Download or read book Optimization of Active Noise Control for Small Axial Cooling Fans written by Brian B. Monson and published by . This book was released on 2006 with total page 63 pages. Available in PDF, EPUB and Kindle. Book excerpt: Previous work has shown that active noise control is a feasible solution to attenuate tonal noise radiated by small axial cooling fans, such as those found in desktop computers. One such control system reduced noise levels of a baffled 80-mm fan in the free field with four small loudspeakers surrounding the fan. Due to industry specified spatial constraints, a smaller fan and speaker configuration was desirable. The smaller configuration maintains similar control performance, further facilitating practical implementation of the control system. The smaller control system employs a smaller fan running at a higher speed. Different loudspeaker configurations for control exist and have been tested. A configuration consisting of four control sources spaced symmetrically around and coplanar to the fan exhibits global control of the tonal component of the fan noise. A configuration with three symmetrically spaced sources is shown to perform similarly, agreeing with theoretical prediction. An analysis of the control system in a non-ideal reflective environment is also discussed.
Download or read book Optimization of Control Source and Error Sensor Locations in Free Field Active Noise Control written by Connor Raymond Duke and published by . This book was released on 2007 with total page 115 pages. Available in PDF, EPUB and Kindle. Book excerpt: Previous work has shown that active noise control (ANC) can be applied to axial cooling fans. Optimization of the control source and error sensor placement is desired to maximize the attenuation using ANC. A genetic algorithm was developed to find the optimal placement of control sources for a given primary source. The optimal configuration of control sources around a single primary source was shown to be a linear arrangement of the sources. This holds true for both two-dimensional as well as three-dimensional configurations. The higher-order radiation of the linear arrangement has also been verified experimentally, but the improvement in the experimental apparatus was not as dramatic as the theoretical model. Multiple flow visualization techniques have been used to find optimal near field error sensor locations. When there is little obstruction to the flow field of the fan, minimal airflow is found along the near field null that is created by minimizing the sound power of the system. Surface mounting of the error sensors can lead to a small increase in the signal-to-noise ratio of the error sensors if vortices exist in the near field of the fan due to obstructions in the main flow. It has also been shown that the introduction of the ANC system does not affect the flow field of the fan.
Download or read book Feedback Applications in Active Noise Control for Small Axial Cooling Fans written by Matthew J. Green and published by . This book was released on 2006 with total page 69 pages. Available in PDF, EPUB and Kindle. Book excerpt: Feedback active noise control (ANC) has been applied as a means of attenuating broadband noise from a small axial cooling fan. Such fans are used to maintain thermal stability inside of computers, projectors, and other office equipment and home appliances. The type of low-level noise radiated from axial cooling fans has been classified as harmful to productivity and human well being.
Download or read book Noise Source Analysis and Control for Small Axial Flow Fans written by Chen Wang and published by Open Dissertation Press. This book was released on 2017-01-26 with total page 232 pages. Available in PDF, EPUB and Kindle. Book excerpt: This dissertation, "Noise Source Analysis and Control for Small Axial-flow Fans" by Chen, Wang, 王晨, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Fan noise is always an important topic in applications ranging from small cooling fans for computers, transport vehicles and machinery, and building ventilation fans, to large compressors and turbo-engine fans in aircraft. When air flow with higher pressure or larger flow rate is needed in some operating conditions, two fans in series or a contra-rotating fan is often adopted. The purpose of this project is to conduct the noise source analysis for two identical small axial-flow cooling fans and a newly designed small axial-flow contra-rotating fan (both about 120 mm in diameter), and to explore some passive methods to reduce the more complex radiated noise, compared with that encountered in a conventional single fan. For two fans in series, a technique of synchronous averaging with time-base stretching is used to decompose the raw sound signals into various noise source components. Acoustic directivity measurements are conducted for two operating conditions: free space and its usual working condition; each condition with two different configurations: free (unobstructed) inlet and distorted inlet by a flat plate covering part of inlet area. For both operating conditions, the rotary noise from the downstream fan dominates over that from the upstream fan for unobstructed inlet while the dominance by the downstream fan is reversed with distorted inlet. The total noise, total broadband noise and rotary noise radiated by the upstream fan all increase gradually with decreased plate-fan spacing. However, the rotary noise radiated by downstream fan is hardly affected by the obstacle plate, whatever the plate-fan spacing is. The flow straightener between the two fans contributes to considerable improvement of aerodynamic performance for free inlet case, while it has a limited role in remedying the severe inlet distortion when placed in front of the upstream fan. From the derived formula of acoustic spectrum from