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.

The flexible hose connecting the deep-sea mining vehicle and the relay station is a key link in the deep-sea mining system and is suspended in a curved configuration above the mining vehicle. This paper extends the applicable conditions of the model from the vertical pipeline to the flexible hose based on the one-dimensional model (VHT_1D), by discretizing the long-distance curved pipelines into a series of inclined pipelines for force analysis. The extended model is fully compared with the key parameters calculated by the two-way coupling method of fluid dynamics and discrete elements (CFD-DEM), and this model shows high accuracy. At the same time, the influence of input parameters such as feed concentration and mixture transport velocity on the flow state in the pipeline is further explored. A reasonable range of input parameters is determined, and the conveying efficiency of the pipeline system is optimized. In addition, the hydraulic gradients in the single-peak and double-peak long-distance curved pipes are compared and analyzed, providing a basis for the design of the conveying pump. The extended model significantly improves computational efficiency while maintaining high accuracy, particularly for long-distance pipeline applications.

In engineering applications, Very Large Floating Structures (VLFS) need to rely on mooring systems to achieve offshore positioning. However, due to their large length-to-width ratio, VLFS have low overall stiffness and are prone to significant elastic deformation under wave action. Based on the rigid body theory, the impact of such deformation on the mooring system cannot be taken into account, nor can the structural dynamic response of the floating structure in the moored state be easily predicted. To address this, this study established a coupled calculation model of the VLFS and the mooring system based on three-dimensional hydroelasticity theory and slender rod mooring dynamics theory. With this model, the structural response of the floating structure under mooring loads is calculable, and the dynamic response of the mooring system to the combined effects of the floating structure’s rigid body motion and elastic deformation is synchronously computable, thereby realizing the high-precision synchronous prediction of mooring tension and structural response. In this paper, this model is used to analyze the coupling performance of a three-module VLFS, and the floating structure’s load response of typical sections and the mooring line tensions are obtained. The results show that the elastic deformation of the floating structure significantly changes the displacement of the mooring points, leading to an increment in mooring line tension reaching the order of 10⁵ N, with the maximum increment being approximately 40% of its pretension.

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.

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.

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.

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.

Applying an acoustic coating to the hull effectively reduces target strength while reducing both mechanical and hydrodynamic noise. In this study, a finite ribbed cylindrical shell is studied based on the modal superposition method. A computational model is developed to predict the acoustic scattering of a finite ribbed cylindrical shell with multilayer gradient acoustic coating in an infinite ideal fluid. The influence of characteristic impedance parameters—such as sound speed and density—on the scattering form function is examined, and an optimized impedance distribution for the multilayer gradient acoustic coating is proposed to suppress scattering across different frequency bands. In addition, the effects of frequency-dependent characteristic impedance of embedded-cavity acoustic coatings and stiffeners of cylindrical shells on the scattering form function are investigated. Results show that multilayer gradient acoustic coating with characteristic impedance gradually increasing from the inner to the outer surface can effectively reduce the scattering form function in lower frequency ranges. Furthermore, frequency-dependent acoustic coatings result in broadband scattering control from low to high frequencies, and applying an optimized layered coating to the rib-stiffened cylindrical shell yields a substantial reduction in its scattering form function for frequencies above 500 Hz.

Flow-Induced Vibration (FIV) energy harvesting is an effective approach for harnessing low-velocity ocean currents. Using a maglev support system to replace traditional metal springs enables better stiffness adjustment and improves underwater operation and maintenance performance. To enhance energy output and stability, dual-oscillator designs are widely used in vortex-induced vibration energy harvesters. However, the vibration characteristics of dual oscillators supported by maglev systems remain underexplored. This study establishes a coupled numerical model that integrates the FIV of rigid cylindrical oscillators with a maglev support system to investigate the influence of the spacing ratio (G/D) on their vibration responses. Results show that a smaller spacing ratio (G/D=2) intensifies hydrodynamic interactions, leading to a downstream oscillator's amplitude reaching over twice that of a single oscillator. The oscillation frequencies decrease monotonically with increasing spacing ratios, and distinct frequency variation patterns are observed between upstream and downstream oscillators. Vortex analysis reveals that the upstream wake reconstructs the flow field and strengthens the excitation forces on the downstream oscillator, thereby amplifying its vibration response. The maglev effect enhances the oscillators' responsiveness to flow field changes through nonlinear magnetic forces, further improving vibration performance and system stability. This study provides theoretical insights for optimizing dual-oscillator FIV energy harvesters with maglev support.