statistically, and on this basis, similar legs are clustered using the hierarchical clustering algorithm. In this way, the waterway partition in the Yangtze River trunk line is completed. Furthermore, the distribution of the energy consumption of ships in different legs is also calculated. The study results indicate that not only the navigational environment of the Yangtze River trunk line but also the energy consumption level of ships have distinctive regional differences. Finally, the laws of the Yangtze River navigational environment are analyzed, and the corresponding energy-saving navigation strategies are proposed, which are useful for crews to operate their ships in energy-efficient and safe conditions.
This study proposes alternative formulations of the ship-specific correction factor (fjRoRo) pertaining to Ro-Ro cargo and Ro-Ro passenger ships, as defined in the Energy Efficiency Design Index equation according to the International Maritime Organization Resolution MEPC 245(66). The alternative formulations were derived by studying a large sample of Ro-Ro cargo ships and Ro-Ro passenger ships, built between the years 1990 and 2012. The estimation of ships’ resistance and powering was conducted by application of Holtrop’s method. The obtained formulae’s exponent values were compared with the corresponding ones from latest International Maritime Organization studies on Energy Efficiency Design Index and they appear to better represent the energy efficiency and environmental impact of the operating fleet of Ro-Ro cargo and Ro-Ro passenger ships. Derived formulae may also be used in the frame of parametric design optimization of Ro-Ro ships.
The revised smoothed particle hydrodynamics method based on Riemann solution has been used to calculate the total horizontal wave force acting on a perforated caisson with a top cover. The interaction process between the wave and perforated caisson is simulated in a two-dimensional numerical wave flume which is verified by linear regular wave theory, water particles flowing in or out of the dissipation chamber are also described in this article, including the distribution of velocity vector. The effect of main non-linear influence factor on total horizontal force is examined here; wave pressure distribution along the height of the perforated caisson in front, inner side or the rear wall of the dissipation chamber is also presented in order to exhibit the more practical performance of perforated caisson with a top cover. The relationship between the total horizontal force and top cover height is anglicized, and the influence of top cover height on components of the total horizontal force is discussed here. A comparison between the numerical total horizontal force results and values tested from the test data is finished; it can be seen that the numerical results agree well with the test data. It is concluded that the smoothed particle hydrodynamics method described in this article can be utilized to calculate the total horizontal force on a perforated caisson with a top cover.
In this article, the concept of properly selecting the number and rated power of all the generators of a ship is discussed, analyzed and investigated. The novelty introduced is that this selection must start from efficiently covering the power demands in port, the most sensitive area for greener shipping. Following this novel concept in sizing the electric power plant of a significant number of ship case studies, it is shown that the resultant electric power plant can be less heavy, less spacey than if the conventional selection methods are used. Furthermore, the discussion is enriched with the beneficial impact of the presented methodology upon the overall ship efficiency in terms of fuel consumption and pollutant emissions.
Prediction of the roll motion is considered as an important problem in planing hull motion, since safety of the craft highly depends on it at high speeds. Accordingly, the main aim of the present study is to analyze this motion in time domain and estimate its amplitude at various frequencies. In many of the earlier works performed for predicting the motion of planing hulls, the 2d + t theory has been used. However, in all of these studies, water entry phenomenon was modeled without considering the asymmetric condition. In order to overcome this problem, a mathematical model is hereby proposed for prediction of the roll motion which is derived by applying an analytical model of the water entry in which asymmetric condition is taken into account. The suggested method may be used for the warped planing boats. Validity of the model is examined by comparing the obtained results against different experimental results. Another objective of the present study is to examine the effects of deadrise angle, longitudinal center of the gravity and the hullform on the amplitude of motion and hull response. The response is investigated at different conditions: (1) sinusoidal exciting moment, (2) a fixed existing moment and (3) an initial roll angle without any exciting moment. The proposed model is also used to evaluate the horizontal forces and moments acting on the hull during the roll motion.
Stepped planning hulls are commonly used on fast planning boats and water-based aircraft, but numerical means for simulating their hydrodynamics are rather limited. In this study, a panel method involving hydrodynamic sources has been applied for modeling a stepped planning hull and accounting for water surface deformations in the air-ventilated cavity and surrounding water domain. Parametric calculations have been carried out for a selected hull with variable deadrise angles and at two speed regimes. Results are shown for the boat attitude, lift–drag ratio, and drag components. The variations of the wetted surfaces on two bodies of a stepped hull are also presented and related to variations in hydrodynamic characteristics of the hull.
Gearboxes are a necessary part of almost any propulsion train and their percentual losses are usually assumed to be small and constant. However, in low-load and part-load conditions, gearbox losses may be significant. With the current trend of slow steaming, the performance of gearboxes is once again in focus. In order to estimate the performance of maritime gearboxes, an evaluation of losses was done using a thermal network. The analysis was done for a standard double-input single-output maritime gearbox and over the entire range of torque and revolutions per minute. Results indicate that the transmission losses are not negligible in low-load condition; in fact they may as high as 10% of delivered power. Further results show that the maximum temperature in the teeth contact can reach 70 °C but this might be an overestimate. Finally, using the investigated thermal network models, a simplified model of transmission losses is proposed together with the fit coefficients for the torque and revolutions per minute.
The traction force or bollard pull and specific function of a tugboat determine the size of its towing gear and deck fittings. These dimensions must enable the tug to carry out a manoeuvre safely. This article considers proposals made in the implementing regulations for calculating the length and diameter of the towline. It analyses the possibility of using high-modulus polyethylene fibre and the way it would affect the design of the towing gear and deck fittings, including the fairleads and bits. It would be useful if regulations provided further guidance on towline length for port tugs. The final part of this study analyses the solutions informed by a sample of 51 port tugs, the majority of which are escort tugs.
The aim of this work is to describe the development of an innovative cleaning tool for underwater applications, to be used in particular in the field of underwater archaeology. This work takes place in the framework of the EU FP7–funded ARROWS project. ARROWS adapts and develops low-cost autonomous underwater vehicle technologies to significantly reduce the costs of underwater archaeological operations, covering the full extent of archaeological campaigns. The project deals with underwater mapping, diagnosis and cleaning tasks. During the first half of the project, a cleaning tool prototype, able to be mounted on underwater vehicles, has been worked out: this cleaning tool will be exploited not only during research missions but also for the periodic monitoring, controlling and maintenance activities of well-known underwater archaeological sites (e.g. periodic cleaning operations).
Remotely operated underwater vehicles are mobile robots increasingly used in underwater applications; these devices are widely used and suitable for different scenarios, for example, for patrolling and monitoring and also for underwater interventions. In the last 30 years, the remotely operated underwater vehicles have become more and more advanced; at the same rate with the progressive technological development of these vehicles, the market of the specialized component industry is fast-increasing. Generally speaking, a remotely operated underwater vehicle allows to investigate areas inaccessible or too dangerous for human beings. The use of remotely operated underwater vehicles during a mission, with the related implication of support ships and specialized pilots, or the involvement of professional divers, is usually associated with high costs. The reduction of these costs is an important topic in the underwater robotic field and the easy piloting of these mobile robots is a crucial aspect in their development. This article describes Nemo remotely operated underwater vehicle, a remotely operated underwater vehicle prototype specifically designed for the exploration of the Costa Concordia wreck, Isola del Giglio, Italy. Nemo remotely operated underwater vehicle can be considered a mini-remotely operated underwater vehicle, that is, a remotely operated underwater vehicle with weight less than 25 kg and easily deployable from a small boat. This article describes the main characteristics of the vehicle: the onboard control logic and on the development of a user-friendly graphical user interface for underwater navigation able to take advantage of its high maneuverability. It is worth to note that the developed graphical user interface enables to operate the vehicle even to inexperienced pilots. Preliminary experimental data collected during navigation are provided.
This article proposes a vision-based target motion analysis and collision avoidance method for unmanned surface vehicles. To estimate the relative position of the target, the calibrated camera model and camera height constraint are used. In addition, the optical flow equation is adopted to estimate the relative velocity of the target. The estimated relative position and velocity are then integrated using the Kalman filter in order to reduce the effect of measurement noise. Once the kinematic information of the target is determined by the vision-based target motion analysis, the collision risk is calculated by a fuzzy estimator. Based on the collision risk, vision-based collision avoidance control is performed. To validate the effectiveness of the suggested method in various encounter situations, a collision avoidance simulation is conducted.
