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Weight Optimized Structural and Acoustic Actuators for the Control of Sound Transmission Into Rocket Payload Compartments

[+] Author Affiliations
Marty Johnson, Ozer Sacarcelik, Tony Harris

Virginia Polytechnic Institute and State University

Paper No. IMECE2004-61205, pp. 55-62; 8 pages
doi:10.1115/IMECE2004-61205
From:
  • ASME 2004 International Mechanical Engineering Congress and Exposition
  • Noise Control and Acoustics
  • Anaheim, California, USA, November 13 – 19, 2004
  • Conference Sponsors: Noise Control and Acoustics Division
  • ISBN: 0-7918-4715-2 | eISBN: 0-7918-4178-2, 0-7918-4179-0, 0-7918-4180-4
  • Copyright © 2004 by ASME

abstract

The reduction of sound transmission into rocket payload compartments is a challenging application for active control due to the broadband nature of the disturbance, the large structural and acoustic space and the very high acoustic levels required. The exterior acoustic field that drives the payload fairing at liftoff is typically in the order of 145dB and the active control system must be able to counteract this high drive level using lightweight actuators. This paper is concerned with the development of structural and acoustic actuators for this application with the emphasis on maximum output level in the 60–200Hz bandwidth for a given actuator weight. The electromagnetic structural actuators are based on powerful rare earth magnets in a two degree of freedom arrangement. It is shown that a two degree of freedom arrangement allows the output in the bandwidth of interest to be increased over a simple one degree of freedom arrangement. The design is termed a distributed active vibration absorber or DAVA as the second degree of freedom is provided by a light and distributed foam element that allows easy attachment and low stress concentration on the structure. The two degree of freedom arrangement also acts as a natural low pass filter to naturally remove unwanted spillover at higher frequencies. The acoustic component is also based on powerful rare earth magnets, however the two degree of freedom arrangement used for the structural actuator is no longer of interest. The main concern is in the reduction of the speaker and cabinet weight. It is shown that careful design of the speaker and cabinet can lead to large reductions in weight without loss of performance. Data taken from an active control experiment on a large composite cylinder, coupled with data from the characterization of the actuators will be used to determine the total actuator weight needed for control in a typical launch environment.

Copyright © 2004 by ASME

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