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Kumar, Pankaj. "Chaos in Pulsed Laminar Flow." Diss., Virginia Tech, 2010. http://hdl.handle.net/10919/39260.
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Fluid mixing is a challenging problem in laminar flow systems. Chaotic advection can play an important role in enhancing mixing in such flow. In this thesis, different approaches are used to enhance fluid mixing in two laminar flow systems. In the first system, chaos is generated in a flow between two closely spaced parallel circular plates by pulsed operation of fluid extraction and reinjection through singularities in the domain. A singularity through which fluid is injected (or extracted) is called a source (or a sink). In a bounded domain, one source and one sink with equal strength operate together as a source-sink pair to conserve the fluid volume. Fluid flow between two closely spaced parallel plates is modeled as Hele-Shaw flow with the depth averaged velocity proportional to the gradient of the pressure. So, with the depth-averaged velocity, the flow between the parallel plates can effectively be modeled as two-dimensional potential flow.
This thesis discusses pulsed source-sink systems with two source-sink pairs operating alternately to generate zig-zag trajectories of fluid particles in the domain. For reinjection purpose, fluid extracted through a sink-type singularity can either be relocated to a source-type one, or the same sink-type singularity can be activated as a source to reinject it without relocation. Relocation
of fluid can be accomplished using either â first out first inâ or â last out first inâ scheme. Both relocation methods add delay to the pulse time of the system. This thesis analyzes mixing in pulsed source-sink systems both with and without fluid relocation. It is shown that a pulsed source-sink system with â first out first inâ scheme generates comparatively complex fluid flow than pulsed source-sink systems with â last out first inâ scheme. It is also shown that a pulsed source-sink system without fluid relocation can generate complex fluid flow.
In the second system, mixing and transport is analyzed in a two-dimensional Stokes flow system. Appropriate periodic motions of three rods or periodic points in a two-dimensional flow are determined using the Thurston-Nielsen Classification Theorem (TNCT), which also predicts a lower bound on the complexity generated in the fluid flow. This thesis extends the TNCT -based framework by demonstrating that, in a perturbed system with no lower order fixed points, almost invariant sets are natural objects on which to apply the TNCT. In addition, a method is presented to compute line stretching by tracking appropriate motion of finite size rods. This method accounts for the effect of the rod size in computing the complexity generated in the fluid flow. The last section verifies the existence of almost invariant sets in a two-dimensional flow at finite Reynolds number. The almost invariant set structures move with appropriate periodic motion validating the application of the TNCT to predict a lower bound on the complexity generated in the fluid flow.Ph. D.
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Finnigan, Sean Matthew. "Pulsed flow ultrafiltration in baffled tubular membranes." Thesis, University of Bath, 1990. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.254875.
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Weeks, Colin. "Pulsed-flow microreactor studies of propene (Amm)oxidation." Thesis, University of Reading, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.266799.
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McCarthy, Larry K. "Steady Flow and Pulsed Performance Trends of High Concentration DMFCs." Thesis, Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/10434.
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Direct Methanol Fuel Cells (DMFCs) are a promising source of energy due to their potentially high energy density, facilitated fuel delivery and storage, and precluded fuel processing. However, DMFCs have several challenges which need to be resolved before they can replace existing energy sources. Some of the challenges include lower power density, relatively high cost, and uncertain reliability. These issues are all promoted, at least in part, by the methanol crossover phenomenon, wherein membrane permeability allows the undesirable species transport of methanol from anode to cathode. This phenomenon also causes the requirement of dilute fuel mixtures, which is undesirable from an energy density viewpoint.
Steady flow polarization curves were first analyzed at various concentrations. An optimal concentration range was found wherein both methanol crossover and concentration losses were effectively minimized. During the study of transient phenomena, the fuel was first temporarily discontinued. It was found that a significant cell potential enhancement occurred due to anodic fuel concentration reduction and thus depleting the reactant crossover. The percentage voltage increase was considerably greater at higher concentrations. Based on the fuel discontinuation, a hydraulic pulsing operation was developed and tested. During some of these continuous pulsing schemes, fuel discontinuation did not result in an instantaneous cell potential enhancement mainly due to the internal inertia of the membrane. Nonetheless, a significant cell potential and fuel efficiency enhancement was observed. In addition, the pulse of both fuel and current density resulted in a significant power density increase.
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Castera, Philippe. "Energy coupling mechanisms in pulsed surface discharges for flow control." Thesis, Châtenay-Malabry, Ecole centrale de Paris, 2015. http://www.theses.fr/2015ECAP0041/document.
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Ce travail s'intéresse aux effets mécaniques créés par les décharges de surface et à leur efficacité comme actionneur. Une géométrie particulière d'électrodes permet de créer de manière pulsée un filament linéaire de plasma et de le chauffer très rapidement par effet Joule (à raison de plusieurs Joules en moins d'une microseconde). Ce chauffage rapide entraîne la formation d'ondes de choc qui peuvent interagir avec l'écoulement ambiant.Nous étudions le comportement électrique de la décharge de surface afin d'évaluer l'énergie déposée dans le filament de plasma par effet Joule. Pour ce faire, nous réalisons une étude paramétrique sur la configuration du circuit et nous déterminons les principaux paramètres qui pilotent la dynamique de la décharge. Différents modèles de résistance sont utilisés dans un code de simulation du circuit électrique, et leurs prédictions du courant et du dépôt d'énergie sont confrontées aux mesures expérimentales.Des mesures spectroscopiques dans différentes configurations de circuit donnent accès à certaines propriétés de la décharge comme la densité électronique, qui atteint des valeurs de 2x1018 cm-3. Le rayon du canal est également mesuré par imagerie rapide. Les ondes de chocs créées par la décharge de surface sont visualisées en imagerie Schlieren pour plusieurs configurations de circuit. Ces ondes de chocs créent une impulsion proportionnelle à l'énergie déposée dans la décharge. Nos développons un modèle de choc pour décrire la trajectoire du choc et pour calculer l'impulsion communiquée par la décharge de surface. Le modèle est en bon accord avec les mesures expérimentales et la décharge de surface a une efficacité mécanique de 0.12mNs/J pour notre configuration d'étude. Nous terminons cette étude en comparant cet actionneur potentiel avec d'autres actionneurs courants et proposons plusieurs pistes pour de futurs travauxIn this study, we investigate the mechanical effects generated by pulsed surface discharges and their efficiency as an actuator. Using a specific electrode configuration, it is possible to create a short-lived, pulsed, rectilinear plasma channel and to heat it up rapidly (several Joules in less than a microsecond) through Joule heating. This fast energy deposition causes the formation of shock waves that can then interact with the surrounding flow.We study the electrical behavior of the pulsed surface discharge to assess the energy deposited in the plasma channel through Joule heating. To do so, we perform a parametric study on the circuit configuration and identify the main parameters driving the discharge dynamics. Several resistance models are implemented in a numerical description of the electrical circuit and their predictions of the current and deposited energy are compared with experimental measurements.Spectroscopic measurements in different circuit configurations give access to some of the plasma properties such as the electron number density that can reach values up to 2x1018 cm-3. Fast imaging also gives insight into the plasma channel radius. The shock waves generated by the pulsed surface discharge in different circuit configurations are visualized through Schlieren imaging. These shock waves generate an impulse that increases linearly with the energy deposited in the discharge. We develop a shock model to describe the shock trajectory and to compute the impulse imparted by the pulsed surface discharge. The model is in good agreement with our measurements and the pulsed surface discharge is found to have a mechanical efficiency of 0.12 mNs/J for our setup configuration. We conclude this study by comparing the proposed pulsed surface discharge actuator with other common designs and offer some directions for future studies
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Nishihara, Munetake. "Low-temperature supersonic flow control using repetitively pulsed MHD force." Columbus, Ohio : Ohio State University, 2006. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1164748794.
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Baluti, Silviu Ioan. "Experimental characterization of flow dynamics of pulsed-chemical vapour deposition." Thesis, University of Canterbury. Mechanical Engineering, 2005. http://hdl.handle.net/10092/6593.
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This research is a study of the precursor mass transport, the first variable that affects the film
deposition rate, uniformity, coverage, and microstructure of resulted films on substrates
inside Chemical Vapour Deposition (CVD) reactors. The Pulsed-CVD reactant flow field
uniformities in pulse flow were compared to equivalent steady flow regimes. For mass
limited transport CVD processes this represents an important matter, as precursor flux
increase leads directly to increased deposition rates.
