The Added Mass And Fluid Damping Of The Riser On Unsteady Flow

In the prediction of vortex induced vibration(VIV),a large number of coefficients need to be obtained by experiment and experience,such as the added mass coefficient and fluid damping.In the past,the research on the added mass and fluid damping of the riser model is not systematic,but these parameters will have a very important impact on the final results prediction.In order to get an accurate prediction of the VIV model,the theoretical derivation and numerical simulation are made to obtain the parameters that affect the added mass and the fluid damping.And this paper will be carried out from the following aspects:Firstly,the cause of added mass and fluid damping is analyzed by vibration equation,then sum up the parameters of the parameters that influence the added mass and fluid damping.The concept of system structure damping is presented;the structure damping is related to the structure model.In vortex induced vibration,structural damping and fluid damping are function together.Secondly,establish the vibration model of vortex induced vibration by "slice method" theory.The numerical simulation model of fluid solid coupling is built at ANSYS and CFX platform.Verify the lift curve,drag curve and vibration frequency in the single degree of freedom and double degree of freedom.Then verify the relationship of the vibration displacement,Velocity and Acceleration at single degree of freedom and double degree of freedom,compare conclusion with related literature.After determination of the model,24 different reduced velocity Ur conditions,13 different mass ratio M* conditions and 12 different Reynolds number(Re)conditions are designed,which user to derive the relationship between the three parameters and additional mass coefficient.Thirdly,the same numerical simulation model used in added mass solution,by changed the fluid domain media is air(air’s fluid viscosity is small and can be ignored in calculating structure damping)and use the free decay method to calculate the structure damping of the model.There is 8 different Reynolds numbers conditions are applied to calculate fluid damping.Different Reynolds numbers means different liquid viscosity and different fluid damping.Finally the relationship between fluid damping and Reynolds numbers is carried.At last,research the effect of the added mass coefficient and the fluid damping value on VIV,including the frequency ratio of f*,Strouhal number St,and the frequency of the vibration.The results shows that the varied added mass coefficient of the system will make the vibration frequency of the vertical tube and Strouhal number less than the theoretical value;and fluid damping affected by Reynolds number will be less than the conclusion of the literature.