Index of content:
Volume 104, Issue 1, July 1998
- STRUCTURAL ACOUSTICS AND VIBRATION 
104(1998); http://dx.doi.org/10.1121/1.423270View Description Hide Description
A mathematical model is developed for the coupling of two finite plates at an arbitrary angle for the prediction of the dynamic response and power flow at the coupling edge and at any cross section. The coupling at the joint edge considers bending, out-of-plane shear, and in-plane longitudinal (perpendicular to the joint edge) vibration. No constraint is imposed on the in-plane displacement perpendicular to the coupling edge. The exact solution for flexural mode shapes and resonance frequencies of rectangular plates with one edge free and the other edges simply supported is considered. This exact solution satisfies both the displacement and force boundary conditions, consequently it is used in the coupling of plate panels. An approximate relation is derived for prediction of the flexural resonance frequencies of higher-order modes with a reasonable accuracy. An approximate solution is presented for the in-plane response of the same plate panels when excited by in-plane forces perpendicular to the free edge. A simple expression is given for an approximate estimation of the cut-off frequencies for the different in-plane modes. The frequency response of the individual plate panels is presented as receptance functions for both flexural and in-plane vibration which are used in the plate coupling. The vibrational power injected into a plate by out-of-plane concentrated force and moment is computationally investigated. The importance of power input by a small moment excitation in some resonant bands even at low frequencies is highlighted. The spatial distribution of the components of flexural power transmitted by shear and moment across a section of the plate are investigated and the reason for the circulatory patterns of active power flow in plates is illustrated. The power flow characteristics in two plates coupled at an arbitrary angle is examined by a computational example. The effect of the coupling angle on the components of input power and power flow across the coupling edge is investigated. It is shown that the coupling of the two plates is mainly due to moment at frequencies up to the cut-off frequency of the first in-plane mode. Above this frequency, the coupling is due to out-of-plane shear and in-plane vibration with a diminishing participation of the moment in transmitting vibrational power through the coupling edge.
104(1998); http://dx.doi.org/10.1121/1.423271View Description Hide Description
This paper discusses distributed parameter sensors designed to extract vibration modes of a structure, as well as its active modal control. Compared to conventional point sensors such as accelerometers or displacement sensors, the distributed parameter sensors are superior to point sensors provided that they are properly designed. First, this paper overviews a conventional modal filter method using point sensors, and enumerates the problems they possess. To overcome the drawbacks of the point sensor-based modal filtering, a novel modal filtering technique based upon distributed parameter PVDF film sensors is proposed. This paper begins by discussing a design methodology for modal filtering using two-dimensional distributed sensors. Then, taking into consideration the applicability of the sensors, a design procedure for modal filtering using one-dimensional sensors is presented, the number, location, and shaping functions for the one-dimensional modal sensors being clarified. Furthermore, the modal filtering using the one-dimensional sensors is found to be applicable for two-dimensional structures subject to any “classical” boundary condition. Experimental results verify the capability of the desired modal filtering for both isolated and degenerate structural modes. Finally, using the modal sensors, experiments on active modal control are conducted, showing a significant suppression of the targeted mode without causing instability of the control system.