Active Control Of Sound Radiation Research Articles

Refracto-vibrometry for active control of sound radiation through an opening

In this study, refracto-vibrometry is proposed for active control of sound radiation through an opening. First, refracto-vibrometry is used to reconstruct sound field in an opening, and a quantitative comparison of sound fields is made with those obtained from a microphone array at 224 locations. Then, the reconstructed sound field by refracto-vibrometry is used for active noise control. Experimental results indicate that using refracto-vibrometry can obtain about 12.9 dB noise reduction at 500 Hz with no increase in noise observed at higher frequencies above 2 kHz. By offering a significantly larger number of error signals without causing obstructions at an opening, refracto-vibrometry outperforms traditional microphone arrays, making it an effective complementary error sensing method for high frequency noise.

Modal Performance Analysis of Compressor for Active Control of Acoustic Radiation

Compressor has a complex internal structure and contains various kinds of motion mechanism. At present, research on compressor’s vibration and sound radiation characteristics is insufficient. In this paper, structure and sound radiation modes of control objects are analysed by mode analysis. Explore the mode distribution law and correspond the structure mode to the sound radiation mode. On this basis, by suppressing the vibration mode, the influence is transmitted to the acoustic domain to realize the active control of sound radiation of the structure as a whole.

A near-field error sensing strategy for compact multi-channel active sound radiation control in free field.

Noise reduction performance of a compact active sound radiation control system is significantly affected by locations of the error microphones which are required to be installed near the primary source. In this paper, near-field error sensing for multi-channel active radiation control systems in free field is investigated, and it is found that the optimal locations of error sensors for minimizing the sum of squared sound pressure are between the primary source and the secondary sources distributed uniformly on a sphere surface surrounding the primary source. Both simulation and experiment results show that the optimal locations of error microphones are independent of the type of primary source when there are sufficient secondary sources. These optimal locations remain unchanged at low frequencies and move toward secondary sources when the secondary source number increases. Therefore, for active radiation control applications in low frequency range, a compact multi-channel system can be developed by locating error microphones between the primary source and secondary sources.

Active control of sound radiation from rib stiffened plate using the weighted sum of spatial gradients as the cost function

The active structural acoustic control of the rib stiffened plate highly improves the sound insulation performance in the low frequency range. This promotes the engineering relevance of the active control technic since the ribbed plate is a classical structural element widely applied in practical engineering. One of the key problems encountered when implementing such system is error sensing strategy. The traditional sensing strategy, such as sensing the radiation modes using distributed piezoelectric sensors, is difficult to implement due to the block of the ribs in the ribbed plate case. The pseudo-uniform structure quantity proposed recently, i.e., the weighted sum of spatial gradients (WSSG) is highly correlated with the radiated sound power of the radiating plate, which can be easily obtained by only sensing vibrating information of single point and is also less sensitive with the sensor location. Hence, WSSG is adopted in this paper to establish the error sensing strategy for the active structural acoustic control of the ribbed plate. The weights in WSSG directly impact the control performance, and should be chosen appropriately for the plates with different parameters. The parameter-based weights, which can be obtained conveniently according to the ratio of the flexural rigidity to the mass per unit area of the plate, are more preferable in real implementation for broadband frequency control. As for the ribbed plate case, due to the coupling effects of the ribs, the flexural rigidity of the ribbed plate is not uniform and varies for different kinds of rib arrangements. This is another parameter that will also affect the parameter-based weights. This paper compares the regions of the near-optimal weights for different locations of the ribs and summarizes the influence of this parameter on choosing the optimal weights. Combining the special resonant characteristics of the ribbed plate induced by the coupling effects of the ribs, the rule of the influence by the ribs are interpreted particularly. Then experiments are carried out to validate the conclusions. Results obtained can help for choosing the optimal weights of WSSG for the ribbed plate case.

Mechanisms of active control of sound radiation from an opening with boundary installed secondary sources.

