Spatial Modulation of Nonlinear Waves and Their Kinematics using a Numerical Wave Tank

J. Ocean Eng. Technol. 2009;23(6):12-16.

Koo Weon-Cheol,Choi Ka-Ram

School of Naval Architecture and Ocean Engineering University of Ulsan,School of Naval Architecture and Ocean Engineering University of Ulsan

수치 파동 수조를 이용한 비선형파의 파형변화와 속도분포 해석

구원철,최가람

울산대학교 조선해양공학부,울산대학교 조선해양공학부

Keywords: Numerical wave tank, Fully nonlinear, Boundary element method, Particle velocity, Nonlinear waves, Wave modulation

핵심용어: 수치 파동 수조, 완전 비선형, 경계요소법, 입자 속도, 비선형파, 파변조

Abstract

In this study, the wave profiles and kinematics of highly nonlinear waves at various water depths were calculated using a 2D fully nonlinear Numerical Wave Tank (NWT). The NWT was developed based on the Boundary Element Method (BEM) with the potential theory and the mixed Eulerian-Lagrangian (MEL) time marching scheme by 4th-order Runge-Kutta time integration. The spatial variation of intermediate-depth waves along the direction of wave propagation was caused by the unintended generation of 2nd-order free waves, which were originally investigated both theoretically and experimentally by Goda (1998). These free waves were induced by the mismatch between the linear motion of wave maker and nonlinear displacement of water particles adjacent to the maker. When the 2nd-order wave maker motion was applied, the spatial modulation of the waves caused by the free waves was not observed. The respective magnitudes of the nonlinear wave components for various water depths were compared. It was found that the high-order wave components greatly increase as the water depth decreases. The wave kinematics at various locations were calculated and compared with the linear and the Stokes 2nd-order theories.