Active Structural Acoustic Control System Research Articles

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.

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.

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.

Active structural acoustic control of helicopter interior multifrequency noise using input-output-based hybrid control

This paper presents the recent advances in reduction of multifrequency noise inside helicopter cabin using an active structural acoustic control system, which is based on active gearbox struts technical approach. To attenuate the multifrequency gearbox vibrations and resulting noise, a new scheme of discrete model predictive sliding mode control has been proposed based on controlled auto-regressive moving average model. Its implementation only needs input/output data, hence a broader frequency range of controlled system is modelled and the burden on the state observer design is released. Furthermore, a new iteration form of the algorithm is designed, improving the developing efficiency and run speed. To verify the algorithm's effectiveness and self-adaptability, experiments of real-time active control are performed on a newly developed helicopter model system. The helicopter model can generate gear meshing vibration/noise similar to a real helicopter with specially designed gearbox and active struts. The algorithm's control abilities are sufficiently checked by single-input single-output and multiple-input multiple-output experiments via different feedback strategies progressively: (1) control gear meshing noise through attenuating vibrations at the key points on the transmission path, (2) directly control the gear meshing noise in the cabin using the actuators. Results confirm that the active control system is practical for cancelling multifrequency helicopter interior noise, which also weakens the frequency-modulation of the tones. For many cases, the attenuations of the measured noise exceed the level of 15dB, with maximum reduction reaching 31dB. Also, the control process is demonstrated to be smoother and faster.

Experimental Realization of a Sound Radiation Filter for Feedforward Control to Improve Active Structural Acoustic Control Systems

Due to the strengthened CO2 and NOx regulations, future vehicles have to be lightweight and efficient. But, lightweight structures are prone to vibrations and radiate sound efficiently. Therefore, many active control approaches are studied to lower noise radiation besides the passive methods. One active approach for reducing Sound radiation from structures is the active structural acoustic control (ASAC). Since the early 90’s, several theoretical studies regarding ASAC systems were presented, but only very little experimental investigations can be found for this alternative to passive damping solutions. The theoretical simulations show promising results of ASAC systems compared to active vibration control approaches. So, for that reason in this paper an experiment is conducted to investigate the performance of an ASAC system in the frequency range up to 600 Hz. A regular sensor grid of 24 accelerometers that are interconnected to establish six radiation signals is applied to an aluminum plate. The plate is excited by a point force and the feedforward control system counteracts these vibrations with 2 inertial actuators. The radiated sound power can be reduced by 4 dB integrated over the targeted frequency band. Compared to an active vibration control system which results only in a 0.2 dB decreased sound radiation, the ASAC system is beneficial. Furthermore, the filter length and the causality aspect of the experiments are analyzed in order to investigate the digital signal processing requirements. It can be shown that short filters are sufficient for an ASAC System compared to the filter length needed for an AVC system. In the last part of this paper some technical simplifications are investigated in order to reduce the complexity of the sound Radiation filters. It is shown that the high pass filters needed to model the radiation efficiency can be neglected with a very small loss of performance.

Vibro-acoustic model of an active aircraft cabin window

This paper presents modeling and design of an active structural acoustic control (ASAC) system for controlling the low frequency sound field transmitted through an aircraft cabin window. The system uses stacked piezoelectric elements arranged in a manner to generate out-of-plane actuation point forces acting on the window panel boundaries. A theoretical vibro-acoustic model for an active quadruple-panel system is developed to characterize the dynamic behavior of the system and achieve a good understanding of the active control performance and the physical phenomena of the sound transmission loss (STL) characteristics. The quadruple-panel system represents the passenger window design used in some classes of modern aircraft with an exterior double pane of Plexiglas, an interior dust cover pane and a glazed dimmable pane, all separated by thin air cavities. The STL characteristics of identical pane window configurations with different piezoelectric actuator sets are analyzed. A parametric study describes the influence of important active parameters, such as the input voltage, number and location of the actuator elements, on the STL is investigated. In addition, a mathematical model for obtaining the optimal input voltage is developed to improve the acoustic attenuation capability of the control system. In general, the achieved results indicate that the proposed ASAC design offers a considerable improvement in the passive sound loss performance of cabin window design without significant effects, such as weight increase, on the original design. Also, the results show that the acoustic control of the active model with piezoelectric actuators bonded to the dust cover pane generates high structural vibrations in the radiating panel (dust cover) and an increase in sound power radiation. High active acoustic attenuation can be achieved by designing the ASAC system to apply active control forces on the inner Plexiglas panel or dimmable panel by installing the actuators on the boundaries of one of the two panels. In some cases, increasing the actuator numbers in the structure advances the active control performance by controlling more structural modes; however, this decreases the STL of the passive control system because of the increase in structure-borne sound transmission paths of the stiffer piezoelectric actuators.

