Browsing by Author "Bai, MR"

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A ring silencer design for reducing noise of axial fan
(2003-09-01)
Wu, JD
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Bai, MR
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機械工程學系
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Department of Mechanical Engineering
In this paper, a ring silencer design for reducing the noise of axial fans is presented. The noise sources on axial fans are usually caused by the fluctuating pressure distribution on the surface of fan blade. Most of the sources are near the trailing edge of blades or boundary region of blades. The ideation of proposed design is based on the principle of Helmholtz resonator for reducing the noise around the fan. The electro-acoustic analogy of this design is presented and simply discussed. Experimental measurement is carried out to evaluate the proposed design for reducing the axial fan noise. The result of experiment indicated that the ring silencer achieved 17 dB in blade passing frequency and 10 dB in other broadband frequency of power spectrum level.
Acoustic analysis and design of miniature loudspeakers for mobile phones
(2005-11-01)
Bai, MR
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Liao, JW
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機械工程學系
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Department of Mechanical Engineering
Miniature loudspeakers are key components of mobile phones in modern-day wireless communication. Although the fundamental principle of miniature loudspeakers is similar to that of larger loudspeakers of other kinds, there are still some distinct features of these devices that may give rise to different design considerations. An extensive electroacoustic analysis is conducted to explore the characteristics of miniature loudspeakers when fitted to the interior of mobile phones. Of particular interest is the modeling of the duct structure in the analysis. Thiele and Small parameters of miniature loudspeakers are experimentally identified. Dynamic response simulation is carried out on the basis of electro-mechano-acoustical (EMA) equivalent circuits. Head diffraction in hands-free application is also simulated. In order to assess the miniature loudspeakers, performance indices including frequency response, sensitivity, and efficiency are measured. An acoustic design that extends the low-frequency bandwidth is also presented to meet the ever-increasing demand of sound quality of miniature loudspeakers.
Active noise cancellation for a three-dimensional enclosure by using multiple-channel adaptive control and H infinity control
(1998-10-01)
Bai, MR
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Lin, Z
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機械工程學系
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Department of Mechanical Engineering
Active noise control (;WC) techniques for a three-dimensional enclosure are compared in terms of two control structures and two control algorithms. The multiple-channel filtered-x least-mean-square (FXLMS) algorithm and the H-infinity robust control algorithm are employed for controller synthesis. Both feedforward and feedback control structures are compared. The Youla's parameterization is employed in the formulation of the multiple-channel feedback FXLMS algorithm. The algorithms are implemented using a floating-point digital signal processor (DSP), Experiments are carried out to validate the ANC approaches for, attenuation of the internal field in a rectangular wooden box Position and number of actuators and sensors are also investigated. A broadband random noise and an engine noise are chosen as the primary noises in the experiments. The experimental results indicate that the feedforward structure yields a broader band of attenuation than the feedback structure. The FXLMS control and H-infinity control achieve comparable performance.
Active noise control of enclosed harmonic fields by using BEM-based optimization techniques
(1996-05-01)
Bai, MR
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Chang, S
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機械工程學系
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Department of Mechanical Engineering
Boundary element methods (BEM) in conjunction with optimization algorithms are employed for active noise control of sound fields in three-dimensional enclosures. Total time-averaged acoustic potential energy is chosen as the cost function for the optimization procedure. The BEM is used to model the monochromatic sound field generated by noise sources in the enclosure. The constrained steepest descent method proves to be effective when both positions and amplitudes of the secondary sources are to be optimized, while the direct matrix inversion, the steepest descent method, and the conjugate gradient method prove to be useful when only the amplitudes of secondary sources are to be optimized. The developed BEM-based optimization techniques are applied to control the noise in a rectangular enclosure and a vehicle cabin.
Active noise control of enclosed harmonic fields by using BEM-based optimization techniques
(1996-05-01)
Bai, MR
;
Chang, S
;
交大名義發表
;
機械工程學系
;
National Chiao Tung University
Boundary element methods (BEM) in conjunction with optimization algorithms are employed for active noise control of sound fields in three-dimensional enclosures. Total time-averaged acoustic potential energy is chosen as the cost function for the optimization procedure. The BEM is used to model the monochromatic sound field generated by noise sources in the enclosure. The constrained steepest descent method proves to be effective when both positions and amplitudes of the secondary sources are to be optimized, while the direct matrix inversion, the steepest descent method, and the conjugate gradient method prove to be useful when only the amplitudes of secondary sources are to be optimized. The developed BEM-based optimization techniques are applied to control the noise in a rectangular enclosure and a vehicle cabin.
