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Dissertations / Theses on the topic 'Doppler spread'
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Eggen, Trym H. 1963. "Underwater acoustic communication over Doppler spread channels." Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/42768.
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Malachias, Nickolaos. "Doppler shift and spread study for ionospherically propagated signals." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1994. http://handle.dtic.mil/100.2/ADA284610.
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Wen, Hui. "Comparison and Evaluation of Doppler Spread Estimation Algorithms in WCDMA." Thesis, KTH, Kommunikationsteori, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-152226.
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In a WCDMA transmission systems, the properties of the radio transmissionchannels can be strongly aected by the movement of User Equipment (UE) orthe surrounding objects. The estimation of Doppler spread is therefore of greatimportance since it is closely related to the mobile speed, as it can also be usedto characterize the fast fading in the radio channel. Thus the Doppler spread estimation can have wide range of applications and the relative research on thistopic has drawn much attention. Many Doppler spread estimation algorithms has been proposed in the literature. In this report, these algorithms are divided into four categories, and the comparison is performed from both performanceand implementation point of view to compare these four types of estimators. During the investigation, the Rayleigh fading and Rician fading model withdierent mobile speed and SNR are simulated to analyze the performance of estimation algorithms under dierent conditions. The effect of Rician factor and angle of arrival of Line Of Sight (LOS) component is also taken into consideration in the evaluation. Furthermore, the computational complexity of each algorithm is calculated. Based on simulation results, the underlying reasons for their performances are analyzed individually. The Moser's estimator (correlation based estimator) demonstrates the best performance among these four estimators from the perspective of estimation accuracy. And it also shows the great value for the implementation in real systems.<br>I ett kommunikationssystem baserat p WCDMA kan egenskaperna hos radiotransmissionskanalernapverkas starkt av mobilens eller omgivningens rrelser.Estimering av Doppler spridningen r drfr av stor betydelse eftersom den r nrabeslktad med mobilens hastighet och den kan ocks anvndas fr att karakteriseraden snabba fdning i radiokanalen. Sledes kan estimat av Dopplerspridning ha ettbrett anvndningsomrde och forskningen om detta mne har varit intesiv. Mngaalgoritmer fr estimatering av Doppler spridning har freslagits i litteraturen. Idenna rapport, dessa algoritmer r indelade i fyra kategorier och analysen utfrsbde med avseende p prestanda och implementerbarhet. Simuleringar r utfrdamed Rayleigh fading och Rician modeller med olika hastigheter hos mobilen,och olika signal till brus frhllanden. Simuleringar har ocks gjorts fr olika vrdenav Ricianfaktorn och vinkel fr inkommande signal. Vidare har den berkningsmssigakomplexiteten av varje algoritm analyserats. Utifrn simuleringsresultathar de bakomliggande orsakerna till de olika algoritmernas prestatandadiskuterats. Dopplerspridningsestimat med Mosers metod (korrelation baseradestimator) visar det bsta resultatet bland dessa fyra estimator med avseendep skattningsnoggrannhet. Denna metod har ven frhllandevis lg berkningskomplexitetvilket gr den implementeringsvnlig.
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Fofanah, Ibrahim, and Wannaw Assegu. "Delay Spread Characterization of the Aeronautical Channel." International Foundation for Telemetering, 2012. http://hdl.handle.net/10150/581653.
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ITC/USA 2012 Conference Proceedings / The Forty-Eighth Annual International Telemetering Conference and Technical Exhibition / October 22-25, 2012 / Town and Country Resort & Convention Center, San Diego, California<br>Radio transmission channel influences greatly the quality of transmitted voice and data signal in terms of data rate and robustness. This degradation is as a result of many factors, notable amongst them are having multiple replica of the transmitted signal at the receiver (multipath), changes of frequency as a result of the movement of the aircraft (Doppler shift) and noise. This paper characterizes the scattered components of the aeronautical channel in terms of delay spread. Geometric representation is used to derive expressions for the maximum delay spread using the 2-ray model and the three dimensional model of the scattered path. Furthermore, the delay and Doppler frequencies are described as a function of the horizontal distance to the specular reflection point between a ground station and a test article. The simulated results are compared to measured data of related articles and the value of the maximum delay spread is compared with the proposed intersymbol guard band for Orthogonal Frequency Division Multiplexing (OFDM) in the Integrated Network Enhanced Telemetry (iNET) program to see if this proposition can be adapted to the aeronautical channel.
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Peng, Ziqi. "Performance and Complexity Comparison of Doppler Spread Estimation for WCDMA Systems." Thesis, KTH, Kommunikationsteori, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-152225.
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In cellular communication systems, the estimation of Doppler spread has a wide range of applications such as handoff, channel assignment scheme, adaptivetransmission, power control, etc. A great quantity of Doppler spread estimation algorithms have been proposed in the literature. But there has been few investigations which gives a comprehensive comparison of these algorithms. Therefore, it is of great signicance to compare and evaluate the performance of the existing algorithms in the same simulation framework. In this report, the uplink of WCDMA is considered. Four different types of Doppler spread estimation algorithms are evaluated and compared in a link level baseband simulator. The performance and the ability to implement are considered as the metrics for evaluation. Both Rayleigh and Rician fading channel model are applied, and the effect of speed, signal to noise ratio, Rician factor and the angle of arrived line of sight component are also tested. Moreover, the computational complexity is analysed to evaluate the practical value for implementation.<br>Estimatering av en mobils hastighet i form av Dopplerspridning har ett brett spektrum av tillmpningar i cellulra kommunikationssystem ssom fr yttningen avmobiler mellan celler, kanaltilldelningsschema, adaptiv sndning, eektstyrning,etc. En stor mngd algoritmer fr estimering av Dopplerspriding har frslagitsi litteraturen, men det r ovanligt med heltckande jmfrelser mellan med dessaalgoritmer. Drfr r det av stor betydelse att jmfra och utvrdera resultaten avbentliga algoritmer inom ramen fr samma simuleringsvertyg.I denna rapport anvnds upplnken fr WCDMA fr utvrdering av fyra olikatyper av algoritmer fr estimering av Dopplerspridning. Metriker fr utvrderingenr prestanda och implementeringsvnlighet. Bde Rayleigh och Rician fdningskanalmodeller har utvrderas, samt eekten av mobilens hastighet, signaltill brus frhllande, Rician faktor och infallsvinkel i ppet flt scenario. Dessutomhar den berkningsmssiga komplexiteten analyseras fr att utvrdera den praktiskaanvndbarheten i riktiga system.
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Scaife, Bradley J. "DOPPLER SHIFTED SPREAD SPECTRUM CARRIER RECOVERY USING REAL-TIME DSP TECHNIQUES." International Foundation for Telemetering, 1998. http://hdl.handle.net/10150/607365.
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International Telemetering Conference Proceedings / October 26-29, 1998 / Town & Country Resort Hotel and Convention Center, San Diego, California<br>In any satellite communication, the Doppler shift associated with the satellite’s position
and velocity must be calculated in order to determine the carrier frequency. If the satellite
state vector is unknown then some estimate must be formed of the Doppler-shifted carrier
frequency. One elementary technique is to examine the signal spectrum and base the
estimate on the dominant spectral component. If, however, the carrier is spread (as in
most satellite communications) this technique may fail unless the chip rate-to-data rate
ratio (processing gain) associated with the carrier is small. In this case, there may be
enough spectral energy to allow peak detection against a noise background.
In this paper, we present a method to estimate the frequency (without knowledge of the
Doppler shift) of a spread-spectrum carrier assuming a small processing gain and binary-phase
shift keying (BPSK) modulation. Our method relies on a simple, averaged discrete
Fourier transform along with peak detection. We provide simulation results indicating the
accuracy of this method. In addition, we will describe an all-digital hardware design
based around a Motorola DSP56303 and high-speed A/D which implements this
technique in real-time. The hardware design is to be used in NMSU’s implementation of
NASA’s demand assignment, multiple access (DAMA) service.
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Landon, David. "DOPPLER BANDWIDTH CHARACTERIZATION OF ARTM CHANNEL SOUNDING DATA." International Foundation for Telemetering, 1999. http://hdl.handle.net/10150/608760.
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International Telemetering Conference Proceedings / October 25-28, 1999 / Riviera Hotel and Convention Center, Las Vegas, Nevada<br>Data from ARTM channel sounding test flights is examined to characterize the dynamic channel behavior of aeronautical telemetry channels. The dynamic behavior is characterized using the Doppler power spectrum. The width of the Doppler power spectrum is the Doppler bandwidth of the channel which indicates the required bandwidth of adaptive detection techniques such as adaptive equalization, adaptive modulation, adaptive channel selection and adaptive error control coding. Data collected from ARTM Flight 11 suggest a Doppler bandwidth exceeding 6.7 Hz for the channel, but greater accuracy and resolution will only be possible with more data.
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Widodo, Slamet. "Wind and Doppler Shift Compensation for Spread Spectrum Sound-based Positioning System." Kyoto University, 2013. http://hdl.handle.net/2433/180518.
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Kyoto University (京都大学)<br>0048<br>新制・課程博士<br>博士(農学)<br>甲第17901号<br>農博第2024号<br>新制||農||1017(附属図書館)<br>学位論文||H25||N4797(農学部図書室)<br>30721<br>京都大学大学院農学研究科地域環境科学専攻<br>(主査)教授 近藤 直, 准教授 小川 雄一, 教授 飯田 訓久<br>学位規則第4条第1項該当
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Jian-zhong, Qi, Gong Yan, and Song Peng. "Realization of Fast Acquisition for Spread Spectrum Signal Based on FFT." International Foundation for Telemetering, 2011. http://hdl.handle.net/10150/595763.
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ITC/USA 2011 Conference Proceedings / The Forty-Seventh Annual International Telemetering Conference and Technical Exhibition / October 24-27, 2011 / Bally's Las Vegas, Las Vegas, Nevada<br>Acquisition based on Fast Fourier Transform (FFT) can acquire Pseudo-random code phase quickly and improve the performance of the satellite navigation receivers. In the paper Real-time receiver adopts the FPGA to realize the function of FFT and uses DSP processor to control the implementation process of Acquisition. For increasing the sensitivity of Acquisition incoherent accumulation were used in the process. Also, in the paper we have discussed the process method for decreasing the negative influence of signal power changes and carrier's Doppler frequency.
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Landon, David. "PARAMETRIC ESTIMATION OF THE SCATTERING FUNCTION FOR ARTM CHANNEL SOUNDING DATA." International Foundation for Telemetering, 2000. http://hdl.handle.net/10150/608249.
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International Telemetering Conference Proceedings / October 23-26, 2000 / Town & Country Hotel and Conference Center, San Diego, California<br>Parameterized data from ARTM channel sounding test flights are used to derive a parameter-based estimate of the scattering function. The Doppler bandwidth and Doppler spread, important measures of channel dynamics, can be estimated from such a scattering function. Data collected from ARTM Flight 11 suggest that the Doppler bandwidth is larger than 6.7 Hz. Even for very small collections of parameterized data, surprising agreement is shown to non-parametric scattering function estimates. This confirms modeling assumptions and offers a way to achieve significant reductions of storage requirements.
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Sanchez, Monica A. "Doppler Extraction for a Demand Assignment Multiple Access Service for NASA's Space Network." International Foundation for Telemetering, 1996. http://hdl.handle.net/10150/611433.
