Numerical simulation of long wave passage over underwater barrier

Abstract

One of the ways to protect population and coastal infrastructure against a tsunami attack is massive vertical walls built around portal area or across the harbors entrance. During major tsunamis, such walls rising above the water often be ruined and fail to perform their function [1]. Compared to such protective structures, the submarine vertical barrier is more stable, although it lesser suppresses the height of tsunami wave passing above it. On the basis of energy relations for a long wave, the internal boundary conditions are formulated that realize partial reflection of the tsunami from submerged vertical barriers during wave passage above them in a course of numerical modeling. The results of calculations are well correlated with measurements of the heights of waves passing over underwater barriers during laboratory modeling in a hydrophysical flume [2]. Such protective structures are able to stop up to 45% of the energy of the tsunami wave, while reducing the height of the tsunami by 25%. A series of calculations of the tsunami wave entry into the harbors of the northeastern Japan was carried out in the presence of a virtual underwater barrier there. For different underwater wall height (relative to depth), wave amplitude was found at different points of the harbor coastline. Comparison of the obtained wave heights with the results of modeling in the absence of a barrier shows the wave suppressing effect of a protective structure of this type. It should be noted that it is not at all necessary to achieve total reduction the tsunami height down to zero with the help of protective walls. It is enough to lower the amplitude of the wave near the shore by 20-30 percent to significantly reduce the damage from this natural disaster.