This thesis examines the role of the bore shape in brass instruments. Difficulties in finding the precise nature of the bore shape in an assembled instruments are discussed. Several measurement methods employed to overcome these are developed, and the overall bore shape found. A model is developed whereby input impedance and pressure transfer function of an instrument may be predicted from the bore shape, and the musically important effect of temperature investigated. Good agreement with experimental measurements of instruments under similar conditions is found. Time domain measurements using a computer controlled impulse source and digital signal acquisition are given which illustrate the effect of small discontinuities of the bore upon the impulse response. Synthesis of bore shape from acoustic data is discussed with reference to reflections from such features. The methods currently employed by manufacturers to design new instruments are discussed, and an iterative process combining the prediction of acoustic properties from bore shape, synthesis, and psychometric techniques postulated.

A transient excitation method is described which allows the free field frequency and impulse responses of a microphone to be measured in a reverberant environment. The pressure transient generated by exciting a loudspeaker with a narrow voltage pulse is detected at a point in the loudspeaker's far field by the test microphone. A reference microphone, whose response is assumed flat over the frequency range of interest, is then substituted in exactly the same position and its response to the transient measured. The outputs of the two microphones are accurately sampled and deconvolved using a discrete Fourier transform technique to give the magnitude and phase parts of the test microphone's frequency response. Inverse transformation then gives the test microphone's response to an impulse of acoustic pressure propagating in the free field. Computed frequency and impulse responses are presented and the practical implementation and accuracy of the method discussed. The use of the method is illustrated by measurements of the free field frequency and impulse responses of several different microphones, including a 1" instrumentation microphone; free field correction curves for this microphone are also presented. Three digital analysis techniques are discussed and applied to some of the measured microphone responses where the discrete Hilbert transform is found to provide a method of calculating the phase part of the 1" microphone's frequency response over its useful frequency range without the ambiguities due to microphone misalignment inherent in the pulse method. The method is then used to measure the pressure which occurs at the centre of the flat end-face of a long cylinder when excited by a delta function of acoustic pressure from various incidence angles. A numerical time domain model is established which allows the impulse responses of this configuration to be computed. The interference effects caused by the proximity of two closely spaced instrumentation microphones in various orientations and configurations are also presented and discussed.

The content of this thesis splits into two distinct areas, investigating the effect of material and its condition on the properties of brass instruments. Firstly, acoustic losses in tubes are studied. A method for deducing losses from impedance and transfer function measurements is developed and applied to a number of tubes having different internal wall finishes. The cases studied are considered representative of the wall finishes found in brass instruments, both in factory condition, and after having been used for some time and not cleaned. Results show that a build-up of deposit on the inside of the tube causes the most significant increase in attenuation of sound propagating down the tube, whereas the results for smooth and roughened tubes are very close to theoretical predictions. An attempt is made to extend the theory to measurements on actual instruments but success is limited due to the flared portions of tubing. Secondly, the vibration properties of trombone and trumpet bells are studied. A Finite Element package is used to model the bells and a post-processor program written to model the acoustic excitation and thus predict the forms of vibration. These calculated responses are compared with some results from experiments performed in conjunction with Southampton University. The finite element model is also used to indicate the properties of the bell structure which are implicit in determining its mechanical response; supports (stays), material of construction, wall thickness, rim size and asymmetries in geometry. It is difficult to give these properties musical significance though some results show that in certain circumstances, they do contribute to an instrument's musical characteristics.

The past thirty years or so have seen rapid developments in the science of ultrasonics and its practical applications as an imaging and measurement modality. One aspect of ultrasound that has recently received increasing attention is the limit of validity of the widely applied theoretical simplification of plane wave propagation, particularly with regard to inhomogeneous media. The work presented in this thesis is concerned with the quantitative experimental investigation of wavefront fluctuations in tissue and other non-uniform materials. A sensitive experimental wavefront detector system was designed and used subsequently to assess the acoustic field distributions radiated by plane disc ultrasonic transducers. This data enabled the system to be further refined and direct measurements to be made of wavefronts emerging from both artificial material (containing scatterers of known size and distribution) and fresh animal tissue (beef liver). The preliminary results on animal tissue suggest that while, under certain circumstances, ultrasonic waves may indeed propagate through tissue as near perfect plane waves, in some tissue regions quite large fluctuations in amplitude and phase are induced by internal scatterers. The physical origin of the scatterers inducing these fluctuations is not obvious and this is identified as a topic for further detailed investigation.

In this thesis an investigation was centered on models of inhomogeneous viscoelastic media, which consisted of glass beads (lead and soda glass) embedded in a silicone rubber matrix (RTV-602). The specimens were classified into groups according to the nominal size of the glass beads content (mean diameter ranging from 63.8 pm to 582 pm) in a range of concentrations (up to 5% volume). Ultrasonic velocity and attenuation as a function of frequency were measured by transmission techniques in the range of 0 to 10 MHz. An extended investigation was centered on the effects of diffraction on velocity and attenuation measurements. The effects of diffraction in distilled water were found to be in good agreement with modified mathematical transducer models. The measured velocity and attenuation in the specimens were compared with theoretical predictions based on the multiple scattering of waves formulation of Waterman and Truell (1961) in combination with the Kramers-Kronig relationship between absorption coefficient and phase-velocity dispersion in the constituent materials of the specimens. Good agreement was obtained between the experimental and the theoretical approaches used, which suggest their applicability for inhomogeneous viscoelastic materials. From the attenuation coefficient and velocity, the composition of materials can be determined. The attenuation coefficient was shown to be a more reliable acoustic parameter than velocity, although both are necessary for a complete characterization of composite materials.

