The Soft Yoke Mooring System (SYMS) is widely adopted in shallow waters due to its cost-effectiveness; however, its dynamic response under extreme double-peak spectral waves, which are common in typhoon-prone regions, remains insufficiently understood. Consequently, investigating the dynamic response of the SYMS under such conditions is essential to elucidate its nonlinear behavior and ensure structural reliability. This study systematically examines the dynamic response of the SYMS under extreme wave conditions characterized by 100-year return period doublepeak spectra. A high-accuracy, fully coupled numerical model is developed and rigorously validated against physical model experiments. The mooring structure is discretized using beam elements, accounting for axial, torsional, and bending effects simultaneously. The validated model is then employed to analyze the dynamic structural response under extreme double-peak spectral wave conditions. The results indicate that extreme structural responses, including both structural motions and mooring tensions, increase as the swell frequency decreases. Spectral analysis attributes this trend to the expansion of frequency components participating in dynamic amplification. Furthermore, Probability Density Function (PDF) analysis of the time lag between extreme structural responses and maximum wave heights reveals the stochastic nature of extreme events, demonstrating that maximum wave height is not the sole determinant of extreme structural responses. Therefore, incorporating double-peak spectra into the design criteria for extreme sea states is critical for ensuring structural safety.
Pneumatic desilting technology provides a non-contact solution for mitigating asymmetric sediment accumulation beneath pile-supported wharves, where conventional mechanical dredging is often restricted. However, the multiphase dynamics governing this process remain poorly understood. This study combines multiphase fluid dynamics experiments with theoretical analyses to systematically elucidate the mechanisms of bed morphology evolution, suspended sediment sorting, and synergistic sediment transport induced by submerged air jets. Based on the principle of gas expansion work, a macroscopic prediction equation for the ultimate desilting volume is established. To evaluate sediment suspension, a modified Rouse equation is employed to quantify the vertical attenuation of suspended sediment concentration. Experimental results indicate that high-energy gas input significantly coarsens the particle size distribution of suspended sediments. Building on these physical findings, a flux matching theory linking pneumatic sediment suspension to natural flow transport is proposed. A globally optimal parameter control trajectory is derived, clearly delineating zones of excess gas energy and ineffective dissipation of flow transport capacity. These results provide a theoretical basis for selecting gas parameters for pneumatic scouring equipment in field desilting operations.
Metal bellows are thin-walled corrugated structures primarily employed as expansion joints in pressure vessels and pipeline systems, particularly within the sealing layers of cryogenic flexible pipes for offshore LNG transportation. Given their complex geometry, investigating the mechanical properties of bellows has remained a focal point of research. Owing to the significantly smaller thickness dimensions relative to the other two directions, finite element models of bellows can be established using either shell or solid elements. While finite element analysis methods based on different element types may yield discrepant results, and the applicability of each type remains unclear. This study focuses on U-shaped bellows, establishing finite element models using solid elements (C3D8R and C3D8I) and shell elements (S4R) to investigate stiffness properties under tension, bending, and torsion. Concurrently, experimental platforms were constructed, and the relevant mechanical experiments were conducted to verify the reliability of the finite element analysis. Comparison with experimental results revealed that the shell element (S4R) analysis exhibited the smallest error, with a maximum deviation of 4.00
Micro-optical cables are critical for modern underwater communication and data transmission, necessitating the rapid establishment of local area networks for underwater applications. Traditional submarine cable laying relies on specialized vessels equipped with cranes, tensioners, and launching bridges, which are typically designed for large-diameter cables, such as umbilical and wind power dynamic cables. However, the delicate nature of micro-optical cables, with diameters of only a few millimeters, makes them challenging to deploy using these large-scale systems, while the operational costs of specialized vessels are prohibitively high for such applications. To address these challenges, this paper proposes a method for the autonomous laying of micro-optical cables using an Autonomous Underwater Vehicle (AUV) and verifies its feasibility through numerical simulation. During deployment, the dynamic marine environment imposes significant tensile and bending loads on the cable, resulting in complex multi-scale motion and coupled dynamics among the AUV, laying device, and cable. Current theoretical and technical frameworks for addressing these issues remain limited. To investigate the failure mechanisms of micro-optical cables during AUV deployment, this study establishes a dynamic analysis model using OrcaFlex simulation software, performs a parametric sensitivity analysis of the cable mechanical response, and systematically examines AUV performance. Key factors influencing cable tension and curvature, including laying speed, distance from the seabed, and environmental loads such as ocean current velocity and direction, are analyzed. The findings provide guidance for establishing safe and reliable deployment conditions, offering valuable technical and theoretical support for subsequent prototype testing.
Metal materials are widely used in vehicle hulls owing to their high strength and toughness; however, their high density increases overall mass, reducing maneuverability, and they are susceptible to oxidation and corrosion. In contrast, composite materials offer significant advantages through their lightweight nature and high specific strength, making them promising candidates for applications such as ships and underwater vehicles. This study employs the coupled Eulerian-Lagrangian method to investigate the water entry of an autonomous underwater vehicle (AUV) fabricated from T700/M21 composite materials. A numerical model of a carbon fiber-reinforced epoxy resin composite AUV is established to evaluate the effects of different stacking sequences and entry angles on hydrodynamic loads, dynamic deformation, and failure mechanisms. The Hashin failure criterion is incorporated into the VUMAT subroutine. Results reveal a distinctive “hump” indentation on the AUV nose during water entry, accompanied by substantial matrix damage in the head region, while the fibers remain largely intact. The surface matrix fails first under high stress, whereas deeper layers experience lower stress levels. A 45° interlaced stacking sequence demonstrates superior impact resistance. Moreover, decreasing the entry angle intensifies material damage, underscoring the critical importance of optimizing entry angles to ensure the structural safety of composite AUVs.
