Active Structural Acoustic Control Research Articles

Double Panel Structure for Active Control of Noise Transmission

Passive noise reduction means are commonly used to reduce noise in the industry but, unfortunately, their effectiveness is poor in the low frequency range. By applying active structural acoustic control to the enclosure walls significant improvement of the insulating properties in this frequency range can be achieved. In this paper a model of double panel structure with ASAC is presented. The structure consists of two aluminium plates separated by an air gap. Two inertial magnetoelectric actuators and two piezoceramic MFC sensors were used for controlling the structure. A multichannel FxLMS algorithm with virtual error microphone technique is used as a control algorithm. The signal of a virtual error microphone is extrapolated basing on signals from MFC sensors. Performance of this actively controlled structure for tonal signals at selected frequencies is presented in the article. During the study, a double panel structure was mounted on one wall of sound insulating enclosure located in an acoustic chamber. During the measurements local and global reduction of noise test signal was investigated.

Active nonreciprocal structural control on a flexible plate

Reciprocity is an acoustic property that describes the symmetry of sound transmission between two points. However, this property is undesirable in certain applications, and this has led to significant interest in the development of nonreciprocal acoustic devices that achieve one-way sound transmission. These devices typically achieve nonreciprocal sound transmission by introducing nonlinearities or directional biasing. Previously proposed nonreciprocal acoustic devices generally have limitations; for example, they may not be fully adaptable, they can introduce signal distortions such as additional harmonics, or they can only exhibit nonreciprocal behaviour over a narrow bandwidth. To overcome these challenges, previous work has demonstrated how an wave-based active control system can be used to drive an array of acoustic sources to achieve reversible and broadband non-reciprocal behaviour. This paper aims to extend this concept to a linear wave-based active structural-acoustic control system that uses an array of structural actuators to control the individual wave components to achieve broadband nonreciprocal transmission through a flexible plate in a three-dimensional environment. The performance of the wave-based active controller has been investigated at a range of incident angles and the limits of this controller have been identified.

Sound transmission loss of a sandwich functionally graded cylindrical shell integrated with magneto-electro-elastic patches

Magneto-electro-elastic materials offers the inherent capability of energy transformation from one type to another, hence making them suitable for improving the vibroacoustic behavior of the structures. The current article is an analytical investigation into the sound transmission characteristics of a smart functionally graded cylindrical shell equipped with magneto-electro-elastic patches while a steady fluid flow exists outside of the cylinder. The complete set of equations of motion are derived after accounting for all components of displacement according to the first-order shear deformation theory. The utilized patches are controlled via an electric field, indicating the smart nature of the structure. The Power-law model is adopted to calculate the effective mechanical properties of the functionally graded core layer. After defining proper boundary conditions, the vibroacoustic equations are obtained with the aid of Hamilton's principle. A comprehensive validation study is also conducted to show the reliability of the developed formulation. In addition, by examining the effect of a large number of electric, magnetic, flow Mach number, geometric and acoustic parameters, recommendations are made to effectively optimize similar structures that benefit from such materials. One of the important findings of this study is that applying electric and magnetic fields in the low frequency band improves the sound transmission loss. Therefore, the magneto-electro-elastic patches can be used in active structural acoustic control approaches as actuators.

Active structural acoustic control using the weighted sum of spatial gradients method

Active structural acoustic control focuses on implementing vibration-based control on a structure with the objective of achieving attenuation of the radiated acoustic field. It has been shown that utilizing control metrics that are integrally associated with the desired control result will generally lead to greatly improved control results. The weighted sum of spatial gradients (WSSG) method has been developed to provide global attenuation of the acoustic field radiated from a structure. It utilizes multiple spatial gradients that form the control metric, and which are correlated with various radiation mechanisms associated with the structure. The WSSG method will be briefly overviewed and the implementation of the method will be discussed. It will also be shown that the method is related to the concept of acoustic radiation modes, which have been used to describe radiation from structures. The WSSG method has been applied to several types of structures, and both computational and experimental results will be shown for flat plates and cylindrical shells to demonstrate the effectiveness of the control method.

Performance Analysis of Active Structural Acoustic Control Applied to a Washing Machine.