Active structural acoustic control using the remote sensor method

Active structural acoustic control (ASAC) is an effective method of reducing the sound radiation from vibrating structures. In order to implement ASAC systems using only structural actuators and sensors, it is necessary to employ a model of the sound radiation from the structure. Such models have been presented in the literature for simple structures, such as baffled rectangular plates, and methods of determining the radiation modes of more complex practical structures using experimental data have also been explored. A similar problem arises in the context of active noise control, where cancellation of a disturbance is required at positions in space where it is not possible to locate a physical error microphone. In this case the signals at the cancellation points can be estimated from the outputs of remotely located measurement sensors using the “remote microphone method”. This remote microphone method is extended here to the ASAC problem, in which the pressures at a number of microphone locations must be estimated from measurements on the structure of the radiating system. The control and estimation strategies are described and the performance is assessed for a typical structural radiation problem.

Design of Shaped PVDF Radiation Mode Sensor and its Application in Active Structural Acoustic Control System

This paper presents a new strategy for the design of radiation mode sensors by using shaped PVDF films for one-dimension structures. Based on a modal approach, the shape of a PVDF sensor is analytically determined in such a way that the output signal of the sensor is directly proportional to amplitude of a particular radiation mode. Other modes are filtered out. A general expression of the PVDF sensor shape is obtained. It is found that the modal sensor shape can be expressed as a function of the second spatial derivative of the structural mode shape function. Finally, with an example of a vibrating beam, the proposed PVDF radiation mode sensor is used in an active structural acoustic control system for reduction of the structural-borne noise.

Experimental investigation of different active noise control concepts applied to a passenger car equipped with an active windshield

The main purpose of this work is the implementation and experimental investigation of different active structural acoustic control (ASAC) concepts for the reduction of interior noise in an automobile passenger compartment. For the control experiments, a medium-class test car was used, which had been equipped with an active windshield. The active windshield consists of the serial-production laminated glass pane augmented with piezoceramic patch-transducers applied to the blackened rim of the windshield. A multi-reference test provided measurement data for the identification of a local discrete-time state-space model (SSM). The subsequent acquisition of frequency response functions (FRF) by way of using the same actuators but measuring on a much finer grid provided the database for the formulation of a least-squares problem to derive a global system model. Based on the local and global discrete-time SSMs, different controllers were designed and experimentally realized. The comparison of the vibration levels in open- and closed-loop showed a global reduction of 5–7dB in the acoustically relevant frequency band containing the second and third structural resonance of the windshield system. The occurrence of complex operational deflection shapes (ODS) was identified as the main limitation concerning the disturbance rejection of the active system. The acoustic performance of the ASAC system is reflected in a reduction up to 15dB in sound pressure level (SPL).

Active control of structurally radiated sound from an elastic cylindrical shell

A numerical and experimental study was presented on active control of structurally radiated sound from an elastic cylindrical shell. An analytical model was developed for the active structural acoustic control (ASAC) of the cylindrical shell. Both global and local control strategies were considered. The optimal control forces corresponding to each control strategy were obtained by using the linear quadratic optimal control theory. Numerical simulations were performed to examine and analyze the control performance under different control strategies. The results show that global sound attenuation of the cylindrical shell at resonance frequencies can be achieved by using point force as the control input of the ASAC system. Better control performance can be obtained under the control strategy of minimization of the radiated sound power. However, control spillover may occur at off-resonance frequencies with the control strategy of structural kinetic energy minimization in terms of the radiated sound power. Considerable levels of global sound attenuation can also be achieved in the on-resonance cases with the local control strategy, i.e., minimization of the mean-square velocity of finite discrete locations. An ASAC experiment using an FXLMS algorithm was implemented, agreement was observed between the numerical and experimental results, and successful attenuation of structural vibration and radiated sound was achieved.

Analytical and experimental study on active control of structurally radiated sound from an elastic cylindrical shell.

This paper presents an analytical and experimental study on active control of structurally radiated sound from an elastic cylindrical shell. An analytical model is developed for the active structural acoustic control (ASAC) of the cylindrical shell. The structural response of a cylindrical shell to the harmonic point force is derived by applying the modal supposition method. Expressions for the far-field radiated sound pressure and radiated sound power are derived by using the Kirchhoff–Helmholtz integral and the appropriate Green’s function. Both global and local control strategies are considered. The optimal control forces corresponding to each control strategy are obtained by using the linear quadratic optimal control theory. Numerical simulations are performed to examine and analyze the control performance under different control strategies. Results show that using point force as the control input of the ASAC system can achieve the global sound attenuation of the cylindrical shell at resonance frequencies. Better control performance can be obtained under the control strategy of minimization of the radiated sound power in terms of the radiated sound power. However, control spillover may occur at off-resonance frequencies with the structural kinetic energy minimization strategy. ASAC experiment was implemented, good agreement was observed between the numerical and experimental results, and successful attenuation of structural vibration and radiated sound was achieved.

