Damping optimization by integrating enhanced active constrained layer and active-passive hybrid constrained layer treatments

The feasibility of integrating the enhanced active constrained layer (EACL) and active-passive hybrid constrained layer (HCL) treatments to achieve a better combination of the system's closed-loop damping and open-loop (fail-safe) damping (without active action) is investigated in this research. Given a uniform strain field in the host structure, the EACL with stiff and equal edge elements (symmetric EACL) has been shown to provide high closed-loop damping by significantly increasing the direct active control authority of the cover sheet. The open-loop damping of the system, however, could be low. On the other hand, the HCL has been demonstrated to offer more balanced open-loop and closed-loop damping actions, although the HCL closed-loop damping is not as high as that of the EACL. The idea here is therefore to combine the two approaches and develop an integrated HCL-EACL treatment. The focus is to maximize the system closed-loop damping while maintaining an open-loop damping margin for fail-safe reasons. For a given strain field in the host structure, optimization routines are used to search for the best design parameters: the optimal control gain, the stiffness of the edge elements and the active material coverage ratio in the constraining layer. It is found that integrating the EACL and the HCL will introduce more flexibility in the design of constrained layer damping treatments with actively enhanced actions. Higher open-loop damping can be achieved for the same closed-loop damping requirement and vice versa. The hybrid cover sheet is found to create significant shear in the viscoelastic layer while the edge elements are used to provide strong direct active control authority for the constraining layer. A better mixture of the open-loop and closed-loop damping can generally be obtained with the integrated system. (C) 2002 Elsevier Science Ltd. All rights reserved.