Previous work has demonstrated that installing secondary sources at the edge of a cavity opening can reduce sound radiation through it, but the mechanisms are not clear, which is investigated in this paper by using the modal decomposition method. It is found that a double layer edge system achieves better performance than a single layer system because secondary sources at the edge of the same layer cannot excite some modes effectively and those at different heights compensate this. There exists an upper limit frequency for the systems with boundary installed secondary sources, which is mainly decided by the length of the short side of the opening. More secondary source layers at the edge will increase the upper limit frequency.

Frequency-independent radiation modes of interior sound radiation: Experimental study and global active control

Active control of structural sound radiation is a promising technique to overcome the poor passive acoustic isolation performance of lightweight structures in the low–frequency region. Active structural acoustic control commonly aims at the suppression of the far–field radiated sound power. This paper is concerned with the active control of sound radiation into acoustic enclosures. Experimental results of a coupled rectangular plate-fluid system under stochastic excitation are presented. The amplitudes of the frequency-independent interior radiation modes are determined in real-time using a set of structural vibration sensors, for the purpose of estimating their contribution to the acoustic potential energy in the enclosure. This approach is validated by acoustic measurements inside the cavity. Utilizing a feedback control approach, a broadband reduction of the global acoustic response inside the enclosure is achieved.

Performance of a multichannel active sound radiation control system near a reflecting surface

Prior research shows that introducing a reflecting surface near an active control system can improve its noise reduction performance; however the mechanism of the performance improvement is not completely clear. This paper investigates the effects of a reflecting surface on multichannel active sound radiation control systems with a primary monopole source located on the surface. By using a genetic searching algorithm, the locations of secondary sources were optimized to maximize the noise reduction and the frequency range that can be beneficial from the reflecting surface is discussed. It is found that the performance improvement by introducing a reflecting surface is due to the increased sound pressure generated by the secondary sources at the primary source location. The beneficial frequency range extends with the number of the channels of the control system and has an upperlimitfrequency determined by the distance between the secondary sources and the primary source. Experiments are conducted to validate the results.

Active sound radiation control with secondary sources at the edge of the opening

Planar virtual sound barriers with secondary sources over the entire opening have been demonstrated an effective way to achieve global control of sound transmission through the opening, but loudspeakers in the middle of the opening affect ventilation, lighting and normal access through it. To avoid the problem, this technical note proposes to implement secondary sources at the edge of a cavity opening and investigates the active sound reduction performance of the system numerically and experimentally. Unlike secondary sources over the entire opening which can achieve sound reduction at any frequency as long as there are sufficient of them, there exists an upper bound of effective frequency for global control when secondary sources are at the edge of the opening; however, local control is always achievable. Preliminary experiments were conducted on an open wooden box and a semi-closed meeting room to support the conclusions.

Robust active sound radiation control of a piezo-laminated composite circular plate of arbitrary thickness based on the exact 3D elasticity model

A multi-objective mixed [Formula: see text]2/[Formula: see text]∞ robust output feedback control synthesis with regional pole placement constraints in a linear matrix inequalities framework is adopted for active low-frequency sound radiation control of an arbitrarily thick, rigidly baffled, simply supported, multi-layered piezo-composite circular panel. The adopted control system concurrently captures the benefits of both [Formula: see text]2 transient control performance and [Formula: see text]∞ robust stability in the face of external disturbances and system uncertainties. Also, the implemented volumetric sensing/actuation configuration avoids the typical problems associated with conventional (spatially discrete) piezoelectric sensor/actuator patches, where the total volume velocity can be effectively cancelled with the main contribution being to the long wavelength acoustic power emission. The elasto-acoustic analysis is based on the spatial state-space method in the context of exact 3D elasticity theory along with the Rayleigh integral formula where Neumann’s addition theorem is incorporated in the associated Hankel transform representation to arrive at a computationally efficient expression for the nonaxisymmetric pressure field within the acoustic half-space, valid in both near and far fields. Subspace system identification of the fully coupled structure–fluid interaction problem is performed, and the truncated modes are considered as multiplicative uncertainties in synthesis of the mixed-norm controller. Numerical simulations establish the ability of the implemented volumetric sensing/actuation methodology in cooperation with the multi-objective robust active control scheme for restraining low-frequency sound radiation from a [Formula: see text]/steel/PZT4 circular piezo-laminated plate, without provoking instability of the closed-loop system. Also, superior bandwidth frequency and tracking performance in comparison to the [Formula: see text] and [Formula: see text] controllers are observed. This work is believed to be the first such attempt to exactly model (and actively control) the 3D nonaxisymmetric acousto-elastodynamic frequency response of an arbitrarily thick, smart piezo-laminated circular plate in heavy fluid loading condition (i.e. without using any kind of far-field, low-frequency, and/or light fluid coupling approximations), with straightforward extensibility for any arbitrary through-thickness variation of distributed material properties.