Active structural acoustic control for a truck oil pan: Actuator placement and efficiency estimation

The oil pan of large diesel engine trucks is identified as a significant contributor to their external noise radiation. This undesired broadband noise is caused by the oil pan's structural vibration and cannot be treated effectively by passive measures, especially in the low frequency range up to 500 Hz. In order to address this challenge, an Active Structural Acoustic Control (ASAC) system was to be realized within the European Union (EU) project �Intelligent Materials for Active Noise Reduction� for the oil pan of a Volvo MD13 truck engine. The technological demonstration was conducted in a laboratory test stand and employs piezoceramic patch actuators to alter the vibrations in a broadband noise reduction manner. The following paper focuses on the tasks of deriving actuator placement and estimating respective broadband sound power minimization capability. First, the oil pan's structural response to typical force excitation at its mounting points was analyzed through finite element simulation, and an actuator placement was derived. The estimation of its sound power minimization capability was then established based on computed structural frequency response functions and numerically derived radiation modes. Finally, the actuator layout was transferred to a serial production oil pan and adjusted by experimental observations

The design of synthesized structural acoustic sensors for active control of interior noise with experimental validation

In this paper, the feasibility of using synthesized structural acoustic sensors (SSAS) for active noise control inside irregularly shaped enclosures is investigated. A SSAS consists of a cluster of inter-connected discrete PVDF elements, located on the surface of a vibrating structure enclosing a sound field. An optimal design ensures the sensor output to be directly related to the acoustical potential energy inside the enclosure. Hence, synthesized structural acoustic sensors can provide error signals for an active noise control system, and the use of microphones inside the enclosure can be avoided. A cylindrical shell with a floor partition, which can be used to model an aircraft cabin, is used as a test case. PZT actuators are used as control actuators. Both SISO (single input and single output) and MIMO (multi-input and multi-output) control systems are optimally designed using Genetic Algorithms and implemented with a Filtered-X Feedforward LMS (least-mean-square) controller. Their control performances are evaluated with different types of disturbances. To show the effectiveness of the optimal design approach, some non-optimal control systems are also tested and compared with the optimal one. It is shown that with optimally designed SSAS, an active structural acoustic control system can effectively reduce noise inside the enclosures without using any acoustic transducers.

Active structural acoustic control of repetitive impact noise

This paper discusses the effectiveness of an Active Structural Acoustic Control (ASAC) system for the reduction of repetitive impact noise, radiated by structures with a high modal density in the controlled frequency range. Although there is a significant difference in nature between periodic and transient noise, up till now no specific research on ASAC of transient noise was reported. The development of the ASAC system is divided into two phases: the definition of the control configuration and the design of a suitable control algorithm. The optimal control configuration as well as the implemented control algorithm for the reduction of impact noise differ significantly from the common solutions in periodic noise control. In the first part of the paper, a practical methodology is presented to define a good control arrangement for transient noise control. The second part of the paper focuses on the design of control algorithms, adapted to the specific properties of impact noise. Since many industrial impact noise problems involve successive impacts with a repetitive behaviour, control algorithms with a learning behaviour are discussed. The efficiency of these Iterative Learning Control (ILC) algorithms is extensively demonstrated in this paper. The developed ASAC strategy has been verified on a thick steel plate, which is excited by successive impacts. The obtained results show that ASAC can be a very efficient transient noise control technique in certain industrial applications (e.g. presses, punching machines, etc.).

Sound Radiation of a Large Truck Oil Pan: Estimation and Experimental Investigation

The oil pan of large diesel engine trucks has been identified as a significant contributor to their external noise radiation. This undesired broadband noise is caused by the oil pan's structural vibration and can not be treated effectively by passive measures especially in the low frequency regime up to 500Hz. In order to address this challenge, an active structural acoustic control system consisting of structural sensors and actuators is suitable to alter the oil pans vibrations in a sound reducing manner. A first step is however to classify the broadband sound radiation such that it allows for a proper and efficient sound power estimation resulting from structural measurements. Therefore, an acoustical model was set up based on a geometrical surface scan of a serial production large truck oil pan mounted in a laboratory test stand. This model served for the numerical computation of a set of principle velocity patterns contributing independently to the active sound power, where its hybrid estimation has been performed employing additionally the measured structural response of the oil pan assembly due to a shaker excitation. Finally, the sound power radiation of the test stand has been measured in a reverberation room to validate this hybrid estimation.

