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.

We carried out the visualization experiment on air-flows over wind waves to investigate an occurrence frequency of an air-flow separation behind a wind wave crest. An air-flow separation behind a wave crest strongly depends on a local wave shape around the wave crest, but the occurrence frequency of the air-flow separation can be explained by the wave steepness. Physical surface roughness (significant wave height) grows as wind speed increases. However, the surface roughness length, z0, doesn't grow. If the air-flow separation occurs over wind waves, the air-flow travels from the wave crest to the next wave crest. Then, the air-flow doesn't sense as physical surface roughness as significant wave height. Therefore, the surface roughness length doesn't grow as wind speed increases.

It's well known that the thin sheet flow on steep slope channels has phenomenon of Roll-wave trains, if Froude number exceeds about 2 (Ultra-rapid flow). This paper's purpose is to make exprimentally clear for internal structures of the flow with Roll-wave trains in view point of specified flow. These Roll-wave flows have remarkable charactaristics that appear in very small water depth, have tremendous water level changes, and are high speed flows. Therefore, these authors adopt two nonintrusive type equipments, that is, ultrasonic levelmeter and Laser-Doppler-Velocimeter to carry out these experiments. The results of experiments indicate that the Roll-wave flows have some universal and specific patterns of velocity profiles.