The simplest source of focussed ultrasound used in medicine is the spherical cap transducer. It appeared that the theory of O'Neil, invariably used for predictions had not been previously tested comprehensively under narrowband low amplitude conditions. Extensive measurements on four weakly focussed transducers in water have shown that this theory is a poor predictor of the field actually radiated under these conditions. If the nominal geometrical parameters of a transducer are replaced in the theory by effective values derived from pressure amplitude extrema, a greatly improved fit between theory and experiment can be realised. A reliable protocol for the determination of effective parameters has been proposed. It has been shown that the effective parameters defined from measurements in water can be used with comparable success to predict the fields in castor oil. A novel method, using a spherical cap transducer and a miniature hydrophone, has been developed for the measurement of ultrasonic attenuation in penetrable media. Use of the technique for measuring the frequency dependence of the coherent scattering component of the attenuation in a suspension of polystyrene beads in a castor oil matrix, presenting refractive index variations of 35%, gave results in good agreement with the theory of Waterman and Truell. Amplitude measurements in the suspension have shown that the coherent part of the field is not defocussed. The defocussing observed in soft human tissue such as breast, by Poster and Hunt, appears to be largely due to the incoherent scattering contribution and its quantification is identified as the subject of future investigation.

<p> An atomic force microscopy beam-like cantilever is combined with an electrical tuning fork to form a shear force probe that is capable of generating an acoustic response from the mesoscopic water layer under ambient conditions while simultaneously monitoring force applied in the normal direction and the electrical response of the tuning fork shear force probe. Two shear force probes were designed and fabricated. A gallium ion beam was used to deposit carbon as a probe material. The carbon probe material was characterized using energy dispersive x-ray spectroscopy and scanning transmission electron microscopy. The probes were experimentally validated by demonstrating the ability to generate and observe acoustic response of the mesoscopic water layer.</p><p>

This study is concerned with the reflection and transmission of spherical waves at a plane interface between two different media. The phenomenon of the reflection and transmission of spherical waves has been studied by means of analytical methods, numerical computation, and experimental tests. A new integral representation for a spherical wave is obtained by transforming Lamb/Sommerfeld's integral representation. The new integral has no singularity so it allows more accurate numerical integration. A new proof of Lamb/Sommerfeld's integral representation for a spherical wave is presented based on the new integral. By using the new form of solutions for reflected waves and existing solutions for transmitted waves, numerical studies have been carried out to examine. the phenomenon of reflection and transmission. of spherical waves at plane surfaces of discontinuity in material properties. It is shown that the effective critical angle for the total reflection of a spherical wave is greater than that of a plane wave at a hard boundary, and that when the source height increases the effective critical angle for the total reflection of a spherical wave tends to that of a plane wave. It is shown that recent predictions of spherical wave reflection and transmission coefficients greater than 1 at normal incidence under certain condition are probably due to numerical integration error. It also has been found that for spherical wave reflection and transmission, the time average energy flux, normal to a plane parallel to the plane of discontinuity, may locally be in the direction opposite to that of the direction of energy transmission over the plane as a whole. This so-called "backward wave" occurs in an interference between the direct and reflected waves, as well as in a transmitted wave. An indirect test on the theory has been performed to check the pressure field, above a rigid boundary, predicted by the spherical wave theory. Theoretical and experimental results were in good agreement.

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.

Airflow management is crucial for the performance of cooling systems in data centers. The amount of energy consumed by data centers is huge and a large amount is related to the cooling. In attempts to develop energy efficient data centers, numerical methods are important for several reasons. Experimental procedures are more expensive and time consuming but when done carefully, experiments provide trustful results that can be used to validate simulations and give additional insights. Numerical methods in their turn have the advantage that they can be applied to proposed designs of data centers before they are built and not only to already existing data centers. In this study, Computational Fluid Dynamics (CFD) is used to study the airflow in data centers. The aim is to use an experimentally validated CFD model to investigate the effects of using different designs in data centers with respect to the performance of the cooling systems. Important parameters such as quality of the computational grid, boundary conditions and choice of turbulence model must be carefully considered in order for the results from simulations to be reliable. In Paper A, a hard floor configuration where the cold air is supplied directly into the data center is compared to a raised floor configuration where the cold air is supplied into an under-floor space instead and enters the data center through perforated tiles in the floor. In Paper B, the performance of different turbulence models are investigated and velocity measurements are used to validate the CFD model. In Paper C, the performance of different cooling systems is further investigated by using an experimentally validated CFD model. The effects of using partial aisle containment in the design of data centers are evaluated for both hard and raised floor configurations. Results show that the flow fields in data centers are very complex with large velocity gradients. The k − ε model fails to predict low velocity regions. Reynolds Stress Model (RSM) and Detached Eddy Simulation (DES) produce very similar results and based on solution times, it is recommended to use RSM to model the turbulent airflow in data centers. Based on a combination of performance metrics where both intake temperatures for the server racks and airflow patterns are considered, the airflow management is significantly improved in raised floor configurations. Using side covers to partially enclose the aisles performs better than using top covers or open aisles.