Narrow Results

This paper reports the results of field surveys of the 2004 Indian Ocean Tsunami in Southern Thailand and Northern Sumatra. After outlining the general state of the tsunami strike, tsunami height and distribution in Sec. 3, aspects of inundated flow such as current velocity (water particle velocity), fluid force, relation between inundation depth and the degree of damage to reinforced concrete buildings, shape and height of surge front, inundated flow with floating bodies, effects of coastal forest on reducing tsunami energy and force are discussed. Damage estimation problems are also discussed. A simplified theory for predicting the moving velocity of floating bodies with inundated flow is presented.

Using the large wave flume, tsunami force experiments were performed subject to breakwater. Tsunami with soliton fission and breaking of split waves were focused on. Tsunami force and vertical distribution of dynamic pressure were investigated in detail experimentally. Two remarkable features of tsunami force were found in experiments. First, tsunami force can show the maximum values at either the attack moment of the first split wave, i.e., starting point of breaking of the first split wave, or the formation moment of the standing waves of tsunami body and split waves on and after the second wave, i.e., after breaking of the first split wave. Second, as the wavelength of incident tsunami body is shorter, tsunami profile can be deformed asymmetrically and the wave front can be steepened more significantly, and tsunami can split more largely by soliton fission. So, larger wave pressure can act on the breakwater under the breaking and prebreaking conditions of split waves. Considering the above remarkable features, new formulae of tsunami is proposed, which is more reasonable to evaluate stability of coastal structure. The new tsunami pressure formula was applied to stability evaluation of coastal structures damaged by 1983 Nihonkai-Chubu Earthquake Tsunami. It was found that the proposed tsunami pressure formula could explain sliding of the seawall caissons by the first wave of tsunami with split waves.

A numerical simulation model on coupled motions of waves and a submerged floating structure is proposed in the present paper. So far, this type of numerical models was based on a potential theory under assumptions of inviscid fluid and irrational fluid motion. The governing equations of the present model consist of the Navier-Stokes equation and continuity equation. The Arbitrary Lagrangian and Eulerian method and the boundary fitting coordinate method are applied. Free surface displacement near the floating structure, wave pressure acting on it and displacement of the structure are compared between calculation and physical model tests to verify the present numerical model.