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Methods and technologies to control the noise coming from turbulent flows impinging on outlet guide vanes in turbofan engines are tremendously needed nowadays to comply with new legislation on acoustic environment pollution. The following paper relies on preliminary research proposing a new experimental design of active noise control system to be further integrated into a jet engine outer guide vane prototype, consisting of multiple flush-mounted piezoelectric cells. Here, three active cells are placed on the bottom wall of a wind tunnel with upstream acoustic excitation generating grazing incident waves for different airflow velocities. Using a downstream microphone as an error sensor, the active system succeeds in improving the transmission loss of the sample by 2.5 dB at the target frequency (670 Hz) corresponding to the main piezo acoustic mode with airflow velocities up to 20 m.s−1. These early experimental results confirm the ability of the concept to interact with the ambient acoustics without disturbing the airflow as in passive solutions using porous materials, for instance, leading the path to future experiments with realistic turbulence generating acoustic sources on the leading edge of the vane profile. [ABSTRACT FROM AUTHOR]

In the process of turning a maglev motorized spindle, there are problems such as system model time-varying, cross-coupling of control parameters, difficult measurement of system state variables, and nonlinear characteristics of active magnetic bearings, which lead to the inevitable cutting chatter phenomenon, difficult control algorithm design, and then the reduction of workpiece surface quality and accuracy, affecting machining efficiency and tool life. In this paper, the "multimodal-distributed parameter" model is extended to the "magnetic bearing-rotor-workpiece" variable mass turning process. An adaptive backstepping fast dynamic terminal sliding mode control is designed to address the model's time-varying parameters and cross-coupling issues. In view of the difficulty in measuring the vibration displacement at the cutting point, the displacement field reconstruction method was introduced to reconstruct the vibration displacement field online and provide effective feedback for the previously designed control strategy. Finally, the proposed controller is applied to adjust and control the turning process of a maglev motorized spindle and compared with other advanced controllers. The simulation results show that the proposed control method has a better control effect than other control methods in the presence of unmodeled dynamics, uncertainties, and external disturbances. [ABSTRACT FROM AUTHOR]

The work tests and analyzes the engine noise distribution in a car with and without active control, where the car's built-in loudspeakers are used as secondary sources to attenuate the engine noise inside the whole cabin. To analyze the sound field in detail, the noise level at 52 microphones on the passenger ears' plane is measured and presented. The distributions of the primary overall noise, first four order noise of the engine, and the sound field generated by the subwoofer at engine orders' frequencies are reported, and the noise reductions corresponding to overall engine noise and each order's noise are analyzed. Besides, jury test is presented and compared with the calculated loudness of residual noise to evaluate the acoustic comfort improvement of the system. The experiment results show that the overall noise reduction is achieved inside the whole cabin by controlling the first four orders' engine noise. The average noise reduction of the measurement area inside the cabin is 6.2 dB and 2.9 dBA. Besides, 93% of the participants feel the acoustic comfort is improved with the active noise control system on. [ABSTRACT FROM AUTHOR]

This paper introduces an energy conversion inspired vibration control methodology and presents a representative prototype of tunable bi-stable energy converters. This work is concerned on improving energy conversion and absorption performance of tunable bi-stable clustered energy conversion inspired dynamic vibration absorbers (EC-DVAs). The deterministic parametric analysis of the energy transfer performance of clustered EC-DVAs is conducted. The nonlinear energy capture behaviors including transient energy transfer and snap-through motions are studied. It can be uniformly understood that the excellent energy transfer and conversion efficiency can be achieved by modulating the length ratio from 0.6 to 0.8. It is found that clustered EC-DVAs with four uniform cells and constant length ratio σ = 0.8 can obtain significant energy conversion and targeted energy transfer performance without requiring tedious active regulation when the system is subjected to wide-amplitude impulsive scenarios. Therefore, the proposed tunable bi-stable system composed of clustered EC-DVAs with state-of-the-art adaptive control strategies is a potential alternative for energy reuse and vibration suppression of mechanical components exposed to kaleidoscopic impulses. [ABSTRACT FROM AUTHOR]