The objective of the research was to develop design relations and define operational
parameter ranges to achieve flow field uniformity through experimental investigations.
Metered gaseous N2 reactant quantities were injected at equal time intervals into the
continuously evacuated reactor. The resulting reactor pressure cycle crosses all the three
pressure flow regimes, from viscous, to transition and finally to molecular flow. Nondimensional
flow parameters for this unique pulse pressure flow regime were developed
from first principles and were studied for relation to design and operation of Pulsed-CVD
equipment and processes.
Because of the reactor low pressures and non-steady conditions, temperature induced
buoyancy driven flows have low effect on the flow field dynamics of the gaseous N2 flow
(low Grashof number). Thus this research into pulsed pressure flow field uniformity was
conducted for isothermal reactor conditions, without the heater powered.
For the reactor flow field uniformity determination, the naphthalene sublimation technique
has been employed. This method is usually employed in viscous flow for the determination
of the convective heat transfer coefficient through the heat and mass transfer analogy. In this
research a method was developed to use the sublimation rate of several samples placed at
different locations in the reactor volume to measure the relative convective and pressure
conditions, and thus the uniformity of the reactor flow field.
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Experiments have been run by subsequently varying the pulsing cycle length, the reactor
pressure (implicitly the injected reactant mass), and the deposition substrate geometry. The
rest of the deposition variables have been kept constant.
The experimental results show that cycle time greater than or equal to four times the reactor
molecular time constant lead to best pulse flow uniformities, and that for these cycle times
the 3D flow field uniformities in pulse flow regimes are always better than in equivalent
steady flow ones. Comparable uniformities in both flows between stacked wafer substrates
have been determined, with slightly better uniformities in pulse flow than in equivalent
steady flow experiments.
In order to determine the steady flow field uniformities inside the experimental reactor, as
well as when varying its geometrical characteristics, the gas flow was simulated using the
finite volume Computational Fluid Dynamics (CFD) method and the commercial software
Fluent 6.1.
Design and process parameters are proposed, and the reactor pressure is analytically
modelled for the pulse flow regime.
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Xu, Ling An. "Pulsed ultrasound cross correlation flowmeter for two component flow measurement." Thesis, University of Manchester, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.277230.
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Rattray, P. "Pulsed flow and time-resolved dielectric spectroscopy of electrorheological fluids." Thesis, Cranfield University, 1994. http://dspace.lib.cranfield.ac.uk/handle/1826/10508.
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Research has been undertaken into the dielectric and rheological properties of
electrorheological (ER) fluids. The fluids studied were based on acene-quinone radical
polymers made within the department dispersed in silicone oil. A commercial
poly(1ithium methacrylate) dispersion was also examined.
As a means of
probing the underlying mechanisms of the E phenomenon, the
permittivity of the fluids was measured from 12 Hz to 100 kHz under both static and
dynamic conditions. Results indicated that a interfacial polarization process was taking
place.
A series of visual observations were made of fluids under different fielding patterns.
A series of
photographs were taken that illustrated the structure formation with elapsed
time in a dilute fluid. Also photographs were taken of the final structure formed under
different field conditions. ..
To
perform permittivity measurements of the fluid when a electric field was applied,
a
high voltage biasing unit was designed, built and proved. This allowed the application
of a continuous DC electric field of up to 3 kVmm" and the permittivity to be
measured from 150 H t 100 kl-Iz. Through a series of experiments it was found that
the low
frequency permittivity increased with increasing electric field. This result was
partially explained by the Sillars model.
The fluids were also subjected to shear rates from 1500 to 60 s". Flow modified
permittivity resonances were found at the predicted frequencies. However, the resonant
frequency did not move significantly under the application of a electric field.
The
structuring process was time resolved and a model was made to predict the sealing
of the characteristic structuring time. The rheological response of the fluids when
subjected
t pulsed DC fields was examined and found to be dominated by a
instrumentational effect.
Al
experimental procedures are given along with a comprehensive examination of the
equipment. The results are discussed as they occur in terms of the models appropriate
to that
particular event.
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Fernelius, Mark H. "Effect of Full-Annular Pressure Pulses on Axial Turbine Performance." BYU ScholarsArchive, 2013. https://scholarsarchive.byu.edu/etd/3825.
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Pulse detonation engines show potential to increase the efficiency of conventional gas turbine engines if used in place of the steady combustor. However, since the interaction of pressure pulses with the turbine is not yet well understood, a rig was built to compare steady flow with pulsing flow. Compressed air is used in place of combustion gases and pressure pulses are created by rotating a ball valve with a motor. This work accomplishes two main objectives that are different from previous research in this area. First, steady flow through an axial turbine is compared with full annular pulsed flow closely coupled with the turbine. Second, the error in turbine efficiency is approximately half the error of previous research comparing steady and pulsed flow through an axial turbine. The data shows that a turbine driven by full annular pressure pulses has operation curves that are similar in shape to steady state operation curves, but with a decrease in turbine performance that is dependent on pulsing frequency. It is demonstrated that the turbine pressure ratio increases with pulsed flow through the turbine and that this increase is less for higher pulsing frequencies. For 10 Hz operation the turbine pressure ratio increases by 0.14, for 20 Hz it increases by 0.12, and for 40 Hz it increases by 0.06. It is demonstrated that the peak turbine efficiency is lower for pulsed flow when compared with steady flow. The difference between steady and pulsed flow peak efficiency is less severe at higher pulsing frequencies. For 40 Hz operation the turbine efficiency decreases by 5 efficiency points, for 20 Hz it decreases by 9 points, and for 10 Hz it decreases by 11 points. It is demonstrated that the specific power at a given pressure ratio for pulsed flow is lower than that of steady flow and that the decrease in specific power is lower for higher pulsing frequencies. On average, the difference in specific power between steady and pulsed flow is 0.43 kJ/kg for 40 Hz, 1.40 kJ/kg for 20 Hz, and 1.91 kJ/kg for 10 Hz.
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Moore, Kenneth Jay Jr. "Large Scale Visualization of Pulsed Vortex Generator Jets." Wright State University / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=wright1133809534.
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Pasumarti, Venkata-Ramya. "Large eddy simulation of heated pulsed jets in high speed turbulent crossflow." Thesis, Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/37291.
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The jet-in-crossflow problem has been extensively studied, mainly because of its applications in film cooling and injector designs. It has been established that in low-speed flows, pulsing the jet significantly enhances mixing and jet penetration.
This work investigates the effects of pulsing on mixing and jet trajectory in high speed (compressible) flow, using Large Eddy Simulation. Jets with different density ratios, velocity ratios and momentum ratios are pulsed from an injector into a crossflow.
Density ratios used are 0.55 (CH4/air), 1.0 (air/air) and 1.5 (CO2/air). Results are compared with the low speed cases studied in the past and then analyzed for high speed scaling. The simulations show that the lower density jet develops faster than a
higher density jet. This results in more jet spread for the lower density jet. Scaling for jet spread and the decay of centerline jet concentration for these cases are established, and variable density scaling law is developed and used to predict jet penetration in the far field.
In most non-premixed combustor systems, the fuel and air being mixed are at different initial temperatures and densities. To account for these effects, heated jets at temperatures equal to 540K and 3000K have been run. It has been observed that, in addition to the lower density of heated jets, the higher kinematic viscosity effects the jet penetration. This effect has been included and validated in the scaling law for the heated jet trajectory.
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Hipp, Kyle D. "Control of a Post-Stall Airfoil Using Pulsed Jets." The Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1458565037.
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DEVARAKONDA, SURENDRA BALAJI. "BIOPARTICLE SEPARATION IN NON-NEWTONIAN FLUID USING PULSED FLOW IN MICRO-CHANNELS." University of Cincinnati / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1155322288.
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Holland, Jeff F. "Nonideal and Pulsed Flow: Applying Residence Time Distributions to Stormwater Treatment Wetlands." The Ohio State University, 2003. http://rave.ohiolink.edu/etdc/view?acc_num=osu1406812534.
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D'Silva, Aecio Moura. "Techniques for integrating aquaculture with agriculture on irrigated farms: Pulsed flow culture systems." Diss., The University of Arizona, 1993. http://hdl.handle.net/10150/186245.
