The environment and structure of the tanks used in aquaculture vessels are remarkably different from those of ordinary ships, and the resulting problem of structural strength is related to breeding safety. In this study, a model of aquaculture tank corrosion was constructed by using the multiphysical field coupling analysis software COMSOL Multiphysics, and wave and sloshing loads were calculated on the basis of potential flow theory and computational fluid dynamics. The influence of different calculation methods for corrosion allowance and sloshing load on the structural responses of aquaculture tanks was analyzed. Through our calculations, we found that the corrosion of aquaculture tanks is different from that of ordinary ships. The corrosion allowance in Rules for the Classification of Sea-going Steel Ships is small, and the influence of the aquaculture environment on corrosion can be ignored. Compared with the method set in the relevant rules, our proposed coupling direct calculation method for the structural response calculation of aquaculture tanks can better combine the specific environment of aquaculture tanks and provide more accurate calculations.

The present work analyzes the interaction of oblique waves by a porous flexible breakwater in the presence of a step-type bottom. The physical models for both scattering and trapping cases are considered and developed within the framework of small amplitude water-wave theory. Darcy’s law is used to model the wave interaction with the porous medium. It is assumed that the varying bottom extends over a finite interval, connected by a finite length of uniform bottom near an impermeable wall, and a semi-infinite length of bottom in the open water region. The boundary value problem is solved using the eigenfunction expansion method in the uniform bottom regions, while a modified mild-slope equation (MMSE) is used for the region with the varying bottom. Additionally, a mass-conserving jump condition is employed to handle the solution at slope discontinuities in the bottom. A system of equations is derived by matching the solutions at interfaces. The reflection coefficient and force on the breakwater and impermeable wall are plotted and analyzed for various parameters, such as the length of the varying bottom, depth ratio, angle of incidence, and flexural rigidity. It is observed that moderate values of flexural rigidity and depth ratio significantly contribute to an optimum reflection coefficient and reduce the wave force on the wall and breakwater. Remarkably, the outcomes of this study are assumed to be applicable in the construction of this type of breakwater in coastal regions.

In this paper, numerical analyses of fluid flow around the ship hulls such as Series 60, the Kriso Container Ship (KCS), and catamaran advancing in calm water, are presented. A commercial computational fluid dynamic (CFD) code, STAR-CCM+ is used to analyze total resistance, sinkage, trim, wave profile, and wave pattern for a range of Froude numbers. The governing RANS equations of fluid flow are discretized using the finite volume method (FVM), and the pressure-velocity coupling equations are solved using the SIMPLE (semi-implicit method for pressure linked equations) algorithm. Volume of fluid (VOF) method is employed to capture the interface between air and water phases. A fine discretization is performed in between these two phases to get a higher mesh resolution. The fluid-structure interaction (FSI) is modeled with the dynamic fluidbody interaction (DFBI) module within the STAR-CCM+. The numerical results are verified using the results available in the literatures. Grid convergence studies are also carried out to determine the dependence of results on the grid quality. In comparison to previous findings, the current CFD analysis shows the satisfactory results.

This paper develops a numerical code for modelling liquid sloshing. The coupled boundary element-finite element method was used to solve the Laplace equation for inviscid fluid and nonlinear free surface boundary conditions. Using Nakayama and Washizu’s results, the code performance was validated. Using the developed numerical mode, we proposed artificial neural network (ANN) and genetic algorithm (GA) methods for evaluating sloshing loads and comparing them. To compare the efficiency of the suggested methods, the maximum free surface displacement and the maximum horizontal force exerted on a rectangular tank’s perimeter are examined. It can be seen from the results that both ANNs and GAs can accurately predict η_max and F_max.

Blasting and shaped charges are the main forms of underwater weapons, and their near-field underwater explosions (UNDEX) can severely damage structures. Therefore, it is of great importance to study underwater explosive load characteristics of different forms of charges. The full physical process of a typical underwater explosion of a sphere/column blasting charge and a shaped charge was simulated using the Eulerian method. The loading characteristics of the underwater blast shock wave and bubble, as well as the projectile, were studied. The results show that the shock wave loads of spherical, cylindrical, and polygonal charges propagate outward in spherical, ellipsoidal-spherical and ellipsoidal- spherical wavefronts, respectively. When the shock wave reaches 16 times the distance-to-diameter ratio, its surface is approximately spherical. In addition, in the shaped charge underwater explosion, the shaped charge liner cover absorbs 30°-90° of the shock wave energy and some of the bubble energy to form a high-speed shaped penetrator. Spherical, ellipsoidal, and ellipsoidal bubbles are generated by underwater explosions of spherical, cylindrical, and shaped charges, respectively. The obtained results provide a reference for evaluating the power of underwater weapons.

