Browsing by Author "Guigou, Catherine"

Now showing 1 - 7 of 7
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    Active control of sound radiation from a plate using a polyvinylidene fluoride volume displacement sensor
    Charette, Francois; Berry, Alain; Guigou, Catherine (Acoustical Society of America, 1998-03-01)
    This paper presents a new volume displacement sensor (made of shaped strips of PVDF film) and the experimental implementation of this sensor in an active control system. A design strategy for a PVDF sensor detecting the volume displacement induced by a vibrating 2D structure is presented. It is based on the modal representation of the plate response. It actually consists in designing a PVDF sensor, composed of several shaped PVDF strips bonded to the surface of the structure, in such a way that the output signal of the sensor is directly proportional to the volume displacement. The design methodology is based on the experimental measurements of the plate mode shapes (eigenfunctions) and is valid for any type of boundary conditions. The experimental implementation of such a volumetric sensor in an active control system is then presented. The experimental results obtained validates this new type of volume displacement sensor.
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    Active control of sound radiation from a simply supported beam: Influence of bending near-field waves
    Guigou, Catherine; Fuller, Chris R. (Acoustical Society of America, 1993-05-01)
    Active control of sound radiation from a baffled simply supported finite beam is analytically studied. The beam is subjected to a harmonic input force and the resulting acoustic field is minimized by applying a control point force. For a single frequency, the flexural response of the beam subject to the input and control forces is expressed in terms of flexural waves of both propagating and near-field types. The optimal control force complex amplitude is derived by minimizing the acoustic radiated pressure at one point located in the far field. The far-field radiated pressure, the displacement of the vibrating beam, and the one-dimensional wave-number spectrum of the beam velocity are extensively studied. In order to further understand control mechanisms, the radiated pressure due to the flexural propagating wave and the flexural near-field wave, respectively, is investigated at the minimization point before and after the control is involved. The analysis shows that, when the control is applied, the combination of the radiated pressure due to the two different types of waves (as their associated radiation is out-of-phase) at the minimization point causes the large pressure attenuation. These results demonstrate that structural near fields are important in terms of predicting performance in active control of structurally radiated sound.
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    Active isolation of vibration with adaptive structures
    Guigou, Catherine; Fuller, Chris R.; Wagstaff, Peter R. (Acoustical Society of America, 1994-07-01)
    The problem of actively isolating the periodic vibrations of a rigid machine mounted on a supporting flexible structure is usually approached by applying the active inputs in parallel or series with the passive inputs. This has a number of disadvantages which are related to the development of a high power, compact yet stiff/active isolation unit. In this experimental work, a new approach in which the receiving structure is considered to have adaptive properties is studied. The aim is to control the transmitted vibrations by distributed arrays of piezoelectric transducers bonded to the receiving structure. The experimental rig consists of a rigid thick plate (the machine) supported at the corners by four elastic springs mounted on a thin clamped-free elastic steel plate (the receiving structure). The thick plate is driven by a harmonic force input. Response in the receiving panel is measured with a scanning laser vibrometer. Active inputs to the receiving structure are induced by three pairs of piezoceramic actuators bonded to the surface and configured to induce bending. The error sensors consist of up to two polyvinylidene fluoride (PVDF) strips attached to the panel surface in various positions. The control approach uses a two channel feedforward adaptive LMS algorithm implemented on a TMS320C25. The results show that the first three modes of the system can be controlled efficiently when driven ''on resonance,'' thus effectively isolating the vibrating structure from the ''machine'' raft input. However, when the system is driven ''off resonance,'' the vibrations of the receiving structure proved more difficult td reduce effectively. The paper presents vibration distribution of the receiving plate with and without control for a number of input frequencies as well as a variety of control transducer configurations.
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    Adaptive feedforward and feedback methods for active/passive sound radiation control using smart foam
    Guigou, Catherine; Fuller, Chris R. (Acoustical Society of America, 1998-07-01)
    This work investigates and compares the potential of adaptive feed forward and feedback methods for a hybrid active/passive radiation control using smart foam. The radiating structure is a vibrating plate mounted in a rigid baffle in an anechoic chamber. The smart foam, designed to reduce sound by the action of the passive absorption of the foam (which is effective at higher frequencies) and the active input of an embedded PVDF element driven by an oscillating electrical input (which is effective at lower frequencies), is positioned on the plate. The first test consists of using a single-input single-output (SISO) adaptive feedforward LMS controller to minimize the error sensor signal provided by a microphone in the close proximity of the active element under narrow-band excitation and broadband random excitation. For feedforward control, two different reference signals are considered: the voltage sent to the piezoceramic actuator driving the plate (disturbance) and the signal from an accelerometer directly mounted on the plate (more realistic in practice). In the latter case, the effect of the smart foam on the reference signal (or acceleration level) can be taken into account (feedback removal). An adaptive feedback controller is also implemented to avoid the use of a reference signal. In this case, a reference signal is obtained from the error signal using the internal model approach. The results from these three different control methods are compared in terms of the sound attenuation achieved. For broadband excitation, a feedforward adaptive control with an external reference is shown to be more efficient for this arrangement than a feedback adaptive control.
