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.

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.

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.

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 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.

In ocean engineering and coastal protection, a precise understanding of the interaction mechanism between breaking waves and offshore structures is a fundamental scientific issue for ensuring operational safety and enhancing protection efficiency. Based on the open-source computational fluid dynamics platform OpenFOAM, this study innovatively combines the thincFoam solver using the THINC/QQ interface capturing scheme with a stable k-ω SST turbulence model to develop a high-fidelity numerical framework for the detailed simulation of wave breaking processes. The proposed model achieves high-resolution capture and quantitative analysis of key physical parameters during wave breaking, including the evolution of free-surface morphology, dynamic flow field structures, pressure peak characteristics, and energy dissipation mechanisms. Numerical verification demonstrates that the proposed model has excellent predictive ability for solitary wave propagation, accurately reproducing the free-surface elevation as well as the spatio-temporal distribution of the velocity and pressure fields. Through systematic numerical experiments, this study elucidates the multi-scale wave dissipation mechanisms of pile-type breakwaters under solitary wave action: Turbulent mixture induced by free-surface fragmentation, oscillatory jets generated in the gaps between piles, vortex structures formed in the wake region, and wave breaking caused by nonlinear interactions between backflow and the remaining wave body. These processes collectively constitute a multiphysics synergy mechanism for wave energy dissipation. The findings not only provide a theoretical foundation for the optimized design of pile-type breakwaters but also offer an effective numerical tool for simulating wave-structure interactions, contributing to the theoretical development and technological progress in the field of ocean engineering.

To improve the C-type turning performance of a biomimetic robotic shark, the kinematics and hydrodynamics of the C-type turning motion of a self-propelled robotic shark were studied using Computational Fluid Dynamics (CFD) simulation method. A simulation model of the robotic shark and its turning kinematic and dynamic equations were established. The influences of parameters such as the minimum curvature radius R₀ of fish body bending, the asymmetry coefficient R_s of caudal fin, and the distance between fish and wall (dh) on turning velocity and hydrodynamic parameters were numerically studied, and the evolution process of flow field structure during C-type turning process was analyzed. The results indicate that the smaller R₀ is, the shorter the turning distance becomes and the larger the turning angle is. The asymmetric caudal fin can contribute to improving turning performance, but excessive R_s will lead to a decrease in turning stability. The wall effect is conducive to increasing turning speed and reducing turning distance.

When the frequency of external wave excitation or that of platform motion approaches the natural frequency of the moonpool structure, intense resonance phenomena occur within the moonpool. Under such conditions, both the water inside the moonpool and the platform motion exhibit strong nonlinear characteristics. Based on computational fluid dynamics (CFD) principles, this study conducts numerical simulations of a deep-draft cylindrical platform under regular wave action to investigate the influence mechanisms of incident wave frequency and environmental wave height on the coupled system of platform motion and moonpool water dynamics. The results indicate that increasing environmental wave height intensifies nonlinear phenomena in the moonpool water motion, characterized by enhanced resonance peaks in high-frequency bands and reduced piston-mode resonance peaks. A strong coupling relationship exists between platform motion and moonpool water dynamics, where both the moonpool resonance phenomena and platform motion responses demonstrate dual-peak characteristics. As the environmental wave height increases, the heave response amplitude operator (RAO) amplitude decreases, while the platform’s pitch RAO amplitude increases.

Under low-speed and deflection conditions, water-lubricated journal bearings (WLJBs) with large length-to-diameter ratios frequently exhibit abnormal wear and frictional vibrations, significantly compromising ship reliability and stealth capabilities. However, comprehensive experimental investigations on full-scale WLJBs remain insufficient, and the evolutionary mechanisms of dynamic behaviors under varying service conditions require further exploration. This study developed a distributed testing system for WLJBs based on a full-scale propulsion shafting test rig, and conducted running-in, speed characteristic, and elevation characteristic tests. From the perspective of tribological characteristics and lubrication zoning, the dynamic behavioral variations of different lubrication sub-regions under operational conditions are systematically revealed. The experimental results demonstrate that increased rotational speeds exacerbate shaft journal deflection, inducing hydrodynamic pressure peak migration toward the free-end lubrication sub-region; elevation modifications alter load distribution patterns among lubrication sub-regions, and distinct lift-off characteristics emerge among different lubrication sub-regions. These results provide critical validation data for developing dynamic models and optimizing structural designs of full-scale WLJBs in marine propulsion systems.

The coexistence of waves and broken ice is a prominent feature in marginal ice zones. Ships navigating in these areas are subjected to combined loads from both ice and wave actions. While current research has obtained substantial findings on ship ice resistance characteristics under either single wave or ice conditions, studies on coupled wave-broken ice interactions remain relatively scarce, resulting in insufficient understanding of the ship-ice-wave interaction mechanisms and their impacts on vessel navigation performance. To investigate ice resistance characteristics in broken ice fields under wave effects, this study developed a numerical model by adopting a coupled Computational Fluid Dynamics-Discrete Element Method (CFD-DEM) for ship navigation in wave-affected broken ice environments. The numerical wave tank was first established using the Finite Volume Method (FVM), while the broken ice model was developed through the Discrete Element Method (DEM). The validity of the ship resistance model under either single wave or ice conditions was verified through comparisons between theoretical solutions and experimental data. Subsequently, the ice resistance characteristics of ships navigating in wave-affected broken ice fields were systematically analyzed, with particular focus on the influences of wave parameters and ice concentrations. The results demonstrated that wave action significantly alters the ship-ice interaction process, inducing distinct periodic fluctuations in ice resistance. Notably, the ice resistance under combined wave-ice conditions consistently exceeds that observed in still water conditions with equivalent ice concentrations. Furthermore, the influence of key parameters including wavelength, wave height, and ice concentration on ice resistance behavior was also elucidated.