To see the other types of publications on this topic, follow the link: Pulse motors.
Dissertations / Theses on the topic 'Pulse motors'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Pulse motors.'
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
Harris, Paul. "Experimental evaluation of pulse-triggered nonlinear combustion instability in solid propellant rocket motors." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape3/PQDD_0015/MQ53952.pdf.
Full text
2
Smoot, Melissa C. "An analysis of noise reduction in variable reluctance motors using pulse position randomization." Thesis, Monterey, California. Naval Postgraduate School, 1994. http://hdl.handle.net/10945/25675.
Full textAbstract:
The design and implementation of a control system to introduce randomization
into the control of a variable reluctance motor (VRM) is presented. The goal is to reduce noise generated by radial vibrations of the stator. Motor phase commutation
angles are dithered by 1 or 2 mechanical degrees to investigate the effect of
randomization on acoustic noise. VRM commutation points are varied using a uniform probability density function and a 4 state Markov chain among other methods.
The theory of VRM and inverter operation and a derivation of the major source of
acoustic noise are developed.
The experimental results show the effects of randomization. Uniform dithering
and Markov chain dithering both tend to spread the noise spectrum, reducing peak
noise components. No clear evidence is found to determine which is the optimum
randomization scheme. The benefit of commutation angle randomization in reducing
VRM loudness as perceived by humans is found to be questionable.
3
Smoot, Melissa C. (Melissa Cannon). "An analysis of noise reduction in variable reluctance motors using pulse position randomization." Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/36501.
Full textAbstract:
Thesis (Nav. E.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, 1994, and Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering, 1994.Includes bibliographical references (leaves 80-82).
by Melissa C. Smoot.
M.S.
Nav.E.
4
Rousseau, Charle Werner. "Establishing a cost effective method to quantify and predict the stability of solid rocket motors using pulse tests." Thesis, Stellenbosch : University of Stellenbosch, 2011. http://hdl.handle.net/10019.1/6793.
Full text
5
Rasmeni, Sibusiso Wiseman. "Simulation of the switched reluctance machine under single pulse mode operation." Thesis, Stellenbosch : Stellenbosch University, 2003. http://hdl.handle.net/10019.1/53590.
Full textAbstract:
Thesis (MScEng)--University of Stellenbosch, 2003.ENGLISH ABSTRACT: Two distinct simulation methods have been developed to simulate the single and the multi-phase excited current waveforms of the switched reluctance machine (SRM) under single pulse mode operation. These simulation methods are explained and evaluated in this thesis. A non-commercial finite element package that takes the SRM's nonlinear magnetic property into account is used in this regard. The simulation program uses the finite element solution directly during the simulation. Both simulation methods have been investigated in terms of result and total simulation time. In this investigation it is shown how feasible the simulation methods will be with the next generation of fast computers. The factors affecting the simulated current waveforms of the SRM under single pulse mode operation are investigated in detail in this thesis. With these factors taken into account, the measured and simulated multi-phase current waveforms are compared with each other and discussed.
AFRIKAANSE OPSOMMING: Twee verskillende simulasie metodes is ontwikkel om die enkel- en multi-fase stroomgolfvorms van die geskakelde reluktansiemasjien (GRM) onder enkelpulsmodus-werking te simuleer. In hierdie tesis word hierdie simulasie metodes verduidelik en geëvalueer. 'n Nie-kommersiële eindige element pakket wat die nielinieêre magnetiese eienskap van die GRM in ag neem is in hierdie verband gebruik. Die simulasie program gebruik die eindige-element oplossing direk gedurende die simulasie. Beide simulasie metodes is ondersoek in terme van resultaat en simulasietyd. In hierdie ondersoek word getoon hoe uitvoerbaar hierdie tipe simulasie metodes gaan wees met die volgende hoë spoed generasie rekenaars. Die faktore wat die gesimuleerde stroomgolfvorms van die GRM onder enkelpulsmodus-werking beïnvloed word deeglik in hierdie tesis ondersoek. Met hierdie faktore in ag geneem word die gemete en gesimuleerde multi-fase stroomgolfvorms met mekaar vergelyk en bespreek.
6
Plooster, Michael G. "Vibrotactile Feedback Generation Using Envelope Waveforms and Eccentric-Mass Motors." BYU ScholarsArchive, 2012. https://scholarsarchive.byu.edu/etd/3497.
Full textAbstract:
The usefulness of vibrotactile feedback as a channel to communicate information has been widely recognized. However, most of the recent work on this subject uses actuators that are either too expensive or too large for many practical applications. This thesis explores the generation of vibrotacatile feedback patterns using a simple, inexpensive eccentric-mass motor that is constrained to use a constant voltage and a low on/off switching frequency. In particular, it explores the pulse timing method, which utilizes the slow transient response of the eccentric-mass motor to calculate pulse and rest times for an arbitrary envelope waveform shape. Several hardware tests were performed to (1) obtain a model of the transient response and (2) to verify that the resulting vibrations match the patterns predicted by the pulse timing method. Two custom built devices consisting of an eccentric-mass motor and a rigid housing were used in addition to a Wii remote. Vibrations for each device were measured and compared to the pattern predicted by the pulse timing method when the device was sitting on a table top and when the device was held in the hand. Results indicate that the vibrations match the predicted patterns very well in both cases. It was also determined that error in the motor's transient response model will result in some error between the measured and predicted vibrations. To assess whether this error affects perception of the intended envelope waveform, a study was performed in which users were asked to identify the envelope waveform of vibration patterns created using curve-fit models that contained various levels of error. An analysis of variance revealed that error in the curve-fit will have an effect on the perception of the envelope waveform if the error is large. Two more user studies were performed to determine the perceptual space of patterns generated using the pulse timing method, and to determine whether users could identify the meanings encoded within vibration features. The Perceptual Space study used a cluster-sorted Multi-Dimensional Scaling analysis to determine that envelope waveform, roughness (deviation from the envelope waveform), and amplitude are vibration features that may be used to encode information. Using these features, participants were presented with vibrations that contained GPS navigation instructions similar to those used in a car, and were asked to identify the associated meaning. Users were able to correctly identify all three features with an average accuracy of 80.6%, and were able to correctly identify the envelope waveform and roughness with accuracies of 96.9% and 94.5% respectively. These results are evidence that the pulse timing method (and eccentric-mass motors in general) are capable of generating complex vibrotactile feedback patterns that can be uniquely identified.
7
Wittmers, Nicole K. "Direct-connect performance evaluation of a valveless pulse detonation engine." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2004. http://library.nps.navy.mil/uhtbin/hyperion/04Dec%5FWittmers.pdf.
Full text
8
Cetin, Nebi Onur. "Design And Implementation Of Advanced Pulse Width Modulation Techniques And Passive Filters For Voltage Source Inverter Driven Three-phase Ac Motors." Master's thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/12612236/index.pdf.
Full textAbstract:
Advanced pulse width modulation (PWM) techniques such as space vector PWM, active zero state PWM, discontinuous PWM, and near state PWM methods are used in three-phase AC motor drives for the purpose of obtaining low PWM current ripple, wide voltage linearity range, and reduced common mode voltage (CMV). In some applications, a filter is inserted between the inverter and the motor for the purpose of reducing the stresses in the motor. The motor current PWM ripple components, terminal voltage overshoots, shaft voltage, and bearing currents, etc. can all be reduced by means of PWM techniques and passive filters. Various PWM techniques and passive filter types exist. This thesis studies the combinations of PWM techniques and filters and evaluates the performance of the motor drive in terms of the discussed stresses in the motor. PWM techniques are reviewed, a generalized algorithm for the implementation of PWM techniques is developed, and implementation on a 4 kW rated drive is demonstrated. Filter types are studied, among them the common mode inductor and the pure sine filter (PSF) configurations are investigated in detail. Filters are designed and their laboratory performance is evaluated. In the final stage the advanced PWM techniques and filters are combined, the incompatibility problem of discontinuous PWM methods with the PSF is illustrated. A cure based on rate of change limiter is proposed and its feasibility proven in the laboratory experiments. With the use of the proposed PWM algorithm and PSF, a motor drive with ideal DC to AC conversion stage (DC to pure sine) is achieved and its performance is demonstrated in the laboratory.
9
Teeters, Bradley W. "Variable frequency control of voltage source inverters using harmonic distortion minimization scheme." Ohio : Ohio University, 1999. http://www.ohiolink.edu/etd/view.cgi?ohiou1175285333.
Full text
10
Espindola, Marcos Fernando. "Estudo e implementação de inversor de tensão a três níveis com modulação em largura de pulsos por vetores espaciais aplicado ao controle vetorial de motor síncrono de imãs permanentes = Study and implementation of three level voltage inverter with space vector modulation by pulse width modulation applied to vector control of permanent magnet synchronous motor." [s.n.], 2012. http://repositorio.unicamp.br/jspui/handle/REPOSIP/259011.