Active control algorithms are widely used in enclosed-space noise control with the nonlinearities of secondary-source loudspeakers ignored. Inspired by nonlinear energy transfer resulting from nonlinear stiffness, this work concerns using a nonlinear loudspeaker to improve enclosed-space noise control. An enclosed-space active noise control system with a nonlinear loudspeaker is modeled. Based on the model, an approximate frequency response function of the noise control system is derived analytically via the harmonic balance method and verified using numerical methods. A globally consistent and bounded Lyapunov function is derived. The effects of the mass, nonlinear stiffness, volume, and area ratio on the noise reduction are also explored. Both analytical and numerical results demonstrate that the improved nonlinear loudspeaker is effective in improving the low-power characteristics of the loudspeaker, increasing noise reduction and improving fault-tolerant and robustness of the active noise control system. [ABSTRACT FROM AUTHOR]

Based on the traditional active noise control method, a phased-array secondary sound source was designed to replace the traditional sound source. Adopting a 4 × 4 array distributed design, we still maintain a single-in single-out system. Simulations show that the phased-array secondary sound source better controls noise reduction in a certain area of space, with better noise reduction effect, larger static area, and less impact on other non-control areas. A verification experiment was performed in a semi-anechoic chamber, with noise reduction conducted in different directions. The noise reduction effect of the phased-array secondary sound source was >10 dB higher than that of the traditional secondary sound source, with less influence on other points. The phased-array secondary sound source can be combined with tracking equipment to achieve a better follow-up noise reduction effect in space. [ABSTRACT FROM AUTHOR]

Noise reduction is very important for cavities such as long ventilation ducts, and train and airplane cabins. This paper seeks to develop, design, and implement an active noise control system to globally reduce narrowband and broadband acoustic noises inside a cylindrical cavity using the Modal FxLMS algorithm along with canceling the feedback effect of the actuator on the reference microphone. In addition, the efficiency of the proposed algorithm is compared to the conventional FxLMS algorithm for broadband noises in terms of acoustic potential energy and energy consumption of the actuators. To this end, the natural frequencies and mode shapes are derived using experimental methods and finite element simulation, and the results are compared. The modal data are used to design and implement a modal filter. The filter output is fed to the Modal FxLMS algorithm as the error signal for updating controller coefficients. Due to the presence of a reference microphone for the proposed algorithm and the effect of the control loudspeaker, it is required to remove the feedback effect. An experimental setup is developed, and an FPGA board and LabVIEW software are adopted to implement and verify the effectiveness of the proposed algorithm. The results indicate that the controller could effectively attenuate the narrowband and broadband acoustic noises globally. Furthermore, although the conventional FxLMS algorithm can suppress the noise around acoustic modes, it produces a larger control signal than the Modal FxLMS algorithm and consumes more energy. [ABSTRACT FROM AUTHOR]

This paper focuses on acoustic modeling for active noise control applications. The desired model must be finite dimensional and efficient numerically to meet implementation requirements. It must also be parameterized by the position considered inside the cavity. This additional characteristic is desirable for addressing specific active noise control applications such as optimizing microphone placement, estimating acoustic pressure at different positions of the considered cavity, and finally attenuating noise level in a subarea of the cavity. The main contribution of this paper is to propose a finite-dimensional, low-order, and parameterized acoustic model of a cavity, suitable for active noise control applications. The resulting model is defined as a gray box that combines a one-dimensional analytical model of acoustic propagation, which handles the physical parameterization, and a black-box model that copes with actuator and sensor dynamics as well as modeling errors. The parameters of the proposed model are optimized in order to reproduce the frequency behavior of the real system (LS2N active noise control platform) in a frequency range. This model allows one to accurately reproduce the dynamics at any position in the considered cavity. The prediction performance of the proposed model was compared to a classical black-box model (usually used for active noise control applications) and validated experimentally using the LS2N active noise control platform. The analysis highlighted that the proposed gray-box model can predict the acoustic behavior in a great range of positions. [ABSTRACT FROM AUTHOR]

