This thesis describes an experimental investigation of high frequency acoustic wave scattering from turbulent premixed flames. The objective of this work was to characterize the scattered incoherent acoustic field and determine its parametric dependence on frequency, flame brush thickness, incident and measurement angles, mean velocity and flame speed. The experimental facility consists of a slot burner with a flat flame sheet that is approximately 15 cm wide and 12 cm tall. The baseline cold flow characteristics and flame sheet statistics were extensively characterized. Studies were performed over a wide range of frequencies (1-24 kHz) in order to characterize the role of the incident acoustic wave length. The spectrum of the scattered acoustic field showed distinct incoherent spectral sidebands on either side of the driving frequency. The scattered incoherent field was characterized in terms of the incoherent field strength and spectral bandwidth and related to the theoretical predictions. The role of the flame front wrinkling scale, i.e., flame brush thickness, was also studied. Flame brush thickness was varied independent of the mean velocity and flame speed by using a variable turbulence generator. Results are reported for five flame brush thickness cases, ranging from 1.2 mm to 5.2 mm. Some dependence of scattered field characteristics on flame brush thickness was observed, but the magnitude of the effect was much smaller than expected from theoretical considerations. The spatial dependence of the scattered field was investigated by measuring the scattered field at four measurement angles and exciting the flame at four incident angles. Theory predicts that these variations influence the spatial scale of the acoustic wave normal to the flame, a result confirmed by the measurements. Measurements were performed for multiple combinations of mean velocities and flame speeds. The scattered field was observed to depend strongly on the flame speed. Further analysis suggested that the change in orientation angle distribution with flame speed had a large influence on the scattered field. The scattered field characteristics did not show any appreciable change with mean velocity. This result was expected since flame brush thickness characteristics themselves exhibit a weak velocity dependence.

A new approach was developed to determine the operational stability margin of a laboratory scale combustor. Applying modern and robust techniques and tools from Dynamical System Theory, the approach was based on three basic steps. In the first step, a gray-box thermoacoustical model for the combustor was derived. The second step consisted in applying System Identification techniques to experimental data in order to validate the model and estimate its parameters. The application of these techniques to experimental data under different operating conditions allowed us to determine the functional dependence of the model parameters upon changes in an experimental control parameter. Finally, the third step consisted in using that functional dependence to predict the response of the system at different operating conditions and, ultimately, estimate its operational stability margin. The results indicated that a low-order stochastic non-linear model, including two excited modes, has been identified and the combustor operational stability margin could be estimated by applying a continuation method.

Supercavitating torpedoes pose new threats to submarines, surface ships, and shore targets whose current countermeasures are inadequate against this technology. These torpedoes have the advantage over their predecessors and companion weapons of dramatically increased speed, which reduces the reaction time available for deploying a countermeasure heightening the threat to their intended target. Proliferation of supercavitating torpedoes has motivated research on countermeasures against them as well as on the fluid phenomenon which makes them possible. The goal of this research was to investigate an envisaged countermeasure; an acoustic field capable of slowing or diverting the weapon by disrupting the cavitation envelope. The research focused on the interactions between high-level sound signals and a supercavity produced by a small free-flying projectile. In order to conduct this study it was necessary to achieve three preliminary accomplishments involving the design of: 1) experimental apparatus that allowed for the study of a small-scale supercavitating projectile in the laboratory environment; 2) apparatus and software for measuring and recording information about projectile dynamics and supercavity geometry; and 3) an acoustic array and power source capable of focusing the desired sound signal in the path of the supercavitating object. Positive results have been found which show that the accuracy of a supercavitating projectile can indeed be adversely affected by the sound signal. This research concludes with results that indicate that it is acoustic cavitation in the medium surrounding the supercavity that is responsible for the reduced accuracy. A hypothesis has been presented addressing the means by which the acoustic cavitation could cause this effect. Additionally, corrugations on the cavity/water interface imposed by the pressure signal have been observed and characterized.

Thesis (Ph.D.)--University of Wollongong, 2006. / Typescript. Includes bibliographical references: leaf 236-258.

Thesis (M.S.)--University of Missouri-Columbia, 2007. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on April 7, 2008) Includes bibliographical references.

Thesis (Ph. D.)--Electrical and Computer Engineering, Georgia Institute of Technology, 2005. / Anderson, David, Committee Chair ; Barnwell-III, Thomas, Committee Member ; Clements, Mark, Committee Member ; Truong, Kwan, Committee Member ; Basu, Saugata, Committee Member. Vita. Includes bibliographical references.

Thesis (Ph. D.)--Florida State University, 2005. / Advisor: Dr. Christopher K. W. Tam, Florida State University, College of Arts and Sciences, Dept. of Mathematics. Title and description from dissertation home page (viewed Sept. 21, 2005). Document formatted into pages; contains xv, 118 pages. Includes bibliographical references.

