Type of Document Master's Thesis Author Finefield, John K. URN etd-10062009-020152 Title Investigation of combined feedback and adaptive control of cylinder vibrations Degree Master of Science Department Mechanical Engineering Advisory Committee
Advisor Name Title Cudney, Harley H. Committee Chair Leonard, Robert G. Committee Member Robertshaw, Harry H. Committee Member Keywords
Date of Defense 1992-05-05 Availability restricted Abstract
A double loop control scheme is developed to control broadband acoustic radiation from a cylinder. An analog feedback loop is investigated and developed to add damping to the cylinder at particular frequencies of interest. Circuitry is developed and refined to condition Polyvinylidene Fluoride Filnl (PVDF) sensor outputs as strain rate signals. The strain rate signals are used in the feedback loop to provide damping to the structure. In conjunction with the feedback loop a feedforward loop is also implemented. The feedforward loop utilizes the filtered-x LMS algorithm.
The result of combining the two control laws was unknown prior to implementation.The resulting control scheme shows that the feedback control law is effective in attenuating undesirable frequency components in the feedforward error sensor. This results in an error sensor signal which is highly correlated with the disturbance. With a more correlated error signal a more effective feedforward control is achieved. The resulting control system provides acoustic control over a wide range of frequencies. The filtered-x LMS algorithm is applied to an effective acoustic radiator. The feedback loop provides for broadband control of the structure. Typical double loop controller results show power spectrum reductions of 35 dB for an effective acoustic radiator and reductions of 10 dB for other frequencies in the excitation range. In addition, the measured controlled plant transfer functions show significant reductions in the transfer of energy through the structure. Overall Sound Pressure Level (SPL) reduction in the acoustic field generated by the cylinder in response to a random excitation with a harmonic component was 4.9 dB for feedback, 18.4 dB for feedforward, and 25.2 dB for the double loop controller.
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