Johannes Tschesche

Response surface methodologies for coupling factor exploration: an application example for noise reduction by means of smart structures

The development of smart structures requires methods to explore the behavior of electromechanical systems. Engineers must take into account various interactions between particular system parameters and the system’s responses. A variety of mathematical models is used to describe the system behavior depending on defined design variables. Based on the mathematical models, system analyses and optimization procedures can be performed. All suitable methods can be summarized as design exploration. This paper describes four mathematical models, their application in design exploration and the resulting differences. The mathematical models are linear interpolation, full second-order polynomials, Kriging interpolation and genetic programming. As an application example a smart thin curved plate is presented. The importance of the electromechanical coupling factor, which is used as the system response considered in this paper, for noise reduction by means of smart structures is pointed out.

An active-system approach for eliminating the wolf note on a cello

Wolf notes are generally undesirable sounds that occur in string instruments, particularly in cellos. State-of-the-art passive wolf note eliminators affect the whole cello sound and can become ineffective when environmental conditions and, therefore, the cellos structural properties change. In this paper, an approach is presented that uses smart materials to eliminate the wolf note with little effects to the cellos sound. Based on preliminary measurements, a mathematical model of the cello for generating the wolf note and for developing a wolf note elimination controller is set up. The controller consists of a wolf detection criterion that triggers a velocity feedback controller to actively induce damping into the cellos body whenever a wolf note is detected. The controller setup is experimentally validated by an implementation on a test cello. The velocity feedback to induce the active damping is implemented by means of a piezoelectric patch actuator attached to the cellos body. Both the results of the mathematical model and the results of the experimental investigation show a good performance in eliminating the wolf note on a cello.