Optimization of frequency separation of laminated shells carrying transversely distributed mass using genetic algorithm

Abstract

Shell structures are primarily used in the aerospace and maritime sectors. Such structures often oscillate, and undesirable oscillations can cause structural damage. So, to eliminate resonance and prevent damage to vibrating structures, it is necessary to build optimal shells. Maximizing the frequency gap between the first two eigenfrequencies is essential so that they do not coincide with the resonance frequency. Depending on the requirements of the design, the external frequencies might be placed between zero and the first natural frequency or between the first and second natural frequencies in order to prevent failure. This study proposes an efficient finite element model based on first-order shear deformation theory in combination with a genetic algorithm to maximize the frequency separation of laminated cylindrical shell panels. The maximum first natural frequency determined by the current FE-GA formulation is verified by previously published data, and it is found that the present results are better than the literature for 56% of the test cases. Moreover, for real-world situations like a clamped shell or a simply supported shell, the present solutions are approximately 0.6 to 2% better than the literature. Effect on the optimal design due to changes in mass ratio, curvature ratios of the shell panels, carrying dispersed mass over the entire shell panel, and dispersed patch mass at the middle is analyzed. The ideal stacking sequence for greatest frequency separation values is presented for a variety of curvature ratios and mass ratios.