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Wave transformation due to vertical barriers in fluids

by Lee, Man-yip

Abstract (Summary)
(Uncorrected OCR) Abstract of thesis entitled Wave transformation due to vertical barriers in fluids Submitted by Mark Man-yip Lee for the degree of Doctor of Philosophy at The University of Hong Kong in June, 1998 Theoretically investigation on the various wave transformation problems involving vertical barriers in fluids are conducted in a attempt to consolidate the understanding of the vertical barrier? interactions with water waves. In this first part of the present work, two categories of the wave transformation problems are focused on, which are the wave scattering and wave radiation problems. The problems of wave scattering due to vertical porous barriers immersed in a homogeneous fluid of finite depth are considered first. For this class of two-dimensional problems, it is sensible to adopt the method of eigenfunction expansion so as to take advantage of the simplified geometry involved and the ease of analyzing the effects of changes in the parameters. The amplitudes of the scattered waves, involving both the transmitted and reflected waves, are determined for the case of monochromatic incoming waves. The performance of the porous barriers of four different basic configurations are studied by examining the characteristic in the variation of their transmission and reflection coefficients, impinging wave force, moment, etc., under different conditions. It is found that in general an increase in the porosity of the barriers results in the decrease of wave amplitudes, wave force, wave moment, etc. The wave radiation problems in a homogeneous fluid of finite depth are investigated by using the same eigenfuction expansion method to determine the amplitude to stroke ratios for the three different types of wavemakers, which essentially are oscillating porous plate. The results for the particular case when the porous wavemaeker extends fully from the bottom to the free surface are in good agreement of the earlier exact analytical work by Chwang (1983). Two-layer fluids are subsequently introduced to these wave scattering and radiation problems. The problems of waves scattering due to a vertical impermeable barrier inserted between a single-layer fluid and a two-layer fluid are investigated for two different kinds of barriers. The results reveal that two distinct scattered wave modes exist in the two-layer, which explains why there was a discrepancy in the theoretical prediction of oil thickness variation near an oil retention boom with the experimental results in the earlier work by Kordyban (1992). The problems of wavemakers in a two-layer fluid are also examined for two categories: piston-type and flap-type. The results show that the flap-type wavemakers are more effective in generating surface waves than the piston-type wavemakers. In the second part of this work, the unsteady problems of oil spreading on a water surface are investigated analytically for both two- and three-dimensional cases. Two specific effects, the effect of water currents and the effect of water waves, on the spreading are investigated. It is demonstrated that both effects will causes the oil to spread faster in the propagating direction of the currents or waves.
Bibliographical Information:

Advisor:

School:The University of Hong Kong

School Location:China - Hong Kong SAR

Source Type:Master's Thesis

Keywords:wave mechanics

ISBN:

Date of Publication:01/01/1998

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