Dissertations / Theses on the topic 'Noise control'
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1
Ma, Xuxin. "Ducted fan noise control." Click to view the E-thesis via HKUTO, 2009. http://sunzi.lib.hku.hk/hkuto/record/B44143072.
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Ma, Xuxin, and 马旭鑫. "Ducted fan noise control." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2009. http://hub.hku.hk/bib/B44143072.
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Belayat, Nadia Bousseksou. "Entertainment noise control in Algeria." Thesis, London Metropolitan University, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.523012.
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These last ten years, in Algeria noise pollution has become an environmental issue where people are exposed to unacceptable levels of noise. The main noise source is from traffic, from neighbourhood and domestic noise particularly {entertainment premises known as wedding halls}. Other significant sources of noise annoyance in Algeria include building construction and household noise as well as car alarms and even barking dogs. In this present study, my concern will be on one of the main noise source in Algeria which is noise from entertainment halls. In Algeria, there is no existing framework or enforceable code for noise control. In view of the absence of a proper noise control standard in Algeria, a large number of wedding halls have been built without any protection {insulation, double glazing ... } causing disturbance and annoyance in the neighbourhood. The noise from these wedding halls is badly affecting neighbours. Modern amplification and music styles make this an increasing problem. Therefore local people saw their lives disturbed by the noise caused by these kinds of recreational halls. As a result of the lack of standards, this study was conducted. A noise survey has never been previously attempted in Algeria. The aim of this survey is to establish noise level limits and measurements according to the WHO guidelines recommended to create the necessary set off regulations and guidelines on which we could rely in treating the different noise problems in Algeria. During my investigations in Algiers concerning this subject I have understood that all the entertainment premises I have visited in the centre of the capital and its suburbs have been working without applying any true ,clear regulations concerning noise in general . I have found out that unfortunately {for these premises neighbourhood} no serious standards or codes of practice have been written in Algeria for the purpose of giving guidance or an objective assessment methodology to assist officers investigating neighbour and neighbourhood noise when they happen to deal with noise complaints. Up to now the only body noise complainers could refer to solve their noise problem is the police who most of the time resolve to make the antagonists meet, to cut the matter short they usually order them to reach a mutual compromise and resolve the problem amicably. In fact, most of the wedding halls which have sprung up everywhere and everyday between 2000 and 2008 have opened up in centre of towns close to places of residence entailing extreme noise nuisance to the neighbourhood. The people affected by noise disturbance do not know who can settle their complaints, except of course, a legal action which of course involves a loss of time and money. The measurements show a considerable increase in the noise level when the 'weddings' are on. This would not prove acceptable in the UK. Arguments will need to be advanced as to the correct criteria to be used in the specific circumstances of Algeria and how they can be achieved using local materials and construction practices.
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Copley-Woods, Djuna S. (Djuna Sunlight) 1977. "Aircraft interior acoustic noise control." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/9330.
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Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1999.Includes bibliographical references (p. 45).
An experimental study was perfonned to determine which materials are best suited for internal aircraft noise reduction. An impedance tube with dimensions of a scaled aircraft was constructed and evaluated, and eleven materials were tested and compared based on their noise reduction properties, weight, and thickness. Polyvinylidene Fluoride was tested for use in active noise control for a large space.
by Djuna S. Copley-Woods.
S.B.
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Farooqui, Maaz. "Innovative noise control in ducts." Doctoral thesis, KTH, Farkost och flyg, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-192927.
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The objective of this doctoral thesis is to study three different innovative noise control techniques in ducts namely: acoustic metamaterials, porous absorbers and microperforates. There has been a lot of research done on all these three topics in the context of duct acoustics. This research will assess the potential of the acoustic metamaterial technique and compare to the use of conventional methods using microperforated plates and/or porous materials. The objective of the metamaterials part is to develop a physical approach to model and synthesize bulk moduli and densities to feasibly control the wave propagation pattern, creating quiet zones in the targeted fluid domain. This is achieved using an array of locally resonant metallic patches. In addition to this, a novel thin slow sound material is also proposed in the acoustic metamaterial part of this thesis. This slow sound material is a quasi-labyrinthine structure flush mounted to a duct, comprising of coplanar quarter wavelength resonators that aims to slow the speed of sound at selective resonance frequencies. A good agreement between theoretical analysis and experimental measurements is demonstrated. The second technique is based on acoustic porous foam and it is about modeling and characterization of a novel porous metallic foam absorber inside ducts. This material proved to be a similar or better sound absorber compared to the conventional porous absorbers, but with robust and less degradable properties. Material characterization of this porous absorber from a simple transfer matrix measurement is proposed.The last part of this research is focused on impedance of perforates with grazing flow on both sides. Modeling of the double sided grazing flow impedance is done using a modified version of an inverse semi-analytical technique. A minimization scheme is used to find the liner impedance value in the complex plane to match the calculated sound field to the measured one at the microphone positions.QC 20160923
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Tu, Yifeng. "Multiple Reference Active Noise Control." Thesis, Virginia Tech, 1997. http://hdl.handle.net/10919/36790.
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The major application of active noise control (ANC) has been
focused on using a single reference signal; the work on
multiple reference ANC is very scarce. Here, the behavior
of multiple reference ANC is analyzed in both the frequency
and time domain, and the coherence functions are provided to
evaluate the effectiveness of multiple reference ANC.
When there are multiple noise sources, multiple reference
sensors are needed to generate complete reference signals.
A simplified method combines those signals from multiple
reference sensors into a single reference signal. Although
this method could result in satisfactory noise control
effects under special circumstances, the performance is
generally compromised. A widely adopted method feeds each
reference signal into a different control filter. This
approach suffers from the problem of ill-conditioning when
the reference signals are correlated. The problem of
ill-conditioning results in slow convergence rate and high
sensitivity to measurement error especially when the FXLMS
algorithm is applied. To handle this particular problem,
the decorrelated Filtered-X LMS (DFXLMS) algorithm is
developed and studied in this thesis.
Both simulations and experiments have been conducted to
verify the DFXLMS algorithm and other issues associated
with multiple reference ANC. The results presented herein
are consistent with the theoretical analysis, and favorably
indicate that the DFXLMS algorithm is effective in improving
the convergence speed.
