Theoretical Study On The Fluid-Structure Interaction Characteristics Of Coaxial Cylindrical Shells Under Free-Clamped Conditions And Its Application

Pool-type sodium-cooled fast reactor main vessel ring fluid domain contains a large number of liquid metal sodium,the main vessel and its heat shield have the characteristics of large size and thin wall thickness.Compared with the PWR pressure vessel,the fast reactor main vessel is a typical flexible shell.In seismic conditions,the main vessel,heat shield and liquid sodium fluid will produce strong fluid-solid interaction phenomenon,which will change the natural frequency of these structures and seriously affect the safety of the reactor structure.Therefore,it is very important for the seismic analysis of fast reactors to carry out research on the fluid-solid interaction characteristics between the fast reactor main vessel and its heat shield.When analyzing the fluid-solid interaction behavior of fluid-containing structures at home and abroad,the method of added mass is generally used.Aiming at the fluidstructure interaction phenomenon of finite-length coaxial cylindrical shells,some studies have given the calculation method of the added mass of the shell.However,this method only studies the fluid-solid interaction effect of the flexible vessel shell in the rigid container.If the container is also a flexible shell,it will be interacted with the internal shell through the interstitial fluid to form a more complex coupling system.At this time,the method is no longer applicable.Moreover,this method is only applicable to cylindrical shells constrained by sp-sp boundary at both ends,and the applicability to the fast reactor main vessel and its heat shield still needs to be further verified.Therefore,it is necessary to study the fluid-solid coupling effect of coaxial multilayer flexible cylindrical shells under different boundary conditions.In this paper,the added mass is firstly solved based on the analytical method.starting from the pressure field of the interstitial fluid in the system,the motion equation of the free vibration of the coupled system is solved by the beam function combination solution.the fluid-structure interaction effect of coaxial multilayer cylindrical shells is studied systematically.In this paper,the added mass is firstly solved based on the analytical method.starting from the pressure field of the interstitial fluid in the system,the motion equation of the free vibration of the coupled system is solved by the beam function combination method,and the fluid-solid interaction effect of the coaxial multi-layer cylindrical shell is systematically studied.The formula for calculating the added mass of the shell under arbitrary boundary conditions is given,and a calculation program for the added mass is developed on this basis.Secondly,aiming at the relatively small length and diameter of the shell,the combined solution of beam functions solves the problem that the natural frequency error is relatively large,and the method of fitting the mode of vibration function by FEA simulation is used to correct the the axial beam mode shape of vibration function,reduce its error.Afterwards,modal experiments and numerical simulations were carried out for the fast reactor main vessel and its heat shield,and it was found that for each mode,the added mass calculation program was in good agreement with the experimental and simulation results.Finally,the fast reactor main vessel and heat shield fluid-solid interacting seismic experiments were carried out,and the acceleration response of the shell and the dynamic pressure distribution of the fluid gap were obtained.Then,the Fourier series is used to separate the mode shapes,and the proportion of each order mode shape of the main vessel and the heat shield under the seismic condition is given.It is found that under seismic conditions,both the shell acceleration and the pressure of the interstitial fluid are dominated by the beam mode vibration in the experimental frequency band.In summary,this study provides a set of accurate theoretical calculation methods for the coaxial double-layer flexible cylindrical shell,and provides an important theoretical basis for the fluid-solid coupling seismic design of the fast reactor.