Analysis and DSP implementation of a broadband duct ANC system using spatially feedforward structure
(2001-04-01)
Bai, MR
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Lin, YJ
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機械工程學系
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Department of Mechanical Engineering
The active control technique for broadband attenuation of noise in ducts, using spatially feedfoward structure. is investigated from the viewpoints of both acoustic analysis and exists an ideal controller for this problem. The ideal controller is a function of the finite control engineering. According to the previous work by Munjal and Eriksson [1], there source impedance and is thus independent of the boundary conditions. Despite the simplicity the ideal controller cannot be practically implemented due to the difficulty of calibration of electro-mechanical parameters. To overcome the problem, the controller is implemented via an equivalent formulation modified from the controller originally proposed by Roure [2]. The modified controller is implemented on a DSP platform, using a FIR filter, an IIR filter and a hybrid filter. The experimental results showed that the system achieved 17.2 dB maximal attenuation in the frequency band 300 similar to 600 Hz. Physical insights and design considerations in implementation phase are also discussed in the paper.
Comparison of active noise control structures in the presence of acoustical feedback by using the H-infinity synthesis technique
(1997-10-02)
Bai, MR
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Lin, HH
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交大名義發表
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機械工程學系
;
National Chiao Tung University
This study compares three control structures of active noise cancellation for ducts: feedback control, feedforward control, and hybrid control. These structures are compared in terms of performance, stability, and robustness by using a general framework of the H-infinity robust control theory. In addition, the H-infinity synthesis procedure automatically incorporates the acoustic feedback path that is usually a plaguing problem to feedforward control design. The controllers are implemented by using a digital signal processor and tested on a finite-length duct. In an experimental verification, the proposed controllers are also compared with the well-known filtered-u least mean square (FULMS) controller. The advantages and disadvantages of each ANC structure as well as the adverse effects due to acoustic feedback are addressed. (C) 1997 Academic Press Limited.
Control design of active vibration isolation using mu-synthesis
(2002-10-10)
Bai, MR
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Liu, W
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機械工程學系
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Department of Mechanical Engineering
Numerical and experimental investigations on active vibration isolation system are presented in this paper. Two configurations are implemented for a statically balanced three-mount system. To reduce the influence of payload dynamics and coupling among the control actuators, intermediate masses are added to the system. Linear quadratic Gaussian control and p-synthesis are employed in the controller synthesis. The controllers are implemented on the platform of a floating-point digital signal processor. The results obtained from simulations and experiments indicated that the optimal controllers achieved the desired performance under the constraint of robust stability. (C) 2002 Elsevier Science Ltd. All rights reserved.
Design and implementation of electromagnetic active control actuators
(2003-08-01)
Bai, MR
;
Ou, KY
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機械工程學系
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Department of Mechanical Engineering
We present the modeling, parameter identification and design procedure of a linear voice-coil motor. A numerical simulation has been carried out to facilitate system integration. In particular, we use electromechanical analogy and the time-domain identification procedure with the eigensystem realization algorithm to predict the system response. In order to evaluate the performance of the voice-coil motor, we conducted an experimental investigation. Voice-coil motors mounted on a ball bearing housing are used for generating counter forces to cancel the transverse vibrations of a shaft. A controller is designed by using generalized predictive control. Multiple channel active control systems are implemented on the platform of a digital signal processor. Numerical and experimental results indicated that the designed actuators were effective in suppressing the periodic disturbances in rotors.
