A study of active-passive damping treatments

Doctoral thesis, 2004

Active Constrained Layer (ACL) treatment is a vibration-damping treatment which consists of a viscoelastic layer constrained by an actuator. It dissipates energy simultaneously by the shearing of the viscoelastic layer and by the action of the actuator. An example of applications for ACL treatments is the damping of vibrations on metal panels with which cars and other vehicles are built. In order to optimise the design of ACL treatments, it is necessary to understand how they function. Therefore, this work proposes experimental and theoretical tools for the investigation of ACL treatments. An accurate model of beams treated with ACL, based on the wave approach, is selected from the literature and validated with experiments. Another model based on the modal approach, less accurate but well suited for gaining insight into the physics of active-passive damping treatments, is proposed and numerically validated. A set of indexes allowing quantification of the different damping mechanisms occurring in ACL treatments is devised. Experiments on beams treated with active-passive damping treatment are carried out to validate and complete the findings from the theoretical models. It is demonstrated that the reduction of power input into the beam by the actuator, which has generally not been taken into account in the literature, is an essential mechanisms of active-passive damping treatments when feedforward control is possible. Also, the distinction between the physics and the control part of active-passive damping treatments is shown to be necessary in order to gain insight into the functioning of these treatments. It is also shown that under optimal control conditions, the vibration reduction obtained with the ACL and AC/PCL treatments depends only on the physical properties of these treatments and is the same for both treatments. Nevertheless, in this optimal situation AC/PCL treatments are better than ACL treatments because they demand a lower control effort. However, it is demonstrated that the type of treatment which is best in a given situation depends on the aims and constraints in this situation.