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International Telemetering Conference Proceedings / October 28-31, 1996 / Town and Country Hotel and Convention Center, San Diego, California<br>NASA's Space Network (SN) provides both single access (SA) and multiple access (MA) services through a pre-scheduling system. Currently, a user's spacecraft is incapable of receiving service unless prior scheduling occurred with the control center. NASA is interested in efficiently utilizing the time between scheduled services. Thus, a demand assignment multiple access (DAMA) service study was conducted to provide a solution. The DAMA service would allow the user's spacecraft to initiate a service request. The control center could then schedule the next available time slot upon owner approval. In this paper, the basic DAMA service request design and integration is presented.
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Huang, Zichen. "A Passive Spread Spectrum Sound-Based Local Positioning System for Robots in a Greenhouse." Kyoto University, 2020. http://hdl.handle.net/2433/259051.
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Kyoto University (京都大学)<br>0048<br>新制・課程博士<br>博士(農学)<br>甲第22783号<br>農博第2426号<br>新制||農||1081(附属図書館)<br>学位論文||R2||N5303(農学部図書室)<br>京都大学大学院農学研究科地域環境科学専攻<br>(主査)教授 近藤 直, 教授 飯田 訓久, 准教授 小川 雄一<br>学位規則第4条第1項該当
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Hassana, Ramesh Rakesh Kashyap. "Transform Domain Acquisition of Spread Spectrum Signals in a Low Signal to Noise Ratio Environment." Ohio University / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1289579500.
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Fu, Ruijun. "Empirical RF Propagation Modeling of Human Body Motions for Activity Classification." Digital WPI, 2012. https://digitalcommons.wpi.edu/etd-theses/1130.
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"Many current and future medical devices are wearable, using the human body as a conduit for wireless communication, which implies that human body serves as a crucial part of the transmission medium in body area networks (BANs). Implantable medical devices such as Pacemaker and Cardiac Defibrillators are designed to provide patients with timely monitoring and treatment. Endoscopy capsules, pH Monitors and blood pressure sensors are used as clinical diagnostic tools to detect physiological abnormalities and replace traditional wired medical devices. Body-mounted sensors need to be investigated for use in providing a ubiquitous monitoring environment. In order to better design these medical devices, it is important to understand the propagation characteristics of channels for in-body and on- body wireless communication in BANs. The IEEE 802.15.6 Task Group 6 is officially working on the standardization of Body Area Network, including the channel modeling and communication protocol design. This thesis is focused on the propagation characteristics of human body movements. Specifically, standing, walking and jogging motions are measured, evaluated and analyzed using an empirical approach. Using a network analyzer, probabilistic models are derived for the communication links in the medical implant communication service band (MICS), the industrial scientific medical band (ISM) and the ultra- wideband (UWB) band. Statistical distributions of the received signal strength and second order statistics are presented to evaluate the link quality and outage performance for on-body to on- body communications at different antenna separations. The Normal distribution, Gamma distribution, Rayleigh distribution, Weibull distribution, Nakagami-m distribution, and Lognormal distribution are considered as potential models to describe the observed variation of received signal strength. Doppler spread in the frequency domain and coherence time in the time domain from temporal variations is analyzed to characterize the stability of the channels induced by human body movements. The shape of the Doppler spread spectrum is also investigated to describe the relationship of the power and frequency in the frequency domain. All these channel characteristics could be used in the design of communication protocols in BANs, as well as providing features to classify different human body activities. Realistic data extracted from built-in sensors in smart devices were used to assist in modeling and classification of human body movements along with the RF sensors. Variance, energy and frequency domain entropy of the data collected from accelerometer and orientation sensors are pre- processed as features to be used in machine learning algorithms. Activity classifiers with Backpropagation Network, Probabilistic Neural Network, k-Nearest Neighbor algorithm and Support Vector Machine are discussed and evaluated as means to discriminate human body motions. The detection accuracy can be improved with both RF and inertial sensors."
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Bergadà, Caramés Pau. "Oblique Sounding and HF Communication Techniques for Very Long Haul Ionospheric Links." Doctoral thesis, Universitat Ramon Llull, 2015. http://hdl.handle.net/10803/285837.
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El sistema de comunicació ràdio d’alta freqüència (HF, en anglès) és usat arreu del món per agències governamentals i no governamentals sempre que calgui una alternativa a les comunicacions via satèl•lit: vaixells a alta mar, avions fora de cobertura de xarxes ràdio amb visió directa, operacions militars, zones on la infraestructura ha estat destruïda per algun tipus de desastre o bé zones llunyanes sense cap altre tipus de comunicació. La ràdio HF representa una alternativa, o un sistema de backup al satèl•lit per a comunicacions de llarg abast i en redueix els costos, evita la vulnerabilitat i els problemes de sobirania.
En aquesta tesi s’ha estudiat l’enllaç HF entre la base antàrtica espanyola Juan Carlos I, situada a l’illa Livingston a l’arxipèlag de les Shetland del Sud, i Espanya. L’objectiu d’aquest treball és estudiar els problemes que afecten la propagació; és a dir, la relació senyal a soroll i interferència, la dispersió multicamí i la dispersió per efecte Doppler, i dissenyar la capa física d’un enllaç HF de baixa velocitat, poca potència i llarg abast. Pel que fa aquest últim punt es fan un parell de propostes: espectre eixamplat per seqüència directa (DSSS, en anglès) i multiplexació per divisió en freqüència ortogonal (OFDM, en anglès). El repte que es planteja és el de la definició de les característiques dels símbols que millor encaixen en aquest canal per tal d’obtenir un benefici de la diversitat temporal i freqüencial que ofereix el canal.
Des de l’any 2003 diverses campanyes han permès estudiar aquest canal HF, però no va ser fins la campanya 2009/2010 que s’obtingué un foto de les característiques, diürnes i nocturnes, de la ionosfera. En els articles que es presenten en aquesta tesi hem estès el rang freqüencial d’estudi respecte a investigacions prèvies i hem mostrat diferències de comportament entre el dia i la nit. Hem usat els resultats de la caracterització del canal per a dissenyar i comparar la bondat dels símbols DSSS i OFDM. Ambdues possibilitats han resultat ser candidates a implementar l’enllaç HF entre l’Antàrtida i Espanya. Tot i així, ambdues tècniques representen visions diferents de la implementació del mòdem: mentre que DSSS obté bons resultats a baixa velocitat en entorns amb baixa relació senyal a soroll, OFDM aconsegueix tasses de velocitat més elevades en canals més benignes.<br>Los sistemas de radio de alta frecuencia (HF, en inglés) son usados por agencias gubernamentales y no gubernamentales en todo el mundo siempre que se necesite una alternativa a las comunicaciones por satélite: barcos en alta mar, aviones fuera del rango de cobertura de las redes radio de visión directa, operaciones militares, zonas donde la infraestructura ha sido destruida por algún desastre. Ésta ofrece una alternativa, o representa un sistema de backup, a las comunicaciones vía satélite, evitando los costes, la vulnerabilidad y los problemas de soberanía de las comunicaciones por satélite.
En esta tesis se ha estudiado el enlace HF entre la base antártica española Juan Carlos I en la isla Livingston, en las Shetland del sur y España. El objetivo de este trabajo es el estudio de las limitaciones de la propagación ionosférica (como la relación señal a ruido e interferencia, la dispersión multicamino y la dispersión por efecto Doppler) y el diseño de la capa física de un enlace HF de baja velocidad, baja potencia y largo alcance. Se han estudiado un par de propuestas para este enlace, como son el espectro ensanchado por secuencia directa (DSSS, en inglés) y la multiplexación por división en frecuencia ortogonal (OFDM, en inglés). El reto ha sido definir las características que mejor se adecuan a este enlace para poder aprovechar la diversidad temporal y frecuencial que ofrece el canal HF.
Desde el año 2003 diversas campañas de sondeo han permitido estudiar el canal HF pero no es hasta la campaña 2009/2010 que se consigue una fotografía de la actividad ionosférica tanto nocturna como diurna. En los artículos que se presentan en esta tesis hemos extendido los estudios previos a todo el rango de frecuencias HF y hemos mostrado las diferencias entre el día y la noche. Hemos usado estos resultados de caracterización del canal para diseñar y comparar símbolos DSSS y símbolos OFDM. Ambas posibilidades han resultado ser posibles candidatas para implementar un enlace HF de baja velocidad entre la Antártida y España. Sin embargo ambas técnicas representan dos aproximaciones distintas a la implementación del módem. Mientras que DSSS consigue un buen funcionamiento a baja velocidad en escenarios con baja relación señal a ruido, OFDM consigue tasas de transmisión más altas en escenarios más benignos.<br>High Frequency (HF) radio is used by governmental and non nongovernmental agencies worldwide whenever an alternative to satellites for sky wave communication is needed: ships at sea, aircraft out of range of line-of-sight radio networks, military operations, disaster areas with communication infrastructure destroyed or distant regions lacking other communications. It offers an alternative to satellites, or a backup, for long-haul communications, thus avoiding the costs, vulnerabilities and sovereignty concerns of satellite communications.
In this thesis the HF link between the Antarctic Spanish Station Juan Carlos I in Livingston Island, South Shetlands and Spain is studied. The aim of this study is to address the impairments that affect HF propagation (i.e., signal-to-noise plus interference ratio, multipath and Doppler shift and spread) and to design the physical layer of a low rate, low power and long-haul HF link. Some proposals regarding this last issue are addressed, i.e., direct sequence spread spectrum (DSSS) and orthogonal frequency division multiplexing (OFDM). The challenge is to define the symbol characteristics that best fit the link to benefit from time and frequency diversity that offers the HF channel.
Since 2003 several transmission campaigns have allowed to study the HF channel but it is not until the 2009/2010 campaign that we have achieved a whole picture of both diurnal and nocturnal ionospheric activity. In the papers presented in this thesis we have extended the previous research to the whole range of HF frequencies and we have shown the differences on performance between day and night. We have used the results from channel characterization to design and compare the performance of DSSS and OFDM symbols. Both techniques have turned out to be possible candidates to implement a low rate HF link between Antarctica and Spain. However, both techniques stand for different approaches of the modem: DSSS achieves good performance at low data rate in low SNR scenarios, whereas OFDM achieves higher data rate in benign channels
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Gunaydin, Ezgi. "Implementation Of Software Gps Receiver." Master's thesis, METU, 2005. http://etd.lib.metu.edu.tr/upload/2/12606305/index.pdf.
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A software GPS receiver is a functional GPS receiver in software. It has
several advantages compared to its hardware counterparts. For instance,
improvements in receiver architecture as well as GPS system structure can be
easily adapted to it. Furthermore, interaction between nearby sensors can be
coordinated easily. In this thesis, a SGR (software GPS receiver) is presented
from a practical point of view. Major components of the SGR are implemented
in Matlab environment. Furthermore, some alternative algorithms are
implemented. SGR implementation is considered in two main sections namely a
signal processing section and a navigation section. Signal processing section is
driven by the raw GPS signal samples obtained from a GPS front-end of
NordNavTM R-25 instrument. The conventional and the block adjustment of
synchronizing signal (BAAS) processing methods are implemented and their
performances are compared in terms of their speed and outputs. Signal
processing section outputs raw GPS measurements and navigation data bits.
Since the output data length is insufficient in our case, navigation section input
is fed from AshtechTM GPS receiver for a moving platform and TrimbleTM GPS
Receiver for a stationary platform. Satellite position computation, pseudorange
corrections, Kalman filter and LSE (least squares estimation) are implemented
in the navigation section. Kalman filter and LSE methods are compared in
terms of positioning accuracy for a moving as well as a stationary platform.
Results are compared with the commercial GPS outputs. This comparison
shows that the software navigation section is equivalent to the commercial GPS
in terms of positioning accuracy.
