A review of past research into sound propagation in woodland is presented. The attenuation of sound in woodland is small between about 800 and 2000Hz and greater at low and high frequencies. Attenuation measurements made in three contrasting woodlands are presented and compared with theoretical models. Propagation models using simple one- and two-parameter impedance models are used to calculate appropriate ground parameters for the prediction of impedance of the woodland soils. The ground parameters varied on different days in a single stand due to differences in moisture content and compaction. The overall differences between the stands are not significant. The woodland soil has a considerably lower impedance than other outdoor ground surfaces such as grassland or sand. A theoretical model for the attenuation of sound by thermoviscous absorption and scattering within an array of cylinders is assessed by means of a model experiment with wooden rods in an anechoic chamber. An input density 60% lower than the actual density gives a good agreement with measured attenuation. This modified model also predicts the attenuation by the cylinders in the presence of a ground surface. The scattering model is compared with the high frequency attenuation measured in the , woodland, using sampled trunk densities and radius, this underpredicts the observed attenuation, particularly in the stands with a dense branch and foliage structure. Addition of a second. dense, array of non rigid scatterers gives a good agreement with the measured data, thus modelling the scattering and absorbing effects of trunks, branches and leaves, in the high frequencies. Finally, a combined model is presented in which the attenuation caused by ground interference effects. at low frequencies. is added to a prediction of attenuation by the scattering model. across the whole frequency range. This model reproduces the frequency dependence of the attenuation of sound in woodland.

Using joint P-wave seismic tomography, receiver functions, and ambient noise we image the magmatic structure beneath Newberry Volcano, located near Bend, Oregon. Use of active source and teleseismic events in a joint tomographic inversion provides the ray crossings necessary to resolve a low velocity body around 4 km depth. Receiver functions show large lateral heterogeneity and are consistent with the location of a low velocity body derived from the tomography but require a larger low velocity anomaly. Ambient noise autocorrelations are used to image a low velocity reflector, located at ~3 km depth, shallower than the imaged low velocity body recovered using tomography and receiver functions. Ultimately, our results reveal a magma chamber at 3-4 km depth beneath Newberry caldera, with an overlying partially molten sill at ~3 km depth. These results show the usefulness of dense seismometer deployments over volcanoes.

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The aim of this investigation was to make a flexible array of pulse-echo ultrasound transducers by etching two orthogonal linear arrays of conducting elements into the metallisation of either side of a sheet of PVdF. These would then be multiplexed under computer control in an X-Y raster, thereby forming an image of subsurface defects in a material specimen. A potential source model was used to predict the sensitivity of a single element air-backed transducer far from resonance. Initial investigations confirmed the predictions, and reaffirmed the results of previous workers. In making a prototype array, it was found necessary to use a bi-laminar arrangement with a central ground plane, due to difficulties with crosstalk and charge leakage into the specimen materials. The radiation pattern of this array was tested and found to agree with the predictions for Fraunhofer (Far-Field) radiation. A 10 MHz analogue to digital converter was constructed to interface with the IBM-PC clone as a transient recorder, through a data capture program written in 'C'. However, the electrical noise generated by the PC was found to interfere strongly with the signal from the array transducer. A wide-band amplifier and full-wave rectifier was then added to the multiplexer and A/D converter, and the system enclosed in an electrically isolated environment, which made it possible to obtain clear signal data from the transducer. Non-linear regression was implemented in the software, to smooth the data and locate echo peaks, and the most frequently occurring peak separation was used to indicate sample thickness at that location in a false-colour mapping on the screen of the PC.

