A Dynamic Stability Analysis of Composite Grid-Stiffened Cylindrical Shells under Harmonic Loads Using the Donnelly Theory

In aerospace structures, due to the fluctuations of excitation sources such as the engine propulsion, there is a possibility of dynamic instability, which is a destructive phenomenon. In this paper, the dynamic stability of composite grid-stiffened cylindrical shells under a combinational loading of static and fluctuating forces has been investigated using the Dunnelly theory for thin-walled shells. Using the equivalent stiffness method, the stiffness of composite grid structures has also been calculated by the method of reinforcements impregnation. The development of a normal mode for motion equations leads to the system of Matthew-Hill equations. The Boltin method is used to determine the instability regions to solve the Matthew-Hill equations. The effect of iso-grid mesh reinforcement parameters such as the rib angle, circumferential and annular rib spacing and the rib cross section as well as the effect of cylindrical shell length to radius and thickness to radius ratios have been tested and compared. The validation of the natural frequency and dynamic stability results has been done by comparison with Abaqus software and other researchers' articles. The results show that by decreasing the angle of the helical ribs, in the shells of composite grid cylinders, the main instability frequency increases and the amplitude of the instability region decreases.