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FLOHRE, NICHOLAS MATTHEW. "EXPERIMENTAL INVESTIGATION OF SPRAY ATOMIZATION PROPERTIES OF AN AIRCRAFT ENGINE SWIRL CUP." University of Cincinnati / OhioLINK, 2003. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1054322000.
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Moreau, Florian. "Évaporation et dispersion d'un spray bi-composant dans un écoulement de canal chauffé fortement turbulent : une approche expérimentale." Thesis, Toulouse, INPT, 2010. http://www.theses.fr/2010INPT0087/document.
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Cette étude s'inscrit dans le cadre de la compréhension des phénomènes ayant lieu dans les chambres de combustion aéronautiques. Ces phénomènes étant multiples et complexes, des simplifications sont nécessaires. L'étude se focalise uniquement sur l'évaporation de gouttelettes bi-composant en écoulements turbulents. De nombreux modèles d'évaporation existent mais l'influence de la turbulence dans le cas d'un spray est encore mal comprise. Alors que la turbulence augmente l'évaporation d'une goutte isolée, elle peut amener à la création d'amas de gouttes qui vont au contraire ralentir l'évaporation. Cette étude a donc pour but de fournir un certain nombre de données quantitatives permettant une meilleure compréhension de ces phénomènes et une amélioration des modèles. L'approche est expérimentale. L'objectif est de quantifier, d'une part l'évaporation et la dispersion de gouttelettes, d'autre part le mélange vapeur dans un écoulement de canal dont les caractéristiques seront connues. Afin de simplifier les conditions expérimentales, la température est moins élevée que dans le cas réel et la pression est la pression atmosphérique. De plus, les gouttelettes sont bi-composant (octane/3-pentanone). Le banc utilisé est divisé en deux parties. Sa partie supérieure est composée d'un système de génération de l'écoulement turbulent et d'un injecteur de gouttelettes. Sa partie inférieure est composée d'une veine dans laquelle l'écoulement diphasique est analysé. L'écoulement porteur est étudié sans le spray par Anémométrie Laser Doppler. L'écoulement présente une forte turbulence, des profils plats de vitesses moyennes et de f uctuations de vitesses, en zone établie. Les propriétés d'isotropie et la décroissance de la turbulence sont proches de celles obtenues en turbulence de grille. La phase dispersée est suivie à chaud à l'aide de deux méthodes : par Anémométrie Phase Doppler et par Fluorescence Laser Induite. L'Anémométrie Phase Doppler permet d'avoir accès simultanément au diamètre et à la vitesse de chaque goutte passant à travers le volume de mesure. En raison de la forte polydispersion, les comportements des gouttelettes vis à vis de la turbulence sont très différents. En revanche, l'homogénéisation est rapide quelque soit la classe de taille. La présence d'amas dont la quantité diminue en aval dans la veine est mis en avant. La Fluorescence Laser Induite mesure la quantité de molécules de 3-pentanone en phase liquide. L'évolution de la concentration liquide, des flux de masse et des amas est décrite. La Fluorescence Induite par Laser permet aussi de suivre la quantité de 3-pentanone en phase vapeur. L'évolution des prof ls radiaux et axiaux de concentration moyenne et des f uctuations de concentration est présentée. L'homogénéisation du mélange est quantifiée<br>This work aims to understand the phenomena that occur in a combustion chamber. Due to the complexity of the phenomena encountered, simplifications are made. This study only focuses on multicomponent droplet evaporation in turbulent flows. Many evaporation models exist, but the influence of turbulence on a spray is yet not well understood. On one hand, turbulence increases the droplet evaporation rate. On the other hand, it may generate clusters, in which saturation stops the process. This study aims to give a database that can be used to improve the physical understanding of the process and to improve model performances. This is an experimental approach. The objective is to measure evaporation and dispersion of droplets and vapour mixing in a well-known turbulent flow. In the simplified test case studied here, the temperature is lower than in a real case and the pressure is atmospheric. The droplets are bi-component(octane/3-pentanone). The experimental set-up is divided into two parts. The first part, at the top, consists in a turbulence flow generator and a droplet injection device. The second part is a channel in which the two- hase flow is analysed. The carrier flow is measured using Laser Doppler Anemometry. The main flow properties are : high turbulence levels, flat profiles for the mean velocity and velocity fluctuations. The turbulence decreases and isotropic properties are close to those of grid turbulence. The dispersed phase is measured using Phase Doppler Anemometry (PDA) and Laser Induced Fluorescence (LIF). The velocity and diameter of each droplet passing through the measurement volume is measured by the PDA technique. There is a large variety of droplet behaviours due to the large polydispersion and turbulence. Droplet clusters are measured. Their amounts decrease with the distance from the injector. The concentration of 3-pentanone can be measured with the LIF technique. The evolution of the liquid concentration, mass flux and droplet clusters is described. The mean vapour concentration and its fluctuations are measured along the axial and radial axis. The mixing of the vapour is characterised
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Mühlbauer, Monika. "Modelling wall interactions of a high-pressure, hollow cone spray /." Aachen : Shaker, 2009. http://d-nb.info/998456616/04.
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Zaremba, Matouš. "Vliv provozních parametrů na kvalitu rozprašování kapalin u dvou-médiových trysek." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2013. http://www.nusl.cz/ntk/nusl-230587.
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This master’s thesis deals with measurement of spray characteristics of Effervescent atomizers intended for burning waste and heavy fuels. Atomizers were tested on cold test bench by means of Phase Doppler Anemometry. Spray characteristics were evaluated for many different regimes of pressure, temperature and Gas to liquid ratio. The aim of this measurement is to compare flow regimes and their influence on the quality of spray characteristics. The theoretical part describes basic fundamental principles of liquid atomization, effervescent atomization and principles of laser diagnostic methods. The practical part is engaged with improvements in test bench and setting up and optimization of the laser measuring system. Results contain visualization of spray, velocity profiles and drop size distribution in various operating flow regimes of the jet.
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Aftel, Robert. "Effect of atomization gas properties on droplet atomization in an "air-assist" atomizer." Master's thesis, Virginia Tech, 1996. http://hdl.handle.net/10919/32599.
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<p>Air, nitrogen, argon and carbon dioxide were used as the atomizing gas in an 'air-assist' spray nozzle to determine the effect of these gases on mean droplet size, number density, velocity and their distributions in kerosene fuel spays and spray flames using a two dimensional phase Doppler interferometer. Data have been obtained with these atomizing gases using a base, air assisted case as a reference, since this is the most commonly used atomizing fluid in almost all applications. Comparisons were made between the gases on a mass and momentum flux basis. Both burning and nonburning sprays were investigated. The results show significant differences in atomization characteristics from the atomizer with different gases and under conditions of constant mass and momentum flux of the gas. The results also show that the presence of oxygen in the air atomized sprays assists in the combustion process, since it produces smaller and faster moving droplets, especially at locations near to the nozzle exit. In nonburning sprays, droplets had similar size and velocity. Lighter gases such as nitrogen more effectively atomized the fuel in comparison to the denser gases. Argon and carbon dioxide produced larger, slower moving droplets than air and nitrogen assisted cases in both the burning and nonburning sprays. Flame photographs revealed the argon and carbon dioxide atomized flames to have greater luminosity than air or nitrogen atomized flames.</p><br>Master of Science
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Fukumasu, Newton Kiyoshi. "Análise experimental da influência da frequência de injeção de combustível em chamas pulsadas de spray de etanol." Universidade de São Paulo, 2014. http://www.teses.usp.br/teses/disponiveis/3/3150/tde-26082015-104625/.
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E consenso que o crescente consumo de combustíveis fósseis na geração de potencia tem provocado uma maior degradação do meio ambiente. Para mitigar os efeitos adversos desse consumo, novas fontes e usos sustentáveis de energia são necessários. O uso de etanol na atual geração de motores de combustão interna demanda informações detalhadas sobre os processos de nebulização, evaporação, mistura e combustão das gotas desse combustível. Adicionalmente, novas estratégias de injeção de combustível em MCIs com injeção direta estão em desenvolvimento, como a injeção estraticada. Essa estratégia consiste na injeção de combustível em elevadas frequências durante as etapas de admissão e combustão do ciclo motor. Neste trabalho, técnicas avançadas de diagnostico a laser são utilizadas para analisar a inuência da frequência de injeção de combustível no processo de combustão de sprays pulsados de etanol, em que as chamas resultantes são estabilizadas por um swirler. A técnica de interferometria por efeito Doppler (PDI) foi utilizada para medir o diâmetro e a componente axial da velocidade das gotas. O campo de velocidades do escoamento de ar foi avaliado pela técnica de velocimetria por imagens de partículas (PIV) em duas taxas de aquisição (7,4 Hz e 2.000 Hz) para avaliar tanto valores médios quanto rastrear estruturas coerentes no escoamento. O mesmo sistema PIV foi utilizado para identificar a posição de aglomerados de gotas pela técnica de espalhamento Mie ao longo de eventos individuais de injeção. Já a técnica de uorescência induzida por laser do radical hidroxila (LIF-OH) foi utilizada com taxa de aquisição de 4.700 Hz para rastrear a região com presença deste radical próximo ao queimador utilizado. Imagens da luminescência química espontânea foram obtidas para observar características globais das chamas. O queimador, posicionado em um ambiente aberto, e composto por um dispositivo swirler e um injetor automotivo. As frequências de injeção de 100 Hz, 250 Hz e 400 Hz foram escolhidas para as análises por produzirem chamas com características que variam desde uma chama estável e ancorada ao queimador até o comportamento similar a uma chama suspensa e instável. Etanol anidro líquido foi utilizado como combustível e fornecido ao injetor a pressão e vazão constantes para todos os casos. Os resultados indicaram que a variação na frequência de injeção produziu sprays com diferentes densidades. A menor frequência de injeção produziu um spray com maior densidade, em que as gotas formaram um aglomerado pouco sensível ao escoamento de ar na linha de centro do queimador. Esse aglomerado produz uma chama ancorada ao queimador com formato alongado e estreito. Já a maior frequência de injeção produziu um spray com menor densidade, permitindo que a dinâmica das gotas seja mais susceptível ao escoamento de ar. Essa maior inuência do escoamento de ar promoveu uma maior dispersão espacial das gotas e um processo de combustão com maior susceptibilidade a instabilidades locais do escoamento. Essas instabilidades locais foram associadas a passagem periódica de estruturas coerentes do escoamento de ar através da região de reação das chamas, produzindo uma chama com presença intermitente do radical OH e ausência de emissão de luminescência química espontânea próximo a saída do queimador.<br>The increase in consumption of petroleum-based fuels promotes environmental degradation and, to mitigate the adverse effects of this consumption, new sustainable sources and uses of energy are required. The use of ethanol as an option to conventional fuels on current generation of engines and gas turbines requires detailed information on atomization, evaporation, mixture and combustion processes of ethanol droplets. In addition, new strategies to fuel injection in ICEs are being developed, such as the stratied fuel injection. In this strategy, fuel is injected in higher injection frequencies along the air intake and combustion phases of the engine cycle. In this work, advanced techniques of laser diagnostic are applied to analyze the inuence of fuel injection frequency on the behavior of the combustion process of pulsed ethanol sprays, in which the resulting ames are stabilized by a swirler. The Phase Doppler Interferometry (PDI) technique is applied to measure both diameter and axial velocity of droplets produced by the injector under different conditions of injection frequency. The velocity eld of the airow is evaluated by the Particle Image Velocimetry (PIV) using two repetition rates (7,4 Hz and 2.000 Hz) to evaluated both mean values and to track coherent structures in the ow. The PIV equipment is also used to evaluate the position of droplet groups by Mie scattering during the individual injection events. A high repetition rate (4.700 Hz) Laser Induced Fluorescence of hydroxyl radical (LIF-OH) system is applied to track the region with presence of OH in a vertical plane near the exit of the burner. Images of spontaneous chemical luminescence are acquired to analyze general aspects of the ames. The burner consists on a swirler and an automotive injector and is positioned in an open space with quiescent air. The analyzed injection frequencies are 100 Hz, 250Hz and 400 Hz, presenting characteristics ranging from a stable anchored ame to a lifted-like unstable ame. Liquid anhydrous ethanol is delivered to the injector with constant pressure and ow rate for all cases. Results show different spray densities produced by the change in the injection frequency. The case with lower injection frequency produced higher spray densities, in which the formation of large groups of droplets prevents the inuence of the recirculating airow on droplet dynamics. This case presented an anchored, elongated, narrow and stable ame. The case with higher injection frequency produced lower spray densities, in which droplet dynamics are more susceptible to the velocities of the airow. This inuence of the airow promotes spatial dispersion of droplets, been more prone to instabilities on the local combustion process. These local instabilities are associated to the inuence of periodic coherent structures of the ow passing through the reaction zone, which leads to the intermittent presence of OH and the absence of spontaneous chemical luminescence near the injection plane of the burner.
