Analysis And Numerical Simulation On Vortex-induced Vibration Of Flexible Risers

Considering the economics and flexibility, offshore platform is usually connected with pipelines in oil exploitation, top tension risers (TTRs) for example, which causes coupling effects among risers, anchor chains, supply lines and platform, especially when there are many risers in a limit area. And the damages coursed by collisions of risers can decrease the service life of the risers; even endanger the safety of platform. In the case of avoiding collisions and excess vortex-induced vibrations, the study of the interactions of the risers is significant to carry out.Regular Vortex Shedding caused by ocean current has a periodicity pulsating effect on the risers, which leads to vortex-induced vibration impacting on the normal production of the platform. And the current studies on damages of ocean risers caused by vortex-induced vibration mainly base on the physical model and numerical simulation, for the model text is too difficult to practice at present. In this paper, ansysll software is used to simulate the viv of the single riser and multi-risers.This paper concerns on three main studies. Firstly, CFX is adopted to simulate the two-dimensions example, including the vortex-induced vibration problems of the single riser as well as the double vertical risers with different center distance. Comparative analysis of the lift and drag force changes etc. are also studied, obtaining some reliable conclusions and the validity of numerical method is proved to be right. Secondly, the simulation of the 3-dimensional multi-flow around the fixation risers is studied with more accurate working conditions and better results compared to the two-dimensional numerical simulation. Finally, and the focus of this article, is the 3D numerical simulation of the flexible risers compared with 3D fixation multi-risers, including analysis of lift coefficient and drag coefficient changes. In this paper, the research process not only obtained reliable results, but also took some useful conclusions for the related practical problems of marine engineering.