Active Noise Control Experiments Research Articles

Experimental research on global active rotor noise control using near-field acoustic holography and sound field reproduction

This study employs a 1.6 m diameter rotor to validate the global active noise control method, developed from our previously work, which is based on near-field acoustic holography and sound field reproduction. The validation is conducted through experiments in an anechoic chamber. Additionally, we achieved control over nearly all acoustic modal components of multiple blade passing frequency (BPF) noises of the rotor by extending the time-domain least mean square (LMS) to the acoustic modal domain. The experimental results from near-field acoustic holography revealed that each BPF noise contained 3–4 main acoustic modal components, accounting for almost 90 % of the sound power. The global active noise control experiments demonstrated that the adaptive algorithm in the acoustic modal domain effectively mitigates the influence of rotation speed fluctuations, resulting in steady-state global noise reduction through sound field reproduction. Furthermore, for the first 3 BPF noise, our method achieved noise reduction of 9, 11, and 6 dB by controlling the first 3–4 main acoustic modal components, respectively. The concurrent reduction of various harmonic noises at all observation points validates the method's capability to globally control multiple harmonic noises.

Active control of vehicle interior engine noise using a multi-channel delayed adaptive notch algorithm based on FxLMS structure

A multi-channel delayed adaptive notch algorithm based on the filtered-x least mean square (FxLMS) structure was proposed for active control of vehicle interior engine noise with prominent harmonic characteristics. First, a complete reference signal model was established utilizing vehicle engine speed. Second, the algorithm procedure was presented systematically, and a new time-delay method was introduced to simplify the filtering process of the reference signal to greatly improve the calculation efficiency. Furthermore, the convergence condition was derived, and mathematical models of the steady-state error and convergence speed were obtained. The simulation results, which were consistent with theoretical calculation values, showed that the two models were highly accurate. They help to theoretically indicate the interval range of the effective convergence coefficient μ and its optimal value. Using the proposed multi-channel delayed adaptive notch algorithm, actual vehicle active noise control experiments were conducted. The results show that, under stationary conditions, the interior overall engine noise reduction in the time-domain reaches 4.05 dB (A), and the corresponding second-order engine noise reduction reaches 13.66 dB (A), however, under nonstationary working conditions, the proposed algorithm still has a good noise reduction effect. This algorithm can be directly applied to the active control of vehicle engine noise and other similar narrowband noise reduction.

A global rotor noise control method based on near-field acoustic holography and sound field reproduction

Aiming at the severe aerodynamic noise generated by the rotor of rotorcrafts, a global active noise control method is proposed based on near-field acoustic holography (NAH) and sound field reproduction (SFR). The microphone array here is not only used to evaluate errors as in existing methods, but also to predict the rotor noise by extracting acoustic modal information. The loudspeaker array reproduces a secondary sound field with the same acoustic modal components but in opposite phase to achieve global noise reduction. Specifically, by arranging microphones on the fuselage, the rotor noise prediction problem is transformed into an external domain problem of the NAH. Then, by extending the SFR to the external domain, the loudspeaker array is used to reproduce a target sound field which just achieves sound-sound cancellation with the rotor noise globally. Further, the application of the acoustic modal analysis shows that the acoustic modal distribution of the rotor noise is determined by the number of blades, which greatly reduces the scale of loudspeaker/microphone array and is conducive to on-line noise control. The acoustic modal decomposition of the rotor noise shows that the amplitude of the main acoustic mode decays the slowest with distance compared with other acoustic modes, and it is the main component of the far-field noise. The comprehensive evaluation of the model rotor noise reduction performance at different scales shows that the global noise reduction effect for controlling all acoustic modes exceeds 40 dB, while for controlling the main acoustic mode reaches 18 dB, and the required power is reduced by 84%. Finally, the global active noise control experiments for the model rotor are conducted. The results show that the global noise reduction can reach 17 dB through controlling the main acoustic mode. The GANC method shows great advantage of global noise reduction and high engineering application potential.

Centralized and decentralized adaptive harmonic control for sinusoidal disturbance rejection

This paper presents two new algorithms for rejection of known-frequency sinusoidal disturbances that act on a completely unknown, multi-input multi-output, asymptotically stable, linear time-invariant system. The first algorithm is centralized adaptive harmonic control (AHC), which does not impose any structural constraints on the input–output channels of the controller. The second algorithm is decentralized AHC, which imposes the constraint that each local control is computed using only local sensor measurements. These new control methods are data-driven, adaptive algorithms that do not rely on any information regarding the system. It is also worth noting that all control computations are performed using discrete Fourier transform data. The stability and closed-loop performance with each algorithm are analyzed. The main analytic results show that each algorithm asymptotically rejects sinusoidal disturbances. Illustrative numerical simulations and active noise control experiments demonstrate the effectiveness of centralized and decentralized AHC.

