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This study investigates the self noise from a ventilated supercavitating vehicle. A ventilated supercavity is a gaseous envelope surrounding an underwater vehicle that significantly reduces the drag felt by the vehicle. But the hydrodynamic noise generated by the creation of the supercavity could impact the successful deployment of the vehicle. A principal source of self noise for these types of vehicles is sound created by the ventilating gas jets impinging on the air-water interface. Analytical models of the radiated sound through the interface have been developed. Sometimes jets impinging on the interface entrain bubbles beneath the surface. This thesis outlines a theory to predict the influence of bubbles near the interface. Experimental measurements were made at the Naval Undersea Warfare Center (NUWC) in Newport, RI to test the accuracy of the model. These measurements include the unsteady force spectrum of a gas jet impinging on a rigid wall. The acoustic pressure spectrum of a gas jet striking the air-water interface was also recorded. The experimental results were compared to theoretical models for validation.

Millions of people across the world currently have noise induced hearing loss, and many are working in conditions with both continuous Gaussian and non-Gaussian noises that could affect their hearing. It was hypothesized that the energy of the noise was the cause of the hearing loss and did not depend on temporal pattern of a noise. This was referred to as the equal energy hypothesis. This hypothesis has been shown to have limitations though. This means that there is a difference in the types of noise a person receives to induce hearing loss and it is necessary to build a system that can easily mimic various conditions to conduct research. This study builds a system that can produce both non-Gaussian impulse/impact noises and continuous Gaussian noise. It was found that the peak sound pressure level of the system could reach well above the needed 120 dB level to represent acoustic trauma and could replicate well above the 85 dB A-weighted sound pressure level to produce conditions of gradual developing hearing loss. The system reached a maximum of 150 dB sound peak pressure level and a maximum of 133 dB A-weighted sound pressure level. Various parameters could easily be adjusted to control the sound, such as the high and low cutoff frequency to center the sound at 4 kHz. The system build can easily be adjusted to create numerous sound conditions and will hopefully be modified and improved in hopes of eventually being used for animal studies to lead to the creation of a method to treat or prevent noise induced hearing loss.

Combustion noise is central to several efforts to curb aircraft emissions. Indeed, acoustic waves originating in the combustor are a major contributor to aircraft noise. Moreover, they can act as a trigger for thermoacoustic instabilities, the consequences of which may range from decreased efficiency to outright failure. Modern engines designed to lower NOx emissions are particularly susceptible to this phenomenon. Unsteady combustion generates acoustic waves — direct noise — as well as convected flow disturbances, such as entropic, vortical or compositional inhomogeneities. These disturbances generate additional acoustic waves — indirect noise — if they are accelerated. The main objectives of this thesis are to examine the validity of current theoretical models for indirect noise, and to propose new ones where needed. First, a one-dimensional theoretical framework for the direct and indirect noise produced in a reflective environment is presented. The direct noise produced by the addition of mass, momentum and energy to a flow is determined analytically. A model for the entropic and compositional noise generated at a compact nozzle is then derived, accounting for nozzles with non-uniform entropy. Finally, the effect of reverberation (i.e. repeated acoustic reflections) is determined analytically. This enables direct and indirect acoustic sources to be identified and separated within experimental data, while eliminating the effect of acoustic reflections. The framework is applied to a model experiment — the Cambridge Wave Generator — in which direct, entropic and compositional noise are generated. Direct and indirect noise models are validated using experimental measurements of the sound field resulting from air injection and extraction, heat addition and helium injection. For the first time, direct, entropic and compositional noise are clearly identified in the experimental data, and shown to be in line with theoretical predictions. The results provide the first experimental demonstration of the compositional noise mechanism, and show that isentropic nozzle models are inadequate in predicting the indirect noise generated at nozzles with substantial losses.

In this thesis an investigation for the identification, measurement and modelling of the gear pump performance under marginal suction condition, created in the suction line and resulting in cavitation at the suction port and cavitation erosion on the delivery side plate is introduced. A new technique for the detection of cavitation in gear pumps has been employed and proved to be more efficient and less expensive than other techniques available. The experimental study has been carried out by monitoring the pressure ripple at the pump inlet and outlet, as well as investigating the pressure distribution around the gear rotor under cavitating and non-cavitating conditions. It was found that the gear pump cavitation appeared in three distinct stages, these being cavitation-inception, discrete-cavitation and continuous-cavitation. These stages of cavit tion were investigated by means of pressure distribution around the gear rotor using a miniature pressure transducer positioned at a gear fillet. The experimental results demonstrate a drop in filling efficiency, of the tooth space due to cavitation, which provides a further understanding of the pump performance characteristics at different inlet conditions. An expression for the definition of transient pressure in the tooth space due to trapped volume has been derived for the first time and proved to give a good correlation with published experimental work. A surface analysis technique has been employed in this work to study the behaviour of the material erosion due to cavitation bubble collapse, using a 'Talysurf 41 instrumentation system, and the results obtained are in good agreement with those published by NEL.

Thesis (MTech (Electrical Engineering))--Cape Peninsula University of Technology, 2016. / Optimum communication can only be achieved with a very sensitive front-end section in the receiver on a satellite because the transmitted signal from the ground station must travel hundreds of kilometres through the earth's atmosphere to a low earth orbit (LEO) satellite. This dissertation presents the design of the front end section of the receiver suitable for use in a nano-satellite. Specifically, various transistor technologies are evaluated by designing five low noise amplifiers to determine the optimum performing amplifier. The bandwidth of the front end section was controlled by designing coupled line microstrip filter. For consistency, the same design technique was followed in the design of each LNA. Simulations were performed and the results were compared to the actual measured results of the constructed amplifiers to facilitate conclusions to be made. Design specifications for the LNAs were obtained from the F'SATI Space CubeSat Programme Technical Specification document. To control the bandwidth of the front end section, various types of band-pass filters were investigated, resulting in a coupled line band-pass filter being simulated and implemented. The simulated results were compared to the measured results of the constructed filter. In the final stage of this dissertation, comparisons of each amplifier’s performance were made, resulting in the final recommendation for this project.