In this study, a computational optimization framework is presented to identify active noise control systems for vehicle enclosures. The adopted optimization approach determines optimum configuration of an array of secondary sound sources to suppress noises with low frequency (under 500 Hz) due to engine performance. The overall framework is conducted via a particle swarm optimization algorithm coupled with a modified modal interaction method developed to estimate sound field inside enclosures. The applicability of the proposed optimization approach has been examined with two enclosures of different size by considering 1-speaker and 2-speaker array options as a secondary sound source. The numerical investigation shows that, with the determined optimum configurations, a significant noise reduction may be obtained in vehicle enclosures. [ABSTRACT FROM AUTHOR]

Conventional adaptive filters for active noise control (ANC) are troubled by the trade-off between convergence speed and steady state error, especially when nonlinearity plays an important role in system model. In this paper, a hybrid ANC algorithm called FBFLANN is constructed by the collaboration of FIR and bilinear functional link artificial neural network. The characteristics of linear and nonlinear sub-filters are analyzed and utilized to facilitate the adaptability in noise reduction. A convex factor is employed to automatically balance the contribution of two sub-filters, achieving faster convergence and higher accuracy in the presence of nonlinear distortions. The mathematical working and updating rules of the controller are derived to regulate the ANC process theoretically. The effectiveness of the proposed FBFLANN algorithm is demonstrated by numerous simulation studies considering diverse nonlinear acoustic path models as well as acoustic feedback interference. Hardware ANC platform is built up to verify the real-time noise control performance in physical noisy environments. The simulation and experiment results confirm the applicability and prospects for further development of the presented architecture in noise control scenarios. [ABSTRACT FROM AUTHOR]

To tackle the active control problem of the heavy platform-struts structure, this paper designs a kind of hydraulic servo actuator that can withstand large static load and generate high-precision, small-amplitude dynamic forces as well, and develops a multi-channel cross-coupling suppression control algorithm that can consider the strong coupling effect in structure. Subsequently, combining the designed actuators with the control algorithm, this paper puts forward an active heavy platform-struts structure vibration control method. By embedding the designed actuators into the support struts, a platform-struts structure experimental system is constructed to assess the vibration suppression effect of the proposed method. Excited by the amplitude-varying disturbing force, four different kinds of experiments are conducted. The experimental results show that the distributed multi-channel adaptive active control method without considering the coupling effect will lead to the instability, and the vibration attenuation of the proposed method in this paper exceeds 90%. The proposed method therefore has an important potential in addressing the problem of vibration suppression in the practical engineering. In addition, it has strong convergence and robustness. [ABSTRACT FROM AUTHOR]

The main intention of this study is to propose general criteria for the locations of the control sources and error microphones that improve the performance of the active noise barrier. Based on the proposed criteria of this study, the greater reduction is attained when the diffracted field of the noise source is canceled with the diffracted field of the control sources, that is, it is suggested to locate the control sources on the incident side and below the path that connects the furthest point in the shadow zone to the edge of the barrier. Furthermore, it is suggested that the error microphones are most suitably placed on the shadow side of the barrier where they are under the diffracted field of both the primary and control sources. The results also show that with these general criteria, the active noise control achieves an extra reduction that varies from 14.9 to 3.9 dB (for the one-third octave bands from 63 Hz to 1 kHz) and 9.3 dB for the broadband noises. [ABSTRACT FROM AUTHOR]

The sound field model of an irregular enclosure with two elastic walls and an inclined wall is established by the modal theory. The modal parameters of the irregular enclosure are obtained by the envelope rectangular technique. The influence of the inclination wall angle on the sound field in the irregular enclosure is discussed. When the inclination angle is increased from 0° to 45°, the resonance frequencies of the acoustic enclosure are basically reduced in the frequency range of 0∼250 Hz. When the inclination angle is increased from 0° to 45° every 15° interval, the amplitude of a certain acoustic mode itself decreases, while the amplitudes of the acoustic modes coupled to it basically increase. The acoustic potential energy peaks in the enclosure basically shift to the low frequency with the increase of the inclination angle. Furthermore, the change trend of the acoustic potential energy is regular in the low-order modes, but relatively chaotic in the high-order modes. In addition, in order to verify that the accurate description of the primary sound field is the basis of effective noise control, the two-elastic plate model is deliberately treated as one-elastic plate model, and its influence on the performance of active noise control is discussed. Also, if the multi-elastic plate model is regarded as a simplified automobile cab, the research results can be used for the preliminary acoustic design of the cab; that is, the research results can be used for the acoustic design of similar models. [ABSTRACT FROM AUTHOR]