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Boëdec, Thomas. "Caractérisation d'un spray dense et à grande vitesse par diagnostics optiques." Ecully, Ecole centrale de Lyon, 1999. http://bibli.ec-lyon.fr/exl-doc/TH_T1822_tboedec.pdf.
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Ce travail constitue une contribution à la caractérisation expérimentale d'un spray dense et à grande vitesse de type spray diesel, au moyen de diagnostics optiques, par des mesures ponctuelles - anémométrie phase doppler (PDA) - ou planes - vélocimétrie par images de particules (PIV) et traitement et analyse d'images (DIP) -. Un écoulement stationnaire est produit par décharge d'eau pressurisée à 10 MPa, à travers un orifice de diamètre 0,2 mm, débouchant dans le milieu ambiant. Grace à des mesures PDA, cinq critères définissant la transition d'un écoulement dense vers un écoulement pleinement développé (semblable à un écoulement d'air charge en particules) ont été établis, bases sur : (i) la valeur asymptotique atteinte par la vitesse moyenne axiale ; (ii) l'évolution linéaire de la masse d'air entrainée ; (iii) l'équilibre atteint par les fluctuations de vitesse ; (iv) l'évolution linéaire du déplacement carré moyen ; (v) l'évolution linéaire de l'épaisseur de mélange. L'adaptation de la PIV a l'étude de ce spray difficile a nécessité de nombreux tests sur le type d'éclairement (deux nappes laser opposées et coplanaires), sur le choix des intervalles de temps entre deux images, sur les tailles de fenêtres d'interrogation pour l'inter corrélation le DIP a fourni des résultats de granulométrie en bon accord avec ceux issus des mesures ponctuelles. Une investigation originale combinant la PIV et le DIP a permis l'étude de la vitesse des gouttes conditionnée par leurs tailles. Enfin, à partir des intensités fluorescées et diffusées, enregistrées simultanément sur deux cameras CCD, l'analyse précédente par PIV et DIP a donne des résultats encourageants sur la dynamique de la phase continue : des écarts de vitesse longitudinale entre les deux phases de l'ordre de 30 m/s ont été mesurés sur l'axe. Les perspectives majeures sont les analyses quantitatives de la vitesse du gaz conditionnée par la vitesse des gouttes ou par leur géométrie<br>The present work is a contribution to the experimental characterisation of a dense and high speed spray, by means of optical diagnostics : one-point measurements - Phase Doppler Anemometry (PDA) - and planar visualisation measurements - Particle Image Velocimetry (PIV) and Digital Image Processing (DIP) -. A steady state spray is produced by discharge of pressurised water at 10 MPa through a 0. 2 mm diameter hole. The spray discharges into quiescent air, at atmospheric pressure and ambient temperature. With PDA measurements, five criteria defining the transition from a dense flow to a fully developped flow (similar to an airjet laden with droplets) have been established, based on : (i) the asymptote reached by the mean velocity on the axis ; (ii) the linear evolution of the air entrainment ; (iii) the equilibrium reached by the fluctuating velocity ; (iv) the linear evolution of the mean-squared displacement ; (v) the linear evolution of the integral thickness. The adaptation of PIV to the study of this dense spray necessitates numerous preliminary experiments concerning the illumination of the droplets (two opposite coplanar laser sheets), the choice of time interval between two images, the interrogation spot size for the cross-correlation process. . . DIP gives droplets size results which are in good agreement with the ones issued from the PDA measurements. An original investigation combining PIV and DIP allows to study the droplets velocity (10 to 100 m/s) conditioned by their size (a few um). Finally, with the fluoresced and diffused light simultaneously recorded on two CCD cameras, the previous analysis by PIV and digital image treatment gives encouraging results on the continuous phase dynamic : differences in longitudinal velocity of about 30 m/s between the two phases were measured on the axis. Future prospects are the quantitative analyses of the gas velocity conditioned by droplets velocity or droplets geometry
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Shang, Lei, and lei shang@ieee org. "Modelling of Mobile Fading Channels with Fading Mitigation Techniques." RMIT University. Electrical and Computer Engineering, 2006. http://adt.lib.rmit.edu.au/adt/public/adt-VIT20061222.113303.
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This thesis aims to contribute to the developments of wireless communication systems. The work generally consists of three parts: the first part is a discussion on general digital communication systems, the second part focuses on wireless channel modelling and fading mitigation techniques, and in the third part we discuss the possible application of advanced digital signal processing, especially time-frequency representation and blind source separation, to wireless communication systems. The first part considers general digital communication systems which will be incorporated in later parts. Today's wireless communication system is a subbranch of a general digital communication system that employs various techniques of A/D (Analog to Digital) conversion, source coding, error correction, coding, modulation, and synchronization, signal detection in noise, channel estimation, and equalization. We study and develop the digital communication algorithms to enhance the performance of wireless communication systems. In the Second Part we focus on wireless channel modelling and fading mitigation techniques. A modified Jakes' method is developed for Rayleigh fading channels. We investigate the level-crossing rate (LCR), the average duration of fades (ADF), the probability density function (PDF), the cumulative distribution function (CDF) and the autocorrelation functions (ACF) of this model. The simulated results are verified against the analytical Clarke's channel model. We also construct frequency-selective geometrical-based hyperbolically distributed scatterers (GBHDS) for a macro-cell mobile environment with the proper statistical characteristics. The modified Clarke's model and the GBHDS model may be readily expanded to a MIMO channel model thus we study the MIMO fading channel, specifically we model the MIMO channel in the angular domain. A detailed analysis of Gauss-Markov approximation of the fading channel is also given. Two fading mitigation techniques are investigated: Orthogonal Frequency Division Multiplexing (OFDM) and spatial diversity. In the Third Part, we devote ourselves to the exciting fields of Time-Frequency Analysis and Blind Source Separation and investigate the application of these powerful Digital Signal Processing (DSP) tools to improve the performance of wireless communication systems.
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Friedman, Jacob A. "Investigating the interaction of an annular air jet with a spray flame using phase-Doppler interferometry and laser-induced fluorescence." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0006/NQ30609.pdf.
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Ďurdina, Lukáš. "Stanovení charakteristik spreje pomocí optických měřících metod." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2012. http://www.nusl.cz/ntk/nusl-230349.
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Diplomová práce se zabývá měřením charakteristik sprejů dvou tlakových vířivých trysek pro spalovací komoru malého turbínového motoru na zkušebním stavu za studena pomocí metod Particle Image Velocimetry (PIV) a fázové Dopplerovské anemometrie (PDA). Cílem měření bylo stanovit a porovnat charakteristiky sprejů obou trysek. Výsledky měření mají objasnit rozdílnost chování trysek za provozu a možný dopad na proces spalování. Úvodní teoretická část pojednává o základních fyzikálních principech atomizace kapalin, konstrukci a oblasti uplatnění tlakových vířivých trysek a o principech laserových diagnostických metod použitých při experimentálním měření. Nasledující část popisuje návrh a montáž zkušební trati a dalších zařízení navržených pro experimentální měření v této práci. Experimentální část se zabývá nastavením parametrů měřícího systému a zpracováním dat. Výsledky měření zahrnují vektorová rychlostní pole, axiální rychlostní profily a distribuce velikosti kapek pro různé provozní podmínky obou trysek.
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Malý, Milan. "Experimentální studie vlastností spreje a funkčnosti malých tlakových vířivých trysek." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2016. http://www.nusl.cz/ntk/nusl-254386.
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Diplomová práce se zabývá experimentální studií vlastností spreje z několika malých tlakových vířivých trysek používaných ve spalovacích komorách proudových motorů. Po desetiletí byla snaha zlepšit jejich rozprašovací charakteristiky a stále jsou možnosti, které nebyly téměř prozkoumány. Výzkum byl proveden za použití různých geometrií jednotlivých dílů trysky za účelem zjištění jejich vlivu na sprej. Byl použit různý počet vstupních portů (2, 3 a 4), různé vířivé komůrky (kulová, kuželová, konvexní, nízká kuželová) a rozdílné návrhy obtokového otvoru (osové, mimosové). Důraz byl kladen na posouzení stability spreje, kde pulzující sprej negativně ovlivňuje provozní charakteristiky spalovací komory. Vlastnosti spreje byly proměřeny fázovým dopplerovským analyzátorem, cirkulární homogenita byla hodnocena mechanickým paternátorem a rozpad kapaliny byl vizualizován pomocí jednoduchého laserového stínografu.
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Delconte, Alain. "Fluorescence induite par laser multibande appliquée à la mesure de température dans les milieux complexes." Thesis, Vandoeuvre-les-Nancy, INPL, 2009. http://www.theses.fr/2009INPL062N/document.