Great efforts are undertaken by scientists and manufacturers to reduce noise generated by devices present in the human environment. This task is particularly difficult in the case of low-frequency noise; however, active noise reduction methods can be a solution to such problems. The purpose of this article is to present the active noise-controlling casing method applied to a washing machine, whose noise generated during the spinning process is to be reduced. The paper presents a set of experimental measurements and analyses. It also provides hardware and software configuration details. The employed active control system can efficiently reduce noise, even by 16 dBA in the low-frequency range up to 300 Hz, which is an important step towards making the technology ready for manufacturing. The conclusions drawn are valid for different active noise-control applications, considering a variety of devices.

The optimal placement of piezoelectric actuator and sensor for active structural noise control of plates

The location optimization of actuators and sensors is a very important step when applying Active Structure Acoustic Control to practical engineering. A good actuator arrangement not only achieves a more effective control effect, but also reduces the required control energy, and a good sensor arrangement can help to collect more obvious and useful information. However, in some commonly used optimization programs, the influence of noise radiation is often ignored and only the controllability of structural vibration is concerned, which may cause the control force to control some modes with low noise radiation, but the modes that need to be controlled cannot be controlled. Therefore, this paper proposes a location optimization method of piezoelectric actuators and sensors in active noise control based on acoustic radiation, and formulates a new cost function, that is, the acoustic power is added as a weight function to the optimization criterion, so that the control energy can control these strong radiation modes as much as possible; at the same time, the Multi-Verse Optimizer algorithm is also improved, and through the optimization of the wormhole existence probability and travelling distance rate, the global search ability of the algorithm is improved to avoid the algorithm from entering the local in-depth development. In addition, the MVO algorithm suitable for continuous variables is discretized to adapt to the optimization problem in this paper.

Sound transmission through a panel with a hybrid active and semi-active control system

Semi-active control systems require significantly less energy than active solutions, while still providing substantial performance. However, active and semi-active systems can be applied in conjunction as hybrid systems, exploiting both solutions and providing high performance and reduced energy consumption. This paper proposes the use of such a hybrid active/semi-active control system for noise reduction barriers. Accounting for time-varying narrow-band noise, active structural acoustic control (ASAC) guarantees enhanced transmission loss for a noise barrier. Simultaneously, a semi-active element with a tunable mass moment of inertia allows the system to adapt to noise with varying characteristics by altering the mechanical properties of the barrier. Obtained control results demonstrate that the addition of a semi-active element is more effective than an additional active control actuator for reducing sound power in targeted frequency bands. Moreover, the proposed hybrid system may operate in two modes, allowing to further reduce overall energy consumption.

Active structural acoustic control for radiated sound power reduction of enclosure with vent holes based on radiation modes

Active structural acoustic control for radiated sound power reduction of enclosure with vent holes based on radiation modes

A compact active structural acoustic control method for minimizing radiated sound power

Active structural acoustic control is an active control method that controls a vibrating structure in a manner that reduces the sound power radiated from the structure. Such methods focus on attenuating some metric that results in attenuated sound power, while not necessarily minimizing the structural vibration. The work reported here outlines the weighted sum of spatial gradients (WSSG) control metric as a method to attenuate structural radiation. The WSSG method utilizes a compact error sensor that is able to measure the acceleration and the acceleration gradients at the sensor location. These vibration signals are combined into the WSSG metric in a manner that is closely related to the radiated sound power, such that minimizing the WSSG also results in a minimization of the sound power. The connection between WSSG and acoustic radiation modes will be highlighted. Computational and experimental results for both flat plates and cylindrical shells will be presented, indicating that the WSSG method can achieve near optimal attenuation of the radiated sound power with a minimum number of sensors.

Active structural acoustic control using an integrated control system with smart structures

An integrated control system with smart structure is proposed for active structural acoustic control (ASAC). It is mainly used to integrate the advantages of centralized and decentralized ASAC. Each smart structure contains a relatively independent controller, which forms a distributed control. The coordination and cooperation between smart structures is mainly realized by sending control factors (secondary generalized modal force) from the upper coordination unit (coordination structure) to each smart structure. The control factor can reflect the weight of each smart structure on vibration noise control, and play a key role in noise control. The control factors are extracted from the blend function in the bottom control units (smart structures) and stored in the coordination structure. This design method ensures the consistency of the internal functions of each smart structure and lays a foundation for decentralized control. In addition, whether the control factor is allocated to the smart structure depends on the real-time changes of the sound field. Through the intelligent allocation of the control factors, the global (centralized) control is realized and the coupling problem between smart structures is solved. Since the control system does not have a centralized controller, it appears as a decentralized control in form; at the same time, the centralized control in algorithm is achieved by extracting and redistributing the control factors. Therefore, the control system integrates the advantages of decentralized and centralized control.

