_ This study presents a comprehensive comparative investigation of the buckling and ultimate strength behavior of flat and curved plates subjected to longitudinal compression, utilizing nonlinear finite element analysis (FEA) with NASTRAN, ABAQUS, and ANSYS and benchmarking the results against the established rules of major classification societies including American Bureau of Shipping (ABS), Bureau Veritas (BV), Det Norske Veritas (DNV), and Germanischer Lloyd (GL). The parametric analysis was conducted on plates with an aspect ratio of 3.0, thicknesses ranging from 10 to 25 mm, widths from 800 to 1000 mm, and curvature radii from 3000 to 10;000 mm (corresponding to flank angles of 5°–45°), encompassing the typical geometric configurations found in large LNG carrier hull structures. The findings reveal that for flat plates, FEA predictions demonstrate excellent correlation with classification society rules, with mean ratios of FEA to rule-based strengths between .988 and 1.036, coefficients of variation below 5%, and coefficients of determination R2 exceeding .985, confirming the adequacy of existing empirical methods for flat plate assessment. Keywords ship structure; buckling; regulations and standards; longitudinal strength; structural analysis
_ The bearing is a key component of an internal combustion engine, which is used to support the crankshaft system. Its lubrication performance and wear life will directly affect the working efficiency and reliability of the internal combustion engine. Among these, the crankshaft and engine bed deformation have an important impact on the bearing performance. Different stiffness and deformation between the crankshaft and bearing seat lead to bearing edge load and lubrication problems. Insufficient stiffness easily causes vibration, and on the contrary, too large stiffness leads to lubrication problems. Therefore, the research on bearing structure, crankshaft, and seat deformation matching for improving shafting stability and lubrication performance of main bearings is of great significance to improve the performance of the internal combustion engine. In this paper, a theoretical coupling model of multibody dynamics and elastohydrodynamic lubrication for a low-speed two-stroke diesel engine is established. The dynamic model was verified by the torsional vibration test. The factors affecting the coordinated deformation ability of crankshaft-bearing seats, including the stiffness of the whole engine and the clearance of the bearing, are selected to investigate the influence of these factors on the bending vibration of the crankshaft, bearing lubrication, and wear. The analysis shows that the lubrication performance of the seventh main bearing is the worst among the eight main bearings under the rated condition of the engine. The multiobjective optimization model optimizes the stiffness of each main bearing seat. The results show that the performance of the shaft can be improved by deformation-coordinated design. The thickness of the minimum oil film of the main bearing increases by 6.78%, the peak value of the maximum oil film pressure decreases by 16.64%, and the bending amplitude of the main journal decreases by 21.67%. The optimized result provides a solution for performance improvement on bearing lubrication and vibration of low-speed two-stroke engines. Keywords marine engine; EHD; main bearing; coordinated design
_ The angle of deck edge immersion, which is related to both intact and damage stability, is a crucial factor in the safety of a vessel. This article presents a direct calculation method for determining the angle of deck edge immersion for an onboard loading computer. In this approach, the deck edge line points and a section model database are established by cutting the stereolithography model of the ship hull in the vertical and longitudinal directions. In addition, the polygon offset algorithm and the Sutherland-Hodgman polygon clipping algorithm are employed to calculate the volume and center of buoyancy. Furthermore, a simplified Newton Iteration Method is used to solve the system of equilibrium equations for the free trim of the ship at given heel angles. Finally, the results of the model are validated with three recently constructed vessels. The proposed method provides a reliable and efficient means of calculating the angle of deck edge immersion for efficient calculation by an onboard loading computer. Keywords angle of deck edge immersion; ship floating state; Newton Iteration Method; loading computer
_ In most of the high-speed planing hulls, the hydrodynamic forces are greater than the hydrostatic forces. With an increase in speed, the rate of increase in drag is greater in such vessels. Studies have developed energy-saving devices, such as stern flaps, wedges, hull vanes, and trim tabs, to reduce drag and trim on high-speed crafts. The investigation and design method for high-speed vessels with stern appendages is important to understand their performance. The approach for predicting the motion of such hulls plays a crucial role. Several studies have been done over the past on hydrodynamic analysis of high-speed vessels mounted with stern devices. The focus of this paper is to review the existing investigations on hydrodynamic studies of high-speed vessels mounted with a stern interceptor. Comprehending the robustness and constraints of these approaches will help designers and researchers to select the best method for the effective design of the stern appendage and examine its performance. An extensive study is made and presented on existing experimental and numerical techniques. Mounting stern appendages for high-speed vessels and their hydrodynamic performance vary for each case. Keywords planing hull; stern appendages; experimental method; numerical approach