Despite the non-contact underwater explosion phenomena (UNDEX) have been studied for decades and several numerical methods have been proposed in literature, its effects on military structures, especially composite ones, are even nowadays matter of research. In early design phases, it is not always possible to verify the shock resistance of hull structures modelling the whole phenomenon, in which fluid, gas and solid properties must be properly set in a fully coupled fluid-structure interaction (FSI) numerical model. These ones are extremely complex to set, computationally demanding and certainly not suitable for everyday design practice. In this paper, a simplified finite element (FE) model, easy to use in an early design phase, is proposed. Both, the structure and the fluid are simulated. In this approximation, the fluid behaviour is simplified, using special finite elements, available in a commercial software environment. This choice reduces the computational time and numerical efforts avoiding the problem of combining computational fluid dynamics (CFD) and FE domains and equations in a fully coupled fluidstructure interaction model. A typical parallel body block of a minesweeper is modelled, using two-dimensional multi-layered shell elements to properly account for the composite materials behaviour. For the fluid instead, three dimensional volumetric elements, directly coupled to the structural elements, are placed. In addition, the same calculation is performed, modelling separately fluid in the CFD environment and structures in the finite element one. Thus, realizing a fully coupled fluid-structure interaction model. The results obtained by applying both numerical models are compared with the structural response measured on board of a composite ship during a full-scale shock test. The simplified proposed procedure provides results in satisfactory agreement with experiments, allowing the validation of the model. Approximations are discussed and differences with the real phenomenon and fully coupled CFD+FE method are shown, providing a better understanding of the phenomena. Eventually, the modelling strategy has been considered a valuable and cost-effective tool for the concept and preliminary design of composite structures subject to underwater explosions.

Fishing boats have unique features that make them prone to changing loading conditions. When the boat leaves the port, the empty fish tank gradually fills up during fishing operations which may result in parametric roll (PR). This dangerous phenomenon that can lead to capsizing. The present study aims to understand better the behaviour of parametric roll in fishing boats and its relation to changing loading conditions. The study considers the effects of displacement and the GM/KM ratio on parametric roll, as well as the longitudinal flare distribution at the waterline. Two assessments to detect the parametric roll occurrence in early stage were carried out by using the level 1 assessment of parametric roll based on the Second Generation of Intact Stability criteria (SGIS) from International maritime Organisation (IMO) and the Susceptibility criteria of Parametric roll from the American Bureau of Shipping (ABS). Then, the CFD method is used to predict the amplitude of the parametric roll phenomenon. The results provide important insights to fishing vessel operators on how to manage loading conditions to maintain stability and avoid hazardous situations. By following the guidelines outlined in this study, fishing boats can operate more safely and efficiently, reducing the risk of accidents and improving the overall sustainability of the fishing industry.

To achieve hydrodynamic design excellence in Autonomous Underwater Vehicles (AUVs) largely depends on the accurate prediction of lift and drag forces. The study presents Computational Fluid Dynamics (CFD)-based lift and drag estimations of a novel torpedo-shaped flight-style AUV with bow-wings. The horizontal bow-wings are provided to accommodate the electromagnetic arrays used to perform the cable detection and tracking operations near the seabed. The hydrodynamic performance of the AUV due to addition of these horizontal bow-wings is required to be investigated, particularly at the initial design stage. Hence, CFD techniques are employed to compute the lift and drag forces observed by the flight-style AUV, maneuvering underwater at different angles of attack and varying speeds. The Reynolds-Averaged Navier-Stokes Equations (RANSE) closure is achieved by employing the modified k-? model and Two-Scale Wall Function (2-SWF) approach is used for boundary layer treatment. Further, the study also highlights the unique mesh refinement and solution-adaptive meshing techniques to perform the CFD simulations in Solidworks Flow Simulation (SWFS) environment. The drag polar curve for flight-style AUV with and without bowwings is generated using the computed lift and drag coefficients. The curve provided essential insights for achieving hydrodynamically efficient and optimized AUV design. From the drag polar curve, it is revealed that due to horizontal bow-wings, the flight-style AUV is capable to generate higher lift with less drag and thus, it gives better lift-to-drag ratio compared to the AUV without bow-wings. Moreover, simulated results of axial drag observed by the AUV have also been compared with free-running experimental results and are found in good agreement.