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The objective of this dissertation was to evaluate the feasibility for integrating aquaculture with agriculture on irrigated farms. I developed a pulsed flow culture procedure for culturing fish in irrigation ditches where water was replaced once daily. Water from the fish culture operation was than used to irrigate ornamental trees (mesquite) for sale to the nursery industry. Twelve and four tenths percent of the channel catfish survived the 90 day experiment whereas 88.5% of the tilapia survived. These differences were statistically (P < 0.05) significant and may indicate that red tilapia are better suited than channel catfish for culture in pulsed flow culture systems. Densities of 10 and 20 tilapia/m³ showed the best performance among the five densities (10, 20, 30, 50, and 70 fish/m³) tested. Water quality limited the density of fish that could be cultured in this type of pulsed flow culture system. Ammonia concentrations and levels were periodically high (5 ppm) and dissolved oxygen levels were periodically low (1.5 ppm). Each 100 meters of ditch could potentially produce between 240 kg and 420 kg of tilapia per growing season. In all treatments, the length and weight of red tilapia predicted by Santos' equation closely followed the empirical data. There was a significant difference (p ≤ 0.001) in the growth (height and stem base area) of mesquite trees irrigated with well water and those irrigated with water that was from the fish culture facility. Trees of the size produced with water from the fish facility could be sold after about six months for prices ranging from $5.50 to $8.50. Trees irrigated with well water would take twice as long to reach a marketable size as those irrigated with water used for fish culture. The integration of aquaculture with agriculture using pulsed flow culture systems seems to have the potential to increase cash flow from irrigated farms. The production of fish and ornamental trees with the same water used to irrigate agronomic crops seems biologically, technically, and economically feasible.
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LeGouguec, Helene A. "Velocity measurement with a 2 MHZ pulsed doppler ultrasound probe in normal and stenosed models of the carotid bifurcation." Thesis, Georgia Institute of Technology, 1991. http://hdl.handle.net/1853/16725.
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Faddoul, R. Y. "A high frequency ultrasound pulsed doppler system for the measurement of skin blood flow." Thesis, University of Manchester, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.355397.
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Li, Datian. "Visualisaton of dynamic flow processes using a novel pulsed multi-element hot-wire anemometer." Thesis, Robert Gordon University, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.282866.
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Lisy, Vladimir, and Jana Tothova. "Multi-pulsed free-induction NMR signal from spins diffusing in a spatially restricted flow." Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-192818.
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A multi-pulsed free-induction NMR experiment is described theoretically for spins diffusing within a cylindrical capillary. The characteristic time for the particles to move on a distance of the capillary diameter is smaller or comparable to the time interval between the applied 90° rf pulses and the relaxation times entering the Bloch equations. In this case the
spin diffusion is restricted and the classical solutions of these equations for unbounded media are not applicable. We have calculated the mean magnetization in the cross-section of the capillary after any of the rf pulses and found the induced NMR signal within the Bloch-Torrey-Stejskal theory for spins reflected at boundaries. The problem is extended by considering a possible macroscopic (plug and Poiseuille) flow of the fluid inside a capillary. It is found that with the increase of the rf pulse number, the maxima of the observed signals do not decay to zero but converge to a nonzero value. The proposed theory thus seems to be suitable for the description of experiments on systems rapidly relaxing due to diffusion and flow.
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Aval, Sattar Motedayen. "A study of pulsed sprays in a high pressure and temperature gas cross flow." Thesis, University of Manchester, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.333238.
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Lisy, Vladimir, and Jana Tothova. "Multi-pulsed free-induction NMR signal from spins diffusing in a spatially restricted flow." Diffusion fundamentals 9 (2009) 6, S. 1-10, 2009. https://ul.qucosa.de/id/qucosa%3A14144.
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A multi-pulsed free-induction NMR experiment is described theoretically for spins diffusing within a cylindrical capillary. The characteristic time for the particles to move on a distance of the capillary diameter is smaller or comparable to the time interval between the applied 90° rf pulses and the relaxation times entering the Bloch equations. In this case the
spin diffusion is restricted and the classical solutions of these equations for unbounded media are not applicable. We have calculated the mean magnetization in the cross-section of the capillary after any of the rf pulses and found the induced NMR signal within the Bloch-Torrey-Stejskal theory for spins reflected at boundaries. The problem is extended by considering a possible macroscopic (plug and Poiseuille) flow of the fluid inside a capillary. It is found that with the increase of the rf pulse number, the maxima of the observed signals do not decay to zero but converge to a nonzero value. The proposed theory thus seems to be suitable for the description of experiments on systems rapidly relaxing due to diffusion and flow.
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Okulan, Nihat. "Fabrication and Characterization of a Pulsed MEMS-based Micro Flow Sensor for Microfluidic Applications." University of Cincinnati / OhioLINK, 2000. http://rave.ohiolink.edu/etdc/view?acc_num=ucin971724680.
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Bellis, Stephen John. "VLSI implementation of a spectral estimator for use with pulsed ultrasonic blood flow detectors." Thesis, Bangor University, 1996. https://research.bangor.ac.uk/portal/en/theses/vlsi-implementation-of-a-spectral-estimator-for-use-with-pulsed-ultrasonic-blood-flow-detectors(aada8831-f06d-4e23-94d6-341d021a3e62).html.
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The focus of this thesis is on the design and selection of systolic architectures for ASIC implementation of the real-time digital signal processing task of Modi- fied Covariance spectral estimation. When used with pulsed Doppler ultrasound blood flow detectors, the Modified Covariance spectral estimator offers increased sensitivity in the detection of arterial disease over conventional Fourier transform based methods. The systolic model of computation is considered because through pipelining and parallel processing high levels of concurrency can be achieved to attain the nec- essary throughput for real-time operation. Systolic arrays of simple processing units are also well suited for implementation on VLSI. The versatility of the de- sign of systolic arrays using the rigorous data dependence graph methodology is demonstrated throughout the thesis by application to all sections of the spectral estimator design at both word and bit levels. Systolic array design for the model order 4 Modified Covariance spectral estima- tor, known to offer accurate estimation of blood flow mean velocity and d1stur- bance at an acceptable computational burden, is initially discussed. A variety of problem size dependent systolic arrays for real-time implementation of the fixed model order spectral estimator are designed using data dependence graph mapping methods. Optimal designs are chosen by comparison of hardware, com- munication and control costs, as well as efficiency, timing, data flow and accuracy considerations. A cost/benefit analysis, based on results from structural simula- tion of the arrays, allows the most suitable word-lengths to be chosen. Problem size independent systolic arrays are then discussed as means of coping with the huge increases in computational burden for a Modified Covariance spec- tral estimator which is programmable up to high model orders. This type of array can be used to reduce the number of PEs and increase efficiency when compared to the problem size dependent arrays and the research culminates in the proposal of a novel spiral systolic array for Cholesky decomposition.
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Xu, Hanjiang. "Measurement of fiber suspension flow and forming jet velocity profile by pulsed ultrasonic doppler velocimetry." Diss., Available online, Georgia Institute of Technology, 2005, 2003. http://etd.gatech.edu/theses/available/ipstetd-1071/.
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Siqueira, Sunni Ann. "Calculation of Time-Dependent Heat Flow in a Thermoelectric Sample." ScholarWorks@UNO, 2012. http://scholarworks.uno.edu/honors_theses/24.
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In this project, the time-dependent one-dimensional heat equation with internal heating is solved using eigenfunction expansion, according to the thermoelectric boundary conditions. This derivation of the equation describing time-dependent heat flow in a thermoelectric sample or device yields a framework that scientists can use (by entering their own parameters into the equations) to predict the behavior of a system or to verify numerical calculations. Allowing scientists to predict the behavior of a system can help in decision making over whether a particular experiment is worthy of the time to construct and execute it. For experimentalists, it is valuable as a tool for comparison to validate the results of an experiment. The calculations done in this derivation can be applied to pulsed cooling systems, the analysis of Z-meter measurements, and other transient techniques that have yet to be invented. The vast majority of the calculations in this derivation were done by hand, but the parts that required numerical solutions, plotting, or powerful computation, were done using Mathematica 8. The process of filling in all the steps needed to arrive at a solution to the time-dependent heat equation for thermoelectrics yields many insights to the behavior of the various components of the system and provides a deeper understanding of such systems in general.
