Flow Field Measurements of Shoaling Breaking Wave Impacts on Vertical and Sloping Walls
Date Issued
2010
Date
2010
Author(s)
Liu, Ai-Tzu
Abstract
In this study the slope of the approaching bed in front of the wall is 1/10. The impacts on the different sloping walls of 0°, 10°, 20°, and 30° by the perfect breaking waves after shoaling are studied, by using particle image velocimetry (P.I.V.) to observe the flow field variations near the walls right before and after the impact of the breaking waves on the walls, from which the velocity fields and vortex fields are analyzed and the wave pressures on the walls right on the instant of impact are evaluated. The distributions of the wave pressures on the walls are derived according to the instant velocity fields obtained from the experiments along with the control volume concept and the second-order Stokes wave equation.
It is observed from the results that, with the increase of the oblique angles, there is more space toward the right hand side after waves impacting the wall; therefore, the variation of the velocity is not so severe, in addition, the fluid sliding down from the walls and the changes of the wave shapes are both mitigated. After impact of the breaking wave on the wall, there is a vortex induced by the sliding of the fluid. This phenomenon is less significant with the increase of the oblique angle of the wall. While the turbulence near the wall is mitigated with the increase of the oblique angle.
In addition, the accuracy of the model for the wave pressure evaluation has been verified. It is found that the observation time scale is significant on the accuracy of the evaluation. Right on the instant of impact, within the proximity of 1 cm to the wall, the pressure increases rapidly; however, away from the wall 3 to 5 cm, the pressure normal to the wall has no much change, similar to the uniform flow impinging on the wall. From the non-dimensional pressure analyses with (P/γH,y/d) and (PH/γhL,y/H) two parameters, the wave pressure distributions for the four different oblique walls are no much difference; therefore, there is no influence on the wave pressure due to the oblique angles.
Subjects
P.I.V.
pressure field
velocity filed
vorticity field
sloping wall
shoaling breaking wave
Type
thesis
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