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La fluorescence induite par laser multibande est une technique non intrusive permettant d’accéder à la température de la phase liquide dans des milieux complexes. L’application de cette technique dans des liquides monophasiques où le chemin optique est variable (produit de la concentration moléculaire du traceur et de la distance dans le milieu liquide entre le volume de mesure et l’optique de détection) a été considérée. Le rapport des intensités de fluorescence collectées sur deux bandes spectrales permet de s’affranchir de la concentration en traceur fluorescent, de l’intensité laser incidente et du volume de mesure. Une troisième bande spectrale de détection permet de prendre en compte le terme de ré-absorption de la fluorescence dans le cas de chemins optiques non-négligeables et variables. Puis l’application de la technique à la mesure de la température de la phase liquide d’un spray est présentée. Un traitement spécifique du signal a été développé afin de tenir compte de la nature aléatoire du signal de fluorescence liée à la présence de gouttes dans le volume de mesure. De plus, ce traitement a été adapté afin de rendre possible le couplage des données de fluorescence avec des mesures granulométriques effectuées par la technique phase Doppler dans la perspective finale d’obtenir des températures de goutte par classe de taille. Cependant plusieurs phénomènes perturbateurs ont été mis en évidence : - une dépendance inattendue et non linéaire à la taille de goutte du rapport des intensités de fluorescence collectées sur deux bandes spectrales. - une forte diffusion de la lumière laser incidente par le nuage de gouttelettes induit une fluorescence bien au delà de la zone d’excitation laser. Cette fluorescence parasite est néanmoins détectée dans la profondeur de champ du dispositif optique et se conjugue avec l’effet non-linéaire de la taille des gouttes. Une stratégie de correction de ces différents phénomènes est proposée et une expérience de validation est réalisée sur un spray chauffé injecté dans une cellule saturée en vapeur<br>Multiband laser-induced fluorescence is a non-intrusive technique able to provide a measurement of the liquid phase of complex media. The application of this technique in single phase liquids, with a variable optical path (product of the fluorescent tracer molecular concentration by the distance between the probe volume and the collection optics in the liquid) was considered. The ratio of the fluorescence intensities collected on two spectral bands allows removing the influence of the fluorescence tracer concentration, incident laser intensity and probe volume. A third spectral band of detection is used to take into account the re-absorption of the fluorescence in the case of non negligible and variable optical paths. Then, the application of this technique to the measurement of the temperature of the liquid phase of a spray is presented. A specific data processing was developed in order to take into account the random presence of droplets in the probe volume. Moreover, the processing was adapted to achieve combined fluorescence and droplet size measurements using the phase Doppler technique. The overall foreseen goal is to measure temperature per droplet size class. However, several disturbing phenomena were highlighted: - an unexpected non-linear dependence on the droplet size of the ratio of the fluorescence intensities collected on two spectral bands, - a strong incident laser light scattering by the droplets cloud, which induces a fluorescence beyond the excitation zone. This fluorescence is also collected in the depth of field of the optical device and combines with the non-linear size dependence. A correction strategy of these phenomena was implemented and a validation experiment on a heated spray injected in a vapour-saturated cell was performed
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Delay, Guillaume Bazile Rudy Charnay Georges. "Analyse des écoulements transitoires dans les systèmes d'injection directe essence effets sur l'entraînement d'air instationnaire du spray /." Toulouse : INP Toulouse, 2006. http://ethesis.inp-toulouse.fr/archive/00000053.
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Torrent, Martí Xavier. "Advances on spray drift assessment in 3d crops." Doctoral thesis, Universitat de Lleida, 2020. http://hdl.handle.net/10803/673105.
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Els productes fitosanitaris són encara imprescindibles per combatre les plagues i malalties que afecten als cultius, i garantir així la producció d'aliments i altres matèries primeres vegetals. El principal efecte no desitjat, associat a l'ús de fitosanitaris, és la contaminació produïda per la deriva (quantitat de producte fitosanitari que es transportat més enllà dels límits de l’àrea tractada a través de corrents d’aire). Aquest fenomen es produeix per via aèria, afectant majoritàriament transeünts i residents locals, i també per sedimentació, contaminant cursos d’aigua, fauna, flora i altres cultius propers. En general, la deriva generada en cultius arboris (cultius 3D) és molt més notòria que en el cas dels cultius extensius (cultius 2D). Per això, es requereixen accions específiques per mitigar el risc potencial que suposen els tractaments de productes fitosanitaris en els cultius 3D (fruiters, vinya, cítrics, olivera i ametller, principalment).
En la línia de l’exposat, aquest treball té com a principal objectiu aprofundir en l'estudi i avaluació de la deriva a la Zona Sud d’Europa, on es situa el 90% de la superfície europea destinada a cultius 3D. Amb aquest objectiu, s'han utilitzat tres mètodes indirectes (anàlisi de partícules utilitzant un làser de fase Doppler (PDPA) i dinàmica de gotes en dos túnels de vent diferents) i dos mètodes directes de mesura de la deriva en camp, un d’ells desenvolupat en el decurs de la tesi i basat en un sistema LiDAR. Els resultats obtinguts han permès validar els diferents mètodes i, per primer cop, classificar els broquets cònics utilitzats en tractaments de cultius 3D d’acord amb el seu potencial de deriva. A més, s’ha establert un model de deriva adaptat als sistemes de formació dels cultius 3D a la Zona Sud d’Europa i s’han proposat dimensions adients de les bandes de seguretat (zones no tractades) a respectar en l’execució dels tractaments. Finalment, s’ha proposat una nova metodologia, basada en l’ús d’un sistema LIDAR, per l’avaluació de la deriva en condicions de camp.<br>Los productos fitosanitarios son todavía imprescindibles para combatir las plagas y enfermedades que afectan a los cultivos, y garantizar así la producción de alimentos y otras materias primas vegetales. El principal efecto no deseado, asociado al uso de fitosanitarios, es la contaminación producida por la deriva (cantidad de producto fitosanitario que es transportado fuera de los límites del área tratada mediante corrientes de aire). Este fenómeno se produce por vía aérea, afectando mayoritariamente transeúntes y residentes locales, y también por sedimentación, contaminando cursos de agua, fauna, flora y otros cultivos próximos. En general, la deriva generada en cultivos arbóreos (cultivos 3D) es mucho más notoria que en el caso de los cultivos extensivos (cultivos 2D). Por ello, se requieren acciones específicas para mitigar el riesgo potencial que suponen los tratamientos de productos fitosanitarios en los cultivos 3D (frutales, viña, cítricos, olivo y almendro, principalmente).
En la línea con lo expuesto, este trabajo tiene como principal objetivo profundizar en el estudio y evaluación de la deriva a la Zona Sud de Europa, donde se ubica el 90% de la superfície europea destinada a cultivos 3D. Con este objetivo, se han utilizado tres métodos indirectos (análisis de partículas utilizando un láser de fase Doppler (PDPA) y dinámica de gotas en dos túneles de viento diferentes) y dos métodos directos de medida de la deriva en campo, uno de ellos desarrollado en el transcurso de la tesis y basado en un sistema LiDAR. Los resultados obtenidos han permitido validar los diferentes métodos y, por primera vez, clasificar las boquillas cónicas utilizadas en tratamientos de cultivos 3D de acuerdo con su potencial de deriva. Además, se ha establecido un modelo de deriva adaptado a los sistemas de formación de los cultivos 3D a la Zona Sur de Europa y se han propuesto dimensiones adecuadas de las bandas de seguridad (zonas no tratadas) a respetar en la ejecución de los tratamientos. Finalmente, se ha propuesto una nueva metodología, basada en el uso de un sistema LiDAR, para la evaluación de la deriva en condiciones de campo.<br>The plant protection products (PPP) are still imperative to control pests and diseases affecting crops and to ensure the production of food and other plant raw materials. The main unwanted effect to the use of PPP is the pollution produced by spray drift (amount of PPP that is carried out of the treated area by the action of air currents during the application process). This phenomenon occurs by air, affecting mostly bystanders and local residents, and also by sedimentation, affecting water bodies, fauna, flora and other nearby crops. In general, the spray drift generated in tree crops (3D crops) tends to be more evident than in the case of field crops (2D crops). For this reason, specific actions are required to mitigate the potential risk posed by the treatments of PPP in 3D crops (mainly fruit trees, vineyard, citrus, olive and almond trees).
In line with the above, the main objective of this work is to conduct an in-depth study and evaluation of the spray drift in the Southern Zone of Europe, where 90% of the European surface intended for 3D crops is located. For this purpose, three indirect methods have been used (particle analysis using a phase Doppler laser (PDPA) and droplet dynamics in two different wind tunnels) and two direct methods for measuring spray drift in field conditions, one of them developed during the course of this dissertation, based on a LiDAR system. The results obtained have allowed to validate the different methods and, for the first time, classify the cone nozzles used in treatments of 3D crops according to their spray drift potential. Furthermore, a spray drift model adapted to the training systems of 3D crops to the EU Southern Zone has been established and suitable dimensions of the buffer zones (untreated area) have been proposed to respect in conducting the treatments. Finally, a new method has been proposed, based on the use of a LiDAR system, for the evaluation of spray drift under field conditions.
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Chishty, Wajid Ali. "Effects of Thermoacoustic Oscillations on Spray Combustion Dynamics with Implications for Lean Direct Injection Systems." Diss., Virginia Tech, 2005. http://hdl.handle.net/10919/28089.
Full textAbstract:
Thermoacoustic instabilities in modern high-performance, low-emission gas turbine engines are often observable as large amplitude pressure oscillations and can result in serious performance and structural degradations. These acoustic oscillations can cause oscillations in combustor through-flows and given the right phase conditions, can also drive unsteady heat release. This coupling has the potential to enhance the amplitude of pressure oscillations. To curb the potential harms caused by the existence of thermoacoustic instabilities, recent efforts have focused on the active suppression and even complete control of these instabilities. Intuitively, development of effective active combustion control methodologies is strongly dependent on the knowledge of the onset and sustenance of thermoacoustic instabilities. Specially, non-premixed spray combustion environment pose additional challenges due to the inherent unstable dynamics of sprays. The understanding of the manner in which the combustor acoustics affect the spray characteristics, which in turn result in heat release oscillation, is therefore, of paramount importance. The experimental investigations and the modeling studies conducted towards achieving this knowledge have been presented in this dissertation.
Experimental efforts comprise both reacting and non-reacting flow studies. Reacting flow experiments were conducted on a overall lean direct injection, swirl-stabilized combustor rig. The investigations spanned combustor characterization and stability mapping over the operating regime. All experiments were performed under atmospheric pressure condition, which is considered as an obvious first step towards providing valuable insights into more intense processes in actual gas turbine combustors. The onset of thermoacoustic instability and the transition of the combustor to two unstable regimes were investigated via phase-locked chemiluminescence imaging and measurement and phase-locked acoustic characterization. It was found that the onset of the thermoacoustic instability is a function of the energy gain of the system, while the sustenance of instability is due to the in-phase relationship between combustor acoustics and unsteady heat release driven by acoustic oscillations. The presence of non-linearities in the system between combustor acoustic and heat release and also between combustor acoustics and air through-flow were found to exist. The impact of high amplitude limit-cycle pressure on droplet breakdown under very low mean airflow and the localized effects of forced primary fuel modulations on heat release were also investigated.
The non-reacting flow experiments were conducted to study the spray behavior under the presence of an acoustic field. An isothermal acoustic rig was specially fabricated, where the pressure oscillations were generated using an acoustic driver. Phase Doppler Anemometry was used to measure the droplet velocities and sizes under varying acoustic forcing conditions and spray feed pressures. Measurements made at different locations in the spray were related to these variations in mean and unsteady inputs. The droplet velocities were found to show a second order response to acoustic forcing with the cut-off frequency equal to the relaxation time corresponding to mean droplet size. It was also found that under acoustic forcing the droplets migrate radially away from the spray centerline and show oscillatory excursions in their movement.
Non-reacting flow experiments were also performed using Time-Resolved Digital Particle Image Velocimetry to characterize modulated sprays. Frequency response of droplet diameters were analyzed in the pulsed spray. These pilot experiments were conducted to assess the capability of the system to measure dynamic data.
Modeling efforts were undertaken to gain physical insights of spray dynamics under the influence of acoustic forcing and to explain the experimental findings. The radial migration of droplets and their oscillatory movement were validated. The flame characteristics in the two unstable regimes and the transition between them were explained. It was found that under certain acoustic and mean air-flow condition, bands of high droplet densities were formed which resulted in diffusion type group burning of droplets. It was also shown that very high acoustic amplitudes cause secondary breakup of droplets.<br>Ph. D.
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Vince, Maxence. "Analyses in situ et approche paramétrique du procédé Spray Flash Evaporation pour l’élaboration d’hexolites." Electronic Thesis or Diss., Strasbourg, 2024. http://www.theses.fr/2024STRAE018.
