Active Structural Acoustic Control Research Articles

Coupled Electro-Mechanical Analysis of Adaptive Material Systems-Determination of the Actuator Power Consumption and System Energy Transfer

This article presents a coupled electromechanical analysis of piezoelectric ceramic (PZT) actuators integrated in mechanical systems to determine the actuator power consumption and energy transfer in the electromechanical systems. For a material system with integrated PZT actuators, the power consumed by the PZT actuators consists of two parts: the energy used to drive the system, which is dissipated in terms of heat as a result of the structural damping, and energy dissipated by the PZT actuators themselves because of their dielectric loss and internal damping. The coupled analysis presented herein uses a simple model, a PZT actuator-driven one-degree-of-freedom spring-mass-damper system, to illustrate the methodology used to determine the actuator power consumption and energy flow in the coupled electromechanical systems. This method can be applied to more complicated mechanical structures or systems, such as a fluid-loaded shell for active structural acoustic control. The determination of the actuator power consumption can be very important in the design and application of intelligent material systems and structures and of particular relevance to designs that must be optimized to reduce mass and energy consumption.

Quelling Cabin Noise in Turboprop Aircraft via Active Control

Cabin noise in turboprop aircraft causes passenger discomfort, airframe fatigue, and employee scheduling constraints due to OSHA standards for exposure to high levels of noise. The noise levels in the cabins of turboprop aircraft are typically 10 to 30 decibels louder than commercial jet noise levels. However, unlike jet noise the turboprop noise spectrum is dominated by a few low frequency tones. Active structural acoustic control is a method in which the control inputs (used to reduce interior noise) are applied directly to a vibrating structural acoustic system. The control concept modeled in this work is the application of in-plane force inputs to piezoceramic patches bonded to the wall of a vibrating cylinder. The goal is to determine the force inputs and locations for the piezoceramic actuators so that (1) the interior noise is effectively damped; (2) the level of vibration of the cylinder shell is not increased; and (3) the power requirements needed to drive the actuators are not excessive. Computational experiments for data taken from a computer generated model and from a laboratory test article at NASA Langley Research Center are provided.

Wavenumber-adaptive control of sound radiation from structures using a “virtual” microphone array method

A method and an apparatus for active structural acoustic control (ASAC) of sound radiation from and noise transmission through a structure. The method derives acoustic far-field information, corresponding to a `virtual` planar array of microphones, from a vibrational field induced on the structure. The far-field information is used to compute error signals which are provided to an adaptive controller which controls actuators mounted on or embedded in the structure so as to suppress the flexural modes of structure vibration generating acoustic energy. The method is generally applicable to any structure and set of environment boundary conditions. An implementation of the method includes an array of accelerometers mounted on one face of a planar panel, an array of piezoceramic actuators mounted on an opposite panel face, and a frequency-domain adaptive controller utilizing a set of wavenumber-space algorithms.

Study on Active Noise Isolation. Modeling and Active Structural Acoustic Control of Flexible Plate.

This paper deals with a study on the active structure-borne sound control of a flexible plate by the feedback control method. It involves modeling a real structure as a reduced-order lumped parameter model on the basis of modal analysis, and then adopting modern control theory to control the vibration of selected multimodes of a plate that has high radiation efficiency. The modeling procedure and the LQ and suboptimal control design are presented; control simulation of the discrete model is carried out in order to demonstrate the effectiveness of the method. Experimental work with vibration control of the plate enables a final verification.

Multivariable active structural acoustic feedback control using piezoelectric sensoriactuators

Analytical and experimental results from the implementation of a feedback, active structural acoustic control (ASAC) system are presented. The test bed is a rectangular, simply supported steel plate inserted in a semi-infinite baffle inside an anechoic chamber. Piezoceramic patches are wired as bending transducers and implemented as adaptive piezoelectric sensoriactuators or self-sensing actuators. The transfer function across a sensoriactuator is minimum-phase, thereby enhancing stability for feedback control applications. Radiation filters are implemented to design the performance cost used in the control synthesis. Several design parameters are examined for different square (equal number of inputs and outputs) control configurations. Both single- and multichannel control system implementations are considered. Sensor and actuator optimization is performed using nonlinear optimization techniques, and both dynamic and static compensation are compared.

