Numerical Study On Vortex-induced Vibration Suppression Devices Of Marine Rise By CFX

Hydrocarbon resources in deep-sea are needed strongly, due to the rapid development ofglobal economy. As the main connector between drilling ship or platform on the surface ofwater and the drilling equipment under the sea, marine risers bear the effects from waves andcurrents in the marine environment. It will generate alternate vortex shedding around the riserwhen the waves and currents pass it. Vortex shedding will produce periodic forces on thesurface of riser which will lead to the vortex-induced vibration(VIV). When the vortexshedding frequency is closed to the natural vibration frequency of the structure, aphenomenon occurs called―lock-in‖which will lead to the fatigue damage of the riser. Thecommon method to eliminate or reduce the VIV at present is installing suppression devices onthe riser, which can prolong the service life of the riser.Two dimensional numerical models of five different cross section form cylinders arefounded using ANSYS(CFX). The feasibility of the numerical model and calculation methodare validated, and the change rules are analyzed for fluid characterization parameters thoughthe simulation results of stationary single cylinder in the range of laminar flow. Then, thelateral displacement of the cylinder and the relationship between the wake and the cylindervibration are studied though the single degree of freedom model of the VIV by using rigidbody.The cylinder models which with the different suppression devices are founded base onthe VIV analysis of the single cylinder. Disturbed flow features of the different cross sectionform cylinders are analyzed. Determine the performances of the four suppression devicespreliminary by comparing the fluid characterization parameters with the single cylinder. Theresults show that every suppression device has an effect on the parameters in different degree.Finally, the single degree of freedom model of the VIV is simulated for two kinds of cylinderswhich with the better results of the suppression devices in terms of disturbed flow analysis.Comparing the results of vibration response with the VIV results of the single cylinder, it shows that both of the vibration suppression devices can reduce the maximal displacementamplitude of the cylinder.