To take the maximum advantage of the TMS320C30 DSP board
used to implement the controller, several DSP programming
issues are discussed, and assembly routines are given in
the appendix. Furthermore, a graphical user interface (GUI)
running under Windows' environment is introduced. The main
purpose of the GUI is to facilitate parameters modification,
real time data monitoring and DSP process control.Master of Science
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Mitchell, Morgan Adrienne. "Passive Noise Control in Incubators." Thesis, Virginia Tech, 2013. http://hdl.handle.net/10919/51603.
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Incubators in the Neonatal Intensive Care Unit (NICU) are known to produce high Sound Pressure Levels (SPL) that can have detrimental effects on infants. Currently measured SPL in NICU's using traditional incubators are above the recommended 45 dB[A] threshold value [1]. Due to operating equipment and environmental noise, the sound level that is perceived by the developing newborn can cause both short and long term hearing loss as well as psychological damage [1].This thesis presents a study on how passive noise control devices can be used to reduce SPL levels in incubator NICU environments. A combination of experimental testing coupled with Finite Element simulations were performed for a modern incubator. In the experimental portion, porous mattresses were analyzed to reduce SPL values. These same test scenarios were modeled using the FE software. Using this model, extensive studies were performed on an arrangement of porous mattress materials with simple foam shapes to determine sound absorbing characteristics of several designs. Data was collected and studied at a NICU at Children\'s Hospital in Norfolk, Va. Experimental work showed improvement in reducing SPL with multiple thicknesses for different sound absorbing mattresses. The experimental outcomes validated the FE simulation model by showing similar trends at the baby\'s ears. In simulation work, polyimide foam had the best low frequency performance while polyurethane had the greatest performance in middle and high frequencies. Designs that used full-width foam treatments across the incubator produced the overall greatest reduction in noise around the baby control volume by approximately 26%.Master of Science
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Yip, Ying-ling. "Review of road traffic noise control." Click to view the E-thesis via HKUTO, 1998. http://sunzi.lib.hku.hk/hkuto/record/B42128523.
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Kaymak, Erkan. "Noise reduction and active noise control of high frequency narrow band dental drill noise." Thesis, Brunel University, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.445923.
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Peng, Dandan, and 彭丹丹. "Compact environmental noise absorber." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2014. http://hdl.handle.net/10722/209491.
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With the development of the industry and the society, noise pollution becomes increasingly severe, especially in large cities. Generally, there are three major noise sources, namely industrial noise, traffic noise and community noise. In response, several measurements have been developed to achieve effective noise control. Examples of noise control methods are reduction of noise at source and abatement of noise during the transmission. Since noise sources are more difficult to control, and sometimes already fixed, noise control during sound transmission is more broadly applied. Traditional passive noise control techniques include Helmholtz resonators and noise absorption materials like felt, glass mineral. The sound absorption materials (SAM) are found to be efficient in attenuating noise in high frequency domain, but their performance at low frequencies is quite poor. On the other hand, the Helmholtz resonator works perfect at any target frequency but suffers from its narrow absorption bandwidth, so that it’s only effective within a limited frequency band.
As an innovative solution to passive noise control problem, micro-perforated panel absorber (MPPA) has attracted great interest in recent years. It turns out to be a competitive alternative to sound absorption materials and Helmholtz resonator. The parallel and series arrangement of MPPAs backed with cavities of different depths allows them to obtain decent noise absorption performance over a relatively broad frequency range. However, the performance of MPPA is restricted by its volume, as large volume is demanded for decent low-frequency absorption, which is also the case for noise absorption materials.
In this thesis, a potential way to improve the low-frequency performance of the MPPA without occupying extra volume is proposed and implemented to tests. The focus is the adjustment of speed of sound and it is beneficial in different applications such as the following. In low frequency noise control, the size of the absorber in at least one dimension is often related to the wavelength and it is often too long. With a reduced speed of sound one can reduce this size while keeping the overall volume constant. Along this line of thinking, the effect of cavity configuration on its acoustic properties is investigated by two steps. Firstly, the property of a waveguide consisting of several identical elements is studied. The number of element is chosen to magnify the effect of the configuration. It turns out the irregularity of the duct shape can slow down the speed of sound of the plane wave by increasing the acoustic mass. Secondly, the absorption performance of an MPPA backed with an irregular cavity is evaluated. The shape of the cavity is the same as the element in the first step. In advance, the parallel arrangement of two MPPAs backed with irregular cavities is investigated, in order to look into the effect of cavity shape on inter-resonator interaction. The final results indicate that cavity design is an effective method to enhance the noise absorption performance of the MPPA arrays in the low-frequency domain.published_or_final_version
Mechanical Engineering
Master
Master of Philosophy
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Ma, Ki-tin. "A review of the implementation of the noise control ordinance in Hong Kong /." Hong Kong : University of Hong Kong, 1996. http://sunzi.lib.hku.hk/hkuto/record.jsp?B1745783X.
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Hedborg, Mårten, and Patrik Grylin. "Active Noise Control of a Forest Machine Cabin." Thesis, Linköping University, Department of Electrical Engineering, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-9065.
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Today, a high noise level is considered a problem in many working environments. The main reason is that it contributes to stress and fatigue. Traditional methods using passive noise control is only practicable for high frequencies. As a complement to passive noise control, active noise control (ANC) can be used to reduce low frequency noise. The main idea of ANC is to use destructive interference of waves to cancel disturbing noises.
The purpose of this thesis is to design and implement an ANC system in the driver's cabin of a Valmet 890 forest
machine. The engine boom is one of the most disturbing noises and therefore the main subjective for the ANC system to suppress.
The ANC system is implemented on a Texas Instrument DSP development starter kit. Different FxLMS algorithms are evaluated with feedback and feedforward configurations.
The results indicate that an ANC system significantly reduces the sound pressure level (SPL) in the cabin. Best performance of the evaluated systems is achieved for the feedforward FxLMS system. For a commonly used engine speed of 1500 rpm, the SPL is reduced with 17 dB. The results show fast enough convergence and global suppression of low frequency noise.
