engleski

Active control of sound transmission through a double-wall structure

This thesis treats the study of an active vibroacoustic control implementation on an aircraft double panel. The control system is implemented using a velocity feedback loop utilising voice coil actuators and MEMS accelerometers. The voice coil actuators are located in the cavity between the two panels so they can exert forces on the panels. Two collocated accelerometers are used at each actuator, one at each panel. They are used to obtain the velocities of the panels. This thesis consists of two parts, a theoretical and an experimental part. The theoretical part starts in section 2.1 by approximating the double panel system using a two DOF lumped parameter model which is a greatly simplified model for the double panel system. Section 2.2 calculates the equations of motion for the passive two DOF system. Section 2.3 studies the natural frequency and corresponding mode shapes of the system. A velocity feedback control implementation is devised for the lumped parameter model in section 2.5. Its stability is also investigated using the Nyquist and the Routh-Hurwitz criterion. Section 2.6 performs a study of the control performance by looking at the vibrational energy of masses in the lumped parameter model. The optimal values for the lumped parameters are calculated in section 2.7 and section 2.8 explains how to implement an extra feedback loop to actively change the damping to its optimal value. The experimental part starts off in chapter 3 with a discussion of the experimental setup used in this thesis to perform the measurements on. Next, chapter 4 implements the theoretical velocity feedback control system on the real double panel test setup. It also investigates the stability of the control system using measurements of the Nyquist plot. The results are then compared with the theoretical Nyquist plots. Chapter 5 studies the performance of the control. In section 5.1 it does so by measuring the kinetic energy of the radiating panel. From these measurements the optimal values for the feedback gains are obtained. Section 5.2 discusses the measurements of the velocity responses of different locations on the panels that are measured by using the accelerometers mounted on each panel. These measurements make it possible to identify structural resonance frequencies of the double panel system and corresponding mode shapes. The sound power radiated by the radiating panel in a broad frequency range is measured in section 5.3. Section 5.4 compares the sound transmission in the frequency domain to the velocity response of the radiating panel.

Active Control; Sound Transmission; Double-wall Structures

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