| dc.description.abstract | On March 11, 2011, a powerful tsunami occurred off the east Japan that makes people to pay attention to the tsunami threat. The powerful tsunami generated by a trench-type earthquake with Mw= 9.0. The wave height was observed about 10 m offshore. More than 400,000 structures were destroyed reported by National Police Agency in Japan. This paper aimed to understand the characteristic of tsunami bores by means of numerical method, and hopefully, for tsunami hazard mitigation. We use 3D LES-VOF model to simulate the interaction of tsunami bore and a square cylinder. The model is validated with the experimental measurements of the long-flume dam-break done by Dr. Arnason（2005）.
Simulating the complete bore propagation before reaching the cylinder is very expensive. The process takes about 75% of the whole computational time. To reduce it, this study implement bore height and velocity obtained from solving the shallow water equation （SWE） as the inflow boundary conditions. The results are compared with the experiment data. The general error is approximated as 10 % in terms for the force acting on the cylinder.
In order to reduce the error, we implement the solution from the 2D simulation. In this method, we simulate the same problem with the cylinder removed from the flume by solving 2D LES model. The solution is them used as the inflow boundary condition. We also compare the result with the experiment data, and the error is under 5 %. After the comparison, this 2D coupling method is then utilized for following simulations and analysis.
From the pressure distribution on the cylinder while the bore is arriving structure, we notice that the maximum pressure occurs at the elevation of half of the bore height, and then moves to the bottom area. This indicates that when the bore is contacting the cylinder, the dominate force is the hydrodynamic dynamic pressure, and transfers the hydrostatic pressure during the bore body passing through. We also discuss the sensitivity of geometric parameters. The result shows that net force increases with the width of the cylinder. However, the effect from changing the length can be neglected. This indicates that the blockage ratio is an important parameter to the net force.
In order to understand the difference between laboratory scale and real scale, this study scales the laboratory setting by magnifying 100 times to simulate the tsunami-structure interaction in the real scale. The result shows that the net force is dominated by Froude number. However, the high frequency disturbance is affected by Reynolds number.
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