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Chau, Pak-lam. "Evaluation on the effectiveness of noise barriers for road traffic noise mitigation /." Hong Kong : University of Hong Kong, 1998. http://sunzi.lib.hku.hk/hkuto/record.jsp?B20038173.
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Casey, Kathleen. "Noise making subjects /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2005. http://wwwlib.umi.com/cr/ucsd/fullcit?p3170240.
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Szoke, Matthew. "Trailing edge noise control using active flow control methods." Thesis, University of Bristol, 2019. http://hdl.handle.net/1983/e45a9e22-3146-4467-90c4-01d3b6aebeb3.
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Active flow control methods are investigated experimentally with the aim of reducing the trailing edge noise on a zero pressure gradient flat plate test rig. Flush-mounted microphones are embedded in the wall of the plate between the flow control section and the trailing edge to study the surface pressure fluctuations exposed on the wall by the turbulent boundary layer. Three different types of active flow control techniques are considered, namely uniform inclined flow suction, uniform inclined flow injection and inclined transverse jets. The velocity statistics reveal that inclined flow suction can relaminarize the boundary layer flow. As the boundary layer reaches a laminar state, flow suction significantly reduces the trailing edge noise at mid-frequencies, while some penalties observed at low and high frequencies. Once laminarisation is achieved, the noise reduction capabilities of flow suction reach its maximum, and further increasing the suction rate does not provide any additional benefit of noise reduction. Flow injection triggers the boundary layer separation and the development of a shear layer. As a result, the trailing edge noise increases in a broadband manner. Increasing the blowing rate to moderate levels can reduce the trailing edge noise at mid and high frequencies, while noise increase is observed at low frequencies. A more significant noise reduction can be achieved at high injection angles and blowing rates when the boundary layer entirely separates from the wall. Finally, a single line of jet nozzles is installed parallel to the trailing edge of the plate. The individual jets merge downstream of the jet nozzles and they form a layer of jet fluid characterized by low energy content. The estimates of the trailing edge noise show that jets injection can reduce the trailing edge noise over the whole range of frequencies under analysis.
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Moodie, Alex Montfort. "A new methodology for sizing and performance predictions of a rotary wing ejector." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/26678.
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Thesis (Ph.D)--Aerospace Engineering, Georgia Institute of Technology, 2009.Committee Chair: Dr. Daniel P. Schrage; Committee Member: Dr. Lakshmi N. Sankar; Committee Member: Dr. Richard J. Gaeta; Committee Member: Dr. Stephen M. Ruffin; Committee Member: Mark H. Waters. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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Forsgren, Fredrik. "Active Noise Control in Forest Machines." Thesis, Umeå universitet, Institutionen för fysik, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-48661.
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Achieving a low noise level is of great interest to the forest machine industry. Traditionally this is obtained by using passive noise reduction, i.e. by using materials for sound isolation and sound absorption. Especially designs to attenuate low frequency noise tend to be bulky and impractical from an installation point of view. An alternative solution to the problem is to use active noise control (ANC). The basic principle of ANC is to generate an anti-noise signal designed to destructively interfere with the unwanted noise. In this thesis two algorithms (Feedback FxLMS and Feedforward FxLMS) are implemented and evaluated for use in the ANC-system. The ANC-system is tuned to the specific environment in the driver’s cabin of a Komatsu forest machine. The algorithms are first tested in a simulated environment and then in real-time inside a forest machine. Simulations are made both in Matlab and in C using both generated signals and recorded signals. The C code is implemented on the Analog Devices Blackfin DSP card BF526. The result showed a significantly reduction of the sound pressure level (SPL) in the driver’s cabin. The noise attenuation obtained using the Feedback FxLMS was approximately 14 dB for a tonal 100 Hz signal and 11 dB using recorded engine noise from a forest machine at 850 rpm.
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Munn, Jacqueline Marie. "Virtual sensors for active noise control /." Title page, abstract and table of contents only, 2003. http://web4.library.adelaide.edu.au/theses/09PH/09phm9668.pdf.
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Rybing, Peter. "Active Noise Control in Home Environment." Thesis, KTH, Reglerteknik, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-109486.
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Disturbing noise is a growing problem in the society. Also in the home environment noise making devices exist, for example the vacuum cleaner. A simple way to decrease the annoyance from a vacuum cleaner is to use personal passive ear defenders. A problem with passive ear defenders is that they also attenuate wanted signals, such as speech or music. In this thesis a pair of prototype active ear defenders for vacuum cleaner noise attenuation have been developed and evaluated. Active noise control technology was used, which solved the problem with wanted signal attenuation. A measured noise reference was used with a pair of open earphones as actuator. The overall cancellation performance of the prototype system was quite low for vacuum cleaner noise. Due to that the coherence between the measured noise reference and the unwanted noise was low. Wanted signals were shown to be just slightly affected by the prototype system.
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Lane, Jeremy David. "Active Control of Noise Through Windows." Thesis, University of Canterbury. Mechanical Engineering dept, 2013. http://hdl.handle.net/10092/10523.
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Windows are a weakness in building facade sound transmission loss (STL). This coupled with the detrimental effects of excessive noise exposure on human health including: annoyance, sleep deprivation, hearing impairment and heart disease, is the motivation for this investigation of the STL improvements active noise control (ANC) of windows can provide.
Window speaker development, ANC window experiments and analytical modelling of ANC windows were investigated. Five different window speaker constructions were characterised then compared with a previously developed window speaker. ANC window testing used three different ANC configurations and was performed in two different
environments, one with a reverberant receiving room, and the other with an anechoic receiving room. Optimisation of ANC systems with particular control source locations was the aim of the modelling. This enabled comparison with the ANC window tests and would aid in further development of ANC windows.
Window speaker constructions were characterised by sound pressure level (SPL) measurements performed in an anechoic room. These measurements were made in a way that enabled comparison with the previously developed window speaker.
Total sound energy reduction calculations were used to determine the relative performance of the tested ANC windows.
An STL model, based on a modal panel vibration model, was initially created and verified against published STL data before it was expanded to include ANC control sources. The model was used to simulate the performed anechoic environment tests and an ideal ANC case.
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Yip, Ying-ling, and 葉影玲. "Review of road traffic noise control." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1998. http://hub.hku.hk/bib/B42128523.