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D'Andrea, Danilo. "Modelling of intra- and inter-species charged particle collisions for flow simulation in pulsed plasma thrusters." Eggenstein-Leopoldshafen Forschungszentrum Karlsruhe GmbH, 2009. http://d-nb.info/999764683/34.
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Kotze, Reinhardt. "Detailed non-Newtonian flow behaviour measurements using a pulsed ultrasound velocimetry method: Evaluation, optimisation and application." Thesis, Cape Peninsula University of Technology, 2011. http://hdl.handle.net/20.500.11838/2183.
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Thesis (DTech (Electrical Engineering))--Cape Peninsula University of Technology, 2011Ultrasonic Velocity Profiling (UVP) is both a method and a device to measure an instantaneous one-dimensional velocity profile along a measurement axis by using Doppler echography. UVP is an ideal technique since it is non-invasive, works with opaque systems, inexpensive, portable and easy to implement relative to other velocity profile measurement methods. Studies have suggested that the accuracy of the measured velocity gradient close to wall interfaces need to be improved. The reason for this is due to, depending on the installation method, distortion caused by cavities situated in front of ultrasonic transducers, measurement volumes overlapping wall interfaces, refraction of the ultrasonic wave as well as sound velocity variations. A new ultrasonic transducer, which incorporates a delay line material optimised for beam forming could reduce these problems (Wiklund, 2007). If these could be addressed, UVP could be used for the measurement of velocity profiles in complex geometries (e.g. contractions, valves, bends and other pipe fittings) where the shape of the velocity profile is critical to derive models for estimating fluid momentum and kinetic energy for energy efficient designs. The objective of this research work was to optimise the UVP system for accurate complex flow measurements by evaluating a specially designed delay line transducer and implementing advanced signal processing techniques. The experimental work was conducted at the Material Science and Technology (MST) group at the Cape Peninsula University of Technology (CPUT). This work also formed part of a collaborative project with SIK - The Swedish Institute for Food and Biotechnology. Acoustic characterisation of the ultrasonic transducers using an advanced robotic setup was done at SI K. Different concentrations of the following non-Newtonian fluids exhibiting different rheological characteristics were used for testing: carboxymethyl cellulose (CMC) solutions, kaolin and bentonite suspensions. Water was used for calibration purposes.
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Graça, Cristo dos Santos Lopes Ruano Maria da. "Investigation of real-time spectral analysis techniques for use with pulsed ultrasonic Doppler blood flow detectors." Thesis, Bangor University, 1992. https://research.bangor.ac.uk/portal/en/theses/investigation-of-realtime-spectral-analysis-techniques-for-use-with-pulsed-ultrasonic-doppler-blood-flow-detectors(f184d2a8-bde7-492a-b487-438704d3ea04).html.
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The goals of the work described here were the development of a method of selection of spectral estimation for use with pulsed Doppler ultrasonic blood flow instruments, and the use of this method to select an estimator and its implementation in a form suitable for real-time applications. A study of estimation accuracy of the mean frequency and bandwidth using a number of spectral estimators was carried out. Fourier based, parametric, and, minimum variance estimators were considered. A Doppler signal simulator was developed to allow the accuracy tests required. A method of selection of spectral estimators based on the accuracy of estimation of decisive signal parameters, under the constraint of low computational complexity has been proposed. This novel cost/benefit criterion, allows the possibility of weighting appropriate to estimator (mean frequency and bandwidth) and signal frequency importance (across the range of signal characteristics). For parametric spectral estimators, this criterion may also be used to select model order, leading to lower orders than FPE, AIC and CAT criteria. Its use led to the selection of a 4t' order modified covariance parametric method. A new version of the modified covariance method for spectral estimation of real signals was developed. This was created with a view to the parallel partitioning of the algorithm for parallel implementation on a transputer-based system, using OCCAM. A number of parallel topologies were implemented. Their performance was evaluated considering estimation of a single, and a sequence of Doppler signal segments, revealing the feasibility of these parallel implementations to be achieved in real-time.
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Thomas, Nicholas. "On the application of the Doppler effect in pulsed Doppler flowmeters and the effect of certain propagation and scattering artifacts." Thesis, King's College London (University of London), 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.297092.
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Schild, Ilissa Brooke. "Influence of Spark Energy, Spark Number, and Flow Velocity on Detonation Initiation in a Hydrocarbon-fueled PDE." Thesis, Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/7527.
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Pulsed Detonation Engines (PDEs) have the potential to revolutionize fight by better utilizing the chemical energy content of reactive fuel/air mixtures over conventional combustion processes. Combustion by a super-sonic detonation wave results in a significant increase in pressure in addition to an increase in temperature. In order to harness this pressure increase and achieve a high power density, it is desirable to operate PDEs at high frequency. The process of detonation initiation impacts operating frequency by dictating the length of the chamber and contributing to the overall cycle time. Therefore a key challenge in the development of a practical PDEs is the requirement to rapidly initiate a detonation in hydrocarbon-air mixtures. This thesis evaluates the influence of spark energy and airflow velocity on this challenging initiation process. The influence of spark energy, number of sparks and airflow velocity on Deflagration-to-Detonation Transition (DDT) was studied during cyclic operation of a small-scale PDE at the General Electric Global Research Center. Experiments were conducted in a 50 mm square transitioning to cylindrical channel PDE with optical access operating with stoichiometric ethylene-air mixture. Total spark energy was varied from 250 mJ to 4 J and was distributed between one and four spark plugs located in the same axial location. Initial flame acceleration was imaged using high-speed shadowgraph and was characterized by the time to reach 20 cm from the spark plug. Measurements of detonation wave velocity and emergence time, the time it takes the detonation wave to exit the tube, was measured using dynamic pressure transducers and ionization probes. It was found that the flame front spread was faster at higher spark energies and with more spark locations. Initial flame acceleration was 16% faster for the 4-spark, 4 J case when compared to the baseline 1-spark, 1 J case. When looking at the effect of airflow on the influence of spark energy, it was found that airflow had a larger effect on emergence time at high energies, versus energies less than 1 J. Finally, for a selected case of 0.25 J spark energy and 4 sparks, the velocity of the fuel-air mixture during fill was found to have a varying influence on detonation initiation and emergence time.
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Cardoso, Jose Carlos Silva. "Investigation and implementation of real-time spectral estimation techniques for use with pulsed Doppler blood flow detectors." Thesis, Bangor University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.389743.
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David, Jean-Yves. "Modern spectral analysis techniques for blood flow velocity and spectral measurements with a 20 MHZ pulsed doppler ultrasound catheter." Thesis, Georgia Institute of Technology, 1989. http://hdl.handle.net/1853/17791.
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Lao, Ieng Kin. "Mechanistic and experimental investigations of pulsed electric field flow fractionation micro device and its applications for nanoparticle and biomolecule separation /." View abstract or full-text, 2004. http://library.ust.hk/cgi/db/thesis.pl?CENG%202004%20LAO.
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Thesis (Ph. D.)--Hong Kong University of Science and Technology, 2004.Accompanying CD-ROM contains supporting information on avi formated video clips. Includes bibliographical references (leaves 172-183). Also available in electronic version. Access restricted to campus users.
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Lim, Chin Wai. "Numerical Modelling of Transient and Droplet Transport for Pulsed Pressure - Chemical Vapour Deposition (PP-CVD) Process." Thesis, University of Canterbury. Mechanical Engineering, 2012. http://hdl.handle.net/10092/6829.
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The objective of this thesis is to develop an easy-to-use and computationally economical numerical tool to investigate the flow field in the Pulsed Pressure Chemical Vapour Deposition (PP-CVD) reactor. The PP-CVD process is a novel thin film deposition technique with some advantages over traditional CVD methods. The numerical modelling of the PP-CVD flow field is carried out using the Quiet Direct Simulation (QDS) method, which is a flux-based kinetic-theory approach. Two approaches are considered for the flux reconstruction, which are the true directional manner and the directional splitting method. Both the true directional and the directional decoupled QDS codes are validated against various numerical methods which include EFM, direct simulation, Riemann solver and the Godunov method. Both two dimensional and axisymmetric test problems are considered. Simulations are conducted to investigate the PP-CVD reactor flow field at 1 Pa and 1 kPa reactor base pressures. A droplet flash evaporation model is presented to model the evaporation and transport of the liquid droplets injected. The solution of the droplet flash evaporation model is used as the inlet conditions for the QDS gas phase solver. The droplet model is found to be able to provide pressure rise in the reactor at the predicted rate. A series of parametric studies are conducted for the PP-CVD process. The numerical study confirms the hypothesis that the flow field uniformity is insensitive to the reactor geometry. However, a sufficient distance from the injection inlet is required to allow the injected precursor solution to diffuse uniformly before reaching the substrate. It is also recommended that placement of the substrate at the reactor’s centre axis should be avoided.