rotor blade forces resulting from the viscous and potential wakes of the upstream counter-rotating blade row impinging in the downstream one, two obvious mechanisms for interaction noise reduction can be easily found, which are either to increase the order of the Bessel function of the first kind, or to reduce the interaction fluctuating forces which can be realized by reducing the magnitude of the wake centerline velocity deficit or broaden the wake width. Several passive methods for reducing the aerodynamic interaction noise of a newly designed small axial-flow contra-rotating fan are explored. These methods include: (1) Perforated trailing edge for the upstream rotor and perforated leading edge for the downstream rotor; (2) Slitted trailing edge serration for the upstream rotor; (3) Chordwise perforated leading edge of the downstream rotor. Up to 5-7 dB overall noise reduction at all directions is achieved through the first two methods compared under the same aerodynamic output. Only 1.3 dB of acoustic benefit is achieved by the third method, but it hardly causes any adverse impact on the aerodynamic performance. The findings are useful and helpful in designing a quiet coaxial fan (two/multiple-stage or contra-rotating) and adopting an appropriate approach for noise mitigation. Subjects: Fans (Machinery) Noise control
Download or read book Fans written by Thomas Carolus and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Fans In a unique approach, this textbook combines the design and construction of centrifugal and axial fans with the problem of their noise generation and its mitigation. Easily applicable methods of fan selection, aerodynamic fan design, and fan noise prediction are compiled, including most of the underlying physical principles. Other features of this book include introductions to numerical and experimental methods, simulation-based optimization techniques for fan design, and psychoacoustic methods for evaluating fan noise. Numerous practical problems illustrate and reinforce the ideas and concepts. Content Fan performance parameters, demand of a plant and fan selection, fan performance characteristics, model laws, flow kinematics, efficiencies - Design methods for centrifugal and axial fans - Mechanisms of fan sound generation, methods for fan sound prediction - Psychoacoustic evaluation of fan noise - Design features of noise reduced fans - Computational fluid dynamics, fan test rigs, simulation-based optimization - Practice problems and solutions. Target group Students of mechanical engineering at colleges and universities Engineers in the industrial fan manufacturing industry, planning engineers for heating, ventilation air conditioning systems and in equipment and plant engineering Author Prof. Dr.-Ing. Thomas Carolus taught fluid mechanics at the Department of Mechanical Engineering at the University of Siegen, Germany, with a focus on fluid machinery. This book is a translation of the original German 4th edition Ventilatoren by Thomas Carolus, published by Springer Fachmedien Wiesbaden GmbH, part of Springer Nature in 2020. The translation was done with the help of artificial intelligence (machine translation by the service DeepL.com), but with a subsequent human revision in terms of content. Springer Nature works continuously to further develop tools for the production of books and on the related technologies to support the authors.
Download or read book Active Noise Control of a Two fan Exhaust mounted Array Using Near field Control Sources and Error Sensors written by Ryan Leonard Rust and published by . This book was released on 2011 with total page 67 pages. Available in PDF, EPUB and Kindle. Book excerpt: Multiple fans are sometimes used in an array configuration to cool various types of electronic equipment. In addition to adding another noise source, using two fans with closely spaced blade passage frequencies (BPF) can create an annoying beat frequency. A two fan array with each fan having a different BPF was considered. The fans were theoretically modeled at the BPF and first harmonics. Each fan has two acoustic paths to the far field. Thus, each fan was modeled as a two source array. The first control configuration consisted of one control filter using six control sources and six error sensors in a fully coupled control system designed to control both fans simultaneously. The second configuration used two independent controllers with three control sources and three error sensors, one controller per fan. Experimentally, the averaged narrow band reduction of the BPFs and the second harmonic of the two independent controllers were 15.6 and 7.4 dB respectively, compared to a reduction of 14.4 and 5.7 dB at the two frequencies using a single control loop. The results suggest that independent controllers perform better than the single control loop for the fan array studied. Optimization of active noise control systems has increased performance but sometimes with decreased robustness. Two control source configurations for the sound power reduction of a simple source were analyzed by modeling the control systems. The two control source configurations were four symmetric control sources surrounding the noise source and an optimized linear array of four control sources. Simulation results show the linear array control source configuration is more sensitive to microphone placement errors, with a 20-33 dB reduction in attenuation for a microphone placement error of 2 mm compared to a 0.8 dB drop in attenuation for the symmetric case. The linear array configuration was found to be more sensitive to the microphone placement errors compared to the symmetric configuration. A 2.5 mm change in one microphone position causes an average of 6 dB loss in attenuation for the linear array configuration compared to a 0.6 dB loss for the symmetric configuration.