ロバスト制御を対象とした遠隔実験環境の構築

This paper deals with the development of the remote experimental system for robust control. Using this system, students can execute an active noise control experiment via network, remotely. Uploading parameter files of a controller to the web page of this system, this system executes an experiment, automatically. About 1 minute later, a hyperlink to the result data will be displayed on the web page. The developed system was introduced in a lecture, ‘advanced automation’, in 2015 and 2016, and was evaluated by a questionnaire. This paper reports details of proposed experimental system and the effectiveness of proposed experimental system on the basis of the questionnaire results.

Co-FXLMS 알고리즘을 이용한 유도전동기의 능동소음제어

In this study, the active noise control experiment has been performed using induction motor noises. While the noises were measured, a induction motor was operated in different speed. For the simulation of ANC(Active Noise Control), test-bed is composed a multi-channel ANC system was constructed. In order to compare the control performance, we performed noise reduction simulations of ANC by Co-FXLMS algorithm and FXLMS algorithm. Through the simulation results, we confirmed that convergence performance and noise decrease effect of the proposed Co-FXLMS algorithm have been improved from existing FXLMS algorithm.

Adaptive Harmonic Steady‐State Disturbance Rejection with Frequency Tracking

AbstractThis paper is concerned with the rejection of sinusoidal disturbances of unknown frequency acting at the output of unknown plants. Disturbance rejection is based on an adaptive harmonic steady‐state (ADHSS) algorithm combined with a magnitude/phase locked‐loop (MPLL) frequency estimator. The harmonic steady‐state method assumes that the plant can be approximated by its steady‐state frequency response. For high‐order plants such as those encountered in active noise and vibration control (ANVC), this assumption greatly reduces the number of parameters and enables online estimation of the plant response using simple algorithms. The paper shows that when the MPLL is integrated with the ADHSS algorithm, the two components work together in such a way that the control input does not prevent frequency tracking by the MPLL, and so that the order of the ADHSS can be reduced. Thus, the addition of the MPLL allows disturbances of unknown frequency to be considered without significantly increasing the complexity of the original ADHSS. After analyzing the reduced‐order ADHSS in the ideal case, the equations describing the complete system are considered. The theory of averaging is used to gain insight into the steady‐state behavior of the algorithm. It is found that the system has a two‐dimensional equilibrium surface such that the disturbance is cancelled exactly. A subset of the surface is proved to be locally stable. Extensive active noise control experiments demonstrate the performance of the algorithm, even when disturbance and plant parameters are changing.

Adaptive rejection of disturbances having two sinusoidal components with close and unknown frequencies

The paper considers the problem of rejecting disturbances with two sinusoidal components in the case where the frequencies are unknown and closely spaced. A natural approach consists of cancelling the components using two separate adaptive algorithms combined in a single scheme. However, experiments in active noise control applications have shown that convergence using such an approach could be very slow. The alternative approach of this paper consists of representing the disturbance signal as a single sinusoid with time-varying magnitude and phase. The theoretical basis and the limitations of this representation are first discussed. Then, an adaptive disturbance rejection algorithm is proposed and the resulting nonlinear system is analyzed using some approximations. Active noise control experiments demonstrate that the proposed algorithm has better convergence properties than an algorithm designed to cancel the two frequency components separately. In some cases, however, the cost is a small residual error on the output signal. Copyright © 2010 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society

Design of a near‐optimal adaptive filter in digital signal processor for active noise control

AbstractAdaptive filter has been applied in adaptive feedback and feedforward control systems, where the filter dimension is often determined by trial‐and‐error. The controller design based on a near‐optimal adaptive filter in digital signal processor (DSP) is developed in this paper for real‐time applications. The design integrates the adaptive filter and the experimental design such that their advantages in stability and robustness can be combined. The near‐optimal set of controller parameters, including the sampling rate, the dimension of system identification model, the dimension (order) of adaptive controller in the form of an FIR filter, and the convergence rate of adaptation is shown to achieve the best possible system performance. In addition, the sensitivity of each design parameter can be determined by analysis of means and analysis of variance. Effectiveness of the adaptive controller on a DSP is validated by an active noise control experiment. Copyright © 2007 John Wiley & Sons, Ltd.

Reduction of Axial Turbomachinery Tonal Noise by Means of Flow Induced Secondary Sources Using an Extremum-Seeking Control Technique

In conventional active noise control experiments, loudspeakers are used to generate the secondary anti-phase sound field to be superimposed destructively with the sound waves radiated from the primary source. In the present study, aerodynamic sound sources are used to actively control the tonal noise of an axial fan. This is achieved by disturbing the flow field around the blade tips in such a way that additional periodic forces are set up which in turn form the secondary sound sources. To disturb the flow, air is blown into the blade tip region through the casing wall. The resulting aerodynamic sound sources are adjustable in both amplitude and phase. Results for closed loop control of the blade passing frequency using an extremum-seeking control technique are presented.