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D'Andrea, Danilo [Verfasser]. "Modelling of intra- and inter-species charged particle collisions for flow simulation in pulsed plasma thrusters / Danilo D'Andrea." Eggenstein-Leopoldshafen : Forschungszentrum Karlsruhe GmbH, 2009. http://d-nb.info/999764683/34.
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Mullen, Christopher. "Radical-molecule reaction dynamics studied using a pulsed supersonic Laval nozzle flow reactor between 53 and 188 Kelvin." Diss., The University of Arizona, 2004. http://hdl.handle.net/10150/280633.
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A pulsed supersonic Laval nozzle flow reactor has been employed to investigate a variety of neutral-radical reaction processes at temperatures between 53 and 188 Kelvin. These supersonic flows simulate the conditions found in the Earth's upper atmosphere as well as certain environments in the interstellar medium and outer planetary atmospheres and thus provide direct information on the chemistry and physical processes occurring in those environments. Studies of this type, in the limit of 0 Kelvin, coupled with modern astronomical observations of planetary atmospheres and dense molecular clouds provide for a global understanding of chemistry in cold environments. With this in mind, the flow reactor was used to conduct fundamental studies involving the reactivity of hydroxyl (OH) and imidogen (NH) radical species with a variety of partners. More specifically, the reactions of OH+HBr and all of the H/D isotopic variants were explored between 53 and 135 K, with the goal of elucidating the kinetic isotope effects, both primary and secondary, for a reaction system occurring over a potential energy surface without an appreciable barrier, that demonstrates inverse temperature dependence. While not of direct astronomical importance, the reaction of OH+HBr does affect the partitioning of Br in the Earth's atmosphere, and knowledge of kinetic isotope effects helps one understand the chemistry leading to H/D fractionation observed in a variety of interstellar environments. The reactions of NH radical with NO, saturated, and unsaturated hydrocarbons were also studied between 53 and 188 Kelvin in the Laval nozzle flow reactor. These species were chosen as most are important constituents in the atmosphere of Titan, which is known to possess a rich organic chemistry. The reactions of NH with the unsaturated hydrocarbons are found to display negative temperature dependence over the window investigated, and are thought to proceed through an addition mechanism. Finally, the flow reactor was also coupled to a tunable vacuum and extreme ultraviolet frequency source based on four wave frequency mixing to allow for studies of radical species with their first electronic transitions in this frequency range. A discussion of the development, implementation, and future directions is included.
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Fernelius, Mark H. "Experimental and Computational Analysis of an Axial Turbine Driven by Pulsing Flow." BYU ScholarsArchive, 2017. https://scholarsarchive.byu.edu/etd/6548.
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Pressure gain combustion is a form of combustion that uses pressure waves to transfer energy and generate a rise in total pressure during the combustion process. Pressure gain combustion shows potential to increase the cycle efficiency of conventional gas turbine engines if used in place of the steady combustor. However, one of the challenges of integrating pressure gain combustion into a gas turbine engine is that a turbine driven by pulsing flow experiences a decrease in efficiency. The interaction of pressure pulses with a turbine was investigated to gain physical insights and to provide guidelines for designing turbines to be driven by pulsing flow. An experimental rig was built to compare steady flow with pulsing flow. Compressed air was used in place of combustion gases; pressure pulses were created by rotating a ball valve with a motor. The data showed that a turbine driven by full annular pressure pulses has a decrease in turbine efficiency and pressure ratio. The average decrease in turbine efficiency was 0.12 for 10 Hz, 0.08 for 20 Hz, and 0.04 for 40 Hz. The turbine pressure ratio, defined as the turbine exit total pressure divided by the turbine inlet total pressure, ranged from 0.55 to 0.76. The average decrease in turbine pressure ratio was 0.082 for 10 Hz, 0.053 for 20 Hz, and 0.064 for 40 Hz. The turbine temperature ratio and specific turbine work were constant. Pressure pulse amplitude, not frequency, was shown to be the main cause for the decrease in turbine efficiency. Computational fluid dynamics simulations were created and were validated with the experimental results. Simulations run at the same conditions as the experiments showed a decrease in turbine efficiency of 0.24 for 10 Hz, 0.12 for 20 Hz, and 0.05 for 40 Hz. In agreement with the experimental results, the simulations also showed that pressure pulse amplitude is the driving factor for decreased turbine efficiency and not the pulsing frequency. For a pulsing amplitude of 86.5 kPa, the efficiency difference between a 10 Hz and a 40 Hz simulation was only 0.005. A quadratic correlation between turbine efficiency and corrected pulse amplitude was presented with an R-squared value of 0.99. Incidence variation was shown to cause the change in turbine efficiency and a correlation between corrected incidence and corrected amplitude was established. The turbine geometry was then optimized for pulsing flow conditions. Based on the optimization results and observations, design recommendations were made for designing turbines for pulsing flow. The first design recommendation was to weight the design of the turbine toward the peak of the pressure pulse. The second design recommendation was to consider the range of inlet angles and reduce the camber near the leading edge of the blade. The third design recommendation was to reduce the blade turning to reduce the wake caused by pulsing flow. A new turbine design was created and tested following these design recommendations. The time-accurate validation simulation for a 10 Hz pressure pulse showed that the new turbine decreased the entropy generation by 35% and increased the efficiency by 0.04 (5.4%).
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Keshav, Saurabh. "Using Plasmas for High-Speed Flow Control and Combustion Control." The Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=osu1222026159.
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Chabert, Timothée. "Contrôle expérimental en boucle fermée du décollement sur un volet." Thesis, Paris 6, 2014. http://www.theses.fr/2014PA066011.
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Le décollement de la couche limite sur un volet est responsable de pertes de performances importantes, telles qu'une chute de la portance et une augmentation de la traînée, lors des phases de décollage et d'atterrissage d'un avion. Les aéronefs modernes sont équipés de volets dont le déploiement laisse apparaître une fente qui permet d'augmenter la portance aux faibles vitesses. Les mécanismes de déploiement associés sont lourds et complexes. Dans le but de les simplifier, l'idée consiste à supprimer la fente entre le volet et l'aile, et à la remplacer par un dispositif de contrôle du décollement de type " soufflage pulsé ". Les travaux de thèse proposent l'adaptation temps-réel en boucle fermée des paramètres du soufflage, c'est-à-dire la quantité de mouvement injectée dans l'écoulement et la fréquence de forçage. Les algorithmes de contrôle développés durant l'étude ont permis de répondre à deux objectifs, le premier étant de maintenir l'écoulement attaché lors d'un braquage progressif du volet, et le second de garantir une portance maximale malgré le décollement qui survient inévitablement aux forts angles de braquage lorsque l'apport de quantité de mouvement du contrôle est trop faible. Ces deux objectifs se classent respectivement dans le cadre du contrôle direct du décollement (flow separation control) et le cadre du contrôle des écoulements décollés (separated-flow control)Boundary layer separation from flaps is responsible for large performance losses during take-off and landing phases of an aeroplane flight, including loss of lift and drag increase. On modern aircraft, a slot located between the wing and the flap enables to increase lift at low speed. To manage this slot, flap deployment systems are very complex and heavy. It would be of interest to simplify them and replace the slot by separation control devices whose parameters such as injected momentum and forcing frequency can be adapted in closed-loop and real-time. The present study aims at developing algorithms to control those parameters in order to fulfill two objectives, the first one is to maintain the flow attached when the flap is progressively deflected, the second one is to provide maximum lift despite of massive separation at high flap deflection angles, when the momentum injected into the flow is no more sufficient to reach full reattachment. In the literature, the first objective is related to the framework of flow separation control, and the second one to the framework of separated-flow control
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STANEK, MICHAEL JOSEPH. "A NUMERICAL STUDY OF THE EFFECT OF FREQUENCY OF PULSED FLOW CONTROL APPLIED TO A RECTANGULAR CAVITY IN SUPERSONIC CROSSFLOW." University of Cincinnati / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1123778509.
