Plate anchors are widely employed in offshore engineering as anchoring systems. However, uncertainties exist for plate anchors used in multi-layered seabed, thereby hindering its practical application. This study investigates the bearing capacity of square plate anchors in normally consolidated (NC) clay overlying silty sand, addressing a critical gap in current design guidelines that assume homogeneous seabed conditions, thereby improving the reliability of offshore mooring systems in stratified deposits. Three-dimensional finite element analysis, with validation against prior experimental and numerical data, is employed to provide insight into the behavior of plate anchor in layered soil deposit, in which the key parameters are examined including the clay shear strength gradient (k), the sand friction angle (φ) and the embedded depth. Soil flow mechanisms under uplift loading are examined as well, revealing distinct mobilization patterns governed by change in strain-localization pattern across the clay–sand interface and hybrid failure mechanisms. Results show that the thickness of the upper clay can affect the bearing capacity of the anchor in sand by up to 30%. Finally, empirical formulas are proposed to predict vertical and horizontal capacity factors of plate anchors which provide practical insights for the design and optimization of plate anchors in layered soils, enhancing offshore mooring system reliability.
To enhance the damage effectiveness against ship structures, shaped charges are commonly employed in engineering practice to inflict damage on target structures. This paper investigates the damage characteristics of ship structures under the action of cylindrical shaped charges and linear shaped charges. First, underwater experiments are conducted on stiffened plate structures under the action of the two types of shaped charges. Second, to capture the dynamic physical processes that cannot be observed in the experiments, a finite element numerical model based on the Arbitrary Lagrangian-Eulerian (ALE) method is established according to the experimental results, which is used to systematically analyze the key mechanical properties of shaped charge penetrators such as morphology and velocity, as well as the multi-mode damage laws of the structures. Subsequently, the numerical simulation results are compared with the experimental data, with all errors being <15%. Finally, numerical models of near-surface ship cabins under the action of blasting charges, cylindrical shaped charges and linear shaped charges are established. The damage characteristics of the cabins are comparatively analyzed, and the influence laws of charge structure and penetration position on the damage effect are revealed. The results show that linear shaped charges exhibit super-caliber penetration capability, with the breach area they create on ship cabins being 53.2% to 72.9% larger than that by cylindrical shaped charges, while cylindrical shaped charges induce more significant deformation of the structures. When the charge acts on the central position of the stiffened plate grid, the deformation of the cabin sidewalls is minimized, yielding the optimal anti-blast protection effect.
Deep-sea oil and gas transportation pipelines are subjected to high external pressure and complex marine environments during long-term service. Liner collapse failure is a critical issue affecting the structural integrity and service reliability of Adhesively Bonded Mechanically Lined Pipe (ABMLP), while the mechanical response and damage evolution behavior of adhesive interfaces have a significant influence on the liner collapse process. In this study, an experimental and numerical approach was adopted. The key adhesive parameters were obtained through single-lap shear tensile tests, and a finite element mechanical model of the composite pipe incorporating adhesive interfaces was established based on the Cohesive Zone Model (CZM). The fluid cavity loading method was employed to simulate the constrained deformation and collapse evolution of the liner under deep-sea conditions. The results demonstrate that the adhesive layer provides an elastic support effect through continuous interface bonding, enhances the load transfer capability between the outer pipe and liner, and changes the collapse evolution mode of the liner from localized instability to progressive coordinated deformation. Compared with Mechanically Lined Pipe (MLP), the critical collapse pressure (Pc) of ABMLP is increased by 52.73 %. Increasing the normal interface stiffness and damage displacement of the adhesive layer enhances the interface constraint capability and delays damage propagation, whereas the adhesive layer thickness has a limited influence on the liner collapse pressure. This study reveals the coupled mechanism between adhesive interface damage evolution and liner collapse failure, providing a reference method for structural design, failure prediction, and integrity assessment of deep-sea composite pipelines.
The U-shaped metal seal ring of the subsea tubing hanger is a critical component ensuring wellhead sealing integrity, with its sealing performance determining the safe operation of oil and gas production systems. Addressing the analytical challenges posed by the seal's multi-parameter and highly nonlinear characteristics, this study establishes an optimization method integrating Optimized Latin Hypercube Sampling (Opt-LHD), XGBoost surrogate modeling, and the multi-objective genetic algorithm (NSGA-II). Initially, Finite Element Analysis (FEA) is utilized to evaluate the stress distribution and contact behavior, elucidating the sealing mechanism. Opt-LHD is then employed to construct a high-coverage sample space. Two surrogate models—XGBoost and BP neural network—are established and compared for the U-shaped metal seal. Through cross-validation and error analysis, the XGBoost model, exhibiting superior generalization, is selected to replace time-consuming FEA. Subsequently, a dual-objective global optimization targeting increased maximum contact pressure and reduced maximum equivalent stress is performed using NSGA-II. The Pareto front is validated through FEA to determine the optimized design. Simulation results demonstrate that the optimized seal ring achieves a 10.07% increase in maximum contact pressure and an 8% reduction in maximum equivalent stress, simultaneously enhancing sealing performance and structural safety, thereby validating the effectiveness of this optimization methodology.
Floating vertical-axis wind turbines (VAWTs) are promising for deep-water wind energy, but basin-scale experiments remain challenging because model-scale rotor aerodynamics cannot be reproduced consistently under Froude-scaled conditions. This study presents a hybrid model test framework with precomputed aerodynamic loads for investigating the dynamic responses of a 5 MW semi-submersible floating VAWT in the wave basin. Aerodynamic thrust and lateral forces are generated numerically and reproduced by a propeller-based loading device. The experimental system was characterized through aerodynamic-load validation and restoring stiffness, free-decay, hammer, and white-noise tests. The reproduced tower-top forces retained identifiable 3P aerodynamic harmonics with stronger narrow-band concentration in the lateral-force component. Tower-top accelerations showed clearer sensitivity to the imposed harmonic content and local upper-structure dynamics than the global platform motions. Platform motions were dominated by low-frequency natural modes and wave-frequency response, with weak higher-order aerodynamic harmonics in roll. Supporting numerical simulations reproduced the principal platform-response frequencies and showed good agreement in surge fluctuations under wind-only loading and pitch fluctuations under combined loading. Mooring tensions exhibited direction-dependent mean-load redistribution and retained limited high-frequency signatures in selected line groups. These results support hybrid testing of floating-VAWT responses under controlled and repeatable multi-directional aerodynamic excitation.
