Efforts to extract information regarding the surficial composition of the ocean bottom have increased in the last decade as increases in the availability of computing power have corresponded with advances in signal processing techniques. The ability to extract information from acoustic echosounders is especially desirable due to the relatively low cost and ease of deployment of such systems. Products already exist for the acquisition and logging of echosounder returns. An acoustic return is comprised of the incoherent backscatter from individual scatterers within the annulus of insonification that occurs when a spherically-spreading transmit pulse intersects with the ocean floor. The return is a convolution of the source ping, and the impulse response modeled by the backscatter profile. Most echosounders, generate an envelope of the received signal. The bottom impulse response undergoes a dilation linear with depth due to simple geometry which can be corrected with time-scale normalization. Under certain circumstances it may be necessary to deconvolve the source ping from the envelope of the return prior to time-scale normalization. It is shown that this can be done by modelling the envelope generation function with a finite sum discrete convolution and the Hilbert transform of the source signal. A second-order Volterra kernel can be derived using a standard predictor network with constrained optimization. Other factors which contribute to the quality of the return include off-vertical transducer angles which in fact improve the classification by eliminating the nulls that occur in the bottom impulse response due to transducer beam pattern. Spatial averaging can have the effect of beam widening if the transducer angle varies. Simple feature extraction algorithms are shown to be moderately effective in providing separability. The computational cost of combining the resulting feature sets can be reduced if the individual feature sets are scaled appropriately, reduced and then combined, prior to a reduction to the final dimensionality. The resulting feature space axes contain contributions from both the principal axes of the individual feature sets, as well as cross-algorithmic terms. Blind clustering of the data is provided through a two-step modification of the K-means algorithm. The first step generalizes it to use arbitrary classification metrics, and the second embeds this generalized kernel within a second kernel which modifies the covariance. The resulting K-stats kernel is very robust when successively applied to a growing number of clusters. / Graduate

M.Ing. (Electrical and Electronic Engineering) / This dissertation presents a comprehensive electrical model of the human auditory periphery. The model focuses on the generation and transmission of otoacoustic emissions (OAEs) under biometric conditions. The auditory system model was divided and studied in three sections, namely the outer, middle and inner ear sections. Existing models were used and improved for the study. The outer ear model was derived using electroacoustic analogies. The middle ear model was derived empirically. The inner ear model was derived by relating the mechanical properties of the inner ear to electrical principles. The outer ear model includes an analog diffraction circuit and a linear transmission line representation of the auditory canal and the concha. The variation of the radius of the auditory canal along its length was incorporated when computing the model of the outer ear. A pair of second order polynomials were used to create a new radius-length function which approximates the relationship between the radius of the auditory canal and its length. The frequency response of the outer ear model obtained using the radius-length function gave a wide frequency range representation of the outer ear characteristics. The middle ear is modelled using an analog network. Only the linear operation region of the middle ear was considered, thus excluding its reflex nonlinear mechanisms, namely; the stapedius muscle action and the stapes clipping displacement. The influence of the middle ear on the transmission of OAEs was evaluated by considering both the forward and reverse transmission characteristics/path of the middle ear. The middle ear response demonstrated great sensitivity to changes in the terminal loads connected to the middle ear as well as the transformer ratio. The inner ear behavior is represented by means of a nonlinear transmission line model. The nonlinear mechanism of the outer hair cells, which are taken as the primary sources of OAEs, are modelled using nonlinear voltage sources. The inner ear model was evaluated for conditions of both the active and inactive outer hair cells voltage sources. Due to limitations in the simulation software, a reduced active inner ear model was computed.The influence of the number of segments of the inner ear was explored. A reduced inner ear model having 40 segments was found to be sufficient in representing the frequency characteristics of the inner ear, whilst preserving the frequency-latency relationship of OAEs. The study not only improved the model of the auditory periphery, but also suggested several factors that can be incorporated in future research in order to better design signal acquisition and processing methods for OAE biometric applications.

No description available.

This thesis generates certain sets of analytical and approximate solutions to a new class of partial differential equations stemming from a version of asymmetricstress elasticity theory appropriate for the study and prediction of the behaviour of fibre-reinforced materials containing fibres that resist bending. These new solutions are of theoretical and practical interest in the static and dynamic analysis of thinwalled, linearly elastic fibre-reinforced structures influenced by couple-stress and unsymmetric stress due to fibre bending stiffness. The static and free vibration solutions are constructed considering bending resistance fibres in a small deformation of beams and plates. Numerical results for displacements, stresses, couple-stress and natural frequencies of vibration are provided to investigate the influence of the fibres resistance in bending on the deformed beams and plates.

