Modeling and control of vibration in mechanical structures

All mechanical systems exhibit vibrational response when exposed to external disturbances. In many engineering applications vibrations are undesirable and may even have harmful effects. Therefore, control of mechanical vibration is an important topic and extensive research has been going on in the field over the years. In active control of vibration, the ability to actuate the system in a controlled manner is incorporated into the structure. Sensors are used to measure the vibrations and secondary inputs to the system are used to actuate the flexible body in order to obtain some desired structural response. In this thesis, feedback and feedforward control of active structures are addressed. The thesis is divided into four parts. The first part contains a general introduction to the subject of active vibration control and also provides an outline of the thesis. The second part of the thesis treats modeling and feedback control of a beam system with strain sensors and piezoelectric actuators. Physical modeling and system identification techniques are utilized in order to obtain a low order parametric model that is suitable for controller design. The third part introduces the concept of a mechanical wave diode, which is based on feedforward control. A controller is derived on the basis of equations that describe elastic waves in bars. The obtained controller is shown to have poor noise properties and is therefore modified and further analyzed. The final part of the thesis treats the same type of wave diode system as part three, but with more general feedforward filters. Especially, a controller based on Wiener filter theory is derived and shown to drastically improve the performance of the mechanical wave diode