Active Junction Control and Piezoelectric Hybrid Damping for Improving the Acoustic Performance of Lightweight Structures

Abstract: Weight reduction is a key factor in lowering the fuel consumption and thereby the greenhouse emissions from vehicles. However, reducing the weight normally results in a deterioration of the acoustic performance. Thus, the purpose of this thesis is to investigate damping treatments for lightweight vehicle panels. Combining active control and passive damping in hybrid control treatments have shown promising. Compared to pure active control, hybrid treatments can have advantages such as reduced control effort or improved fail-safe characteristics. The thesis is dived into two parts, investigating two different concepts for hybrid damping. In the first part of the thesis, a concept of active junction control is developed. Active inputs are used at structural junctions in order to confine vibrational energy to highly dissipative parts of the structure. Theoretical models of beam junctions including active forces and moments are employed to conduct parameter studies. Results show that such an approach can offer advantageous compared to pure active control, e.g. by reducing the control effort. However, it is very sensitive to variations in the properties of the structure. In the second part of this thesis, piezoelectric elements are used for controlling vibrations and/or sound radiation. The piezoelectric element is either shunted by a passive electrical network or by a voltage source in series with a passive electrical network. Analytical models of plates and beams with surface-bonded piezoelectric elements are developed, and experimentally verified. Parameter studies are conducted in order to find the shunt which is optimal under different conditions and control criteria. Results show that for lightly damped structures, passive shunt damping may offer efficient reduction of both the kinetic energy and radiated sound power over a wide frequency range. A properly designed shunt network may also improve the characteristics of an actively driven piezoelectric element, e.g. by reducing the control effort.