Active structural acoustic control for an enclosure using subjective measures

In order to improve subjective effects, the response of human auditory system is taken into account in active structural acoustic control (ASAC) by adding several loudness filters in the system. The audio frequencies, which human ear is insensitive to, are attenuated properly by those filters, while sensitive frequencies are amplified. Loudness-LMS algorithm is derived and used in ASAC system. As an example, the new ASAC is applied to a rectangular enclosure. A comparison is made between the new and conventional ASAC system. The simulation results indicate that the new ASAC can achieve better subjective effects than the conventional system.

Analytical modeling of active structural acoustic control

AbstractSince the reduction of disturbing noise is highly important in industrial and civil engineering, much research and development has been done in this field over the past decades. The application of smart structures provides a way to reduce unwanted noise radiation. A smart structure is an integrated system consisting of the passive base structure attached with actuators and sensors. Piezoelectric ceramics are widely used as sensors and actuators, because they can easily be bonded on or imbedded into conventional structures. An often used concept for noise reduction is active structural acoustic control (ASAC). This concept means that the noise radiation will be reduced by minimizing or changing the vibrational behavior of a structure using additional actuator forces. The development and industrial use of smart structures for ASAC requires efficient and reliable simulation and design tools. Usually the design process of smart structures is based on numerical methods. In order to verify numerical techniques, the paper presents an analytical reference solution for an ASAC system. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Feasibility analysis of an active technology to improve acoustic comfort in buildings

In buildings, windows and glazed facades are often the preferred noise path for exterior disturbing noise towards the interior. Since passive means for improving sound transmission loss (STL) of glazed facades are very expensive and are effective only at high frequencies, an active controller that increases the STL in the low-frequency range is an attractive approach for reducing the noise level in buildings with glazed facades, guaranteeing the performance required by the 89/106/CEE European Directive, which made protection against noise a compulsory requirement for buildings. As buildings are often inserted in highly inhabited urban areas, near infrastructures and plants radiating high noise levels, the strategic importance of this task is increasing, together with the importance of acoustic comfort inside buildings.This paper concerns a feasibility study on the implementation of an active structural control system for glazed facades, in order to improve their STL at low frequencies. At present, applications for the reduction of noise level inside cars and planes are known. Relative to the use of active structural acoustic control (ASAC) systems, these systems are based on the reduction of structural vibrations through the use of actuators bonded on the vibrating surfaces, driven by an automated control system, whose task is minimizing those vibrations, and the radiated sound as a consequence. In this work, it is shown that actuators bonded on the vibrating surfaces, driven by an automated control system, are able to dramatically reduce those vibrations and, consequently, the radiated sound. The proposed technology is tested through experiments and numerical simulations, in order to compute the reduction of interior noise that could be pursued through the use of piezoelectric stack actuators.

Optimal design of PZT actuators in active structural acoustic control of a cylindrical shell with a floor partition

Genetic algorithms (GAs) are employed to optimize locations of PZT actuators in an active structural acoustic control (ASAC) system comprising a cylindrical shell with an internal floor partition. The effect of PZT actuators is simulated using a bending model and an in-plane force model, respectively. The characteristics of the optimal placements of both models are discussed and compared. Numerical simulations demonstrate that for the investigated structure, the in-plane force model has a better control performance than the bending model in the low-frequency range. The underlying physics of the control results are analyzed. Considering the practical applicability of optimally designed ASAC systems, the control performance of the optimal configuration obtained at a single frequency is assessed in the low-frequency range between 100 and 500 Hz, with results showing a significant sound attenuation in the whole range of interest.

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In this paper, through the study on locations of structural transducers for active control of the radiated sound from the vibrating plate, the active structural acoustic control (ASAC) system is proposed. And, for the evaluation of the proposed location, the experiment of the active structural acoustic control is implemented using the multi-channel filtered-x LMS algorithm and an additional filter (Acoustic Prediction Filter) to estimate the radiated sound using the acceleration signals of the plate. The structural transducers are piezoceramic actuator (PZT) and accelerometer. PZT is used as an actuator to reduce the vibration and the radiated sound. To maximize the control performance, each PZT actuator is located at the position that has the largest control sensitivity of the plate bending moment in the direction of x and y coordinates and the optimal PZT location is validated experimentally. Also, to find the acoustic prediction filter accurately, two accelerometers are located at the positions that have the largest radiation efficiencies of the plate, and the proposed locations are validated by simulation using the Rayleigh integral. The multi-channel filtered-x LMS algorithm is introduced to control a complex 2-D structural vibration mode. Finding the locations of structural transducers for active structural acoustic control of the radiated sound, the active structural acoustic control (ASAC) system can be presented and validated by experiments using a real time control system.