Model experiment is an essential approach for investigating ice-structure interaction. The model ice employed in different ice tank laboratories and ice indentation tests (including saline ice, urea ice, and EG/AD/S ice, etc.) exhibits variations, and studying the mechanical characteristics of various model ices is crucial for conducting model experiments. In this study, the aforementioned three types of model ice were prepared in a low-temperature laboratory, uniaxial compression tests were performed, and the macroscopic failure characteristics of the model ice under different strain rates were comparatively analyzed; based on the Digital Image Correlation (DIC), the full-field strain and crack propagation process of the model ice were analyzed in detail, and the differences in the mechanical properties of the model ice were ultimately examined. The results indicate that saline ice exhibits the most similar failure behavior to sea ice, urea ice presents layered failure at high strain rates, and EG/AD/S model ice demonstrates predominantly ductile failure characteristics; the three types of model ice exhibit distinct crack propagation characteristics, with saline ice and urea ice possessing ductile and brittle failure intervals comparable to those of sea ice.

In the single-point mooring (SPM) system, the main bearing is a critical component that withstands mooring force, making its load-bearing performance under actual working conditions of great significance. However, research on this type of bearing remains limited, and existing studies have not considered the actual mooring force and installation structure. Therefore, this study focuses on the Soft Yoke Mooring System (SYMS) and proposes an overall finite element equivalent modeling method for the main bearing, by considering the mooring force and installation structure. In addition, to avoid extensive nonlinear contact problems, rollers and bolts are equivalently modeled using nonlinear springs and beam elements. After verifying the model's accuracy, we compare it with the traditional model under equivalent load and analyze the effects of upper load, bolt preload, and friction coefficient on the load-bearing performance of the main bearing. Finally, based on the maximum roller load obtained from both the overall and traditional models, a local contact model is established to calculate the safety factor of the main bearing. The results indicate that the overall equivalent model more accurately reflects the load distribution and deformation characteristics of the main bearing. Both the overall displacement and the bolt displacement decrease with increasing preload and friction coefficient, while contact pressure exhibits an increasing trend. The calculated safety factor of the main bearing in the overall model is 1.43, which is significantly lower than the safety factor of 2.51 obtained from the traditional model. This indicates that the traditional model overestimates the load-bearing capacity of the main bearing, while the overall model provides a more accurate assessment. Thus, the overall model provides a more reliable basis for the design of such bearings.

Thermoplastic composite pipes (TCP) have been widely used in marine structures. In this paper, a residual attention Brownian covariance neural network is established to study the damage identification of TCP composite delamination. Firstly, the curvature modes of multiple groups of thermoplastic composite tubes with single damage, multiple damages and different damage degrees were calculated using the finite element method. Then, the delamination damage identification method of thermoplastic composite tubes was discussed. Finally, the residual attention Brownian covariance network model was constructed using the curvature modes as input parameters to identify the delamination damage location and damage degree of TCP. The results show that the damage identification model based on residual attention Brownian covariance network can identify the location and degree of damage. The accuracy of damage location identification is 100%, and the error of damage degree identification is less than 6%. The research results provide a reference for non-destructive testing of marine engineering structures.

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 plastic deformation behavior of E40 steel in the tensile state was investigated by unidirectional tensile experiments, and the results showed that it has significant anisotropic characteristics. Based on the experimental results, three yield models, Hill48, Yld2000-2d, and Yld2004-18p, were parametrically calibrated, and their strain hardening behaviors were described using a modified Hockett-Sherby model. A VUMAT subroutine was developed and implemented using ABAQUS software and combined with a sheet metal stamping experimental system to evaluate the engineering applicability of different yield models. Comparison between numerical simulations and experimental results shows that under bending radii of $ r $ = 200 mm and $ r $ = 500 mm, the prediction error of the Yld2004-18p model is less than 4%, with its prediction accuracy approximately three times higher than that of the Hill48 model. The study shows that the Yld2004-18p model can more accurately portray the anisotropic response of E40 steel, which provides an effective constitutive modeling strategy for the simulation of precision forming of ship components.

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.

To address the practical requirements for enhancing the prediction methods of submarine maneuverability and seakeeping performance under complex sea conditions, overset mesh and sliding mesh techniques were employed to simulate the six-degree-of-freedom (6-DOF) coupled motion of the submarine, independent deflection of X-stern control surfaces, and rotation of the propeller. By integrating the Volume of Fluid (VOF) method to capture the free surface, a numerical simulation methodology for near-surface maneuvering motion of the free-running submarine model was developed. Through systematic investigations on the near-surface turning maneuvers of an X-rudder submarine under varying submergence depths in calm water and in regular waves of different wavelengths, critical challenges were resolved, including hydrodynamic coupling modeling of the hull-propeller-rudder system and the free surface, PD (Proportional-differential) control of the X-type autopilot, and PI (Proportional-integral) control of propeller rotational speed. The results demonstrated that when the submarine maneuvered excessively close to the free surface, the turning diameter, lateral advance, and maximum longitudinal advance of the X-rudder submarine increased drastically. This was primarily attributed to a significant degradation in rudder effectiveness, with secondary contributions from increased lateral forces on the propeller. Under specific wavelengths, vertical-plane motion attitude variations in the fourth quadrant during turning maneuvers induced substantial fluctuations in the normal force of the X-rudder, leading to pronounced adjustments in the drift angle and significant deviations in turning trajectories. These findings provide critical technical support for the prediction and evaluation of submarine maneuverability and seakeeping performance, as well as for the refinement of free-running submarine model experiments.

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.

In order to evaluate the fatigue performance and potential application prospects of a certain type of titanium alloy K-TIG welded joint for marine equipment, this study conducted high cycle fatigue tests and fatigue life prediction models research on titanium alloy welded joints with docking form based on the Basquin formula theoretical method and statistical P-S-N probability analysis method. Research results show that the yield and tensile strengths of the titanium alloy welded joint used in marine equipment are 941 MPa and 985 MPa, respectively, with a yield to strength ratio exceeding 0.95 and low plasticity. The high cycle fatigue strength of titanium alloy welded joints expressed as maximum stress under the condition of stress ratio R = 0.1 is 297 MPa, and the ratio to tensile strength (fatigue ratio) is only 0.3. Characterization of fatigue fracture characteristics using electron scanning microscopy indicates that fatigue cracks originate at the weld toe of the welded joint, fatigue striations appear in the fatigue crack propagation zone, with a large number of ductile dimples in the instantaneous fracture zone. The median curves of maximum stress, stress amplitude, maximum load, and fatigue life of welded joints were obtained based on the Basquin formula. Meanwhile, P-S-N fatigue assessment models were provided under different survival rate conditions. The research in this article has reference value for the service safety assessment of marine equipment structures.