Active Control of Structural Sound Radiation in an Acoustic Enclosure Using Distributed Point Force Actuators

This paper demonstrates an investigation about the active control of sound radiation in the enclosure cavity consists of two flexible plates. One of the flexible plates is driven by a point force to generate the primary sound field in the cavity, and using some point forces which are located at different locations on the receiving plate to suppressing the panel vibration and then to minimum the cavity sound pressure level (SPL); meanwhile some actuators are located on the other panel surfaces to reduce the sound pressure level at some frequencies that can’t be well reduced by only effect on one panel. The better result shows the possibility of applying distributed cooperative control method to the structural-acoustic coupled system.

Active sound radiation control of a submerged piezocomposite hollow sphere

A spatial state-space approach based on the linear three-dimensional exact piezoelasticity theory along with the Helmholtz equations for the internal/external acoustic domains are employed to describe the coupled vibroacoustic response of an arbitrarily thick, spherically isotropic, functionally graded, radially polarized piezolaminated hollow sphere, immersed in and filled with ideal compressible fluids, and under the actions of arbitrary (non-axisymmetric) distributed time-harmonic transverse mechanical excitations at its inner and/or outer boundaries. A frequency domain subspace–based identification technique is applied to estimate the coupled fluid-structure dynamics of the system in the controller design stage. Subsequently, a standard linear quadratic Gaussian optimal controller is synthesized and simulated based on the identified model, and the optimal control input voltages for suppressing the sensor output voltage (total radiated power) of the submerged sphere are calculated for selected weighting parameters associated with the system response and control input. Numerical simulations establish the effectiveness of the selected (partial/full) sensor/actuator configuration in conjunction with the adopted control strategy for attenuating the predicted sound radiation response of an air-filled, water-submerged, sandwich piezocomposite (PZT4/steel/PZT4) sphere, in both frequency and time domains. Also, the trade-off between dynamic performance and control effort penalty is examined for impulsive and Gaussian random external mechanical disturbances. Furthermore, the effect of piezoelectric material gradient variation on sound radiation control performance of the smart piezocomposite structure is briefly discussed. The validity of the acousto-elastic model is demonstrated by use of a commercial finite element package as well as by comparison with the data available in the literature.

Active sound radiation control of a thick piezolaminated smart rectangular plate

A spatial state-space formulation based on the linear three-dimensional piezoelasticity theory in conjunction with the classical Rayleigh integral acoustic radiation model is employed to obtain a semi-analytic solution for the coupled vibroacoustic response of a simply supported, arbitrarily thick, piezolaminated rectangular plate, set in an infinite rigid baffle. The smart structure is composed of an orthotropic supporting core layer integrated with matched volume velocity spatially distributed piezoelectric sensor and uniform force actuator layers. To assist controller design, a frequency-domain subspace-based identification technique is applied to estimate the coupled fluid–structure dynamics of the system. A standard linear quadratic Gaussian (LQG) optimal controller is subsequently synthesized and simulated based on the identified model and the optimal control input voltage for minimizing the estimated net volume velocity (total radiated power) of the panel is calculated in both frequency and time domains. Numerical simulations demonstrate the effectiveness of the adopted volumetric sensing/actuation technique in conjunction with the optimal control strategy for suppressing the predicted sound radiation response of a three-layered (Ba2NaNb5O15/Al/PZT4) sandwich panel in both frequency and time domains. The trade-off between dynamic performance and control effort penalty is examined for two different types of loading (i.e., impulsive and broadband random disturbances). Validity of the results is demonstrated by comparison with a commercial finite element package, as well as with the data available in the literature.

