해양구조물 주변의 파랑 운동과 이에 따른 파랑하중 예측을 위한 경계요소법 기반의 수치파수조 개발

Abstract

This paper presents recent accomplishments of the development of the Boundary Element Method (BEM) for nonlinear waves around offshore structures and resulting wave forces. Conventionally, this kind of method is known as BEM-based Numerical Wave Tank (NWT) technique in the field of naval architecture and ocean engineering. In this paper, the basic characteristics of the present method of solution are briefly stated with a state-of-the-art review on computational methods of prediction for nonlinear wave forces on offshore structures by using BEM. In summary, the boundary of the domains and all the variables are discretized by means of iso-parametric bi-quadratic elements. In order to resolve the intersection problem, discontinuous elements are introduced around corners and edges. The GMRES (Generalized Minimal RESidual) algorithm is implemented to solve the reduced linear algebraic equations. Time marching is constructed with the fourth-order Runge-Kutta method with minimum truncation error. The incident waves and diffracted wave field are numerically generated by applying artificial boundary condition of the free surface and vertical truncation boundary. The Chebycheve smoothing is utilized for suppression of saw-tooth waves on the free surface. In order to investigate the capability of the present method, nonlinear diffraction problem of a truncated circular cylinder is simulated. It is found out that the present method is fairly accurate for wave forces and run-ups on the whole when compared with experimental results and also with other numerical results. The qualitative comparison is made for magnitudes of harmonic components up to third order and second-order mean value. The discrepancy and its potential causes are demonstrated. According to numerical analysis and comparison with experiments, some recommendations are suggested for further studies of other methodologies as well as of BEM-based NWT technique.