Some species of fish are able to alter their mode of swimming to interact with naturally produced vortices; the use of these gaits reduces the energy expended by the fish. To analyse the feasibility of autonomous underwater vehicles replicating these gaits, a series of experiments are performed with unpowered rigid and flexible bodies positioned in the Kármán wake of a rigid cylinder. Simple motion capture techniques are used to capture the bodies’ lateral and upstream motion in the flow. The results demonstrate that manufactured bodies are capable of passively mimicking fish behaviours, to a limited extent. More importantly, it was concluded that while significant upstream movement was possible for a manufactured object, it was achievable irrespective of the stiffness of the material. For autonomous underwater vehicles operating in unsteady flow regimes, an ability to utilise energy-saving gaits may improve the range or operational time.
This article proposes a novel trial-and-error control strategy for buoyancy-driven underwater profilers that can be used for water column observation. The proposed strategy is based on the design of a characteristic function utilizing the profiler’s buoyancy adjustment components by automatically triggering a pump and a valve. To facilitate the elaboration of the proposed control strategy, a Bottom Ocean Stationing Ocean Profiler and its buoyancy adjustment system are introduced. Based on this buoyancy adjustment system, a characteristic function uses the difference between the current depth and the desired depth to determine a target velocity. Then, the trial-and-error control strategy based on error in velocity is implemented on the control of the buoyancy engine by determining whether positive or negative buoyancy adjustment is needed and by how much. This method has been applied to the depth control for our profilers resulting in field application results to validate the analysis.
The prediction of wave resistance in naval architecture is an important aspect especially at high Froude numbers where a great percentage of total resistance of ships and submerged bodies is caused by waves. In addition, during hull form optimization, wave resistance characteristics of a ship must closely be observed. There are potential, viscous and experimental methods to determine the wave resistance of a ship. Reynolds-averaged Navier–Stokes equation–based methods usually follow the experimental method that determines the form factor first. However, it is proven in recent studies that the form factor changes with the Reynolds number. As the Reynolds number increases, this change in the form factor is being neglected. In this study, a Reynolds-averaged Navier–Stokes equation–based prediction of wave resistance is presented that overcomes this flaw. The methodology is validated with the benchmark problems of submerged and surface-piercing bodies to determine the effectiveness of the proposed method. The method is also validated by experiments carried out at the Ata Nutku Ship Model Testing Laboratory of Istanbul Technical University for a totally submerged ellipsoid and the benchmark KRISO Containership. Results reveal the robustness of the present methodology.
Rules, standards and regulations have to be observed in every step of the ship design process. Ignoring these constraints in any case leads to higher costs going along with potentially lower product quality. Numerous investigations have shown that product data model correction activities require considerable resources (man-hours and although money = cost) to obtain an acceptable quality level, and in the worst case, a redesign of potentially larger parts of the ship structure has to be performed. Computer-aided design systems offer a large set of functions to define a product data model. However, in the current situation, these tools are not capable to fully ensure the correctness of the product data model while observing the relevant quality criteria which are generally shipyard specific as they are mainly imposed by the production facilities. A quality management system is introduced which is based on the ISO 10303-59 focusing on quality criteria to be applied for an efficient ship structure production process. The functions of the system will be demonstrated on weldability criteria. These criteria demand notches at distinctive constellations of components depending on their function and, for example, minimum distances and angles between structural parts due to welding processes and material requirements. As an additional criterion, sufficient excess material has to be assigned to plate edges functioning as block boundaries to allow for the correction of inaccuracies in the production process at even late stages. The integration of the product data quality management algorithms with the computer-aided design system, in this case AVEVA marine, shows an efficient correction of inapt data as the automatically detected errors can easily be fixed by means of a guided process including the visualization of the structural parts with the help of the computer-aided design system being applied for data modelling.
This article presents a novel fuzzy–logic based multi-sensor data fusion algorithm for combining heading estimates from three separate weighted interval Kalman filters to construct a robust, fault-tolerant heading estimator for the navigation of the Springer autonomous surface vehicle. A single, low-cost gyroscopic unit and three independent compasses are used to acquire data onboard the vehicle. The gyroscope data, prone to sporadic bias drifts, are fused individually with readings from each of the compasses via a weighted interval Kalman filter. Unlike the standard Kalman filter, the weighted interval Kalman filter is able to provide a robust heading estimate even when subject to such gyroscope bias drifts. The three ensuing weighted interval Kalman filter estimates of the vehicle’s heading are then fused via a fuzzy logic algorithm designed to provide an accurate heading estimate even when two of the three compasses develop a fault at any time. Simulations and real-time trials demonstrate the effectiveness of the proposed method.
The paper presents the application of Monte Carlo simulation in the behavior analysis of an autonomous underwater vehicle. Due to the highly nonlinear dynamics and existence of uncertain parameters in the models, there is not a straightforward method to analyze the behavior of an autonomous underwater vehicle. The objective of this article is to introduce a Monte Carlo campaign for an autonomous underwater vehicle 6-degree-of-freedom model to examine the effects of uncertain parameters on the mission objectives. Uncertainties in the model are considered in several categories, consisting of hydrodynamic and added mass coefficients, control instruments (sensors and actuators), environmental conditions and initial conditions. Monte Carlo simulations are run for a typical autonomous underwater vehicle moving from the water surface to reach a predetermined depth and heading during the mission time. For this purpose, 6-degree-of-freedom software is developed in C++ which is a fast and visual programming software. Using an example, it is shown that simulation results can be used for tuning of guidance algorithm. Moreover, the proposed concept is applicable for analysis of other types of autonomous ocean systems.
Double-sandbar systems are common along sandy, wave-dominated coastlines. The evolution of a double-sandbar system is a complex process and is affected not only by the time-varying wave forcing but also by the local seabed morphology itself. The influences and relative importance of both wave condition and morphological variability on the evolution of a double-sandbar system still remain unclear and are investigated in this study using a well-established operational quasi-three-dimensional coastal evolution model. Results show that these two factors contribute to the final double-sandbar morphology in different ways. For energetic waves with high angles of wave incidence, waves determine the final sandbar morphology, regardless of the antecedent bathymetry. For moderate waves with small angles of wave incidence, however, the pronounced morphological variability (crescentic pattern of sandbars) will dominate the evolution, which remarkably enhances the existing morphological pattern regardless of the changed wave condition. A nondimensional index is proposed to quantitatively evaluate the relative importance of these two mechanisms. Further quantitative analysis reveals that the relative importance of wave condition and morphological variability depends on the alongshore current velocities over the bar crests. There also appears a critical value for these alongshore current velocities, below which morphological variability tends to be dominant and wave forcing is of less importance.
This article focuses on the optimisation of cargo handling operations of tankers. A combined hydraulic-energy model has been developed and adapted to the design characteristics of AFRAMAX tankers, allowing the simulation of a tanker’s cargo discharging procedures, while monitoring all related ship parameters, like characteristics of pumps/manifolds, piping system, flow rates, pressures, ship responses, etc. A preference-based multi-criteria optimisation methodology has been additionally applied to the modelled simulation procedure, which results in practical guidelines for the optimisation of discharging procedure in terms of energy–fuel consumption and discharging time. These guidelines have proven very valuable in the decision-making process during cargo handling operations.
Different configurations of stiffened panels used in shipbuilding are analysed. From this analysis, data models are produced and a description is given of the functionalities required for their generation as solid models. The methodologies for their geometric definition and representation are presented for application in systems in which the hull-moulded shape is described by parametric surfaces. The concepts presented provide the basis for the implementation of a tool for the creation of stiffened panels, which is to be a general-purpose component in a computer-aided ship design system.
The daisy chain is one of the main layout types of the subsea production system in the development of deepwater oil and gas fields. The number of production loops, length of subsea pipelines, and partition of subsea wells are the main concerns in pigging loop design, pipeline laying, and flow assurance, which become important factors for the capital and operating expenditures and the risk management of deepwater fields. This article focuses on the basic optimal partition problem of production loops for subsea wells in the layout of daisy chains. It proposes to find the optimal partition method at the lowest layout cost, where a mathematical model is proposed and its dedicated algorithm is developed. Numerical simulations are conducted to evaluate the validity of the proposed model and the performance of the algorithm. The results show that the model can accurately describe the optimal partition problem of daisy chains in practice, and a mathematical solution to the optimal partition can be obtained by the algorithm programmed in MATLAB, which can provide the engineers a quantitative reference for the layout of daisy chains in engineering.
