Semi-active six degree of freedom vibration control
Wilson, Nicholas Louis
Wereley, Norman M
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This body of work develops a modular, semi-active isolation suspension for 6-DOF vibration control of ground support equipment near a rocket launch. The objective is to provide vibration and shock attenuation for a broad disturbance spectrum with semi-actively controlled magnetorheological (MR) dampers. MR dampers have adaptable rheological properties that can be quickly altered by the application of an external magnetic field, allowing the device to be tailored to the source disturbance. These changes are large, reversible, and rapid (10 -3 s), which make MR fluid an excellent medium for mechanical vibration damping. This work addresses several practical issues the MR suspension may face, including perturbations in operating temperature, payload mass, and center of gravity. A model of a single, linear-stroke MR damper is developed to capture the force behavior for practical operating temperatures between 0°C and 100°C. The impact of temperature and payload mass on the attenuation performance is evaluated through a simplified 1-DOF system. The analysis is extended to a multi-damper suspension for 6-DOF vibration control and a mathematical model is derived to describe the system dynamics. Several control laws are formulated in the 6-DOF framework, considering both centralized and decentralized algorithms. The mathematical model is validated experimentally with a full-scale, deliverable system tested at George Washington University's Earthquake Engineering Laboratory shake table in response to simulated disturbances from NASA's Space Shuttle Mobile Launch Platform during the STS-31 launch. The model is used to analyze the attenuation ability of the suspension considering MR damper orientation, control strategy, and perturbations in payload mass, center of gravity location, and operating temperature. The semi-active suspension is shown to be a robust, adaptable solution with low power consumption requirements compared to the state of the art.