Optimum design of multi-ring composite flywheel rotor using a modified generalized plane strain assumption

A numerical method for calculating the stress and strength ratio distributi on of the hybrid rim-type composite flywheel rotor is presented with a cons ideration of the thermally induced residual stresses. The axisymmetric roto r is divided into several rings and the stiffness matrix for each ring is d erived by solving the radial equilibrium equation and the stress-strain-tem perature relations. The ring stiffness matrices are assembled into a symmet ric global matrix satisfying the continuity equations at each interface wit h the assumptions of a modified generalized plane strain (MGPS). In the MGP S, the z=directional axial strains are assumed to vary linearly along the r adial direction; epsilon (z) = epsilon (0) + epsilon (1)r. The conditions t hat the z-directional force and the circumferential moment resultants vanis h are thus used to solve the z-directional axial strains as well as the rad ial and circumferential strains. After solving the strain distributions, th e on-axis stresses and the strength ratios are calculated at each ring. Thr ee-dimensional finite element method (3D FEM) is then used to verify the ac curacy of the present method. The results are also compared with those base d on the assumption of a plane stress (PSS). In this case, the analysis of MGPS better matches with 3D FEM results than PSS. An optimum design is then performed maximizing total stored energy (TSE) with the thickness of each composite rim as design variables. The optimal design obtained in this stud y, which considers material sequence, provides a more effective way of maxi mizing TSE. It is found that the consideration of the residual stress ill t he design of the hybrid flywheel rotor is crucial. The result of the optima l designs shows that TSE with consideration of DeltaT reduces by about 30%. (C) 2001 Elsevier Science Ltd. All rights reserved.