Design Optimization and Health Monitoring for Multi-Directional Composite Flywheel Energy Storage Systems

Abstract

Flywheels are used to store kinetic energy through the rotation of an inertial mass, which usually rotates at very high speeds. Generally, that energy can be extracted (using a motor-generator system) in the form of electricity. For space applications, where most advanced designs are used, weight is a major consideration. Storing as much energy as possible in as little mass as possible is a fundamental requirement for such systems. Rotational speeds for certain designs may exceed 60,000 RPM, which introduce very high stress levels into the hub and rim. Failure of the structure can result in an almost explosive disintegration, which can prove deadly to anyone in the vicinity of such a disaster. Accordingly, two major and often contradictory challenges in flywheel design are improved energy storage density and operational safety. In order to address these challenges, a new approach to strengthen rotating structures with additional reinforcement in the radial direction, along with the typical hoop direction reinforcement, which is called multi-direction composites (MDC), has been developed. This work explores basic issues of safety and energy storage density with specific application to the MDC approach. Specifically, the goals of this research effort were to:

·Develop a methodology to optimize the design, based upon maximizing the energy storing density (ESD) of the complete flywheel system (including shaft, hub, and rim). ·Design and evaluate a prototype configuration consisting of a steel shaft, a multiple-layer domed hub and a multi-directional composite rim. ·Develop and evaluate a health monitoring methodology for such systems based upon variations in imbalance level. ·Investigate the application of the Gabor analysis technique, a joint time-frequency method, as a vibration analysis tool for crack identification. ·Investigate the natural frequency variations due to the presence of the cracks in a composite disk rotor system, both experimentally and numerically.