To calculate the electromagnetic fields induced by the flow around moving objects in the ocean, Maxwell’s equations for a moving conductive medium were derived based on the principle of relativity, and the Lorentz covariant problem of Ohm's law was addressed. By applying the Lorentz transformation to shift the problem into a reference frame moving with the object, the calculation of electromagnetic fields induced by the wake becomes a steady-state problem, significantly simplifying the process.Formulas for electromagnetic fields induced by point sources and dipole flow fields are provided, revealing that a vortex field is a necessary condition for generating induced charge. An approximate calculation model for the induced electromagnetic fields in the wake of a marine moving object is established, with which it is estimated that the induced magnetic intensity at a distance of 1 kilometer behind the object is approximately 0.0006 nT.

To analyze the propagation of pressure waves generated during spherical projectile water entry within liquid-filled structures, this study establishes a computational model for the pressure wave considering reflection from a preset air layer. The model combines the virtual and real mirror methods with potential flow theory, and its accuracy is validated through numerical simulations. Using the established model, the propagation processes of the pressure wave during projectile water entry within liquid-filled structures configured with either a top air layer or a centrally located spherical air layer are examined. The effects of air layer height h, spherical air layer center location D and radius r on the strength and propagation of the pressure wave in water are analyzed. The results show that the rarefaction wave reflected from the air layer interface induces a truncation effect on the pressure wave propagation, significantly reducing the duration of positive pressure and the specific impulse. Moreover, the specific impulse decreases as h and r increase. A smaller D leads to more significant attenuation of the initial pressure wave specific impulse, while a larger D results in more noticeable attenuation of the secondary pressure wave peak and its specific impulse.

Seaplanes are subjected to hydrodynamic forces, including slamming, splashing, and wave interference during aquatic operations. When planing or gliding on the water surface, seaplanes may experience slamming, where the aircraft impacts the water at high speed, resulting in significant vertical acceleration and impact forces. A numerical model of the aircraft was initially developed using Computational Fluid Dynamics (CFD). To account for the interaction between air and water, the Volume of Fluid (VOF) model was employed to solve the Reynolds-averaged Navier-Stokes equations. The Dynamic Fluid-Body Interaction (DFBI) method was applied to simulate the six-degree-of-freedom motion of the seaplane. Numerical simulations were performed at different gliding speeds. Next, the simulation results are compared with experimental data, validating the applicability of the numerical method for investigating the motion characteristics of the seaplane while gliding over waves. Finally, simulations under different wave conditions were carried out. The influence of wave parameters on the motion of the seaplane was investigated using the CFD method. The results indicate that the hydrodynamic load significantly affects the motion characteristics of the seaplane during gliding over waves.

To address the difficulty in self-starting for vertical-axis water turbines with fixed pitch angles and to improve the efficiency of marine energy utilization, a hybrid power generation device was proposed that incorporated a Savonius-type wind rotor to assist in starting the vertical-axis water turbine. Numerical simulations were conducted to investigate the dynamic output characteristics of this integrated device. Firstly, a three-dimensional two-phase flow numerical tank was constructed using Fluent software, and the mesh partitioning scheme was determined by comparing the values of the power output parameters of the device under different mesh densities, and at the same time, the validity of the numerical tank was confirmed. Secondly, the established numerical tank was used to simulate the variation law of torque, speed and power coefficient of power generation devices under different flow field conditions with different water wheel blade numbers, radius ratios and height ratios. The results show that the device performs better in terms of torque stability, speed characteristics, and energy utilization in the simulated working condition range when the water wheel blades are 3 to 4, the radius ratio is 0.25 to 0.375, and the height ratio is 1/6 to 1/3. The device is able to start quickly in the presence of wind, and the power coefficient reaches 0.3 to 0.4 or even exceeds 0.4, with good starting and power generation performance. The research results can provide a reference for the design and application of the device.