Design of a broadband active silencer using mu-synthesis
(2004-01-06)
Bai, MR
;
Zeung, PS
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機械工程學系
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Department of Mechanical Engineering
A robust spatially feedforward controller is developed for broadband attenuation of noise in ducts. To meet the requirements of robust performance and robust stability in the presence of plant uncertainties, a mu-synthesis procedure via D-K iteration is exploited to obtain the optimal controller. This approach considers uncertainties as modelling errors of the nominal plant in high frequency and is implemented using a floating point digital signal processor (DSP). Experimental investigation was undertaken on a finite-length duct to justify the proposed controller. The mu- controller is compared to other control algorithms such as the H-2 method, the H-infinity method and the filtered-U least mean square (FULMS) algorithm. Experimental results indicate that the proposed system has attained 25.8 dB maximal attenuation in the band 250-650 Hz. (C) 2003 Elsevier Science Ltd. All rights reserved.
Determination of optimal exciter deployment for panel speakers using the genetic algorithm
(2004-01-22)
Bai, MR
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Liu, BW
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機械工程學系
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Department of Mechanical Engineering
A large multi-exciter panel speaker has been constructed in this work. In order to achieve the best design, an optimization procedure using the genetic algorithm (GA) has been developed. A total numerical model was first established for simulation, where the electrical system, the mechanical system, and the acoustical coupling in the panel speaker are accounted for within a coupled framework. Performance indices including the frequency response, the sound power, and the directional response are calculated. The simulation model also serves as the basis for the optimal design that aims at achieving omni-directional responses at high efficiencies. A GA-based optimization scheme was exploited to search for the positions of exciters and the delays of input signals which render the optimal performance. The optimal design was verified by experimental investigations. The results indicate that the optimal configuration indeed produced better performance in terms of efficiency and omni-directionality than the non-optimal one. (C) 2003 Elsevier Science Ltd. All rights reserved.
Development and implementation of a semi-adaptive H-infinity active control algorithm for duct noise
(1999-01-01)
Bai, MR
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Lin, H
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Lin, Z
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機械工程學系
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Department of Mechanical Engineering
A hybrid active noise control (ANC) scheme for suppressing duct noise based on the H-infinity control synthesis is proposed. The controllers are designed in terms of performance, and robustness using a general framework of the H-infinity robust control theory. In addition to the fixed controller, the system is further enhanced by introducing an adaptive compensator based on the least-mean-square (LMS) algorithm. Youla parameterization is employed in designing the adaptive compensator so that the resulting system is stable. Experimental investigations demonstrate that the proposed methods are effective in suppressing broadband random noise in finite-length duct.
Development of a feedforward active noise control system by using the H-2 and H infinity model matching principle
(1997-03-27)
Bai, MR
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Chen, HP
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交大名義發表
;
機械工程學系
;
National Chiao Tung University
Two novel active noise control techniques on the basis of feedforward H-2 and H-infinity optimal model matching principle are proposed. These methods effectively overcome the problem of unstable inverse plant resulting from the inherent non-minimum phase property of the cancellation path. The proposed algorithms are implemented by using a digital signal processor. The experimental results obtained by using H-2 and H-infinity feedforward techniques show attenuation for stationary noise in a duct as comparable to those of conventional methods. The proposed methods also have potential in suppressing transient noises that have been the major difficulty in adaptive methods. Comparisons of the methods are summarized. (C) 1997 Academic Press Limited.
Development of a feedforward active noise control system by using the H-2 and H infinity model matching principle
(1997-03-27)
Bai, MR
;
Chen, HP
;
機械工程學系
;
Department of Mechanical Engineering
Two novel active noise control techniques on the basis of feedforward H-2 and H-infinity optimal model matching principle are proposed. These methods effectively overcome the problem of unstable inverse plant resulting from the inherent non-minimum phase property of the cancellation path. The proposed algorithms are implemented by using a digital signal processor. The experimental results obtained by using H-2 and H-infinity feedforward techniques show attenuation for stationary noise in a duct as comparable to those of conventional methods. The proposed methods also have potential in suppressing transient noises that have been the major difficulty in adaptive methods. Comparisons of the methods are summarized. (C) 1997 Academic Press Limited.
