Objectives With the continuous development of modern ships with increasing size and speed, and the application of high-strength steel, the problem of ship hydroelastic vibration has become more prominent due to the reduction in hull natural frequencies. Springing and whipping loads significantly contribute to the wave loads of large ships. However, existing research on ship wave loads and hydroelasticity mainly focuses on the symmetric responses of ships sailing in head regular waves. In actual sea conditions, ships encounter waves from various directions. Due to the complexity of analyzing ship asymmetric responses, research on wave loads and hydroelasticity of ships in oblique waves remains limited. It is of great significance to accurately predict the asymmetric wave loads and structural responses of ships under extreme wave conditions. This study aims to develop a hydroelasticity analysis method for ships using two-way CFD-FEM fluid-structure coupling to predict the motions and wave loads of ships in oblique regular waves, accounting for asymmetric loads, structural responses, and nonlinear load effects. This method can provide a new approach for evaluating the hydrodynamic and structural load performance of ships in oblique sea conditions, enhancing the understanding of hydroelastic effects on ships.

Methods The methodology employed in this research involves several steps. First, a computational domain for oblique regular waves is established using CFD software. The three-dimensional N-S equations are solved within the fluid domain to calculate the nonlinear wave loads on the model-scale ship. The computational domain of the numerical wave tank consists of a background region and an overset region. The Euler Overlay method is used to generate fifth-order Stokes waves. Second, a finite element model integrating the hull beam and the ship hull is developed. The massless hull surface is represented using shell elements, while the backbone beam is modeled with 3D uniform beam elements. The total mass and roll moment of inertia of the ship model are similar to those of the full-scale ship. To ensure the longitudinal weight distribution and roll moment of inertia in the FE model to be consistent with the experimental model, concentrated mass and moment of inertia are added to the reference points in two stages. Finally, a two-way fluid-structure coupling analysis is performed. Both the motions and structural deformations of flexible structure derived from the FEA are fed back to the CFD solver to update the hydrodynamic grid data. The fluid loads on the deformed structure, calculated using CFD with a morphing grid technique, are then applied to the structural FE model for the subsequent FEA.

Results The results show that the numerical method is effective, as confirmed by the CFD grid and time step sensitivity analysis and the comparison with free roll decay test results. It can accurately predict the trends and amplitudes of pitch motion, vertical bending moment (VBM), and torsional moment (TM) compared to experimental results. For instance, in the motion response analysis of a ship in oblique waves, the numerical simulation results of heave, pitch, and roll are generally consistent with the experimental results, with a pitch peak error within 8%. In terms of load analysis, the VBM and TM calculated by the numerical method align well with the experimental trends, though there are some differences. Under extreme sea conditions, the high-frequency components caused by slamming primarily contribute to the total bending moments. The wave-frequency horizontal bending moment (HBM) and TM increase linearly with the wave height, while the high-frequency components exhibit significant nonlinear growth. Under typical extreme sea conditions, the HBM at typical sections is comparable to the VBM loads.

Conclusions In conclusion, the established CFD-FEM method can accurately predict the motion and load responses of ships under asymmetric waves. It provides a novel approach for evaluating the hydrodynamic and structural load performance of ships in oblique sea conditions. The research also reveals the significant impact of hydroelastic effects on VBM, HBM, and TM under severe sea conditions. This study provides valuable insights into ship design and performance evaluation in complex sea environments, promoting the development of ship hydroelasticity research.