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Wang, Lin. "Active control of fluid-borne noise." Thesis, University of Bath, 2008. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.501639.
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Fluid-borne noise is one of the main components of hydraulic noise. Its attenuation may have a significant effect on the cost of hydraulic systems. Standard passive silencers and dampers can be useful in reducing it in certain frequency ranges; however, these tend to be heavy, bulky and expensive. Active control algorithms, which are a comparatively recent means of reducing fluid-borne noise, can be applied to overcome this compromise. The work presented in this thesis is the development of some active control algorithms utilized in a simple hydraulic system to cancel a number of harmonic orders of fluid-borne noise generated by a servo valve or a real pump. To realize cancellation the filtered reference least mean square (FXLMS) adaptive control method is mainly presented. Furthermore, a fast response servo valve is applied as an actuator to generate a proper anti-noise flow signal in real-time. For simplicity, an off-line identification method for the secondary path is applied in the time invariant working condition. Moreover, ripple reflection from both ends of the hydraulic circuit can produce different effects under different working conditions. In order to execute the cancellation without any prior information about the dynamics of hydraulic systems, the on-line secondary path identification method is discussed. However, in this algorithm an auxiliary white-noise signal applied to an on-line method may contribute to residual noise and an extra computation burden may be added to the whole control system. The performance of these control algorithms is firstly investigated via simulation in a hydraulic pipe model and the real-time application on a test rig using a servo valve as a noise source. Finally, these schemes are realized in a simple hydraulic system with a real pump noise source. The fluid-borne noise can be attenuated by about 20 dB in normal working conditions.
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Kirkwood, A. D. "Aerdynamic noise generation in control valves." Thesis, University of Manchester, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.517180.
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An experimental study into the phenomenon of aerodynamic noise generation in control valves has been performed. Several model representations of control valves have been studied, in addition to making measurements on several full size control valves. A high speed computer based data acquisition system, coupled with miniature high frequency surface mounted pressure transducers, has been used to obtain measurements of both the mean and fluctuating wall static pressures at several locations throughout the length of the flow apparatus. For known flow conditions, it has been possible to determine the relative performance of each particular model or commercial valve design by examining the various recorded levels of the wall static pressure fluctuations. A series of flow visualisation experiments, in which both wall static pressures and photographs of the flow through a rectangular duct have been obtained simultaneously, has provided a valuable insight into the mechanisms that determine the performance of multi-plate models. These findings have led to the design and commissioning of a new working section constructed from lengths of circular pipe. This apparatus has been used to investigate the performance of models constructed from two circular multi-holed test plates placed normal to the flow, with the downstream test plate being significantly more porous. Relationships between parameters such as test plate hole diameter, test plate separation, hole pitch to diameter ratio and pressure ratio have been examined extensively for many combinations of model configuration. Subsequently, the vast amounts of experimental data produced by this systematic testing have been reduced to identify the clear links between the various parameters. This, in turn, has enabled the author to determine optimum values for the non-dimensional parameters which govern the design of such multi-plate systems. As a consequence of this study, the author has proposed an alternative approach to the design of 'Low Noise' control valves which offers the prospect of improved overall performance. Thus, it is envisaged that the findings from this investigation will have implications for the future design of 'Low Noise' control valves.
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Spiteri, Matthew. "Aerodynamic control of bluff body noise." Thesis, University of Southampton, 2011. https://eprints.soton.ac.uk/181529/.
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The main aim of this study was to investigate noise reduction techniques for bluff body noise. Three methods were investigated, using a splitter plate on a fairing- strut configuration, applying flow control to the surface of a fairing and fitting a splitter plate behind a isolated bluff body. Aerodynamic tests were performed in wind tunnel facilities using particle image velocimetry (PIV), hotwire anemometry, pressure sensors and a force balance. Acoustic tests using a microphone array, on-surface microphones and freefield mi- crophones were performed to investigate the noise generated by the models. The splitter plate fitted to the fairing-strut configuration was found to be dominated by large scale vortex shedding. The addition of the splitter plate blocked the interaction between the two opposing shear layers aft of the shell's trailing edge thereby reducing their interaction with the downstream strut. Broadband noise reductions were observed as well as reduction in the noise levels of the peaks asso- ciated with the shedding. Applying flow control showed noise reductions for both cases when suction and blowing were applied. These reductions were observed at the lower tested Reynolds numbers (ReDshell = 1.75 x 105), at higher Reynolds numbers (ReDshell = 3.5 x 105) the noise reductions decreased when compared to the baseline case. The splitter plate fitted behind an isolated bluff body modified the wake, decreasing shedding frequency and drag with an increase in the splitter plate length. Broadband noise reductions were observed with all three splitter plate lengths and the tonal peak of the vortex shedding noise was suppressed. The study shed light on the possibility of achieving noise reductions using the three methods. However more research is required to apply these findings on a landing gear.
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Rose, Michael Thomas. "Noise Control of Vacuum-Assisted Toilets." BYU ScholarsArchive, 2019. https://scholarsarchive.byu.edu/etd/8789.
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Vacuum-assisted toilets make use of a large pressure difference between the ambient pressure and a vacuum tank to transport waste from the toilet bowl to the septic tank. This process requires 98% less water per flush making it an attractive product for transport vehicles such as airplanes, cruise ships, and trains. Unfortunately, the water savings come at the cost of high noise levels. This thesis investigates the acoustic characteristics of a vacuum-assisted toilet flush and several methods to reduce the radiated noise. Some methods include changing rinse parameters such as rinse pressure, rinse length, and rinse timing, adding structural damping of the bowl to reduce re-radiation, inserting a tube between the bowl and valve that utilizes a larger bend radius and longer tube length than what is currently installed, and modifying the valve. The most effective solution without requiring more water per flush was to insert a tube. The initial peak level was reduced by 16 dB and the steady-vacuum noise was reduced by 5 dB. Evidence of evanescent decay and reduced flow velocity as possible mechanisms for the noise reduction are presented and discussed. Rinse variations show a strong impact of the rinse-tube interaction on the noise reduction. In addition to these techniques, a modified flush plate opening and closing velocity profile is suggested which optimizes the sound generated by the opening and closing of the valve. Finally, a promising dual-valve solution that may take extra coordination of vacuum-assisted toilet manufacturers and airplane/cruise ship/train manufacturers is presented. By placing a secondary valve near the septic tank, the main noise from the valve is significantly reduced.
