전단유동장내 유연관에 대한 와유기진동 수치시뮬레이션

Abstract

ANSYS multi-physics software was applied to a numerical simulation of fluid-structure interaction (FSI) for a long flexible riser with vortex-induced vibration (VIV). The main purpose of the research works is to investigate the fluid-structure interaction taking place between a tensioned flexible pipe and the surrounding fluid in shear flow. In this paper, a complete three dimensional numerical FSI solution is looked for to provide supplementary information for a model test. For the simulated riser is subject to shear flow with linearly reduced velocity along the pipe, remarkable VIV tends to be excited more easily than the riser system undergoing uniform current. In general, the vortex-induced vibration would be a multi-mode process, having both natural frequencies/modes and some arbitrary frequencies of the riser system. Visualizations of the vortex wake indicate a hybrid mode of vortex shedding along the pipe in many simulation cases. 2S mode is manifested in regions of low amplitudes or small reduced velocity, changing into 2P mode in regions of larger amplitudes and high reduced velocity. The position where transition of modes occurs varies with the reduced velocity and RMS value of instantaneous vibration amplitude.