This article presents the results of an investigation of the noise reduction performance of a single-channel active noise control system in the presence of a tilting reflective plane. It is shown that the noise reduction achieved by the system depends upon the orientation angle of the panel and on the separation distances between both the primary and the secondary source and the reflective panel. It is also observed that the maximum noise reduction is obtained when the reflective panel is vertical and when the separation distance is less than about 0.13 of the wavelength at the frequency of interest. When the panel is moved away, the maximum noise reduction occurs at other tilting angles. Experiments were carried out in a real living room which is close to real-life situations. It is found that there is an improvement in the extent of the quiet zone in the presence of the panel. The reduction in sound pressure level is also better with the reflective panel, which is up to 20 dB. [ABSTRACT FROM AUTHOR]

Active noise control systems are generally application-specific, and an appropriate algorithm with an optimal configuration is desirable in the first stage of active noise control system design and deployment. This study presents a design of the subband active noise control system with optimal parameters for a practical broadband active noise control. Although the delayless subband active noise control has gained wide attention for broadband noise cancellation, an optimal design remains a challenge because of the complex interplay between multiple factors such as spectral leakage, delay and weight stacking distortion subject to a number of configurable parameters, and weight stacking method. The configurable parameters can hardly be optimized independently because the active noise control performance depends on the combined configuration. A simple near black box active noise control algorithm optimization model is thus established by incorporating the genetic algorithm optimization into the parametric design of the delayless subband algorithm. The automated process does not require an understanding of the performance characteristics for different parameters. The significance of applying the automated genetic algorithm optimization to the complex multiparameter nonlinear active noise control design is revealed by numerical simulations, particularly for the multichannel low-frequency broadband active noise control system configured with the delayless subband algorithms. This provides a way for the optimal parametric design of subband active noise control before being used in a practical complex scenario. [ABSTRACT FROM AUTHOR]

In this article, a decentralized strategy is applied for active control of sound inside the automobile cabin by considering the uncertainty caused by the movement of the occupants. A coupled structural-acoustic analysis is done on the simplified geometry of the automobile cabin with passengers by the finite element method. The uncertainty caused by changes in the occupants' head positions and angles is also considered. Then, a decentralized robust feedback control strategy is proposed to reduce the sound pressure level in the ears of all the occupants using the H∞ method for each individual control unit by considering the unstructured uncertainty of the plant. The efficiency of the proposed control strategy in minimizing the sound pressure level caused by the structural disturbance on the firewall panel is investigated. [ABSTRACT FROM AUTHOR]

Active noise control (ANC) is a methodology that aims to attenuate acoustic noise creating a silent zone around the target. ANC techniques are particularly useful in the presence of low frequency noise, where passive control is ineffective and impractical. However, the computational cost of ANC applications involving a high number of sensors and actuators, such as active shielding, appears to be an important limitation. One possible approach to deal with this problem is to resort to decentralized control. This is a technique that decomposes a complex control problem into smaller ones that are addressed independently using different controllers. This article studies a decentralized scheme for ANC from a game-theoretical perspective. This formalizes the Nash equilibrium (i.e., the simultaneous best strategy) in the interaction between the controllers. Indeed, in the Nash Equilibrium, the control signals achieve stable conditions. In this framework, it is straightforward to analytically compare the decentralized control scheme to the standard centralized one. [ABSTRACT FROM AUTHOR]