_ This study develops a stochastic load model for ship structures that accounts for the temporal correlation of wave-induced load pulses and the stochastic process governing voyage duration. The distribution of the extreme values of the still water bending moment and its combination with wave-induced bending moment is formulated using a stochastic renewal process, accounting for the possible nonexponential distribution of voyage duration and the associated uncertainty across different ship operations. The correlated wave-induced loads are modeled as a stochastic Markov process, and closed-form expressions are derived to estimate the extreme value distribution of the load combination. The applicability and accuracy of the proposed approaches are investigated for an Aframax tanker under full load conditions, and the results obtained are compared with those of existing formulations. In addition, the impact of different stochastic processes, voyage duration models, and wave correlation on the extreme value distribution of ship structural loads is investigated. The proposed approaches are straightforward and can be readily adopted in practical engineering applications for probabilistic load modeling of ship structures. In addition, they can be extended to perform reliability analysis of ship hull girders at the ultimate limit state by incorporating a statistical description of the structural capacity. Keywords still water load effects; wave-induced load effects; stochastic process; temporal correlation; load combination
_ The focus of this paper is the optimization of a ship propeller with regard to its acoustic emission, taking advantage of its flexible material. For this purpose, an optimization method is developed based on a partitioned approach for the simulation of the fluid–structure problem. A boundary element method is applied on the hydrodynamic side whilst the structural problem is solved via a finite element approximation. The approach is validated referring to the hydrodynamic performance of model propellers at different stiffness values. Two optimization approaches are applied. In the first approach, only the hydrodynamic part of the problem is simulated. The second approach considers the fully coupled fluid–structure interaction. The optimized propeller is simulated using a partially nonlinear model for sheet cavitation to evaluate the noise level. Finally, the results are compared with those of the reference propeller. Keywords propeller; hydroacoustics; cavitation; Ffowcs Williams and Hawkings equation; partitioned fluid-structure interaction; finite element method; boundary element method
_ Water pump units are essential in water conservation projects. Axial flow pumps, crossflow pumps, and mixed-flow pump units are commonly implemented in new pumping station projects. The technology related to water pump units has been substantially developed in recent years. Nonetheless, the large vertical submersible mixed-flow pump unit is still considered a relatively novel pumping station unit. The operational status of a submersible pump unit can be influenced by the gate or flapper door of the outlet during its startup and shutdown process. During this process, the pump speed, flow rate, and other external characteristic parameters of the unit undergo significant changes in a short time period. The appearance of unstable flow phenomena, such as flow separation and vortex, inside the unit has a significant impact on its safety and stability. Hence, studying the normal shutdown process of the pump unit is essential to investigate factors influencing the unit’s stability. This paper presents a numerical simulation and analysis of the normal shutdown process of a large vertical submersible mixed-flow pump unit. Analysis of the results revealed that the “backflow” phenomenon of water flow occurs during all four cases of the normal shutdown transition process. The unit’s operating conditions are largely determined by the closing time of the flapper door. The unit will experience runaway conditions when the flapper door’s closing time is longer (4 seconds). Keywords vertical submersible mixed flow pump; normal shutdown process; numerical simulation
_ Wind propulsion systems (WPS) for commercial ships can be a key ingredient to achieving the IMO green targets. Most WPS installations will operate in conjunction with propellers and marine engines in a hybrid mode, which will affect their performance. The present paper presents the development of a generic, fast, and easy tool to predict the propeller and engine performance variation, along with the cost, as a function of the wind power installed in two operation conditions: fixed ship speed and constant shaft speed. Specific focus is directed toward showing generic trends and trade-offs that inform economic decision-making. To this end, a key feature of the presented work is the ability to assess the cost–benefit of both controllable pitch propellers and fixed pitch propellers (CPPs and FPPs). This provides advice on when, in terms of WPS installation size, it is worthwhile to install which kind of propeller. CPPs are found to be more suitable for newly built wind-powered ships (>70% wind power), while a conventional FPP is satisfactory for wind-assisted ships (<70% wind power) and retrofitted installations. The results for a 91,373 GT bulk carrier showed that a WPS unloads the propeller and the engine, which leads to an increase in the propulsive efficiency and a detrimental rise of the engine specific fuel oil consumption. However, propeller gains are found to be greater than engine losses, which result in extra savings. Thus, not only does a WPS save fuel and corresponding pollutant emissions, but it also increases the entire propulsive efficiency. Keywords Windship; sailing ship; wind propulsion technologies; propulsion; performance prediction; marine engines; decarbonization; alternative propulsion
