The Influence of Elastic Boundary on Modal Parameters of Thin Cylindrical Shell

Abstract

This research combines theory with experiment to investigate the influence of an elastic boundary on modal parameters of a thin cylindrical shell (TCS). First, artificial stiffness method and finite element method (FEM) are employed to calculate natural frequencies and modal shapes of TCS under condition such that vibration characteristics of elastically supported shell can be roughly mastered. Then, the following measurements and identification techniques are used to get precise frequency, damping, and shape results: non-contact laser Doppler vibrometer and vibration shaker with excitation level being precisely controlled are used in the test system; “pre-experiment” is adopted to determine the required tightening torque as well as to verify whether or not the tested shell is under constraint boundary; and small-segment FFT processing technique is employed to accurately measure nature frequency, and laser rotating scanning technique is used to get shape results with high efficiency. Finally, based on the accurate measured data, the influences on natural frequencies, modal shapes, and damping ratios of TCS under elastic boundary are analysed and discussed. It can be found that an elastic boundary can significantly affect frequency and damping results, clearly reducing high order damping and decreasing natural frequencies of most modes. However, high order natural frequencies and mode shapes are still the same as the ones under the constraint condition, and the changing trend of natural frequencies with mode shapes is constant when the order of axial mode is m = 1, which agrees well with the results calculated by artificial stiffness method and FEM.