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Nov 1990

Volume 88, Issue S1, pp. S1-S200

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back to top Session 7SA: Structural Acoustics and Vibration: Active Vibration and Noise Control
Contributed Papers
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Experiments on active control of structurally radiated sound using multiple piezoceramic actuators (A)

Robert L. Clark, Jr. and C. R. Fuller

J. Acoust. Soc. Am. Volume 88, Issue S1, pp. S147-S148 (1990); (2 pages)

Online Publication Date: 14 Aug 2005

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Active control of sound radiation from a vibrating rectangular plate excited by a steady‐state harmonic point force disturbance is experimentally studied. Control structural inputs are achieved by three piezoceramic actuators bonded to the surface of the panel. Microphones were implemented as error sensors, while the control approach was based upon a filtered‐X version of the adaptive lms algorithm. Both position and number of piezoceramic actuators were varied during the test to determine the effects on control authority. The influence of increasing the number of channels of control was also considered. A variety of test cases was studied for controlling sound radiation due to a disturbance both on and off resonance. Results from these experiments indicate that piezoceramic elements provide an efficient method for distributed modification of structural response to attenuate sound radiation. In addition, the adaptive lms algorithm is shown to be an effective narrow‐band controller which, in contrast to feedback approaches, requires no system modeling. [Work supported by ONR/DARPA.]
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An experimental study of the use of PVDF piezoelectric sensors in active structural acoustic approaches (A)

Robert L. Clark, Jr. and C. R. Fuller

J. Acoust. Soc. Am. Volume 88, Issue S1, pp. S148-S148 (1990); (1 page)

Online Publication Date: 14 Aug 2005

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An experimental investigation was performed to determine the feasibility of implementing polyvinylidene fluoride (PVDF) piezoelectric distributed sensors on the surface of a structure as error sensors in an adaptive lms control approach to minimize acoustic radiation. A simply supported rectangular plate was chosen as the test structure and was excited by a point‐force steady‐state harmonic disturbance. Structural inputs achieved by three piezoceramic actuators bonded to the surface of the panel. Two narrow strip PVDF sensors were positioned on the plate such that the dominant observed response was due to the odd modes (i.e., the more efficient radiators). The error sensors in effect act as spatial wavenumber filters and only observe those components that contribute significantly to far‐field sound radiation. Both position and number of piezoceramic actuators were varied during the test to determine the effects on control performance. A variety of test cases was studied for controlling sound radiation due to a disturbance both on and off resonance. Results from these experiments indicate that PVDF sensors and piezoceramic actuators (i.e., an “intelligent” structure) show much promise for controlling acoustic radiation from structures, to a large degree overcoming the need for error microphones in the far field. [Work supported by ONR/DARPA.]
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Theory of feed‐forward controlled system eigenproperties (A)

Ricardo A. Burdisso and Chris R. Fuller

J. Acoust. Soc. Am. Volume 88, Issue S1, pp. S148-S148 (1990); (1 page)

Online Publication Date: 14 Aug 2005

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Adaptive feed‐forward algorithms have been successfully applied in the active control of sound and vibration. However, the actual mechanisms of control inherent in the technique remain an area of much interest. The main objective of this research is to study the dynamic characteristics of a feed‐forward controlled system. The structure is assumed to be subjected to a harmonic input excitation, and the system controlled by another force. The controller is defined by minimizing the mean‐square value of an error sensor signal. The error sensor is an accelerometer mounted on the structure or a microphone placed in the acoustic field for the active control of vibration or sound radiated, respectively. An entirely new mathematical approach to predict the dynamics of the controlled system is presented, which shows that the controlled system effectively has new eigenproperties. They are a function of the control force and error sensor locations, and independent of the input disturbance. Numerical examples demonstrate the formulation. These results are also corroborated experimentally using a feed‐forward controller implemented on a TMS320C20 DSP processor. [Work supported by ONR.]
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Active control of sound radiation due to subsonic wave scattering from discontinuities on fluid‐loaded plates (A)

Yi Gu and Chris R. Fuller

J. Acoust. Soc. Am. Volume 88, Issue S1, pp. S148-S148 (1990); (1 page)

Online Publication Date: 14 Aug 2005

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Active control of sound radiation from a fluid‐loaded infinite plate with either a line constraint or reinforced by a uniform rib is analytically studied. The incidient field is assumed to be a subsonic structural wave and sound radiation is due to wave scattering from the discontinuity. The mathematical models are based on the coupled plate vibration and sound radiation due to a line force or a line moment solved in the spectral kdomain. Feed‐forward control is applied by up to two active forces located near the discontinuity. The amplitudes of the control forces are determined by the optimal solution of a cost function that integrates the farfield radiated acoustic intensity in a semicylindrical space around the discontinuity. The results show that for subsonic incident waves, high global reduction in radiated pressure due to spectral wave scattering at the discontinuities is possible with the two active control forces. The amount of sound reduction, as well as the residual directively pattern, is shown to depend upon the number and location of the control forces. The far‐field directivity pattern, the transverse plate velocity, and the near‐field intensity distribution are extensively studied. [Work supported by ONR.]
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The effect of modal coupling characteristics on one mechanism of active noise control (A)

Scott D. Snyder and Colin H. Hansen

J. Acoust. Soc. Am. Volume 88, Issue S1, pp. S148-S148 (1990); (1 page)

Online Publication Date: 14 Aug 2005

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When using vibration sources to actively control sound transmission into coupled enclosures, two physical control mechanisms are possible. The first is an increase in the input impedance of the primary coupled structural mode(s), which results in a decrease in their amplitude. The second is an alteration in the relative phasing and amplitudes of the coupled structural modes. The ability of this second mechanism to provide global sound control is greatly dependent upon the structural/acoustic coupling characteristics of the system. This dependency is demonstrated analytically by contrasting systems of differing coupling characteristics.
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Active control of sound radiated from NITINOL‐reinforced composite plates (A)