Development of a modal LQG active noise canceler
(1995)
Bai, MR
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Shieh, CF
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Lee, DJ
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機械工程學系
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Department of Mechanical Engineering
Development of a multiple channel active noise cancellation system for car cabins
(2003)
Chen, HH
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Wu, JD
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Bai, MR
;
機械工程學系
;
Department of Mechanical Engineering
This paper describes the development of a multiple-channel active pp noise cancellation system for car cabins. Various active techniques are compared in terms of control structures and control algorithms. The filtered-x least-mean-square algorithm with synthetic reference and the linear quadratic gaussian control are employed for controller synthesis. Feedback, feedforward and hybrid configurations are adopted as the major control structures. The plant model is identified using a frequency-domain method. The controllers are implemented by using a digital signal processor. Experiments are carried out to evaluate the proposed techniques for attenuation of the internal field in a car cabin. The experimental results indicate that the hybrid control structure yields the best performance in terms of noise attenuation and convergence speed.
Development of a zero spillover controller for broadband cancellation of noise in ducts
(2001-11-01)
Wu, JD
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Bai, MR
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機械工程學系
;
Department of Mechanical Engineering
In this paper, an active noise control (ANC) system for broadband cancellation of noise in ducts. where a nonacoustical reference is unavailable and thus the ANC structure is "spatially feedforward" is presented. In this structure, acoustic feedback that is known to be detrimental to system stability and performance must be taken into account in controller design. in this case, difficulties generally arise in implementing the ideal controller. or the zero spillover controller due to plant uncertainties. In the present study, an equivalent approach based on the 2-norm (H-2) optimal model matching principle is proposed in controller design. The control algorithm is implemented on a digital signal processor (DSP). by finite impulse response (FIR), infinite impulse response (IIR) and hybrid filters. The experimental results indicate that the proposed controller was effective in suppressing periodic noise and random noise sources. without and with airflow.
Digital signal processor implementation of active noise control systems for broadband noise cancellation in engine exhaust systems
(2000-08-01)
Wu, JD
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Bai, MR
;
機械工程學系
;
Department of Mechanical Engineering
This paper describes the principle and application of broadband active noise control (ANC) for engine exhaust systems using a spatially feedforward structure. The algorithm of the proposed controller is obtained from previous work by Roure (1985), Munjal and Eriksson (1988), Hong and Bernstein (1998), and there exist some conclusions for this structure. The self-adaptive broadband controller is discussed and implemented on a digital signal processor (DSP), using finite impulse response (FIR) and infinite impulse response (IIR) filters. Experiments were carried out to evaluate the proposed system for reducing the noise under different engine operating conditions. The experimental results indicate that the ANC system is effective in reducing the broadband noise for engine exhaust systems using the spatially feedforward structure.
Effects of directional microphone and transducer in spatially feedforward active noise control system
(2001-10-01)
Wu, JD
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Bai, MR
;
機械工程學系
;
Department of Mechanical Engineering
In this paper, an experimental study concerning the effects of a directional microphone and transducer in a duct active noise control (ANC) system in the presence of acoustic feedback is described. In the duct ANC system, a spatial feedforward system is used for broadband noise cancellation in ducts, where a non-acoustical reference is unavailable. In this structure, acoustic feedback that is known to be detrimental to the system stability and performance must be taken into account in the controller design. The algorithm of the proposed control system is based on the previous work by Roure (1985), Munjal and Eriksson, Hong and Bernstein (1998), and there exists some discusses for spatially feedforward structure. The algorithm is implemented on a digital signal processor (DSP), using finite impulse response (FIR) and infinite impulse response (IIR) filters. Experiments are carried out to evaluate the effects of a directional microphone and transducer in proposed the system for reducing the noise at the broadband noise source. The results of the experiment indicated that the proposed system with a directional microphone and loudspeaker improved the ANC system attenuation performance in the presence of acoustic feedback.
Experimental characterization of the vibrational behavior of a fluid-filled thin shell for the purpose of response estimation
(1995-12-01)
Bai, MR
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Lin, YY
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交大名義發表
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機械工程學系
;
National Chiao Tung University
Experimental techniques are proposed for developing a model to estimate structural vibrations induced by internal acoustic pressure at low frequencies. In these methods, the acoustic field and the structure are treated as a coupled system with the acoustic loading effect taken into account. The response model between the internal pressure and the surface vibration is established by a modified modal test on the coupled system. Experiments are performed to investigate the surface vibrations of a closed steel cylindrical shell excited by a loudspeaker inside. The experimental results show that developed techniques provide accurate estimation for the acoustically induced vibrations. (C) 1995 Acoustical Society of America.