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.

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.

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.

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.

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.

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.

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.