A well-made flute is always a compromise and the job of flute makers is to achieve a musically and aesthetically satisfying compromise; a task that involves much trial and-error. The practical aim of this thesis is to develop a mathematical model of the flute and a computer program that assists in the flute design process. Many musical qualities of a woodwind instrument may be calculated from the acoustic impedance spectrum of the instrument. A technique for fast and accurate measurement of this quantity is developed. The technique is based on the multiple-microphone technique, and uses resonance-free impedance loads to calibrate the system and spectral shaping to improve the precision at impedance extrema. The impedance spectra of the flute and clarinet are measured over a wide range of fingerings, yielding a comprehensive and accurate database. The impedance properties of single finger holes are measured using a related technique, and fitformulae are derived for the length corrections of closed finger holes for a typical range of hole sizes and lengths. The bore surface of wooden instruments can change over time with playing and this can affect the acoustic impedance, and therefore the playing quality. Such changes in acoustic impedance are explored using wooden test pipes. To account for the effect of a typical player on flute tuning, an empirical correction is determined from the measured tuning of both modern and classical flutes as played by several professional and semi-professional players. By combining the measured impedance database with the player effects and various results in the literature a mathematical model of the input impedance of flutes is developed and implemented in command-line programs written in the software language C. A user-friendly graphical interface is created using the flute impedance model for the purposes of flute acoustical design and analysis. The program calculates the tuning and other acoustical properties for any given geometry. The program is applied to a modern flute and a classical flute. The capabilities and limitations of the software are thereby illustrated and possible contributions of the program to contemporary flute design are explored.

This thesis represents the work that has been done by the author during his Master of Engineering Science candidature in the area of vibration control of flexible structures at the School of Mechanical Engineering, The University of Adelaide, between March 2003 and June 2004. The aim of this research is to further extend the application of the Spatial Control Approach for two-dimensional flexible structures for attenuating global structural vibration with the possible implication of reduction in noise radiation. The research was concentrated on a simply supported thin flexible plate, using piezoelectric ceramic materials as actuators and sensors. In this work, active controllers were designed for the purpose of controlling only the first five vibration modes (0-500Hz) of the plate. A spatial controller was designed to minimize the total energy of the spatially distributed signal, which is reflected by the spatial H2 norm of the transfer function from the disturbance signal to the vibration output at every point over the plate. This approach ensures the vibration contributed by all the in bandwidth (0-500 Hz) vibration modes is minimized, and hence is capable of minimizing vibration throughout the entire plate. Within the control framework, two cases were considered here; the case when the prior knowledge of the incoming disturbance in terms of reference signal is vailable and the case when it is not available. For the case when the reference signal is available, spatial feedforward controller was designed; whereas for the case when the reference signal is not available, spatial feedback controller was designed to attenuate the global disturbance. The effectiveness of spatial controllers was then compared with that of the standard point-wise controllers numerically and experimentally. The experimental results were found to reflect the numerical results, and the results demonstrated that spatial controllers are able to reduce the energy transfer from the disturbance to the structural output across the plate in a more uniform way than the point-wise controllers. The research work has demonstrated that spatial controller managed to minimize the global plate vibrations and noise radiation that were due to the first five modes. / Thesis (M.Eng.Sc.)--School of Mechanical Engineering, 2005.

Thermoacoustic engines convert thermal energy into acoustic energy with few or no moving parts, thus they require little maintenance, are highly reliable, and are inexpensive to produce. These traits make them attractive for applications in remote or portable power generation, where a linear alternator converts the acoustic power into electric power. Their primary application, however, is in driving thermoacoustic refrigerators, which use acoustic power to provide cooling at potentially cryogenic temperatures, also without moving parts. This dissertation examines the feasibility of a new type of thermoacoustic engine, where mean flow and an internal pulse combustion process replace the hot heat exchanger in a traditional closed cycle thermoacoustic engine, thereby eliminating the heat exchangers cost, inefficiency, and thermal expansion stresses. The theory developed in this work reveals that a large temperature difference must exist between the hot face of the regenerator and the hot combustion products flowing into it, and that much of the convective thermal energy input from the combustion process is converted into conductive and thermoacoustic losses in the regenerator. The development of the Thermoacoustic Pulse Combustion Engine, as described in this study, is designed to recover most of this lost thermal energy by routing the inlet pipes through the regenerator to preheat the combustion reactants. Further, the developed theory shows that the pulse combustion process has the potential to add up to 7% to the engines acoustic power output for an acoustic pressure ratio of 10%, with linearly increasing contributions for increasing acoustic pressure ratios. Computational modeling and optimization of the Thermoacoustic Pulse Combustion Engine yield thermal efficiencies of about 20% for atmospheric mean operating pressures, though higher mean engine pressures increase this efficiency considerably by increasing the acoustic power density relative to the thermal losses. However, permissible mean engine pressures are limited by the need to avoid fouling the regenerator with condensation of water vapor out of the cold combustion products. Despite lower acoustic power densities, the Thermoacoustic Pulse Combustion Engine is shown to be well suited to portable refrigeration and power generation applications, due to its reasonable efficiency and inherent simplicity and compactness.

No description available.

Thesis (Ph.D)--Mechanical Engineering, Georgia Institute of Technology, 2009. / Committee Chair: Rogers, P. H.; Committee Member: Ferri, A. A.; Committee Member: Ruzzene, M.; Committee Member: Smith, M. K.; Committee Member: Trivett, D.; Committee Member: Zinn, B. T. Part of the SMARTech Electronic Thesis and Dissertation Collection.

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