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Sun, Guohua. "Active Control of Impact Acoustic Noise." University of Cincinnati / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1413542213.
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Berritta, Marco. "Coherent Nanostructures: Dynamics control and noise." Doctoral thesis, Università di Catania, 2013. http://hdl.handle.net/10761/1432.
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In the last three decades the scienti c community has been attracted by
the possibility of controlling quantum system, for example for quantum
computing or quantum simulators. Initially this idea was exploited only in
microscopic quantum system as atoms and molecules. However these sys-tems present diffi culties on the large scale application due to the extreme
laboratory condition that they need, for example ultra low temperature
of the order of 1 microKelvin. On the other hand, great progress has been made with superconducting nanodevices, that can be more easily scaled. One of the most important problems that arise in quantum control is decoherence. We will study quantum control for coherent superconducting nanodevices. This devices are aff ected by a Broad Band Colored and Structured (BBCS) noise, which is qualitatively di fferent to what encountered in atomic physics, since
it is chatacterized by a strong non-Markovian low-frequency component
with a characteristic power spectrum S (f) proportional to 1/f.
In this thesis we will present a roundup of physical situations, inolving both undriven and externally driven open quantum systems, which need to be analyzed in the perspective of quantum control. Promising applications to superconducting nanodevices, as the implementation of "Lambda" systems, possibly allowing control of microwawe photons, are discussed in detail.
The thesis is structured as follows. Chapter 1 is an overview of the
theoretical background of quantum control and quantum computation. In
chapter 2 an archetypical problem for driven quantum systems, namely the
Rabi problem, is studied in the presence of BBCS low-frequency noise
which is not accounted for in standard Master Equation treatments based
on the Markovian assumption. In chapter 3 a protocol named STImulated
Raman Adiabatic Passage (STIRAP) is studied in the presence of BBCS
noise, in view of its implementation in a class of superconducting nanode-vices named Cooper Pair Box. This is done in chapter where Design and
control requirements to achieve large e fficiency are discussed, and a new figure of merit is introduced to characterize the tradeoff between effi cient coupling of the control and noise. Actually selection rules due to charge-parity simmetry make impossible operate STIRAP in these device in the regime of maximum protection from noise. Therefore in chapter 5 we propose a new implementation of STIRAP with superconductive device that allows us to circumvent selection rules, based on three-photon coherent processes and suitable crafted pulses compensating the Stark shifts. In chapter 6 we will study the problem of the tunneling of a quantum particle with strongly coupled environment in a bistable pontential. Finally in chapter 7 the study of the motion of a chiral quasiparticle in graphene a ffected by white noise will be presented.
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Chan, T. M. "Active control of sound in ducts." Thesis, University of Southampton, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.390327.
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Cheung, Shuk-ching, and 張淑晶. "Broadband noise control through a ducted opening." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2012. http://hub.hku.hk/bib/B48329678.
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Fresh air ventilation openings or windows are essential to most buildings but the openings allow considerable portions of noise to be transmitted from the outdoor into the indoor environment. This project studies relevant theoretical models through accurate numerical solutions, and seeks better designs to gain extra noise attenuation through the openings.
The spectral method of Chebyshev collocation and the corresponding technique of out-going wave boundary conditions, for both ducted and flanged opening, are developed as numerical tools and validated by analytical examples.
After establishing the numerical tools, two prototype problems are studied. The first is one in which there is no special sound attenuation device. The configuration includes aperture of negligible thickness, aperture of finite thickness and aperture of semi-infinite length. The characteristics of the noise transmission through aperture of finite thickness are investigated with examples of sonic boom and traffic noise. The second prototype problem is the sound attenuation performance of side-branch design of the ducted opening. Side-branch configurations including porous material, single micro-perforated panel, double-layer micro-perforated panels, parallel micro-perforated panels and parallel micro-perforated panels with connected cavity are investigated. They are tested individually with parameters optimized for each of two examples of noise sources. The sound attenuation performances compared using appropriate subjective ratings of the noise sources. It is found that the parallel micro-perforated panels give the best performance for the sonic boom and the double-layer micro-perforated panels serve as the best substitute for the porous material with traffic noise source. Results from experiment are also presented to validate some numerical results.published_or_final_version
Mechanical Engineering
Doctoral
Doctor of Philosophy
30
Strass, Michael. "Shot noise control in coherent nanoscale conductors." [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=979705819.
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Pei, Sun. "Noise Resistant Least Squares Based Adaptive Control." Thesis, KTH, Reglerteknik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-92628.
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Zafeiropoulos, Nikolaos. "Active noise control in a luxury vehicle." Thesis, University of Salford, 2015. http://usir.salford.ac.uk/37606/.
Full textAbstract:
Structure-borne road noise is a critical sound attribute for the overall Noise Vibration & Harshness (NVH) performance of modern luxury vehicles. Current passive NVH solutions require structural design modifications, in order to control low frequency sources that cause structure-borne noise. Active Road Noise Control (ARNC) has been demonstrated to several commercial vehicles as an alternative solution that does not compromise other performances of the car, especially vehicle dynamics. Automotive manufacturers of luxury vehicles, such as Bentley Motors Limited, are expected to build cars that meet high standards of driving performance and refinement levels. This thesis focuses on the development of an active sound technology for road noise with the use of NVH analysis methods, which are a common practice in the vehicle development process. Modern NVH methods of road noise analysis reveal the locations of the most predominant structure-borne noise sources. There are significant advantages in using NVH analysis techniques for the design of ARNC systems, since they o_er integrated solutions to the automotive industry in terms of time and cost reduction. A method for defining the accelerometer sensors number and their locations on the axles has been developed as an alternative to existing methodologies, which are applied from the early stages of the NVH development. A physical road noise simulator was developed for replicating road noise. Four random uncorrelated forces were applied on the tyres for analysing and evaluating ARNC systems. In terms of feedforward control, a computer model of a causal adaptive feedforward system was used to investigate the relationship between the locations, DoF and the performance of the control system. An adaptive system was installed on a Bentley vehicle for conducting the ARNC measurements. The adaptive ARNC system was tested on the physical road noise simulator. The vehicle's tyres were excited by broadband random forces and maximum 10 dB(A) reduction at the centre frequency of the tyre cavity resonance was achieved. When the control was focused on the road rumble, then overall 3 dB(A) up to 500 Hz were removed from the noise levels measured at the rear headrests. In terms of road noise testing, a portable multichannel controller was integrated with the vehicle electrical system for road noise data acquisition and real-time ARNC. Finally, the performance of the portable controller is predicted based on data acquired by the same multichannel system and therefore highlight the potential use of this system as an ARNC controller.
