ABSTRACT:

The dynamic response of the generated internal wave as surface water propagating over a submarine trench is investigated in a wave flume. The image processing technique is used to observe the response of density-stratified interface. Two typical distinct phenomena of internal waves were caught in the experiments, which are the traveling internal waves usually occurred as the density of lower layer fluid is higher, and the standing internal waves usually occurred as the density of lower layer fluid is lower. The quantitative results would be presented in the future.

INTRODUCTION

When waves propagate across a submarine trench which is partially filled with heavier fluid, the generation of internal wave is an interesting topic on engineering. Such a situation may exist in navigational channels and harbors where bottom is composed of very fine sediment. It is observed that when the frequency of the incoming surface waves corresponds to the natural frequency of the internal waves in the trench, the amplitude of the internal waves becomes large compared to the amplitude of the surface waves. In these extreme events, the dense fluid in the trench will be excited in a mode of resonant oscillation. Therefore, large amplitude of internal wave results in large velocity near boundary hen enhances the process of erosion and affects ship maneuverability. An example of a harbor where this type of dense lower layer is present is Holland, where the bottom was defined as a region where the specific gravity of the fluid was larger than 1.2 (Marine Board National Research Council, 1983). The nature of the internal waves in the trench is a major interest in this study. Thorpe (1968) has made an extensive study, both theoretical and experimental, of standing internal waves at the interface of two fluids and in a continuously stratified fluid.

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