Mechanical Radial Force Identification of a Finite Cylindrical Shell by an Inverse Method

This paper presents a numerical method to identify exciting force from the dynamic response of a finite cylindrical shell. Knowing the displacements, the force distribution is computed by introducing them and their derivatives (using finite difference schemes) in the shell equation of motion. The main advantage of this method is that the force distribution can be computed from part of the displacement field independently to boundary conditions. In the case of cylindrical shells, the presence of the longitudinal and tangential deformations poses some problems especially in measurement. As a fist approximation, these quantities are supposed very small and are neglected. The advantage of this procedure is that measurement can be limited only to the radial displacements (w). The results shows this assumption is possible when the frequency is upper than the ring frequency. However, the results are better if the longitudinal and tangential deformations are taken into account at low frequencies. To verify the modal approach, the first ten natural frequencies were obtained with the finite elements method using I-Deas code. The frequencies were compared and the agreement between them was good. The proposed method gives also good results when the displacements are computed by FE method. This confirms that the present method is convenient, effective and accurate.