Robust feedback control of flow-induced structural radiation of sound

Heatwole, Craig M. PhD., Purdue University, May 1997. Robust Feedback Control of Flow Induced Structural Radiation of Sound. Major Professors: Dr. Robert J.Bernhard and Dr. Matthew A. Franchek, School of Mechanical Engineering. 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, # 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. xvii The controllerdesignmethodologydevelopedin this work wasverifiedexperimentally. A multiple-input-multiple-output controller using accelerometerfeedbackand shaker control was able to achieverobust control up to 1000Hz. Sound pressure level reductionsof asmuchas15dB wereachievedat multiple microphonelocations. Overall reductions over the 100-1000Hz band were approximately 5 dB. The controller wasfound to be robust to largechangesin the systemparametersdueto speed variations from 35.8m/s to 51.5 m/s and changes in the plate mass up to 40 percent. CHAPTER