Combining the strengths of Lagrangian and Eulerian descriptions, the coupled Lagrangian-Eulerian methods play an increasingly important role in various subjects. This work reviews their development and application in ocean engineering. Initially, we briefly outline the advantages and disadvantages of the Lagrangian and Eulerian descriptions and the main characteristics of the coupled Lagrangian-Eulerian approach. Then, following the developmental trajectory of these methods, the fundamental formulations and the frameworks of various approaches, including the arbitrary Lagrangian-Eulerian finite element method, the particle-in-cell method, the material point method, and the recently developed Lagrangian-Eulerian stabilized collocation method, are detailedly reviewed. In addition, the article reviews the research progress of these methods with applications in ocean hydrodynamics, focusing on free surface flows, numerical wave generation, wave overturning and breaking, interactions between waves and coastal structures, fluid-rigid body interactions, fluid-elastic body interactions, multiphase flow problems and visualization of ocean flows, etc. Furthermore, the latest research advancements in the numerical stability, accuracy, efficiency, and consistency of the coupled Lagrangian-Eulerian particle methods are reviewed; these advancements enable efficient and highly accurate simulation of complicated multiphysics problems in ocean and coastal engineering. By building on these works, the current challenges and future directions of the hybrid Lagrangian-Eulerian particle methods are summarized.

The dynamic stiffness of polyester rope presents a complex mechanical performance, and the search for an appropriate calculation method to simulate this property is important. Distorted simulation results eventually yield inaccurate line tension and vessel offset predictions, with the inaccuracy of vessel offset being particularly large. This paper proposes a flexible calculation method for the dynamic behavior of polyester rope based on the dynamic stiffness model. A real-time varying stiffness model of polyester rope is employed to simulate tension response through rope strain monitoring. Consequently, a simulation program is developed, and related case studies are conducted to explore the differences between the proposed method and analytical procedure of the DNV standard. Orcaflex is used to simulate the results of the latter procedure for comparison. Results show the convenience and straightforwardness of the procedure in the selection of an approximate dynamic stiffness model for polyester rope, which leads to an engineering-oriented approach. However, the proposed method is related to line property, which can directly reflect the dynamic behavior of polyester rope. Thus, a flexible calculation method may provide a reference for the simulation of the dynamic response of polyester mooring systems.

The tripod foundation (TF) is a prevalent foundation configuration in contemporary engineering practices. In comparison to a single pile, TF comprised interconnected individual piles, resulting in enhanced bearing capacity and stability. A physical model test was conducted within a sandy soil foundation, systematically varying the length-to-diameter ratio of the TF. The investigation aimed to comprehend the impact of altering the height of the central bucket on the historical horizontal bearing capacity of the foundation in saturated sand. Additionally, the study scrutinized the historical consequences of soil pressure and pore water pressure surrounding the bucket throughout the loading process. The historical findings revealed a significant enhancement in the horizontal bearing capacity of the TF under undrained conditions. When subjected to a historical horizontal loading angle of 0° for a single pile, the multi-bucket foundation exhibited superior historical bearing capacity compared to a single-pile foundation experiencing a historical loading angle of 180° under pulling conditions. With each historical increment in bucket height from 150 mm to 350 mm in 100 mm intervals, the historical horizontal bearing capacity of the TF exhibited an approximately 75% increase relative to the 150 mm bucket height, indicating a proportional relationship. Importantly, the historical internal pore water pressure within the bucket foundation remained unaffected by drainage conditions during loading. Conversely, undrained conditions led to a historical elevation in pore water pressure at the lower side of the pressure bucket. Consequently, in practical engineering applications, the optimization of the historical bearing efficacy of the TF necessitated the historical closure of the valve atop the foundation to sustain internal negative pressure within the bucket. This historical measure served to augment the historical horizontal bearing capacity. Simultaneously, historical external loads, such as wind, waves, and currents, were directed towards any individual bucket within the TF for optimal historical performance.

