Index of content:
Volume 106, Issue 3, September 1999
- STRUCTURAL ACOUSTICS AND VIBRATION 
Analysis of lateral vibration behavior of railway track at high frequencies using a continuously supported multiple beam model106(1999); http://dx.doi.org/10.1121/1.427171View Description Hide Description
The lateral vibration of railway track at high frequencies is a more difficult research topic, compared with the vertical vibration, because the complex cross-sectional deformation of the rail has to be taken into account. The commonly used models for the lateral vibration are based on the FEM/FSM or a derivation of the FEM. It is inconvenient to calculate responses of the rail to external excitation by these models, especially when the discrete supports of the rail are taken into account. To overcome this barrier a new model for studying the lateral vibration behavior of railway track is developed in this paper. It is a simple model consisting of two infinite Timoshenko beams connected by an array of finite beams. Detailed investigation of the lateral vibration for a free rail and a continuously supported rail has been carried out efficiently using this model. The free wavedispersion relation calculated using this model has been shown to be in good agreement with a FE model. Quite good agreement between the predictions and the measurement data has also been reached in terms of accelerances.
106(1999); http://dx.doi.org/10.1121/1.427172View Description Hide Description
Analysis of the measured response of a near-periodic framed shell to a point force reveals that the higher-order azimuthal modes on the shell are significantly localized. A quantitative analysis of the data yielding the spatial attenuation rates, the measured group speeds, and the total measured damping factors for various azimuthal orders is presented. The two principal mechanisms which could account for the spatial attenuation rates, damping and Anderson localization, are investigated. Predictions based on these underlying phenomena are obtained and compared with the measurements. The spatial attenuation rates resulting from damping are typically a factor of 2.3 times too small to account for the measurements, while the spatial localization due to irregularity and the data are in reasonable agreement. This evidence, along with the strongly fluctuating nature of the response, indicates that Anderson localization is the dominant mechanism at work in this system.
Implications of using colocated strain-based transducers for output active structural acoustic control106(1999); http://dx.doi.org/10.1121/1.427142View Description Hide Description
Piezoceramic transducers have become popular elements of smart structures that are used for active vibration control and active structural acoustic control. A spatial differentiation is performed by the piezoceramic transducers since they couple into the strain field of the piezostructure. This differentiation causes higher-frequency modes to be emphasized more heavily, causing the effective compliance of the structure as seen by the piezoceramic transducer to increase with frequency. This nonuniform compliance has significant impact on the performance that can be achieved through colocated direct rate feedback control. It is shown that the rectangular piezoceramic transducer is a low-pass wave number filter with a cutoff frequency inversely proportional to the aperture size. Thus DRFB performance can be greatly improved simply by making the size of the piezoceramic transducer large relative to the size of the structure. The resulting increase in coupling to the lower-frequency modes, which are generally targeted by the control system, results in a much reduced control effort. In the event that a large aperture is not practical, it is shown that dynamic compensation can be used to obtain good performance at the cost of much increased computational complexity. Analytical open and closed loop results for an acoustically radiating simply supported plate piezostructure are presented.
106(1999); http://dx.doi.org/10.1121/1.427143View Description Hide Description
Current research in Active Structural Acoustic Control (ASAC) relies heavily upon accurately capturing the application physics associated with the structure being controlled. The application of ASAC to aircraft interior noise requires a greater understanding of the dynamics of the curved panels which compose the skin of an aircraft fuselage. This paper presents a model of a simply supported curved panel with attached piezoelectric transducers. The model is validated by comparison to previous work. Further, experimental results for a simply supported curved panel test structure are presented in support of the model. The curvature is shown to affect substantially the dynamics of the panel, the integration of transducers, and the bandwidth required for structural acoustic control.