Research project: Tuneable vibration absorbers

The tuned vibration absorber (TVA) is a well-established vibration control device, which can be used to suppress a troublesome resonance or to attenuate the vibration of a structure at a particular forcing frequency. In order to be effective it needs to be lightly damped and to be precisely tuned to problematic frequency. In fact, although such a device may have different shapes it acts like a spring-mass system. Two of the drawbacks of such a device, however, are that it can detune during operation because of changes in forcing frequency, or that there may be differences between the designed and in-situ behaviour.

A variable stiffness element can be used to maintain a tuned condition so that the natural frequency of the absorber can be adjusted with time. This can be achieved in a number of different ways. Three different approaches have been explored so far:

• Temperature control of shape memory alloy elements : such material changes its mechanical properties (elastic modulus) with temperature.

• Temperature control of viscoelastic elements : viscoelastic materials are cheap, widespread and their mechanical properties (elastic modulus and loss factor) change with temperature

• Rotation control of elastic elements : this approach exploits structures that have different stiffness values along two orthogonal axes; the rotation of such structures permits to tune the absorber to the desired frequency.

During the project design, modelling and experimental work has been carried out. Prototypes have been built and tested for each configuration. Control algorithms to automatically tune the vibration absorber, which are based on the displacement of the base and mass of the TVA, have been realised and tested.