Full textAbstract:
Les nanodiamants (NDs) font l'objet de recherches intenses dans les domaines biomédical, militaire et de la mécanique quantique. Pour produire ces NDs, le recours à la détonation d'un mélange RDX/TNT, aussi appelé hexolite, est souvent préféré. Cependant, pour produire des NDs aux propriétés physico-chimiques performantes, il est nécessaire d’avoir au préalable des particules fines d’hexolites, et des mélanges intimes et homogènes. Pour parvenir à cela, le laboratoire NS3E a développé le procédé de recristallisation par évaporation flash de spray (Spray Flash Evaporation, SFE). Cependant, l'influence des différentes conditions opératoires du procédé sur les caractéristiques physico-chimiques des particules est encore mal comprise. Améliorer cette compréhension permettrait une plus grande maîtrise des propriétés des particules recristallisées. Cette thèse vise donc, à l'aide d'analyses in situ telles que l'ombroscopie et le PDPA (Phase Doppler Particle Analyzer), à apporter des réponses. Les recherches se structurent en deux axes principaux. Le premier axe explore en profondeur les phénomènes physico-chimiques de l'évaporation flash d'un solvant (acétone) et l'impact du soluté (hexolite) sur le comportement du spray d'acétone. Le second axe porte quant à lui sur la caractérisation des particules d'hexolite, notamment en ce qui concerne leur sensibilité, leur taille et leur morphologie et les raisons qui ont conduit à de telles propriétés par rapport au comportement du spray<br>Nanodiamonds (NDs) are the subject of extensive research in biomedical, military, and quantum mechanics applications. To produce these NDs, the detonation of a RDX/TNT mixture, commonly referred to as hexolite, is frequently employed. However, to achieve NDs with high-performing physicochemical properties, it is essential to begin with finely divided hexolite particles and to ensure that the mixture is both intimate and homogeneous. In pursuit of this goal, the NS3E laboratory has developed a recrystallization process based on Spray Flash Evaporation (SFE). Despite this advancement, the influence of various operating conditions on the physicochemical characteristics of the resulting particles remains poorly understood. Gaining a deeper understanding of these influences would enable more precise control over the properties of the recrystallized particles. This thesis therefore aims to address these issues by employing in situ analytical techniques, such as shadowgraphy and Phase Doppler Particle Analysis (PDPA).The research is organized around two principal axes. The first focuses on an in-depth investigation of the physicochemical phenomena underlying the flash evaporation of a solvent (acetone) and examines how the presence of a solute (hexolite) affects the behavior of the acetone spray. The second axis centers on characterizing the resulting hexolite particles—specifically their sensitivity, size, and morphology—and elucidating the underlying reasons for these properties considering the spray’s behavior
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Delay, Guillaume. "Analyse des écoulements transitoires dans les systèmes d'injection directe essence : effets sur l'entraînement d'air instationnaire du spray." Phd thesis, Toulouse, INPT, 2005. http://oatao.univ-toulouse.fr/7367/1/delay1.pdf.
Full textAbstract:
L'objectif de cette étude est de déterminer l'effet des fluctuations de débit liquide instantané d'un injecteur sur l'entraînement d'air instationnaire d'un spray conique creux de type injection directe essence. Pour ce faire, nous utilisons plusi eurs outils, expérimentaux et numériques. Une méthode de mesure de débit liquide instantané, basée sur la modélisation physique des écoulements pulsés est utilisée. La mesure de la vitesse (Anémométrie Laser Doppler) de l'écoulement à l'axe de la conduite alimentant l'injecteur suffit pour reconstruire l'écoulement avant l'injecteur. Un logiciel de modélisation hydraulique et mécanique (AMESim) permet d'obtenir le débit liquide instantané en sortie de l'injecteur. La validation est réalisée grâce aux résultats de la méthode de reconstruction et à des mesures de pression de rampe d'injection. La Vélocimétrie par Images de Particules Fluorescentes (FPIV), adaptée aux milieux diphasiques denses, donne accès à l'écoulement d'air autour et à l'intérieur du spray cônique. Des mesures de vitesse d'air à proximité de la nappe diphasique permettent de déterminer l'entraînement d'air instationnaire du spray. En se basant sur des données de granulométrie et de vitesse du carburant en sortie de l'injecteur, l'analyse des échanges de quantité de mouvement des gouttes vers l'air permet enfin de proposer un modèle d'entraînement instationnaire fidèle aux mesures FPIV.
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Lojewski, Brandon. "A Linear Multiplexed Electrospray Thin Film Deposition System." Master's thesis, University of Central Florida, 2013. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5981.
Full textAbstract:
Liquid spray is essential to industries requiring processes such as spray coating, spray drying, spray pyrolysis, or spray cooling. This thesis reports the design, fabrication, and characterization of a thin film deposition system which utilizes a linear multiplexed electrospray (LINES) atomizer. First, a thorough review of the advantages and limitations of prior multiplexed electrospray systems leads to discussion of the design rationale for this work. Next, the line of charge model was extended to prescribe the operating conditions for the experiments and to estimate the spray profile. The spray profile was then simulated using a Lagrangian model and solved using a desktop supercomputer based on Graphics Processing Units (GPUs). The simulation was extended to estimate the droplet number density flux during deposition. Pure ethanol was electrosprayed in the cone-jet mode from a 51-nozzle aluminum LINES atomizer with less than 3% relative standard deviation in the D10 average droplet diameter as characterized using Phase Doppler Interferometry (PDI). Finally a 25-nozzle LINES was integrated into a thin film deposition system with a heated, motion controlled stage, to deposit TiO2 thin films onto silicon wafers from an ethanol based nanoparticle suspension. The resulting deposition pattern was analyzed using SEM, optical profilometry, and macro photography and compared with the numerical simulation results. The LINES tool developed here is a step forward to enabling the power of electrospray for industrial manufacturing applications in clean energy, health care, and electronics.<br>M.S.M.E.<br>Masters<br>Mechanical and Aerospace Engineering<br>Engineering and Computer Science<br>Mechanical Engineering; Miniature Engineering Systems
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Milea, Andrei-Silviu. "Experimental investigation of innovative Low NOx / low soot injection systems for spinning combustiοn technology using advanced laser diagnostics". Electronic Thesis or Diss., Normandie, 2024. http://www.theses.fr/2024NORMIR43.
Full textAbstract:
Les effets anthropogéniques sur l’environnement posent un défi majeur pour l’industrie aéronautique. Des réglementations de plus en plus strictes et la nécessité de rendre le transport aérien durable orientent les recherches actuelles vers des systèmes propulsifs innovants. Dans ce contexte, Safran Helicopter Engines développe sa technologie brevetée de combustion giratoire (SCT), visant à améliorer les performances des moteurs d’hélicoptères. Déjà implémentée sur le moteur Arrano, cette technologie est davantage optimisée pour réduire significativement les émissions de NOx et de suies. Dans le cadre du programme européen LOOPS, deux nouveaux systèmes d’injection de carburant sont étudiés : l’un conçu pour un régime riche dans une chambre RQL, et l’autre pour une combustion pauvre. Cette thèse évalue expérimentalement ces systèmes à l’aide de diagnostics laser avancés, adaptés aux environnements réactifs à haute pression. Le banc HERON, développé au CORIA, permet d’analyser leurs performances de combustion et évaluer les émissions dans des conditions représentatives des moteurs d’hélicoptères : pressions de 8 à 14 bar, températures d’entrée d’air de 570 à 750 K, et richesses de 0,6 à 1,67. Des diagrammes de stabilité de flamme sont établis, suivis d’analyses des propriétés du spray liquide par PDPA (Phase Doppler Particle Anemometry). Les champs aérodynamiques sont mesurés en conditions réactive et non-réactive par PIV (Particle Imaging Velocimetry) ultra-rapide à 10 kHz. La structure des flammes est caractérisée par PLIF-OH, tandis que la PLIF-kérosène permet d’étudier l’évaporation du carburant en détectant les mono- et di- aromatiques. Les diagnostics couplés simultanément PLIF-NO, PLIF-OH et PLIF-kérosène corrèlent les structures des flammes, les distributions des phases liquide et vapeur, et les zones de formation de NO. De même manière, la PLII (Planar Laser-Induced Incandescence) couplé avec PLIF-OH, PLIF-kérosène permets d’analyser les mécanismes de formation et d’oxydation des suies. Des méthodes spécifiques déterminent des distributions 2D des concentrations de NO, OH et des fractions volumiques de suies. Les résultats montrent une flamme asymétrique pour l’injecteur riche, avec une efficacité de combustion élevé dans la partie supérieure grâce à une injection liquide augmenté localement. Malgré des richesses élevées, les niveaux de suies restent modérés, tandis que le NO se forme principalement près de la flamme, confirmant le mécanisme thermique de Zeldovich. L’injecteur en régime pauvre présente une structure de flamme typique des flammes swirlées stratifiées, malgré la légère asymétrique. Une meilleure évaporation du carburant y favorise une combustion plus efficace, réduisant la longueur de flamme et les NO, grâce à des températures de flamme plus basses. Cependant, des niveaux modérés de suies sont également observés malgré le régime pauvre. Les conditions opératoires influencent fortement les performances. À haute pression, l’atomisation du spray est accélérée, l’angle d’expansion du spray augmente, et les zones de recirculation interne sont renforcées, modifiant la structure des flammes. L’augmentation des émissions de suies par la haute pression est observée pour l’injecteur en régime riche, gardant une richesse constante sur l’ensemble des conditions testées, tandis que les niveaux de NO restent stables. Pour l’injecteur en régime pauvre, les conditions réactives avec une richesse minimale à haute pression atténuent les effets de la pression, stabilisant la production de suies tout en réduisant les concentrations de NO. Ces résultats mettent en évidence le potentiel des deux systèmes d’injection pour optimiser les performances tout en réduisant les émissions des futurs moteurs d’hélicoptères<br>Anthropogenic effects on the environment present a major challenge for the aeronautical industry. Increasingly stringent pollution regulations and the necessity for sustainable air transport are driving the nowadays research toward innovative propulsion systems. In this context, Safran Helicopter Engines is advancing its patented Spinning Combustion Technology (SCT), aimed at improving helicopter engine performance. Already implemented in the Arrano engine, SCT is now being refined to significantly reduce NOx and soot emissions. As part of the European LOOPS program, two novel fuel injection systems are under investigation: one operating in a rich combustion regime tailored for an RQL combustion chamber and the other designed for lean combustion. The scientific activity of this thesis focuses on the experimental characterization of these injection systems using state-of-the-art laser diagnostics optimized for high-pressure reactive environments. The HERON combustion facility at CORIA enables the analysis of combustion and pollutant performance under conditions representative of helicopter engines, with pressures from 8 to 14 bar, air inlet temperatures from 570 to 750 K, and equivalence ratios ranging from 0.6 to 1.67. Initial flame stability maps are established, followed by in-depth analyses of liquid spray properties using Phase Doppler Particle Anemometry (PDPA). High-speed Particle Imaging Velocimetry (PIV) captures aerodynamic fields under reactive and non-reactive conditions at 10 kHz. Flame structures are examined via OH-PLIF fluorescence imaging, while kerosene-PLIF evaluates liquid and vapor fuel distributions, particularly probing aromatic components in Jet A-1 kerosene. Furthermore, NO-PLIF imaging, combined with OH-PLIF and kerosene-PLIF, enables spatial correlations between flame structure, fuel distribution, and NO production zones. Soot formation and oxidation mechanisms are explored through Planar Laser-Induced Incandescence Imaging (PLII), integrated with OH-PLIF and kerosene-PLIF. Specific methods are developed to obtain 2D distributions of quantitative concentrations of NO, OH and soot volume fraction. Results reveal that the rich-burn injector produces an asymmetrical flame with enhanced upper-zone combustion efficiency due to locally intensified liquid fuel injection. Moderate soot levels are observed despite high equivalence ratios, while localized NO production, primarily near the flame, is attributed to the Zeldovich thermal mechanism. Conversely, the lean-burn injector forms a flame structure characteristic of stratified swirl flames, despite the minor asymmetry. Improved fuel evaporation leads to higher combustion efficiency, shorter flame lengths, and a reduction in NO formation, attributed to lower flame temperatures. In spite of the lean combustion conditions, moderate soot levels are measured for the second injector. Operating conditions strongly influence performance. Higher pressures accelerate spray atomization, increase spray expansion angles, and strengthen internal recirculation zones, reshaping flame structures. The increase in soot production at higher pressure is particularly demonstrated by the rich-burn injector due to constant equivalence ratios across all test conditions, while NO levels remain stable. For the lean-burn injector, leaner operation at elevated pressures moderates pressure effects, maintaining consistent soot levels and reducing NO concentrations. These findings highlight the potential of both injection systems for optimizing performance and reducing emissions in future helicopter engines
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Zhang, Hong. "Doppler spread estimation in mobile fading channels." Thesis, 2007. http://library1.njit.edu/etd/fromwebvoyage.cfm?id=njit-etd2007-031.
