Investigation of the Force Characteristics of a Cylinder in Internal Wave Environments with a Complex Topography

The trapezoidal slope-coupled terrain model that comprises a trapezoidal obstacle and a two-layer slope based on the topography of guyots and gentle continental slope shelves in the South China Sea is proposed. The large eddy simulation (LES) technology is employed to investigate the propagation characteristics of internal waves (IWs) over complex terrain and their impact on cylindrical structures. The results indicate that complex terrain induces a multistage response in the forces exerted on the cylinder. As compared with the single-slope terrain, the trapezoidal slope terrain, influenced by the secondary bank slope terrain, transforms the force response from a single-negative peak stage to a double-negative peak stage, with the second-stage negative peak exceeding the first. The trapezoidal obstacle effectively weakens the impact of internal waves on the cylinder, particularly in the first stage, when it impedes the flow of the lower layer, thereby reducing the internal wave energy. In the second stage, influenced by the secondary slope terrain, internal waves undergo reflection and interact with trailing waves, leading to drastic changes in the flow field structure and a reversal of the force direction on the upper and lower parts of the cylinder. Furthermore, as wave amplitude increases, the weakening effect of the trapezoidal barrier becomes more pronounced, especially in the second stage.