LEZINGENMIDDAG Active noise control

6 juni 2012
Beatrixgebouw Jaarbeurs Utrecht
Dagvoorzitters:
dr. ir. Y.H. (Ysbrand) Wijnant
dr. ir. A.P. (Arthur) Berkhoff

NAG, mei 2012

Programma

12.00 – 13.00 Ontvangst en koffie/thee met broodjes

13.00 – 13.45
Control strategies for active reduction of noise and vibration
Arthur Berkhoff, TNO Technical Sciences, Acoustics & Sonar, Den Haag en Universiteit Twente, Faculteit EWI & CTW, Enschede

Several applications exist in which an active noise and vibration control system may be useful. However, in few applications active control has been a commercial success. The choice of the control strategy, which involves the choice of the actuators, sensors, algorithm and hardware architecture, is critical for the success in a particular application. Based on examples of active noise and vibration control systems for different applications, the advantages and disadvantages of several control strategies will be discussed. Examples will be given for active reduction of noise transmission through panels, noise reduction using virtual sensors, active vibration control in gearboxes, and vibration reduction in highprecision equipment. Recent developments will be presented for active noise control applied to energyefficient ventilation systems in houses. It will be shown that the techniques for the design of active noise and vibration control systems can also be useful for other applications, e.g. directional sound sources, characterization of the dynamic stiffness of vibration isolation mounts and calibration of particle velocity sensors.

13.45 – 14.25
Cavity Control and Panel Control Strategies in Double-Panel Structures for Transmitted Noise Reduction
Jen-Hsuan Ho¹, Jurgen Klaverboer¹ en Arthur Berkhoff^{1 2},
¹ EWI, University of Twente, Enschede
²TNO, Acoustics Department, Delft

Investigation and comparisons of the cavity control and the panel control in a double-panel structure are presented in this paper. The double-panel structure, which comprises two panels with air in the gap, provides the advantages of low sound-transmission at high frequency, low heat-transmission and low weight. Therefore, the double-panel structure is adopted in various applications such as aerospace and vehicle industry. However, the resonance of the air cavity and the high sound-transmission at low frequency limit its noise control performance. Furthermore, the resonant behaviors and the sound radiating modes of single panel structures are different from double-panel structures. As a consequence, the panel control strategy, which is widely applied in structural acoustic control, for singlepanel structures needs to adapt to double-panel structures. In this paper, a structural-acoustic coupled model is developed to investigate and to compare various panel control and cavity control methods. A detailed investigation of the structure and the cavity resonance is showed. Both the numerical analysis and the real time control results show that the panel control should apply to these two panels simultaneously. And the cavity control by loudspeakers with pressure source can provide remarkable noise reduction in the double-panel structures. Finally, the combination of the feedforward panel control and the feedback cavity control can further reduce the transmitted noise.

14.25 – 15.05
Noise Quieting Directives and Active Control - When Poorly Drafted, Understood, or Executed Rules Hurt Both Hearing and Technology
Dr. Christian E. Carme and
dr. Daniel J. Maguire, Technofirst

Noise regulations and guidelines exist all around the world. Those regulations - including Directive 2002/49/EC - were drafted with the purpose of reducing noise levels to maintain hearing and increasing work or life quality for a wide array of environments and describe measurement methods and limits. Sound signatures and levels vary widely across the regulated environments. Because of this, the regulations often do not - and, in fact, cannot - guarantee a valid assessment of human harm. Examples of this include: guidelines in regulations that dictate measurement locations that are in direct conflict with human harm; regulations that require filter functions that reduce the measurement of harmful energy; and regulations that are too vague in defining when alternatives measurements are allowed. This paper describes direct conflicts between regulations and active impact. One result is humans are being exposed to sounds that are harmful to them in environments that are deemed "safe." A second result is active control is not being adopted in applications where it would be beneficial because the improvement is penalized. For the active community to advance both technology and commercial scope, noise regulations that are harming hearing and technology need to be corrected or improved.