33
Grad, Janet R. "H¦0¦0 control of acoustic noise." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape15/PQDD_0010/NQ30614.pdf.
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So, K. L., and 蘇建霖. "A study of construction noise control technology." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2000. http://hub.hku.hk/bib/B31254743.
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Hamilton, Antonia Felicity de Courcy. "The role of noise in sensorimotor control." Thesis, University College London (University of London), 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.404931.
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Trinder, M. C. J. "Active noise control in finite length ducts." Thesis, University of Essex, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.371924.
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Louie, Lisa Lai Yee. "Active control of pipe-borne pump noise." Thesis, Massachusetts Institute of Technology, 1991. http://hdl.handle.net/1721.1/13267.
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Patidar, Sandhya. "Noise-induced cooperative dynamics and its control." Thesis, Loughborough University, 2009. https://dspace.lboro.ac.uk/2134/36026.
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The possibility to manipulate the purely noise-induced behaviour in the large ensemble of globally coupled excitable systems is central to my research work. We employ globally coupled noise-driven FitzHugh-Nagumo units as a prototype of excitable system, which serve as a rough model of a neural network. Such a network is capable of demonstrating various kinds of behaviour with non-synchronized or synchronized units, with the mean field demonstrating periodic or chaotic small oscillations, or periodic or aperiodic spiking. Delayed feedback control applied through the mean field is shown capable of manipulating the basic features of the network behaviour, namely, to induce or suppress collective synchrony, to regularize the system behaviour in both synchronous and non-syncrhonous states, to shift the basic time scales of oscillations. These results are relevant to the control of unwanted behaviour in neural networks.
39
Sohrabi, Shahin. "Active control of noise transmitted from barriers." Doctoral thesis, Universitat Politècnica de Catalunya, 2022. http://hdl.handle.net/10803/674002.
Full textAbstract:
Active noise cancellation is a unique approach that helps passive noise control in reducing sound levels at low frequencies; nevertheless, successful use of active noise cancellation necessitates performing numerous and tedious experiments together with defining several parameters properly. The locations and quantity of active control system transducers are among these parameters.
The present research provides a comprehensive framework for placing control sources and error microphones near a noise barrier in order to improve its efficiency in both narrowband and broadband noise spectra. To accomplish this, the appropriate locations for the control sources are first determined using a repetitive computation method, and then the optimizations are completed by determining the best position for the error microphone.
Several alternative transducer locations near the barrier are incorporated in the repetitive computation, and the optimal sites for the control sources and error microphones are found using two-step optimization methods as well as the genetic algorithms approach.
The findings reveal that the best places to put the control sources are on the incident side, below the barrier's edge, and the best locations to place the error microphones are on the shadow side, as close as possible to the target area. The effect of ground reflection on the efficiency of the active noise control system is also investigated, and it is discovered that while ground reflection has no significant effect on the performance of the active noise control system for broadband frequency ranges, it does reduce the control system's efficiency at tonal noises.
In order to optimize more parameters, further calculations are performed based on the genetic optimizer. The output of the GA calculations found new configurations for the control units that result in higher noise level reduction at the target area.
In addition to the active noise barrier, the application of active noise cancellation for open windows as a particular case of the barrier is explored as a particular case of the barrier. Different arrangements are studied for the control units close to the open windows, including linear, boundary, and planar control arrangements.
The effect of several parameters such as the incident angle of noise waves, the distance between error microphones and the opening, and the number of control units are investigated. The results demonstrate that the active noise control system with obliqued linear placements of transducers have higher performance than the other arrangements. Furthermore, when the frequency and incident angle increase, the effectiveness of active noise reduction decreases.La cancelación activa de ruido es un enfoque único que ayuda al control pasivo del ruido a reducir los niveles de sonido a bajas frecuencias; sin embargo, el uso exitoso de la cancelación activa de ruido requiere la realización de numerosos y tediosos experimentos junto con la definición adecuada de varios parámetros. La ubicación y la cantidad de transductores del sistema de control activo se encuentran entre estos parámetros. La presente investigación proporciona un marco completo para colocar fuentes de control y micrófonos de error cerca de una barrera de ruido con el fin de mejorar su eficiencia en espectros de ruido de banda estrecha y banda ancha. Para lograr esto, primero se determinan las ubicaciones apropiadas para las fuentes de control usando un método de cálculo repetitivo, y luego se completan las optimizaciones determinando la mejor posición para el micrófono de error. Varias ubicaciones de transductores alternativas cerca de la barrera se incorporan en el cálculo repetitivo, y los sitios óptimos para las fuentes de control y los micrófonos de error se encuentran utilizando métodos de optimización de dos pasos, así como el enfoque de algoritmos genéticos. Los hallazgos revelan que los mejores lugares para colocar las fuentes de control están en el lado del incidente, debajo del borde de la barrera, y los mejores lugares para colocar los micrófonos de error están en el lado de la sombra, lo más cerca posible del área objetivo. También se investiga el efecto de la reflexión del suelo sobre la eficiencia del sistema de control de ruido activo, y se descubre que si bien la reflexión del suelo no tiene un efecto significativo en el rendimiento del sistema de control de ruido activo para rangos de frecuencia de banda ancha, sí reduce el rendimiento del sistema de control. eficiencia en ruidos tonales. Para optimizar más parámetros, se realizan más cálculos basadosen el optimizador genético. El resultado de los cálculos de GA encontró nuevas configuraciones para las unidades de control que dan como resultado una mayor reducción del nivel de ruido en el área objetivo. Además de la barrera de ruido activa, se explora la aplicación de la cancelación de ruido activa para ventanas abiertas como un caso particular de la barrera. Se estudian cuatro disposiciones para las unidades de control cercanas a las ventanas abiertas. Las unidades de control en una configuración de límite se colocan en el borde de la abertura, mientras que en el control plano, se ubican en la superficie de la abertura. En una configuración de contorno, las unidades de control se colocan en el borde de la abertura, mientras que en un diseño plano, se colocan en la superficie de la abertura. Se investiga el efecto de varios parámetros como el ángulo de incidencia de las ondas de ruido, la distancia entre los micrófonos de error y la apertura, y el número de unidades de control. Los resultados demuestran que el sistema de control de ruido activo con configuración plana tiene un rendimiento más alto que el control de límites. Además, cuando la frecuencia y el ángulo de incidencia aumentan, la eficacia de la reducción activa del ruido disminuye.