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    Design of active structural acoustic control systems using a nonvolumetric eigenproperty assignment approach
    Li, Zhonglin; Guigou, Catherine; Fuller, Chris R.; Burdisso, Ricardo A. (Acoustical Society of America, 1997-04-01)
    Sound radiation of planar radiators such as beams and plates is known to be directly related to the velocity distribution over the structural surface at low frequencies. For example, nonvolumetric modes correspond to poor sound radiators for small k(0)a. In this work, to achieve significant sound attenuation in the low-frequency range, the SISO eigen assignment technique is used to modify the eigenproperties of a planar structure using structural actuators and sensors so that all the modes of the controlled structure are nonvolumetric. The main advantage of such an approach is that the design is independent of the disturbance characteristics (i.e., type, position, and frequency content) and does not require sensors in the radiation field. The design procedure for the control system in the modal domain is presented. The formulation is applied to a simply supported beam with SISO feedforward control. Radiation efficiency, far-field sound radiated power and mean-square surface velocity are extensively studied. The results show that the control scheme proposed here is very efficient in reducing sound radiation at low frequencies. (C) 1997 Acoustical Society of America.
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    Optimum design for feedforward structural-acoustic control of complex structural systems
    Rodríguez-Dávila, Héctor M. (Virginia Tech, 1996)
    An efficient design formulation for feedforward Active Structural Acoustic Control (ASAC) systems for complex structures and disturbances is presented. The approach consists in a multi-level optimization procedure. The upper level part is carried out in the modal domain, where the optimum modal control forces and modal error sensor components which minimize the total radiated power are obtained. These optimum modal parameters are then used in a set of lower level optimization problems to find the physical characteristics of the actuators and sensors to be implemented. In this work, the developed formulations are demonstrated in three systems of increasing complexity. First, a simply supported plate excited by at a single frequency is presented. The study of this relatively simple case serves as a benchmark for more complex systems permitting the evaluation of the performance of the design approach. Then, the formulation is implemented for the case of a simply supported cylinder under multiple frequency excitations. In this case numerical techniques are used to obtain the structural and acoustic responses showing the capabilities of the formulations to be implemented to complex structures. In both cases (i.e., the simply supported plate and cylinder), the results show that the optimum configurations yield significant reductions in the total radiated acoustic power depending on the number of control channels and allowed control effort. Moreover, it is demonstrated that the proposed design approach gives a clear insight into the relative contributions of the modes to the sound field providing a better understanding of how they have to be controlled in order to minimize sound radiation. Finally, the design approach is validated in an experimental arrangement for the attenuation of sound radiation from and enclosed box structure under a realistic periodic disturbance. Up to 36dB of attenuation in the acoustic power is obtained in the experiment demonstrating the effectiveness of the proposed design approach for practical applications.
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    Smart foam for applications in passive-active radiation control
    Gentry, C. A.; Guigou, Catherine; Fuller, Chris R. (Acoustical Society of America, 1997-04-01)
    The development of a smart foam for passive-active noise control is discussed. The smart foam consists of cylindrically curved sections of PVDF film embedded in partially reticulated polyurethane acoustic foam forming a very thin, compact arrangement. The device is designed to reduce sound by the simultaneous action of the passive absorption of the foam (effective at high frequencies) and the active input of the PVDF element driven by an oscillating electrical input (effective at low frequencies). The PVDF actuator is configured to behave in a linear sense and to couple in-plane strain associated with piezoelectric effect with out-of-plane motion needed to radiate sound from the foam surface. The performance of the passive-active device is studied for controlling sound radiation from a vibrating piston. A feedforward LMS controller is used to minimize the signal from a far-field error microphone, Results of harmonic and broadband control are presented. The potential of the smart foam for globally reducing sound radiation in the low- and high-frequency range is demonstrated. (C) 1997 Acoustical Society of America.