Full textAbstract:
Orientadores: Ernesto Ruppert Filho, Marcelo Gradella VillalvaDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação
Made available in DSpace on 2018-08-21T14:53:53Z (GMT). No. of bitstreams: 1 Espindola_MarcosFernando_M.pdf: 5114547 bytes, checksum: 1601ee84cd6d17c671ba644a288c398d (MD5) Previous issue date: 2012
Resumo: Apresenta-se a implementação de um inversor trifásico de tensão a três níveis para ser utilizado no controle de velocidade de um motor síncrono trifásico a imãs permanentes usando o método de controle vetorial. Realizou-se o estudo, projeto e construção de um inversor de tensão a três níveis com neutro grampeado ou inversor NPC neutral point clamped. Utilizou-se modulação em largura de pulsos por vetores espaciais no controle vetorial de velocidade do motor. Foram realizadas simulações do sistema proposto usando os aplicativos computacionais Matlab/Simulink e PSIM. Realizou-se em seguida uma montagem experimental constituída de um motor síncrono a imãs permanentes de 0,75 kW acoplado a um freio eletromagnético que lhe serviu de carga mecânica. O sistema motor e carga foi acionado pelo inversor com modulação em largura de pulsos por vetores espaciais e os resultados obtidos do controle de velocidade realizado, incluindo reversão de velocidade e frenação do motor, são apresentados no trabalho. Comparou-se também o desempenho de um inversor a três níveis usando modulação em largura de pulsos por vetores espaciais com o desempenho de um inversor a dois níveis usando modulação em largura de pulsos por vetores espaciais na alimentação de uma carga resistiva. Resultados de simulação e resultados experimentais são apresentados. Neste trabalho realizou-se uma comparação qualitativa entre o uso do inversor a dois níveis e do inversor a três níveis que mostra em que situações é conveniente utilizar o inversor a três níveis
Abstract: It is presented the implementation of a three phase three level voltage inverter to be used in the speed control of a three phase permanent magnet synchronous motor using the vector control method. To achieve this goal, it was carried out the study, design and construction of a three level neutral point clamped voltage inverter or NPC inverter. For the control of the motor it was used a space vector modulation. The proposed system was simulated using Matlab/Simulink and PSIM softwares. It was carried out an experimental assembly consisting of a 0.75 kW permanent magnet synchronous motor coupled to an electromagnetic brake as a mechanical load. The motor and load system were triggered by the inverter with space vector modulation. The results of the speed control, including reversal of speed and motor breaking, are presented in the study. The performance of a three level inverter using space vector modulation is compared to the performance of a two level inverter using space vector modulation feeding a resistive load. The simulation and experimental results are presented. In this work a qualitative comparison between the two level inverter and three level inverter was done showing in wich situations it is better to use the three level inverter
Mestrado
Energia Eletrica
Mestre em Engenharia Elétrica
11
Qian, Xin. "Flow field investigation in pulse 1 motor of a two-pulse solid rocket motor." Thesis, This resource online, 1990. http://scholar.lib.vt.edu/theses/available/etd-03122009-040826/.
Full text
12
Zhang, Yong. "A single-pulse cycloconverter induction motor drive." Thesis, University of Sussex, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.260012.
Full text
13
Mirkazemi-Moud, Mehran. "Digital pulse width modulators for induction motor control." Thesis, Heriot-Watt University, 1993. http://hdl.handle.net/10399/1431.
Full text
14
Sun, Zhen M. S. Massachusetts Institute of Technology. "High efficiency pulse motor drive for robotic propulsion." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/81719.
Full textAbstract:
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2013.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 155-156).
The goal of this research is to improve the power efficiency of robotic locomotion through the use of series elastic actuation, with a focus on swimming motion. To achieve high efficiency, electromechanical drives need to be actuated at high speed and low torque. However, in many robots, the drives are actuated in a low speed and high torque mode, resulting in lower efficiency. Implementing gear trains is one option to rise the input speed and lower the input torque. However gear trains have their own loss which are particularly severe at high gear ratios, and are not back drivable in some cases. In this thesis, we envision and design a new pulse drive type of series elastic electromechanical actuators that seeks to break such tradeoffs and improve overall robotic propulsion drive efficiency. An energy storage element, such as a spring, is installed between the EM actuator and the load. In the fast actuation phase, a pulse displacement/ torque trajectory is applied to the actuator shaft so that the spring is rapidly charged with potential energy. In the slow driving phase, the actuator shaft is locked by a low power mechanical latch and the spring slowly transfers energy into the load. We analytically determine that the most efficient pulse condition is reached when the frequency of the pulse trajectory is close to the natural frequency of the actuator inertia-spring system. Our first low power hardware demonstration without the gearbox transmission shows that the pulse drive achieves an energy efficiency of 80% compared to an efficiency of 50% achieved in the conventional direct drive where an electromechanical actuator is driving a viscous load equal to its own motor constant. Another low power hardware demonstration using gear motors at two loads, whose impedances are 10 times and 20 times as high as the driver motor constant, shows that the pulse drive using a motor with a one-stage gearbox transmission achieves an efficiency of 50%, which are approximately 20% higher than the conventional drive with either a one-stage or a two-stage gearbox transmission. An analytical study on the influence of motor size shows that the efficiency gain of the pulse drive becomes larger at smaller motors and that the best option for the pulse drive is to use a motor with a one-stage gearbox. In a third hardware demonstration, we scale up the power level to match that of a small robotic fish, and use a real viscous load. By using the same brushless motor with a one-stage gearbox, we achieve a pulse drive efficiency of 70% compared to 15% in the conventional gear drive. Some potential targets are robots with cyclical propulsions and high impedance load, e.g., tail actuation in fish-like swimming robots, wing actuation in flying robots and crawling and other motions in snake-like robots.
by Zhen Sun.
S.M.
15
Balakrishnan, Guha. "Analyzing pulse from head motions in video." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/87942.
Full textAbstract:
Thesis: S.M. in Computer Science and Engineering, Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2014.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 71-73).
We extract heart rate and beat lengths from videos by measuring subtle head oscillations that accompany the cardiac cycle. Our method tracks features on the head, temporally filters their trajectories and performs principal component analysis (PCA) to decompose the trajectories into a set of ID component motions. It then chooses the component that is most periodic as the pulse signal. Finally, we identify peaks of the chosen signal, which correspond to heartbeats. When evaluated on 18 subjects our approach reported heart rates nearly identical to an electrocardiogram (ECG) device for all subjects and obtained similar beat length distributions for 17. In addition we obtained pulse rate from videos of the back of the head and of sleeping newborns. Initial findings also show that our method can measure heart rate from body parts other than the head and can measure respiration rate by selecting a different frequency band. Finally, we present visualization techniques such as motion magnification for subjective analysis of body motions
by Guha Balakrishnan.
S.M. in Computer Science and Engineering
16
Guzik, Stephen Michael Jan. "Venting Optimization of a Pulse Detonation Engine." Master's thesis, Québec : Université Laval, 2003. http://www.theses.ulaval.ca/2003/21167/21167.pdf.
Full text
17
Ertugrul, Suat Erdem. "The Effects Of Geometric Design Parameters On The Flow Behavior Of A Dual Pulse Solid Rocket Motor During Secondary Firing." Master's thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12615184/index.pdf.
Full textAbstract:
The ability of a propulsion system is very crucial for the capability of a missile or a rocket system. Unlike liquid propellant rocket motors, the only control mechanism of the thrust value is the propellant geometry in solid propellant rocket motors. When the operation of solid propellant rocket motor has started, it cannot be stopped anymore. For this main reason the advance of dual pulse motor technology has started. The aim of this study is to investigate the geometrical effects of design parameters on the flow behavior of a dual pulse solid propellant rocket motor by using commercial Computational Fluid Dynamics (CFD) methods. For the CFD analysis, a generic dual pulse rocket motor model is constituted. Within this model, initially four different geometry alternatives of Pulse Separation Device (PSD) are analyzed. To begin PSD analyses, mesh sensitivity analyses are performed on one PSD geometry alternative. By defined grid size, the analyses of PSD geometry alternatives are performed. Computed results were compared in terms of flow behavior (flow streamlines, velocity distribution, turbulent kinetic energy&hellipetc.) with each other. With the selected PSD geometry alternative the effects of L/D ratio (Length/Diameter ratio) of first pulse chamber, Achamb/APSD ratio (Chamber area/PSD opening area) and APSD/Ath ratio (PSD opening area/Throat area) on the flow behavior is investigated. Flow analyses are performed by simulating the unsteady flow of second pulse operation. With the performed analyses, it is aimed to identify generic geometric definitions for a dual pulse rocket motor.
18
Andrys, Michal. "Optimalizace výfukového potrubí přeplňovaného zážehového motoru." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2010. http://www.nusl.cz/ntk/nusl-228907.
Full textAbstract:
Abstract Michal ANDRYS Optimalization of Exhaust Manifold for SI Turbo Engine DP, IAE, 2010, 67 pp., 75 fig. The Diploma thesis is oriented on the design of exhaust manifold for si turbo engine. It specifies suitable manifold connection to the separate branches, folowed by CFD analysis.
19
Lange, Martin T. "INFLUENCE OF VOLTAGE SOURCE PULSE WIDTH MODULATED SWITCHING AND INDUCTION MOTOR CIRCUIT ON HARMONIC CURRENT CONTENT." Wright State University / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=wright1230942161.
Full text
20
Delvendahl, Igor, Norbert Gattinger, Thomas Berger, Bernhard Gleich, Hartwig R. Siebner, and Volker Mall. "The role of pulse shape in motor cortex transcranial magnetic stimulation using full-sine stimuli." Universitätsbibliothek Leipzig, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-158142.
