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.

Integrated self-adaptive control system for controlling noise characteristic of elastic cavity covered with active constrained layer

Abstract: The utility model provides an integrated self-adaptive control system for controlling the noise characteristic of an elastic cavity covered with an active constrained layer, which adopts the ACLD (Active Constrained Layer Damping) mechanism to reduce noise, and relates to the technical field of noise control. The control system comprises a DSP (Digital Signal Processor)-based main controller, as well as an intelligent drive circuit, an RFID (Radio Frequency Identification) signal receiving circuit, a system power supply circuit, a keyboard interface circuit, a liquid crystal interface circuit, damping materials pasted on the outer surfaces of controlled cavity walls, piezoelectric diaphragms pasted on the damping materials and intelligent piezoelectric transducers pasted on the inner surfaces of the controlled cavity walls, which are respectively connected with the main controller, wherein the intelligent drive circuit is connected with the piezoelectric diaphragms; the main controller receives signals sent by the intelligent piezoelectric transducers and calculates the drive data according to the signals; the intelligent drive circuit converts the drive data into voltage signals and transmits the voltage signals to actuators (the piezoelectric diaphragms) pasted on the damping materials; and the piezoelectric diaphragms generate a restraining force to restrain the shearing deformation of the damping materials, so as to dissipate vibrational energy of the controlled cavity walls to reduce noise.

A simplified finite‐element modeling approach for constrained layer damping

Abstract: In formulating finite‐element models for multilayer structures, designers usually use a detailed model that contains many degrees of freedom. In order to reduce the modeling complexity for structures containing constrained layer damping, some researchers have attempted to develop equivalent properties that are applied to regular single‐layer finite elements. For example, the analytical formulation developed by Ross, Ungar, and Kerwin is sometimes used to find an equivalent bending stiffness. However, that stiffness is based on an infinite or simply‐supported beam, which is often inappropriate. The research presented here uses the governing equations of a regular beam or plate to derive the frequency transfer function between two points on the structure. Curve fitting this transfer function to a reference value found using a more detailed model provides a complex bending stiffness at the first few peak frequencies. The goal is to develop an improved approach for extracting equivalent properties for the simplified modeling of multilayer structures. Numerical examples show that extracted properties can lead to good results when calculating the response of the structure. This approach may provide a means of reducing the modeling requirements for viscoelastically damped structures.

Complex Rayleigh's Quotient - A means of estimating loss factors for damped systems

Abstract: A complex Rayleigh's Quotient is defined and explored as a means of estimating natural frequencies and damping in structures containing dissipative elements. The complex modulus or structural damping model is used to characterize the damping elements, leading to complex stifrhess matrices. Estimates of the resulting complex mode shapes are then used in the Complex Rayleigh Quotient to produce the desired estimates of a complex natural frequency, from which natural frequencies and damping may be determined. Demonstrations of the application to both discrete and continuous systems are given, and suggest that the method is an effective means of providing satisfactory estimates of frequencies and loss factors for damped systems. Introduction In this paper, an approximate method for predicting natural frequencies and damping in structures is considered. The Complex Rayleigh Quotient is suggested for use in the analysis of structures whose components have out of phase displacements. The method produces an estimate of the complex natural frequency for the system from a quotient of terms similar in form to Rayleigh's Quotient. The terms in this quotient are developed from approximations to the complex modes of the system. The system damping may then be estimated from the ratio of imaginary to real parts of the complex frequency. The form of the Complex Rayleigh Quotient is first considered for discrete linear damped systems, modeled with a complex stiffness (i.e., a structural damping model). A two degree of freedom system is used to illustrate the method, which is then applied through an iterative process to a five degree of freedom system. The Complex Rayleigh Quotient is then applied to continuous systems, and is illustrated with constrained layer damping treatments of various configurations.. Approximate complex solutions for constraining layer displacements are * Professor of Aerospace Engineering and Engineering Mechanics; Fellow: AIAA, ASME. Formerly Graduate Student; now Technical Manager, Vibration and Acoustics Section, Wright Laboratories. found by solving the constraining layer equations after approximating the deflections of the underlying structure by the corresponding undamped mode shape(s). Results from using this approach are compared with an exact solution. If real-valued approximations to the mode shapes are used, the Complex Rayleigh Quotient method is found to be equivalent to the Modal Strain Energy approach. It is demonstrated, for both discrete and continous systems, that the Complex Rayleigh Quotient produces a better estimate of the loss factor than does the Modal Strain Energy approach Ravleigh's Quotient Rayleigh's Quotient, based on the principle that a conservative system vibrating at a natural frequency has maximum system kinetic energy equal to the maximum system potential energy, is a popular means of estimating frequencies in linear undamped vibratory' systems More detailed treatments are available' Rayleigh's Quotient is obtained by setting expressions for maximum kinetic and maximum strain energy equal to each other, then solving for the natural frequency, fl. To apply Rayleigh's Quotient to a general system consisting of N individual components, estimates of the mode shape are used to estimate the maximum kinetic energies, Q Ta and maximum strain energies, Un , of each component of the system. The form of Rayleigh's Quotient then becomes: