Hydrodynamic impact of internal solitary waves on a cylinder close to free surface*

Surface currents generated by internal solitary waves (ISW) are known to induce a significant hydrodynamic force on surface platforms and offshore infrastructures, which can potentially affect their normal operations. Quantifying this force is challenging because ISW-induced flows are transient, and free surface proximity is known to cause complexity in the fluid dynamics. In this study, we perform direct numerical simulations (DNS) of a cylinder close to the free surface using the volume-of-fluid method. We first examine the hydrodynamic forces acting on the cylinder and the vortex shedding patterns for a steady inlet flow in different cases with varying cylinder submergence depths and Froude numbers. We then perform simulations where the inlet velocity is specified by the transient surface current adapted from the ISW solution computed from the classical Dubreil-Jacotin-Long (DJL) equation. Our analysis shows a notable difference in the hydrodynamic forces between the transient inlet case and their corresponding steady inlet cases.