In the context of limited availability of fossil fuel and the impact of fossil-based energy utilization to the environment, novel porous materials have been extensively investigated for applications in environmentally friendly energy generation and storage. This thesis describes work wherein porous carbons and mesoporous silica materials have been systematically studied to include new synthesis strategies, material characterization. Two main themes of this thesis are, firstly, to investigate how porosity affects the utilization of activated carbons in energy storage and gas adsorption, and secondly, explore the stabilization of mesoporous silica materials. Chapter 1 discusses structures and classifications of pores. Porous carbons and mesoporous silica materials are introduced including the fundamental properties, preparation and important applications of the materials. Chapter 2 gives the basics of techniques used for characterization of the porous materials fabricated in this work. Gas sorption techniques applied for hydrogen storage and carbon dioxide uptake are introduced. The chapter also presents the electrochemistry and electrochemical methods used in this work. Chapter 3 briefly describes the preparation of highly porous carbons from lignin via hydrothermal carbonisation followed by chemical activation using KOH as activating agent. The work evidences the influence of activation temperature and KOH/carbon weight ratio on the structure of activated carbon and the performance of the gas storage capacity. Activation at KOH/carbon ratio of 2 generates highly microporous carbons which exhibit excellent CO2 uptake capacity; up to 4.6 mmol/g at 1 bar and 25 oC. Activation at KOH/carbon ratio of 4 can, on the other hand, generate lignin-derived carbons with ultrahigh porosity. These higher surface area lignin-derived carbons exhibit attractive hydrogen uptake capacity of up to 6.2 wt% at -196 oC and 20 bar. Chapter 4 is devoted to the use of lignin-derived activated carbons (LAC) as electrode materials for supercapacitors in aqueous and ionic liquid electrolytes. The study shows several factors affecting the electrochemical performance of carbon electrodes. It is demonstrated that a high surface area carbon (designated as LAC4800) electrode in 2 M H2SO4 exhibits a high capacitance value of 223 F/g or surface capacitance of 11.49 µF/cm2 and good cycling stability over 1000 cycles. The LAC electrodes also showed attractive capacitive performance with 175 F/g (6.92 µF/cm2) and the energy density can be enhanced in ionic electrolytes to reach 97.2 Wh/kg and power density of 2.0 kW/kg at 0.5 A/g for sample LAC4800 in BMImBF4 electrolyte. Chapter 5, regarding non-carbon materials, new forms of MCM-41 type silica mesostructures have been prepared by increasing the applied crystallization temperature to between 150 and 190 oC. The high temperature crystallisation resulted in enlargement of pore size and generated thicker pore walls. The sample prepared at 190 oC shows exceptional hydrothermal and thermal stability, even retaining long-range mesostructural ordering after refluxing in boiling water for 24 h or heating at 1000 oC for 4 h, which is unprecedented for pure silica MCM-41 materials. Finally, the conclusions for the thesis including the suggestion for future work are proposed in Chapter 6.

The purpose of this study was to investigate the phenomenon of choral blend through acoustical analysis of individual vocal sounds. One aspect of the study involved identifying and comparing the acoustical qualities of sounds produced in the usual solo manner and sounds produced by the same singers attempting to blend with a unison ensemble. Another aspect of the study involved identifying and comparing the acoustical qualities of vocal sounds identified as blending well and poorly with a unison ensemble. Singers attempting to blend adjust their overall intensity not only to affect the perceived loudness of their tones, but also to facilitate other acoustical changes which are helpful for achieving blend. Vocal blend apparently may be achieved more readily on vowels having few upper partials than on vowels having numerous upper partials. Where vibrato is employed, certain vocal sounds can achieve a good blend even though their fundamental frequencies only approximate the theoretically correct frequency. There apparently is an interaction between the vibrato of a vocal tone and its spectral features, making it advantageous for the singer to adopt mutually beneficial approaches to both factors in order to blend. Vowel modification effective for achieving vocal blend- -at least for sopranos-- appears to consist primarily of changes in the intensity relationships between the vowel formants. Singers' variations in frequency extend beyond the boundaries of any system of tuning or temperament.

A caracterização das patologias da laringe até o presente momento é predominantemente realizada de forma qualitativa. Alguns trabalhos recentes têm quantificados parâmetros acústicos no intuito de discriminar as diversas patologias. Este trabalho verifica os valores médios das diversas medidas acústicas da voz e as relaciona com as diferentes patologias. Desta forma, futuramente será possível utilizar estes valores para quantificar e acompanhar diferentes estágios do tratamento da patologia. O conjunto de valores médios compõem o que chamamos de perfil acústico. / Until now the characterization of larynx pathologies has been done in a subjective manner. Recently some researches have been conducted in order to quantify acoustic parameters mainly to discriminate the larynx pathologies. In this work several acoustic parameters of voice was evaluated and their correlation with the pathologies were established. In the future, would be possible to use these parameters to quantify and to follow the therapy procedures. These values constitute the acoustic profile of the pathologies.