Toa MATSUUCHI

A Trial of Tsunami Simulation off the Coast of Kamakura Using OpenFOAM

Hongxuan YANG,Toshiro KUMAKURA

Numerical simulation plays a vital role in disaster prevention planning and the design of coastal infrastructure. Tsunami analysis is generally conducted by numerically solving the 2D Shallow Water Equations. This research aims to develop a specialized tsunami solver within OpenFOAM, an open-source continuum mechanics toolbox. OpenFOAM offers distinct advantages, such as the Finite Volume Method on unstructured meshes for high-fidelity modeling and a flexible framework for discretization schemes, which significantly reduces the developmental burden for large-scale linear systems.
Standard OpenFOAM solvers are limited by their inability to incorporate ground roughness and specific tsunami boundary conditions. Therefore, this study developed a solver that integrates Manning’s roughness coefficients and a moving boundary algorithm using a wetting-drying threshold to determine the presence of water. The simulation utilized six field variables and four non-field parameters. Validation was performed using a 14.47m baseline wave, followed by comparisons with a 25.0m wave and varying seawall heights (10m, 20m, and 40m).
The results for the baseline case demonstrated physical consistency, as inundation progressed from low-lying areas to higher elevations. The 25.0m wave case exhibited higher velocities and a wider inundation area, with the propagation speed aligning closely with the theoretical value v=√gh. Regarding coastal protection, 10m and 20m dikes provided attenuation for approximately two minutes; however, their effectiveness diminished over time as overtopping occurred. Notably, a "damming effect" was observed during the recession phase, where the dikes prevented water from draining back to the sea. In contrast, the 40m dike maintained high attenuation throughout the event, confirming that seawalls with sufficient crest height relative to the wave amplitude are essential for effective protection.