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Tsai, Chia-Hung, and 蔡嘉鴻. "Low-complexity ML Doppler Spread Estimation for OFDM Systems." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/91485105639865188737.
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Targi, Ali Hassan M. "Doppler effects and coding performance of hybrid spread spectrum systems." Thesis, 1990. http://spectrum.library.concordia.ca/3059/1/ML56097.pdf.
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Lee, William Weiham. "Radar Space-Time Processing for Range-Folded Spread-Doppler Clutter Mitigation." Diss., 2011. http://hdl.handle.net/10161/4976.
Full textAbstract:
<p>Pulsed radars have an ambiguous relationship between range and velocity which is proportional to the pulse repetition frequency (PRF), leading to potential tradeoffs. High PRFs are necessary to avoid velocity aliasing but suffer at the expense of unambiguous range. Obscuration due to ambiguous range foldover from distant clutter echos seriously degrades target detectability. For the case of skywave HF over-the-horizon (OTH) radar, ionospheric motion causes spreading of surface clutter in Doppler space and coupled with range folded clutter, introduces the effect of so-called 'separated' spread Doppler clutter (SDC). Selection of a nonrecurrent waveform (NRWF) with a quadratic phase interpulse code has been shown to mitigate long-range SDC by folding the multi-hop returns into known disassociated Doppler regions.</p><p>Utilizing multiple receive elements, spatial processing can be preformed to exploit the correlation between spatial frequency and Doppler shift produced by ionospheric winds. Adaptive beamforming is known to provide asymptotically optimal array gain if sufficient training data is available. In highly nonstationary environments however, obtaining this asymptotic performance is difficult as neither knowledge of the target wavefront nor signal-free training data is easily obtainable for training. A blind adaptive spatial processing (BASP) technique has been proposed, combining minimum variance (MV) adaptive beamforming and blind source separation (BSS). The unique idea of BASP is the formulation of a signal-free covariance matrix from BSS clutter and noise components at a single range bin, and utilizing it in adaptive beamforming to suppress clutter.</p><p>This research explores a clutter mitigation method that will combine NRWF and BASP in order to recover targets masked by Doppler-spread surface backscatter from points beyond the radar's maximum unambiguous range while maintaining target detectability elsewhere in Doppler. Current methods for mitigating range-folded clutter, such as reducing the pulse-repetition frequency or the use of non-recurrent waveforms, suffer loss in the usable Doppler space available for target detection or a reduction in target revisit rate. The proposed research uses BSS methods to exploit the known Doppler separation afforded by NRWF in order to estimate the spatial wavefront of the clutter across a linear receive array. Spatial adaptive processing using this estimated wavefront is then used to suppress range-folded clutter at each range bin without sacrificing the radar timeline or usable Doppler space.</p><p>Simulation is conducted to understand the NRWF and its ability to separate range-folded clutter in Doppler. The BASP method is applied to the NRWF and its results demonstrate performance improvement in terms of achievable signal-to-clutter and noise ratio gain. Laboratory experimental results show the NRWF's ability to separate range-folded clutter into designed Doppler regions. BASP is then applied and demonstrated to mitigate the separated range folded clutter and recover usable Doppler space.</p><br>Dissertation
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Huang, Chun-I., and 黃俊溢. "Doppler Spread and Line-of-sight Component Estimation in Rician Fading Channels." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/31795079026047502923.
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陳彥齊. "EM-Based Algorithm for Joint Channel and Doppler Spread Estimation over Doubly-Selective Fading Channels." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/56706357504467008378.
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Chang, Ming-Jou, and 張明洲. "Pseudo-Noise Code Synchronization of Direct Sequence Spread Spectrum Systems under Doppler shift and/or Multiple Fading." Thesis, 2000. http://ndltd.ncl.edu.tw/handle/92938304440946417812.
Full textAbstract:
博士<br>國立中正大學<br>電機工程研究所<br>88<br>Four issues and solutions are investigated in the thesis with regard to the pseudo-noise (PN) code synchronization for single- and multi-carrier direct sequence spread spectrum (DS-SS) systems operating on additive white Gaussian noise (AWGN) and/or multipath fading channels.
In the first part, code tracking with code-Doppler compensation for single carrier DS-SS systems on AWGN channels is proposed. Code Doppler compensation
is introduced to the traditional noncoherent digital delay lock loop (DLL)
in addition to carrier Doppler compensation. Thanks to the code Doppler compensation, the simple-to-implement active correlation with a large correlation length can be employed to improve the loop performance. The code Doppler compensation significantly improve the loop performance with the presence of a large code Doppler.
In the second part, new tracking loop analysis with A/D quantization for single carrier DS-SS systems on AWGN channels is considered. In particular, the performance of non-coherent second-order all digital delay lock loops with the presence of Doppler shift is analyzed. A new method based on a regenerative Markov chain modeling of the tracking process is proposed with the loop A/D quantization being taken into account that has been neglected in previous analyses. Numerical results show that A/D
quantization has a significant impact on the loop performance, including loop transient responses, lock-in range, mean time to lose lock (MTLL) and mean square error (MSE). In addition, by using saddle point integration
for the evaluation of the transition probabilities of the Markov chain, MTLL and MSE is evaluated more accurately than previous methods.
In the third part, the code acquisition for multicarrier direct sequence code division multiple access (DS-CDMA) systems on multipath fading channels is investigated. For multipath fading channels, the exact analysis of code acquisition becomes difficult because of the channel memory incurred by multipath fading. In this part, a new analysis is given to accurately evaluate the mean acquisition time performance of the serial search multiple dwell code acquisition for the multicarrier DS-CDMA systems. Our analysis can take the fading correlations into account, the effects of system parameters on the acquisition performance such as carrier and user numbers, fading correlations, dwell''s number, times and thresholds can be easily evaluated, and, therefore, facilitating the design of the acquisition subsystem.
Finally, code tacking for multicarrier DS-CDMA systems on multipath fading channels is investigated. In this part, the tracking error performance of the traditional noncoherent DDLL with diversity reception is analyzed for the multicarrier DS-CDMA systems, under the effects of automatic gain control (AGC), multipath fading, and multiple access interference. AGC is used to eliminate the inherent stability problem of a DDLL. And, a new decision-directed noncoherent tracking loop based on a differentially-detected phase detector is proposed and analyzed. The new tracking loop outperforms the traditional DDLL.
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Yen, Nan-Yang, and 顏楠源. "PN Synchronization Performance Analysis of Direct-Sequence Spread-Spectrum Communication System in the Presence of Doppler Shift." Thesis, 1997. http://ndltd.ncl.edu.tw/handle/47587343241026882128.
Full textAbstract:
博士<br>國立成功大學<br>電機工程學系研究所<br>85<br>The use of direct-sequence spread-spectrum (DS-SS) in communication systems
is considered a promising technique to obtain higher bandwidth
efficiency and power efficiency,
in addition to its well-knownmerits in the field of secure communications.
However, the efficiency of a spread-spectrum system is highly
dependent on the capability of the receiver to obtain accurate
and fast synchronization between the received and the
locally generated PN codes. In severe Doppler environm
ent, such asthe low-earth-orbit (LEO) satellite communication, the effectsof D
oppler include not only the carrier frequency shift, but alsothe PN code chip
rate offset, which may result in the PN code synchronization
to be hard to accomplish. Thus, we shall investi
gate the effects of Doppler shift on the PNcode synchronization, including the
combined acquisition-trackingsynchronization loops and the digital delay lock
loops (DDLL). Moreover, we intend to findsome simple and feasible designs to
diminish the influencesof Doppler effect.
In this thesis,
we first analyze the overall acquisition performanceof the combined acqu
isition-tracking synchronization loopsin the presence of Doppler shift. Both t
he change of effectivesearch rate and the impact onthe detection probability d
ue to Doppler are taken into account. Furthermore, the influence of
the DDLL acquiring capability on the complete acquisition process is investi
gated and some numerical results are presented to
demonstratethe acquisition performance of this combined loop whichare quite di
fferent from the previous reports.
The delay lock loop is a we
ll-known technique to track the PN codes for DS-SS system.
This thesis considers discrete time analys
es of thefirst- and second-order digital delay lock loops (DDLL), and pre
sents the results of an investigation concerning the performance degradation d
ue to Doppler. The performance measures eva
luated include the pull-in capability, the steady-state timing error
probability density function (pdf),and the mean time to lose lock (MTLL).
The linear approximations are also providedand confirmed by computer
simulations.
44
Zhang, Yihai. "Intercarrier interference reduction and channel estimation in OFDM systems." Thesis, 2011. http://hdl.handle.net/1828/3462.
Full textAbstract:
With the increasing demand for more wireless multimedia applications,
it is desired to design a wireless system with higher data rate.
Furthermore, the frequency spectrum has become
a limited and valuable resource, making
it necessary to utilize the available spectrum efficiently
and coexist with other wireless systems.
Orthogonal frequency division multiplexing (OFDM)
modulation is widely used in communication systems to meet the
demand for ever increasing data rates. The major advantage of OFDM
over single-carrier transmission is its ability to deal with severe
channel conditions without complex equalization. However, OFDM systems suffer from
a high peak to average power ratio, and they are sensitive to carrier frequency offset and Doppler spread.
This dissertation first focuses on the development of intercarrier interference (ICI) reduction and signal detection
algorithms for OFDM systems over time-varying channels.
Several ICI reduction algorithms are proposed for OFDM systems over
doubly-selective channels. The OFDM ICI reduction problem over time-varying channels
is formulated as a combinatorial optimization problem based on the maximum likelihood (ML)
criterion. First, two
relaxation methods are utilized to convert the ICI reduction problem
into convex quadratic programming (QP) problems. Next, a low
complexity ICI reduction algorithm applicable to $M$-QAM signal
constellations for OFDM systems is proposed.
This formulates the ICI reduction problem as a QP problem with non-convex constraints. A
successive method is then utilized to deduce a sequence of
reduced-size QP problems. For the proposed algorithms, the QP
problems are solved by limiting the search in the 2-dimensional
subspace spanned by its steepest-descent and Newton directions to
reduce the computational complexity. Furthermore, a low-bit descent
search (LBDS) is employed to improve the system performance.
