Investigation of Passive Control Devices for Potential Application to a Launch Vehicle Structure to Reduce the Interior Noise Levels During Launch
Abstract
The work discussed in the report is an extension of work undertaken by Dr. Steve Griffin of the Air Force Research Lab at Kirtland AFB, NM, during his participation in an AFOSR Windows on Science program at the University of Adelaide, South Australia in 1998. The previous work involved an investigation of the application of active feedback control of the launch vehicle structural vibration using radiation mode vibration levels as the cost function to minimize interior noise levels and led to the publication of three papers. The small benefit of action control, compared to the passive effect of the un-excited actuators attached to the structure has been the impetus behind the work conducted in the paper which is directed at optimizing the passive effect of vibration reducing devices. The objectives of the study were achieved. A numerical framework for the study of the response of an irregular shaped vibro-acoustic system excited by an external pressure field has been developed. The method used the modal coupling technique which coupled the in- vacuo modal model of the structure to the rigid -walled modal model of the cavity. The solution times of the (modal coupling) method were found to be extremely fast, solving two to three orders of magnitude faster than a fully coupled FEA. The modal coupling technique was validated against a fully coupled FEA. The FE model of the structure was adjusted so as to accurately emulate the physical structure. The effect of the VAD was analyzed and optimized for two bandwidths, namely 50-200Hz ands 50-400Hz. It was found that the optimal VAD design used the TMD as a highly reactive device to reduce the structural modal density within the frequency band of interest and the optimal diaphragm configuration was highly lossy to reduce the modal amplitude of the single acoustic mode. Local flexure of the panel reduced the effectiveness of the VAD's and alternative attachment techniques were investigated to reduce such flexure.
Document Details
- Document Type
- Technical Report
- Publication Date
- Nov 14, 2000
- Accession Number
- ADA386404
Entities
People
- Colin Hansen
Organizations
- University of Adelaide