Fluid-Structure Interaction Analysis of Tsunamis Generated by the Falling Impact of Rigid Objects

Abstract

This study investigated the hydrodynamic characteristics associated with the shape and descent height of falling objects, focusing on the generation, propagation, and deformation of landslide-generated tsunamis (LGTs). It also examined the run-up, wave pressure, and wave force against a simplified dam model through numerical analysis using LS-DYNA based on fluid-structure interactions. The initial wave is characterized by a drastic increase in the water-surface elevation owing to the falling impact, followed by a secondary wave induced by the ascent of the displaced air mass. Objects with a low shape ratio produce a concentrated impact load that generates LGT waves with high amplitudes, strong nonlinearity, and asymmetry. These highly nonlinear waves gradually transform into stable waveforms, balancing the dispersion and nonlinearity as they propagate. When the shape ratio of the falling object reaches 2.04, the run-up height at the vertical wall peaks, and the hydrodynamic pressure distributed over higher positions increases, which shifts the fluid force application point and significantly increases the moment. Consequently, for gravity dam designs accounting for the LGT wave pressure, a trapezoidal cross-section with a wider base is essential to enhance structural stability, considering that the dam must withstand shear forces and moments that exceed those generated under hydrostatic pressure. This study identifies the critical conditions under which LGTs pose the greatest risk and emphasizes the need to consider nonlinear wave interactions in engineering calculations for dam design and reinforcement strategies.