15.05 – 15.20 Koffie/thee pauze

15.20 – 16.00
Application of a Kalman filter in active noise control
Sjoerd van Ophem, Universiteit Twente, EWI – SAS

The filtered reference least mean squares algorithm is widely used in active noise control systems to adapt the controller. It is relatively easy to implement and it is robust, but it also has a few disadvantages, such as a low rate of convergence and a slow tracking behavior. This is due to the assumption used in the derivation of the algorithm, which states that the secondary path and the filter can be interchanged. A possible way to evade this assumption is to rewrite the adaptive system to an estimation problem in a state space form. A Kalman filter is chosen to solve this estimation problem. Simulation shows a potentially much higher rate of convergence. To investigate the performance in a real-time environment, the filter was implemented in an active noise control experiment in which the goal was to reduce the noise at the end of a duct. This was done with different kind of state matrices. The results of the experiment show a comparable rate of convergence to simulations. Also the performance of the filter, when subjected to changing noise spectra and changing transfer functions, was tested.

16.00 – 16.40
Active Vibration Control of gradient coils to reduce acoustic noise of MRI systems
Bert Roozen, Delft University of Technology, NOVIC Noise and Vibration Control

Lorentz-force induced vibrations in Magnetic resonance imaging (MRI) systems cause significant acoustic noise levels during scanning, the main acoustic noise source being the vibrating gradient coil. In the presentation a novel active vibration control technique is presented to reduce vibrations of the gradient coil and hence achieve a reduction of acoustic noise during scanning. The active vibration control technique uses seismic masses that are actuated by means of piezo actuators to create forces on the gradient coil counteracting its vibrations. Using 4 seismic mass actuators, a vibration reduction of 3 to 8 dB at resonance frequencies is achieved, giving an overall vibration reduction of 3 dB for a typical FE-EPI gradient sequence, as substantiated by measurements. Using 8 actuators, an overall vibration reduction of 5 dB is predicted for this sequence.

(Presentatie is in het Nederlands)

16.40 – 17.20
Robust active damping in a wafer scanner using Piezo Active Lens Mounts
Jan Holterman

High-precision machines are usually designed according to a limited number of well-known design principles. The dynamic behaviour is optimised mainly by means of proper stiffness management: the design of the mechanical structure is aimed at minimisation of the mass, and maximisation of the stiffness. Damping management is not yet a mature design principle. This is due to the difficulties in designing passive damping mechanisms that do not endanger accuracy. As an example of a vibration problem within an industrial high-precision application, the need for active damping management in a wafer scanner is discussed. Vibrations of the lenses of this machine pose a practical limit to the accuracy of the lithography process. For that reason, active structural elements have been developed for supporting the lenses. These so-called Piezo Active Lens Mounts (PALM), consisting of a piezoelectric actuator and a collocated piezoelectric force sensor, are especially suited for implementing robust active damping. In the presentation the conflicting requirements in the mechanical design of the active elements are discussed and illustrated by means of experimental active damping results that have been obtained on a wafer scanner

17:20 Borrel

Opgave voor deelname aan deze bijeenkomst kan geschieden door middel van een aanmeldingsformulier, verkrijgbaar via secr@nag-acoustics.nl. De kosten voor de lunch bedragen € 15,00 per persoon, te voldoen ter plaatse. U wordt verzocht alleen dan voor de lunch in te schrijven als u daaraan ook met zekerheid zult deelnemen, dit in verband met de aan de organisatie verbonden financiλle verplichtingen.

Niet-leden zijn eveneens welkom op deze lezingendag. De kosten voor deelname en lunch voor nietleden bedragen € 70,00. Bij betaling van dit bedrag hebben deelnemers recht op vrijstelling van het 1e jaar contributie van het NAG bij aanmelding als lid. Studerende niet-leden kunnen gratis deelnemen aan de lezingendag en betalen uitsluitend, voor zover van toepassing, € 15,00 voor de lunch.

 

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