Browsing by Author "Fuller, Chris R."
Now showing 1 - 20 of 43
Results Per Page
Sort Options
- Acoustics 1991: Active structural acoustic controlFuller, Chris R.; Silcox, Richard J. (Acoustical Society of America, 1992-01-01)In summary, the ASAC technique has demonstrated much potential in aerospace and marine applications. Future work will center on extending these techniques to broadband disturbances, more complex structures and improved modeling. It is known that optimizing transducer positions is as important as increasing the number of control channels. A multidisciplinary approach is required to synthesize a design procedure that integrates the elements of structural acoustics, transducer, and control technology. The pay off will be in significant cost and weight savings, and in performance improvements for other industrial applications.
- Active control of aircraft engine inlet noise using compact sound sources and distributed error sensors(United States Patent and Trademark Office, 1996-05-07)An active noise control system using a compact sound source is effective to reduce aircraft engine duct noise. The fan noise from a turbofan engine is controlled using an adaptive filtered-x LMS algorithm. Single multi channel control systems are used to control the fan blade passage frequency (BPF) tone and the BPF tone and the first harmonic of the BPF tone for a plane wave excitation. A multi channel control system is used to control any spinning mode. The multi channel control system to control both fan tones and a high pressure compressor BPF tone simultaneously. In order to make active control of turbofan inlet noise a viable technology, a compact sound source is employed to generate the control field. This control field sound source consists of an array of identical thin, cylindrically curved panels with an inner radius of curvature corresponding to that of the engine inlet. These panels are flush mounted inside the inlet duct and sealed on all edges to prevent leakage around the panel and to minimize the aerodynamic losses created by the addition of the panels. Each panel is driven by one or more piezoelectric force transducers mounted on the surface of the panel. The response of the panel to excitation is maximized when it is driven at its resonance; therefore, the panel is designed such that its fundamental frequency is near the tone to be canceled, typically 2000-4000 Hz.
- Active control of aircraft engine inlet noise using compact sound sources and distributed error sensors(United States Patent and Trademark Office, 1994-10-11)An active noise control system using a compact sound source is effective to reduce aircraft engine duct noise. The fan noise from a turbofan engine is controlled using an adaptive filtered-x LMS algorithm. Single multi channel control systems are used to control the fan blade passage frequency (BPF) tone and the BPF tone and the first harmonic of the BPF tone for a plane wave excitation. A multi channel control system is used to control any spinning mode. The multi channel control system to control both fan tones and a high pressure compressor BPF tone simultaneously. In order to make active control of turbofan inlet noise a viable technology, a compact sound source is employed to generate the control field. This control field sound source consists of an array of identical thin, cylindrically curved panels with an inner radius of curvature corresponding to that of the engine inlet. These panels are flush mounted inside the inlet duct and sealed on all edges to prevent leakage around the panel and to minimize the aerodynamic losses created by the addition of the panels. Each panel is driven by one or more piezoelectric force transducers mounted on the surface of the panel. The response of the panel to excitation is maximized when it is driven at its resonance; therefore, the panel is designed such that its fundamental frequency is near the tone to be canceled, typically 2000-4000 Hz.
- Active control of coupled wave propagation in fluid-filled elastic cylindrical shellsBrevart, Bertrand J.; Fuller, Chris R. (Acoustical Society of America, 1993-09-01)A control approach to reduce the total power propagating along fluid-filled elastic cylinders is analytically investigated. The motion of the cylinder is described by the Kennard shell equations fully coupled to the interior acoustic field. The vibration disturbance source is a pre-determined free propagating wave of either n = 0 or n = 1 circumferential order and the control forces considered are appropriate harmonic line forces radially applied to the structure. The radial displacement of the shell wall at discrete locations downstream of control forces is minimized using feedforward quadratic optimal theory. The difference of total power flow through the system before and after control is then used to evaluate the impact of the fluid on the performance of the control approach. For the breathing circumferential mode (n = 0), owing to the coupling between the two media, the fluid decreases the control performance when the disturbance is a structural-type incident wave. When the disturbance is a fluid-type incident wave, with a pressure near field concentrated at the shell wall, significant reductions of the transmitted power flow can be achieved. For the beam mode (n = 1), even though the control is applied to the structure, the fluid increases the control performances below the first acoustic cut-off frequency and decreases it above this frequency.
