OPTIMUM DESIGN OF THICK-WALLED COMPOSITE RINGS FOR AN ENERGY-STORAGE SYSTEM

An optimum design has been performed to maximize the specific energy d ensity (SED) of a composite flywheel rotor for an energy storage syste m. The flywheel rotor consists of multiple rings, and the interference s and ply angles vary in the radial direction. For the structural anal ysis the rotor is assumed to be an axisymmetric thick laminated shell with a plane strain state. Considering the ring-by-ring variation of f iber orientations, a symmetric local stiffness matrix was derived for each ring. Using the stiffness matrix, the continuity conditions of ra dial stresses and displacements between the rings with a consideration of the interferences can be easily incorporated. A symmetric global s tiffness matrix is then obtained assembling the local stiffness matric es. Displacements are obtained by solving the global stiffness matrix, and the stresses in each ring are then calculated. Three-dimensional intra-laminar quadratic Tsai-Wu criterion for the strength analysis is used yielding the strength ratio for each ring. The optimization has been also performed maximizing the kinetic energy stored in the rotor. For that purpose the sensitivities of the strength ratios and displac ements with respect to the design variables have been derived. As a re sult, the optimal design has attained 2.4 times of total energy compar ed to the case of 0 degree ply angle and no interference. The effects of interferences are found to be much more considerable than those of fiber orientations.