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Dutta, Ashim. "Cavity Ignition and Flameholding of High Speed Fuel-Air Flows by a Repetitively Pulsed Nanosecond Discharge." The Ohio State University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=osu1313179906.
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Shamu, Tafadzwa John. "Evaluation and characterisation of an ultrasound based in-line rheometric system for industrial fluids." Thesis, Cape Peninsula University of Technology, 2015. http://hdl.handle.net/20.500.11838/2189.
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Thesis (MTech (Electrical Engineering))--Cape Peninsula University of Technology.Pulsed Ultrasound Velocimetry combined with Pressure Difference (PUV+PD) measurement is a non-invasive in-line rheometric technique which is used to analyse the complex flow properties of industrial fluids for quality control purposes. Cape Peninsula University of Technology (CPUT) and Technical Research Institute of Sweden (SP) have developed and patented a new PUV+PD based system, called Flow-Viz™. Despite this advancement, the system and ultrasound sensor technology have not been fully tested and evaluated in a wide range of industrial fluids. Acoustic characterisation tests were carried out at SP, with the aim of understanding the ultrasound beam properties after propagating through industrial stainless steel (316L) pipe walls. For these tests, a high-precision robotic XYZ-scanner and needle hydrophone setup were used. Different ultrasound sensor configurations were mounted to a stainless steel pipe while using different coupling media between the transducer-to-wedge and sensor wedge-to-pipe boundaries. The ultrasound beam propagation after the wall interface was measured by navigating the needle hydrophone within a predefined 2-dimensional spatial grid. The most suitable coupling material was determined from the acoustic characterisation, and then used in the in-line rheological characterisation tests to evaluate the performance of the Flow-VizTM rheometric unit against conventional tube viscometry. The in-line rheological tests were conducted with bentonite, kaolin and Carboxymethyl cellulose (CMC) model fluids. The flow loop used consisted of three different pipe test sections; and two concentrations of each fluid were tested in order to ascertain the consistency of the measurements. The in-line rheological tests showed good agreement (±15%) between the two techniques and Flow-VizTM was able to provide important data at very low shear rates. Acoustic characterisation indicated that variations in the beam properties were highly dependent on the acoustic couplants used to mount the sensors to the stainless steel pipes. Furthermore, the in-line results showed the effectiveness of Flow-VizTM as an industrial rheometer. The non-invasive ultrasound sensor technology, was for the first time acoustically characterised through stainless steel. This information will now be used to further optimise the unique technology for advanced industrial applications, e.g. oil drilling fields, complex cement grout and food processing applications.
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Gargano, Ronaldo Gomes. "Ultrassonografia Doppler do fluxo arterial digital associado à alteração do coxim digital dos bovinos." Universidade de São Paulo, 2015. http://www.teses.usp.br/teses/disponiveis/10/10136/tde-07102015-105755/.
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O objetivo do estudo foi avaliar, por meio da ultrassonografia bidimensional e da ultrassonografia Doppler, as inter-relações entre a alteração de espessura do coxim digital com os índices vasculares da artéria digital dorsal comum dos membros pélvicos dos bovinos. A avaliação ultrassonográfica Doppler é uma técnica não invasiva de avaliação de índices vasculares, assim como, indiretamente, do volume de sangue do leito vascular. Para isso, foram realizados exames ultrassonográficos da espessura do coxim digital e também avaliação ultrassonográfica Doppler da referida artéria de 13 vacas primíparas da raça Holandesa, em intervalos de 14 dias, durante 126 dias após o parto. Ao longo do experimento o coxim digital apresentou diminuição não significativa de espessura (p=0,1715) e apresentou forte correlação positiva com a média do escore de condição corporal (p=0,03, r=0,71). Ao longo do período avaliado, o fluxo de sangue aumentou significativamente (p<0,0001) e apresentou correlação negativa com os índices que denotam impedância ao deslocamento de sangue, isto é, índice de resistividade (p<0,0001, r=-0,34911) e pulsatilidade (p<0,0001, r=-0,5035). Além disso, realizou-se correlação entre a diferença diária do fluxo de sangue e a diferença da espessura do coxim digital para cada animal e constatou-se uma forte tendência à correlação entre as diferenças das variáveis (p=0,0515, r=-0,5729). Por meio dos resultados encontrados foi possível concluir que o escore de condição corporal teve forte correlação com a espessura do coxim digital, ao longo do estudo. Além disso, o fluxo de sangue, os índices referentes à velocidade de deslocamento das hemácias e o diâmetro da artéria aumentaram ao longo do trabalho. E, também, que a discreta diminuição do coxim digital não foi um fator que influenciou no aumento do fluxo de sangue e nos índices vascularesThe aim of this study was to evaluate, by bidimensional and pused Doppler ultrasound, the interrelationship between the changes of the thickness of digital cushion with vascular indices of the common dorsal digital artery of the hind limbs of cattle. Pused Doppler sonography is a non-invasive tool to assessment the vascular indices, as well as, the blood flow volume in vascular bed. So, were performed ultrasound exams of soft tissue thickness and also the Doppler ultrasonographic evaluation of that artery in thirteen first lactation Holstein cows and followed them up during 126 days in milk. Throughout the experiment the digital cushion showed a slight decrease without significance (p=0,1715), this also was strongly correlated with body condition score (p=0,03, r=0,71). The blood flow volume had significance increase (p<0,0001) and was negatively correlated with both impedance indices, resistance index (P<0,0001 r =-0,34911) and pulsatility index (p <0,0001 r =-0,5035). In addition, a correlation was performed with both daily differences of the blood flow and the thickness of the digital cushion for each animal and it was observed a strong tendency of correlation between the different variables (p=0,0515 r =-0,5729). Therefore, we can conclude that body condition score was strong correlated with the thickness of digital cushion, throughout the study. In addition, the blood flow volume, the velocity indices and the artery diameter increase throughout the days in milk. And, so, the slight decrease in the thickness of digital cushion was not a factor that influenced the increase of blood flow and vascular indices
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Lögdberg, Ola. "Turbulent Boundary Layer Separation and Control." Doctoral thesis, KTH, Linné Flow Center, FLOW, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-9821.
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Boundary layer separation is an unwanted phenomenon in most technical applications, as for instance on airplane wings, ground vehicles and in internal flow systems. If separation occurs, it causes loss of lift, higher drag and energy losses. It is thus essential to develop methods to eliminate or delay separation.In the present experimental work streamwise vortices are introduced in turbulent boundary layers to transport higher momentum fluid towards the wall. This enables the boundary layer to stay attached at larger pressure gradients. First the adverse pressure gradient (APG) separation bubbles that are to be eliminated are studied. It is shown that, independent of pressure gradient, the mean velocity defect profiles are self-similar when the scaling proposed by Zagarola and Smits is applied to the data. Then vortex pairs and arrays of vortices of different initial strength are studied in zero pressure gradient (ZPG). Vane-type vortex generators (VGs) are used to generate counter-rotating vortex pairs, and it is shown that the vortex core trajectories scale with the VG height h and the spanwise spacing of the blades. Also the streamwise evolution of the turbulent quantities scale with h. As the vortices are convected downstream they seem to move towards a equidistant state, where the distance from the vortex centres to the wall is half the spanwise distance between two vortices. Yawing the VGs up to 20° do not change the generated circulation of a VG pair. After the ZPG measurements, the VGs where applied in the APG mentioned above. It is shown that that the circulation needed to eliminate separation is nearly independent of the pressure gradient and that the streamwise position of the VG array relative to the separated region is not critical to the control effect. In a similar APG jet vortex generators (VGJs) are shown to as effective as the passive VGs. The ratio VR of jet velocity and test section inlet velocity is varied and a control effectiveness optimum is found for VR=5. At 40° yaw the VGJs have only lost approximately 20% of the control effect. For pulsed VGJs the pulsing frequency, the duty cycle and VR were varied. It was shown that to achieve maximum control effect the injected mass flow rate should be as large as possible, within an optimal range of jet VRs. For a given injected mass flow rate, the important parameter was shown to be the injection time t1. A non-dimensional injection time is defined as t1+ = t1Ujet/d, where d is the jet orifice diameter. Here, the optimal t1+ was 100-200.QC 20100825
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Memory, Curtis L. "Turbulent Transition Behavior in a Low Pressure Turbine Subjected to Separated and Attached-Flow Conditions." The Ohio State University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=osu1290996104.