The disturbance at error sensors will degrade the performance of active noise control (ANC) systems, resulting in slow convergence and decreased noise reduction problems. This paper analyzes the disturbance effects on narrowband ANC (NANC) systems and proposes modified algorithm to enhance both the transient and steady-state performance. A delayless bandpass filterbank is designed to eliminate out-of-band disturbance in the generated individual error signals for updating the corresponding adaptive filters. The theoretical analysis and improved performance are verified by computer simulations using measured transfer functions from the experimental setup. [ABSTRACT FROM AUTHOR]

This paper presents the modeling and simulation results of active noise control (ANC) in a small room using the wave-based approach defined by particle velocities and sound pressure within the defined boundary conditions. The ANC system excitation is a single-frequency noise with an adaptive feedforward configuration. The Finite Difference Time Domain (FDTD) algorithm is used to model the room acoustics due to a boxed loudspeaker of single frequency. A control system based on the filtered-x least mean-squared (FxLMS) algorithm is utilized to synthesize a cancelling noise using a secondary loudspeaker. The single channel system is modified into a multichannel system and genetic algorithm (GA) is used to optimize the sensors and actuators placements simultaneously. Numerical results are plotted to demonstrate the performance of the control system. These show that the numerical modelling technique can be used to combine room acoustic simulation and FxLMS adaptive control. This provides a way for the optimum placement of the microphones and loudspeakers before being used in a practical complex enclosure. [ABSTRACT FROM AUTHOR]

In this paper, the active control of sound transmission through a simply supported soft-core sandwich panel is analytically studied. Since, the sound transmission through soft-core sandwich panels in the low-frequency region mainly occurs due to flexural and dilatational modes, and therefore to control these structural modes, volume velocity and weighted sum of spatial gradients (WSSG) are used to drive a piezoceramic actuator (PZT) attached on the exterior side of the bottom face plate. Sound power level and voltage required to drive the PZT are compared for different values of isotropic core loss factor. Numerical studies indicate that both control metrics are capable of attenuating the flexural and the dilatational modes of the sandwich panel, and hence, reduce significant amount of sound power in a wider frequency range. By carefully selecting the modes to calculate the scaling factors, WSSG provides comparable control to volume velocity. However, the necessary voltage required to drive the PZT to minimize the WSSG is less as compared to minimize the volume velocity. [ABSTRACT FROM AUTHOR]

Wavelet frames are an appropriate alternative approach for signal approximation especially for noise/vibration signals. This paper presents an active noise control scheme using various wavelet frames with an innovative structure. In this structure, the authors employ a nonlinear static mapping cascaded with an infinite impulse response filter to model the dynamic part of the network. Online dynamic back propagation learning algorithms are applied based on the gradient descent method to adjust the network parameters. Simulations are carried out to compare the performance of filtered-x least mean square and filtered-x back propagation neural network algorithms with the proposed method. Experiments are then designed and conducted to evaluate the developed algorithms. Both simulation and experimental results show the superior performance of the proposed method in terms of a fast convergence rate and noise attenuation while avoiding the curse of dimensionality. [ABSTRACT FROM AUTHOR]

Two strategies for adaptive feedback active noise control (ANC) systems are presented here based on wavelet frames. In the first strategy, the noise at the cancellation point is estimated and used as the reference signal in the feedforward ANC system. In the second strategy only the error signal is utilized in the wavelet-based ANC system. The advantages of the second method are: simple structure and less computational load (no need to estimate noise) as well as less sensitivity to the accuracy of estimated secondary path filter. Its disadvantage is high sensitivity to learning rate. To treat this, an adaptive learning rate is proposed to maintain the stability and convergence rate simultaneously. Simulations are carried out for typical linear/nonlinear cases to compare the proposed methods with FxLMS and neural network-based ANC algorithms. Experiments are then conducted to evaluate the developed algorithms. Results show the superior performance of proposed methods in terms of the convergence rate and noise attenuation especially in the presence of an inaccurate identified secondary path filter. [ABSTRACT FROM AUTHOR]

