宮島 昌弘

本研究は，鉛直壁に衝突する陸上遡上津波の内部流速場を可視化計測し，波圧や水位の同時計測結果と併せて，衝突流速が支配的となる衝撃波圧から浸水深が支配的となる持続波圧への遷移過程を明らかにしたものである．津波が鉛直壁に衝突すると鉛直壁と底面との隅角部において大規模な渦が発生する．津波の主流はその渦の上部を流れるようになるため，底面付近は主流が直接衝突しなくなることから動圧分の波圧が低下し，その時の打ち上がり水位による静水圧となる．一方，渦の上部においては主流が角度をもって衝突することから，底面付近に生じる衝撃波圧よりは小さいものの衝撃波圧が発生することが分かった．また，鉛直壁によって打ち上がった水塊が落水する瞬間にすべての高さの波圧が極大値を持ち，その時に水平波力が最大となる場合があることが分かった．

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.

本研究は, 風による波・流れの発達過程を明らかにするために, Level set-CIP法を用いた数値風洞水槽の開発を行ったものである. 静止水面に十分に発達した気流乱流を与えて計算を行った結果, 水面に波長3-5cm程度のリップルが発生し, 内部流速場の結果から, それらが波動ではなく風波のごく初期に発生する渦列に伴う水面変動であることが確認できた. これらの結果は既往の実験結果と定性的に一致するものであり, 本計算モデルの妥当性を示すことができた. また, リップルの発生過程における水面形と気圧・水圧分布の特性との関係についても示すことができ, 今後の運動量輸送過程の解明につながる結果を得ることができた.

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.