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Dias, Ana Cristi Basile. "\"Sistemas de análises químicas em fluxo explorando multi-impulsão e detecção espectrofotométrica: aplicação a formulações farmacêuticas e a extratos de solos\"." Universidade de São Paulo, 2006. http://www.teses.usp.br/teses/disponiveis/64/64135/tde-01062007-151046/.
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Os sistemas de análises em fluxo com multi-impulsão (MP) empregam bombas solenóides como unidade propulsora de fluidos, as quais proporcionam um fluxo pulsante. Esta característica foi avaliada em função do funcionamento, operação e desempenho do sistema, das condições de mistura entre as soluções envolvidas e da dispersão da solução inserida. A avaliação geral dos sistemas MP envolveu estudos de precisão e exatidão volumétrica dos pulsos, bem como da robustez da unidade propulsora, os quais envolveram medidas gravimétricas. Ainda, dispersão envolvendo uma solução colorida como amostra foi espectrofotometricamente avaliada. Os resultados foram corroborados por meio de aplicações analíticas. Limitações quanto ao uso de bombas com maiores volumes de pulso (> 25 l) foram observadas a elevadas frequências de pulsação (> 4,0 Hz). Os volumes experimentalmente determinados concordaram com os valores esperados (erro relativo < 2,0 %). A dispersão da amostra foi menor relativamente àquela inerente a fluxo constante (sistema explorando multi-comutação, MC). O fluxo pulsante promoveu melhoria no desenvolvimento reacional devido principalmente à agitação dos elementos de fluido vizinhos. Este aspecto foi importante com relação à determinação espectrofotométrica de bromexina em fármacos. O método se fundamentou no acoplamento eletrofílico da bromexina com 3-metil-2-benzotiazolinona hidrazona (MBTH), e posterior oxidação com Ce(IV) em ambiente ácido. Boa sensibilidade analítica foi conseguida com baixo consumo de reagentes e rapidez nas análises (300 h-1). O sistema comparativo, envolvendo fluxo constante, não apresentou a mesma sensibilidade analítica. Outra aplicação foi a determinação espectrofotométrica de fosfato em extratos de solos envolvendo a formação do azul de molibdênio. Melhores resultados analíticos foram obtidos para freqüências de pulsação < 0,5 Hz, devido ao maior tempo disponível para a interação entre as espécies quínicas envolvidas. O sistema MP proposto requer menor volume de amostra (48 l) relativamente ao sistema MC (96 l), sendo caracterizado por maior frequência analítica (MP: 144 h-1; MC: 67 h-1). Os resultados referentes às análises de extratos de solos foram concordantes entre si e com relação ao método referência. A visualização de uma amostra se dispersando no fluxo pulsante foi possível empregando-se a técnica de despolarização da fluorescencia induzida por laser envolvendo Rodamina B. Os experimentos foram conduzidos sob alta (3,0 Hz) ou baixa (0,5 Hz) freqüência de pulsação na inserção de amostra, ausência ou presença de reator entre o local de introdução de amostra e o detector, e sentido horizontal ou vertical da cela de fluxo. Análise dos gráficos obtidos permitiu se vizualizar a re-distribuição de massas em função do tempo. Em geral, observou-se formação de vórtices no centro da zona de amostra e uma migração bastante intensa no sentido radial. No sentido axial, melhores interações amostra / fluxo transportador foram observadas quando a freqüência de pulsação foi baixa e em presença de um reator de 60 cm. O estabelecimento de vórtices resultou em uma mistura bastante rápida e pontual, o que foi confirmado pelas aplicações analíticasMulti-pumping flow systems (MP) utilize solenoid pumps as fluid propelling devices, which deliver pulsed flows. This feature was evaluated in relation to the design, operation and performance of the system, to the mixing conditions, and to the dispersion of the introduced solution. The general evaluation of the MP systems involved investigations about precision and accuracy of the pulse volumes, as well as the pump ruggedness. To this end, gravimetric measurements were carried out. Moreover, dispersion was evaluated by exploiting a colored solution and spectrophotometric monitoring. Results were corroborated through analytical applications. Use pumps delivering higher pulse volumes (> 25 l) was limited when the pulsation frequency was > 4.0 Hz. The experimentally measured volumes were in agreement with to the expected values (relative error < 2.0 %). Sample dispersion was lower in relation to that inherent to laminar flow (multi-commuted flow system, MC).Exploitation of pulsed flow led to a enhanced reaction development mainly due to shaking of neighboring fluid elements. This aspect was important in relation to spectrophotometric determination of bromhexine in pharmaceuticals The method was based on electrophylic coupling of bromhexine with 3-methyl-2-benzothiazolinone hydrazone (MBTH), with further oxidation by Ce(IV) under acidic medium. Analytical sensitivity was fair, reagent consumption was low and sampling rate was 300 h-1. These figures of merit were not compared with those inherent to the MC system due to the lack of sensitivity of this system. Another application was the spectrophotometric determination of phosphate in soil extracts relying the molybdenum blue formation. Best analytical results were obtained for < 0.5 Hz pulse frequency, due to the higher available time for interaction among the involved chemical species. The proposed MP system required lower sample volume (48 l) in relation to the MC system (96 l), being characterized by higher sampling rate (MP: 144 h-1; MC: 67 h-1). Analytical results related to soil extracts were in agreement between them and with the reference method. Visualization of a dispersing sample in a pulsed flow became feasible using the laser induced fluorescence technique applied to Rhodamine B, RB. Experiments were performed under high (3.0 Hz) or low (0.5 Hz) pulse frequency, optional insertion of a reactor between the injection point and detection, and vertical or horizontal positioning of the flow-cell. Analyses of the graphs obtained allowed the visualization of the mass re-distribution in function of time. In general, vortex formation at the central portion of the sample zone and a high RB migration in the radial direction, were noted. Concerning axial direction, better sample / carrier stream interactions were observed for lower pulse frequency and insertion of the 60-cm reactor. Vortex establishment led to a punctual and fast mixing, as confirmed by the analytical applications
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Sasaki, Milton Katsumi. "Comparação entre analisadores com fluxo constante ou pulsado: aplicação a amostras de relevância farmacêutica, agronômica e/ou ambiental." Universidade de São Paulo, 2015. http://www.teses.usp.br/teses/disponiveis/64/64135/tde-26012016-152115/.