Full textAbstract:
A full-sine (biphasic) pulse waveform is most commonly used for repetitive transcranial magnetic stimulation (TMS), but little is known about how variations in duration or amplitude of distinct pulse segments influence the effectiveness of a single TMS pulse to elicit a corticomotor response. Using a novel TMS device, we systematically varied the configuration of full-sine pulses to assess the impact of configuration changes on resting motor threshold (RMT) as measure of stimulation effectiveness with single-pulse TMS of the non-dominant motor hand area (M1). In young healthy volunteers, we (i) compared monophasic, half-sine, and full-sine pulses, (ii) applied two-segment pulses consisting of two identical half-sines, and (iii) manipulated amplitude, duration, and current direction of the first or second full-sine pulse half-segments. RMT was significantly higher using half-sine or monophasic pulses compared with full-sine. Pulses combining two half-sines of identical polarity and duration were also characterized by higher RMT than fullsine stimuli resulting. For full-sine stimuli, decreasing the amplitude of the halfsegment inducing posterior-anterior oriented current in M1 resulted in considerably higher RMT, whereas varying the amplitude of the half-segment inducing anterior-posterior current had a smaller effect. These findings provide direct experimental evidence that the pulse segment inducing a posterior anterior directed current in M1 contributes most to corticospinal pathway excitation. Preferential excitation of neuronal target cells in the posterior-anterior segment or targeting of different neuronal structures by the two half-segments can explain this result. Thus, our findings help understanding the mechanisms of neural stimulation by full-sine TMS.
21
Analouei, A. R. "On-line adaptive control of an induction motor fed from a pulse-width-modulated inverter." Thesis, Manchester Metropolitan University, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.370489.
Full text
22
Cirstea, Marcian Nicolae. "An investigation into ASIC control of a 6-pulse cycloconverter for a quad winding induction motor." Thesis, Nottingham Trent University, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.309820.
Full text
23
Huang, Zhen. "A fully high temperature superconducting synchronous motor using pulsed field magnetization, bulks, and 2G HTS coils." Thesis, University of Cambridge, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.709396.
Full text
24
Galligan, Carrie. "Catalytic Cracking of Jet Propellant-10. For Pulse Detonation Engine Applications." Thesis, Université Laval, 2005. http://www.theses.ulaval.ca/2005/22529/22529.pdf.
Full textAbstract:
Le carburant hydrocarbure JP-10 est étudié comme agent propulsif destiné aux
moteurs à détonation ainsi qu’à d’autres applications concernant les vols à vitesses
élevées. La précraquage catalytique du JP-10 pourrait produire un mélange d’oléfines
légères plus facile à détoner. Un mélange d’hydrocarbures aliphatiques, pour la plupart
légers, présente l’avantage d’être moins enclin à la carbonisation que des mélanges
comportant de fortes teneurs en hydrocarbures aromatiques. Cette réaction
endothermique de précraquage offre le même potentiel que celui d’un puits de chaleur
trouvé dans des applications de vols à vitesses élevées pour lesquelles toute hausse de
la masse du système de refroidissement contrevient à une plus grande efficacité du
moteur. Plusieurs essais de craquage catalytique hétérogène furent réalisés à l’aide
d’un réacteur tubulaire et les gaz produits analysés par GC/MS et par GC. Deux
formes de zéolithe nanocristalline (n) ZSM-5(24h) et nZSM-5 (6h) et trois formes de
silico-aluminophosphate SAPO-5A, SAPO-5B et SAPO-11 furent testées. SAPO-5 et
nZSM-5(24h) apparaissent être les candidats les plus propices au précraquage du
JP-10. Ces dernières ont permis de convertir plus de 90 % de JP-10 en un mélange
d’hydrocarbures principalement composé de molécules en C4 et moins (C3 à C1).
nZSM-5(24h) ont procuré le plus petit rapport de masse de carbone, CR (C5+:C4−),
à des températures situées entre 350 oC et 450 oC et le taux de conversion le plus
élevé à des températures supérieures à 500 oC. SAPO-5A & B ont présenté le taux de
conversion le plus élevé mais le plus petit CR entre 400 oC et 500 oC.The hydrocarbon jet-fuel, JP-10, is being studied as a possible propellant for the Pulse Detonation Engine (PDE) and other high-speed flight applications. Catalytic pre-cracking of JP-10 could provide a more easily detonated mixture of light olefin products. A mixture of mostly light hydrocarbons has the added benefit of being less prone to coking than a product mixture heavy in aromatics. This endothermic reaction also offers potential as a heat sink in high-speed flight applications where the extra weight of an onboard cooling system would hinder engine efficiency. Several heterogeneous catalytic cracking tests have been done using a Bench Top Tubular Reactor and the products were analyzed with GC/MS and GC. Two forms of nanocrystalline zeolites, nZSM-5(24h) and nZSM-5(6h), and three forms of silico-alumino-phosphates, SAPO-5A, SAPO-5B, and SAPO-11 successfully catalyzed the cracking of JP-10; however, SAPO-5 and nZSM-5(24h) have proven to be the most promising catalyts. Both catalysts converted over 90 % of JP-10 (∼ 3s residence time) into a mixture of hydrocarbon products consisting mainly of C4 and lower chain hydrocarbons (C3 to C1). nZSM-5(24h) demonstrated the lowest carbon mass ratio, CR (C5+:C4−), between 350 oC and 450 oC and the highest conversion rates above 500 oC. SAPO-5A & B demonstrated the highest conversion rates and the lowest CR between 400 oC and 500 oC.
25
Hundák, Vladimír. "Algoritmy pro řízení asynchronního motoru." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2014. http://www.nusl.cz/ntk/nusl-220893.
Full textAbstract:
Hlavným cieľom tejto práce je vytvorenie simulácií rôznych algoritmov riadenia asynchrónneho motora a vzájomné porovnanie ich vlastností. Zaoberá sa taktiež možnosťami konfigurácie náhradného zapojenia na T-článok, -článok a -článok. Obsahuje jednak teoretický rozbor, a taktiež aj simulácie jednotlivých spôsobov riadenia spolu s podrobným návodom na ich realizáciu. Celkovo budú vykonané 3 simulácie – simulácia vektorového riadenia s orientáciou na rotorový tok, vektorového riadenia s orientáciou na statorový tok a simulácia takzvaného prirodzeného riadenia. Ide o úplne nový typ riadenia, ktorého autorom je vedúci tejto diplomovej práce. Jeho simulácia bola vôbec prvým pokusom o funkčnú realizáciu tohto typu riadenia.
26
Archila, Manuel. "Directionality effects of pulse-like near field ground motions on seismic response of tall buildings." Thesis, University of British Columbia, 2014. http://hdl.handle.net/2429/51615.
Full textAbstract:
Earthquake ground shaking at near-field sites has produced severe damage to buildings and infrastructure, caused large economic and human losses. These earthquakes continue to pose a great threat to many populous urban centers around the world. Over the last 4 decades, major research efforts have been devoted to characterize near-field ground motions and their effects on the response of buildings.
A challenging engineering problem that remains unsolved in the seismic design of buildings is the directionality effect of near-field pulse-like ground motions on tall buildings. This dissertation presents a computationally efficient method to calculate the critical displacement response of tall buildings. In this method, the duration and amplitude of the ground velocity pulses contained in the input motion and the building’s first mode translational period are compared to determine the orientation of the Conditional Maximum Velocity (CMV), a new ground motion metric. Nonlinear response history analyses (NRHA) using the CMV ground motion provide a close estimate of the critical displacement response of a tall building along the structural axis.
The CMV Method is developed on the basis of a series of parametric studies. First synthetic pulse-like excitations and simple structures were used to systematically investigate the effects of pulse duration and amplitude on the dynamic elastic and inelastic response of structures. It is found that the critical displacement response is influenced significantly by the CMV ground motion.
This finding is further validated through series of NRHA of simple structures and several case study tall buildings to near-field ground motion records. It is shown that the NRHA using CMV ground motions result in approximate, but significantly accurate estimates of the critical displacement with small errors and moderate dispersion.
Ground motion pairs rotated to fault-normal (FN) orientation do not always result in the critical displacement response. Neither does the maximum direction (MD) ground motion at the fundamental period of the building. Analyses made using FN or MD may result in significant underestimates of critical displacement response compared to the proposed CMV. The use of the CMV Method may lead to a better quantification of potential seismic demands on tall buildings.Applied Science, Faculty of
Civil Engineering, Department of
Graduate
27
Mikuška, Martin. "Střídač pro trojfázový motor." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2014. http://www.nusl.cz/ntk/nusl-220710.
Full textAbstract:
This master’s thesis goes into design of particular circuits for three phase inverter. Inverter’s control is ensured by digital signal controller MC56F8013 with his program. Principle of control is suggested for individual motors. Inverter design considerate universal use and capability for any three phase motor. Particular blocks are compatible each other.
28
Ofori, Ernest. "A Pulse Injection Based Sensorless Position Estimation Method for a Switched Reluctance Motor over a Wide Speed Range." University of Akron / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=akron1403130339.
Full text
29
Wiberg, Johan. "Controlling a Brushless DC Motor in a Shift-by-Wire System." Thesis, Linköping University, Department of Electrical Engineering, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-2096.
Full textAbstract:
Shift-by-Wire is about replacing the mechanical link between the automatic transmission and the shift lever with an electromechanical system. This will make new safety functions possible and assist the driver in other ways.
To do this, an actuator with a brushless DC motor is built into the transmission. It controls the position of the shift valve, which decides the driving position.
This thesis concerns the controlling of the brushless DC motor. This is done by programming a shift control unit with a Motorola HC12 microcontroller. The performance of the motor is then tested and evaluated.
30
Ronceros, Aparicio Gianina María. "Análisis y simulación de un motor síncrono de imánes permanentes empleando el método de control orientado de campo mediante la modulación por ancho de pulso de vector espacial." Bachelor's thesis, Pontificia Universidad Católica del Perú, 2019. http://hdl.handle.net/20.500.12404/15190.
Full text
31
Ramin, Latifi. "Effect of pulse-like near-fault ground motions on inelastic response of structures including foundation flexibility." Thesis, University of British Columbia, 2013. http://hdl.handle.net/2429/45534.
Full textAbstract:
For the sites in close proximity to a causative fault where formation of near fault long period velocity pulses is conceivable, consideration of flexibility of the foundation system is very important. This is due to the fact that when the flexibility of the base is taken into account the period of the system is longer than the period of the same system assuming a fixed base. Depending on the depth and the stiffness of the underlying soil the period of the system approaches the period of the near fault long period pulses, hence the response of the structure could be much larger.
The purpose of this research is to study the nonlinear response of structures to pulse-like near fault ground motions with and without allowing for the foundation system flexibility.
To highlight the impact of the near fault ground motions the nonlinear responses of single degree of freedom systems (resembling fixed base structures) to the near fault ground motions are compared to the responses of the same systems to the equivalent far field ground motions.
The effects of (translational and rocking) flexibility of the foundation system is also considered using equivalent linear springs and lumped masses added to the base of the single degree of freedom systems.
A major parametric study is performed to determine which parameter has the most significant impact on the response of the structure for near fault ground motions when effect of flexibility of the foundation system is explicitly accounted for.
An efficient procedure has been developed for predicting the response of a structure with a flexible base to near fault ground motions deduced from the response of an equivalent single degree of freedom system to the equivalent far field ground motions. Validity of the proposed procedure for assessing the effects of near fault ground motions, and the influence of flexibility of the foundation system on the structures’ responses is verified using different analytical models, including a full 3D analysis of a bridge structure; the results proved to be quite satisfactory.
32
Bláha, Martin. "Elektronicky komutovaný motor." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2008. http://www.nusl.cz/ntk/nusl-217634.
Full textAbstract:
This work discusses about nowadays problematic of the electronic comutation motors.This work also describes the opportunity of electronic control of these motors. The result of this work is realization of electronic control circuit from discreet components. There also are mentioned is proposal of electronic control board from SMD components. This control board include temperature control with ventilator switching , commutation logic, PWM speed control. In the last part of this paper are results of evaluation measurements of EC motor.
33
Pinďák, Michal. "Třífázový střídač pro napájení vysokootáčkového asynchronního motor." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2018. http://www.nusl.cz/ntk/nusl-376934.
Full textAbstract:
The goal of this master´s thesis is primarily the theoretical analysis of three-phase inverters and subsequent familiarization of the reader with their detailed practical structure. The first part is devoted to the general definition of the power semiconductor converter as such. The following part describes the principle of three-phase pulse width modulation including the widely used principle of scalar control of induction motors. The second half of the thesis is already focused on the practical design of a three-phase inverter for a 50 kW high-speed induction motor. This section explains the problem of sizing and selecting all of the sub-elements of the inverter based on the parameters specified by the end user of the device.
34
Ciaralli, Simone. "A study of the lifetime of miniaturized ablative pulsed plasma thrusters." Thesis, University of Southampton, 2014. https://eprints.soton.ac.uk/379251/.
Full textAbstract:
Miniaturized satellites are one of the fastest growing sectors in the space industry, allowing cheap access to space. These satellites are currently limited by their lack of orbit control and their lifetime is therefore determined by the natural, drag-induced, de-orbiting. These issues can be solved using a dedicated propulsion system. Cold-gas micro-thrusters, successfully flown on miniaturized satellites, are characterised by a very low specific impulse (typically less than 100 s), which considerably limits their capabilities. Moreover, they require pressurized tanks, pressure regulators and valves that may significantly increase the dry mass of the system. Pulsed Plasma Thrusters (PPTs) represent an excellent alternative to the chemical thrusters thanks to their high scalability in terms of geometry, power input and performance. Within this research programme, the factors that affect the lifetime of solid state propellant PPTs for miniaturized satellites (e.g. Cubesat and nanosatellites) applications have been studied and addressed. Moreover, efforts have been made to optimise a PPT as a sub-system to be integrated into a satellite spacecraft. This included the characterization of the electromagnetic noise that PPTs generate and that may cause failures on the other Cubesat subsystems and a study aimed at the optimization of the PPT ignition process to produce a lighter and more reliable conditioning electronics. To complete all these tasks, a miniaturized PPT (called PPTCUP, which stands for PPT for Cubesat Propulsion) has been developed and tested in collaboration with Mars Space Ltd and Clyde Space Ltd. Results from the PPTCUP test campaign have proved the reliability of the thruster, being able to perform a number of shots almost two times bigger than the nominal number required to demonstrate the discharge chamber lifetime. Moreover, it has been found that the unit can work correctly in the range of the Cubesat operating temperatures, withstands the mechanical vibrations during launch and has main natural frequencies compliant with the Cubesat requirements. The results of the EMC characterization test show that the electromagnetic noise generated during the main PPT discharge is mostly compliant with the requirements or small enough to be impossible to distinguish from the facility background noise. The dedicated study to identify the best spark plug system working with a relative low breakdown voltage has shown that the semiconductor- coated spark plug insulator are able to trigger the PPT main discharge at a lower voltage (i.e. about 1700 V against the 7500 V needed for the no-coated propellant rods) without affecting the overall thruster performances.
35
Shehada, Ahmed. "Novel Multilevel Converter for Variable-Speed Medium Voltage Switched Reluctance Motor Drives." Diss., Virginia Tech, 2017. http://hdl.handle.net/10919/85111.
Full textAbstract:
A novel multilevel converter that is especially suited for high speed multi-megawatt switched reluctance motor drives operating at the medium voltage level is presented. The drive is capable of variable speed, four-quadrant operation. Each phase leg of the converter contains an arbitrary number of cascaded cells connected in series with the phase winding. Each cell contains a half-bridge chopper connected to a capacitor. The converter is named the cascaded chopper cell converter. The modular nature of the converter with the ability to add redundant cells makes it very reliable, which is a key requirement for medium voltage drive applications. A comprehensive control algorithm that overcomes the challenges of balancing and controlling cell capacitor voltages is also proposed. A suitable startup algorithm to limit startup current and switching losses, as well as ensure that cell capacitor voltages remain controlled at startup, is suggested. Details of the drive design such as component sizing and control parameter selection are also discussed. A detailed simulation model is developed and explained, and simulation results are provided for primary validation. Operation with standard current and speed control is first simulated. Then a scheme that gives way to a controller that operates the drive in single-pulse mode is developed and presented. This single-pulse control scheme controls the turn-on and turn-off angles, as well as the energization voltage level, in order to obtain high efficiency. Practical considerations related to the drive such as reliability, efficiency, and cost considerations are also discussed. Finally, a detailed comparison of the proposed converter to another competing converter is performed. Besides its scalability to high voltages and powers, the reliability and efficiency of the proposed converter makes it also a candidate for sub-megawatt applications requiring minimum downtime, or any application where high efficiency or improved performance is required.
A small part of this work is also dedicated to brushless dc machines. Control methods for a new converter for brushless dc machines are proposed and verified via simulation. The main advantage of this converter with the proposed control is that it allows exact control of torque or speed up to twice the rated speed, without resorting to current phase advancing or other flux-weakening techniques.Ph. D.
36
Noya, Claudemiro Vigo. "Análise de inibição pré-pulso do reflexo de sobressalto acústico com obtenção simultânea de potenciais evocados auditivos." reponame:Repositório Institucional da UFABC, 2016.
Find full textAbstract:
Orientador: Prof. Dr. Francisco José Fraga da SilvaDissertação (mestrado) - Universidade Federal do ABC, Programa de Pós-Graduação em Engenharia da Informação, 2016.
Inibição pré-pulso (IPP) consiste numa redução na magnitude do reflexo de sobressalto a um estímulo auditivo forte (pulso), quando este é precedido por um fraco (pré-pulso). Em humanos, a IPP, geralmente, é medida por eletromiografia (EMG),. Este comportamento tem sido extensivamente investigado em estudos relacionados à esquizofrenia, uma vez que este déficit sensório-motor desempenha um papel central na sua fisiopatologia. No entanto, os mesmos estímulos auditivos que provocam o reflexo de sobressalto acústico também provocam intensas respostas auditivas evocadas, que podem ser medidas por eletroencefalografia (EEG). Analisar estes dois tipos de resposta adquiridos simultaneamente é uma grande oportunidade para investigar a dependência e interdependência de suas vias neurais. Este trabalho teve como objetivo registrar e analisar simultaneamente o reflexo de sobressalto acústico (usando EMG) e as respostas auditivas evocadas (utilizando EEG), para caracterizar o fenômeno de IPP em voluntários saudáveis, visando futura aplicação em pacientes esquizofrênicos. Utilizando técnicas avançadas de remoção de artefatos por meio da Análise de Componentes Independentes, verificou-se que após a remoção de artefatos houve uma melhor caracterização da IPP usando EEG. Especificamente, houve um aumento substancial na quantidade de diferenças estatisticamente significativas entre as respostas auditivas evocadas (medidas em vários eletrodos) com e sem pré-pulso, em comparação com os dados de EEG brutos (sem remoção de artefatos), bem como um aumento no número e na intensidade de correlações estatisticamente significativas entre o reflexo de sobressalto acústico (usando EMG) e as respostas auditivas evocadas, medidas em diversos eletrodos do EEG. Tais resultados promissores são motivadores no sentido de se tentar aplicar as mesmas técnicas em um próximo estudo envolvendo pacientes esquizofrênicos.
Prepulse inhibition (PPI) is a reduction in the magnitude of the acoustic startle reflex when a strong auditory stimulus (pulse) is preceded by a weaker one (prepulse). In humans, PPI is usually measured by electromyography (EMG). This behavior has been extensively minvestigated in studies related to schizophrenia, since the sensorimotor deficit plays a central role in its physiopathology. However, the same auditory stimuli that produce the acoustic startle reflex also trigger strong auditory evoked responses, which can be measured by electroencephalography (EEG). Analyzing these two response types acquired simultaneously is a great opportunity to investigate the dependence and interdependence of their neural pathways. This study intended to record and analyze both the acoustic startle reflex (using EMG) and the auditory evoked responses (using EEG), to characterize PPI in healthy volunteers, aiming future application in schizophrenic patients. Using advanced artifact removal techniques by means of Independent Component Analysis, it was found that after artifact removal there was a better characterization of PPI using EEG. Specifically, there was a substantial increase in the number of statistically significant differences between the auditory evoked responses (measured on multiple electrodes) with and without pre-pulse when compared to raw EEG data (without removing artifacts), as well as an increase in the number and intensity of statistically significant correlations between the acoustic startle reflex (using EMG) and the auditory evoked responses, measured in several EEG electrodes. These promising results are encouraging in order to try to apply the same techniques in a following study of schizophrenic patients.
37
Intini, Marques Rodrigo. "A mechanism to accelerate the late ablation in pulsed plasma thrusters." Thesis, University of Southampton, 2009. https://eprints.soton.ac.uk/67314/.
Full textAbstract:
Pulsed Plasma Thrusters (PPTs) are long standing electric propulsion thrusters that are reliable, relatively simple and low cost. One of the main issues with the PPT is its poor utilization of the propellant and low efficiency. Typically only 40-60% of the propellant contributes to the production significant impulse and the efficiency is around 8%. The cause of the PPT’s poor propellant utilization is the late time ablation (LTA), which has a major impact on the efficiency. LTA is the sublimation of propellant that takes place after the main discharge, due to the propellant, usually Polytetrafluoroethylene (Teflon®), being at a temperature above its sublimation point. The LTA produces a low speed gas and macro particles that do not contribute significantly to the thrust. This work presents a way of accelerating the late time ablation by employing an additional discharge after the main discharge, in a separate pair of electrodes. A new thruster, called the two-stage pulsed plasma thruster (TS-PPT) was built and tested. This thruster has two pair of electrodes: primary and secondary. The primary is placed in contact with the propellant surface, as in a regular PPT. The secondary is placed downstream, relatively far from the propellant. A new approach, dividing the PPT thrust generation in two phases, was envisioned. The first phase is responsible for the ablation process and takes place in the first pair of electrodes. The second phase takes place in the second pair of electrodes and is responsible for the acceleration process. The phase division allowed for propellant metering and better propellant utilization. Evidence was found that a pair of electrodes placed downstream, further from the propellant surface is able to discharge in the late ablation portion of the propellant and can impart extra energy into the exhaust and improve propellant utilization. A simple analytical model was developed to predict trends. A prototype of a TS-PPT was designed and built. A vacuum facility was modified, adapted, partially designed and built. An average mass bit consumption test was carried out. A simple time-of-flight experiment revealed that the fastest portions of the plasma from the primary electrodes discharge were travelling at around 33 km/s. Several current measurements were performed and calculations of the total electrical resistance, total inductance, electromagnetic impulse bit, specific impulse, efficiency, and other parameters were calculated based on experimental data. Experimental results indicated that significant improvements in the specific impulse and efficiency are possible by utilising a two-stage PPT. Specific impulses as high as 4000s were calculated based on experimental results, indicating a better propellant utilization.
38
Bílý, Lukáš. "Simulační modely elektrických pohonů vozidel." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2011. http://www.nusl.cz/ntk/nusl-219228.
Full textAbstract:
The work deals with creating a DC electric motor drive. The model is composed of electrical power from the engine model and transistor pulse converter load, which are joined together and completed the anchor and regulate the flow control engine speed. Great attention was paid to the determination of losses in the load drive electric vehicles and create a model of electric power load. The real work was verified by an experimental model of an electric vehicle Car4 the available parameters.
39
Fontes, Ivo Reis. "Controle de velocidade de motor de indução trifasico alimentado por inversor PWM atraves de microcomputador." [s.n.], 1993. http://repositorio.unicamp.br/jspui/handle/REPOSIP/261448.
Full textAbstract:
Orientador : Jaime SzajnerDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica
Made available in DSpace on 2018-07-18T08:55:24Z (GMT). No. of bitstreams: 1 Fontes_IvoReis_M.pdf: 5616120 bytes, checksum: c194c8d7d82860311abf979055cf7bf1 (MD5) Previous issue date: 1993
Resumo: Encontra-se em desenvolvimento no Laboratório de Engenharia de Computação e Automação Industrial (LCA) um protótipo de veículo elétrico autoguiado (AGV) com controle através de computador. Os AGVs encontram diversas aplicações dentro do ambiente industrial automatizado, pela possibilidade que os mesmos oferecem em receber controle de um computador supervisor, através de sistemas de comunicações, a fun de realizar a várias tarefas envolvidas no processo produtivo. Sua aplicação também pode ser extendida a ambientes agressivose de alto risco para o homem, como é o caso em mineração ou em laboratórios onde se manipula substâncias tóxicas. Por se tratar de um desenvolvimento complexo, o projeto de um AGV integra o conhecimento de várias áreas da Engenharia, daí a sua interdisciplinaridade. O projeto do AGV em desenvolvimento incorpora um sistema de tração e um sistema de direção controlados por computador, que por sua vez se u~ de um sistema de aquisição de dados e uma unidade sensora de posição, de forma que o veículo possa seguir uma rota pré-estabelecida constitui da de uma fita refletiva fixa no solo. Este trabalho aborda a fundamentação teórica do controle de velocidade de motores a serem empregados neste tipo de veículo, bem como em outros acionamentos industriais e tem como finalidade principal estabelecer uma metodologia adequada para o controle de velocidade dos motores de acionamento dos sistemas de tração e direção do AGV, através de um microcomputador
Abstract: Presently is in development at the Laboratory of Computational Engineering and Industrial Automation (LCA) a prototype of automated electric vehicle (AGV) controlled through computer. The AGVs find several applications at the automated industrial environment by the possibilities that it offers to receive control from a supervisor computer through communications systems with the aim to do several tasks at the productive processo Its application can be extended to hazardous environment which presents high life risks to the men, case of milling and laboratories where toxic substances are handled. It is a complex development task, since the project of a AGV involves several branches of knowledgment of Engineering and such fact leads to a very high degree of interdisciplinarity. This project incorporates a traction and a steering system controlled by computer which uses a data acquisition system and a position sensor unity in such way that the vehicle is able to follow a reflective path assembled at the ground of the plant. This work shows the theoretic basis for electric drives usually used in this type of vehicle as well in others industrial drives and the maio objective is to investigate a suited methodology for computer control of the velocity for the electrical drives to be used in this AGV
Mestrado
Automação
Mestre em Engenharia Elétrica
40
Hayakawa, Naoki, Hiroshi Inano, Yusuke Nakamura, and Hitoshi Okubo. "Time Variation of Partial Discharge Activity Leading to Breakdown of Magnet Wire under Repetitive Surge Voltage Application." IEEE, 2008. http://hdl.handle.net/2237/12126.
Full text
41
Daniau, Emeric. "Contribution à l'étude des performances d'un moteur à détonation pulsée." Poitiers, 2001. http://www.theses.fr/2001POIT2335.
Full textAbstract:
Les travaux réalisés dans le cadre de cette étude ont eu pour objectif de quantifier les performances propulsives d'un moteur à détonations pulsées (moteur à réaction à fonctionnement alternatif) et d'aborder sa configuration aérobie. L'étude des performances propulsives (impulsion spécifique, poussée) a été réalisée avec le mélange C2H4 O2, l'usage du mélange H2 air étant restreint au démonstrateur aérobie. Dans un premier temps, une étude analytique et théorique basée sur des résultats antérieurs a permis d'établir un modèle de performances pour le cas idéal de la chambre de combustion cylindrique entièrement remplie, fermée à l'une de ses extrémité et ouverte à l'autre sur l'atmosphère à la pression ambiante pa, l'écart à l'idéalité a été abordé en diminuant la pression de détonation devant la pression pa. Dans un deuxième temps, plusieurs études expérimentales (réalisées sur banc monocycle) ont été menées pour évaluer l'influence de i) la présence d'entrées d'air, ii) le remplissage partiel de la chambre iii) la présence de tuyères, iv) la présence d'obstacles proche de la section d'éjection, sur les performances réelles accessibles par ce type de moteur. Pour ce faire, des méthodes expérimentales spécifiques ont été mises en œuvre et validées (mesure de la pression sur le mur de poussée, visualisation par strioscopie, mesure de l'impulsion par pendule balistique) pour l'obtention des deux paramètres fondamentaux contrôlant les performances, l'impulsion spécifique et le temps de cycle, ce dernier déterminant le débit massique de mélange réactif maximal possible ou la fréquence maximale de fonctionnement. La réalisation d'un banc d'essai multicycle "en conditions réelles" a enfin permis de valider des solutions techniques (nécessité d'initier la détonation du mélange principal H2 - air- à l'aide d'un système de pré-détonation utilisant un mélange réactif très détonant C2H4 O2-) et d'observer certains phénomènes spécifiques du fonctionnement multicycle.
42
Saletti, Patrícia Grandizoli. "Caracterização da inibição por pré-pulso em primatas não-humanos (Sapajus spp.) e avaliação dos efeitos da dizocilpina e canabidiol na modulação do filtro sensório-motor." reponame:Repositório Institucional da UnB, 2015. http://repositorio.unb.br/handle/10482/19006.
Full textAbstract:
Tese (doutorado)—Universidade de Brasília, Instituto de Ciências Biológicas, Programa de Pós-Graduação em Biologia Animal, 2015.Submitted by Raquel Viana (raquelviana@bce.unb.br) on 2015-10-29T18:00:03Z No. of bitstreams: 1 2015_PatríciaGrandizoliSaletti.pdf: 47057297 bytes, checksum: f3315f28ce8b31713e5d97266adc91b6 (MD5)
Approved for entry into archive by Marília Freitas(marilia@bce.unb.br) on 2015-12-20T16:34:07Z (GMT) No. of bitstreams: 1 2015_PatríciaGrandizoliSaletti.pdf: 47057297 bytes, checksum: f3315f28ce8b31713e5d97266adc91b6 (MD5)
Made available in DSpace on 2015-12-20T16:34:07Z (GMT). No. of bitstreams: 1 2015_PatríciaGrandizoliSaletti.pdf: 47057297 bytes, checksum: f3315f28ce8b31713e5d97266adc91b6 (MD5)
O reflexo de sobressalto acústico é uma resposta primitiva de defesa dos animais após um estímulo sonoro intenso e repentino. Essa resposta é inibida quando um estímulo de baixa intensidade é apresentado previamente. A inibição por pré-pulso (IPP) da reposta de sobressalto é uma maneira de mensurar o filtro sensório-motor, mecanismo utilizado para filtrar o excesso de informação do meio. O teste de IPP é muito utilizado de forma experimental para testar déficits no filtro sensório-motor em modelos animais. Alguns transtornos neurológicos humanos apresentam danos na resposta de IPP, como por exemplo a esquizofrenia, devido a déficits no funcionamento do filtro sensório-motor comuns em pacientes com esse transtorno. Algumas drogas podem ser utilizadas para gerar efeitos esquizotípicos, como antagonistas de receptores glutamatérgicos NMDA. Sabe-se que essas drogas causam déficits no teste de IPP em roedores. Com a validação de um protocolo experimental que envolve a resposta de IPP é possível realizar testes de substâncias que provocam efeitos esquizotípicos, bem como substâncias que apresentam características antipsicóticas. Geralmente os animais utilizados como modelos de esquizofrenia são roedores e poucos estudos tem sido realizados para avaliar o efeito de substâncias no teste de IPP em primatas nãohumanos. Assim, o presente trabalho teve como objetivo desenvolver um teste de IPP para ser utilizado em macacos-pregos (Sapajus spp.). Além disso, objetivou-se avaliar o papel do colículo superior na resposta de IPP e testar os efeitos de dois fármacos, a dizocilpina (MK-801) e o canabidiol na medida de IPP desses primatas. Para isso, esse trabalho foi dividido em dois estudos. O estudo 1 avaliou a resposta de IPP em oito macacos-pregos utilizando um protocolo experimental que mensura o movimento do corpo do animal. Após essa primeira análise, dois animais com lesão no colículo superior, dois animais submetidos à lesão fictícia e os oito macacos acima citados foram testados nesse protocolo para que fosse identificada alguma alteração na resposta de IPP. Os resultados do primeiro estudo mostraram que o gênero Sapajus segue o mesmo padrão de resposta de IPP que outros primatas não-humanos. Observamos que as intensidades de 115 dB e 80 dB foram suficientes para gerar sobressalto e inibir essa resposta, respectivamente. Além disso, observamos que o intervalo entre os dois estímulos apresentados que melhor inibiu a resposta de sobressalto foi o de 120 ms. Os animais com lesão no colículo superior apresentaram uma tendência a diminuição da IPP corroborando estudos realizados em roedores, que indicam participação dessa estrutura cerebral na via neural da IPP. O estudo 2 foi realizado para determinar os efeitos do MK 801 e do canabidiol na resposta de IPP em primatas não-humanos. Novamente, oito macacos-pregos foram submetidos ao teste após administrações das drogas. O MK-801 foi administrado em três diferentes doses (0,01; 0,02; 0,03 mg/kg) antes do teste de IPP. Após algumas semanas os animais foram submetidos ao teste após o tratamento com canabidiol também em três doses (15, 30, 60 mg/kg). Posteriormente, os animais receberam MK-801 por quatro semanas consecutivas e foram expostos ao teste de IPP. Na quarta semana, além do MK-801, os animais foram pré-tratados com canabidiol e submetidos ao teste de IPP. Os resultados do estudo 2 mostraram que a MK-801, na maior dose testada diminuiu a resposta de IPP nos macacos de forma aguda. Entretanto, ao contrário do que é observado em roedores, a administração repetida do MK-801, concomitantemente ao teste de IPP, gerou uma interação droga-treino que reverteu o efeito inicial gerado pelo MK-801. Devido a isso, não foi possível detectar efeito antipsicótico do canabidiol. Porém, corroborando estudos prévios realizados em roedores, o canabidiol isoladamente não alterou a resposta de IPP dos macacos-pregos. Concluímos assim, que animais do gênero Sapajus são bons modelos experimentais para o teste de IPP e que o MK-801 pode ser utilizado para gerar déficits de IPP de forma aguda nesses animais para avaliação de antipsicóticos. O processo de habituação observado nos animais indica que efeitos adversos do MK-801, como prejuízo no filtro sensório-motor, podem ser reduzidos pela tolerância e pela familiarização ao teste de IPP. Ademais foi possível identificar diferenças neurofarmacológicas entre roedores e primatas e a importância desses animais para pesquisas básicas e testes pré-clinicos. ______________________________________________________________________________________________ ABSTRACT
The acoustic startle reflex is a primitive defense response in animals that occurs after an intense and sudden acoustic stimulus. This response can be inhibited when a low stimulus is presented previously. The prepulse inhibition (PPI) of the startle response is a useful way to measure sensorimotor gating mechanisms. This mechanism protects against an excess of information. PPI test is widely used experimentally to test deficits in sensorimotor gating in animal models. PPI deficits are commonly observed in some human neurological disorders, such as schizophrenia, due to damage in sensorimotor gating caused by cognitive deficits. Some drugs can be used to induce schizophrenic-like effects, such as NMDA receptor antagonists. These drugs induce deficits in PPI response in rodents. Validation of an experimental protocol on PPI response makes it possible to perform tests on substances that cause schizophrenic-like effects, as well as compounds with antipsychotic properties. Studies usually employ rodents as experimental models of schizophrenia and only few studies have been performed with nonhuman primates to test pharmacological effects in the PPI paradigm. Thus, the present study aimed to develop a PPI test to be applied in capuchin monkeys (Sapajus spp.) to evaluate the role of the superior colliculus in PPI response and test the effects of two drugs in these animals: dizocilpine (MK-801) and cannabidiol. Therefore, two studies were conducted. The first study characterized the PPI response of eight capuchin monkeys using a whole-body prepulse inhibition protocol. After that, two animals with superior colliculus (SC) lesion, two SC sham lesion and the eight monkeys cited above were tested to evaluate the role of this brain structure in the PPI response. Results showed that Sapajus follows the same PPI pattern as other nonhuman primates. The intensities of 115 dB and 80 dB were sufficient to induce a startle response and to inhibit this response, respectively. We also observed that 120 ms was the best interstimuli interval for PPI. Animals with superior colliculus lesion showed a downward tendency of PPI response, corroborating studies in rodents that indicate a participation of this brain structure in the neural pathway of PPI. The second study was conducted to determine the effects of MK-801 and cannabidiol on nonhuman primates’ PPI response. MK-801 was administered in three different doses (0.01; 0.02; 0.03 mg/kg) before the PPI assay. After a few weeks, the animals were submitted to PPI test after receiving cannabidiol also in three doses (15, 30, 60 mg/kg). Subsequently, animals received MK-801 during four consecutive weeks and were then exposed to the PPI test. On the fourth week, subjects were pre-treated with cannabidiol before the MK-801 administration and then the PPI test was performed. Results from the second study demonstrated that MK-801, at the dose of 0.03 mg/kg, decreased the PPI response of an acute administration. However, repeated administration of MK-801 throughout the PPI test induced a drug-training interaction that reversed the effects of MK- 801 on PPI disruption, unlike reports in rodents. As such it was not possible to detect an antipsychotic effect for cannabidiol. However, cannabidiol alone did not change the PPI response in the capuchin monkeys, corroborating previous studies in rodents. Therefore, we conclude that capuchin monkeys are useful experimental models to test PPI response. Moreover, MK-801 can be used to induce PPI deficits in this species. The habituation process observed in our study indicates that the adverse effects of MK-801, as sensorimotor gating impairments, may be reduced by MK-801 tolerance effect such as after familiarization with the PPI test. Furthermore, our results underscore neuropharmacological differences between rodents and nonhuman primates and the importance of primates in basic research and preclinical assays.
43
Pothuraju, Maneesha. "A Study on the Electromagnetic and Mechanical Vibrations of a Dynamometer Using Spectral Analysis." University of Cincinnati / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1613747909641685.
Full text
44
Lungu, A. "Wavelet-based characterization and stochastic modelling of avelet-based characterization and stochastic modelling of pulse-like ground motions on the time-frequency plane." Thesis, City University London, 2014. http://openaccess.city.ac.uk/8341/.
Full textAbstract:
A novel non-separable non-stationary stochastic model for the representation and simulation of pulse-like earthquake ground motions (PLGMs), capable to accurately represent peak elastic and inelastic structural responses, is proposed in this work. Further, the model is employed for assessing the performance of several time-frequency representation techniques (the harmonic wavelet transform, the Meyer wavelet packets transform, the S-transform and the empirical mode decomposition) in capturing salient features of pulse-like accelerograms. The significantly higher structural demands posed by PLGMs in comparison with similar intensity pulse-free motions led to comprehensive investigations in order to mitigate the damage experienced in the affected areas, such as those located near seismic faults. In this regard, time-frequency analysis methods are frequently employed for the analysis of signals recorded during these events, due to their adaptability to the specific evolutionary behaviour. Alongside with characterization, stochastic modelling of PLGMs is of interest since it allows for systematic variations of the input parameters in order to enhance the understanding of their influence on the structural behaviour. This is particularly useful since only a limited number of PLGMs are available in the existing earthquake databases. Accordingly, inspired by the time-frequency distribution of their total energy, a versatile PLGM model is defined as a combination of amplitude-modulated stochastic processes. Each process models the time-varying distribution of the energy for adjacent frequency ranges. Two alternative formulations are proposed for representing the low-frequency content characterizing the pulses. Considering a set of pulses from the literature, numerical results show that the pulse models‟ parameters can be calibrated to simulate in average the structural impact of these pulses represented using the model herein defined. Further, the capability of the PLGM model to generate elastic and inelastic spectral responses matching a given field recorded accelerogram in the mean sense is illustrated. The applicability of the proposed model to account for near-fault effects to spectrum compatible representations of the seismic action is illustrated by generating a fully stochastic process compatible with the response spectrum of the European aseismic code (EC8). Furthermore, the model can be employed in various applications including generation of accelerograms for nonlinear dynamic analyses of structures, probabilistic seismic demand analyses or as input in stochastic dynamic techniques such as statistical linearization. Finally, the capability of several time-frequency analysis methods to characterize PLGM accelerograms is evaluated through comparative numerical studies within a novel methodology, namely by considering artificial time-histories as samples of the proposed model. The results highlight the potential of the S-transform to be used for pulse identification/extraction and of the harmonic wavelet transform for record characterization/pulse extraction. Additionally, they confirm that from an engineering perspective the structural natural period is an appropriate and representative parameter for the definition of “pulses”. Overall, these analyses shed light into the challenges experienced when attempting to detect the pulse content in the accelerograms, in an effort to inform best practices for PLGMs characterization.
45
Moreno, Martinez Rodolfo Manuel. "Uma contribuição ao estudo e projeto de um inversor trifasico de tensão a tres niveis." [s.n.], 1997. http://repositorio.unicamp.br/jspui/handle/REPOSIP/259003.
Full textAbstract:
Orientador: Ernesto Ruppert FilhoDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia e de Computação
Made available in DSpace on 2018-07-22T21:13:02Z (GMT). No. of bitstreams: 1 MorenoMartinez_RodolfoManuel_M.pdf: 9266365 bytes, checksum: 28a887f54983817261be9938956bbcd1 (MD5) Previous issue date: 1997
Resumo: : O objetivo deste trabalho é o de estudar, através de simulações, o comportamento em regime permanente de um sistema constituído por um motor de indução trifásico acionando uma carga mecânica, alimentado por um inversor trifásico de tensão a três níveis. Estabeleceu-se modelos matemáticos dinâmicos para o motor e para o inversor e utilizou-se para as simulações os ambientes computacionais Matlab e Pspice de acordo com o tipo de estudo realizado. Para a operação do inversor a três níveis considerou-se as técnicas de modulação em largura de pulso por eliminação seletiva de harmônios e por modulação vetorial que são as técnicas que estão, hoje, em maior evidência na literatura. Mostra-se no trabalho comparações do desempenho do inversor a três níveis com o desempenho do inversor a dois níveis chateados por modulação em largura de pulso senoidal, eliminação seletiva de harmônicos e modulação vetorial. Os inversores a três níveis apresentam baixo conteúdo harmônico em tensão e corrente de saída com baixa freqüência de chaveamento enquanto os de 2 níveis exigem freqüências maiores de chaveamento para a obtenção do mesmo conteúdo do harmônicos resultando em diminuição da vida das chaves e em redução da eficiência. Os inversores a três níveis, pelo fato de terem suas chaves, quando desligadas, submetidas a tensões menores são sujeitos a menos ?stress? de tensão ou passíveis de operar em potências maiores. Neste trabalho também apresenta-se uma técnica de projeto baseada em resultados de simulação
Abstract: The main goal of this thesis is to simulate the steady-state performance of a three-level, three-phase, voltage-controlled inverter driving a three-phase induction motor. Dynamic mathematical models for the motor and the inverter were done and the Matlab and Pspice computational ambients were used according to the type of the study to be performed. To study the operation of the three-level inverter it was considered the following PWM techniques: a) Selective harmonic elimination (SHE), b) Vector modulation. Both techniques are today in great evidence in the concemed literature. It is shown performance comparisons with the two-level inverter switched by sinusoidal PWM, selective harmonic elimination and vector modulation. The three-level inverter presents a small output voltage and current harmonics contents even with small switching frequency while the two-level inverter needs higher swiching frequencies to get the same harmonic contents. This results in the switch life and efficiency deceasing. If the three-level inverter switch is off it is submitted to half voltage, when compared with the two-level inverters, so they are less stressed than the two-level ones and they are able also to operate in higher rates. It is also presented a tree-level inverter design technique based on simulation results
Mestrado
Mestre em Engenharia Elétrica
46
Mihaila, Vasile. "Nouvelle conception des bobinages statoriques des machines à courant alternatif pour réduire les effets négatifs des dV/dt." Thesis, Artois, 2011. http://www.theses.fr/2011ARTO0212/document.
Full textAbstract:
L’émergence du concept d’un avion plus électrique implique une refonte en profondeur des réseaux embarqués. L’axe principalement développé repose sur une augmentation de la tension du réseau et un passage au bus continu. Le contrôle des actionneurs électriques embarqués passe alors par l’utilisation massive de convertisseurs électroniques qui vont imposer des fronts de tension très raides et des contraintes particulières aux enroulements des machines. Les oscillations pseudopériodiques qui suivent ces fronts raides sont à l’origine de champs électriques intenses qui peuvent dépasser le seuil d’apparition des décharges partielles (PDIV) et de ce fait provoquer une dégradation rapide des isolants classiques qui sont à base de polymères. Le travail effectué dans cette thèse est centré sur l’étude d’une nouvelle méthode de conception des bobinages permettant la réduction des problèmes de décharges partielles. Un dispositif expérimental mis au point dans ce cadre reproduit les contraintes imposées par des convertisseurs modernes et permet de mesurer les tensions inter-spires d’une bobine. L’étude expérimentale met en évidence les phénomènes àprendre en compte avec ce type d’alimentation et donne une première idée des axes d’optimisation envisageables. Un modèle prédictif capable de donner la distribution des tensions inter-spires, en réponse à un front raide de tension, aide à identifier les points critiques. Les paramètres constitutifs de ce modèle ont été déterminés en utilisant des méthodes analytiques, expérimentales et numériques. Compte tenu de la complexité du modèle, un outil numérique automatisé a été élaboré afin de simuler le modèle des bobines étudiées. Plusieurs types de bobinage ont été analysés et optimisés avec succès. Cette optimisation consiste à diminuer la tension inter-spires en agissant sur l’arrangement des fils dans les encoches. L’utilisation des bobines optimisées avec cette méthode permet d’envisager une nette amélioration de la fiabilité des machines électriquesThe emergence of the concept of a more electric aircraft requires a major overhaul of onboard grid. The main developed axis is based on an increase in the grid voltage and a switch to DC bus. In this context, the onboard electric actuators are supplied through power electronic converters that will impose very fast voltage fronts and particular constraints in the windings of the machines. The transient over-voltages that follow the steep-fronted pulses are the source of intense electric fields which may exceed the partial discharge inception voltage (PDIV) and cause a rapid deterioration of polymer based insulators. This thesis focuses on the study of a new design method of the windings in order to reduce problems of partial discharges. An experimental device developed in this framework reproduces the constraints of modern converters and allows measuring the turn-to-turn voltages of a coil. The experimental study shows the phenomena to be considered with this type of power supply and gives an idea of possible areas for optimization. A predictive model able to give the distribution of turn-to-turn voltages, in response to a steep-fronted voltage, helps to identify critical points. The constitutive parameters of this model were determined using analytical, experimental and numerical methods. Given the complexity of the model, an automated numerical tool has been developed in order to simulate the model of studied coils. Several types of coil have been analyzed and optimized successfully. This optimization consists in reducing the turn-to-turn voltages by acting on the arrangement of the wires in the slots. The use of optimized coils with this method allows envisaging a significantimprovement in the reliability of electrical machines
47
Dundáček, Martin. "Mikroprocesorový modul řízení SS motoru se zpětnou vazbou." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2008. http://www.nusl.cz/ntk/nusl-217259.
Full textAbstract:
This thesis deals with DC motor control. Main goal was design and realization of DC motor controler module with feedback. The first part dwells on methods for DC motor control and HW design of control module. The second part describes development of software for the module, testing and sums up results.
48
Gomes, Rodrigo San Martin Ignacio. "Avaliação do filtro sensório-motor através de registro de eletroencefalograma (EEG) e teste de inibição pré-pulso (IPP) em pacientes após primeiro episódio psicótico." reponame:Repositório Institucional da UFABC, 2017.
Find full textAbstract:
Orientadora: Profa. Dra. Cristiane Otero Reis SalumCoorientador: Prof. Dr. Francisco José Fraga da Silva
Dissertação (mestrado) - Universidade Federal do ABC, Programa de Pós-Graduação em Neurociência e Cognição, São Bernardo do Campo, 2017.
Pacientes de transtorno bipolar e esquizofrenia apresentam déficits no processamento de informação. Dentre esses déficits está uma disfunção do mecanismo de filtragem sensorial, que pode ser observada através do teste de Inibição Pré-Pulso (IPP), que acessa a inibição das respostas muscular, observada por eletromiografia (EMG) e neural, observada por eletroencefalograma (EEG) através da inibição de potenciais evocados, como o P2-N1. No fenômeno da IPP, é observado que a resposta iniciada por um estímulo de alta intensidade é reduzida quando este é precedido em alguns milissegundos (30-300ms) por outro estímulo de baixa intensidade. Esses estímulos são respectivamente chamados de Pulso (P) e Pré-Pulso (PP). A porcentagem de redução da resposta ao P, quando este é precedido por um PP é calculada em relação à magnitude de resposta que seria evocada pelo P quando este não é precedido por PP algum. O presente estudo visou avaliar o filtro sensorial através do registro simultâneo dos sinais eletromiográficos e eletroencefalográficos em pacientes brasileiros de primeiro episódio psicótico de transtorno bipolar (BP) e esquizofrenia (SZ). Vinte pacientes BP, quinze pacientes SZ e 22 sujeitos sadios participaram do estudo. Pacientes SZ apresentam redução da %IPP observada por EMG em relação a pessoas sadias, ao passo que pacientes do grupo BP não apresentam redução da filtragem sensório-motora. Para a IPP neural, foi observada redução na amplitude de P do grupo BP na região frontal, avaliada pelo eletrodo Fz e redução da amplitude de P e também na %IPP para os grupos BP e SZ na região parietal, avaliada pelo eletrodo Pz. Os resultados indicam que a redução da filtragem sensorial foi observada em diferentes estágios do processamento sensorial. E a divergência entre IPP clássica e IPP neural para o grupo BP sugere que a IPP medida por EMG clássica e medida por EEG refletem filtros sensoriais diferentes e que pacientes de diferentes grupos podem exibir déficits em um desses filtros apenas. O presente trabalho é o pioneiro na utilização de ferramentas de atenuação de artefatos contaminantes do sinal neural no teste de IPP neural.
Patients with bipolar disorder and schizophrenia have deficits in information processing. Among these deficits is a dysfunction of the sensory filtering mechanism, which can be observed through the Prepulse Inhibition (PPI) test, which accesses the inhibition of muscle responses, observed by electromyography (EMG) and neural, observed by electroencephalogram (EEG) through inhibition of evoked potentials, such as P2-N1. In the PPI phenomenon, it is observed that the response initiated by a high intensity stimulus is reduced when it is preceded in a few milliseconds (30-300ms) by another low intensity stimulus. These stimuli are respectively called Pulse (P) and Prepulse (PP). The reduction percentage of the response to P when it is preceded by a PP is calculated in relation to the magnitude of response that would be evoked by P when it is not preceded by any PP. The present study aimed to evaluate the sensory filter through the simultaneous recording of electromyographic and electroencephalographic signals in Brazilian patients with first psychotic episode of bipolar disorder (BP) and schizophrenia (SZ). Twenty BP patients, fifteen SZ patients and 22 healthy subjects participated in the study. SZ patients presented a reduction in the %PPI observed by EMG when compared to healthy individuals, whereas patients in the BP group did not show reduction of sensory-motor filter. For the neural PPI, a reduction in BP group P amplitude was observed in the frontal region, evaluated by the Fz electrode. Also, was observed a reduction in the P amplitude and in the %PPI for the BP and SZ groups in the parietal region, evaluated by the Pz electrode. These results indicate that the reduction of sensorial filtration was observed at different stages of sensorial processing. And the divergence between classical IPP and neural IPP for the BP group suggests that PPI measured by classical EMG and measured by EEG reflect different sensory filters and that patients from different groups may exhibit deficits in one of these filters only. The present work is the pioneer in the use of attenuation tools to reduce contaminating artifacts in PPI test neural signal.
49
Malleichervu, Govind N. "PROPORTIONAL FEEDBACK CONTROL OF DUTY CYCLE FOR DC HYBRID ACTIVE POWER FILTER." UKnowledge, 2008. http://uknowledge.uky.edu/gradschool_theses/555.
Full textAbstract:
This thesis deals with the design and implementation of a feedback control scheme for a DC Hybrid Active Power Filter used to filter harmonics from a Switched Reluctance Motor (SRM) Drive load. Power electronic systems are non-linear & dynamic [1,3,5]. Power electronic systems employ switching circuits to maximize their efficiency at the penalty that switching circuits generate electrical noise called ripple current and voltage or conducted electromagnetic interference (EMI). The ripple current drawn by the power electronic systems needs to be attenuated to an acceptable level. Filters attenuate this to an acceptable level. Traditionally filters with passive inductors and capacitors are used. Active filters contain switching elements in addition to passive inductors and capacitors which reduce overall size of passive components used.
Two control approaches, full-state state space, and plain proportional feedback, are evaluated for this filter. Circuit models are simulated in SPICE and mathematical models are simulated in Matlab/Simulink for evaluating these control approaches. Proportional feedback control was chosen for implementation and the reason for this is provided in the thesis. The active filter was tested with chosen feedback control and experimental results were compared with simulation results. Inferences and scope for further work are finally presented.
50
Bury, Yannick. "Structure de jets légers ou lourds en écoulement externe fortement pulsé : expérimentation modèle du mélange de carburants gazeux dans les moteurs alternatifs." Toulouse, INPT, 2000. http://www.theses.fr/2000INPT045H.
Full textAbstract:
Cette thèse s'inscrit dans le cadre de l'étude des écoulements turbulents fortement instationnaires avec larges variations de densité. Elle s'insère dans une action globale de compréhension des mécanismes physiques régissant le mélange air/carburant dans les moteurs à piston du secteur automobile, notamment de carburants gazeux tels que le GNV. La dynamique et le mélange dans un jet à densité variable en écoulement cocourant fortement pulsé sont étudiés. Cette configuration modélise la situation moteur. Une importante base de données sur des jets léger, homogène et lourd est obtenue pour des vitesses de cocourant stationnaire et instationnaire contrastées. Les champs de vitesse sont mesurés par anémométrie Laser Doppler bicomposantes, les champs de fraction massique et de densité moyenne par tomographie laser. Les mesures et l'analyse physique permettent de comprendre ces écoulements. Une partition du jet en régions quasi statique et instationnaire est proposée. Les effets de mémoire observés dans la zone instationnaire peuvent être appréhendés par un modèle hyperbolique. Un front de vitesse de type jet naissant se développe lors de l'accélération et se traduit par un effet important sur le champ turbulent. L'étude phasée de la topologie du jet montre que ce front s'assimile à une boule de fluide concentrée, analogue au vortex des jets naissants ou aux jets pulsés. Le mélange avec le fluide extérieur est réduit à son passage et plus généralement pendant toute l'accélération. Au contraire il semble légèrement accru pendant la décélération. Le rôle des couples baroclines sur le champ moyen et la turbulence est identifié. Des nombres sans dimension sont mis en évidence pour traduire ce régime de convection mixte instationnaire. La confrontation de ces résultats avec des simulations numériques en éprouvera la validité en situation fortement instationnaire.