MULTIPLE BAR FORMATION BY BREAKER-INDUCED VORTICES: A LABORATORY APPROACH

Proceedings of the International Conference on Coastal Engineering

Tsuguo Sunamura¹  Da Ping Zhang¹ 

[1] Institute of Geoscience, University of Tsukuba

关键词: bar;    bar formation;    laboratory approach;    breaker induced vortices;    vortex;   

DOI  :  10.9753/icce.v24.%p

学科分类：建筑学

来源: Coastal Engineering Research Council

【 摘 要 】

Using a two-dimensional wave flume and a two-videocamera system, mechanism and process of multiple bar formation were investigated in the light of breaker-induced vortices. A fixed-bed experiment revealed that (1) the vortex formed at the wave break point can be classified into three: oblique, A-type horizontal, and B-type horizontal vortices; (2) the vortex formed in the surf zone is always oblique; and (3) the location of a vortex reaching bottom can be described by wave properties and the bottom slope, and its water depth can be expressed by breaker height alone. A movable-bed experiment indicated that bars are initiated by the vortices reaching bottom in the surf zone; the number of bars formed coincides with the number of such vortices. Suspension of the bottom sediment due to vortex action and the mean-drift-velocity pattern can play an important role in multiple bar formation; mechanism for break-point bar formation is "convergence", while that for inner bar formation is "congestion". Two major modes for the development of multiple bars were found: simultaneous and successive: these depend on the interaction of vortex action and topography in the surf zone. Multiple-bar features such as trough spacing and crest depth could be explained from vortex features found through the fixed-bed experiment.

【 授权许可】

Unknown