Performance results are given to demonstrate that the proposed
ICI reduction algorithms provide excellent performance with
reasonable computational complexity.
A low complexity joint semiblind
detection algorithm based on the channel correlation and noise
variance is proposed which does not require channel state information.
The detection problem is relaxed
to a continuous non-convex quadratic programming problem. Then an
iterative method is utilized to deduce a sequence of reduced-size
quadratic programming problems.
A LBDS method is also employed
to improve the solution of the derived QP problems. Results are
given which demonstrate that the proposed algorithm provides
similar performance with lower computational complexity compared to
that of a sphere decoder.
A major challenge to OFDM systems is how to obtain accurate
channel state information for coherent detection of the transmitted signals. Thus
several channel estimation algorithms are proposed for OFDM systems
over time-invariant channels.
A channel estimation method is developed to utilize
the noncircularity of the input signals to
obtain an estimate of the channel coefficients.
It takes advantage of the nonzero cyclostationary
statistics of the transmitted signals,
which in turn allows blind polynomial channel estimation using
second-order statistics of the OFDM symbol.
A set of polynomial equations are formulated based on the correlation
of the received signal which can be used to obtain an
estimate of the time domain channel coefficients.
Performance results are presented which show that the proposed algorithm
provides better performance than the least minimum mean-square error (LMMSE)
algorithm at high signal to noise ratios (SNRs), with low
computational complexity.
Near-optimal performance can be achieved with large OFDM systems.
Finally, a CS-based time-domain channel estimation method is presented
for OFDM systems over sparse channels. The channel estimation
problem under consideration is formulated as a small-scale
$l_1$-minimization problem which is convex and admits fast and
reliable solvers for the globally optimal solution. It is
demonstrated that the magnitudes as well as delays of the
significant taps of a sparse channel model can be estimated with
satisfactory accuracy by using fewer pilot tones than the channel
length. Moreover, it is shown that a fast Fourier transform (FFT)
matrix of extended size can be used as a set of appropriate basis
vectors to enhance the channel sparsity. This
technique allows the proposed method to be applicable to
less-sparse OFDM channels. In addition, a total-variation (TV)
minimization based method is introduced to provide an alternative
way to solve the original sparse channel estimation problem. The
performance of the proposed method is compared to several
established channel estimation algorithms.<br>Graduate
45
Roudini, Mehrzad. "Experimental investigation of spray characteristics of prefilming airblast atomizers." 2019. https://monarch.qucosa.de/id/qucosa%3A37723.
Full textAbstract:
Für technische Zerstäubungsprozesse wird häufig eine Flüssigkeitsmenge durch die kinetische Energie eines Hochgeschwindigkeitsgases in einem Luftstromzerstäuber in Einzeltropfen dispergiert. In einem Prefilming-Luftstromzerstäuber befindet sich die zu zerstäubende Flüssigkeit zuerst auf einer Oberfläche (Prefilming-Oberfläche) um einen dünnen Flüssigkeitsfilm zu bilden, bevor sie einem Hochgeschwindigkeitsluftstrom ausgesetzt wird. Das erste Ziel dieser Untersuchungen ist, den Zerstäubungsmechanismus der Prefilming-Zerstäuber zu verstehen und den Effekt variierender Parameter des Sprühsystems beim Zerfallsmechanismus zu ermitteln. Zerfallsregime in der Nähe des Zerstäuberauslasses wurden mittels Schattenverfahren und begleitend durch Partikelverfolgung bestimmt. Im nächsten Schritt wird die Sprühleistung des Prefilming-Luftstromzerstäubers in einer Reihe von Testbedingungen charakterisiert. Die Sprühcharakterisierung wurde mittels Phasen-Doppler-Anemometrie (PDA) durchgeführt um den Einfluss verschiedener Parameter auf die lokale Tropfengröße und Geschwindigkeit im Spray zu untersuchen. Zuletzt werden Zukunftsansätze zu Entwicklung und Design eines Prefilming-Luftstromzerstäubers aufgezeigt. Um einen einzigartigen funktionellen Zusammenhang der experimentellen Daten zu entwickeln, wurde eine Dimensionsanalyse durchgeführt. Darauffolgend zeigt der Einfluss von zwei dimensionslosen Kennzahlen unterschiedliche Sensitivitäten in Abhängigkeit vom Druckbereich und es wurde durch Anpassen der Daten eine geeigneten Korrelationsfunktion hergeteiltet.<br>A bulk of liquid dispersed into single droplets using the kinetic energy of a high-velocity gas in an air-blast atomizer is frequently employed in technical atomization processes.
In a prefilming air-blast atomizer, the atomizing liquid is primary situated on a surface (prefilming surface) to form a thin liquid film before exposing to a high-velocity air flow. The first purpose of this study is to understand atomization mechanisms close to prefilming atomizers and to determine the effect of spray system parameter variations on breakup mechanisms. Breakup regimes in the vicinity of the atomizer exit were determined using the shadowgraphy technique associated with particle tracking. In a next step, the spray performance of prefilming air-blast atomizers are characterized in a wide range of test conditions. For the spray characterization, a phase Doppler anemometry (PDA) was utilized to investigate the influence of variable parameters on the local droplet size and velocity in a spray.
Finally, prediction approaches are determined for the development and design of a prefilming air-blast atomizer. In order to develop a unique functional relationship from experimental data, a dimensional analysis has been performed. Subsequently, the influence of two main nondimensional numbers shows different sensitivities depending on the pressure range and was
quantified by fitting the data to appropriate correlation functions.
46
Doudou, Abdelkader. "ETUDE MACRO/MICROSCOPIQUE DES SPRAYS DIESEL INJECTES PAR LE SYSTEME COMMON RAIL AVEC LA TECHNIQUE D'OMBROSCOPIE ET L'ANÉMOMÈTRE PHASE DOPPLER." Phd thesis, 2007. http://tel.archives-ouvertes.fr/tel-00629877.
Full textAbstract:
Le présent travail a pour objet, l'étude macro et microscopique des sprays diesel injectés à hautes pressions par le système d'injection Common-Rail à travers un injecteur mono trou de petit diamètre dans un environnement inerte isotherme, évitant l'évaporation du combustible à pression de gaz élevée. L'étude effectuée est une contribution aux recherches, menées sur les sprays diesel complètement atomisés dès la sortie de l'injecteur, et présente une base de données solide pouvant servir entre autres à la validation des codes de calcul de simulation (computational fluid dynamics: CFD). Deux techniques sont utilisées: D'une part, la technique d'ombroscopie qui permet l'étude macroscopique du spray diesel (pénétration, angle du cône et volume du spray), et d'autre part, la technique de l'anémométrie phase Doppler (PDPA) (mesures de la vitesse et du diamètre des gouttes), utilisée pour l'étude microscopique. La combinaison des deux techniques permet une quantification de la concentration du combustible. La corrélation des paramètres macroscopiques s'ajuste parfaitement aux mesures de la pénétration après le temps de transition sans la prise en compte de l'angle du cône du spray. Cette corrélation semi-empirique ressemble à l'expression obtenue par l'analyse dimensionnelle se basant sur une forme du débit massique rectangulaire. La pénétration durant la phase de transition est modélisée par une loi linéaire en fonction du temps. La prise en compte de l'angle du cône du spray dans la corrélation améliore l'ajustement. L'angle du cône du spray est dépendant de la masse volumique du gaz. La valeur de l'angle du cône est de 36° pour le cas d'une masse volumique du gaz égale à 30 kg/m3. Pour l'étude microscopique, le spray est divisé en trois parties; le bord d'attaque "BA", la partie centrale "PC" et le bord de fuite "BF". La durée d'injection dans ce cas est ramenée à 3ms au lieu de 1.5ms pour allonger la PC du spray. Les évolutions temporelles de la vitesse moyenne et de la rms de la vitesse longitudinale des gouttes montrent des pics. Les pics de la rms de la vitesse longitudinale dans le BA sont une indication de la forte dispersion, due aux phénomènes de rattrapage de gouttes freinées par les rapides ou d'atomisation secondaire. Le pic de vitesse s'explique par un apport d'énergie de l'air entraîné par les vortex frontaux aux gouttes les plus petites. La décroissance de la vitesse longitudinale sur l'axe dans la PC du spray ressemble à celle des jets gazeux. Cependant, la décroissance de la rms de la vitesse longitudinale est plus rapide que celle des jets gazeux libres. La coalescence est effective dans toutes les parties du spray pour les pressions d'injection faibles très près de l'injecteur. Par contre, pour les pressions de l'injection élevées, la coalescence dans le BA ne se manifeste que loin de l'injecteur. La vitesse longitudinale et la concentration des gouttes ont des profils radiaux homothétiques et le coefficient de Schmidt effective est <1. Cependant, près de l'axe du spray, les vitesses sont parfois trop élevées. La distribution radiale de l'intensité de turbulence est homothétique, mais elle est similaire à celle d'un jet gazeux libre dans la zone r/r0,5<1 et élevée audelà. L'intensité de turbulence dans le BA est plus élevée que dans la PC et le BF; et elle prend des valeurs de l'ordre de 40-60%. Les pdfs de vitesse sont asymétriques (Su>0 ou Su<0) et étroites (Fu>3) ou élargies (Fu<3) dans le BA, mais elles deviennent Gaussiennes dans le reste. Cependant, les pdfs du diamètre des gouttes sont aplatis (Fd>3) et quasi-symétriques (Sd≈0) dans toutes les parties du spray. L'origine virtuelle du spray au début de l'injection est variable et se stabilise après dans l'intervalle 11-15 mm. Dans cette zone, le spray est dense et les mesures par le système PDA sont impossibles. L'angle dynamique du cône du spray est d'environ 32°. L'origine virtuelle et l'angle du cône sont indépendants de la pression d'injection.
47
Saikesava, Govindu. "Multi-connectivity for Urllc and Coexistence with Embb in Time-varying and Fading Channels." Thesis, 2022. https://etd.iisc.ac.in/handle/2005/5919.
Full textAbstract:
Ultra-reliable and low latency communications (URLLC) is a novel use case of 5G. It has challenging requirements like such as low block error rates (BLERs) and stringent latency targets. Multi-connectivity, in which multiple base stations (BSs) transmit the same data to the user, is a key technique in 5G to meet the stringent reliability requirements. URLLC data is immediately transmitted by puncturing the ongoing enhanced mobile broadband (eMBB) transmission to satisfy the latency constraint. However, this results in an increase in the BLER of the eMBB users.
We first propose a low complexity multi-connectivity MCS selection algorithm (MCMSA) to select the subset of co-operating BSs and the modulation and coding schemes (MCSs) they employ. The goal is to minimize the eMBB throughput loss while satisfying the URLLC constraints. We study two types of multi-connectivity: orthogonal transmission (OT) and joint transmission (JT). We derive tractable expressions to calculate the achievability, which is the probability that the URLLC reliability requirement can be satisfied by the multi-connectivity. We do so for flat fading and frequency-selective fading scenarios. Our results highlight the trade-offs between URLLC achievability, eMBB throughput loss, and channel state information (CSI) feedback overhead of OT and JT.
We then consider time-varying channels, in which the CSI report from the URLLC user to the BSs about the downlink channel gains becomes partially outdated by the time the BSs transmit data. We propose a novel stochastic BLER constraint for selecting MCSs at the time of transmission. We derive expressions for the conditional probability that the BLER of an MCS at the time of transmission is less than the target given the CSI fed back. These expressions enable the selection of MCS at the time transmission and meets the URLLC error target with high probability. Our results bring out the significant impact of feedback delays on reliability even at moderate Doppler spreads.