The thesis consists of 135 pages and the CD enclosure. Pictures, charts and colour graphs are included. The thesis and the CD enclosure contain data presented in charts and from the charts graphs have been made.

The aim of the work is to determine the noise pollution of the weekend house area around Dehtář. Receiver locations were chosen to find out noise levels in places with the highest intensity of human activity and at each observed source of noise. Noise levels were recorded in four seasons of the year. The equivalent continuous sound pressure levels were quantified. and compared with local noise law limits.

Orientador: Stelamaris Rolla Bertoli / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Civil, Arquitetura e Urbanismo / Made available in DSpace on 2018-08-11T19:33:52Z (GMT). No. of bitstreams: 1 Santos_DulceClaudiaJoseViana_M.pdf: 1865213 bytes, checksum: dd7cd6494e4bd0ee9f87996a87c4893d (MD5) Previous issue date: 2004 / Resumo: O ruído aparece como um dos problemas ambientais mais freqüentes nos grandes centros urbanos. As atividades ruidosas estão atingindo também as cidades menores do interior do Estado de São Paulo. Nessas cidades nem sempre existem legislações específicas relacionadas a ruído ou condições técnicas para o controle das fontes ruidosas. Nos casos mais graves as reclamações por incômodo devido a ruído chegam a via judiciária onde um perito é designado para fazer a avaliação do ruído ambiental baseado na norma NBR 10151-Avaliação do ruído em áreas habitadas, visando o conforto da comunidade. Nesse trabalho o enfoque de ruído ambiental é analisado através do levantamento dos incômodos gerados por fontes sonoras fixas em dezesseis cidades da região da Equipe de Perícias de São João da Boa Vista. As fontes sonoras são identificadas, mensuradas e catalogadas como aceitáveis ou não de acordo com o nível de critério de avaliação da norma NBR 10151. Paralelamente foi levantado junto aos municípios a existência de legislações municipais específicas sobre ruído ambiental e pessoal técnico para avaliação. Os resultados obtidos nesse trabalho indicaram como está sendo tratada a poluição sonora nessas cidades e quais as principais fontes sonoras de incômodo. Verificou-se também que os critérios de avaliação dos ruídos propostos pela Norma são adequados a esses municípios. O trabalho sugere pontos importantes para estabelecimento de uma legislação e procedimentos específicos relativos a ruído para esses municípios. / Abstract: The noise is shown as the most frequent environmental problem in big cities. The noisy activities are getting also in small cities of São Paulo State. In these cities, not always there is a specific legislation about noise or technical conditions of noisy sources control. In the most serious case, the reclamation for annoyance due the noise, gets, at the judicial mean, where an expert is designated to do the evaluation of the environmental noise based in the NBR 10.151 rule- Evaluation of the noise in inhabit areas, aiming the confort of the community. In this paper the main point of the environmental noise is analysed through the survey of the annoyances generated by fixul noise sources into sixteen cities from the region of São João da Boa Vista Criminal Expert team. The noise sources are identified, measured and catalogue as acceptable or not in accordance to the level of the criterious of evaluation of NBR 10.151 rule. Paralled was raised with the cities the existence of specific municipal legislation about environmental noise and technicals staff (personal) for evaluation. The results obtained in this work indicated how is being treated the noise pollution in these cities and what the major noise source of annoyance is. It had verified if the criterion of evaluation propose by the rule is adequated in the cities. The work suggests important points for the establishment of a specific legislation and special procedures to these municipalities. / Mestrado / Edificações / Mestre em Engenharia Civil

Sub-surface or through-the-earth communication using electromagnetic fields - and specifically magnetic induction equipment - plays a key role in search and rescue systems used in the mining industry and, increasingly, by cavers and pot-holers. Similar equipment is used for radio-location, sub-surface surveying and geophysical measurements. The use of fast desktop computers allows a mathematical model of the propagation to be investigated in detail, demonstrating the preferred orientation of the antennas and the existence of an optimum frequency that is dependent on depth and other parameters. Computer simulations demonstrate a reduction in accuracy of radiolocation at skin depth distances, and methods of correcting this inaccuracy are introduced. The transmitter and receiver antennas for portable induction loop systems are usually aircored loops or magnetic-cored solenoids, tuned to resonance. However, the preferred antenna often depends on the intended use of the communication system, with untuned antennas having an advantage in some situations. The use of toroid (anapole) structures and rotating magnets as transmitters is discussed briefly. A figure of merit - the specific aperture - is introduced as an aid to antenna design. Internal (amplifier) noise can be reduced by noise-matching, although special account has to be taken of the inductive antenna. Internal noise is often swamped by external (atmospheric) noise, for which several mitigation strategies are discussed. Differing up-link and down-link noise performance may dictate different antennas. External noise is frequently characterised by the atmospheric noise temperature ratio, but data derived using the standard electric field antenna cannot be applied to a study of magnetic noise. The design of a wide-band low-frequency channel sounder is described, with which it is intended to perform a detailed channel evaluation using a binary sounding sequence. A simple method of calculating the inverse of such a sequence is introduced, for which cross-correlation with the inverse sequence at the receiver results in a system identification signal that is used to maintain synchronism with the transmitter. The extreme wideband nature of the system results in a low efficiency, which is countered by using signal-averaging techniques at the receiver. Preliminary results are reported, in which the sounder was used to capture background noise.