Robust feedback control of flow-induced structural radiation of sound
Abstract
A significant component of the interior noise of aircraft and automobiles is a result of turbulent boundary layer excitation of the vehicular structure. In this work, active robust feedback control of the noise due to this non-predictable excitation is investigated. Both an analytical model and experimental investigations are used to determine the characteristics of the flow induced structural sound radiation problem. The problem is shown to be broadband in nature with large system uncertainties associated with the various operating conditions. Furthermore the delay associated with sound propagation is shown to restrict the use of microphone feedback. The state of the art control methodologies, $\mu$ synthesis and adaptive feedback control, are evaluated and shown to have limited success for solving this problem. A robust frequency domain controller design methodology is developed for the problem of sound radiated from turbulent flow driven plates. The control design methodology uses frequency domain sequential loop shaping techniques. System uncertainty, sound pressure level reduction performance, and actuator constraints are included in the design process. Using this design method, phase lag was added using non-minimum phase zeros such that the beneficial plant dynamics could be used. This general control approach has application to lightly damped vibration and sound radiation problems where there are high bandwidth control objectives requiring a low controller DC gain and controller order. The controller design methodology developed in this work was verified experimentally. A multiple-input-multiple-output controller using accelerometer feedback and shaker control was able to achieve robust control up to 1000 Hz. Sound pressure level reductions of as much as 15 dB were achieved at multiple microphone locations. Overall reductions over the 100-1000 Hz band were approximately 5 dB. The controller was found to be robust to large changes in the system parameters due to speed variations from 35.8 m/s to 51.5 m/s and changes in the plate mass up to 40 percent.
Degree
Ph.D.
Advisors
Franchek, Purdue University.
Subject Area
Mechanical engineering|Acoustics
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