Thesis (Ph.D.)--Aberdeen University, 2008. / Title from web page (viewed on July 1, 2009). Includes bibliographical references.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1973. / Vita. Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Inaug.-Diss.--Berlin. / Vita. eContent provider-neutral record in process. Description based on print version record. Bibliography: p. 115-132.

Thesis (Ph. D.)--Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Mechanical Engineering; and the Woods Hole Oceanographic Institution), 2006. / Includes bibliographical references (p. 155-169).

Originally issued as the author's thesis (Ph. D.)--Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2006. / "February 2006". "Doctoral dissertation." "Department of origin: Applied Ocean Physics and Engineering." "Joint Program in Oceanography/Applied Ocean Science and Engineering"--Cover. Bibliography: p. 197-206.

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.

Thesis (M.Sc.Eng.) PLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you. / When a circular piston vibrates within an aperture of a baffle, the flow within the annular gap between the piston and the baffle is opposite in phase, which causes a reduction in the radiated sound. That is, the acoustic power is always less than in the absence of a leaking edge flow. However, when the piston is backed by a cavity, the overall acoustic power can be increased. This thesis focuses on approximating the effect of the ‘leakage’ for a piston of radius a in a cylindrical cavity of radius b within a rigid baffle. First we consider the piston within a baffle without a cavity, which leads to a reduced acoustic power, then we examine the two cases of a closed cavity and an open cavity. The acoustic power is found to increase when the piston vibrates close to a resonant frequency of the closed or open cavity. The smallest resonant frequency fmin depends on the cavity depth and end-correction. The maximum ‘gain’ in acoustic power ~ 10 dB which depends on the nonlinear edge flow and also depends on the ratio a/b, the aspect ratio b/L and ζ0/b, where L is the cavity depth and ζ0 is the amplitude of piston displacement. / 2031-01-01

abstract: The project is mainly aimed at detecting the gas flow rate in Biosensors and medical health applications by means of an acoustic method using whistle based device. Considering the challenges involved in maintaining particular flow rate and back pressure for detecting certain analytes in breath analysis the proposed system along with a cell phone provides a suitable way to maintain the flow rate without any additional battery driven device. To achieve this, a system-level approach is implemented which involves development of a closed end whistle which is placed inside a tightly fitted constant back pressure tube. By means of experimentation pressure vs. flowrate curve is initially obtained and used for the development of the particular whistle. Finally, by means of an FFT code in a cell phone the flow rate vs. frequency characteristic curve is obtained. When a person respires through the device a whistle sound is generated which is captured by the cellphone microphone and a FFT analysis is performed to determine the frequency and hence the flow rate from the characteristic curve. This approach can be used to detect flow rate as low as low as 1L/min. The concept has been applied for the first time in this work to the development and optimization of a breath analyzer. / Dissertation/Thesis / M.S. Mechanical Engineering 2012

This work investigates brass instruments in the time domain, rather than the traditional frequency domain, and considers first, impulse measurements and secondly, their analysis. An existing apparatus for measuring the response to an acoustic impulse at the input of a brass instrument has been refined. Problems of impulse inconsistency, ambient temperature variation and source reflections have been resolved. Developments of the above equipment are used to test the quality of brass instruments on a factory production line. A prototype and a test instrument are compared by taking the arithmetical difference of their impulse responses. The equipment has detected small faults missed by normal inspection methods. The usefulness of this technique to brass instrument manufacturers is discussed. Links between the instrument's measured transient response and its bore geometry have been developed. The stages involved are deconvolution and bore reconstruction. Various deconvolution methods have been studied systematicaly by applying them to simulated noiseless and noisy data. Noise introduces errors, particularly at high frequencies, so deconvolution of real measured data is distorted. Techniques to reduce the effects of noise have been investigated. Attempts to employ the Gerchberg restoration algorithm 'to restore high frequency information proved unsuccessful. A new inverse method, based on an iterative z-transform procedure, of reconstructing an instrument's bore shape and damping profile from its transient response has been developed. It produces perfect results for noiseless model data, but even the smallest amount of noise renders the method unstable. Regularisation is therefore required. The corresponding direct process of predicting the transient response from bore and damping data is stable and produces results which compare well with measured responses. The work strengthens relationships between an instrument's shape and its musical quality, and will enhance the design of better instruments. Further research on the link between transient response and subjective quality is recommended.

To understand how speech is produced by individual human beings, it is fundamentally important to be able to determine exactly the three-dimensional shape of the vocal tract. The vocal tract is inaccessible so its exact form is difficult to determine with live subjects. There is a wide variety of methods that provide information on the vocal tract shape. The technique of Electropalatography (EPG) is cheap, relatively simple, non-invasive and highly informative. Using EPG on its own, it is possible to deduce information about the shape, movement and position of tongue-palate contact during continuous speech. However, data provided by EPG is in the form of a two-dimensional representation in which all absolute positional information is lost. This thesis describe the development of an enhanced Electropalatography (eEPG) system, which retains most of the advantages of EPG while overcoming some of the disadvantages by representing the three-dimensional (3D) shape of the palate. The eEPG system uses digitised palate shape data to display the tongue-palate contact pattern in 3D. The 3D palate shape is displayed on a Silicon Graphics workstation as a surface made up of polygons represented by a quadrilateral mesh. EPG contact patterns are superimposed onto the 3D palate shape by displaying the relevant polygons in a different colour. By using this system, differences in shape between individual palates, apparent on visual inspection of the actual palates, are also apparent in the image on screen. The contact patterns can be related more easily to articulatory features such as the alveolar ridge since the ridge is visible on the 3D display. Further, methods have been devised for computing absolute distances along paths lying on the palate surface. Combining this with calibrated palate shape data allows measurements accurate to 1 mm to be made between contact locations on the palate shape. These have been validated with manual measurements. The sampling rate for EPG is 100Hz and the data rate is equivalent to 62 bits per 10ms. In the past few years, some coding (parameterization) methods have been introduced to try to reduce the amount of data while retaining the important aspects. Feature coding methods are proposed here and several parameters are investigated, expressed in terms of both conventional measures such as row number, and in absolute measures of distance and area (i.e. mm and mm2). Features studied include location of constriction and degree of constriction. Finally, in order to reduce the amount of data while retaining the spatial information, composite frames that represent a series of EPG frames are computed. Measures of goodness of the composite frames that do and do not use 3D data are described. Some example are given in which fricative data has been processed by generating a composite frame for the entire fricative, and computing an area estimate for each row of the composite frame using the assumption of a flat tongue. This thesis demonstrates the current capability and inherent flexibility of the enhanced electropalatography system. In the future, the eEPG system can be extended to compute volume estimates again using a flat tongue model. By incorporating information on the tongue surface provided by other imaging methods such as ultrasound, more accurate area and volume estimates can be obtained.