Traditional direction of arrival (DOA) estimation methods based on sparse reconstruction commonly use convex or smooth functions to approximate non-convex and non-smooth sparse representation problems. This approach often introduces errors into the sparse representation model, necessitating the development of improved DOA estimation algorithms. Moreover, conventional DOA estimation methods typically assume that the signal coincides with a predetermined grid. However, in reality, this assumption often does not hold true. The likelihood of a signal not aligning precisely with the predefined grid is high, resulting in potential grid mismatch issues for the algorithm. To address the challenges associated with grid mismatch and errors in sparse representation models, this article proposes a novel high-performance off-grid DOA estimation approach based on iterative proximal projection (IPP). In the proposed method, we employ an alternating optimization strategy to jointly estimate sparse signals and grid offset parameters. A proximal function optimization model is utilized to address non-convex and nonsmooth sparse representation problems in DOA estimation. Subsequently, we leverage the smoothly clipped absolute deviation penalty (SCAD) function to compute the proximal operator for solving the model. Simulation and sea trial experiments have validated the superiority of the proposed method in terms of higher resolution and more accurate DOA estimation performance when compared to both traditional sparse reconstruction methods and advanced off-grid techniques.

In the field of array signal processing, uniform linear arrays (ULAs) are widely used to detect/separate a weak target and estimate its direction of arrival from interference and noise. Conventional beamforming (CBF) is robust but restricted by a wide mainlobe and high sidelobe level. Covariance-matrix-inversed beamforming techniques, such as the minimum variance distortionless response and multiple signal classification, are sensitive to signal mismatch and data snapshots and exhibit high-resolution performance because of the narrow mainlobe and low sidelobe level. Therefore, compared with the wideband CBF, this study proposes a robust focused-and-deconvolved conventional beamforming (RFDCBF), utilizing the Richardson-Lucy (R-L) iterative algorithm to deconvolve the focused conventional beam power of a half-wavelength spaced ULA. Then, the focused-and-deconvolved beam power achieves a narrower mainlobe and lower sidelobe level while retaining the robustness of wideband CBF. Moreover, compared with the wideband CBF, RFD-CBF can obtain a higher output signal-to-noise ratio (SNR). Finally, the performance of RFD-CBF is evaluated through numerical simulation and verified by sea trial data processing.

The estimation of sparse underwater acoustic (UWA) channels can be regarded as an inference problem involving hidden variables within the Bayesian framework. While the classical sparse Bayesian learning (SBL), derived through the expectation maximization (EM) algorithm, has been widely employed for UWA channel estimation, it still differs from the real posterior expectation of channels. In this paper, we propose an approach that combines variational inference (VI) and Markov chain Monte Carlo (MCMC) methods to provide a more accurate posterior estimation. Specifically, the SBL is first re-derived with VI, allowing us to replace the posterior distribution of the hidden variables with a variational distribution. Then, we determine the full conditional probability distribution for each variable in the variational distribution and then iteratively perform random Gibbs sampling in MCMC to converge the Markov chain. The results of simulation and experiment indicate that our estimation method achieves lower mean square error and bit error rate compared to the classic SBL approach. Additionally, it demonstrates an acceptable convergence speed.

The ultimate strength of platings under compression is one of the most important factors to be addressed in the ship design. Current Rules for ship structural design generally provide explicit strength check criteria against buckling for simply supported and clamped platings. Nevertheless, ship platings generally exhibit an intermediate behaviour between the simple support and the clamped conditions, which implies that the torsional stiffness of supporting members should be duly considered. Hence, the main aim of this study is the development of new design formulas for the ultimate strength of platings under uniaxial compression, with short and/or long edges elastically restrained against torsion. In this respect, two benchmark studies are performed. The former is devoted to the development of new equations for the elastic buckling coefficients of platings with edges elastically restrained against torsion, based on the results of the eigenvalue buckling analysis, performed by Ansys Mechanical APDL. The latter investigates the ultimate strength of platings with elastically restrained edges, by systematically varying the plate slenderness ratio and the torsional stiffness of supporting members. Finally, the effectiveness of the new formulation is checked against a wide number of finite element (FE) simulations, to cover the entire design space of ship platings.

