ABSTRACT:

The uni-directional oblique waves are generated by serpent-type wave maker in a large wave basin and their reflection coefficients in front of wave dissipating works are analyzed with two kind methods; Goda's and Guza's methods. It is verified that the expanded Guza's method is applicable even to obliquely long-period waves in the basin. As the incident angle is larger, the reflection coefficients slightly increase for wind waves and swells as unexpected, though they decrease for longperiod waves. Moreover, it is verified that such wave reflections can be reproduced in calculations using the improved Porous Layer Boundary, PLB equipped in a Boussinesq-type wave model.

INTRODUCTION

Generally, reflection coefficients on the breakwaters and the seawalls covered with wave-dissipating blocks are estimated at from 0.3 to 0.5 for wind waves and swells. They are usually examined in a wave flume. The long-period wave absorber which consists of wide-width rubble mound is also designed for the normal direction of incident waves (ex) Hiraishi et.al., 2009). However, the reflection coefficients on it are not clear for wind waves and swell. In addition, the wave reflection coefficients seem to be reduced for obliquely incident waves because an oblique distance is longer than the normal distance in a horizontal wave dissipating work. Moriya and Mizuguchi (1996) have suggested the analysis method of reflection coefficient for obliquely incident waves as an expansion of the method proposed by Guza et. al. (1984). However, it is not usually to evaluate reflection coefficients of such oblique waves though that is much important for estimating harbor tranquilities. Actually they seem to be assumed to be constant or reproduced naturally in direction of incident waves in harbor wave calculations. In this paper, those fundamental characteristics are checked in two kind of preliminary tests at first.

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