Enginyeria mecànica, fluïds i aeronàutica
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Duke, Cole Victor. "Analog Feedback Control of Broadband Fan Noise." BYU ScholarsArchive, 2012. https://scholarsarchive.byu.edu/etd/3646.
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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 a 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.
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Pettit, Michael D. "A compreshensive review of the hearing conservation program at XYZ Company." Online version, 2009. http://www.uwstout.edu/lib/thesis/2009/2009pettitm.pdf.
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Rai, Arunkumar R. "Characterization of noise and design of active noise control technology in longwall mines." Morgantown, W. Va. : [West Virginia University Libraries], 2005. https://eidr.wvu.edu/etd/documentdata.eTD?documentid=4412.
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Thesis (M.S.)--West Virginia University, 2005.Title from document title page. Document formatted into pages; contains xi, 65 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references (p. 63-64).
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Balaban, Murat. "Noise Source Identification And Adoption Of Proper Noise Control Strategies On Wheeled Tractors." Master's thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/12611838/index.pdf.
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This thesis is aimed at identifying the noise sources of a wheeled tractor to reduce the noise levels below the legislative limits by controlling noise sources through proper methodologies.
The study focuses firstly on identifying the noise sources of a wheeled tractor by using proper noise source identification techniques. These techniques can be summarized as sound intensity measurements, sound power level determination studies and spectral analysis of the noise data acquired in the
tests. Simple sound intensity mapping techniques are used and the intensity contour maps are generated to identify the noise sources.
Most important and effective noise sources are identified and the critical noise sources are focused to apply appropriate noise control strategies not only at the prototype production stages but also at the early design stages.
Consequently, upon consideration of both structure-borne and flow-induced noise, the pass-by noise level and the operator&rsquos ear noise levels of the tractor are reduced by nearly 3 dB (A) through application of proper noise control strategies.
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Johansson, Marcus. "An indicative case-control study of noise perception due to environmental noise sources." Thesis, KTH, Marcus Wallenberg Laboratoriet MWL, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-280546.
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The subject of the thesis was proposed by the acoustic consultancy firm Brekke & Strand, which is of relevance for their additional understanding and development of services and contribution to robust solutions. The aim with this thesis is to give indicative results and to dig deeper into the relation between environmental noise and the perception of the same, specially focusing on construction related noise but also permanent noise sources that originates from infrastructure. The area of interest to evaluate the study is a central location in Stockholm, specifically around Slussen.The importance of a study within this field is vital, especially when considering possible negative health effects that can be related to the perceived noise exposure. With that background it is worth to consider the amount of healthy-life-years lost in Europe each year, which is assumed to be one million. The correlation between lost life years and noise is one of many, but it is also proven to be a catalyst when it comes to stress related or cardiovascular diseases. For instance, if one is living closer than 50 meters from a major road the risk can be four times higher to be annoyed, which in extension can be coupled to the diseases mentioned above.The practical implementation of the study is conducted with a survey and field measurements, with a psychoacoustical perspective and within the frames of a case-control study. Partially this includes to inform the participants of the study at different stages regarding construction noise. The provided information, survey and field measurements aims to be a substantial part of the evaluation regarding the perceived noise whether it is due to construction work, infrastructure or other stochastic sources.The result is presented and distinguished based on distance to noise source, differentiated by gender as well as which type of source that tends to be most annoying. The implemented ranking is displayed as the ICBEN score of each category or source which aims to measure the perceived impact. Even though the results are indicative, the conclusion yields an information dependency as well as a noise source dependency. Further on, the result yields an interesting pattern between genders where women tend to be more disturbed by construction- and other-noise, whereas men tend to be more disturbed by rail- and road-noise.Ämnet för uppsatsen föreslogs av akustiskkonsultföretaget Brekke & Strand, vilket är av relevans för deras ytterligare förståelse och utveckling av tjänster och bidrag till robusta lösningar. Syftet är att ge vägledande resultat och gräva djupare i förhållandet mellan samhällsbuller och uppfattningen av detsamma, med särskilt fokus på konstruktionsrelaterat buller men också permanenta bullerkällor som härstammar från infrastruktur. Studien och utvärderingen av den samma har fokuserats till Slussenområdet i centrala Stockholm.Betydelsen av en studie inom detta område är avgörande, särskilt när man överväger eventuella negativa hälsoeffekter som kan relateras till den upplevda bullerexponeringen. Med den bakgrunden är det värt att ta hänsyn till hur många hälsosamma levnadsår som går förlorade i Europa varje år, vilket antas vara en miljon. Korrelationen mellan förlorade levnadsår och buller är en av många, men det har också visat sig vara en katalysator när det gäller stressrelaterade eller hjärt- och kärlsjukdomar. Om man till exempel bor närmare än 50 meter från en huvudväg kan risken vara fyra gånger högre för att bli störd och påverkad av buller, vilket i förlängning kan kopplas till ovan nämnda sjukdomar.Det praktiska genomförandet av studien utförsmed en enkätundersökning, fältmätningar,med ett psyko-akustiskt perspektiv och inom ramen för en fallkontrollstudie. Detta inkluderar delvis att informera deltagarna i studien i olika stadier beträffande konstruktionsrelaterat buller. Den tillhandahållna informationen, undersökningen och fältmätningarna syftar till att vara en väsentlig del av utvärderingen av det upplevda bullret oavsett om det beror på byggnadsarbete, infrastruktur eller andra stokastiska källor.Resultatet presenteras och skiljer sig utifrån avstånd till bullerkälla, uppdelat efter kön samt vilken typ av källa som tenderar att vara mest irriterande. Den implementerade rangordningen visas som ICBEN-skalan för varje kategori eller källa, som syftar till att mäta den upplevda effekten. Även om resultaten är vägledande så visar resultaten ett informationsberoende samt ett bullerkällaberoende. Vidare ger resultatet ett intressant mönster mellan könen, där kvinnor tenderar att bli mer störda av konstruktions- och andra-bullerkällor, medan män tenderar att bli mer störda av järnvägs- och väg-buller.
