Numerical Similation Of Passive Control Of VIV By Small Control Rods

Cylindrical structures such as marine risers can produce vortex-induced vibration under the impact of currents.The vortex-induced vibration phenomenon is the main cause of fatigue damage of the riser.Therefore,in order to protect the marine environment and reduce economic losses,it is necessary to effectively suppress the vortex-induced vibration to ensure the safety of the riser and extend the service life of the riser.Installing the control rods on the riser is one of the ways to reduce the vortex-induced vibration of the riser.Therefore,this paper focuses on the optimal distribution of the control rod on the riser.The main work and achievements of this paper are as follows:(1)Firstly,the UDF program was compiled based on the dynamic equation of the two-degree-of-freedom vibrating cylinder.Then,by loading the UDF program into the FLUENT software,the numerical simulation of the two-degree-of-freedom vortex-induced vibration at different reduced speeds is carried out for the low-mass ratio single cylinder.The numerical simulation results are compared with the experimental results,which show the numerical simulation results.Correctness.Then using this algorithm to simulate,the time-history curve,displacement time-history curve,motion trajectory,Stallauer number change trend graph and vorticity contour of different rising speeds are obtained,and the single cylinder is determined.The locking regime is 4.5<Ur?10.In the locking regime,the lift coefficient and the displacement amplitude of the bare cylinder are larger.When the reduced velocity is 5,the amplitude reaches the maximum value,and the maximum amplitude corresponds to the Strouhal number of the working condition is close to 0.2.When the vibration enters the upper branch from the initial branch,the vortex shedding mode changes from 2S to P+S mode,and the change causes the cylindrical amplitude to change from a rising trend to a decreasing trend.(2)Numerical simulation of vortex-induced vibration under different working conditions with different number of control rods,different inflow angles and different spacing conditions.From the research results,under the condition that the spacing ratios is 1.2,the flow inflow angles is 0 and the reduced velocity is 5,the additional control rod(the number is from 3 to 36)can make the vortex shedding mode change from P+S to 2S,the Strouhal number is far from 0.2,and the amplitude can be greatly reduced,indicating that the additional control rod can effectively suppress the cylindrical vortex vibration.When the number of levers is 8,the amplitude reduced speed is maximized,so taking 8 contorl rods is the optimal number.Under the condition that the number of control rods is 8,the spacing ratios is 1.2 and the reduced velocity is 5,different inflow angles of the incoming flow have a certain suppression effect on the amplitude of the cylinder,and the amplitude suppression rate reaches the maximum when the inflow angles is 0.Therefore,the best incoming inflow angles is zero.Under the condition that the number of the control rod is 8,the flow inflow angles is 0 and the reduced velocity is 5,the amplitude suppression rate reaches the maximum when thespacing ratios is 0.6,and 0.6 is the optimum spacing ratios.(3)When the fixed reduced velocity is 5,the number of control rods is 8,the inflow angles is 0,and the spacing ratios is 0.6.A layout method in which the control rods are juxtaposed are proposed,numerical simulation is carried out and its influence is analyzed,and Checking the flow rate.(4)Select the optimal operating condition by comparing the dimensionless amplitude of the unit number of control rods.