Made available in DSpace on 2014-06-11T19:27:13Z (GMT). No. of bitstreams: 0 Previous issue date: 2013-03-21Bitstream added on 2014-06-13T19:35:07Z : No. of bitstreams: 1 000739559.pdf: 4760352 bytes, checksum: 3378b244511252baafbe8d913eba826f (MD5) / Ruído é, na maioria dos países, o agente nocivo que prevalece na maioria dos ambientes de trabalho. Um trabalhador gasta em média 20% a mais de energia em ambientes com altos níveis de pressão sonora. As estatísticas do INSS comprovam que o ruído tem sido um agente causador de doenças, estresse ocupacional e acidentes de trabalho. A exposição de pessoas a níveis elevados de ruído pode causar comprometimentos orgânicos diversos, sendo também o principal responsável por distúrbios auditivos temporários e permanentes. Assim, é de fundamental importância a caracterização e avaliação do ruído e do seu campo de propagação no ambiente de trabalho. Isso permite a avaliação e, caso necessário, a implementação de ações de controle e mitigação dos seus efeitos. Nesse trabalho foi realizado um estudo das principais técnicas utilizadas para a simulação de ruído em ambientes industriais fechados, visando obter as informações e o conhecimento necessário para a elaboração de modelos de simulação e predição do campo acústico de ambientes industriais, mais especificamente, do piso de geradores de uma Usina Hidrelétrica. O trabalho foi desenvolvido com base na abordagem experimental e teórico e na interação entre elas. Na abordagem experimental foram realizadas diferentes medições para um conjunto de pontos pré-determinados e os dados obtidos foram processados e analisados visando caracterizar o ambiente e identificar as principais fontes de ruído. Os modelos de simulação do ruído foram elaborados com base nas informações e dados da construção predial do ambiente, nas características das fontes identificadas e na disposição espacial dos equipamentos e maquinários auxiliares. O software utilizado para simulação e obtenção dos mapas acústicos do ambiente foi o CadnaSAK que utiliza um método híbrido envolvendo o método fonte imagem virtual e traçado dos raios e tem como base as... / Noise is, in most of the countries, the harmful agent which prevails in most of workplaces. A worker spends, on average, 20% more energy in environments with high sound pressure levels. Statistics from INSS bear out that noise has been a causing agent of diseases, occupational stress and accidents at work. Thus, it is fundamental to know the effects of noise propagation so it is possible to control environment noise levels. The exposure of people to high level noise may cause several organic compromises, and it is further the main responsible for temporary and permanent hearing disorders. Due to it, a study has been done to understand and evaluate the best techniques involved in noise simulation in closed industrial environment, aiming to provide important information to the implementation of a simulation model for the acoustic field of the floor of the generators for the hydroelectric plant at Ilha Solteira. The work has been developed basing on two approaches, experimental and theoretical. On the experimental approach, measurements have been done to an ensemble of predetermined points around each identified source in the environment; the data acquired has been processed and analyzed for further comparison with the values obtained from the simulation model. On the theoretical approach, simulation models for the noise from the floor of the generators at the hydroelectric plant at Ilha Solteira have been done, regarding the actual data from the building construction, as well as identified sources of the environment. The software used was CadnaSAK which uses a hybrid method involving virtual image source method, rays’ track and patterning contained in the German standard VDI 3760 to the simulation and achievement of the environment acoustic map. The simulation model has been validated comparing the values acquired through the model with data measured experimentally. The comparison of the values has been done to an ensemble of points ...

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Made available in DSpace on 2014-10-09T12:32:35Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:08:57Z (GMT). No. of bitstreams: 1 01536.pdf: 1546999 bytes, checksum: 6f67a3de9c8959c9d9b4408584d2f8fb (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Noise is considered to be a physical form of environmental pollution which can influence the health of exposed persons. Excessive exposure to noise can interfere with performance at work and with the ability to relax or sleep. Also it may impair hearing and it can evoke other physiological and pathological symptoms to the detriment of health. The sources of noise may be local or general. Industrial processes are an important source of indoor or localised noise. Persons exposed to noise as a consequence of their employment are legally protected to some extent by European Directives and National Regulations which limit the maximum permissible noise levels to 85-90dB. A research project was launched with the full co-operation of the Don and Low Group of Companies, Forfar and Perth, Scotland. Study indicates that the proportion of employees who have noise-induced hearing loss is higher amongst those who work in higher than 85dB, (e.g. Group 1 < 85dB-11%; Group 2 85<90dB-44%; Group 3 90<95dB-44%; Group 4≥95dB-39% = 138% in total). In all groups social and economic status, sex, age and average number of years' service are almost identical. In general, the study indicates a higher number of employees suffered from ear problems between groups exposed to 85dB and more, (e.g. perforated eardrum, noise tinnitus, vertigo, wax in ears). The danger of noise has been studied in detail regarding the general health of employees as follows: 1. Sleep disturbance It appeared that most of the cases who suffered from sleep disturbance were found amongst employees exposed to greater than 85dB, averaging about 33%. On the other hand, only 8% of the employees in category <85dB complained of sleep disturbance. 2. Blood Pressure According to job categories 10% of employees had heart problems in job category higher than 85dB, but only one case reported heart problems in job categories less than 85dB. 3. Stress Smoking was one of the subjects studied in detail in this project and the results were significant. An average of 40% of employees were smokers among groups exposed to higher than 85dB compared to 10% of smokers among employees exposed to less than 85dB. Industrial accidents occur at a higher rate among employees who worked in noisy environments (~85dB) with regard to reported or unreported accidents. From the result of the research, industrial noise should be studied in a more comprehensive way to measure all effects of noise regarding employees health by using the statistical data and always noise should be controlled at source. Industrial noise is still a major danger to employees. From the results in this study it appears there is a need for more co-operation between employer and employee and not just depend on the health and safety regulations and try to solve the problem.

Eigen-mode matching techniques offer a versatile approach for solving acoustic scattering problems in ducts. However, until recently, these techniques have been restricted to problems in which the boundary conditions contain at most one derivative, that is, Neumann, Dirichlet or Robin's conditions. Here a method is developed to solve scattering problems in ducts that are discontinuous in height and have at least one surface described by a high order boundary condition. Attention is focussed on the membrane condition, but the method can be extended to elastic plates and other higher order conditions. An original orthogonality condition is derived and used to solve two problems. Limiting cases of the results are compared with some special cases solveable by standard Fourier techniques and (for the case of no height discontinuity) the Wiener-Hopf technique.

Spectrograms are perhaps the most commonly used method for studying the characteristics of speech waveforms. Producing a spectrogram can conveniently be divided into two parts, the analysis and the display, and this thesis describes a study of both these aspects.