Fraunhofer Adaptronics Alliance

Distributed adaptive vibration absorbers

Image 1: 6-cylinder diesel engine of a rescue boat
Image 2: Boat segment with unbalance exciter and adaptive vibration absorbers

As a demonstration for the distributedvibration absorbers a segment of a 10m rescue boat was chosen. The aim is to reduce the structure-borne sound entry through the contact points of the internal combustion engine. The test structure shows an elastic behavior in the relevant frequency range. The excitation is provided by a multi-axis unbalance exciter. This iscapable to replicate the forces of the built-in 6-cylinder diesel engine in the dominant third engine order in the frequency range up to about 150 Hz.

The adaptive vibration absorbers are at­tached between the unbalance exciter and the boat segment. Via a control algorithm they can be tuned independently to the rotational frequency of the unbalance exci­ter. For this purpose the phase difference between the acceleration on the seismic mass and the connection point of the vibra­tion absorber is determined. By a specific shift of the absorber masses using stepper motors the phase difference is set to 90°. As accelerometers low-cost MEMS sensors are used. The signal processing is perfor­med on a dSPACE real-time system.