Download or read book Multi channel Active Control of Axial Cooling Fan Noise written by Kent L. Gee and published by . This book was released on 2002 with total page 126 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Error Sensor Placement for Active Control of an Axial Cooling Fan written by Benjamin Michael Shafer and published by . This book was released on 2007 with total page 114 pages. Available in PDF, EPUB and Kindle. Book excerpt: Recent experimental achievements in active noise control (ANC) for cooling fans have used near-field error sensors whose locations are determined according to a theoretical condition of minimized sound power. A theoretical point source model, based on the condition previously stated, reveals the location of near-field pressure nulls that may be used to optimize error sensor placement. The actual locations of these near-field pressure nulls for both an axial cooling fan and a monopole loudspeaker were measured over a two-dimensional grid with a linear array of microphones. The achieved global attenuation for each case is measured over a hemisphere located in the acoustic far field of the ANC system. The experimental results are compared to the theoretical pressure null locations in order to determine the efficacy of the point source model. The results closely matched the point source model with a loudspeaker as the primary source, and the sound power reduction was greatly reduced when error sensors were placed in non-ideal locations.
Download or read book Optimization of Secondary Source Locations for Active Noise Control in Three dimensional Spaces written by D. K. Holger and published by . This book was released on 1993 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Analog Feedback Control of Broadband Fan Noise written by Cole V. Duke and published by . This book was released on 2012 with total page 74 pages. Available in PDF, EPUB and Kindle. Book excerpt: Active noise control (ANC) has been implemented using analog filters to reduce broadband noise from a small axial cooling fan. Previous work successfully attenuated narrow-band, tonal portions of the noise using a digital controller. The practical performance limits of this system were reached and it was desirable to attenuate the noise further. Additional research, therefore, sought to attenuate broadband noise from the fan using digital controller, but performance was limited by the group delay inherent in the digital signal processor (DSP). Current research attempts to further attenuate broadband noise and improve performance of the system by combining the tonal controller with an analog feedback controller. An analog controller is implemented in parallel with the digital controller without degrading the performance of either individual controller. Broadband noise is attenuated in a certain frequency region, but at the expense of increasing noise in adjacent frequency regions. Results show that a single-input single-output (SISO) controller is preferable to a multiple-input multiple-output (MIMO) controller for this system.
Download or read book Active Noise Control of a Centrifugal Fan Mounted in a Mock Laptop Enclosure written by J. James Esplin and published by . This book was released on 2012 with total page 113 pages. Available in PDF, EPUB and Kindle. Book excerpt: Noise from information technology (IT) equipment is a significant problem in today's modern society. Active Noise Control (ANC) has shown promise in reducing the effect of IT fan noise on users. Though ANC has been applied to axial fans (such as those found in desktop computers), it has not been applied to centrifugal fans, such as those found in laptop computers. This work applies an ANC method to a centrifugal fan mounted in a mock laptop enclosure. This method is applied in four steps. First, secondary sources are placed in the vicinity of the fan. Second, an accurate model of the radiation from the fan and secondary sources is constructed. Third, the total power radiated from this system is minimized. This creates nodal lines in the vicinity of the fan. Fourth, ANC error sensors are placed on the nodal lines predicted by the model. This creates these nodal lines experimentally, thus creating the minimum power condition. The noise from the exhaust and inlets of the fan will first be controlled individually. Then the method will be applied to the combined system. Global sound power radiation will be measured in all cases.
Download or read book The Journal of the Acoustical Society of America written by Acoustical Society of America and published by . This book was released on 2006 with total page 1114 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Scientific and Technical Aerospace Reports written by and published by . This book was released on 1995 with total page 704 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Inter noise written by and published by . This book was released on 1989 with total page 1442 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book International Aerospace Abstracts written by and published by . This book was released on 1999 with total page 1020 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Applied mechanics reviews written by and published by . This book was released on 1948 with total page 400 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Noise news International written by and published by . This book was released on 1995 with total page 724 pages. Available in PDF, EPUB and Kindle. Book excerpt:
