Dissertations / Theses on the topic 'Acoustic transfer function'
To see the other types of publications on this topic, follow the link: Acoustic transfer function.
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 41 dissertations / theses for your research on the topic 'Acoustic transfer function.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Kim, Young Seon. "Transfer function of the embryonic avian middle ear /." free to MU campus, to others for purchase, 2002. http://wwwlib.umi.com/cr/mo/fullcit?p3074415.
Full text
2
Elwali, Wael. "Vehicle Vibro-Acoustic Response Computation and Control." University of Cincinnati / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1382373197.
Full text
3
Bellows, Benjamin Davis. "Characterization of nonlinear heat release-acoustic interactions in gas turbine combustors." Diss., Available online, Georgia Institute of Technology, 2006, 2006. http://etd.gatech.edu/theses/available/etd-03262006-205604/.
Full textAbstract:
Thesis (Ph. D.)--Aerospace Engineering, Georgia Institute of Technology, 2006.Dr. Jeffrey Cohen, Committee Member ; Dr. Jerry Seitzman, Committee Member ; Dr. Jeff Jagoda, Committee Member ; Dr. Ben Zinn, Committee Member ; Dr. Tim Lieuwen, Committee Chair.
4
Betlehem, Terence, and terenceb@rsise anu edu au. "Acoustic Signal Processing Algorithms for Reverberant Environments." The Australian National University. Research School of Information Sciences and Engineering, 2005. http://thesis.anu.edu.au./public/adt-ANU20051129.121453.
Full textAbstract:
This thesis investigates the design and the analysis of acoustic signal processing algorithms in reverberant rooms. Reverberation poses a major challenge to acoustic signal processing problems. It degrades speech intelligibility and causes many acoustic algorithms that process sound to perform poorly. Current solutions to the reverberation problem frequently only work in lightly reverberant environments. There is need to improve the reverberant performance of acoustic algorithms.¶
The approach of this thesis is to explore how the intrinsic properties of reverberation can be exploited to improve acoustic signal processing algorithms. A general approach to soundfield modelling using statistical room acoustics is applied to analyze the reverberant performance of several acoustic algorithms. A model of the underlying structure of reverberation is incorporated to create a new method
of soundfield reproduction.¶
Several outcomes resulting from this approach are: (i) a study of how more sound capture with directional microphones and beamformers can improve the robustness of acoustic equalization, (ii) an assessment of the extent to which source tracking can improve accuracy of source localization, (iii) a new method of soundfield reproduction for reverberant rooms, based upon a parametrization of the acoustic transfer function and (iv) a study of beamforming to directional sources, specifically exploiting the directionality of human speech.¶
The approach to soundfield modelling has permitted a study of algorithm performance on important parameters of the room acoustics and the algorithm design. The performance of acoustic equalization and source tracking have been found to depend not only on the levels of reverberation but also on the correlation of pressure between points in reverberant soundfields. This correlation can be increased by sound capture with directional capture devices. Work on soundfield reproduction has shown that, though reverberation significantly degrades the performance of conventional techniques, by accounting for the reverberation it is possible to design reproduction methods that function well in reverberant environments.
5
Black, Paul Randall. "Acoustic Transfer Functions Derived from Finite Element Modeling for Thermoacoustic Stability Predictions of Gas Turbine Engines." Thesis, Virginia Tech, 2007. http://hdl.handle.net/10919/33978.
Full textAbstract:
Acoustic Transfer Functions Derived from Finite Element Modeling for Thermoacoustic Stability Predictions of Gas Turbine Engines
Design and prediction of thermoacoustic instabilities is a major challenge in aerospace propulsion and the operation of power generating gas turbine engines. This is a complex problem in which multiple physical systems couple together. Traditionally, thermoacoustic models can be reduced to dominant physics which depend only on flame dynamics and acoustics. This is the general approach adopted in this research. The primary objective of this thesis is to describe how to obtain acoustic transfer functions using finite element modeling. These acoustic transfer functions can be coupled with flame transfer functions and other dynamics to predict the thermoacoustic stability of gas turbine engines. Results of this research effort can go beyond the prediction of instability and potentially can be used as a tool in the design stage. Consequently, through the use of these modeling tools, better gas turbine engine designs can be developed, enabling expanded operating conditions and efficiencies.
This thesis presents the finite element (FE) methodology used to develop the acoustic transfer functions of the Combustion System Dynamics Laboratory (CSDL) gaseous combustor to support modeling and prediction of thermoacoustic instabilities. In this research, several different areas of the acoustic modeling were addressed to develop a representative acoustics model of the hot CSDL gaseous combustor. The first area was the development and validation of the cold acoustic finite element model. A large part of this development entailed finding simple but accurate means for representing complex geometries and boundary conditions. The cold-acoustic model of the laboratory combustor was refined and validated with the experimental data taken on the combustion rig.
The second stage of the research involved incorporating the flame into the FE model and has been referred to in this thesis as hot-acoustic modeling. The hot-acoustic model also required the investigation and characterization of the flame as an acoustic source. The detailed mathematical development for the full reacting acoustic wave equation was investigated and simplified sufficiently to identify the appropriate source term for the flame. It was determined that the flame could be represented in the finite element formulation as a volumetric acceleration, provided that the flame region is small compared to acoustic wavelengths. For premixed gas turbine combustor flames, this approximation of a small flame region is generally a reasonable assumption.
Both the high temperature effects and the flame as an acoustic source were implemented to obtain a final hot-acoustic FE model. This model was compared to experimental data where the heat release of the flame was measured along with the acoustic quantities of pressure and velocity. Using these measurements, the hot-acoustic FE model was validated and found to correlate with the experimental data very well.
The thesis concludes with a discussion of how these techniques can be utilized in large industrial-size combustors. Insights into stability are also discussed. A conclusion is then presented with the key results from this research and some suggestions for future work.
Master of Science
6
Febrer, Alles Gemma. "A hybrid approach for inclusion of acoustic wave effects in incompressible LES of reacting flows." Thesis, Loughborough University, 2012. https://dspace.lboro.ac.uk/2134/11979.
Full textAbstract:
LLean premixed combustion systems, attractive for low NOx performance, are inherently susceptible to thermo-acoustic instabilities - the interaction between unsteady heat release and excited acoustic wave effects. In the present work, a hybrid, coupled Large Eddy Simulation (LES) CFD approach is described, combining the computational efficiency of incompressible reacting LES with acoustic wave effects captured via an acoustic network model. A flamelet approach with an algebraic Flame Surface Density (FSD) combustion model was used. The ORACLES experiments - a perfectly premixed flame stabilised in a 3D sudden expansion - are used for validation. Simulations of the inert flow agree very well with experimental data, reproducing the measured amplitude and distribution of turbulent fluctuations as well as capturing the asymmetric mean flow. With reaction the measured data exhibit a plane wave acoustic mode at 50Hz. The influence of this plane wave must be incorporated into the LES calculation. Thus, a new approach to sensitise the incompressible LES CFD to acoustic waves is adopted. First an acoustic network model of the experimental geometry is analysed to predict the amplitude of the 50Hz mode just before the flame zone. This is then used to introduce a coherent plane wave at the LES inlet plane at the appropriate amplitude, unlike previous LES studies, which have adopted a "guess and adjust" approach. Incompressible LES predictions of this forced flow then show good agreement with measurements of mean and turbulent velocity, as well as for flame shape, with a considerable improvement relative to unforced simulations. To capitalise on the unsteady flame dynamics provided by LES, simulations with varying forcing amplitude were conducted and analysed. Amplitude dependent Flame Transfer Functions (FTFs) were extracted and fed into an acoustic network model. This allowed prediction of the stable/unstable nature of the flame at each forcing amplitude. An amplitude at which the flame changed from unstable to stable would be an indication that this coupled approach was capable of predicting a limit cycle behaviour. With the current simple FSD combustion model almost all cases studied showed a stable flame. Predictions showed considerable sensitivity to the value chosen for the combustion model parameter but specially to the acoustic geometric configuration and boundary conditions assumed showing evidence of limit cycle behaviour for some combinations. Nevertheless, further work is required to improve both combustion model and the accuracy of acoustic configuration and boundary condition specification.
7
Zhang, Nan. "SCALE MODELS OF ACOUSTIC SCATTERING PROBLEMS INCLUDING BARRIERS AND SOUND ABSORPTION." UKnowledge, 2018. https://uknowledge.uky.edu/me_etds/119.
Full textAbstract:
Scale modeling has been commonly used for architectural acoustics but use in other noise control areas is nominal. Acoustic scale modeling theory is first reviewed and then feasibility for small-scale applications, such as is common in the electronics industry, is investigated. Three application cases are used to examine the viability. In the first example, a scale model is used to determine the insertion loss of a rectangular barrier. In the second example, the transmission loss through parallel tubes drilled through a cylinder is measured and results are compared to a 2.85 times scale model with good agreement. The third example is a rectangular cuboid with a smaller cylindrical well bored into it. A point source is placed above the cuboid. The transfer function was measured between positions on the top of the cylinder and inside of the cylindrical well. Treatments were then applied sequentially including a cylindrical barrier around the well, a membrane cover over the opening, and a layer of sound absorption over the well. Results are compared between the full scale and a 5.7 times scale model and correlation between the two is satisfactory.
8
Hemchandra, Santosh. "Dynamics of turbulent premixed flames in acoustic fields." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/29615.
Full textAbstract:
Thesis (Ph.D)--Aerospace Engineering, Georgia Institute of Technology, 2009.Committee Chair: Lieuwen, Tim; Committee Member: Menon, Suresh; Committee Member: Peters, Norbert; Committee Member: Yang, Vigor; Committee Member: Zinn, Benjamin. Part of the SMARTech Electronic Thesis and Dissertation Collection.
9
Khanna, Vivek K. "A Study of the Dynamics of Laminar and Turbulent Fully and Partially Premixed Flames." Diss., Virginia Tech, 2001. http://hdl.handle.net/10919/28527.
Full textAbstract:
This present research effort was directed towards developing reduced order models for the dynamics of laminar flat flames, swirl stabilized turbulent flames, and in evaluating the effects of the variation in fuel composition on flame dynamics. The laminar flat flame study was conducted on instrument grade methane, propane, and ethane flames for four total flow rates from 145 cc/sec to 200 cc/sec, and five equivalence ratios from 0.5 to 0.75. The analysis was done by measuring the frequency resolved velocity perturbations, u', and the OH* chemiluminescence, as a measure of unsteady heat release rate, q'. The experimental data showed the corresponding flame dynamics to be fourth order in nature with a pure time delay. One of the resonance was shown to represent the pulsation of the flame location caused by fluctuation in the flame speed and fluctuating heat losses to the flame stabilizer. The other resonance was correlated to the dynamics of the chemical kinetics involved in the combustion process. The time delay was correlated to the chemical time delay. Upon comparing the results of the experiments with the three fuels, it was concluded that for all equivalence ratios studied, propane flame had a higher dynamic gain than methane flames. Ethane flames exhibited a higher dynamic gain than methane flame in the frequency range of 20-100 Hz. Thus, burning of propane instead of methane increased the likelihood of the occurrence of thermo-acoustic instabilities. The experimental techniques developed during the dynamic studies conducted on laminar flat flames were applied to swirl stabilized turbulent flames. Experiments were performed for QAir = 15 scfm and 20 scfm, F = 0.55, 0.6, 0.65, and S = 0.79 and 1.19. The results of fully premixed experiments showed that the flame behaved as a 8th order low pass filter. The results of the partially premixed experiment exhibited a rich spectra, which maintained its bandwidth over the entire range of frequency studied. Comparison of fully and partially premixed flames in the frequency range of 200-400 Hz, indicated that at overall lean conditions the dynamic gain of the totally premixed flames was almost an order of magnitude lower than that of the partially premixed conditions. Thus, it was concluded that combustors with fully premixed flames have a higher probability of being thermo-acoustically stable than those with partially premixed flames.Ph. D.
10
Webber, Michael L. "Phase Shift Control: Application and Performance Limitations With Respect to Thermoacoustic Instabilities." Thesis, Virginia Tech, 2003. http://hdl.handle.net/10919/36418.
Full textAbstract:
Lean premixed fuel-air conditions in large gas turbines are used to improve efficiency and reduce emissions. These conditions give rise to large undamped pressure oscillations at the combustor's natural frequencies which reduce the turbine's longevity and reliability. Active control of the pressure oscillations, called thermoacoustic instabilities, has been sought as passive abatement of these instabilities does not provide adequate damping and is often impractical on a large scale. Phase shift control of the instabilities is perhaps the simplest and most popular technique employed but often does not provide good performance in that controller induced secondary instabilities are generated with increasing loop gain.
This thesis investigates the general underlying cause of the secondary instabilities and shows that high average group delay through the frequency region of the instability is the root of the problem. This average group delay is then shown to be due not only the controller itself but can also be associated with other components and inherent characteristics of the control loop such as actuators and time delay, respectively. An "optimum" phase shift controller, consisting of an appropriate shift in phase and a low order, wide bandwidth bandpass filter, is developed for a Rijke tube combustor and shown to closely match the response of an LQG controller designed only for system stabilization. Both the optimal phase shifter and the LQG controller are developed based on a modified model of the thermoacoustic loop which takes into account the change in density of the combustion reactants at the flame location. Additionally, the system model is coupled with a model of the control loop and then validated by comparison of simulated results to experimental results using nearly identical controllers.
Master of Science
11
Kypraiou, Anna-Maria. "Experimental investigation of the response of flames with different degrees of premixedness to acoustic oscillations." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/275743.
Full textAbstract:
This thesis describes an experimental investigation of the response of lean turbulent swirling flames with different degrees of premixedness (i.e. different mixture patterns) to acoustic forcing using the same burner configuration and varying only the fuel injection strategy. Special emphasis was placed on the amplitude dependence of their response. Also, the behaviour of self-excited fully premixed flames was examined. kHz OH* chemiluminescence was used to study qualitatively the heat release response of the flames, while kHz OH Planar Laser Induced Fluorescence (PLIF) was employed to understand the response of the flame structure and the behaviour of the various parts of the flame. The Proper Orthogonal Decomposition (POD) method was used to extract the dominant structures of the flame and their periodicity. In the first part of the thesis, self-excited oscillations were induced by extending the length of the duct downstream of the bluff body. It was found that the longer the duct length and the higher the equivalence ratio, the stronger the self-excited oscillations were, with the effect of duct length being much stronger. The dominant frequencies of the system were found to increase with equivalence ratio and bulk velocity and decrease with duct length. For some conditions, three simultaneous periodic motions were observed, where the third motion oscillated at a frequency equal to the difference of the other two frequencies. A novel application of the POD method was proposed to estimate the convection velocity from the most dominant reaction zone structures detected by OH* chemiluminescence imaging. For a range of conditions, the convection velocity was found to be in the range of 1.4-1.7 bulk flow velocities at the inlet of the combustor. In the second part, the response of fully premixed, non-premixed with radial fuel injection (NPR) and axial fuel injection (NPA) flames was investigated and compared. All systems exhibited a nonlinear response to acoustic forcing. The highest response was observed by the NPR flame, followed by the fully premixed and the non-premixed with axial fuel injection flame. The proximity of forced flames to blow-off was found to be critical in their heat release response, as close to blow-off the flame response was significantly lower than that farther from blow-off. In the NPR and NPA systems, it was shown that the acoustic forcing reduced the stability of the flame and the stability decreased with the increase in forcing amplitude. In the fully premixed system, the flame area modulations constituted an important mechanism of the system, while in the NPR system both flame area and equivalence ratio modulations were important mechanisms of the heat release modulations. The quantification of the local response of the various parts of the flame at the forcing frequency showed that the ratio RL (OH fluctuation at 160 Hz to the total variance of OH) was greater in the inner shear layer region than in the other parts in the case of NPR and NPA flames. In fully premixed flames, greater RL values were observed in large regions on the downstream side of the flame than those in the ISL region close to the bluff body. The ratio of the convection velocity to the bulk velocity was estimated to be 0.54 for the NPR flame, while it was found to be unity for the respective fully premixed flame. In the last part of the thesis, the response of ethanol spray flames to acoustic oscillations was investigated. The nonlinear response was very low, which was reduced closer to blow-off. The ratio RL was the highest in the spray outer cone region, downstream of the annular air passage, while RL values were very low in the inner cone region, downstream of the bluff body. Unlike NPR and fully premixed flames, in case of spray and NPA systems, it was found that forcing did not affect greatly the flame structure. The understanding of the nonlinear response of flames with different degrees of premixedness in a configuration relevant to industrial systems contributes to the development of reliable flame response models and lean-burn devices, because the degree of premixedness affects greatly the flame response. Also, the understanding of the behaviour of forced spray flames is of great interest for industrial applications, contributing to the development of thermoacoustic models for liquid fuelled combustors. Finally, the estimation of the convection velocity is of importance in the modelling of self-excited flames and flame response models, since the convection velocity affects the flame response significantly.
12
Brebion, Maxence. "Joint numerical and experimental study of thermoacoustic instabilities." Phd thesis, Toulouse, INPT, 2017. http://oatao.univ-toulouse.fr/17840/1/Brebion_1.pdf.
Full textAbstract:
From small scale energy systems such as domestic boilers up to rocket motors, combustion chambers are often prone to combustion instabilities. These instabilities stem from the coupling of unsteady heat release rate and acoustic waves. This coupling is two sided: flame front perturbations generate acoustic waves while acoustic waves impinging on flame holders can disturb flames attached on them. Important pressure and velocity oscillations can be reached during unstable regimes, that can alter its efficiency or even damage the entire combustion chamber. One major challenge is to understand, predict, and prevent from these combustion instabilities. The objectives of this thesis are twofold: (1) take into account acoustic dissipation and (2)analyze flame/acoustic coupling to obtain Reduced Order Model (ROM) for combustion instabilities. This work is divided into three parts. First, the concept of ROM that gives the acoustic modes of a combustion chamber is introduced. This modeling strategy is based on the acoustic network theory and may take into account flame/acoustic coupling as well as acoustic dissipation. An efficient numerical algorithm dedicated to solve ROMs was designed on purpose and validated on several academical configurations. Second, an experimental rig was commissioned to study mean and acoustic pressure losses across a diaphragm and two swirl injectors. Results show that these two phenomena are linked and can be simply incorporated into ROMs. Finally, flame/acoustic coupling is investigated by using both direct numerical simulations and experiments: a lean premixed V-shaped laminar flame is anchored on a cylindrical bluff-body and we show that its temperature greatly influences the flame mean shape as well as its dynamics.
13
Bakhtiari, Nejad Marjan. "Dynamics of Multi-functional Acoustic Holograms in Contactless Ultrasonic Energy Transfer Systems." Diss., Virginia Tech, 2020. http://hdl.handle.net/10919/102414.
Full textAbstract:
Contactless ultrasonic power transfer (UPT), using piezoelectric transducers, is based on transferring energy using acoustic waves, in which the waves are generated by an acoustic source or transmitter and then transferred through an acoustic medium such as water or human tissue to a sensor or receiver. The receiver then converts the mechanical strain induced by the incident acoustic waves to electricity and delivers to an electrical load, in which the electrical power output of the system can be determined. The execution and efficiency of this technology can be significantly enhanced through patterning, focusing, and localization of the transmitted acoustic energy in space to simultaneously power pre-determined distributed sensors or devices. A passive 3D-printed acoustic hologram plate alongside a single transducer can generate arbitrary and pre-designed ultrasound fields in a particular distance from the hologram mounted on the transmitter, i.e., a target plane. This dissertation presents the use of these simple, cost-effective, and high-fidelity acoustic holograms in UPT systems to selectively enhance and pattern the electrical power output from the receivers. Different holograms are numerically designed to create single and multi-focal pressure patterns in a target plane where an array of receivers are placed. The incident sound wave from a transmitter, after passing through the hologram, is manipulated, hence, the output field is the desired pressure field, which excites the receivers located at the pre-determined focal points more significantly. Furthermore, multi-functional holograms are designed to generate multiple images at different target planes and driving frequencies, called, respectively, multi-image-plane and multi-frequency patterning holograms. The multiple desired pressure distributions are encoded on the single hologram plate and each is reconstructed by changing the axial distance and by switching the frequency. Several proof-of-concept experiments are performed to verify the functionality of the computationally designed holograms, which are fabricated using modern 3D-printers, i.e., the desired wavefronts are encoded in the hologram plates' thickness profile, being input to the 3D-printer. The experiments include measurement of output pressure fields in water using needle hydrophones and acquisition of receivers' voltage output in UPT systems.
Another technique investigated in this dissertation is the implementation of acoustic impedance matching layers deposited on the front leading surface of the transmitter and receiver transducers. Current UPT systems suffer from significant acoustic losses through the transmission line from a piezoelectric transmitter to an acoustic medium and then to a piezoelectric receiver. This is due to the unfavorable acoustic impedance mismatch between the transducers and the medium, which causes a narrow transducer bandwidth and a considerable reflection of the acoustic pressure waves at the boundary layers. Using matching layers enhance the acoustic power transmission into the medium and then reinforce the input as an excitation into the receiver. Experiments are performed to identify the input acoustic pressure from a cylindrical transmitter to a receiver disk operating in the 33-mode of piezoelectricity. Significant enhancements are obtained in terms of the receiver's electrical power output when implementing a two-layer matching structure. A design platform is also developed that can facilitate the construction of high-fidelity acoustically matched transducers, that is, the material layers' selection and determination of their thicknesses. Furthermore, this dissertation presents a numerical analysis for the dynamical motions of a high-intensity focused ultrasound (HIFU)-excited microbubble or stable acoustic cavitation, which includes the effects of acoustic nonlinearity, diffraction, and absorption of the medium, and entails the problem of several biomedical ultrasound applications. Finally, the design and use of acoustic holograms in microfluidic channels are addressed which opens the door of acoustic patterning in particle and cell sorting for medical ultrasound systems.Doctor of Philosophy
This dissertation presents several techniques to enhance the wireless transfer of ultrasonic energy in which the sound wave is generated by an acoustic source or transmitter, transferred through an acoustic medium such as water or human tissue to a sensor or receiver. The receiver transducer then converts the vibrational energy into electricity and delivers to an electrical load in which the electrical power output from the system can be determined. The first enhancement technique presented in this dissertation is using a pre-designed and simple structured plate called an acoustic hologram in conjunction with a transmitter transducer to arbitrarily pattern and shape ultrasound fields at a particular distance from the hologram mounted on the transmitter. The desired wavefront such as single or multi-focal pressure fields or an arbitrary image such as a VT image pattern can simply be encoded in the thickness profile of this hologram plate by removing some of the hologram material based on the desired shape. When the sound wave from the transmitter passes this structured plate, it is locally delayed in proportion to the hologram thickness due to the different speed of sound in the hologram material compared to water. In this dissertation, various hologram types are designed numerically to implement in the ultrasonic power transfer (UPT) systems for powering receivers located at the predetermined focal points more significantly and finally, their functionality and performances are verified in several experiments. Current UPT systems suffer from significant acoustic losses through the transmission from a transmitter to an acoustic medium and then to a receiver due to the different acoustic impedance (defined as the product of density and sound speed) between the medium and transducers material, which reflects most of the incident pressure wave at the boundary layers. The second enhancement technology addressed in this dissertation is using intermediate materials, called acoustic impedance matching layers, bonded to the front side of the transmitter and receiver face to alleviate the acoustic impedance mismatch. Experiments are performed to identify the input acoustic pressure from a transmitter to a receiver. Using a two-layer matching structure, significant enhancements are observed in terms of the receiver's electrical power output. A design platform is also developed that can facilitate the construction of high-fidelity acoustically matched transducers, that is, the material layers' selection and determination of their thicknesses. Furthermore, this dissertation presents a numerical analysis for the dynamical motions of a microbubble exposed to a high-intensity focused ultrasound (HIFU) field, which entails the problem of several biomedical ultrasound applications such as microbubble-mediated ultrasound therapy or targeted drug delivery. Finally, an enhancement technique involving the design and use of acoustic holograms in microfluidic channels is addressed which opens the door of acoustic patterning in particle and cell sorting for medical ultrasound systems.
14
Kahana, Yuvi. "Numerical modelling of the head-related transfer function." Thesis, University of Southampton, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.326799.
Full text
15
Brown, Tara J. (Tara Janet) 1978. "Characterization of acoustic head-related transfer functions for nearby sources." Thesis, Massachusetts Institute of Technology, 2000. http://hdl.handle.net/1721.1/8945.
Full textAbstract:
Thesis (M.Eng. and S.B.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, February 2001.Includes bibliographical references (leaf 60).
Head Related Transfer Functions (HRTF) for nearby sources were characterized for human subjects and the Knowles Electronics Manikin for Acoustic Research (KEMAR). The HRTFs were measured in several reverberant room conditions for sound source positions at 0, 45, and 90 degrees in azimuth and 15cm and 1m from the center of the head using maximum-length sequences. The effects of reverberation on interaural time difference, interaural level difference, magnitude response, and spectral content were examined. Results were consistent with acoustic theory. Reverberation was found to decrease ILD, cause comb-filtering, and to distort and add frequency-to-frequency variations to acoustic cues. These affects were most pronounced in room positions with the most reverberant energy.
by Tara J. Brown.
M.Eng.and S.B.
16
Waddington, David Charles. "Acoustical impedence measurement using a two-microphone transfer function technique." Thesis, University of Salford, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.304606.
Full text
17
Venturini, Nicolas. "Experimental Broadband Signal Reconstruction for Plate-like Structures." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2020. http://amslaurea.unibo.it/20470/.
Full textAbstract:
In the Structural Health Monitoring (SHM) field, the Acoustic Emission (AE) technique is a passive method by which damage is localized and identified by capturing Lamb Waves (LW) signals propagating in a plate-like structure. The reconstruction of emitted signals from damage at the source location constitutes one of the main challenges faced by the SHM community. Recently, the application of a Frequencies Compensation Transfer Function (FCTF) has been used to reconstruct narrowband and broadband signals through a hybrid experimental and numerical Time Reversal (TR) process on aluminum plates.
This study aims to reconstruct through experimental methods different types of narrowband and broadband signals on different plate-like structures making use of FCTF. In particular, Hanning Window (HW) and numerical broadband signals have been reconstructed for aluminum and steel plates. The results obtained in this study show how the FCTF method can be applied to different types of materials in plate-like structures. Moreover, the FCTF method has been applied on real broadband signals emitted by the Pencil Lead Break (PLB) technique and Rock Impact (RI) test. These last results prove that the FCTF method is able to compensate for the frequency changes on a single wave packet. Such results are fundamental, as they open the possibility to reconstruct any type of source signals emitted by any damage type.
18
Padden, Dereck J. "Recursive modeling of interpositional transfer functions with a genetic algorithm aided by an adaptive filter for the purpose of altering free-field sound localization /." Online version of thesis, 2007. http://hdl.handle.net/1850/4484.
Full text
19
Kuprenaite, Sabina. "Heterogeneous integration of functional thin films for acoustic and optical devices." Thesis, Bourgogne Franche-Comté, 2019. http://www.theses.fr/2019UBFCD039.
Full textAbstract:
Le contrôle de la microstructure et de la morphologie de surface est essentiel pour que les couches minces soient appliquées dans des dispositifs optiques et acoustiques. Des couches minces de TiO2, LaNiO3 et ZnO et leurs hétérostructures ont été obtenues par des techniques de pulvérisation cathodique à radio fréquence et de dépôt chimique en phase vapeur (CVD). L'optimisation des paramètres de dépôt, tels que la température, la pression totale de la chambre, la pression partielle d'O2 et la vitesse de croissance, a conduit à une amélioration de la qualité structurelle et fonctionnels des films minces et de leurs hétérostructures. L'orientation des couches minces épitaxiales de ZnO et TiO2 a été ajustée non seulement par le lien épitaxial avec divers substrats, mais également par les conditions de dépôt. La qualité optique des films de TiO2 a été principalement optimisée par l'élimination des défauts de microstructure et l'augmentation de la non-stoechiométrie en oxygène. Il a été démontré que les défauts ponctuels et microstructuraux dans les films polycristallins et épitaxiaux jouent un rôle clé dans les pertes de propagation optique. L'effet de la polarité du substrat sur les propriétés structurelles, optiques et acoustiques des films minces à base de ZnO a également été étudié. Les couches sacrificielles et / ou d'initiation de croissance ont été identifiées pour l'intégration hétérogène de films acoustiques et optiques fonctionnels sur substrats semi-conducteursThe control of microstructure and surface morphology is essential for the thin films to be applied in optical and acoustic devices. Thin films of TiO2, LaNiO3 and ZnO and their heterostructures in this work were obtained by radio frequency (RF) magnetron sputtering and metalorganic chemical vapor deposition (MOCVD) techniques. The optimization of deposition parameters, such as temperature, total chamber pressure, O2 partial pressure and growth rate, led to high structural quality of functional thin films and their heterostructures. The orientation of epitaxial ZnO and TiO2 thin films was tuned not only through lattice matching with various substrates, but as well through deposition conditions. The optical quality of TiO2 films was mostly optimized through elimination of microstructural defects and increasing oxygen non-stoichiometry. It was shown that microstructural and lattice defects in polycrystalline and epitaxial films played a key role in optical propagation losses. Effect of substrate polarity on the structural, optical and acoustic properties of ZnO-based thin films was studied, as well. The sacrificial and/or seed layers were identified for heterogeneous intégration of functional acoustical and optical films with semiconductor substrates
20
Dunn, Derrek Butler. "Real-Time Image Processing Using Acousto-Optic Bragg Diffraction." Diss., Virginia Tech, 1998. http://hdl.handle.net/10919/30563.
Full textAbstract:
Optical image processing systems using an acousto-optic cell have been studied previously. However, these previous studies have been limited to two diffracted order in the Bragg regime and two spatial dimensions. Some comparisons between experimental data and theoretical predictions have been made. This dissertation studies image processing by acousto-optic Bragg diffraction to perform image enhanment. Theoretical results involving two diffracted orders in three spatial dimensions is presented. Experimental data is presented that confirms the validity of the theoretical results. Detailed analysis of several optical image processing system using acousto-optic modulators is presented. Also, the methodology use to derive an analytically expression in three spatial dimension for the interaction of an arbitrary light profile and a rectangular sound column in an acousto-optic cell is presented. Lastly, the ability to change the characteristics of the derived transfer function that mathematically represents the interaction of light and sound inside the acousto-optic cell is discussed and future research topics is given.Ph. D.
21
Húserka, Jozef. "Návrh reverberátoru pro simulaci akustiky prostoru." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2014. http://www.nusl.cz/ntk/nusl-220649.
Full textAbstract:
This thesis deals with artificial simulation of acoustic spaces by using reverberators. Output of this document consists of four reverberation algorithms and function that evaluates objective parameters of acoustic space from impulse responses. Reverberators and script were implemented using Matlab. Graphical user interface is used to present all of the algorithms for easier usability. First chapter deals with objective parameters of acoustic spaces and the ways they are computed from impulse response. Second chapter describes various structures which are used to build reverberators. Those structures are used in third chapter in implementations of reverberators. Third chapter also compares all implemented reverberators . In last chapter experiment was made. Impulse responses of three spaces were measured and subsequently aproximated by algorithms implemented in this thesis.
22
Reed, Darrin Kiyoshi. "Virtual audio localization with simulated early-reflections and generalized head-related transfer functions." Thesis, Montana State University, 2009. http://etd.lib.montana.edu/etd/2009/reed/ReedD1209.pdf.
Full textAbstract:
In a natural sonic environment a listener is accustomed to hearing reflections and reverberation. It is conceived that early reflections could reduce front-back confusion in synthetic 3-D audio. This thesis describes experiments which seek to determine whether or not simulated reflections can reduce front-back confusions for audio presented with non-individualized head-related transfer functions (HRTFs) via headphones. To measure the contribution of the reflections, 13 human subjects participated in localization experiments which compared their localization ability with anechoic HRTF processing versus HRTF processing with a single early-reflection. The results were highly subject dependent; some showed improvement while others seemed to be inhibited by the reflections. Statistical analysis of the overall results concluded that a single reflection does not provide a significant difference in localization ability. Although this data rejects the hypothesis of this investigation, some suspicion regarding the contribution of lateral reflections in an auditory environment remains.
23
Shen, Jianming. "Functional transfer of musical training to speech perception in adverse acoustical situations." The Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1405107128.
Full text
24
Gürtler, Johannes, Felix Greiffenhagen, Jakob Woisetschläger, Daniel Haufe, and Jürgen Czarske. "Non-invasive seedingless measurements of the flame transfer function using high-speed camerabased laser vibrometry." SPIE, 2017. https://tud.qucosa.de/id/qucosa%3A34893.
Full textAbstract:
The characterization of modern jet engines or stationary gas turbines running with lean combustion by means of swirl-stabilized ames necessitates seedingless optical field measurements of the ame transfer function, i.e. the ratio of the uctuating heat release rate inside the ame volume, the instationary ow velocity at the combustor outlet and the time average of both quantities. For this reason, a high-speed camera-based laser interferometric vibrometer is proposed for spatio-temporally resolved measurements of the ame transfer function inside a swirl-stabilized technically premixed ame. Each pixel provides line-of-sight measurements of the heat release rate due to the linear coupling to uctuations of the refractive index along the laser beam, which are based on density uctuations inside the ame volume. Additionally, field measurements of the instationary ow velocity are possible due to correlation of simultaneously measured pixel signals and the known distance between the measurement positions. Thus, the new system enables the spatially resolved detection of the ame transfer function and instationary ow behavior with a single measurement for the first time. The presented setup offers single pixel resolution with measurement rates up to 40 kHz at an maximum image resolution of 256 px x 128 px. Based on a comparison with reference measurements using a standard pointwise laser interferometric vibrometer, the new system is validated and a discussion of the measurement uncertainty is presented. Finally, the measurement of refractive index uctuations inside a ame volume is demonstrated.
25
Dietrich, Pascal [Verfasser]. "Uncertainties in acoustical transfer functions : modeling, measurement and derivation of parameters for airborne and structure-borne sound / Pascal Dietrich." Aachen : Hochschulbibliothek der Rheinisch-Westfälischen Technischen Hochschule Aachen, 2013. http://d-nb.info/1047970368/34.
Full text
26
Gutiérrez, Daniel. "Green Fuel Simulations." Thesis, Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-79244.
Full textAbstract:
Many industries have entered a new global phase which takes the environment in mind. The gas turbine industry is no exception, where the utilization of green fuels is the future to spare the environment from carbon dioxide and NOx emissions. Hydrogen has been identified as a fuel which can fulfil the global requirements set by governments worldwide. Combustion instabilities are not inevitable during gas turbine operations, especially when using a highly reactive and diffusive fuel as hydrogen. These thermoacoustics instabilities can damage mechanical components and have economic consequences in terms of maintenance and reparation. Understanding these thermoacoustic instabilities in gas turbine burners is of great interest. COMSOL Multiphysics offers a robust acoustic module compared to other available acoustic simulation programs. In this thesis, an Acoustic finite element model was built representing an atmospheric combustion rig (ACR), used to test the burners performance and NOx emissions. Complementary computational fluid dynamics (CFD) simulations were performed for 100 % hydrogen as fuel by using the Reynolds average Navier-Stokes (RANS) lag EB k - epsilon turbulence model. Necessary data was successfully imported to the Acoustic finite element model. Different techniques of building the mesh were used in COMSOL Multiphysics and NX. Similar results were obtained, proving that both mesh tools work well in acoustic simulations. Two different ways of solving the eigenvalue problem in acoustics were implemented, the classic Helmholtz equation and Linearized Navier-Stokes equations, both in the frequency domain. The Helmholtz equation proved to be efficient and detected multiple modes in the frequency range of interest. Critical modes which lived in the burner and the combustion chamber were identified. Defining a hard and soft wall boundary condition at the inlets and outlet of the atmospheric combustion rig gave similar eigenfrequencies when comparing the two boundary conditions. The soft wall boundary condition was defined with a characteristic impedance, giving a high uncertainty whether the results were trustworthy or not. A boundary condition study revealed that the boundary condition at the outlet was valid for modes living in the burner and combustion chamber. Solving the eigenvalue problem with the Linearized Navier-Stokes equations proved to be computationally demanding compared to the Helmholtz equation. Similar modes shapes were found at higher frequencies, but pressure perturbations were observed in the region where the turbulence was dominant. A prestudy for a stability analysis was established, where the ACR and the flame was represented as a generic model. Implementing a Flame Transfer Function (FTF), more specifically a linear n - tau model, showed that the time delay tau is most sensible for a parametric change and hence needs to be chosen cautiously
27
Mejia, Daniel. "Effets de la température de paroi sur la réponse de la flamme à des oscillations acoustiques." Thesis, Toulouse, INPT, 2014. http://www.theses.fr/2014INPT0026/document.
Full textAbstract:
Les instabilités de combustion induites par le couplage combustion-acoustique se produisent dans de nombreux systèmes industriels et domestiques tels que les chaudières, les turbines à gaz et les moteurs de fusée. Ces instabilités se traduisent par des fluctuations de pression et un dégagement de chaleur qui peuvent provoquer une défaillance mécanique ou des dégâts désastreux dans certains cas extrêmes. Ces phénomènes ont été largement étudiés par le passé, et les mécanismes responsables du couplage ont déjà été identifiés. Cependant, il apparaît que la plupart des systèmes se comportent différemment lors du démarrage à froid ou en régime permanent. Le couplage entre la température des parois et les instabilités de combustion reste encore méconnu et n’a pas été étudié en détail jusqu’à présent. Dans le cadre de ces travaux de thèse, on s’intéresse à ce mécanisme. Ces travaux présentent une étude expérimentale des instabilités de combustion pour une flamme laminaire de pré-mélange stabilisée sur un brûleur à fente. Pour certaines conditions de fonctionnement, le système présente un mode instable autour du mode de Helmholtz du brûleur. Il est démontré que l’instabilité peut être contrôlée, et même supprimée, en changeant uniquement la température de la surface du brûleur. Une analyse de stabilité linéaire peut être mise en œuvre afin d’identifier les paramètres jouant un rôle dans les mécanismes d’instabilité, et il est possible de modéliser analytiquement les phénomènes observés expérimentalement. Des études expérimentales détaillées de différents processus élémentaires impliqués dans le couplage thermo-acoustique ont été menées pour évaluer la sensibilité de ces paramètres à la température de la paroi. Enfin un modèle théorique du couplage entre le transfert de chaleur instationnaire à la paroi et la fluctuation du pied de flamme a été proposé. Par ailleurs, d’autres mesures expérimentales ont permis de comprendre les mécanismes physiques responsables de la dépendance de la réponse de la flamme à la température de paroiCombustion instabilities, induced by the resonant coupling of acoustics and combustion occur in many practical systems such as domestic boilers, gas turbine and rocket engines. They produce pressure and heat release fluctuations that in some extreme cases can provoke mechanical failure or catastrophic damage. These phenomena have been extensively studied in the past, and the basic driving and coupling mechanisms have already been identified. However, it is well known that most systems behave differently at cold start and in the permanent regime and the coupling between the temperature of the solid material and combustion instabilities still remains unclear. The aim of this thesis is to study this mechanism. This work presents an experimental investigation of combustion instabilities for a laminar premixed flame stabilized on a slot burner with controlled wall temperature. For certain operating conditions, the system exhibits a combustion instability locked on the Helmholtz mode of the burner. It is shown that this instability can be controlled and even suppressed by changing solely the temperature of the burner rim. A linear stability analysis is used to identify the parameters playing a role in the resonant coupling and retrieves the features observed experimentally. Detailed experimental studies of the different elementary processes involved in the thermo-acoustic coupling are used to evaluate the sensitivity of these parameters to the wall temperature. Finally a theoretical model of unsteady heat transfer from the flame root to the burner-rim and detailed experimental measurements permit to establish the physical mechanism for the temperature dependance on the flame response
28
Vigoureux, Dorian. "Déconfinement de sources acoustiques par utilisation d'une méthode holographique à double information." Phd thesis, INSA de Lyon, 2012. http://tel.archives-ouvertes.fr/tel-00759412.
Full textAbstract:
L'identification et la caractérisation des sources acoustiques restent encore aujourd'hui deux sujets d'importance pour les industriels qui ont besoin de techniques permettant d'identifier des sources acoustiques ou vibratoires sur des surfaces complexes dans un environnement acoustique non contrôlé. La thèse que nous présentons ici s'inscrit dans ce cadre. Nous y étudions les qualités d'une méthode inverse, appelée iPTF (pour inverse Patch Transfer Functions, pour la résolution de ce problème particulier. Nous consacrerons le premier chapitre de notre étude à la synthèse bibliographique des méthodes les plus pertinentes permettant de résoudre des problèmes similaires. Nous soulignerons également les difficultés de ces méthodes pouvant être liées à leurs applications pratiques ou à leurs fondements théoriques. Dans un second chapitre, nous présenterons la méthode iPTF à partir de sa formulation directe, c'est-à-dire de la source vers le bruit rayonné. Celle-ci est une approche par sous-structuration de domaines permettant l'étude des problèmes vibro-acoustiques en basses et moyennes fréquences. Nous montrerons particulièrement la façon dont l'association des deux formulations directe et indirecte permet de définir une méthode pouvant conduire jusqu'à l'identification des trois champs de vitesses, de pressions et d'intensités sur la surface de l'objet source. Notre troisième chapitre sera consacré à la présentation des premiers résultats d'identification dans un cas d'application numérique simple. Nous effectuerons, dans les chapitres quatre et cinq, une étude des principaux paramètres conditionnant les résultats donnés par la méthode. Le premier de ces deux chapitres présentera la mise en place d'un code de calcul permettant de résoudre rapidement le problème de rayonnement d'une structure simple. La méthode ainsi définie sera utilisée dans le chapitre cinq afin de générer de nombreux champs rayonnés présentant des caractéristiques différentes de façon à étudier la stabilité de la méthode iPTF face à la variation de différents paramètres. Un sixième chapitre présentera une étude approfondie faite sur les ondes évanescentes qui prennent une part non négligeable dans le champ rayonné par les structures. Ces ondes évanescentes, par définition, ne peuvent pas être mesurées au delà du champ proche, ce qui peut être la cause d'une part des défauts d'identification rencontrés lors de l'application de notre méthode. L'étude faite ici aura pour but de déterminer l'importance de ces ondes évanescentes dans le champ rayonné. Nous présenterons enfin, dans un dernier chapitre, les résultats de mesures expérimentales réalisées.
29
da, Cunha Daise Nunes Queiroz. "Properties of Flow Through the Ascending Aorta in Boxer Dogs with Mild Aortic Stenosis: Momentum, Energy, Reynolds Number, Womersley’s, Unsteadiness Parameter, Vortex Shedding, and Transfer Function of Oscillations from Aorta to Thoracic Wall." The Ohio State University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=osu1243910694.
Full text
30
Tuleja, Peter. "Využití Hilbert Huangovy transformace pro analýzu nestacionárních signálů z fyzikálních experimentů." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2014. http://www.nusl.cz/ntk/nusl-220614.
Full textAbstract:
This paper discusses the possible use of Hilbert-Huang transform to analyze the data obtained from physical experiments. Specifically for the analysis of acoustic emission in the form of acoustic shock. The introductory section explains the concept of acoustic emission and its detection process. Subsequently are discussed methods for signal analysis in time-frequency domain. Specifically, short-term Fourier transform, Wavelet transform, Hilbert transform and Hilbert-Huang transform. The final part contains the proposed method for measuring the performance and accuracy of different approaches.
31
Mainka, Alexander, Anton Poznyakovskiy, Ivan Platzek, Mario Fleischer, Johan Sundberg, and Dirk Mürbe. "Lower Vocal Tract Morphologic Adjustments Are Relevant for Voice Timbre in Singing." Public Library of Science, 2015. https://tud.qucosa.de/id/qucosa%3A29495.
Full textAbstract:
The vocal tract shape is crucial to voice production. Its lower part seems particularly relevant for voice timbre. This study analyzes the detailed morphology of parts of the epilaryngeal tube and the hypopharynx for the sustained German vowels /a/, /e/, /i/, /o/, and /u/ by thirteen male singer subjects who were at the beginning of their academic singing studies. Analysis was based on two different phonatory conditions: a natural, speech-like phonation and a singing phonation, like in classical singing. 3D models of the vocal tract were derived from magnetic resonance imaging and compared with long-term average spectrum analysis of audio recordings from the same subjects. Comparison of singing to the speech-like phonation, which served as reference, showed significant adjustments of the lower vocal tract: an average lowering of the larynx by 8 mm and an increase of the hypopharyngeal cross-sectional area (+ 21.9%) and volume (+ 16.8%). Changes in the analyzed epilaryngeal portion of the vocal tract were not significant. Consequently, lower larynx-to-hypopharynx area and volume ratios were found in singing compared to the speech-like phonation. All evaluated measures of the lower vocal tract varied significantly with vowel quality. Acoustically, an increase of high frequency energy in singing correlated with a wider hypopharyngeal area. The findings offer an explanation how classical male singers might succeed in producing a voice timbre with increased high frequency energy, creating a singer‘s formant cluster.
32
Mainka, Alexander, Anton Poznyakovskiy, Ivan Platzek, Mario Fleischer, Johan Sundberg, and Dirk Mürbe. "Lower Vocal Tract Morphologic Adjustments Are Relevant for Voice Timbre in Singing." Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-202679.
Full textAbstract:
The vocal tract shape is crucial to voice production. Its lower part seems particularly relevant for voice timbre. This study analyzes the detailed morphology of parts of the epilaryngeal tube and the hypopharynx for the sustained German vowels /a/, /e/, /i/, /o/, and /u/ by thirteen male singer subjects who were at the beginning of their academic singing studies. Analysis was based on two different phonatory conditions: a natural, speech-like phonation and a singing phonation, like in classical singing. 3D models of the vocal tract were derived from magnetic resonance imaging and compared with long-term average spectrum analysis of audio recordings from the same subjects. Comparison of singing to the speech-like phonation, which served as reference, showed significant adjustments of the lower vocal tract: an average lowering of the larynx by 8 mm and an increase of the hypopharyngeal cross-sectional area (+ 21.9%) and volume (+ 16.8%). Changes in the analyzed epilaryngeal portion of the vocal tract were not significant. Consequently, lower larynx-to-hypopharynx area and volume ratios were found in singing compared to the speech-like phonation. All evaluated measures of the lower vocal tract varied significantly with vowel quality. Acoustically, an increase of high frequency energy in singing correlated with a wider hypopharyngeal area. The findings offer an explanation how classical male singers might succeed in producing a voice timbre with increased high frequency energy, creating a singer‘s formant cluster.
33
Soria, Sergio Gilberto Rodriguez. "Estudos sobre personalização da função de transferência relativa à cabeça em sistemas biaurais de reprodução acústica virtual." Universidade de São Paulo, 2006. http://www.teses.usp.br/teses/disponiveis/3/3142/tde-21032006-144134/.
Full textAbstract:
Este trabalho apresenta diversas propostas associadas ao uso ótimo de funções de transferência relativas à cabeça (HRTFs) em sistemas de reprodução acústica virtual por fones de ouvido. Estas propostas permitem personalizar a HRTF a indivíduos particulares, tomando como base uma combinação da modelagem estrutural e morfológica de HRTFs. Dentro do contexto da modelagem estrutural, o presente trabalho se concentrou no estudo da contribuição do pinna à HRTF. O pinna é a estrutura anatômica responsável pela percepção de elevação. Assim, o primeiro passo foi extrair um conjunto de funções de transferência relativas ao pinna (PRTFs) das HRTFs de uma base de dados. Para tanto, foram usadas diversas técnicas como análise preditiva linear para rastrear as ressonâncias, janelamento para eliminar a influência do torso, funções de autocorrelação e de atraso de grupo para salientar as antirressonâncias, e outros algoritmos para combinar ressonâncias e antirressonâncias em apenas uma magnitude espectral. Usando essa nova base de dados de PRTFs e parâmetros antropométricos propostos mais outros registrados na base de dados, um espaço vetorial correspondente à antropometria do pinna foi mapeado linearmente em um espaço vetorial correspondente às características espectrais da PRTF, calculando-se assim várias transformações lineares para estimação de novas PRTFs fora da base de dados. A estimação atingiu 66% de reconstrução no grupo de treino. O trabalho está orientado à exploração das características espectrais importantes na percepção de elevação, portanto, está limitado ao plano médio do hemisfério frontal, onde não existem diferenças interaurais significativas nem efeitos difrativos da cabeça. Finalmente é proposto um sistema de testes de localização de fonte sonora para validar o modelo.This work presents several proposals associated with the optimal use of head-related transfer functions (HRTF) in virtual auditory spaces presented via headphones. These proposals lead to personalization of the HRTF to particular individuals, using a combination of the structural and morphological modeling techniques. In the context of structural modeling, this work focuses on modeling the contribution of the pinna to the HRTF. The pinna is the anatomical structure responsible for vertical sound localization. Thus, the first step was to extract a set of pinna-related transfer functions (PRTFs) from HRTFs published in a database. This was accomplished using several techniques like linear prediction analysis for tracking the resonances, windowing for eliminating the torso influence, autocorrelation and group delay functions for emphasizing the notches and other algorithms for combining resonances and notches in only one magnitude response. Using this novel database of PRTFs and a set of proposed anthropometric parameters plus some others registered in the database, a vector space corresponding to pinna anthropometry is linearly mapped into a vector space corresponding to spectral features of the PRTF, being calculated, in this way, several linear transformations for estimation of new PRTFs, outside the database. The estimation attains 66% of reconstruction in the training group. The work focuses on the exploration of spectral characteristics important for elevation perception, therefore, it is limited to the median plane where there are no meaningful interaural differences nor head diffraction effects. Finally, a system for sound localization tests is proposed in order to validate the model.
34
Wickman, Erik. "Taluppfattbarhet med strupmikrofon." Thesis, Uppsala universitet, Signaler och System, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-353351.
Full textAbstract:
Contact microphones, especially throat microphones, have been developed to be used in environments with high background noises to improve the speech intelligibility in communication. They pick up vibrations from the surface they are attached to and are therefore less sensitive to sound and noise from the air. Comparison of the speech intelligibility with other types of microphones have previously been done by letting test persons examine the communication devices in question. This study examines the possibility to make use of the STI-method instead and therefore make a comparison faster, more cost-efficient and customizable. The thought is that if the relationship between speech signals and vibrations were known, it could be used to transform the STI test signal to vibrations and then use the STImethod to estimate the speech intelligibility for the chosen contact microphone. This study, containing 22 men and women, evaluated the vibrations at the most suitable locations on the head for contact microphones and compared it with the speech signal of the same test person. Frequency responses were calculated for all locations of the head and a more detailed study showed that the frequency response of the neck may be approximated as a second order lowpass filter with a cut-off frequency of about 300 Hz that attenuates speech signals with higher frequencies. Experiments were also done to measure the STI value of a throat microphone with the known relationship. However, the results pointed out several problems that needs to be addressed before a STI method can be performed successfully. The results from this study may also be used to deeper study the relationships between different vibrations resulting from speech signals and suggestions on how the performance of contact microphones may be improved are given.
35
Mohamed, Fathi Husain Alhadi. "Mitigation of Amplitude and Phase Distortion of Signals Under Modified Von Karman Turbulence Using Encrypted Chaos Waves." University of Dayton / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1467943201.
Full text
36
Snyder, Mark Alan. "Long-Term Ambient Noise Statistics in the Gulf of Mexico." ScholarWorks@UNO, 2007. http://scholarworks.uno.edu/td/595.
Full textAbstract:
Long-term omni-directional ambient noise was collected at several sites in the Gulf of Mexico during 2004 and 2005. The Naval Oceanographic Office deployed bottom moored Environmental Acoustic Recording System (EARS) buoys approximately 159 nautical miles south of Panama City, Florida, in water depths of 3200 meters. The hydrophone of each buoy was 265 meters above the bottom. The data duration ranged from 10-14 months. The buoys were located near a major shipping lane, with an estimated 1.5 to 4.5 ships per day passing nearby. The data were sampled at 2500 Hz and have a bandwidth of 10-1000 Hz. Data are processed in eight 1/3-octave frequency bands, centered from 25 to 950 Hz, and monthly values of the following statistical quantities are computed from the resulting eight time series of noise spectral level: mean, median, standard deviation, skewness, kurtosis and coherence time. Four hurricanes were recorded during the summer of 2004 and they have a major impact on all of the noise statistics. Noise levels at higher frequencies (400-950 Hz) peak during extremely windy months (summer hurricanes and winter storms). Standard deviation is least in the region 100-200 Hz but increases at higher frequencies, especially during periods of high wind variability (summer hurricanes). Skewness is positive from 25-400 Hz and negative from 630-950 Hz. Skewness and kurtosis are greatest near 100 Hz. Coherence time is low in shipping bands and high in weather bands, and it peaks during hurricanes. The noise coherence is also analyzed. The 14-month time series in each 1/3- octave band is highly correlated with other 1/3-octave band time series ranging from 2 octaves below to 2 octaves above the band's center frequency. Spatial coherence between hydrophones is also analyzed for hydrophone separations of 2.29, 2.56 and 4.84 km over a 10-month period. The noise field is highly coherent out to the maximum distance studied, 4.84 km. Additionally, fluctuations of each time series are analyzed to determine time scales of greatest variability. The 14-month data show clearly that variability occurs primarily over three time scales: 7-22 hours (shipping-related), 56-282 hours (2-12 days, weather-related) and over an 8-12 month period.
37
Hojatpanah, Roozbeh. "Empirical study of acoustic instability in premixed flames: measurements of flame transfer function." 2012. http://hdl.handle.net/1805/3366.
Full textAbstract:
Indiana University-Purdue University Indianapolis (IUPUI)In order to conform to pollutant-control regulations and minimize NOx emissions, modern household boilers and central heating systems are moving toward premixed combustors. These combustors have been successful with regards to emissions along with efficiency. However, their implementation has been associated with acoustical instability problems that could be solved through precise optimization in design rather than trial and error experimentation. This thesis introduces an experimental apparatus, which is designed to investigate the acoustic instability problem at the flame level. The goal is an experimental determination of the flame transfer function and comparison of the experimental data with a theoretical model of the flame. An experimental procedure is designed to diagnose the origins of the combustion instabilities by measurement of the flame transfer function. This research is carried out in three steps. The first step is to understand the acoustic instability problem through study of the theoretical models of the flame transfer function and selection of a model, which is most functional in industrial applications. A xiii measurement technique for the flame transfer function is developed according to the required accuracy in measurements, repeatability, and configurability for a wide range of operating conditions. Subsequently, an experimental apparatus is designed to accommodate the flame transfer function measurement technique. The components of the acoustic system are carefully sized to achieve precise measurement of the system parameters such as flows, pressures, and acoustic responses, and the apparatus is built. The apparatus is operated to measure the flame transfer function at several operating conditions. The experimentally measured flame transfer function is compared with a theoretical model for further verification. The experimental apparatus provides an improved assessment of the acoustic instability problem for industrial applications.
38
Mejia, Daniel. "Wall-temperature effects on flame response to acoustic oscillations." Thesis, 2014. http://oatao.univ-toulouse.fr/12001/1/mejia.pdf.
Full textAbstract:
Combustion instabilities, induced by the resonant coupling of acoustics and combustion occur in many practical systems such as domestic boilers, gas turbine and rocket engines. They produce pressure and heat release fluctuations that in some extreme cases can provoke mechanical failure or catastrophic damage. These phenomena have been extensively studied in the past, and the basic driving and coupling mechanisms have already been identified. However, it is well known that most systems behave differently at cold start and in the permanent regime and the coupling between the temperature of the solid material and combustion instabilities still remains unclear. The aim of this thesis is to study this mechanism.
This work presents an experimental investigation of combustion instabilities for a laminar premixed flame stabilized on a slot burner with controlled wall temperature. For certain operating conditions, the system exhibits a combustion instability locked on the Helmholtz mode of the burner. It is shown that this instability can be controlled and even suppressed by changing solely the temperature of the burner rim. A linear stability analysis is used to identify the parameters playing a role in the resonant coupling and retrieves the features observed experimentally. Detailed experimental studies of the different elementary processes involved in the thermo-acoustic coupling are used to evaluate the sensitivity of these parameters to the wall temperature. Finally a theoretical model of unsteady heat transfer from the flame root to the burner-rim and detailed experimental measurements permit to establish the physical mechanism for the temperature dependance on the flame response.
39
Wu, Wei-Chin, and 吳威進. "Application of the transfer function method to acoustic feedback reduction for active noise control in a duct." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/34613078036398244549.
Full textAbstract:
碩士南台科技大學
機械工程系
95
In most practical applications of active noise control, the acoustic feedback is a major problem that often interferes with the operation of the control system and even renders it unstable. The optimal collocated positions of secondary source with two microphones are studied and the separate of transfer function method that reduce the influence of acoustic feedback are developed based on plane wave transmission theory of sound and concept of transfer function in a duct. After, In order to identify the variation of the signals and find out individual correlation coefficient, cross correlation function analysis between primary noise signal and reference input signal is processed. In this study, we use LabVIEW programming language of PC-Based to carry out the reduction of actively noise with theoretical equations of acoustic feedback cancellation and incorporate Filtered-X LMS algorithm. Furthermore, it was to verify that the reliable of simulation and analysis for the processed of signal by the concept of cross correlation function. The results showed and compared that the method of acoustic feedback cancellation incorporated with the Filtered-X LMS algorithm can effectively improve the influence of acoustic feedback, and reduce the noise in a duct.
40
Han, Je Heon. "Investigation on Wave Propagation Characteristics in Plates and Pipes for Identification of Structural Defect Locations." Thesis, 2013. http://hdl.handle.net/1969.1/151345.
Full textAbstract:
For successful identification of structural defects in plates and pipes, it is essential to understand structural wave propagation characteristics such as dispersion relations. Analytical approaches to identify the dispersion relations of homogeneous, simple plates and circular pipes have been investigated by many researchers. However, for plates or pipes with irregular cross-sectional configurations or multi-layered composite structures, it is almost impossible to obtain the analytical dispersion relations and associated mode shapes. In addition, full numerical modeling approaches such as finite element (FE) methods are not economically feasible for high (e.g., ultrasonic) frequency analyses where an extremely large number of discretized meshes are required, resulting in significantly expensive computation.
In order to address these limitations, Hybrid Analytical/Finite Element Methods (HAFEMs) are developed to model composite plates and pipes in a computationally-efficient manner. When a pipe system is used to transport a fluid, the dispersion curves obtained from a “hollow” pipe model can mislead non-destructive evaluation (NDE) results of the pipe system. In this study, the HAFEM procedure with solid elements is extended by developing fluid elements and solid-fluid boundary conditions, resulting in the dispersion curves of fluid-filled pipes. In addition, a HAFEM-based acoustic transfer function approach is suggested to consider a long pipe system assembled with multiple pipe sections with different cross-sections. For the validation of the proposed methods, experimental and full FE modeling results are compared to the results obtained from the HAFEM models.
In order to detect structural defect locations in shell structures from defect-induced, subtle wave reflection signals and eliminate direct-excitation-induced and boundary-reflected, relatively-strong wave signals, a time-frequency MUSIC algorithm is applied to ultrasonic wave data measured by using an array of piezoelectric transducers. A normalized, structurally-damped, cylindrical 2-D steering vector is proposed to increase the spatial resolution of time-frequency MUSIC power results. A cross-shaped array is selected over a circular or linear array to further improve the spatial resolution and to avoid the mirrored virtual image effects of a linear array. Here, it is experimentally demonstrated that the proposed time-frequency MUSIC beamforming procedure can be used to identify structural defect locations on an aluminum plate by distinguishing the defect-induced waves from both the excitation-generated and boundary-reflected waves.
41
Γεωργαντή, Ελευθερία. "Μοdelling, analysis, and processing of room responses and reverberant signals." Thesis, 2013. http://hdl.handle.net/10889/7516.
Full textAbstract:
The main focus of this thesis is to analyse signals (signal-dependent analysis) and room responses (system-dependent analysis) from a statistical point of view, attempt to determine the underlying statistical relationships between the reverberant signals and the room responses and propose relevant statistical models. Based on such a statistical framework, this thesis aims to propose novel methodologies for the extraction of room acoustical information and parameters from reverberant signals. Schroeder's theory is experimentally evaluated for various Room Transfer Functions (RTFs) measured in many source/receiver positions in various enclosures and several related aspects are discussed. Using a statistical approach, the effects of reverberant energy on the histograms and statistical measures are discussed and models describing the relationship of statistical measures between the reverberant signal and the RTFs are extracted. Then, the statistical properties of Binaural Room Transfer Functions (BRTFs) and binaural cues are examined. The well-known property of the spectral standard deviation of the magnitude of RTFs, that is its convergence to 5.6 dB for diffuse fields, is examined for the case of BRTFs, using a similar approach and a generic model for the relationship of the spectral standard deviation of RTFs and BRTFs.
This thesis is also concerned with the distance estimation problem from a perceptual and computational point of view. Two novel methods for the estimation of the source/receiver distance using speech signals are proposed. The first method is able to detect the distance between the speaker and the microphone in a room environment using single-channel signals. The distance-dependent variation of several temporal and spectral statistical features of single-channel signals is studied and a novel sound source distance detector, based on these features is developed. The second method estimates distance from binaural speech signals (two-channel signals). This method does not require a priori knowledge of the room impulse response, the reverberation time or any other acoustical parameter and relies on a set of novel features extracted from the reverberant binaural signals. For this method, a novel distance estimation feature is introduced exploiting the standard deviation of the difference of the magnitude spectra of the left and right binaural signals (termed here as Binaural Spectral Magnitude Difference Standard Deviation (BSMD STD)). Moreover, an extended and novel set of additional features based on the statistical properties of binaural cues (ILDs, ITDs, ICs) is extracted from an auditory front-end which models the peripheral processing of the human auditory system. Both methods rely on novel distance-dependent features, related to statistical parameters of speech signals.
Finally, a novel method for the estimation of the direct-to-reverberant-ratio (DRR) from dual-channel microphone recordings without having knowledge of the source signal is presented.Η παρούσα διατριβή ασχολείται με τη μελέτη και ανάλυση των στατιστικών χαρακτηριστικών ηχητικών σημάτων και των ακουστικών αποκρίσεων χώρου, έχοντας ως πρωταρχικό σκοπό να προτείνει σχέσεις που περιγράφουν τη συσχέτιση των στατιστικών χαρακτηριστικών των σημάτων με αντήχηση με τις ακουστικές αποκρίσεις χώρων. Βάσει ενός τέτοιου θεωρητικού πλαισίου, η διατριβή αυτή αποσκοπεί στο να προτείνει νέες μεθοδολογίες για την εξαγωγή πληροφορίας που σχετίζεται με τα ακουστικά χαρακτηριστικά των χώρων, κάνοντας χρήση ηχογραφημένων ηχητικών σημάτων (π.χ. σήματα ομιλίας) στους εκάστοτε κλειστούς χώρους. Το θεωρητικό υπόβαθρο αυτής της διατριβής βασίζεται σε υπάρχοντα θεωρητικά μοντέλα για το ηχητικό πεδίο μέσα σε ένα κλειστό χώρο, όπως, για παράδειγμα, το στατιστικό μοντέλο του Schroeder. Το μοντέλο του Schroeder επιβεβαιώνεται πειραματικά για ακουστικές αποκρίσεις που έχουν μετρηθεί σε διάφορες θέσεις, μέσα σε κλειστούς χώρους, οι οποίοι διαφέρουν στα ακουστικά χαρακτηριστικά τους. Βάσει στατιστικής ανάλυσης, εξάγονται στατιστικά μοντέλα, τα οποία περιγράφουν την επίδραση της αντήχησης στα ηχητικά σήματα, όταν αυτά αναπαραχθούν μέσα σε ένα κλειστό χώρο. Στη συνέχεια, λαμβάνοντας υπόψη αντιληπτικά μοντέλα ακοής, τα οποία προϋποθέτουν την ύπαρξη δυο ηχητικών σημάτων (δυο αυτιά, αμφιωτική ακοή) σε αυτή τη διατριβή, μελετώνται κάποιες παράμετροι οι οποίες εξάγονται από αμφιωτικές ακουστικές αποκρίσεις χώρου. Η ιδιότητα της φασματικής τυπικής απόκλισης συναρτήσεων μεταφοράς χώρων να συγκλίνει στην τιμή των 5.6~dB για διάχυτα ηχητικά πεδία, επεκτείνεται στην περίπτωση των αμφιωτικών αποκρίσεων χώρου και προτείνεται ένα γενικευμένο μοντέλο που συσχετίζει τη φασματική τυπική απόκλιση μονοφωνικών και αμφιωτικών συναρτήσεων μεταφοράς χώρου. Η διατριβή αυτή, επίσης, ασχολείται με το πρόβλημα της εκτίμησης της απόστασης μεταξύ πηγής και δέκτη. Προτείνονται δυο νέες μέθοδοι για την εκτίμηση της απόστασης μεταξύ πηγής και δέκτη, κάνοντας χρήση ηχητικών σημάτων ομιλίας. Η προτεινόμενη μέθοδος βασίζεται σε μια σειρά από στατιστικές παραμέτρους των οποίων οι τιμές μεταβάλλονται είτε στο πεδίο του χρόνου είτε στο πεδίο της συχνότητας. Η δεύτερη προτεινόμενη μέθοδος αφορά, επίσης, στην εκτίμηση της απόστασης πηγής/δέκτη, αλλά από αμφιωτικά σήματα. Η μέθοδος αυτή δεν προαπαιτεί γνώση της ακουστικής απόκρισης του χώρου, του χρόνου αντήχησης ή άλλης ακουστικής παραμέτρου και βασίζεται σε μια σειρά από νέες παραμέτρους, οι οποίες μπορούν να υπολογισθούν από τα αμφιωτικά σήματα με αντήχηση. Οι παράμετροι συνδυάζονται με δυο διαφορετικές τεχνικές αναγνώρισης προτύπων των οποίων τα μειονεκτήματα και πλεονεκτήματα συζητώνται. Στα πλαίσια αυτής της μεθόδου, προτείνεται μια νέα παράμετρος, η οποία βασίζεται στη διαφορά της φασματικής τυπικής απόκλισης του αριστερού και του δεξιού αμφιωτικού ηχητικού σήματος, η οποία αποδεικνύεται ότι σχετίζεται με τα στατιστικά της αντίστοιχης μονοφωνικής ακουστικής απόκρισης. Τέλος, προτείνεται μια σειρά από παραμέτρους οι οποίες βασίζονται στα στατιστικά χαρακτηριστικά αμφιωτικών παραμέτρων και σχετίζονται με το αντιληπτικό μοντέλο της ανθρώπινης ακοής. Τέλος, προτείνεται μια νέα μέθοδος για την εκτίμηση της στάθμης λόγου κατευθείαν προς ανακλώμενου ήχου από στερεοφωνικά σήματα.