ABSTRACT

The nonlinear interaction of a slitary wave and a vertical circular cylinder is examined. The wave field was measured at various locations near the cylinder and the detailed process of wave reflection, diffraction and scattering is discussed. The formation of the first and second scattered wave is observed as the incident wave first encounters the cylinder and as it leaves the cylinder respectively. Comparisons are made to the generalized Boussinesq (gB) model which is found to give quite good results for the wave heights except very close to the cylinder surface and in the immediate wake region behind the cylinder. The net force on the cylinder in the direction of incident wave propagation was measured as a function of time, and good agreement with the gB model is obtained.

INTRODUCTION

The diffraction and scattering of shallow water waves by large structures has important applications in many fields of ocean engineering. Linear and second order theories have been extensively applied for periodic waves (Sarpkaya & Isaacson 1981, Eatock Taylor & Hung 1987 and Niedzwecki & Duggal 1992), but nonlinear diffraction of long waves m shallow water has received relatively little attention. As the size of offshore structures increases, the scattering of nonlinear waves becomes more critical to the determination of wave run up and wave forces on these structures. There have been extensive studies on the behavior and propagation of solitary waves in the absence of flow boundaries, but comparatively little on their three dimensional scattering. Isaacson {1982} used an integral-equation method based on Green's theorem to compute the wave forces on a cylinder when hit by a solitary wave. A linear diffraction solution was also developed by Isaacson (1983) using a Fourier integral method.

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