Investigation of Low-Frequency Sound Radiation Characteristics and Active Control Mechanism of a Finite Cylindrical Shell

In this paper, the radiation characteristics and active structural acoustic control of a submerged cylindrical shell at low frequencies are investigated. First, the coupled vibro-acoustic equations for a submerged finite cylindrical shell are solved by a modal decomposition method, and the radiation impedance is obtained by the fast Fourier transform. The modal shapes of the first ten acoustic radiation modes and the structure-dependent radiation modes are presented. The relationships between the vibration modes and the radiation modes as well as the contributions of the radiation modes to the radiated sound power are given at low frequencies. Finally, active structural acoustic control of a submerged finite cylindrical shell is investigated by considering the fluid-structure coupled interactions. The physical mechanism of the active control is discussed based on the relationship between the vibration and radiation modes. The results showed that, at low frequencies, only the first several radiation modes contributed to the sound power radiated from a submerged finite cylindrical shell excited by a radial point force. By determining the radiation modes that dominate the contribution to the radiated sound, the physical mechanism of the active control is explained, providing a potential tool to allow active control of the vibro-acoustic responses of submerged structures more effectively.

Acoustic radiation-based optimization of the placement of actuators for active control of noise transmitted through plates

Active Structural Acoustic Control (ASAC) is mostly performed using a passive noise barrier, vibration actuators, sensors and a control system. ASAC reduces or alters the vibration of the barrier structure in a way that blocks the noise propagation through it. However, it is crucial that the actuators are appropriately arranged to be able to effectively control the vibration of the barrier. If the actuators were not optimally arranged, then certain modes of the structure may be uncontrollable, or require a very high control effort. Hence, the locations of the actuators should be determined by a careful optimization process employing a model of the structure. A common approach is to maximize the controllability of the system over a defined frequency range of operation. However, such an optimisation procedure often results in a solution that considers numerous vibration modes, only some of which are acoustically-relevant. That is, certain structural modes may vibrate considerably, but their contribution to the noise transmission and radiation would be negligible. Therefore, in the presented research a new acoustic radiation-based approach to the optimisation of the arrangement of actuators is proposed. A model of acoustic radiation is introduced and new cost functions are formulated to focus on modes that strongly contribute to noise transmission or radiation by the noise barrier. For the considered system, this enables an increase in the controllability measure of more than 5 dB for acoustically-relevant modes, which is similar to the level of improvement achieved when the number of actuators is doubled.

Simultaneous optimization of control parameters and placements of piezoelectric patches for active structural acoustic control of shell structures under random excitation

Simultaneous optimization of multiple parameters of an active structural acoustic control system under random force excitation is presented in this article. A method integrating the pseudo excitation method, finite element method, and boundary element method is proposed to analyze the random acoustic radiation. The active structural acoustic control of randomly vibrating structures is developed using the velocity feedback control scheme with the help of the pseudo excitation method. The acoustic design optimization model is proposed, in which the auto power spectral density of sound pressure is taken as the objective function and the placements of actuators/sensors as well as control gains are assigned as design variables. Taking into account the operational efficiency and control cost, the number of actuators/sensors and the total actuation energy are considered as constraints. A simulated annealing algorithm is employed for the optimization problem with discrete and continuous variables coexisting. Numerical examples are given to demonstrate the effectiveness of the proposed methods and the programs, and several key factors on the optimized designs are also discussed.

Active structural acoustic control using an experimentally identified radiation resistance matrix.

Active structural acoustic control (ASAC) is a widely used active noise control technique that provides control of structurally radiated noise through actuation of the radiating structure. Typically, ASAC drives structural actuators to minimise a real-time measurement of the radiated sound field. However, it is often not practical to position error microphones in the radiated sound field. To overcome this limitation, a number of methods have previously been proposed. One such method utilises the radiation resistance matrix to map structural response measurements to the acoustic response and, thus, enable an estimate of the structurally radiated sound power from structural measurements alone. This has previously relied upon precise modelling of the radiating structure which, for practical structures, can lead to limitations in the accuracy of the estimate. In this paper, an ASAC strategy that utilises an experimentally identified radiation resistance matrix is presented. The robustness of both the sound power estimation and the ASAC controller to system uncertainties is investigated, and it has been shown that the proposed ASAC strategy is able to achieve effective control of the radiated sound power.

