Masahiro Miyajima

In this study, internal velocity fields of tsunami acting on a vertical wall were measured by PIV with measurements of wave pressure and surface elevation at the wall. A large scale vortex appears at the corner of the bottom of the wall. The main stream of tsunami avoids the vortex and then the acting point of the main stream moves up along the wall. As the result, the wave pressure values around the bottom of the wall correspond to the hydrostatic pressure value calculated by the surface elevation at that time. The wave pressure values above the vortex exceed the hydrostatic pressure values, because of the action of the dynamical pressure of the main stream of tsunami. When the splashed water falls down on the main stream, the all of wave pressure values have the maximal values. At that time, the horizontal wave force also has the maximal value.

Impact tsunami wave pressure acting on near the bottom of a land structure was measured with high speed video images of fluid motion in front of the structure. The value of the maximum impact pressure reached 10 times that of the hydrostatic pressure. The impact pressure changed with some patterns of the fluid motion. The patterns also changed with Fr number. Under low Fr number conditions, the gauge pressure is composed of the dynamic pressure by the maximum of the fluid velocity and the hydrostatic pressure which depends on the height of fluid raising along the front wall. However, Fr number becomes higher, the gauge pressure is getting equal to the dynamic pressure only. The maximum value of the impact pressure can be fit into the function of 0.5 times square of the velocity.