DESIGN OF CYLINDRICAL SHELLS FOR STATIC AND DYNAMIC LOADS.

Abstract

Cylindrical shells which are used as fluid or (granular) solid retaining structures and which are subjected to vibration are usually designed as having uniform thickness. However it is known that for shells under hydrostatic (and static) loads the bending and hoop stresses vary with the height of the shell. Moreover the natural frequencies of the shell can be elevated by not conforming to uniform thickness. This can enable vibration isolation of the shell and elimination from the destructive effects of resonance. In the present work, the optimum design of a cylindrical shell is treated such that the maximum stresses are near the allowable values and such that the fundamental natural frequency is made as high as possible. The static and dynamic aspects are carried out separately. In both cases the inner radius of the shell is kept constant, while the thickness (and hence the outer radius) is varied along the shell axis. Since analytical solutions are either impossible or tedious to carry out, a numerical procedure using the finite element method has been adopted. The results confirm that the design of cylindrical shells can be optimised so that material economy is achieved and the performance is enhanced.