Control of sound radiation from panels using multiple globally detuned vibration absorbers

In this paper, the results of an investigation on using multiple globally detuned vibration absorbers to minimize sound radiation from vibrating elastic panels will be presented. The vibration absorbers consist of lumped mass–spring systems whose characteristics (i.e., resonance frequency) can be electronically varied. A fully coupled multiple-channel control algorithm, implemented on a DSP, is used to adapt the characteristics of the multiple absorbers so as to minimize the radiated sound at selected positions in the far field. Both theoretical and experimental results are presented and are compared to those obtained using tuned (i.e., to the disturbance frequency) vibration absorbers. Improved sound attenuation is shown to be obtained using the globally detuned vibration absorbers. The results are very similar in characteristics to those obtained previously using active structural acoustic control implemented with electrodynamic shakers or piezoelectric actuators. The results thus suggest a combined active–passive method to minimize structural sound radiation which requires lighter, smaller actuators and much lower control electrical power. [Work supported by ONR and NASA LaRC.]

Characterization of Transfer Functions for Piezoceramic and Conventional Transducers

This paper analytically derives the transfer functions for piezoceramic and conventional tranducers and characterizes their relationships in terms of frequency response function (FRF) and modal parameters such as natural frequencies, damping ratios, and mode shapes. The FRFS between accelerometer/point force actuator, accelerometer/PZT actuator, PVDF sensor/point force actuator, and PVDF sensor/PZT actuator are determined, respectively. Those FRFs are expressed in conventional modal model format which can clearly get insight of physical meaning of modal parameters. In particular, the mode shapes of accelerometer, point force actuator, PVDF sensor, and PZT actuator are identified and are proportional to the displacement mode shapes. The point and transfer FRFs are then studied to characterize their properties for either pair of transducer applications. This work leads to the basis for active structural vibration and acoustic control and also draws on ideas for applications of smart structural testing to system identification and diagnosis.

Optimal placement of microphones and piezoelectric transducer actuators for far-field sound radiation control

This paper presents an optimization solution technique to determine the optimal locations of piezoelectric transducer (PZT) actuators and far-field microphone sensors for active structural acoustic control in conjunction with the use of least-mean-square (LMS) feedforward control algorithm. A simply supported beam in an infinite rigid baffle subject to an harmonically excited point force is considered. The piezoceramic patches are adhered to the beam and act as control transducers, while microphones located in the far field are used as error sensors. The objective function is first defined as the total radiated sound power. The design variables which are the locations of PZT actuators and microphone sensors are then identified and determined. The genetic algorithm (GA) incorporated with the use of linear quadratic optimal control theory (LQOCT) to calculate the control voltages to the actuators is adopted to solve the optimization problem. Results show that the optimally placed PZT actuators and microphone sensors can perform better sound radiation control than the arbitrarily selected ones. In particular, for off-resonance excitation cases the optimized PZT actuators and microphone sensors can efficiently control the sound radiation and eliminate the control spillover. The control mechanisms of PZT actuators and microphone sensors are demonstrated through the studies of radiation directivity patterns and beam displacement distributions as well as the wave-number analysis. The effect of the number of microphone sensors are also presented. The use of optimally positioned PZT actuators and microphone sensors can efficiently achieve structural sound radiation control.

Response to ‘‘Comments on ‘Design of active structural acoustic control systems by eigenproperty assignment’ ’’ [J. Acoust. Soc. Am. 99, 1785–1788 (1996)

The authors thank Professor Cunefare for his interest in our paper on the design of active structural acoustic control systems. This Letter is to clarify questions raised in his Comments.

Comments on ‘‘Design of active structural acoustic control systems by eigenproperty assignment’’ [J. Acoust. Soc. Am. 96, 1582–1591 (1994)

The recent article by Burdisso and Fuller [‘‘Design of active structural acoustic control systems by eigenproperty assignment,’’ J. Acoust. Soc. Am. 96, 1582–1591 (1994)] does not fully illuminate the contributions of a number of prior authors for a crucial part of the work, that is, the development of weak radiator modes. This comment places the subject development of Burdisso and Fuller in context with the prior art. Further, it demonstrates the similarities of the subject development to prior work published by K. A. Cunefare [‘‘The minimum multimodal radiation efficiency of baffled finite beams,’’ J. Acoust. Soc. Am. 90, 2521–2529 (1991)]. The authors recognize and acknowledge that Burdisso and Fuller’s implementation of the concept, through eigenproperty assignment, is unique and valuable.

