A Finite Element Model for Sound Transmission Through Laminated Composite Plates

The finite element method is used to model the noise transmission through unstiffened and stiffened laminated composite panels of finite size into a closed cavity. Plate and acoustic finite elements are coupled and the frequencies of the coupled modes are determined. The model is then used to calculate the noise reduction of the panel. Results are compared to experimental values obtained at the NASA Langley Research Center. The purpose of this paper is to demonstrate the use of finite elements to model, for noise transmission calculations, complex structures, such as a stiffened composite panel or a composite panel with windows

Application of the Finite Element Method in the Calculation of Transmission Loss of Flat and Curved Panels

This investigation represents an extension of a study of Roussos (1985) who considered the noise transmission loss of a rectangular plate in an infinite baffle. Roussos, who employed an analytical formulation, considered an unstiffened plate. While it is difficult to consider stiffeners by means of analytical methods, the difficulties can be avoided by employing a finite element procedure. For this reason, the present study is concerned with the implementation of a finite element method. The representation of the panel transmission loss is discussed, and the determination of the panel motion by means of the finite element technique is described, taking into account an isotropic flat panel, the exciting force, an eigenvalue problem, the radiation pressure, a plate element, and a cylindrical shell element. Numerical results are considered for a flat panel, a curved panel, and a stiffened flat panel

Control of Large Space Structures Using Reduced-order Models

Simulation of space structures forms a critical part of the space station design process. The distributed parameter system is discretized by suitable approximation techniques such as Rayleigh-Ritz or finite element methods and is represented by a finite set of ordinary differential equations. From the control engineer\u27s perspective, this finite set of equations is often too large for control computations and reduced-order models are synthesized and used for controller design. The current work addresses the finite element modeling, reduced-order model synthesis and the design and validation of suboptimal controllers for a realistic model of a space station. The balanced realization technique and the Routh approximation method are used to develop meaningful lower-order models for controller design. If the state variables are not available for feedback, then an appropriate state estimator has to be designed. This aspect of the design is not considered in the paper. Extensive simulations for the control tasks of vibration suppression, attitude control and minimization of line-of-sight errors demonstrate that any performance degradation incurred by using suboptimal controllers is minimal

Multivariable Routh-approximant Model Reduction Method in the Time Domain

The time-domain Routh-approximant method for model reduction of large-scale systems is modified and enhanced in this paper. a new transformation matrix that overcomes a limitation of earlier work is proposed. This feature greatly enhances the multivariable method. Some interesting results on symmetry properties are developed in conjunction with a structure example. a sufficiency condition of stability of the reduced-order model is identified. the response of the reduced-order model traces the original system very well. Thus the Routh method offers promise for application in the suboptimal control of large space structures, given its inherent simplicity