_ Flanders Hydraulics and the Maritime Technology Division of Ghent University have proposed a hybrid testing platform for the development and validation of motion control algorithms for autonomous navigation in shallow and confined water, which consists of towing tank facilities and simulators. Within this framework, the towing tank at Flanders Maritime Laboratory, Ostend, Belgium, featured in large size, tuneable water depth, and a state-of-the-art free-running system, a series of autonomous manoeuvering tests with increasing complexity are designed and carried out. These manoeuvres, including acceleration with heading keeping, path following, speed control, and their combinations, are enabled by implementing guidance and control algorithms on a physical ship model, namely the benchmark ship KVLCC2 at a scale of 1/75. The controllable environment and large space of the tank basin facilitate the upgrade of the existing algorithms and the development of new algorithms. The definition of the autonomous manoeuvres, experimental setup, and parameter settings are elaborated and the effect of implementing different guidance strategies is discussed. Recorded results demonstrate good agreement between the measurements and the expectations, and control accuracy is quantified with evaluation indices. In summary, the feasibility and flexibility of the testing platform and the effectiveness of the algorithms are proved through extensive experiments. Keywords guidance and control; free-running test; physical testing platform; path following; speed control
_ Aiming at the problem of equipment accuracy of ship-borne weighing systems in a ship environment, this paper proposes a weighing optimization system algorithm based on finite element analysis. Firstly, the finite element analysis of the ship-borne equipment system is carried out, and the stress analysis is carried out by grasping the characteristics of the sensor to find out the improvement of the weighing system and optimize it. Then, the improved and optimized weighing system is used to collect the data information under the typical swing state, and the neural network algorithm is introduced to dynamically compensate the data. Finally, the accuracy of the weighing system optimized by the algorithm is evaluated by using the environmental test standard of electrical and electronic products. The research results show that the accuracy of the result data of the weighing system optimized by the neural network algorithm is more than 99%, which proves that the proposed algorithm can improve the accuracy of the shipborne weighing system equipment. Keywords weighing system; sensor; neural network; dynamically compensate; accuracy
_ Ant colony optimization is an intelligent evolutionary algorithm that has been widely used in the field of path planning, and the research on its improved methods is proliferating. In this paper, the improvement methods of single and hybrid ant colony optimization in path planning are reviewed in terms of initial pheromone concentration, heuristic function, state transition rule, pheromone update rule, and parameter optimization, respectively. The future research directions of ant colony optimization have been prospected in terms of theoretical aspects, parameter setting and optimization, integration with other algorithms, and multiobjectives. Keywords ant colony optimization; path planning; single ant colony optimization; hybrid ant colony optimization; improvement methods
_ Ship maneuvering performance can be predicted using various methods, including physical model tests, rapid simulations using coefficient-based forces, and high-fidelity computational fluid dynamics. This article considers the application of computational fluid dynamics for the prediction of hull force coefficients to be used as inputs to rapid maneuvering simulations. The open-source software OpenFOAM was used to simulate forces on the destroyer model DTMB 5415 for steady drift, oscillatory pure sway motion, and oscillatory yaw motion. Recommendations are provided regarding best practices in a number of areas, including domain size, mesh refinement, time step size, and turbulent modeling. Predicted forces for steady drift angles up to 12 degrees are typically within 10%of experimental values. For oscillatory sway and yaw motions, predicted forces are typically within 25%of experimental values. Keywords maneuvering; OpenFOAM; best modeling practices
_ Definite stereotype for the outward look of submarines was worked out in the process of evolution. It is very difficult to take into account all inner and outside factors having an influence on the choice of submarine hull shape. Choosing either factor, designers’ model a great variety of outside lines. A light hull of a submarine is the outer nonwatertight hull which provides a hydrodynamically efficient shape. The pressure hull is the inner hull of a submarine; this holds the difference between outside and inside pressure. Closed algebraic surfaces with the main cross-sections in the form of three superellipses lying in three coordinate planes can help to select a submarine form during early-stage design. Having used a parallel middle body, one can extend considerably the choice of suitable shapes. In this paper, a method of modeling smooth compound closed algebraic surfaces that approximates the outside lines of a submarine is presented. The authors offer to form an outside submarine hull from six fragments of algebraic surfaces. The whole hull surface and its fragments are given by the same parametric equations. A method is illustrated in three examples, and it is realized easily in the form of a computer program. The initial data contain large quantities of constants, and it gives an opportunity to consider an infinitely large quantity of variants of submarine hull surfaces. Keywords submarine hull surface; superellipse; compound algebraic surface; buttock line; waterline; midship section
_ The original goal of the present research is to investigate the influence of surge on green water and slamming. Long-running experiments with forward velocity and irregular waves were repeated with and without surge. Surge is found to increase the probability of green water events, but the impact pressures on deck and the probability of a green water event reaching the deck box decreases when the ship is free to surge. Green water and slamming events turned out to not occur independently as both event types cluster for large probabilities of occurrence. Clusters are caused by large pitch motions. Larger pressures on deck are found for clustered events. Keywords green water; slamming; surge; clustering; probability
_ The paper establishes the lumped parameter vibration mathematical model of shafting and uses the system matrix method to calculate and analyze steady-state frequency domain vibration characteristics of the shaft system in the range of diesel engine speed. Then in order to further study the transient torsional vibration of the shaft system under the resonance speed point, the state space method and finite element analysis method were used to compare and analyze the transient time domain response characteristic curve of the shaft system; finally, the test data of the real ship was compared with the theoretical calculation results, which verified the correctness of the mathematical model and the theoretical calculation method. This study has certain theoretical significance for carrying out the design of low-noise and vibration of shaft systems and improving the safety of ship navigation. Keywords shafting torsional vibration; transient time domain; finite element method; vibration test
_ With the effects of global warming, the North Sea Route has become an economic option for cargo transportation because of the shorter distance between East Asia and Europe. Generally, conventional mechanical propulsion systems installed in ice-capable tankers suffer from significant drawbacks because of poor fuel efficiency when sailing at low speed, therefore, advanced technologies have been applied such as diesel electric and nuclear-powered propulsion; however, drawbacks still exist. Hybrid propulsion is a more environmental-friendly, economical solution for ships with icebreaking capability, which can address the drawbacks in both diesel electric and nuclear power systems. In this paper, modeling of system components is presented and implemented in MATLAB Simulink. A primary control strategy is applied to the system to ensure system stability, and an advanced secondary strategy is developed and applied to the power sources to minimize fuel consumption. Given two scenarios, the simulation results of the hybrid propulsion system developed in this research and those of diesel electric propulsion systems with DC and AC distribution systems are compared and indicate that the hybrid system can offer up to 22.4% fuel savings over ice-loading condition, and 39.5% fuel reduction over the particular voyage of varying speed in open water is applied in this paper. Introduction In recent years, some sea routes that were previously blocked by ice have become increasingly accessible in the warmest months of the year due to the effects of global warming. Researchers have estimated that, by 2030, the percentage of Arctic shipping will have increased to 25% of cargo trade between Europe and Asia (Lasserre 2019). Northern Sea Route (NSR) shipping provides benefits for international trade, but challenges still exist. Increasing carbon emissions have seriously impacted the Arctic environment (Hassol & Corell 2006). Table 1 shows the total number of ships using Heavy Fuel Oil (HFO) in Arctic waters in 2015, and associated black carbon emissions, as published by the IMO (Comer et al. 2017). As it is shown, oil tankers made up just 4.5% of all ships entering Arctic waters but despite their low proportion, they were responsible for 17% of black carbon emissions. Thus, an environmentally friendly and fuel-efficient propulsion system to reduce these emissions from tankers trading in Arctic waters is required.
Hull optimization is an important aspect of ship design to improve safety and economic-technical efficiency for ships. This problem has been studied for a long time and has achieved many significant results, but in practical applications, there are still some contents that need to be improved such as the presentation and transformation of the existing hulls, an optimal mathematical model suitable for a specific type of ship, or method for solving the objective function, etc. On that basis, in this paper, a method for optimizing the hull form of fishing vessels is presented, including algorithms using interpolating cubic spline to generate the existing hulls that pass exactly through the given offsets and are constructed in a format to use both Computational Fluid Dynamics (CFD) analysis in resistance prediction and Lackenby method in hull form transformation, a suitable mathematical model for hull optimization problem of fishing vessels, an effective solver based on a combination of CFD, Kriging surrogate models, and traditional optimization techniques. In addition, solutions for improving the accuracy of CFD-based resistance predictions are also presented based on ensuring the accuracy of the 3D hull models and determining the suitable input parameters used for CFD simulations. This study was applied to optimize the hull form of a Vietnamese traditional wooden fishing vessel, symbol MH076, and obtained results that are consistent with the theoretical and practical trends, with the deviations of CFD-based resistance values and corresponding model test data are within the range of 63% and the reduction in total resistance or required power at design operating is around 8.81%.