The approaching marine fuel sulphur regulations will result in reductions in emissions of sulphur oxides to air. Importantly, also particle emissions that impose health risks will be lessened by these regulations. Combustion particles from marine engines are complex mixtures of organic compounds, soot, sulphate, metals and other inorganic species. Their composition and abundance are determined both by fuel and engine characteristics. Health risks from particles are thought to be related to the size of particles and chemical composition of particles which makes particle mass a coarse parameter for indication of how harmful emissions are. This article presents emission measurements conducted on board two ships with a focus on comparing number concentrations of ultrafine particles (Dp<100 nm) in diluted exhaust for three different fuel qualities. The fuels are chosen based on their relevance to existing and coming into force regulations on sulphur in fuel. Implications of these regulations for Sulphur Emission Control Areas on health risks from a shift from heavy fuel oils to low-sulphur marine gas oil are discussed with the measurement results as a basis. The results from the presented measurement emphasise the effect of fuel type on particle formation. The strong relation between sulphur content of fuel and particle emissions is obvious for particle mass but not for particle number and particle sizes.
Cold ironing (or onshore power supply) addresses airborne emissions while ships are berthed in port. By providing the electrical power demands from shoreside electricity, the onboard auxiliary generators can be switched off for a locally emission-free solution. The net emissions will of course be dependent on the actual shoreside electricity mix, but reductions can be realised in most cases. This study looks at the various electrical configurations available for cold ironing of berthed vessels. Shoreside generation using liquefied natural gas as an alternative fuel is also considered as a complement to cold ironing. This provides the possibility of hybridised solutions combining power supply from the grid or from clean, onsite generators. Using real data from an operational European port, the various cold ironing configurations are modelled and optimal trade-off solutions were identified. This is achieved by considering the reduction in emissions and minimisation of component costs as a multi-objective non-linear optimisation problem. The results show that CO2 emissions can be reduced by up to 40% by using cold ironing, while the use of liquefied natural gas shore generation can reduce the sulphur and particulate emissions in port to extremely low levels.
Perturbation methods up to first order with respect to motion or wave amplitude are common in seakeeping predictions. For higher than first order, lengthy theoretical analyses are required. They result in complicated formulae requiring high programming effort, and often the well-established numerical methods for first-order quantities fail when applied to second-order flow quantities. Both the derivation of the required expressions and their programming are simplified by using mathematical entities called perturbators. The concept of perturbators is described, and their application is demonstrated, for a two-dimensional test problem: A cylinder with horizontal axis partly immersed into an ideal fluid. The cylinder performs sinusoidal heave, sway, and roll motions. Stationary and double-frequency second-order forces are determined. For a heaving semicircle, vertical forces are determined numerically and compared to published results.
There are various propulsion, maneuvering, and stabilization mechanisms in nature, which can provide inspiration for similar mechanisms in man-made vehicles. This study aims to elucidate and compare the propulsive vortical signature and performance of a foil in two important natural mechanisms of pure pitching and undulatory oscillations. Governing equations are solved with a pressure-based finite volume method solver, in an arbitrary Lagrangian–Eulerian framework domain containing a NACA 0012 foil moving with prescribed kinematics. The results show that in a given Reynolds number (Re), the undulating mechanism produces thrust at a higher Strouhal number (St) and with smaller growth slope, but mostly higher efficiency, versus St, than pitching mechanism. In addition, vortical structures of these mechanisms have significant differences and also vary considerably with St. One of the distinguishable features of vortical signatures is the presence of the leading-edge vortices for the pitching foil, which are not appearing in the undulating foil’s vortical pattern.
Hull girder reliability assessment of the MSC Napoli at the time of accident is presented. Loads considered in the study are still water bending moments, vertical wave bending moments and whipping bending moments, while structural capacity is represented by the hull girder ultimate strength. Load combination between wave and whipping bending moments is considered. The probability of failure is calculated using a first-order reliability method. Sensitivity study is performed in order to investigate influence of the pertinent random variables. The uncertainty model of the basic random variables involved is consistent with the recent proposal by the International Maritime Organization, thus enabling direct comparison of the obtained results with reliability levels proposed by International Maritime Organization.
In the article by Sobey (Rodney J. Sobey, 2006. Normal mode decomposition for identification of storm tide and tsunami hazard. Coastal Engineering 53, 289–301), the author proposed a normal mode decomposition method to calculate the eigenfrequencies, the eigenmodes and the response amplitudes of different resonant modes in natural harbors that are subjected to storm tides and tsunamis. However, the numerical method to address the no-flow boundary condition in that article is imprecise, which would lead to inexact eigenfrequencies and eigenmodes. In this article, the mirror-image method was proposed to improve this handling process. The accuracy of the improved normal mode decomposition method was verified using three verification tests. With a set of numerical experiments, it was determined that during the process of decomposing the response amplitudes of different resonant modes, the numerical fitting error between the simulated free surfaces and the corresponding fitted ones gradually increases with the wave nonlinearity inside the harbor. This article sought to identify the critical wave condition under which the normal mode decomposition method can accurately decompose the response amplitudes of different modes.
This article describes the modelling of a container terminal using Petri nets with predicates. It starts by describing this extension of the basic Petri net theory and demonstrates its applicability and adequacy to solving complex logistic processes and reliability problems more intuitively and easily than the basic Petri net theory. The developed computational model allows the evaluation of different configurations and combinations of transport equipment, providing a very complete port system’s simulation. Such simulation, based on an estimated container flow, allows the calculation of several waiting times, time in port, attendant time, queuing time, equipment and resource occupation and so on. Changing the internal configuration of the terminal or the external conditions will result in different costs and profits to the terminal, making it possible to perform a terminal optimization based on the study of long-term performance indicators under different conditions. This systematic approach is implemented in a specific case study related to the operational cargo handling procedures of a container terminal. The study will be made considering verified operation performance over some months where the mean values of the variables considered are representative of the ‘typical’ operation of that particular terminal, which allows a validation of the model.
Economic and population growths are the most important drivers of growing global energy demand. They led to a rapid development of international seaborne trade and an increase in the number of global vessels. Air pollution from these ships is of great concerns and regulations are currently enforced since May 2005 by the International Maritime Organization to limit such pollution. In this study, we will first review the current global energy demand and its driving forces over next decades, second evaluate the existing alternative fuels that can be used as a bunker fuel to reach sustainability with relatively small changes in the existing marine propulsion options and finally focus on near-term solution, which has the potential for large-scale use. The different alternative fuels were compared in terms of several parameters such as availability, renewability, safety, cost, performance, economy and compliance with emission regulations. This comparison revealed that liquefied natural gas could be considered as the future replacement to the current marine bunker fuel. This conclusion has been further verified by comparing diesel engine with different powers when using both heavy fuel oil and liquefied natural gas. The engines were compared against fuel consumption, cost saving as well as emissions. Liquefied natural gas has proved to be better than heavy fuel oil due to fuel cost reduction by about 31% per year and decrease in emissions of SOx, NOx, CO2 and particulate matter by about 98%, 86%, 11% and 96%, respectively. The resulted emissions from using liquefied natural gas were found to comply with the current International Maritime Organization regulations. Moreover, this article highlights the latest rules and regulations that govern the use of liquefied natural gas as marine fuel onboard ships.
Natural vibration analysis of stiffened panels represents an important issue in different kinds of engineering applications. In this article, a procedure for the vibration analysis of stiffened panels with arbitrary edge constraints is presented. It is based on the assumed mode method, where natural frequencies and modes are determined by solving an eigenvalue problem of a multi-degree-of-freedom system matrix equation derived by using Lagrange’s equations of motion. The Mindlin thick plate theory is applied for a plate, while the effect of stiffeners having the properties of Timoshenko beams is accounted for by adding their strain and kinetic energies to the corresponding plate energies. The accuracy of the proposed procedure is justified by several numerical examples which include the natural vibration analysis of stiffened panels with different framing sizes, their lengths and orientations, plate thicknesses and different combinations of boundary conditions. A comparison of results with those obtained by the finite element method is provided, and good agreement is achieved.
