고차경계요소법을 이용한 파와 구조물의 비선형 상호작용 해석

Abstract

The demand for the coastal space utilization is increasing as the standard of living improves and necessity of safe coastal structure is also being concerned as the intensity of natural disasters increases. But the reliable numerical tool for designing coastal structure in heavy ocean condition has not been existed. Numerical Wave Tank(NWT) that is developed as the basic frame on the interaction between waves and a structure can consider the nonlinear effect in order to give the correct and reliable results. NWT is also able to execute the wide range of parametric study for the numerical model with the reduced time and expense, compared to the laboratory experiment. In this thesis, the nonlinear interaction between waves and a structure(submerged horizontal plate, submerged step) as well as the nonlinear wave generation in 2-diemensional wave tank have been investigated under the assumption of nonlinear potential theory. Boundary value problem for NWT was transformed into Boundary Integral Equation(BIE) using Green's identity. In order to obtain the unknown values along the boundary, the boundaries enclosing the fluid domain were divided into several elements. And then a higher order Boundary Element Method(BEM), which expresses a higher order shape function and node value for shapes and variables, was applied to each element. A higher order Taylor expansion was used for updating the free surface shape and the potential value in time. Numerical calculation has been performed to verify the nonlinear interaction between waves and a structure(horizontal plate and a submerged step). It was found that the reflection and transmission coefficients by a structure shows good agreements with the experimental results of Patarapanich and Cheong(1989) and Losada(1997) respectively. Moreover, it was noted that the higher harmonics, which is generated in shallow water due to a horizontal plate or a submerged step installed in NWT, is transferred to the transmission side. The variety of regular and irregular waves by controlling the wavemaker motion was generated in NWT for future analysis of nonlinear interaction between irregular waves and a structure.