Runup and green water velocities due to breaking wave impinging and overtopping |
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Authors: | Yonguk Ryu Kuang-An Chang Richard Mercier |
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Institution: | (1) Zachry Department of Civil Engineering, Texas A&M University, College Station, TX 77843-3136, USA;(2) Present address: Water Resources Research Department, Korea Institute of Construction Technology, Goyang, Gyeonggi-Do, Republic of Korea |
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Abstract: | The present study investigates, through measurements in a 2D wave tank, the velocity fields of a plunging breaking wave impinging
on a structure. As the wave breaks and overtops the structure, so-called green water is generated. The flow becomes multi-phased
and chaotic as a large aerated region is formed in the flow in the vicinity of the structure while water runs up onto the
structure. In this study, particle image velocimetry (PIV) and its derivative, bubble image velocimetry (BIV), were employed
to measure the velocity field in front and on top of the structure. Mean and turbulence properties were obtained through ensemble
averaging repeated tests. The dominant and maximum velocity of the breaking wave and associated green water are discussed
for the three distinct phases of the impingement–runup–overtopping sequence. Initially the flow is mainly horizontal right
before the breaking wave impinges on the structure. The flow then becomes primarily vertical and rushes upward along the front
wall of the structure right after the impingement. Subsequently, the flow becomes mainly horizontal on top of the structure
as the remaining momentum in the wave crest carries the green water through. The distribution of the green water velocity
along the top of the structure has a nonlinear profile and the maximum velocity occurs near the front of the fast moving water.
Using the measured data and applying dimensional analysis, a similarity profile for the green water flow on top of the structure
was obtained, and a prediction equation was formulated. The prediction equation may be used to predict the green water velocity
caused by extreme waves in a hurricane. |
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