Polymer materials are usually applied to the sheath layers on the surface of marine flexible pipes. Such kind of material exhibits certain nonlinear characteristics, specifically manifested as a stress-strain nonlinearity and stress relaxation phenomena. In this paper, specimens are specially designed, and specific testing instruments are used according to relevant international standards to conduct tensile and stress relaxation tests on polymer materials for marine non-bonded pipes under high temperature environments. The tensile stress-strain curve and stress relaxation curve are obtained, and the Prony series constitutive parameters describing their stress relaxation characteristics are then identified from the stress relaxation test data, and verified using finite element method. Finally, the characteristics of stress relaxation in polymer materials are discussed. It is found that there is no pure elastic deformation stage in polymer materials during tensile deformation, and that the coexistence of elastic deformation and plastic deformation is reflected from the beginning of tensile deformation. The essence of stress relaxation phenomenon in polymer materials is the transformation from elastic to plastic deformation of the material. When plastic deformation accounts for the majority of internal deformation of the material, the percentage of stress reduction during the relaxation process will be smaller compared with the case when elastic deformation accounts for the majority. In engineering, if considering to reduce the effects of stress relaxation, polymer materials can be approximately taken as directly entering plastic deformation stage.

This paper investigates the effects of different overload conditions on crack propagation behavior of AH32 steel, including tensile overload ratios, overload-underload, underload-overload and underload. The residual stress distribution in the region near the crack tip under different overload ratios and overload conditions all result from plastic deformation of the material near the crack tip during fatigue crack propagation. It is shown that applying tensile overload postpones the crack growth, while underload promotes the crack growth. Furthermore, it is also observed that the crack closure level shows a fast increase with the increase of overload ratio. Finally, it can be seen that the mechanism of residual stress at the crack tip and the mechanism of plastic deformation at the crack tip controlling the transient crack growth behavior under variable amplitude loading are essentially the same.

Fatigue life evaluation for marine structures subjected to the cyclic loading comprising low-frequency and high-frequency load components is an important issue at design stage. In this study, prediction models for fatigue crack growth in marine structural steel under high-low frequency superimposed loading are respectively developed by using three machine learning algorithms: genetic algorithm-optimized back-propagation (GA-BP) neural network, radial basis function (RBF) neural network and Bayesian-optimized random forest (BO-RF). The models are trained and validated by using dataset of fatigue crack growth tests under various loading conditions with different load amplitude ratios, load frequency ratios and mean load levels. The predictive performance of the machine learning models is compared with each other as well as theoretical models including the modified Wheeler model and the Huang model. Results demonstrate that the machine learning models exhibit better agreement with experimental data compared to the theoretical models, and the GA-BP neural network model achieves the best accuracy. It indicates that the neural network models, by effectively capturing the interaction effects between LF and HF load components represent a robust and promising tool for predicting fatigue crack growth behaviour in marine structural steel.

To enhance the bending mechanical properties of fiber-reinforced plastics (FRP) and address rapid damage repair under multiple bending loads, an improved shape memory alloy hybrid composite (ISMAHC) was developed by embedding layered orthogonal shape memory alloy (SMA) wires into FRP. Three-point bending and water bath recovery tests were performed on traditional single-layer unidirectional SMA hybrid composites (SMAHC), ISMAHC and FRP. The effects of layered orthogonal SMA configuration on stiffness, strength, and recovery capability were compared and investigated. Results demonstrate that SMA wires form a coupling effect with FRP, increasing the bending modulus. Furthermore, ISMAHC has higher stiffness due to its orthogonal architecture. The water bath recovery tests indicate that SMAHC and ISMAHC possess good deflection recoverability and mechanical property recoverability after multiple bending loadings. The deflection recovery rate of the first bending test is greater than 60%, and that of the second bending test is greater than 30%. Additionally, the bending modulus and bending strength recover more than 30%, with ISMAHC showing superior recoverability.

With in-depth research on honeycomb structures for ship protection, diverse 3D honeycomb configurations have emerged. This paper aims to explore the traits of different 3D honeycomb designs and offer ideas for the future structural layouts. Both experimental tests and numerical analysis on the mechanical properties of 3D plate-frame and truss honeycombs were carried out. The test samples, made of nylon via laser sintering in an additive manufacturing process, underwent quasi-static compression tests to uncover the disparities in deformation patterns between the two honeycombs. By closely examining typical cell deformations during compression, the differences in failure modes were revealed. Because the load-bearing capacity of a structure and its density, the authors while studying these two types of honeycombs, also explored the relationship between the specific stiffness and nominal density of various typical 2D and 3D structures. Finally, a parametric analysis was performed to assess the impact of internal concavity angles, cell thicknesses, and materials on mechanical properties.

The maritime environment and loading conditions encountered by large ore carriers are highly complex. It is a problem worth studying to scientifically describe the uncertain load of ore carriers and evaluate the safety margin of hull beams quantitatively. This paper investigated the stochastic characteristics of environmental loads and ship internal loads and explored methods for combining multiple loads and their nature mechanics. This research also revealed the still-water bending moment characteristics under typical loading conditions. WALCS hydrodynamic analysis software was used to calculate the wave load response function of the target ship. The extreme values of the wave bending moments were obtained using the extreme value type I (Gumbel type I) long-term forecasting method. The statistical characteristics of the wavebending moments were analyzed. Based on the uncertainty load combination method, the hull girder safety margin of the target ship was obtained as 1.10-1.20. The rationality of the load system specified in the CCS rules for ore carriers is further validated. The results show that the method can be applied to the formulation of relevant ore ship rules by CCS and effectively reveal the safety margins behind the rules. Understanding of the GBS-type ship rule has been enhanced. This research provides an important reference for the development of large ore carriers.

Corrosion-fatigue coupling presents significantly greater risks than damage mechanisms in isolation. This review synthesizes recent research advancements in theoretical frameworks, computational simulations, and experimental methodologies, with a focus on the pitting evolution and crack propagation stages. Existing models of pitting morphology are commonly constrained by single-defect assumptions and geometric regularization, which hinder a comprehensive and multidimensional characterization of pits. In the modeling of crack propagation, three primary paradigms have emerged: mechanism-driven models, data-driven models, and hybrid-enhanced models. Among these approaches, physics-informed neural networks demonstrate considerable potential in addressing complex interactions between corrosion and fatigue. A critical issue identified is the empirical oversimplification in pitting characterization, particularly the assumption of geometric regularity, which serves as a key bottleneck in quantifying corrosion-fatigue synergies. To overcome this limitation, there is a need to develop integrated multidimensional quantification methods that incorporate size, shape, irregularity, and statistical distribution. This area represents a pivotal research frontier. Advancements in this field will lead to transformative insights into the fundamental coupling mechanisms and the assessment of structural integrity for engineering systems. Ultimately, this will facilitate the development of highly accurate corrosion-fatigue life prediction models, which are essential for ensuring the safety of infrastructure.

Extreme ice floe impact events on polar ship structures are very common in ice regions. The inelastic deformation of structures under ice impact loadings reflects directly the damage states of the structures and is thus an important and convenient parameter in structural strength assessment and design. Therefore, the aim of this paper is to review the recent research progress on dynamic inelastic response of polar ship structure subjected to ice floe impact. Some important experimental, numerical and theoretical work was introduced to study dynamic plastic responses of ship plates under single and repeated ice impact loadings. The effects of ice deformation and damage characteristics on the plastic energy absorption of ship plates were evaluated in this paper by comparing with rigid mass impact responses. In addition, the plastic deformation accumulation, energy-sharing mechanisms and pseudo-shakedown phenomenon of ship plates subjected to identical repeated ice impacts were explored. Based on the analytical solutions for inelastic response of ship plates under ice impact, some plastic design formulae and curves were proposed to determine the thickness of ship plates under ice impact loading, which can provide useful references for the structural design of ice-going ships.