The ship design and construction industry serves a considerable range of market segments, with different levels of required customization, different demand volumes, and other product and market variations. In order to effectively respond to various market requirements, strategies and related work processes need to be differentiated. An important strategic concept to make distinctions among strategies is the customer order decoupling point, that is, the point in the value chain where the product is linked to a specific customer order. This article aims to analyse and compare strategies for customized, low-volume ship design and construction from the perspective of the customer order decoupling point and to link them to product and market characteristics. It is based on a case study at the Ulstein Group, an established Norwegian ship designer and builder. The study allowed us to define ‘customized design’ and ‘standardized design’ as two different strategies that fundamentally differ in terms of the customer order decoupling point. In the former, customized ships are offered in a process where most activities are driven by the expectations and requirements of a particular customer. In the latter, the customer is given only a limited choice of predefined, standardized, and well-proved options. We conclude that customer order decoupling point positions upstream in the value chain imply high levels of flexibility and customization, while downstream positions allow short lead times, high delivery precision, and lower prices. The customer order decoupling point perspective provides a useful framework in which to analyse the ship design and construction industry.
The purpose of this article is to propose an integrated approach for measuring the financial risk in the shipping business. The integrated approach combines the autoregressive conditional heteroskedasticity model, historical data distribution goodness-of-fit test and Monte Carlo simulation. First, a typical forecasting based on the autoregressive conditional heteroskedasticity model is presented to evaluate future cash flows and find that it continues to fall at short periods. Second, the cash flow at-risk measurement by simulation is to understand maximum potential cash flow deficit, and through exposure to develop a risk management strategy that will enable the shipowners or operators to effectively identify, quantify and control most financial risks and exposures.
A core aspect of assessing the environmental footprint of ships during the conceptual design phase is the estimation of the total air emission during the vessel life cycle. This process must take into account not only the design of an appropriate propulsion system and air emission controls but also the uncertainty related to changes in the vessel mission, such as future market conditions, new regulations, and contract opportunities. In this article, we model possible realizations of uncertain operational life-cycle scenarios using the responsive systems comparison method. This complex systems engineering method includes a strong emphasis on the structural and behavioral aspects of complexity, by mapping of function and form via machinery configuration variables and performance attributes. However, it also has the capacity to handle additional complexity aspects, discretizing the context into epoch variables, time into epochs and eras, and perception into utilities through the life cycle. We present a theoretical example related to the design of a general cargo container. The study illustrates the challenge in striking the correct balance between minimizing the emissions for an initial scenario, while providing additional performance capabilities to be efficient in the uncertainty of future market requirements.
Uncertainty is inherent to risk analysis. Therefore, it is extremely important to properly address the issue of uncertainty. In the field of risk analysis for maritime transportation systems, the effect of uncertainty is rarely discussed or quantified. For this reason, this article discusses a case study dealing with risk analysis for a chemical spill in the Gulf of Finland and analyses the related uncertainties by adopting a systematic framework. Risk is assessed in terms of the expected spill frequency and spill volumes caused by collisions between ships and chemical tankers in the Gulf of Finland. This is done by applying a collision consequence with a novel approach-to-collision-speed linkage model and Gulf of Finland–specific causation factors, which are based on reanalysing accident data. This article also presents a metamodel for assessing collision probability with initial vessel speeds for any given scenario where a chemical tanker is about to be struck by another vessel. Even when conducting a risk analysis using state-of-the-art methods, there is still a medium-high degree of uncertainty in the model presented in this article, which only becomes apparent when conducting a systematic uncertainty assessment analysis. However, an uncertainty assessment is an important part of quantitative maritime risk analysis. For this purpose, a qualitative framework for uncertainty assessment analysis is introduced for general use in the field of maritime risk analysis.
A numerical analysis of the inviscid flow over base-ventilated intercepted hydrofoils is presented. The low-order, non-linear boundary element formulation used is described along with the significant issues concerning the modelling of supercavities with this method. The use of transom-mounted interceptors is well established for the manoeuvring and trim control of high-speed vessels. The flow field over a forward-facing step at the trailing edge of a blunt-based hydrofoil section, with consequent cavity detachment from the outer edge of the step, is similar to that of the transom-mounted interceptor operating at high speed with free surface detachment from the outer edge. Due to this similarity, the term ‘intercepted’ hydrofoil is used to describe this arrangement. The results presented show that a number of geometric parameters, in particular thickness, leading-edge radius and trailing-edge slope, have a significant effect on the hydrodynamic performance of base-ventilated intercepted hydrofoils.
Severe working conditions on board high-speed craft adversely affect not only the safety, health and performance of the crew but also the performance of the vessel as a technical system. Human factors–based ship design combined with appropriate vibration mitigation techniques and work routines for the crew can improve the working conditions and reduce the risks for performance degradation and adverse health effects. To enable development and use of such means, methods for prediction and evaluation of working conditions are needed for both existing high-speed craft and craft under design. This article presents a 2-degree-of-freedom seat model compatible with both measured and simulated input data. The interaction between seat and human is treated using the concept of apparent mass. The model is validated against experiment data collected on board a 10-m, 50-knot high-speed craft equipped with high-standard suspension seats. Evaluation measures defined in ISO 2631-1 and ISO 2631-5 are used to compare experiment data to modelled data. The seat model slightly overestimates the experiment S ed dose by a mean of 6.5% and underestimates the experiment vibration dose value (8 h) by 4.0%. It is concluded that model data correlate well with experiment data.
The Mechatronics and Dynamic Modelling Laboratory of the Department of Industrial Engineering, University of Florence, as a partner of THESAURUS (Italian acronym for ‘TecnicHe per l’Esplorazione Sottomarina Archeologica mediante l’Utilizzo di Robot aUtonomi in Sciami’) project, has developed an innovative low-cost, multirole autonomous underwater vehicle, called Tifone. This article deals with the adopted methodologies for the autonomous underwater vehicle design: in particular, the main focus of this study is related to its propulsion system. According to the expected performances and requirements of THESAURUS project, the vehicle has to maintain good autonomy and efficiency (typical features of an autonomous underwater vehicle), with high manoeuvrability and hovering capabilities, which are more common of remotely operated vehicles. Moreover, cooperative underwater exploration and surveillance involve the use of a swarm of vehicles. In particular, the optimization of costs versus benefits is achieved through the design of a fleet of three multirole vehicles. Each autonomous underwater vehicle has five controlled degrees of freedom, thanks to four thrusters and two propellers: in this article, the preliminary design criteria concerning the vehicle and the design and testing of its actuation system are described.
The J-lay method is regarded as the most feasible way to lay pipeline in ultra-deep water; however, the time required to compute the forces generated is considerable. In this article, a new and simple mechanical model is developed in order to reduce the calculation time required. It comprises two parts: the first is a pipe–soil interaction model based on the linear beam theory and the Winkler foundation model, and the second is a nonlinear, large deflection beam theory to calculate the forces on the suspended segment. The accuracy of the numerical calculations has been verified against the output of commercial software with good results. Furthermore, high-order shear effect, which has been largely ignored in other publications, is discussed. The results show that computational accuracy can be improved by 3.1% by taking this effect into account. Therefore, the mechanical model proposed in this article is quicker and more accurate for determining the forces encountered during J-lay operations.
This study focuses on the importance of the development of maritime container ports in the case involving transatlantic container transport in order to ascertain an optimal model of container flows between container terminals in the eastern coast of the United States and those in Western and Northern Europe. The model proposed by the authors is developed using the following eight key elements: transport infrastructure and suprastructure, use of intelligent information systems, economic growth, transport ecology, cargo flows, innovations, safety and security, and transport energy. The research builds mainly upon secondary statistics data analysis. The authors suggest that there is a close and strong connection between the development rate of maritime containers ports and the proposed model for transport optimization, which considerably influence the level of attractiveness of maritime container terminals.
The main purpose of this article is to study cargo damage risk management in the export operations of ocean freight forwarders in Taiwan. This study applies the five risk management procedures of the formal safety assessment method as a basis for risk management assessment. The fuzzy analytical hierarchy process method is first employed via a first questionnaire to evaluate key risk identification factors. Second, a risk matrix model is constructed to evaluate the risk levels via a second questionnaire. Third, cost and benefit analysis is implemented to evaluate the feasibility of risk control strategies through the use of a third questionnaire. The empirical results obtained in this study revealed that the most severe risk factor comes from the process of consolidation, and all risk factors fall into "as low as reasonably practicable" area via the risk matrix model method. Finally, the cost and benefit analysis shows that all risk management strategies are feasible. This study recommends that ocean freight forwarders strengthen communication with new cargo owners in order to gain a better understanding of the cargo owners’ backgrounds and their cargo characteristics. This will help the ocean freight forwarders to make better-informed decisions concerning the handling of cargo and allow them to form links in customers’ risk management chains.
