Analysis of Integrated Cylinder-Shaped Steel Flywheels in Flywheel Energy Storing Systems

In this paper, integrated cylinder-shaped flywheels are analysed. Two models of integrated flywheels are considered: the “shaftless” flywheel model and the “fully-integrated” flywheel model. In the former model, no shaft is needed; just an axel around which it rotates, and in the later, the flywheel rim is integrated with a hub and a shaft. The models are subjected to rotational speed 10,000 rpm. Firstly, theoretical analyses were carried out to derive the equations of the hoop and radial stresses in cylinder-shaped flywheels. In addition, relationships were derived, and used, to determine the shape factor K of cylinder-shaped flywheels. The commercial Finite Elements package (Abaqus) was used to model flywheels using axisymmetric elements. It was found that both the shape factor and the energy density (energy stored per kg) of the shaftless” flywheel are higher than that of the “fully-integrated” flywheel. However, the stress-affected zone in the “fully-integrated” flywheel is less than that in the “shaftless” flywheel. Moreover, it was found that in both models of the flywheel, the maximum generated hoop stress does not depend on the flywheel length. It greatly depends on the rotating speed of the flywheel. In addition, it was concluded that, a thin flywheel has more energy density rather than a thick flywheel if both have the same mass. Both models of the flywheel studied here are suitable to be used in fully-integrated flywheel energy storing systems (FESS). However, the “fully-integrated” flywheel is preferred for its simplicity of assemblage and bearing fixation