The capabilities of wavelet networks in function approximation make them appealing for black box system identification. In this paper, a new active noise control (ANC) algorithm is developed based on adaptive wavelet networks. The proposed adaptive nonlinear noise control approach employs frames from POLYnominal WinOwed with Gaussian wavelets. Also, a novel network structure for active noise control is derived incorporating a nonlinear static mapping cascaded with an infinite impulse response filter to model the dynamic part of the network. Online dynamic backpropagation learning algorithms based on gradient descent method are applied to adjust the network parameters. Local convergence of the closed-loop system is proved using discrete Lyapunov function.The performance of the proposed ANC system is examined for typical linear/nonlinear cases. The simulation results demonstrate superior performance of this method in terms of stability, fast convergence rate and noise attenuation while avoiding curse of dimensionality. [ABSTRACT FROM AUTHOR]

This paper presents a framework for model-based analysis of robust stability and performance for a multi-axis active vibration isolation system with constant but unknown payload and subject to modelling errors associated with structural flexibility. The theoretical treatment involves a linear time-invariant system subject to real parameter uncertainty associated with the unknown payload. A set of performance indices are formulated based on generalized H2 (Hg) and H∞ measures. A method for stability/performance verification is then developed using a parameter-dependent Lyapunov function that incorporates the kinetic energy of the uncertain payload mass. This allows nonconservative bounds on the performance indices to be established via numerical solution of a corresponding set of matrix inequalities. The approach is especially suitable, and computationally efficient, for multi-degree-of-freedom systems as the overall (symmetric positive-definite) properties of the system mass matrix are accounted for without involving information for each scalar parameter. The associated LMIs can therefore be solved in polynomial time with respect to the number of unknown parameters. Numerical examples for the case of sky-hook damping control and multi-objective Hg/H∞ control are provided that demonstrate the effectiveness of the method as a tool for model-based controller evaluation and multi-objective optimization. [ABSTRACT FROM PUBLISHER]

The 3D piezoelasticity theory and the spatial state-space approach are used to study the steady-state non-axisymmetric sound radiation and scattering characteristics of an infinitely long, arbitrarily thick, orthotropic functionally graded hollow circular cylinder, coupled with an inner (actuator) layer of functionally graded piezoceramic material. The method of stationary phase is employed for evaluation of the radiated far-field pressure integral. Numerical simulations include water-submerged air-filled steel-PZT4 composite cylinders driven by harmonic electromechanical loads or insonified by an obliquely incident plane sound wave. Also, when the actuator layer is operating in the active vibration mode, the effects of the number of control modes on the input voltage required for partial or complete cancellation of the far-field and internal radiated pressures as well as on the backscattering form function and noise reduction amplitudes are examined. Limiting cases are considered and validity of formulation is established by comparison with available data as well as with the aid of a commercial finite element package. [ABSTRACT FROM PUBLISHER]

In this paper we present a novel approach to reducing blade-rate noise of axial-flow fans. By using magnetic bearings as a noise control actuator, it is possible to collocate the anti-noise source with the disturbance noise source. This approach allows for global noise reduction throughout the sound field. A DC motor connected to a fan by a short rigid shaft was used to demonstrate this approach. The shaft was supported in the radial and axial directions by magnetic bearings. The beatings provide position control of the shaft and fan; this position control can be used to vibrate the fan at a desired frequency and amplitude. Controlled vibration of the fan allows its use as a speaker in an active noise control scheme. Noise control was implemented on a dedicated digital signal processor using a least mean square algorithm. The output of the noise control algorithm supplies the position commands for the magnetic bearing controller. Experimental data showed that by actuating the axial thrust bearing, the noise output of a fan could be reduced by 4 dB at the error microphone, and 3 dB at points away from the error microphone. [ABSTRACT FROM AUTHOR]

In this paper we apply a filtered-X algorithm to an active feedback control structure and derive the transfer function of a closed-loop control system. Simulation studies are then carried out on the closed-loop property while varying the parameters (input frequency, delays in plant, amplitude and phase of modeling filter). Several properties of adaptive feedback control are revealed. Experimental studies on feedback active noise control of noise in a finite duct and a small enclosure are described, and outstanding active noise control effects are achieved. Experimental results of closed-loop frequency response are also provided. [ABSTRACT FROM AUTHOR]