The design concept for a ‘clean energy producing vessel’ proposes the exploitation of remote offshore gas reserves, primarily from stranded fields, using a floating electrical power generation plant. In comparison to conventional approaches utilising liquefied natural gas and pipeline technologies, the clean energy producing vessel represents a highly innovative approach to the production and transportation logistics of natural gas for electricity generation. The main objective of this article is to undertake a financial evaluation of the clean energy producing vessel design concept. This is achieved by developing a financial model comprising cost and revenue modular elements that reflect the major technical components of the design concept: the floating production, storage and offloading unit; the electrical generation plant; cable transmission; carbon capture and electricity prices. The results for net present value and internal rate of return are derived for all combinations of either high- or low-revenue scenarios and for high- or low-cost scenarios. With a rather low internal rate of return of just 15.53%, the only scenario that yields a positive outcome is that of the high-revenue and low-cost combination. Accounting for savings in carbon dioxide emissions exerts only a negligible impact upon the results. Analysis of future research required concludes that following its deployment and implementation, the feasibility of the clean energy producing vessel design concept depends on the outcomes of economic and technological assessments, which are difficult to predict with any degree of certainty.
In this article, a fuzzy analytic hierarchy process method is presented to evaluate handling equipment operated in a container yard. To begin with, there were 19 criteria established for the evaluation, and then, a factor analysis was used to extract five dimensions, namely, operating environment, reliability, productivity, storage capacity and managing costs. Furthermore, an expert questionnaire of analytic hierarchy was established based on the 5 dimensions, 19 criteria and 5 alternative solutions. Finally, the proposed fuzzy analytic hierarchy process was used to verify the evaluation model, with handling equipment operated in Container Center A of Kaohsiung Harbor taken as an illustration. The research results showed that the storage capacity was the most important factor to the evaluation. Among the 19 criteria, the first 5 were a 20-foot container ground slot, the acquisition cost of the handling equipment, annual handling capacity of the storage yard, handling methods and the equipment failure rate, in the ascending order of precedence, and the handling equipment best fits Container Center A of Kaohsiung Harbor was rail-mounted gantry cranes. It is hoped that the proposed evaluation model will help container yard operators select the most suitable handling equipment for their operations.
Welding is the primary joining process in ship production and inherently causes shrinkage and angular distortion that degrade the dimensional quality (adherence to tolerance specifications) of ship blocks during assembly. Considering that intermediate products of low quality are not scrapped but must be reworked, the productivity of each workstation greatly depends on the dimensional quality of these intermediate products. One of the major "design for assembly" methodologies to control welding shrinkage in shipbuilding is a shrinkage compensation design. This allows the artificial redesign of nominally shaped pieces of plate, to include optimal expansion values that accommodate welding shrinkage. This minimizes the amount of reworking caused by degraded dimensional quality. This research presents a new shrinkage compensation design methodology and technique combining computer-aided design with computer-aided engineering, which overcomes the shortcomings of the empirical approach used until now. An optimization procedure is proposed, by which to find the best shrinkage compensation design shape on the basis of the object function, which would minimize total rework cost (due to shrinkage) predicted for the next block-to-block assembly. The proposed design scheme was successfully applied to shipyard production design and was found to enhance the dimensional quality, as well as the productivity, of shipbuilding.
This article presents a methodology for analysing the cost of operating marine systems under varying conditions. Data obtained from a previously developed Monte Carlo analysis are applied to assess the operational costs for various maintenance and inspection policies. The concept of total insured value is also applied to determine the cost attributed to risk. The aim is to show that Monte Carlo analysis can be adapted to provide information on various factors affecting operational costs to be used for decision-making to optimise the efficiency of marine systems. A method of modelling the effects of lead times due to un-stocked items has also been included to increase the scope of the analysis.
For rapid modelling of ship structure and sharing of product data for a computer-integrated manufacturing system in shipbuilding, this research proposes a data exchange method between two-dimensional drawings and three-dimensional finite element models. The report of the research is followed by appropriately planning the structure of the extracted data based on the Standard for the Exchange of Product Model Data. A set of rules for two-dimensional feature recognition is established, and then the method for the extraction of graphic and non-graphic design information from two-dimensional drawings of transverse sections is presented. An algorithm for rapid modelling of the longitudinal hull structure is proposed, based on data extracted from the transverse sections. This algorithm bypasses the geometric modelling stage required in traditional manual modelling, exclusively making use of the extracted information. The proposal also enriches data exchange, greatly reduces human error in modelling and consequently improves the accuracy of the finite element modelling for the shipbuilding industry.
This article provides a simple analytical method which can be used to give estimates of the Stokes drift based on long-term variation of wave conditions. This is achieved by providing bivariate distributions of significant wave height with surface Stokes drift as well as with volume Stokes transport. These Stokes drift parameters are defined in terms of significant wave height and characteristic wave periods. This article presents the mean value and the standard deviation of these Stokes drift parameters, that is, more precisely the conditional expected values and the conditional variances for given significant wave height, as well as examples of results corresponding to typical field conditions. Based on, for example, global wave statistics, the present analytical results can be used to make estimates of the Stokes drift.
Marine energy in the United Kingdom is undergoing a period of growth in terms of development and implementation. The current installed tidal energy capacity is expected to rise to provide 20% of the United Kingdom’s electricity demand by 2050. This article used life cycle assessment to study four tidal energy devices, comparing their embodied energy and carbon dioxide emissions. The device designs studied included a multi-blade turbine, two three-blade horizontal axis turbine machines and an Archimedes’ screw device. These machines were chosen to represent a cross section of design for the device, foundation, installation and operation. Embodied energy was considered over the lifetime of each device. Energy use from fabrication, transport, installation, maintenance, decommissioning and recycling was all calculated and compared to the energy generated by each device. Finally, the embodied energy, CO2 intensity and energy payback periods were compared to those of conventional power generating systems and other renewable energy sources. Devices were studied based on a functional unit, defined as a 10 MW array installed for 100 years. Of the devices studied, the OpenHydro Open Centre turbine was found to have the best ratio of generated to embodied energy. All devices achieved CO2 and energy payback within 12 years and exhibited CO2 intensity between 18 and 35 gCO2/kW h. This compares favourably against current energy sources such as wind (8–12 gCO2/kW h), solar photovoltaic (~30 gCO2/kW h), nuclear (~70 gCO2/kW h) and coal (~1000 gCO2/kW h).
Rotating machinery in marine engine systems experiences the base excitation and the additional gyroscopic moment from the pitching and rolling motion of the ship. For some cases, the motion can cause the rotor system damage. The nonlinear model of the journal bearing–rotor system for marine turbo machinery considering the pitching and rolling motion is established by coupling the basement motion and nonlinear oil film force together. Then the nonlinear dynamic characteristics for the system with the unbalanced mass are studied. By employing the Newmark method, the dynamic response of the rotor-bearing system is simulated. The orbit diagram, spectrum diagram, waterfall diagram, amplitude versus rotating speed diagram and the bifurcation diagram are obtained. The effect of the pitching and rolling motion on the journal bearing–rotor system is investigated. The results indicate that the additional stiffness matrix, additional gyroscopic and additional exciting force vector will act on the journal bearing–rotor system, which are generated from the pitching and rolling motion for marine turbo machinery. The dynamic characteristics of the system such as destabilizing angular velocity will be changed by affecting the nonlinear oil film force.
This article presents a numerical study of the coupled ship motions and tank sloshing of a liquefied natural gas carrier. To solve this coupled problem, we have developed a time-domain numerical method. The method combines a ship motion solver based on strip theory and a computational fluid dynamics sloshing solver. The method has been applied to a liquefied natural gas carrier model to investigate the coupling effect in regular waves. Simulations for four different loading conditions were carried out, and the results of ship motion response amplitude operators and free surface movement amplitudes were presented in frequency domain. The coupling effect on ship motions and sloshing has been discussed. Based on the assumption of linearity of ship motions and wave, the authors used the ship motion response amplitude operators (with coupling effect) obtained in regular wave conditions to generate ship motion time histories in irregular waves. Sloshing in tanks was then simulated by using the ship motion time histories in irregular wave conditions. The calculated impact pressure time histories were analyzed by using the exceedance probability function.
