Numerical Simulation On Vortex-induced Vibrations With Fluid-Structure Interaction For Risers By CFD

Based on Computational fluid dynamics (CFD) and Computational structuredynamics (CSD), the vortex induced vibration (VIV) of circular cylinder is simulatednumerically. The variation regularity of the force coefficients, the amplitude ofvibration and the patterns of vortex shedding in different cases are studied, and thephenomenon of marine risers under vortex induced vibration is explored. The VIVmotion of cylinder with suppressions is analyzed, and the effect of suppressions isdiscussed. Furthermore, the interference among multi-cylinder with VIV is involved,and the quasi-3D study on the VIV motion of the deepwater risers is established. Themain content of this dissertation is as follows:1. Study on the numerical simulation of the fluid-structure interactionBased on summarizing and analyzing the CFD research status of thefluid-structure interaction both at home and abroad, a dimensionless numerical modelfor the analysis of the vortex-induced vibration of fluid-structure interaction(FSI) isestablished. Based on the coefficients of VIV and CFD method, the SST k modelis chose for the establishment the model of fluid field, and the boundary motion of thecylinder is simulated by the Newmark-β method. Finally, a computational procedureon FSI is given to solve the dynamic response of cylinder.2. Numerical simulation on vortex induced vibration of single cylinderThe numerical model of vortex-induced vibration for single cylinder is established.And the dynamic response of a single cylinder is achieved by employing acombination of program fsi-xy.c and FLUENT. By simulating structure and flowtogether, the force coefficients and the vibration amplitude can be achieved.According to the results, the pattern of oscillating cylinder is analyzed, and therelationship between cylinder vibration and the vortex shedding model is revealed.3. Numerical simulation on vortex induced vibration of cylinder with suppressiondevice by FSIThe dynamic response of cylinder with suppression device is simulatednumerically by fluid-structure interaction. In this section, three kinds of fairings arestudied, which is triangular fairing of10mm length, triangular fairing of14mm lengthand plate-shaped fairing of18mm. By analyzing numerically based on the procedure above, the dynamic response of cylinders with different cross-section can be achieved.The results show that there is influence on the vibration of cylinder because offairings. And under the effect of vibration of cylinder with fairing, the flow field isdamaged in varying degrees. Compare to the dynamic response of single, the effectsof the fairing are further explained.4. The effect of the interference of two cylinder in tandem and side-by-sidearrangement.Based on the FSI model of single cylinder, a numerical calculation method offluid-solid interaction vibration system of multi cylinders under elastic support isdeveloped. Two cylinders are arranged at space interval ratio L/D=3~10in tandemand at space interval ratio G/D=5~10at side-by-side. The motions of two cylinders indifferent arrangement are solved by the programme fsi-2c-xy.c. And depended on thespecial macro, two cylinders move together in the same time step. The range of Re isfrom6300to18000. The results achieved by simulating are the amplitude of vibration,force coefficients and the x-y trajectory, which show that there is different interferenceeffect on the different arrangement.5. The quasi-3D numerical simulation on dynamic response of the riserThe vibration of riser is more complex under the influence of Reynolds number,characters of structure and fluid. The numerical model in2D can’t solve the problemof the vibration of3D risers well. So in this section a quasi-3D numerical is modeledby CFD. The quasi-3D model is based on the combination of3D structure model and2D fluid model. The riser is transformed into the multi particle model, and every masspoint is considered as the spring-damping vibration model. Based on the FSI model ofsingle cylinder, the dynamic responses of mass points are calculated in2D flow field,respectively. Depended on the results of every mass points, the dynamic response ofthe riser is approximately achieved. In order to verify the quasi-3D model, anexperiment on vortex-induced vibration of rise is conducted. By compared the resultsbetween experiment and numerical simulation, the non dimensionless displacementenvelopes between two studies is similar. It is shown that the quasi-3D model cansimulate the dynamic response of the structure in3D approximately.