Linear diffraction and radiation on a vertical circular cylinder in finite water depth.

摘要

In the research described herein, the first-order impingement of waves upon large offshore structures in finite water depths was examined. The approach taken, like that of many others, was a combined analytical and numerical study of how first-order waves impinge upon such monolithic structures, and included both internal and external effects. It is generally considered to be useful to represent such structures as simple vertical 'cylindrical' objects in trying to reach a sound understanding of the effects of linear first-order waves, from a diffraction point of view. The work focused on the mathematical derivation of the velocity potential, the wave loads, and the resulting moments on structures resting on the sea-bottom but extending above the surface.;The fluid was assumed to be homogeneous, incompressible, inviscid and the motion was irrotational. Forces and moments were found to be independent of water depth for large values of the wave number, ka. Large values of knh were approximated by npi and small values of knh by 3 n. The application of the derived velocity potential enabled the determination of both forces and moments. The computed forces and moments were found to compare well with those of previous investigators.;A limited study was then made of the radiation problem, in which the column was allowed to interact with the waves. Simple oscillations of the vertical cylinder were examined. Added mass and damping effects were considered. Again, the derivation of the velocity potential was the primary focus. Radiated forces and moments were found to be negative and very small for large values of ka.;In this study we also found out that in the analyses of diffraction and the radiation problem, the computed results of forces and moments are more meaningful for about ka ≤ 8.0.