- Active control of far-field sound radiated by a rectangular panel - a general analysisPan, Jie; Snyder, Scott D.; Hansen, Colin H.; Fuller, Chris R. (Acoustical Society of America, 1992-04-01)In this paper a general analysis is presented for the active control of the far-field harmonic sound radiated by a rectangular panel that is built into an infinite baffle. In this analysis, the panel vibration may be generated by either airborne sound (incident sound field) or by structure borne vibrations. The far-field radiated sound is controlled either by acoustical sources or vibration sources. Minimization of both the local sound pressure and the total power output is considered. Analytical results for the particular case involving minimization of the sound pressure at a single point are compared with experimental data. The physical mechanisms involved for different control sources (vibration or acoustic) are demonstrated analytically. For the case of vibration control sources, the panel modal velocity components are adjusted to produce far-field sound control. This can be done either by decreasing their amplitudes, and/or by changing the temporal phases of the panel modes. However, for acoustic control sources, the far-field sound is minimized by alteration of the radiation impedance seen by the vibrating panel and the control sources.
- Active control of noise transmission through rectangular plates using multiple piezoelectric or point force actuatorsWang, Bor-Tsuen; Fuller, Chris R.; Dimitriadis, Emilios K. (Acoustical Society of America, 1991-11-01)This paper analytically demonstrates the use of multiple piezoelectric actuators bonded to the surface and point force actuators applied directly to a plate to reduce sound transmission through the plate. A harmonic plane wave incident on a simply supported, thin rectangular plate mounted in an infinite baffle was considered as the primary source. Both multiple piezoelectric and point force actuators are separately used as secondary (control) sources to attenuate the sound transmission through the plate. An optimal process was applied to obtain the input voltages of the piezoelectric actuators and the magnitude of the point forces, so that the radiated acoustic power can be minimized. Results show that a reduction of sound transmission through the plate is successfully; achieved, if the proper size, number, and position of the piezoelectric or point force actuators are selected. Additionally, a comparison showed that point force actuators provide more effective control of the sound transmission than piezoelectric actuators; however, piezoelectric patches have more practical implementation than point force shakers, because of their low cost and light weight.
- Active control of sound radiation due to subsonic wave scattering from discontinuities on fluid-loaded plates. I: Far-field pressureGu, Yi; Fuller, Chris R. (Acoustical Society of America, 1991-10-01)Active control of sound radiation due to subsonic wave scattering from discontinuities represented by a line constraint or by a uniform reinforcing rib positioned on a fluid-loaded infinite plate is analytically studied. The mathematical models are based on the plate vibration and sound radiation due to a line force or a line moment solved in the spectral k domain. For simplicity, the far-field pressure is estimated by the stationary phase approach. Feed-forward control is achieved by adding secondary line forces applied to the plate near the discontinuity. The amplitudes of control forces are determined by the optimal solution of a cost function that integrates the far-field radiated acoustic intensity in a semicylindrical space around the discontinuity. The results show that for subsonic incident waves, high reduction in radiated pressure due to spectral wave scattering at the discontinuities is possible with two active control forces located near the discontinuity. The amount of sound reduction as well as the residual directivity pattern is shown to depend upon the number and location of the control forces.
- Active control of sound radiation from a fluid-loaded rectangular uniform plateGu, Yi; Fuller, Chris R. (Acoustical Society of America, 1993-01-01)Active control of sound radiation from a simply supported rectangular fluid-loaded plate is analytically studied. The plate is assumed to be excited by a point force at subsonic frequencies. The solution to the plate motion is based on the admissible functions for an in vacuo homogeneous plate, which is also the basis for Fourier decomposition of the fluid loading [B. E. Sandman, J. Acoust. Soc. Am. 61, 1502-1510 (1977) ]. Feed-forward control is carried out by using point forces applied to the plate. The amplitudes of the control forces are determined by the optimal solution of a quadratic cost function that integrates the far-field radiated acoustic pressure over a hemisphere in the radiation half-space. The results show that for subsonic disturbances, a high global reduction in radiated pressure is possible. For on-resonant excitations, a reasonable sound reduction can be achieved with up to two properly located active control forces, and for off-resonant excitations, up to four control forces may be necessary. The results thus indicate that the active structural acoustic control approach will provide large attenuations in radiated sound when edge mode coupling induced by heavy fluid loading is present. The number and location of the control forces are determined so as to suppress the efficiently radiating modes. The far-field directivity pattern, the plate velocity autospectrum in the two-dimensional wave number domain, and the near-field pressure distribution are studied.
- Active control of sound radiation from a simply supported beam: Influence of bending near-field wavesGuigou, 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.