Control of Broadband Acoustic Radiation with Adaptive Structures

Active Structural Acoustic Control has been demonstrated for harmonic disturbances on various structures. This paper presents an extension of this work to the attenuation of acoustic radiation from planar structures subject to broadband disturbances. An adaptive, multiinput multi-output (MIMO), feedforward broadband acoustic control system has been developed. The control approach is the least mean squares (LMS) algorithm. The compensators are adaptive finite impulse response (FIR) filters. The control inputs are implemented with piezoceramic actuators. Both far-field microphones and polyvinylidene fluoride (PVDF) distributed structural sensors are used as error sensors. Both the actuator locations and the PVDF sensor configurations were optimally chosen to minimize radiated sound power assuming multiple frequency excitation. The disturbance is band-limited zero mean white noise and is implemented with a point force shaker. In the control of harmonically excited systems, satisfactory attenuation is possible with a single-input single-output (SISO) controller. In contrast, for systems excited with broadband disturbances, a MIMO controller is necessary for significant acoustic attenuation. Experimental results for the control of a simply supported plate are presented.

Optimizing actuator locations in active noise control systems using subset selection

This numerical simulation uses multiple linear regression with subset selection to optimize the locations of control actuators in a feedforward active noise control system. By formulating the feedforward control problem as a regression, subset selection can find the actuator locations that provide the best system performance. Subset selection provides benefits over continuous optimization approaches because of its computational efficiency; subset selection can examine systems for which the system response is expensive to compute, such as fluid–structure interaction problems, and can efficiently optimize large numbers of actuators. This paper describes a method for exhaustive-search subset selection, and provides numerical results for a simple active structural-acoustic control problem.

Active control of aircraft cabin noise

Aircraft cabin noise control in the past has relief heavily on improving sidewall attenuation by passive ‘‘add-on’’ treatments. The conventional passive methods, such as adding mass, damping, or acoustic absorption, etc., not only impose a stiff weight penalty, they are also ineffective in improving the low-frequency sound transmission loss of an aircraft fuselage sidewall. Active control of sound inside aircraft cabins has been the focus of research in recent years and has shown considerable promise. Laboratory and in-flight tests of prototype active control systems for tonal noise reduction using secondary speakers have demonstrated the feasibility of active noise control (ANC) in aircraft cabins. In recent years active structural acoustic control (ASAC) has also been applied to aircraft fuselage structures in controlling low- to mid-frequency structural sound radiation. In the ASAC technique, control forces are applied directly to the vibrating structure by actuators (such as piezoelectric transducers) instead of using loudspeakers to minimize the radiated sound field. The ASAC approach is also important in the design of ‘‘smart structures,’’ which incorporate both sensors and actuators in the structure for noise and vibration control. This paper presents results of investigations (conducted at McDonnell Douglas) of application of both ANC and ASAC techniques to a full scale aircraft fuselage. Significant sound pressure reductions were achieved throughout the cabin for multiple tonal frequencies of excitation. The performance of the ASAC method is compared with that of the ANC system using speakers. The flight test results with a prototype ANC system in an MD-80 aircraft will also be presented.

The use of neural networks for optimum actuator grouping in time domain active control applications

Previous work has demonstrated the benefit of grouping actuators to decrease the number of degrees of freedom in an active control system. In this work, a time‐domain cost function was developed for on‐line actuator grouping and active structural acoustic control (ASAC) of a simply‐supported beam excited with a broadband disturbance. Actuators are considered grouped when their compensators are equal. Therefore, the cost function presented here incorporates a mean‐square error term related to the structure‐borne noise and an additional nonquadratic term which penalizes the controller for differences between respective compensator coefficients. The backpropagation neural network algorithm provides the proper procedure to determine the minimum of this cost function. The main disadvantage of using such a stochastic gradient technique while searching the prescribed control surface is converging to local minima. A resolution to this problem is discussed which incorporates using a variety of initialization conditions. Two scenarios are considered here: grouping actuators based upon weights determined by converging the filtered‐x LMS algorithm and simultaneously grouping and controlling with the compensator weights started at zero. Computer simulations demonstrate the ability of this new form of the cost function to simultaneously group actuators and control the structure‐borne noise with either initial conditions.

Smart foam design and applications in active structural acoustic control

Acoustic foams possess inherent high‐frequency sound absorbing capabilities for radiation and reflection control of structures. Comparatively, active noise control systems generally do not perform well at high frequencies due to the increasing complexity of the physical model and the necessary high speed digital signal processing. The ‘‘smart foam’’ concept and design originates from the combination of these two control strategies formulating a passive/active noise suppression device that can efficiently operate over a broad range of frequencies. In this research, the experimental device is comprised of a layer of piezoelectric material embedded in a partially reticulated polyeurethane foam. Depending on the specific application, the distributed actuator alters the surface impedance of the passive absorber such that an incident acoustic wave is totally reflected or absorbed. Error sensor configurations include microphones or piezoelectric sensors integrated directly into the noise suppression device creat...