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Sistemas de análises químicas em fluxo com multi-impulsão empregam bombas solenoide como unidade propulsora de fluidos, as quais proporcionam fluxos pulsados. Estes provêm um eficiente transporte radial de massas, o que garante boa homogeneização das soluções envolvidas, mesmo em situações de dispersão limitada. O objetivo principal deste trabalho foi então comparar o desempenho de metodologias envolvendo reagentes imobilizados em sistemas de análises em fluxo com fluxos constantes ou pulsados. Para isto, foram selecionadas as determinações espectrofotométricas de ácido ascórbico em produtos farmacêuticos, utilizando reator tubular de polietileno (50 cm) com MnO2(s) imobilizado, e reação com formaldoxima (0,25 mol L-1); e de carbaril em águas naturais, explorando extração líquido-líquido com xileno imobilizado em membrana de PVDF, e solução de NaOH a 0,1 mol L-1 como fluxo aceptor. Adicionalmente, compararam-se os dois tipos de fluxo em uma nova titulação em fluxo, a titulação monitorada por traçador; a determinação de acidez total em vinagres foi selecionada e utilizaram-se as titulações por injeção em fluxo e programada em triângulo, ambas empregando solução de NaOH a 0,01 mol L-1 como titulante e fenolftaleína como indicador ácido-base, com monitoramento por traçador empregando azul brilhante FCF (ca. 6 mg L-1). Na determinação de ácido ascórbico, o desempenho do sistema com fluxos pulsados foi superior àquele com fluxos constantes quanto ao limite de detecção: 0,33 contra 0,60 mg L-1 (critério 3,3 ?), e à repetibilidade: d.p.r. estimado como 2,5 contra 5,6% (n = 20); quanto à exatidão, não foi encontrada diferença estatisticamente significativa entre o método proposto e o da Farmacopeia Britânica ao nível de confiança de 95%. Na determinação de carbaril, o uso de fluxos pulsados favoreceu a extração do analito, obtendo-se uma sensibilidade 9,3% maior relativamente ao emprego de fluxos constantes, além de uma melhor linearidade da curva analítica; entretanto, o método mostrou-se susceptível a interferência de outros metilcarbamatos, o que comprometeu sua aplicação à análise de águas naturais. Na determinação de acidez total, a exploração de fluxos pulsados proporcionou menores variações da razão dos valores de absorbância relativos ao monitoramento do traçador e do indicador; não foi encontrada diferença estatística entre as titulações em fluxo propostas e o método titulométrico de referência ao nível de confiança de 95%Multi-pumping flow systems use solenoid pumps as fluid propelling devices, which deliver pulsed flows. These flows provide an efficient radial mass transport, thus good mixing conditions even in limited sample dispersion situations. The main objective of this work was then to compare the performance of methodologies involving immobilized reagents in flow systems with constant or pulsed flows. To this end, the spectrophotometric determinations of ascorbic acid in pharmaceutical products using a 50-cm polyethylene tubular reactor with immobilized MnO2(s) with further colour-forming reaction with 0.25 mol L-1 formaldoxime; and carbaryl in natural waters exploiting liquid-liquid extraction with xylene immobilized in a PVDF membrane and a 0.1 mol L-1 ¬¬NaOH solution as acceptor stream, were selected. Moreover, constant and pulsed flows were compared in relation to a novel strategy for flow titration, named tracer-monitored titration; the determination of total acidity in vinegars was selected and flow injection and triangle-programmed titrations were applied, both using a 0.01 mol L-1 NaOH solution as titrant, phenolphtalein as acid-base indicator and ca. 6 mg L-1 brilliant blue FCF as tracer. Regarding ascorbic acid determination, the pulsed flow system was superior in relation to the constant flow system for detection limit: 0.33 against 0.60 mg L-1 (3.3 ? criterion), and for repeatability: r.s.d. estimated as 2.5 against 5.6% (n = 20); in relation to accuracy, no significant differences between the proposed method and that of the British Pharmacopoeia were found at the 95% confidence level. Regarding carbaryl determination, use of pulsed flows favored the analyte extraction, leading to a 9.3% sensitivity improvement in relation to use of constant flows; besides the attainment of better linearity of the analytical curve. The method was however susceptible to interference of other methylcarbamates, thus the application to natural water analyses was impaired. Regarding total acidity determination, pulsed flows exploitation provided lower variations in the ratio of absorbance values related to the monitoring of tracer and indicator; no significant differences between the proposed titrations and the reference method were found at the 95% confidence level
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Chabert, Timothee. "Contrôle expérimental en boucle fermée du décollement sur un volet." Phd thesis, Université Pierre et Marie Curie - Paris VI, 2014. http://tel.archives-ouvertes.fr/tel-00966550.
Full textAbstract:
Le décollement de la couche limite sur un volet est responsable de pertes de performances importantes, telles qu'une chute de la portance et une augmentation de la traînée, lors des phases de décollage et d'atterrissage d'un avion. Les aéronefs modernes sont équipés de volets dont le déploiement laisse apparaître une fente qui permet d'augmenter la portance aux faibles vitesses. Les mécanismes de déploiement associés sont lourds et complexes. Dans le but de les simplifier, l'idée consiste à supprimer la fente entre le volet et l'aile, et à la remplacer par un dispositif de contrôle du décollement de type " soufflage pulsé ". Les travaux de thèse proposent l'adaptation temps-réel en boucle fermée des paramètres du soufflage, c'est-à-dire la quantité de mouvement injectée dans l'écoulement et la fréquence de forçage. Les algorithmes de contrôle développés durant l'étude ont permis de répondre à deux objectifs, le premier étant de maintenir l'écoulement attaché lors d'un braquage progressif du volet, et le second de garantir une portance maximale malgré le décollement qui survient inévitablement aux forts angles de braquage lorsque l'apport de quantité de mouvement du contrôle est trop faible. Ces deux objectifs se classent respectivement dans le cadre du contrôle direct du décollement (flow separation control) et le cadre du contrôle des écoulements décollés (separated-flow control).
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Szmigiel, Mathieu. "Etude du flux de soubassement sur la dynamique du sillage d'un corps non profilé à culot droit : Application du contrôle actif pour la réduction de traînée de véhicule industriel." Thesis, Lyon, 2017. http://www.theses.fr/2017LYSEC016/document.
Full textAbstract:
Cette thèse CIFRE est le fruit d’une collaboration entre Renault Trucks et le LMFA dans la perspective d’une évaluation de la pertinence du contrôle actif pour la réduction de traînée de véhicule industriel. Les deux principaux objectifs de ces travaux expérimentaux consistent à l’analyse de l’influence de l’écoulement de soubassement sur la dynamique du sillage et l’étude d’une stratégie de contrôle d’écoulement combinant des volets déflecteurs (positionnés sur les bords supérieurs et latéraux du culot) à des actionneurs de type jets pulsés dans l’optique d’une réduction de la traînée aérodynamique d’un corps non profilé à culot droit. Le développement du sillage pour différentes vitesses de soubassement évoluant de 10% à plus de 80% de la vitesse de l’écoulement infini amont est étudié sur une maquette simplifiée de véhicule poids lourd à l’échelle 1/43e. Des mesures de pression au culot permettent d’identifier quatre classes d’écoulement associées à des structures de sillage différentes mises en évidence par des mesures PIV 2D-3C. Le sillage de la première classe d’écoulement obtenu pour les très faibles vitesses de soubassement ressemble au sillage derrière une marche 3D. Pour des vitesses de soubassement plus élevées, l’écoulement de soubassement décolle au niveau du sol et impacte soit le culot ou soit la couche de cisaillement supérieure favorisant le développement des instabilités de type Kelvin-Helmoltz dans ce dernier cas. Enfin, la dernière classe est caractérisée par un sillage comparable à celui d’un corps d’Ahmed. L’ajout de volets déflecteurs à l’arrière du culot engendre une augmentation de la pression au culot pour l’ensemble des classes d’écoulement. Cette augmentation réside principalement dans l’effet de vectorisation de l’écoulement. Un système de contrôle actif est intégré sur une maquette 1/8e géométriquement identique à celle à l’échelle 1/43e et équipée de volets déflecteurs. Deux angles de volet supérieur sont testés afin d’obtenir en moyenne (i) un écoulement naturel attaché à la paroi du volet et (ii) un écoulement naturel détaché du volet. Par rapport au cas sans contrôle actif, des gains sur la traînée sont obtenus pour une certaine gamme de fréquence d’actionnement uniquement dans le cas (ii). Ces gains sont obtenus suite au recollement de l’écoulement sur le volet. Enfin, la robustesse des gains sur la pression au culot est testée avec succès en mettant la maquette en dérapage pour simuler un vent de traversThis PhD thesis was realized in the scope of a collaboration with Renault Trucks and the LMFA in view of an evaluation of the relevance of active flow control for the drag reduction industrial vehicle. The two main objectives of this experimental work are to analyze the impact of the underbody flow on the wake dynamics and to study a flow control strategy combining inclined flaps (located on the upper and lateral edges of the rear base) with pulsed jet actuators for reducing the aerodynamic drag of a square-back bluff body. The wake development for several underbody velocities ranging from 10% to more than 80% of the free-stream velocity is studied on a simplified truck model at scale 1 :43. Rear base pressure measurements lead to the identification of four flow classes associated with different wake structures highlighted by 2D-3C PIV measurements. The wake of the first flow class obtained for very low underbody velocities looks like that of the wake of a 3D backward facing step. For higher underbody velocities, the underbody flow is separated from the ground impaging either the rear base or the upper shear layer triggering Kelvin-Helmoltz instabilities for this last case. Finally, the fourth class is characterized by a wake comparable to that of the Ahmed body. The implementation of inclined flaps at the rear base increases the base pressure for all classes. This increase is mainly due to the vectoring effect of the flow. An active control system is integrated to a 1 :8 scale model geometrically identical to that of the 1 :43 scale model with flaps. Two upper flap angles are tested to have (i) a natural flow attached to the flap and (ii) a natural flow detached from the flap. In comparison to the case without active flow control, drag reductions are obtained only for a specific range of actuation frequencies only in case (ii). These gains are associated with the reattachment of the flow on the flap. Finally, the robustness of the pressure gains is successfully tested in crosswind conditions