Free Vibration Analysis of Laminated Stiffened Shells

The free vibration of the laminated composite anticlastic doubly curved stiffened shells is investigated using the finite element method. The stiffened shell element is obtained by appropriate combination of the nine-node doubly curved isoparametric thin shallow shell element with the three-node curved isoparametric beam element. The shell forms include the hyperbolic paraboloid, hypar, and conoidal shells. The accuracy of the formulation is validated by comparing the authorsʹ results of specific problems with those available in the literature. The additional problems are taken up for parametric studies to include the effects of fiber orientation and lamina stacking sequence of shells and stiffeners. Moreover, the effects of number, types, and orientations of stiffeners, and stiffener depth to shell thickness ratio on the fundamental frequency are also included in the present study. Further, mode shapes corresponding to the fundamental frequency for typical cases are obtained to verify the parametric trend of the results of the fundamental frequency.