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Clark, Ian Andrew. "Bio-Inspired Control of Roughness and Trailing Edge Noise." Diss., Virginia Tech, 2017. http://hdl.handle.net/10919/77531.
Full textAbstract:
Noise from fluid flow over rough surfaces is an important consideration in the design and performance of certain vehicles with high surface-area-to-perimeter ratios. A new method of noise control based on the anatomy of owls is developed and consists of fabric or fibrous canopies suspended above the surface. The method is tested experimentally and is found to reduce the total far-field noise emitted by the surface. The treatment also is found to reduce the magnitude of pressure fluctuations felt by the underlying surface by up to three orders of magnitude. Experimental investigations into the effects of geometric parameters of the canopies lead to an optimized design which maximizes noise reduction.
The results obtained during the canopy experiment inspired a separate new device for the reduction of trailing edge noise. This type of noise is generated by flow past the wing of an aircraft or the blades of a wind turbine, and is a source of annoyance for those in surrounding communities. The newly developed treatment consists of small fins, or "finlets," placed near the trailing edge of an airfoil. The treatment is tested experimentally at near-full-scale conditions and is found to reduce the magnitude of far-field noise by up to 10 dB. Geometric parameters of the finlets are tested to determine the optimal size and spacing of the finlets to maximize noise reduction. Follow-up computational and experimental studies reveal the fluid mechanics behind the noise reduction by showing that the finlets produce a velocity deficit in the flow near the trailing edge and limit the magnitude and spanwise correlation lengthscale of turbulence near the trailing edge, factors which determine the magnitude of far-field noise.
In a final experiment, the finlets are applied to a marine propeller and are found to reduce not only trailing edge noise, but also noise caused by the bluntness of the trailing edge. The results of this experiment show the potential usefulness of finlets to reduce noise from rotating systems, such as fans or propellers, as well as from structures which feature blunt trailing edges.Ph. D.
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Law, See-hon. "Implementing control on road traffic noise in Hong Kong /." [Hong Kong : University of Hong Kong], 1994. http://sunzi.lib.hku.hk/hkuto/record.jsp?B13813973.
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Loon, Astrid. "The economic and social implications of implementing noise pollution controls at Amsterdam International Airport, Schiphol /." [St. Lucia, Qld.], 2002. http://www.library.uq.edu.au/pdfserve.php?image=thesisabs/absthe16684.pdf.
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Tong, Soen. "Noise mitigation in urban railway operations /." Hong Kong : University of Hong Kong, 1999. http://sunzi.lib.hku.hk/hkuto/record.jsp?B21301463.
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Law, Kam-wah. "Traffic noise mitigation in Hong Kong." Click to view the E-thesis via HKUTO, 2005. http://sunzi.lib.hku.hk/hkuto/record/B31596617.
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Wong, Yee-Jun. "Active control of fan noise and vortex shedding." University of Western Australia. School of Mechanical Engineering, 2005. http://theses.library.uwa.edu.au/adt-WU2005.0056.
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[Truncated abstract] The subject of fan noise generating mechanisms and its control has been studied intensively over the past few decades as a result of the ever-increasing demand for more powerful fans. A unique feature of fan noise is that it consists of high-level discrete frequency noise related to the blade passing frequency, and low-level broadband noise due mostly to turbulent airflow around the fan. Of the two types of fan noise, the discrete frequency noise is the more psychologically annoying component. Past research into fan noise has shown that the discrete frequency fan noise are dipole in nature and are caused predominantly by the fluctuating lift acting on the surfaces of the fan blades. Based on this, several theoretical models have been established to correlate these fluctuating lift forces to the far-field sound pressure. However, one general assumption in these models is that the fan blades are assumed rigid, and the consequence of such an assumption is that it is unclear if the far-field sound pressure is caused solely by the aerodynamic lift force, or whether the blade vibration also plays a substantial role in the generation of the far-field fan noise. One of the goal of this thesis was thus to experimentally quantify the contribution of blade vibration to far-field fan noise and it was found that blade vibration, whilst coherent with the far-field fan noise, did not contribute significantly. Aside of this, several experiments aimed at filling knowledge gaps in the understanding of fan noise characteristics were also be conducted, in particular, to understand the relationship between far-field sound pressure level to blade lengths as well as the number of blades on the fan. The experiments showed that for fans with many blades, the dependency of the far-field sound pressure on blade length is stronger than fans with less blades. Furthermore, dipole measurements showed that the dipole characteristics of fan noise does not occur only at the discrete frequencies, but also within a range of broadband frequencies, implying that the source for both discrete and broadband is the same. The second section of this thesis deals with the study of vortex shedding and its active control. When a circular cylinder (or any object) is placed in a flow within a specified Reynolds number range, flow separation and periodical wake motion is formed behind the cylinder, which is known as vortex shedding. It has been found in previous research that this wake motion is affected by acoustic field imposed on it via loudspeakers. This suggests that there is a strong acoustic-vortex relationship. However, little of this relationship is understood as conventional methods of studying vortex centre around the use of hot-wire anemometry, which effectively measures the velocity fluctuation in the flow. This thesis is the first in using a microphone to study the acoustic characteristic of the vortex wake, and experimental results shows that the two parallel shear layers of the wake carry the strongest pressure signals at the vortex shedding frequency, whilst the entrapped region between the layers carries the strongest pressure signals at the first harmonic.