- Active control of sound transmission/radiation from elastic plates using multiple piezoelectric actuatorsWang, Bor-Tsuen (Virginia Tech, 1991)This thesis presents a theoretical analysis of active control of sound radiation from elastic plates with the use of piezoelectric transducers as actuators. A strain-energy model (SEM), based upon the conservation of strain energy, for a laminate beam with attached or embedded finite-length spatially distributed induced strain actuators was first developed to determine the induced strain distribution. The equivalent axial force and bending moment induced by the embedded or surface bonded actuators were also calculated. The one-dimensional SEM was then extended to a two-dimensional model by employing the classical laminate plate theory and utilizing Heaviside functions to integrate the actuator influence on the substructure. The mechanics model can determine the structural coupling effect and predict the structural response as a result of piezoelectric actuation. A baffled simply-supported rectangular plate subjected to harmonic disturbances was considered as the plant. Piezoceramic materials bonded to the surfaces of the plate or point force shakers were applied as control actuators. Both microphones in the radiated far-field and accelerometers located on the plate were considered as error sensors. In addition, distributed sensors for pressure and structural motion were modelled. The cost function was formulated as the modulus squared of the error signal. Linear quadratic optimal control theory was then applied to minimize the cost function to obtain the optimal input voltages to the actuators. Both near-field and far-field pressure and intensity responses as well as plate displacement distributions were presented to show the effectiveness and mechanisms of control for various configurations of the actuators and sensors. Plate wavenumber analysis was also shown to provide a further insight into control technique. The results show that piezoelectric actuators perform very well as control sources, and that pressure sensors have many advantages over acceleration sensors while distributed sensors are superior to discrete sensors. The optimal placement of multiple fixed size piezoelectric actuators in sound radiation control is also presented. A solution strategy is proposed to calculate the applied voltages to piezoelectric actuators with the use of linear quadratic optimal control theory. The location of piezoelectric actuator is then determined by minimizing an objective function, which is defined as the sum of the mean square sound pressure measured by a number of error microphones. The optimal location of piezoelectric actuators for sound radiation control is found so as to minimize the objective function and shown to be dependent on the excitation frequency. In particular, the optimal placement of multiple piezoelectric actuators for on-resonance and off-resonance excitation is presented. Results show that the optimally placed piezoelectric actuators perform far better in sound radiation control than arbitrarily selected. This work leads to a design methodology for adaptive or intelligent material systems with highly integrated actuators and sensors. The optimization procedure also leads to a reduction in the number of control transducers.
- Active isolation of vibration with adaptive structuresGuigou, 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.
- Adaptive feedforward and feedback methods for active/passive sound radiation control using smart foamGuigou, 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.
- Advanced time domain wave-number sensing for structural acoustic systems. I. Theory and designMaillard, Julien P.; Fuller, Chris R. (Acoustical Society of America, 1994-06-01)This paper discusses new work concerned with developing structural sensors and associated signal processing techniques that provide time domain estimates of far-field pressure or structural wave-number information. The sensor arrangement consists of multiple accelerometers whose outputs are passed through an array of linear filters. The impulse response of each filter is constructed from the appropriate Green's function for the elemental source area associated with each sensor. The outputs of the filter array are then summed in order to predict far-field pressure or wave-number information somewhat analogous to the well-known boundary element technique. A major significance of the approach is that it provides time domain information and can thus be efficiently applied to active structural acoustic control approaches.
- Advanced time domain wave-number sensing for structural acoustic systems. II. Active radiation control of a simply supported beamMaillard, Julien P.; Fuller, Chris R. (Acoustical Society of America, 1994-06-01)A real time structural acoustic sensor and associated signal processing is developed and applied to the active control of sound radiated by a simply supported beam. The sensor consists of multiple accelerometers mounted on the structure. An array of FIR filters processes the measured structural information to provide an estimate of the structural wave-number component coupled to acoustic radiation in a prescribed direction. This time domain signal is used as the error information in a feedforward adaptive control approach. The single channel filtered-X LMS algorithm is implemented here. Computer simulations in the discrete time domain demonstrate the ability of the sensor to replace the use of error microphones in the far field. The described sensor represents a significant alternative to the use of distributive structural sensors (for example piezoelectric material) by providing accurate radiation information over a broadband frequency range.
- Advanced time domain wave-number sensing for structural acoustic systems. Part III. Experiments on active broadband radiation control of a simply supported plateMaillard, Julien P.; Fuller, Chris R. (Acoustical Society of America, 1995-11-01)The present work gives further developments and experimental testing of a new time domain structural sensing technique for predicting wave-number information and acoustic radiation from vibrating structures. Most structure-borne active sound control approaches now tend to eliminate the use of microphones located in the far field by developing sensors directly mounted on the structure. In order to reduce the control authority and complexity required to minimize sound radiation, these sensors should be designed to provide error information that is solely related to the radiating part of the structural vibrations, e.g., the supersonic wave-number components in the case of planar radiators. The approach discussed in this paper is based on estimating supersonic wave-number components coupled to acoustic radiation in prescribed directions. The spatial wave-number transform is performed in real time using a set of point structural sensors with an array of filters and associated signal processing. The use of the sensing approach is experimentally demonstrated in the time domain LMS active control of broadband sound radiated from a vibrating plate. Comparisons of the control performances obtained with the wave-number sensor and error microphones in the far field show that only a few point sensors are required to provide accurate radiation information over a broad frequency range. The approach demonstrates good broadband global control of sound radiation. (C) 1995 Acoustical Society of America.