Active control of acoustic radiation from laminated cylindrical shells integrated with a piezoelectric layer

Active control of sound radiation from piezoelectric laminated cylindrical shells is theoretically investigated in the wavenumber domain. The governing equations of the smart cylindrical shells are derived by using first-order shear deformation theory. The smart layer is divided into lots of actuator patches, each of which is coated with two very thin electrodes at its inner and outer surfaces. Proportional derivative negative feedback control is applied to the actuator patches and the stiffness of the controlled layer is derived in the wavenumber domain. The equivalent driving forces and moments generated by the piezoelectric layer can produce distinct sound radiation. Large actuator patches cause strong wavenumber conversion and fluctuation of the far-field sound pressure, and do not make any contribution to sound reduction. Nevertheless, suitable small actuator patches induce weak wavenumber conversion and play an important role in the suppression of vibration and acoustic power. The derivative gain of the active control can effectively suppress sound radiation from smart cylindrical shells. The effects of small proportional gain on the sound field can be neglected, but large proportional gain has a great impact on the acoustic radiation of cylindrical shells. The influence of different piezoelectric materials on the acoustic power is described in the numerical results.

Dynamic behaviour and active sound radiation control of a two-stage vibration isolation system equipped on a flexible plate

This paper presents a general model of a two-stage vibration isolation system involving a flexible base plate with arbitrary boundary conditions. The dynamic behavior of the coupling system was obtained by using an impedance method in which the impedance matrix of the base plate was derived from a combined use of an improved Fourier series expansion and the Rayleigh-Ritz method. Subsequently, with the purpose of attenuation of sound radiation from the base plate structure, the optimal force information is formulated under various active control strategies including: 1) minimizing the total vibratory power of the coupled structure, 2) minimizing the sound power radiation from the base plate, 3) minimizing the vibratory power transmitted to the base plate, and 4) minimizing the mean square velocities at the isolator locations on the flexible plate. Numerical results were presented and discussed in detail. Finally, some concluding remarks are made.

Active control of sound radiation and transmission into a cavity consisting of multi-flexible plates

This paper presents an investigation into the active control of sound radiation and transmission into a structural-acoustic coupled system. A rectangular enclosure involving two simply supported flexible plates is considered. One of the two plates is driven by the combination of a point force and incident plane wave. The characteristics of the coupled system with two plates are described by a modal superposition method. The differences between our model and one-plate model are analyzed. Then, the locations of point force actuators for effective control are determined by considering three aspects: the noise reduction level, control force amplitude and structural vibration level. The control mechanisms and performances for the enclosure are determined when one, two and three control forces are applied on one of the plates. The results demon¬strate that acoustic potential energy in the enclosure, kinetic energy of the two plates and the maximum amplitude of optimal control force are greatly reduced when multiple actuators are used. Considering the practical feasibility, the local control is also examined, and the performances of the local and global control are compared by simulations.

Comparison of Passive and Active Methods for Minimization of Sound Radiation by Vibrating Clamped Plate

The paper is an analytical and experimental study of a smart structure consisting of steel plate with bonded piezoelectric transducers and porous elastomer layer. Active control of sound radiation from a plate clamped at the edge square is examined. Simulations and numerical computation of the experiment are performed in Ansys environment. Calculations of plate vibration and sound radiation under stepped harmonic force are performed. The experimental setup consists of two rooms with the test opening in between. A variety of test cases were studied for three different configurations: steel plate + piezoelectric transducer, steel plate + elastomer layer, steel plate + piezoelectric transducer + elastomer layer. The aim of the paper is to illustrate the possibilities of using piezoelectric materials as an active control with elastomer layers as passive methods in one structure to improve the transmission loss.