S. Poh, A. Baz, and J. Gilheany

J. Acoust. Soc. Am. Volume 88, Issue S1, pp. S149-S149 (1990); (1 page)

Online Publication Date: 14 Aug 2005

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Shape memory alloy (NITINOL) wires are embedded at the mid‐plane of a fiberglass composite plate as means of controlling the sound radiated from the plate. Activation of the shape memory effect, by heating the wires beyond their martensitic transformation temperature, increases the strain energy of the plate which results in altering its characteristic response parameters, i.e., the modes and mode shapes. With proper activation strategies of the NITINOL fibers, a significant change in the radiation efficiency can be achieved. Experiments are conducted on a 23‐ ×23‐ ×0.156‐cm fiberglass plate mounted on an anechoic chamber and subjected to broadband incident sound waves. The plate is reinforced by 33 NITINOL wires that are 0.055 cm in diameter. The effect of initial preload of the wires, as well as the number and location of activated wires on the modes and mode shapes of the plate, radiated sound pressure, directivity patterns, and transmission loss, is determined. The results obtained suggest the potential of this class of composite plates as a means of designing sound enclosures for critical applications. [Work supported under grant from ARO.]
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Active acoustical control of broadband structural disturbances (A)

William T. Baumann, William R. Saunders, and Harry H. Robertshaw

J. Acoust. Soc. Am. Volume 88, Issue S1, pp. S149-S149 (1990); (1 page)

Online Publication Date: 14 Aug 2005

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The objective is to actively suppress the acoustic power radiated from a structure that is steadily excited by narrow‐band or broadband disturbances. The problem is constrained by the assumption that the far‐field pressure cannot bc measured directly. Therefore, a method for estimating the total radiated power from measurements on the structure is developed. Using this estimate as a cost function and assuming knowledge of the spectrum of the disturbance, a controller is designed using the LQG theory to minimize the cost. Computer simulations of a clamped‐clamped beam show that there may be significant difference in the total radiated power between a system with a vibration‐suppression controller and a system with an acoustic controller that accounts for the coupling of these vibrations to the surrounding fluid. In some cases, the acoustic controller increases the system vibration in order to minimize the radiated power. Experimental verification of these theoretical results is given in the subsequent paper “An experiment in state‐space acoustic control of a plate excited by steady disturbances” [J. Acoust. Soc. Am. Suppl. 1 88, S149 (1990)]. [Supported by DARPA/ONR.]
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An experiment in state‐space acoustic control of a plate excited by steady disturbances (A)

S. P. Rubenstein, W. R. Saunders, and H. H. Robertshaw

J. Acoust. Soc. Am. Volume 88, Issue S1, pp. S149-S149 (1990); (1 page)

Online Publication Date: 14 Aug 2005

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A demonstration of active acoustic control of radiation from a simply supported plate is presented. First, open‐loop characteristics of a 0.5×0.6‐m rectangular plate are shown to validate the assumption of nearly simply supported boundary conditions. Next, a state‐space design method for closed‐loop control of acoustic radiation is discussed. The design procedure is used to generate controllers that reject either narrowband or broadband point‐force disturbances of the plate's first four resonant modes. Simulation and experimental results are provided to illustrate the difference between active vibration control and active acoustic control. Radiation filters, derived from the radiation efficiencies of the modal basis, are implemented for these subsonic acoustic control experiments. During the acoustic cost experiments, the controller places a priority on actively damping only those modes that are contributing significantly to the acoustic radiation. The results of this active acoustic control experiment validate the built‐in selectivity of this control approach for suppression of structural acoustic radiation. The theoretical foundation for these experimental results is given in a companion paper, “Active acoustical control of broadband structural disturbances” [J. Acoust. Soc. Am. Suppl. 1 88, S 149 (1990)]. [Work supported by DARPA/ONR.]
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Modification of transducer characteristics using active feedback (A)

Robert D. Corsaro, Joel F. Covey, Kin W. Ng, and Rose M. Young

J. Acoust. Soc. Am. Volume 88, Issue S1, pp. S149-S149 (1990); (1 page)

Online Publication Date: 14 Aug 2005

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Active feedback in a hydrophone‐projector system is used to modify the transmit or receive efficiency of the system. Hence, the output from the hydrophone layer can be used to broaden the bandwidth of the projector or, conversely, the driver can be used to correct the response of the hydrophone. The principal features of the system can be represented by a one‐dimensional model resembling a four‐media system, consisting of water, a receiver layer, a projector layer, and a backing impedance. Since the output of the receiver layer is amplified and applied to the projector layer, an active acoustic feedback system results. Experimental data using a large‐area projector bonded to a transparent large area polymer (LAP) hydrophone are presented.
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Visualizing the effect of active control on structural vibrations using vein diagrams (A)

Joel F. Covey, Nai‐chyuan Yen, Robert D. Corsaro, Kin W. Ng, Chris Ross, and Tim Yoder

J. Acoust. Soc. Am. Volume 88, Issue S1, pp. S149-S149 (1990); (1 page)

Online Publication Date: 14 Aug 2005

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The vein diagram is a new method of visualizing the time‐frequency characteristics of acoutic signals [Yen et al., J. Acoust. Soc. Am. 87, 2359–2370 (1990)]. It is based on the modified Wigner distribution function. Previously this technique has been used for analysis of acoustic scattering including the inverse scattering problem. Here, the vein diagram, is employed as a visualization tool to display the effect of a surface mounted projector on acoustic scattering from a submerged complex structure. The projector is part of an active vibration control system. The important feature of this technique is that is allows distinct observation of the influence of the control signal on each of the various types of structural vibrations.
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