The assessment of passenger comfort in modern cruise ships is considered from a hydrodynamic point of view, in addition to improvement using stabilizing fins. Passenger comfort is evaluated in this study based on the symptoms of motion sickness on ships provoked by low-frequency whole-body vibration. Motion sickness dose value is an index used to quantify seasickness and is chosen as a primary index to evaluate passenger comfort. To calculate motion sickness dose value in the time domain, a time series of vertical accelerations should be processed using frequency filters, which are defined in the international standards and guidelines provided by classification societies as forms of transfer functions in the frequency domain. Digital frequency band–limiting and weighting filters are formulated as a form of infinite impulse response filter and then applied to the present case. Two pairs of stabilizing fins are equipped to reduce the roll and pitch motions and to improve the passenger comfort on a model cruise ship. A linear optimal control algorithm, linear quadratic Gaussian, is considered to actuate each stabilizing fin. Numerical computations are carried out based on practical operating conditions for the cruise ship model using a time-domain ship motion program, which integrates the motion control algorithm and the passenger comfort analysis. The results of computations show that passenger comfort on a cruise ship can be evaluated appropriately by computing the index motion sickness dose value in the time domain. The motion stabilization by the stabilizing fins can be considered as a good method to reduce the motion of the present cruise ship model and eventually contribute to improve passenger comfort.
A comparative study of honeycomb rubber coatings of the same material and total mass subjected to underwater explosion has been carried out in this article. Three types of cell topologies were considered: hexachiral honeycomb, reentrant honeycomb, and circular honeycomb. Three groups of live underwater explosion tests with different attack angles and stand-off distances were conducted on the stiffened metal boxes covered with the coatings. The free field water pressure and wall pressure near the coating’s wet surface were monitored. The acceleration peaks at typical test locations on the inner structure were selected as the major comparative criterions. As a theoretical extension to the test work, finite element simulations have been undertaken using ABAQUS/Explicit software package to provide insights into the coating’s working mechanism and the relation between compression behavior and water blast shock resistance. The results show that the protective effects of different coatings are consistent under different attack angles and stand-off distances. Compression performance depends on the coating structure and plays a dominant role in the underwater shock resistance. Although structural absorbed energy has a significant contribution in the shock resistance, soft coating can substantially reduce the total incident impulse at the initial fluid–structure interaction stage. Furthermore, a smaller fraction of incident impulse is transferred to the honeycomb coating with lower compressive strength.
In this article, the mapping of the performance and emission parameters of a merchant vessel propulsion system over the ship operating envelope was carried out by using a model capable of representing the ship propulsion system behaviour. The model was developed based on a modular approach and was implemented in the MATLAB/Simulink environment. The various parts of the propulsion engine as well as the shafting system, the propeller and ship hull were represented by separate submodels having the appropriate interface for exchanging the required variables to each other. The output of the model includes the performance and emission parameters of the engine as well as the operating parameters of the propeller and ship. Initially, the propulsion engine operation under steady-state conditions was simulated and the predicted engine performance parameters results were validated. Then, simulations of the ship propulsion system operating points at various resistance curves were performed. Based on the derived results, the mapping of the ship propulsion system performance and emission parameters was presented and their variation throughout the ship operating envelope was discussed. Finally, an example of using the derived results in order to minimise the fuel consumption and CO2 emissions for a typical ship route is presented and discussed.
The main purpose of this article is to apply the fuzzy analytic hierarchy process model to evaluate the key risk factors affecting cross-Strait shipping market for liner carriers. At first, according to the historical literature and experts’ opinions, a hierarchical structure with 4 risk aspects and 13 assessment criteria was constructed. Then, a fuzzy analytic hierarchy process algorithm model is proposed. Finally, based on the analytic hierarchy process experts’ questionnaires, we used the fuzzy analytic hierarchy process model to evaluate the key risk factors. The results show that (1) the "political risk" is the most important aspect affecting shipping market operations across the Taiwan Strait for liner carriers. (2) The top three critical risk factors are "shipping rate fluctuations and uncertainty," "political interference from local governments," and "discriminatory treatment and unfair competition," respectively. Furthermore, some recommendations concerning effective control and remedial measures addressing potential risk incidents are provided for liner carriers operating cross-Strait shipping market.
In order to optimise the structural design of large lightweight high-speed catamarans, a thorough understanding of the structural loads is required. Not only is slam severity an important factor in the structural design, but also the occurrence rates of such events in realistic sea conditions is vital for long-term load estimations. The slamming behaviour of a 2.5-m hydroelastic segmented model representative of an Incat wave piercer catamaran was investigated over a range of realistic irregular sea conditions. The model was instrumented with strain gauges to record centrebow slam loads, pressure transducers, wave probes and linear variable displacement transducers. More than 2000 slam events were identified over 22 test conditions, providing an extensive database of slam events. Slam events were identified from the pressure transducer measurements and two important slam parameters investigated: occurrence rates and slam severity. The slam magnitudes were found to be scattered; numerous outliers were detected with magnitudes up to 4 times the median observed in every tested condition. Slam occurrence rates and severity are generally greater in conditions where motions are large. A slam occurrence threshold was identified by extrapolating the experimentally measured occurrence rates. For a 112-m vessel with speeds between 20 and 38 knots and with a modal wave period of 8.5 s, slams are shown not to occur at significant wave heights less than 1.5 m. The slam loads and occurrence data obtained through scale model testing can be used by high-speed catamaran ferry designers to assist the development of structural load cases and operation limits for future designs.
An immersed boundary method is presented, which uses an approximate projection method on nonstaggered grids for computing flows with submerged and moving boundaries. The incompressible Navier–Stokes equations are discretized using a second-order accurate finite difference technique on a nonstaggered grid system, and the new immersed boundary method is proposed based on an approximate projection method with two pressure correction techniques, the Armfield method and the geometrical grid Reynolds modified method on nonstaggered grids. By using this method, the results obtained from (1) flow past a rigid cylinder in two dimensions with different Reynold numbers and (2) flow around an oscillatory circular cylinder in flow at low Keulegan–Carpenter numbers are in agreement with the reported experimental and numerical data, demonstrating that this convenient method of constraining the interface is a reliable and robust numerical approach for solving unsteady fluid flow with a submerged moving rigid object. This method has the advantage of using significantly less computation time and lower computation sources than the traditional immersed boundary methods.
The purpose of this article is to present the design procedure and the main results of its validation through the liquid natural gas carrier structural optimization. The work has been carried out through the EU FP6 project IMPROVE. The objective of the developed optimization process was to distribute the material more effectively in order to reduce weight/cost and to improve the structural safety in the allocated time frame. A coarse mesh finite element method model (three holds) has been developed, using MAESTRO software. Strength calculation has been carried out according to the Bureau Veritas Rules for direct calculation. Sensitivity analysis has been performed to investigate the influence of web frame spacing, longitudinal stiffener spacing and material type on the specified design objectives. Design procedure applied for the structural optimization of the liquid natural gas structure (one cargo hold) resulted in mass decrease of about 424 t (after standardization of scantlings), or 10.8%; the cost of the structure was reduced by about 5%; structural safety was increased and vertical center of gravity was slightly reduced by about 20 cm compared to the prototype structure.
The Energy Efficiency Design Index (EEDI) is made mandatory by the International Maritime Organization to reduce emissions of greenhouse gases from international shipping. In this study, wave energy recovery using a pair of hydrofoils fixed at the ship bow to realize energy efficient propulsion is proposed. This so-called wave devouring hydrofoil (WDH) functions both as an anti-motion fin and a wave energy device, which can help reduce the ship wave added resistance, heave and pitch responses. To evaluate its performance, the coupled interaction between the hydrofoils and the ship under head sea condition is first modeled in the frequency domain together with the evaluation of wave added resistance in the presence of the WDHs. Model test is then conducted using a sample containership. Both the beneficial effect of the WDHs and the validity of the numerical model are proved. The peak response is reduced by 80%, 30% and 25% for added resistance, heave and pitch, respectively. This model is then further modified to include other wave directions. Based on frequency domain results, short-term and long term predictions of speed loss, engine power increase and propeller racing are performed for a 3100TEU containership along her transportation route. The merit of this prediction model is that the hull -propeller -engine interactions is considered from a system balance point of view. It is demonstrated that the WDHs can contribute to the energy-efficient ship propulsion at actual seas, achieving a slight reduction of EEDI and ensuring less speed loss and propeller racing.