This paper numerically evaluates the effect of the crack position on the ultimate strength of stiffened panels. Imperfections such as notches and cracks in aged marine stiffened panels can reduce their ultimate strength. To investigate the effect of crack length and position, a series of nonlinear finite element analyses were carried out and two cases were considered, i. e., case 1 with thin stiffeners and case 2 with thick stiffeners. In both cases, the stiffeners have the same cross-section area. To have a basis for comparison, the intact panels were modeled as well. The cracks and notches were in the longitudinal and transverse direction and were assumed to be in the middle part of the panel. The cracks and notches were assumed to be through the thickness and there is neither crack propagation nor contact between crack faces. Based on the numerical results, longitudinal cracks affect the behavior of the stiffened panels in the postbuckling region. When the stiffeners are thinner, they buckle first and provide no reserved strength after plate buckling. Thus, cracks in the stiffeners do not affect the ultimate strength in the case of the thinner stiffeners. Generally, when stiffeners are thicker, they affect the postbuckling behavior more. In that case, cracks in the stiffeners affect the buckling and failure modes of the stiffened panels. The effect of notch was also studied. In contrast to the longitudinal crack in stiffeners, a notch in the stiffeners reduces the ultimate strength of the stiffened panel for both slender and thick stiffeners.

This study investigates the mechanical properties of Q235B steel through quasi-static tests at both room temperature and elevated temperature. The initial values of the Johnson-Cook model parameters are determined using a fitting method. The global response surface algorithm is employed to optimize and calibrate the Johnson-Cook model parameters for Q235B steel under both room temperature and elevated temperature conditions. A simulation model is established at room temperature, and the simulated mechanical performance curves for displacement and stress are monitored. Multiple optimization algorithms are applied to optimize and calibrate the model parameters at room temperature. The global response surface algorithm is identified as the most suitable algorithm for this optimization problem. Sensitivity analysis is conducted to explore the impact of model parameters on the objective function. The analysis indicates that the optimized material model better fits the experimental values, aligning more closely with the actual test results of material strain mechanisms over a wide temperature range.

Considering the uncertainty of the speed of horizontal transportation equipment, a cooperative scheduling model of multiple equipment resources in the automated container terminal was constructed to minimize the completion time, thus improving the loading and unloading efficiencies of automated container terminals. The proposed model integrated the two loading and unloading processes of "double-trolley quay crane + AGV + ARMG" and "single-trolley quay crane + container truck + ARMG" and then designed the simulated annealing particle swarm algorithm to solve the model. By comparing the results of the particle swarm algorithm and genetic algorithm, the algorithm designed in this paper could effectively improve the global and local space search capability of finding the optimal solution. Furthermore, the results showed that the proposed method of collaborative scheduling of multiple equipment resources in automated terminals considering hybrid processes effectively improved the loading and unloading efficiencies of automated container terminals. The findings of this study provide a reference for the improvement of loading and unloading processes as well as coordinated scheduling in automated terminals.

A novel semi-submersible platform is proposed for 5 MW wind turbines. This concept focuses on an integrated system formed by combining porous shells with a semi-submersible platform. A coupled aerodynamic-hydrodynamic-mooring analysis of the new system is performed. The motion responses of the novel platform system and the traditional platform are compared. The differences in hydrodynamic performance between the two platforms are also evaluated. The influence of the geometric parameters (porosity, diameter, and wall thickness) of porous shells on the motion response behavior of the new system is studied. Overall, the new semi-submersible platform exhibits superior stability in terms of pitch and heave degrees of freedom, demonstrating minimal effects on the motion response in the surge degree of freedom.

Air pollution from shipping is becoming a critical issue, particularly in dense hub port cities. One proposed solution to minimize ship-based emissions at ports is the implementation of an Onshore Power Supply (OPS) system. OPS allows ships to shut off their auxiliary engines and instead connect to the port grid. While there have been numerous studies conducted on ports in Europe and the United States, little research has been done on Egyptian ports. Therefore, this paper aims to investigate the feasibility of implementing OPS at Port Said West Port in Egypt, aligning with Egypt Vision 2030’s goals for addressing climate change. The research primarily focuses on analyzing data collected from calling ships to generate socio-economic and cost-effectiveness analyses of OPS. To further enhance the environmental benefits of OPS, the paper proposes the use of solar energy as the OPS electricity source. The findings of the study revealed that by relying on the national grid, emissions can be reduced by 28%. Moreover, it is predicted that this reduction could reach 100% if electricity generation is solely based on solar energy. Additionally, the economic analysis demonstrates promising profitability, with a payback period of approximately two years.