Surf-zone velocity field in a spilling breaker

• Main Authors: Wen-Yang Hsu, 許文陽
• Other Authors: Hwung-Hweng Hwung
• Format: Others
• Language: zh-TW
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/36815824095956164655

碩士 === 國立成功大學 === 水利及海洋工程學系碩博士班 === 94 === The hydrodynamics in surf zone has been an important subject for scientist and engineers due to its importance and complexity. The characteristics of vorticity and turbulence in surf zone were investigated by many researchers. Their researches demonstrate both qualitative and quantitative details in surf zone. However the temporal and spatial distributions of flow structures are not completely discussed. The objective of this paper is to investigate the internal flow structures of spilling breakers on 1/20 slope. The experiments were conducted in a wave flume in Tainan Hydraulics Laboratory. Because the resolution of CCD camera is not high enough to capture the whole breaking process in one single frame, the whole measuring region is divided into 7 sub-areas by the mosaic method. The measured width of velocity distribution is over one wavelength from initiation of wave breaking to inner surf zone. The detections of water surface interface and entrained bubbles in images are the challenges in data analysis procedure. Therefore, an image process method is adopted to detect the edges of surface and obtain our interesting areas. The mean velocities are obtained by the ensemble average method with 15 repeats, the error of surface elevation is less than 0.3% in every test. The temporal and spatial flow structures in the whole surf zone were completely presented in this thesis. The velocity of wave crest reaches maximum in the initial breaking region, and the distributions of velocities correspond with the shallow water theory. The head of lower speed region under the crest of bore is so called a mixing region. Behind it there still exists a decay of wake region due to the dissipation caused by the stretch of rotational structures generated from the head of the bore. The vorticties are generated in the breaking process, and they extend and elongate toward offshore as wave propagate onshore.