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.

Active Structural Acoustic Control of an Active Casing Placed in a Corner

Electric appliances used in workplaces and everyday life often generate a low-frequency noise, which affects human body systems. Passive methods employed to reduce noise are not effective at low frequencies. The classical approach to active noise control practically involves the generation of local zones of quiet, whereas at other areas the noise is reinforced. Moreover, it usually requires a large number of secondary sound sources. Hence, an active casing approach has been developed. The active casing panels’ vibrations are controlled to reduce the device noise emission. Efficiency of this method has been previously confirmed by the authors and the results have been reported in multiple journal publications. However, in the previous research experiments, the active casing was placed at a distance from the enclosure walls. In this research, the active casing is located in a corner and such placement is intentionally used to facilitate the active control system’s operation. The noise reduction performance is investigated at multiple configurations, including a range of distances from the corner and different error microphone arrangements. The analysis of both primary and secondary paths is given. Advantages and drawbacks of different active casing configurations are presented and discussed.

A uniform theory of diffraction formulation for acoustic radiation modes

Acoustic radiation modes have recently regained the attention of the literature, with applications ranging from active structural acoustic control to acoustical holography. Typically the calculation of these modes requires boundary element methods for all but flat plate and full sphere geometries. This paper presents a radiation mode formulation for cylindrically curved structures with small curvature, based on the uniform theory of diffraction. This formulation shows promise, as it produces analytical expressions for the radiation resistance matrix, leading to computationally efficient radiation mode calculation. Radiation modes are shown for cylindrically curved plates, and the calculation of sound power with these modes is compared to that calculated using boundary element methods. The extension of this formulation to other curved structures is discussed.

Vehicle interior noise active control based on piezoelectric ceramic materials and improved fuzzy control algorithm

An active control approach for interior noise of vehicle based on the piezoelectric ceramic materials and fuzzy control algorithm is presented in this paper. According to the electromechanical coupling characteristics and the positive/inverse mechanism of a piezoelectric material, a theoretical model of piezoelectric ceramic plate with a sandwich structure is deduced by using impedance analysis method. The size of a piezoelectric ceramic transducer (or actuator) and its sticking position on the plate frame are determined. The structural modes and dynamic responses of a vehicle cavity model are calculated by finite element analysis for selecting optimal positions of actuator on the front wall. Furthermore, a fuzzy controller is designed for active vibration control. The fuzzy algorithm is improved by adjusting quantization factors, such as the deviation and its changing rate. Following the derived piezoelectric equations and the improved fuzzy algorithm, an active structural acoustic control (ASAC) system is developed and a functional prototype is set up by using the dSPACE platform. Experimental results show that the developed ASAC system can significantly reduce not only the vibrations of the front wall, but also the interior noises of the cavity. This implies that the proposed vibration-based ASAC method is effective and feasible, which might be a potential approach for interior noise control of vehicles.

A quasi-analytical formulation for acoustic radiation modes of simple curved structures

Acoustic radiation modes have become a useful and widespread analysis tool in situations involving sound radiation from vibrating structures. They have found use in applications such as active structural acoustic control, optimization of structures for minimal sound radiation, and acoustical holography. Analytical expressions for the radiation resistance matrix, from which the radiation modes are obtained, are available only for a small number of simple source geometries, while the obtaining of radiation modes for more complicated structures typically requires BEM or similar computational methods. This paper details the development of quasi-analytical expressions for the radiation resistance matrices of singly-curved structures such as curved plates, cylinders, and angularly truncated cylinders. It is shown that the radiation modes of these structures may be obtained with a relatively low computational load compared to conventional methods.

Active control of composite fuselage type structures with enclosed acoustic cavity

An active structural–acoustic control system for a composite fuselage type structure is developed in this paper. The focus of the active control system is the global reduction of the sound field in an enclosed acoustic cavity using structure-integrated sensors and actuators. Active structural–acoustic control systems are commonly designed based on the acoustic radiation modes which diagonalize a radiation operator. In the case of interior sound radiation, this radiation operator is derived in this paper from the coupled acoustic modes, which take into account the boundary conditions of the coupled velocity from the fuselage type structure. This results in frequency-independent radiation modes which do not rely on the validity of the modal interaction approach. The latter one violates the continuity condition of the velocity along the coupling surface. Parameter studies regarding active control implementations are conducted in order to evaluate how many radiation modes need to be considered for achieving a global sound attenuation.