Auxiliary drives can provide an alternative propulsion system for marine vessels giving the potential to achieve improved environmental performance during low-speed sailing. In this work, two case vessels were considered for analysis, a Roll-On–Roll-Off ship and a harbour tug boat. Actual sailing operational profiles were used as the basis for energy considerations to assess the potential for lower emissions. An energy-centric simulation model was built to estimate the emission of various pollutants, considering different machinery set-ups. Results have shown that savings are possible, especially for vessels which run on residual fuels, where auxiliary drives provide a way of exploiting the advantages of cleaner sources for manoeuvring instances.
This article presents a study into the forward propulsion of a free swimming, custom-built biomimetic underwater vehicle called the RoboSalmon developed at the University of Glasgow, Scotland. As the name implies, the design of this vehicle is based on the dimensions of an Atlantic salmon. It realises fish-like propulsion through a tail assembly that utilises a tendon drive actuation system driven by a single servo motor. A brief overview of the experimental hardware is given followed by a discussion of the accompanying mathematical model of the vehicle. Experimental results are presented for straight swimming trials that show the surge velocity performance of the vehicle. In the context of forward swimming, the efficiency and power consumption of the vehicle are analysed, and the adverse effect of tail recoil is discussed.
This article presents the statistical analysis of sloshing-induced random impact pressure. To obtain the pressure signal, three-dimensional sloshing model tests were conducted at two different filling depths. Several different methods were applied to identify sloshing peaks and to define the rise and decay times of the peak pressure signals. Statistical properties acquired from these methods were compared, and their consistency and/or discrepancy were observed. In addition, 200-h duration test data were acquired by running forty 5-h tests under each test condition. Based on the long-duration test data, the uncertainty of the test results with respect to the test duration was studied using the bootstrap method.
Knowledge of the behaviour of ship operators relating to their investment in retrofitted equipment or systems is of fundamental importance to those engaged in designing and developing products. Evaluation of product offerings is often undertaken on the basis of return on investment over its full life but this may not be convincing to buyers for existing ships who may only expect to own the ship to which the equipment is fitted for a limited period, not its full life. Knowledge of the typical period of ship ownership then becomes important to enable a realistic payback period to be taken into account in the evaluation of developments. While many involved in shipping will give an anecdotal opinion of the typical length of ship ownership, there is an absence of research to give any precision to such anecdotal opinions or even to confirm them. This article uses secondary sources to present a retrospective analysis of the average period of ship ownership for that portion of the fleet that was approaching the end of its economic life at the time the study was undertaken. The results question the widely held view of speculation being the prime motivator in ship sale and purchase. The pattern of behaviour of owners is found to vary significantly between the first and subsequent owners, with the first owner keeping the vessel for considerably longer than subsequent owners and with the influence of speculation increasing as the owner number increases. Rational values are proposed for what constituted short term and long term in relation to ownership periods for the vessels reviewed, and further analysis is recommended to investigate how these values may vary as the market changes.
Orthotropic Plate Model of Hat Stiffened Plate has been developed based on the equal rigidity concept that makes use of orthotropy rescaling technique. This Orthotropic Plate Model can readily be analyzed using an orthotropic plate finite element available in the element library of any general-purpose finite element software, which will reduce the effort for modeling, computation and storage required considerably. Orthotropic Plate Model has been developed from representative unit cell of Hat Stiffened Plate for all edges simply supported boundary condition and two edges clamped and two edges simply supported boundary condition. It has been found that the Orthotropic Plate Model developed herein can serve as a structural substitute for Hat Stiffened Plate with four edges simply supported boundary condition. Limitations on the Orthotropic Plate Model with two edges clamped and two edges simply supported boundary condition have been reported.
A container supply chain includes a large number of stakeholders who can physically come into contact with containers and their contents and are potentially related with the container trade and transportation. Security-based disruptions can occur at various points along the supply chain. Experience has shown that a limited percentage of inspection, coupled with a targeted approach based on risk analysis, can provide an acceptable security level. Thus, in order not to hamper the logistics process in an intolerable manner, the number of physical checks should be chosen cautiously. The aim of this article is to employ a set of data elements (i.e. an importer security filling, shipping documents, the value of an ocean or a sea carrier’s reliability, the security scores of various commercial operators and their premises) to exploit a mathematical decision-making model for evaluating a container’s security score. For evaluating a container’s security score, a combination of different decision-making techniques such as Bayesian network and analytic hierarchy process is used. The methodology developed has been applied to a case study in order to demonstrate the process involved. Accordingly, control options to avoid unnecessary delays and security scanning in dealing with containers are suggested.
The bending strength of the sea ice cover is crucial in the design of ice-going vessels. Therefore, a series of in situ four-point bending tests have been performed earlier, which are now utilized to present a particle swarm optimization–based procedure to identify the material parameters needed for numerical simulations. The resulting numerical simulations are found to comply well with the experimental results in terms of force, failure time, and displacement. Therefore, it can be concluded that the presented optimization-based material parameter identification procedure can also be used in the future if similar material parameters are to be found.
This study gives a semi-analytical solution for gap resonance between twin fixed, partially immersed rectangular boxes based on the linear potential theory. The fluid region between and below the boxes is treated as dissipative domain. A new method is proposed to introduce energy dissipation into the dissipative domain by adding the artificial resistance force. Two different dissipative boundary conditions are imposed on the gap-free surface and the boundary between the dissipative domain and the non-dissipative domain. A complex dispersion relation is used to describe the wave motion in the dissipative domain with free surface. The newly developed semi-analytical solution is confirmed by previous analytical results, results by independently developed multi-domain boundary element method solution, experimental data and numerical results based on viscous fluid model. A simplified formula is developed to evaluate the resistance coefficient for the dissipative domain. The present model with artificial energy dissipation is simple and efficient and is expected to be valid for more relevant problems.
The research explained in this article was carried out to investigate the hydrodynamic characteristics of the puller and pusher azimuthing podded drive propulsion at various yaw angles and different operating conditions. The method is finite volume–based Reynolds-averaged Navier–Stokes. The renormalization group k- model is employed using the differential viscosity model and swirl-dominated flow to simulate turbulence. For the purposes of this research, two different propellers (B-series and David Taylor Model Basin (DTMB)) are analysed in pusher and puller of azimuthing podded drive configurations. The performance curves of the propellers obtained by numerical methods are compared and verified by the experimental results. Characteristic parameters including torque and thrust of propeller and axial force and side force of the unit are presented as functions of advance coefficients and yaw angles.
Short sea shipping is facing harder requirements on exhaust emissions in the coming years as stricter regulations are enforced in some regions of the world. In addition, shortage of conventional fuels as well as restrictions on greenhouse gas emissions makes the search for new fuels of interest. The objective of this article is to assess important characteristics to evaluate when selecting fuels for short sea shipping. The following four criteria are considered: (1) local and regional environmental impacts, (2) overall environmental impact, (3) infrastructure and (4) fuel cost and competition with other transport modes. Special focus is put on environmental impact, and life cycle assessment is used for the environmental assessment. The fuels compared in this study are heavy fuel oil, marine gas oil, biomass-to-liquid fuel, rapeseed methyl ester, liquefied natural gas and liquefied biogas. This study shows that liquefied natural gas will reduce the local and regional environmental impacts more relative to the other fuels investigated here. Furthermore, liquefied biogas is found to be the most preferable if all environmental impact categories are considered. This study also highlights the importance to consider other impact categories for short sea shipping compared to deep sea shipping and shows that NOX emission is the dominant contributor to all assessed environmental impact categories with local and regional impacts.
This article focuses on the mathematical model of the pitch control mechanism for a marine controllable pitch propeller, with the aim of describing the dynamic behaviour of this kind of system and its influence on ship performance. Too great a load on the blades can result in high pressures in the actuating system, response delays and control system problems, which are ultimately responsible for most mechanism failures. The behaviour of the controllable pitch propeller actuating mechanism is considered in terms of blade position, oil pressures inside the controllable pitch propeller hub and magnitudes of the forces acting on the blades. In the proposed mathematical model, the forces acting on the propeller blade are evaluated taking into account the yaw motion of the ship, the propeller speed (including shaft accelerations and decelerations) and the turning of the blade during the pitch change. On the basis of the introduced procedure, a controllable pitch propeller numerical model as part of an overall propulsion and manoeuvrability simulator representing the dynamic behaviour of a twin-screw fast vessel is developed. The aim of this work is to represent the ship propulsion dynamics through time-domain simulation, based on which the designers can develop and test several design options, in order to avoid possible machinery overloads with their consequent failures and to obtain the best possible ship performances. In this aspect, the controllable pitch propeller model is an essential design tool.