- Analytical investigation of active control of radiated inlet fan noiseRisi, John D.; Burdisso, Ricardo A.; Fuller, Chris R. (Acoustical Society of America, 1996-01-01)An analytical mode has been de loped to study the potential of active noise control techniques for Ie reducing radiated tonal inlet noise from turbofan engines. The analytical model consists of multiple control sources placed in the periphery of the engine inlet duct which inject antinoise into the duct to destructively interfere with the tonal sound field generated by the fan. The development of the analytical expressions of the radiated sound fields due to both the disturbance and the control
- A biologically inspired control approach for distributed elastic systemsFuller, Chris R.; Carneal, James P. (Acoustical Society of America, 1993-06-01)A multi-degree of freedom control approach, which is largely inspired by biological systems, is presented. Control inputs to a structure are achieved by multiple piezoelectric actuators. One actuator chosen as the ''master'' actuator is under the direction of the central, sophisticated controller. The other ''slave'' actuators derive their control inputs by localized, simple learning rules related to the behavior of their neighbor actuators including the ''master.'' Simulations on the control of the vibrational energy density of a harmonically excited simply supported beam demonstrate a significant improvement in control performance over a single actuator case, particularly for off-resonance frequencies. Thus high attenuations are achieved with a multiple degree of freedom actuator with a single main channel of control.
- A biologically inspired controllerCarneal, James P.; Fuller, Chris R. (Acoustical Society of America, 1995-07-01)A biologically inspired control approach for reducing vibrations in distributed elastic systems has been derived and experimentally verified for narrow-band excitation. The control paradigm approximates natural biological systems for initiating movement, in that a low number of signals are sent from an advanced, centralized controller (analogous to the motor cortex of the brain) and are then distributed by local simple rules to multiple control actuators (analogous to muscle fiber). Both theoretical and experimental investigations of three different local rules were carried out including a stability analysis for reducing beam vibrations. In general the results have demonstrated that the biological control approach has the potential to control multimodal response in distributed elastic systems using an array of many actuators with a reduced order main controller. Thus significant reductions in control system computational complexity have been realized by this approach. ï¿_ï¿_ï¿_ 1995 Acoustical Society of America
- Broadband control of plate radiation using a piezoelectric, double-amplifier active-skin and structural acoustic sensingJohnson, Brody D.; Fuller, Chris R. (Acoustical Society of America, 2000-02-01)The potential of a piezoelectric, double-amplifier active-skin with structural acoustic sensing (SAS) is demonstrated for the reduction of broadband acoustic radiation from a clamped, aluminum plate. The active-skin is a continuous covering of the vibrating portions of the plate with active, independently controllable piezoelectric, double-amplifier elements and is designed to affect control by altering the continuous structural radiation impedance rather than structural vibration. In simulation, acoustic models are sought for the primary and secondary sources that incorporate finite element methods. Simulation indicates that a total radiated power attenuation in excess of 10 dB may be achieved between 250 and 750 Hz with microphone error sensing, while under SAS the radiated power is reduced by nearly 8 dB in the same frequency range. In experiment, the adaptive feed forward filtered-x LMS (least mean square) algorithm, implemented on a Texas Instruments C40 DSP, was used in conjunction with the 6I6O control system. With microphone error sensing, 11.8-dB attenuation was achieved in the overall radiated power between 175 and 600 Hz. while inclusion of SAS resulted in a 7.3-dB overall power reduction in this frequency band.
- Causality analysis of feedforward-controlled systems with broadband inputsBurdisso, Ricardo A.; Vipperman, Jeffrey S.; Fuller, Chris R. (Acoustical Society of America, 1993-07-01)In recent years adaptive feedforward control algorithms have been successfully implemented to attenuate the response of systems under persistent disturbances such as single and multiple tones as well as random inputs. System causality is not an issue when the excitation is sinusoidal because of its deterministic nature. However, causality is a very important factor in broadband control. Though significant deterioration in the performance of noncausal control systems have been reported in the literature, analytical tools are virtually nonexistent to predict the behavior of broadband controllers. The main objective of this research is to develop an approach to investigate system causality. A formulation is presented to address the effectiveness of a control configuration as a function of the filter size, delay time, and dynamic properties of the structure. The technique is illustrated in a simple numerical example and the results are also corroborated experimentally.
- «
- 1 (current)
- 2
- 3
- »