Three analysis models of torsional frequency of stiffening cylindrical shell

For simplifying the analysis of stiffening cylindrical shell in rocket, the computational method of torsional rigidity in the area-equivalence method was studied for the stringers in stiffening cylindrical shell, it is shown that the effect of stringers on the torsional rigidity of stiffening cylindrical shell is negligible. The equivalent beam or shell model with uniform thickness, the equivalent shell model with varied thickness and three dimensional (3-D) beam-shell model were proposed to solve the inherent torsional vibration frequency, and the features of these models were discussed. It was theoretically revealed that the obtained equivalent thickness by the area-equivalence method could not be directly used to calculate the torsional rigidity. Two modification methods, namely, the rigidity reduction method and frequency modified method, were presented when the equivalent thickness was directly utilized to solve the torsional frequencies. Numerical comparisons validate the proposed methods and models.