This paper presents the numerical modeling of a twisted stiffened cylindrical shell employing finite element approach to investigate the transient response due to impact of multiple masses, wherein the shell and the stiffener are modeled as 8 noded isoparametric shell element with five degrees of freedom per node and 3 noded isoparametric curved beam element having four degrees of freedom per node, respectively. The stiffener element is considered as a discrete beam element and its nodal degrees of freedom are transferred to the corresponding degrees of freedom of the shell element considering curvature and eccentricity. The impact force is predicted by employing modified Hertzian contact law relating the contact force to local indentation. As indentation takes place the impactor induces damage and permanent deformation in the contact zone of stiffened panel, as a result the loading and unloading curves are different. Different mathematical equations are considered for both loading and unloading cases in the stiffened panel during low-velocity impact. The accuracy and effectiveness of the finite element approach is verified by comparing the results with the corresponding solutions of analytical as well as standard computational methods available in the open literature. The optimum design of a structure can only be obtained by understanding the impact behavior and the roles of various parameters affecting the response. Hence, parametric study has been carried out to predict the time histories of contact force, displacement of the impact point and in-plane stresses during low-velocity concurrent/delayed impact at multiple locations of the stationary and rotating stiffened shell.

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