Constrained-layer damping

About: Constrained-layer damping is a research topic. Over the lifetime, 795 publications have been published within this topic receiving 15758 citations.

Structural vibration damping of a vacuum-assisted toilet

Abstract: Vacuum-assisted toilet noise can be unsettling and even uncomfortable. One common way to reduce noise levels is to damp structural vibrations that radiate sound. We investigated whether constrained layer damping (CLD) treatments could reduce the radiated noise level on a vacuum-assisted toilet. To find the structural anti-node locations of a toilet, we excited an airplane toilet with a shaker and scanned the velocity response of the inside of the bowl with a 3-dimensional scanning laser Doppler vibrometer (3D SLDV). We also scanned the bowl with an accelerometer during a repeated flush cycle. A microphone placed one meter above the bowl measured the radiated sound level. We applied 3M 4014, 3M 2552, Pyrotek Decidamp CLD, and Velcro individually to the bowl and determined the reduction in structural vibrations and sound radiation. The bowl’s rim on the front vibrated the most. Structural vibrational energy concentrated around 100-400 Hz while radiated sound concentrated around 400 Hz–2 kHz. Applying damping materials reduced structural vibrations, sometimes by 20 dB. We conclude that CLD treatments are able to reduce structural vibrations. Further results of the investigation will be shown and discussed.

Control of sound radiation from an active constrained layer Damping treated plate into an acoustic cavity using structural intensity approach

Abstract: Considerable attention has been devoted to actively and passively control of the sound radiating from vibrating plates into closed cavities. With the advent of smart materials, extensive efforts have been exerted to control the vibration and sound radiation from flexible plates using smart sensors/actuators. Active Constrained Layer Damping (ACLD) treatment has been used successfully for controlling the vibration of various flexible structures. The treatment provides an effective means for augmenting the simplicity and reliability of passive damping with the low weight and high efficiency of active controls to attain high damping characteristics over broad frequency bands. The proposed study is investigated using a numerically simulated example consisting of an ACLD treated plate/acoustic cavity system excited by a point harmonic force. In this study, an ACLD treated plate/acoustic cavity coupled finite element model is utilized to calculate the structural intensity and sound pressure radiated by vibrating plates. In the passive control, the optimum placements of ACLD patches are determined by structural intensity of ACLD treated plates and compared to the results obtained by modal strain energy approach. The influence on structural intensity of plate due to damping treatment is investigated.

Active Vibration Control of Smart Composite Shells

Abstract: This paper addresses the active control of mechanical vibrations induced in laminated composite doubly curved shells. A three dimensional energy based finite element model has been developed for this analysis. The laminated shell is integrated with a patch of active constrained layer damping (ACLD) treatment in which vertically reinforced 1-3 piezoelectric composite is used as the material of the constraining layer. Both in-plane and out-of-plane actuations of the constraining layer of the ACLD treatment have been utilized for deriving the finite element model. Investigation has been carried out to see the performance of the patch when the orientation angle of the piezoelectric fibers of the constraining layer is varied in the two mutually orthogonal vertical planes. The analysis revealed that the vertically reinforced 1-3 piezoelectric composites which are in general being used for the distributed sensors can be potentially used for the distributed actuators of high performance light-weight smart composite shells.

Optimi sation of passive and active constrained layer dampers for panel vibrations over broad frequency and temperature ranges

Abstract: *† ‡ § This paper ex tends current understanding of optimum constrained layer damping (CLD) coverage for beams to more complicated strain regimes and applies it to panel vibrations. The ratio between the shear stiffness of the viscoelastic layer and the extensional stiffness o f the constraining layer is shown to be an important parameter in finding optimum performance. The Differential Evolution algorithm is used to locate and size CLD patches on a plate. The effectiveness (added damping over added weight) is plotted against sh ear parameter to demonstrate compliance with optimum shear stiffness hypothesis. A numerical study is used to show that active CLD requires higher shear stiffness in the viscoelastic layer. High damping is also noticeable in passive systems around the del amination frequency where the shear stiffness ratio is very low. For active CLD systems however, it is shown that the through -thickness region is best avoided. Above the delamination zone, the active layer has no effect while at the delamination zone itsel f, the control effort sometimes be to increase vibration effect.