Effect of flowing fluid on vibration frequencies of a thin-walled cylindrical tube

A clamped-clamped thin-walled circular cylindrical tube was considered as a Timoshenko beam model.The natural frequencies and normal modes of the thin-walled circular cylindrical tube without liquid were deduced by using the vibration theory of the beam bending and the finite element model with the effect of the concentrated mass.The differential vibration equations and natural frequency equation of the tube with flowing fluid were derived.A set of experiment equipment was designed and made to test the first three natural frequencies and normal modes of a thin-walled cylindrical tube without fluid,with static liquid and with flowing fluid.The frequency-response curve of the thin-walled cylindrical tube with static liquid was of nonlinear soft-type.The data obtained from the experiments were very close to theoretical values.The liquid in the thin-walled cylindrical tube made its natural frequencies decline.