New analytical model for the filtered-x least mean squares algorithm verified through active noise control experiment

This paper presents a new analytical model for the behavior of the Filtered-x LMS adaptive algorithm when applied to active noise control (ANC) in a finite duct. The new model is derived using a stochastic differential equation (SDE) approach. The theoretical predictions are verified through experimental results. The real-time system has been implemented using only I/O cards and a general purpose computer. Automation of the experimental setup allows the practical verification of the theoretical statistical model using Monte Carlo techniques. It is verified that the behavior of the algorithm is accurately predicted by the theoretical model.

318 多数モードロバスト制御のための動吸振器駆動法 : アクティブ騒音制御への応用(能動的騒音制御,OS-20:サイレント工学)

The control system driving the vibration absorber with the force proportional to the velocity of the primary structure is unstable. This problem can be solved by implementing a target absorber equation that can be obtained by replacing the eigenfrequency of the original absorber equation by arbitrary frequencies of excitation and treating the squared arbitrary frequencies as an operator -d^2/dt^2. In this paper, this idea is applied to the active noise control experiment by considering a control speaker an absorber. The effectiveness of the present control method in controlling plural acoustic modes excited by broadband excitation is demonstrated by experiments.

Multi-channel active noise control for periodic sources—indirect approach

This paper presents a multi-channel active noise control algorithm that is designed to reject periodic signals of unknown frequency. It is based on a so-called indirect approach, where the frequency of the disturbance is estimated in real time, and the estimate is used in a disturbance rejection scheme designed for a known frequency. Improvements over an earlier algorithm include an extension to multi-channel systems, a better frequency estimation algorithm, and a thorough experimental evaluation. For disturbance rejection, a so-called inverse G algorithm is proposed and its properties are compared through analysis and experiments to those of a gradient algorithm. A new frequency estimator is also considered that is simple and flexible in design, and is able to use multiple harmonics or multiple signals in order to estimate the fundamental frequency of the noise source. In this manner, the algorithm maintains tracking of the fundamental frequency despite significant changes in signal characteristics. The ability of the indirect approach to reject periodic noise with fixed or time-varying frequency and amplitudes is demonstrated in active noise control experiments. The algorithm may also be useful in other control applications where periodic disturbances of unknown frequency must be rejected.

EXPERIMENTAL STUDY OF SMART SEGMENTED TRIM PANELS FOR AIRCRAFT INTERIOR NOISE CONTROL

A smart trim panel used as a secondary source for active noise control in aircraft is developed and tested. The smart trim panel is a rectangular segment of aircraft trim panel which is suspended by a flexible support. This support converts the stiff trim panel into flexibly mounted pistons which can be driven by light-weight and low-profile force actuators. The smart trim panel has many advantages as an acoustic source over traditional loudspeakers: it is of lower profile, lower mass, and requires only a simple modification of materials already installed on aircraft. The static and dynamic properties of a smart trim panel are studied, verifying that when subjected to low-frequency (<500 Hz) excitation, it vibrates in the efficiently radiating piston mode. Real-time active noise control experiments are conducted in a laboratory-scale fuselage model using the smart trim panels as secondary sources. Global attenuation of sound pressure levels of up to 15 dB is realized.

Multichannel Adaptive Active Noise Control Taking Account of Channel Changes

This paper is concerned with adaptive active noise control of a multichannel system which involves a multiple number of primary sources, reference microphones, secondary control sources and canceling error microphones. First, on the assumption that the secondary path response matrices are known a priori, we give a structure of a multi-channel adaptive feedforward controller and propose a stability guaranteed robust adaptive algorithm with variable step size for updating the FIR type of controllers. Secondly, in cases of unknown secondary path matrices, we also present two identification-based adaptive algorithms for realizing controllers preserving the stability of the adaptive system. The effectiveness is examined by comparing the proposed algorithms with ordinary filtered-x algorithm through active noise control experiments.

A transform domain optimization to increase the convergence speed of the multichannel filtered-X least-mean-square algorithm

The main drawback of the multichannel filtered-X LMS (FX-LMS) algorithm for the active noise control (ANC) of broadband disturbances is its low convergence speed when the filtered reference signals are strongly correlated, producing a large eigenvalue spread in the global correlation matrix. This correlation can be caused either by autocorrelation of the signals of the reference sensors, or by coupling between the ‘‘error paths’’ which introduces intercorrelation in the filtered reference signals. Multichannel versions of fast convergence monochannel algorithms exist (Newton-LMS, RLS, fast Kalman), but these algorithms either require too many computations for practical implementations, or they require the optimization of the controller to be performed at each sample, which can be a serious constraint. The purpose of this paper is to introduce a multichannel algorithm that has a high convergence speed and a low computational load, close to the FX-LMS. It is called the cosine transform filtered-X LMS (CTFX-LMS) because it uses a discrete cosine transform to eliminate the correlation that slows down the convergence process. The fundamental differences between this algorithm and many previously published frequency domain algorithms will be explained. Results of active noise control experiments in ducts will validate the convergence behavior of the new algorithm.