Environmental pollution caused by ships’ green house gas emissions and worldwide concern about air quality and oil supplies have led to stricter emissions regulations and fuel economy standards. In this regard, respective limits are set, while efforts to provide general guidelines for the achievement of economic and green ship operation with an urge to ship operators to apply them and return feedback. Also, specific design and operation indicators have been proposed in order to ensure compliance with new emissions regulations and fuel economy standards. Up to now, these indices are limited to ships comprising conventional propulsion systems, while full electric propulsion systems are not examined. In this article, an integrated control system that attains economically optimized and environmentally friendly operation is proposed. Moreover, appropriate reformulation of energy efficiency operation indicator is proposed for real-time assessment of gas emissions. The study is supported with the presentation of results obtained from the simulation of the operation of a ship power system comprising full electric propulsion.
Semiactive control of a fixed offshore jacket platform using linear quadratic regulator (LQR) control algorithm is presented, for deepwater conditions. The control devices are the semiactive hydraulic dampers (SHDs), installed in the bracings of the jacket structure. The optimum choice of the damping coefficient of the dampers is generated based on a law that considers variable values of the damping coefficients subjected to specified upper and lower bounds. The response quantities of interest, which are targeted for control, include acceleration and displacement of the deck, and the base shear. A four-legged steel jacket platform in a water depth of 183 m (600 ft) and under two sea states is considered as an example problem for finding out the controlled responses. The results of the parametric study indicate that significant reductions in the peak values of response quantities of interest can be achieved by semiactive control, using SHDs.
This study gives an analytical solution of wave interaction with a new-type pile–rock breakwater in the context of linear potential theory. The pile–rock breakwater consists of two rows of closely spaced piles and a rock core between them. The matched eigenfunction expansion method is used to obtain the analytical solution. The analytical solution is confirmed by other solutions for several limiting cases of the present structure. The solution is also validated by a multi-domain boundary element method solution. The reflection coefficient, the transmission coefficient and the energy loss coefficient of the pile–rock breakwater are examined. Their significance for practical engineering is discussed.
Previous studies have shown how the use of composite materials and application of sophisticated design methods can give significantly lighter high-speed craft structures than what is normally achieved for traditional aluminium designs. A reduction in structural mass and a corresponding reduction in displacement improve the craft calm water performance but can be unfavourable regarding the rough water performance. Here, the rough water performance of two versions of a fast patrol vessel, one in aluminium and the other in carbon fibre sandwich, is studied with simplified semi-empirical methods and more advanced non-linear time domain simulations. In speeds up to 30 knots, the rough water performance of the two craft versions is found to be practically equal. At higher speeds, the lighter composite craft experiences higher vertical accelerations than the heavier aluminium craft, which implies less operational availability. Using trim ballast tanks, the rough water performance of the lighter craft is improved, and it is shown that the acceleration levels can be reduced and even lowered relative to the heavier aluminium craft. This means that the calm water advantages of a lighter composite vessel can be utilized with the same ride comfort and operational availability as for a heavier aluminium vessel.
This paper demonstrates an approximation to the numerical solution of the dynamic equilibrium of a catenary riser. The approximant is obtained in the frequency domain when the structure is excited by motions applied at the top. The dynamic equilibrium is formulated mathematically through six nonlinear partial differential equations which involve both geometric and hydrodynamic nonlinearities. The latter are represented by the Morison’s formula. The numerical solution of the six nonlinear differential equations is used to generate spatio-temporal data series for riser bending moments induced by sinusoidal heave motions of various amplitudes and frequencies. The data series are transformed to the frequency domain where a complex singular value decomposition scheme is applied in order to reconstruct the full nonlinear spectrum. The significant harmonics of the riser’s spectrum are then identified as the three lower odd harmonics. The method finally provides a set of orthogonal modes for all significant harmonics; that is, the fundamental, the third and the fifth harmonic of the bending moment in the 2D plane of reference. The nonlinear, frequency-domain modal decomposition proposed is also examined in a typical test case.
The demand for energy is steadily increasing and, at least for the coming decades, the world has to rely on oil and gas to address this need. Most of the easiest accessible offshore petroleum reservoirs have been discovered and a great part developed over the last six decades. Thus, development of new oil and gas fields faces a lot of challenges as most of them are in remote areas, in deep waters and/or in areas with extreme environments like the Arctic region. One of the major trends in the offshore petroleum industry points towards deeper waters (e.g. outside West Africa, the Brazilian Pre-Salt developments and in the Gulf of Mexico). This trend also includes increased use of subsea installations instead of platforms, more subsea processing and increased use of pipelines to transport the hydrocarbons to shore or into a pipeline grid.
This paper addresses some of the challenges pipeline design, installation and operation may face in deep and ultra-deep waters. The main design challenge is related to the high external pressure that may cause collapse of the pipeline. This potential failure mode is normally dealt with by increasing the pipe wall thickness, but at ultra-deep water depths this may require a very thick walled pipe that becomes very costly, difficult to manufacture and hard to install due to its weight. One approach to overcome this is to improve some of the parameters that determine the collapse resistance by an improved manufacturing process. Other approaches are to ensure a minimum internal pressure is maintained in the pipeline during all phases, or to install a buoyant pipeline that is anchored at a moderate water depth rather that laying on the sea bed.
The fundamental vibration characteristics and the mode shapes of a semi-submersible platform determine its operation conditions and long-term structural response. The current investigation presents a procedure for identification of the global natural frequencies and the mode shapes of a semi-submersible platform. The purpose is to evaluate the separation in frequency between the semi-submersible’s global natural frequencies and the exciting wave spectrum. Two types of finite element model are developed and compared: a beam element model and a shell element model. The main differences in the models are the level of resolution in the details and the model complexity. It is shown that both the beam element model and the shell element model can be used for the analysis. However, the beam element model is recommended for a first approximate assessment of the fundamental natural frequency and the interval and spectrum of the global resonance frequencies compared with the wave spectrum. The shell element model is recommended when a more thorough analysis is required. In addition, the natural frequencies of the semi-submersible are calculated for free vibrations in air. The fundamental frequency was 1.9 Hz for the beam element model and 1.5 Hz for the shell element model. When the masses corresponding to a submerged structure in operation mode are considered, including the effects of the added mass, the fundamental frequency for the first mode was decreased to 0.7 Hz when using the beam element model, and to 0.6 Hz when using the shell element model. When compared with the world wave spectrum’s highest frequency of 0.29 Hz reported by Det Norske Veritas, it is concluded that the natural frequencies of the semi-submersible are at a sufficient distance from the exciting wave spectrum.
This paper presents a tagline proportional–derivative control method for suppressing the swing motion of a heavy load suspended by a floating crane in an ocean environment. The tagline mechanism, which is connected between the floating crane and the heavy load, is applied to the floating crane. The winch, which is mounted on the deck of the floating crane, is used to control the tension of the tagline. A proportional–derivative control algorithm is applied to generate the control force of the winch. Swing angle feedback of the proportional–derivative control is supplied by the encoder attached at the boom tip of the floating crane. To demonstrate the performance of the tagline control method, numerical simulations are performed on a non-linear six-dimensional mathematical model of the floating crane and the heavy load. The mathematical model of the floating crane is constructed to consider both the three-degree-of-freedom principle of the floating crane and the heavy load, based on multi-body system dynamics. The numerical and experimental simulation results are compared using a one-hundredth-scale model of the floating crane in the model basin. The results of the numerical simulation and experiment show that the tagline proportional–derivative control method suppresses the swing motion of the load.
The present study investigates the out-of-plane buckling behaviour of catenaries conveying fluids and subjected to end-imposed axial excitations. The mathematical formulation is generic with no restrictions in the amount of sag in the plane of reference. The theoretical model is treated using the Galerkin expansion and employing the actual mode shapes. It is shown that under a parametric excitation the physical model behaves as a multiple-degree-of-freedom system. The novelty of the present study is that it finds the equivalent system that governs the dynamics of the catenary, while in addition it accounts for the internal flow effects which arise from ‘compressive loading’ and Coriolis forces. The stimulation of potential instabilities is investigated using the Floquet theory and the method of multiple scales.