Strategies for using strain sensing in active control of acoustic radiation

Sensing approaches used in active structural acoustic control (ASAC) are mainly concerned with monitoring acceleration, velocity or displacement of the structure, typically by means of accelerometers or PVDF, thereby eliminating the need for far‐field acoustic sensor(s). The radiation of the structure is estimated from this information, either directly or from a model of the radiating structure. The direct approach has the advantage of not being dependent on the accuracy of any model. A new sensing strategy is herein presented, in both direct‐ and model‐based approaches, where the estimation of acoustic radiation involves monitoring the strain field of the structure. Such information is directly given by fiber optics sensors, for example, so that significant gain is expected at this level. Two approaches are presented using strain information. The first formulation is obtained by integrating by parts the Rayleigh’s formula. Dependence on boundary conditions then appears and has to be dealt with. The second formulation utilizes a finite‐difference scheme in order to estimate, from the strain information, the displacement field in Rayleigh’s formula. Simulations are performed using a given displacement field and the two formulations are compared in order to evaluate their effectiveness for use in active control schemes.

Optimum design for feedforward active structural acoustic control of complex structures

An efficient design formulation for feedforward active structural acoustic control systems for complex structures and disturbances is presented. The approach consists in a multilevel 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 model parameters are then used in the lower level optimization to obtain the physical characteristics of the transducers to be implemented. This separation between the modal domain and the physical domain during the design process allows the designer to investigate different control system configurations in the upper level part with minimum computational effort. The formulation is capable to handle the design of multiple‐inputs, multiple‐outputs control systems and multiple frequency excitations. The proposed approach is demonstrated for the case of a simply supported plate excited by a periodic point force. ...

Active structural acoustic control of noise transmission through double panel systems

A preliminary parametric study of active control of sound transmission through double panel systems has been experimentally performed. The technique used is the active structural acoustic control (ASAC) approach where control inputs, in the form of piezoelectric actuators, were applied to the structure while the radiated pressure field was minimized. Results indicate the application of control inputs to the radiating panel resulted in greater transmission loss due to its direct effect on the nature of the structural-acoustic coupling between the radiating panel and the receiving chamber. Increased control performance was seen in a double panel system consisting of a stiffer radiating panel with a lower modal density. As expected, more effective control of a radiating panel excited on-resonance is achieved over one excited off-resonance. In general, the results validate the ASAC approach for double panel systems and demonstrate that it is possible to take advantage of double panel behavior to enhance control performance, although it is clear that further research must be done to understand the physics involved

Numerical simulation of active structural-acoustic control for a fluid-loaded, spherical shell

Numerical methods are used to investigate active structural-acoustic control, a noise control technique in which oscillating force inputs are applied directly on a flexible structure to control its acoustic behavior. The goal is to control acoustic radiation from a thin-walled shell submerged in a dense fluid and subjected to a persistent, pure-tone disturbance. For generality the fully coupled responses are found numerically, in this case using the computer program that combines finite-element and boundary-element techniques. A feedforward control approach uses linear quadratic optimal control theory to minimize the total radiated power. Results are given for a thin-walled spherical shell, and are compared to analytical results. The numerical solution is shown to be suitably accurate in predicting the radiated power, the control forces, and the residual responses as compared to the analytical solution. A relatively small number of control forces can achieve global reductions in acoustic radiation at low frequencies (k0a<1.7). A single point-force actuator reduces the radiated power due to a point-force excitation by up to 20 dB at resonance frequencies; between resonance frequencies, more actuators are required because of modal spillover. With multiple control forces, radiation can be reduced by 6–20 dB over the frequency range 0<k0a<1.7.

Power consumption of piezoelectric actuators driving a simply supported beam considering fluid coupling

An electromechanical impedance model is applied to the case of a simply supported beam in an infinite rigid baffle with a fluid medium on one side. The effects of the fluid medium are included in the impedance analysis by considering fluid–structure interaction. The use of static and impedance model for structural acoustic analysis is discussed. Various power consumptions of PZT actuator-driven underwater beam structures will be quantified. The analysis discussed in this paper will be used to determine radiated structural acoustic power without using microphones. This work is the first step toward the determination of power requirements for underwater active structural acoustic control.