_ Hydrofoils made of metal alloys were broadly used on high-speed boats in the past. Nowadays, much lighter hydrofoils made of composite materials are finding increasingly more applications on sailing yachts and powerboats. However, these hydrofoils are usually rather flexible, and their design requires computationally demanding analysis, involving hydroelastic calculations. In this study, exploratory high-fidelity simulations have been carried out for surface-piercing hydrofoils in unsteady conditions with help of a computational fluid dynamics solver for fluid flow coupled with a finite element solver for the foil structure. To model unsteady foil deformations, the morphing mesh approach was utilized, and the volume-of-fluid method was applied for multiphase flow simulations. The computational setup, as well as verification and validation study, is described in this paper. Three hydrofoils of different stiffness, including a perfectly rigid foil, were simulated in both calm water conditions and regular head waves. Representative examples of foil deflections and wave patterns, as well as time-dependent structural and hydrodynamic characteristics, are presented. Introduction Hydrofoils are efficient lift-generating devices intended for application in water flows. Hydrofoils have streamlined shapes, and when operating at small incidence angles, they can produce high lift forces at relatively low drag, when moving in a certain speed range. Due to this ability, hydrofoils and their derivatives are commonly used as control and propulsive devices, e.g., as rudders, fins, and propeller sections. In the second half of the last century, hydrofoils found broad applications on fast boats, such as passenger ferries and military ships (McLeavy 1976; Matveev & Duncan 2005). These craft were able to achieve high speeds at lift–drag ratios (LDR) around 12–15, significantly higher than LDR of other hulls, such as planing boats. However, due to rather limited favorable operational conditions with regard to speed and payload, popularity of hydrofoils somewhat receded. One of drawbacks was that hydrofoils were usually made of metal alloys, thus being relatively heavy and difficult to service.
_ Considering the main structures of typical underwater vehicles, three types of numerical model are established, including the beam model, the shell-beam model, and the whole shell model. The results of the three models are compared during the analyses of global vibration, local vibration of cabins, and underwater acoustic radiation. Giving consideration to both the computational cost and accuracy, the proposed shell-beam model is appropriate for the calculation of low-medium frequency acoustic radiation of the main structures of underwater vehicles. The rationality and the frequency range of application of the shell-beam model are verified by calculating the fluid-structure coupling vibration response and the underwater acoustic radiation of the hull subjected to the transverse load excitation, which also demonstrate the significance of this model in engineering practice. Introduction The calculation research on the acoustic radiation of typical underwater vehicle structures can be generally divided into three types based on the calculation methods: analytical methods (Caresta & Kessissoglou 2009), numerical methods, and analytical-numerical hybrid methods (Zhu et al. 2014; Meyer et al. 2016; Qu et al. 2017). The analytical methods can be used for the study of basic laws and mechanisms, and can also be treated as benchmarks for numerical algorithms. However, when it comes to real ships with complex structures, it is difficult to accurately predict the forced vibration and underwater acoustic radiation characteristics by analytical methods. Previously, due to the limitation of the computer hardware, a whole ship was usually simplified as a free–free beam of variable cross section (the hull beam) when conducting the analysis of global vibration. In recent years, with the development of computer technology, whole shell models are usually established during analyses of the low-medium frequency vibration and acoustic radiation of underwater vehicles.
Many tools have been developed to simulate unmanned underwater vehicle (UUV) motion and autonomous behaviors to evaluate UUV capabilities. However, there is no simulator that performs real-time modeling of the complex hydrodynamic interaction forces that a UUV experiences when operating near a moving submarine. These hydrodynamic interactions must be determined in real time to simulate the launch and recovery of UUVs from submarines. Potential flow models may be fast enough to solve the hydrodynamic interactions in real time, but by oversimplifying the physics and neglecting viscosity, they introduce inaccuracies into the simulations. Computational fluid dynamics (CFD) is capable of accurately modeling these hydrodynamic interactions, but simulations take hours or days to solve. To overcome this obstacle, a machine learning method known as Gaussian process (GP) regression is used to create a surrogate reduced-order-model that predicts the hydrodynamic interactions in real time. The GP regression model is trained by actively sampling CFD simulations in order to accurately model complex hydrodynamic interactions. This new approach allows the GP regression model to be incorporated into a UUV motion simulator and evaluate how the UUV is affected by the hydrodynamic interactions. Operating envelopes are developed that outline regions where the UUV safely overcomes the hydrodynamic interactions and where the UUV is overpowered and collides with the submarine. By incorporating this surrogate model into the autonomy architecture, new autonomous behaviors are created that compensate for the hydrodynamic interactions by adjusting the desired UUV heading and speed which allows it to better stay on course.