Secondary actuation and error sensing for active acoustic structure

A typical approach to active control of sound radiation or transmission from vibrating structures involves active structural acoustic control (ASAC) and active noise control (ANC), which introduce respectively force input and compacted sound source to apply on or be close to the vibrating structure. However, for the ASAC approach, arrangement for secondary force and error sensor is heavily dependent upon the properties of the primary structure and acoustical space; for the ANC approach, a large number of compacted secondary sources are required. Hence, in this paper, based on distributed secondary sound source and near-field error sensor, active acoustic structure is proposed to construct adaptive or smart structure as a versatile module or element for controlling sound radiation or transmission at low frequencies. First, a theoretical model based on a minimization of the total sound radiation from the primary and secondary panel is established, after which, taking into consideration the relationship between the vibration modes pattern and sound radiation characteristics for secondary panels, optimal arrangement for the secondary panels is examined in detail. Finally, a near-field pressure-based error sensing approach is presented, based on two kinds of object function, and active control of sound radiation is performed.

The design of structural acoustic sensors for active control of sound radiation intoenclosures

This paper introduces a design method for polyvinylidene fluoride (PVDF) structuralacoustic sensors for the active control of sound radiation into enclosures. It combinesgenetic algorithms and the quadratic optimal approach to search for a sensor configurationcapable of detecting vibration components with strong sound-radiation ability. In thisresearch, one PVDF sensor is not limited to one single piece of continuous PVDF film. Itcan consist of a cluster of small PVDF pieces, which could be discrete. Therefore, theparameters to be optimized are the number and the locations of PVDF pieces involved in asensor. The design method is applied to a cylindrical shell with a floor partition. Thegeneral design guidelines are discussed. To show the effectiveness of the method, thecontrol performance of an optimal sensor arrangement is compared with that ofnon-optimal ones. Physical insights are obtained using structural modal responseanalysis, modal spectrum analysis of the PVDF sensor output, and structuralacoustical coupling analysis. The performance of a PVDF sensor configurationdesigned at one acoustic resonant frequency is also investigated for other disturbancefrequencies below 500 Hz, showing that a significant reduction of acoustic potentialenergy can be achieved over a wide frequency range. It is demonstrated that,with PVDF sensors optimally designed using the proposed method, the activecontrol of sound radiation into enclosures can be achieved without using acoustictransducers.

A detailed experimental comparison between active and passive approaches for the reduction of total far-field radiated sound power from a point-driven simply support plate

Passive and active control of sound radiation from plates has been a challenging problem for a number of years where numerous surface treatments have been examined. The two most viable active surface treatments are active constrained layer damping (ACLD) and modal restructuring (MR). ACLD minimizes the total radiated power through a combination passive/active damping mechanisms as well as by applying restoring forces/moments. MR, on the other hand, achieves far-field attenuation by reducing the plates radiation efficiency through a restructuring of its mode shape. These active approaches show considerably more performance when compared to an optimized (Ross–Kerwin–Ungar) passive constraint layer damping design. The performance is evaluated by scanning near-field acoustic holography (NAH) measurements at several mode frequencies associated with strong radiation. The quantities determined via NAH include the power radiated in the half space as well as spatially dense surface motions of the plate. Both ACLD and MR show ∼50 dB reductions of total far-field radiated sound power (per unit input power). These experimental results will be discussed with particular emphasis placed on the tradeoffs between the passive and active surface treatments as well as the level of performance that can be obtained through other control approaches.

Active Control of Sound Radiation by Structures Using Near-field Sensing Strategies

Active Control of Sound Radiation by Structures Using Near-field Sensing Strategies