Dissertations / Theses: 'DSMC'

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Piekos, Edward S. (Edward Stanley). "DSMC modeling of micromechanical devices." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/11149.

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Lunde, Dominic Charles. "A Homegrown DSMC-PIC Model for Electric Propulsion." DigitalCommons@CalPoly, 2019. https://digitalcommons.calpoly.edu/theses/2066.

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Powering spacecraft with electric propulsion is becoming more common, especially in CubeSat-class satellites. On account of the risk of spacecraft interactions, it is important to have robust analysis and modeling tools of electric propulsion engines, particularly of the plasma plume. The Navier-Stokes equations used in classic continuum computational fluid dynamics do not apply to the rarefied plasma, and therefore another method must be used to model the flow. A good solution is to use the DSMC method, which uses a combination of particle modeling and statistical methods for modeling the simulated molecules. A DSMC simulation known as SINATRA has been developed with the goal to model electric propulsion plumes. SINATRA uses an octree mesh, is written in C++, and is designed to be expanded by further research. SINATRA has been initially validated through several tests and comparisons to theoretical data and other DSMC models. This thesis examines expanding the functionality of SINATRA to simulate charged particles and make SINATRA a DSMC-PIC hybrid. The electric potential is calculated through a 7-point 3D stencil on the mesh nodes and solved with a Gauss-Seidel solver. It is validated through test cases of charged particles to demonstrate the accuracy and capabilities of the model. An ambipolar diffusion test case is compared to a neutral diffusion case and the electric field is shown to stabilize the diffusion rate. A steady state flow test case shows the simulation is able to stabilize and solve the electric potential for a plume-like scenario. It includes additional features to simplify further research including a comprehensive user manual, industry-standard version control, text file inputs, GUI control, and simple parallelism of the simulation. Compilation and execution are standardized to be simple and platform independent to allow longevity of the code base. Finally, the execution bottlenecks of linking particles to cells and particle moving were removed to reduce the simulation time by 95%.

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Palaniswaamy, Geethpriya. "DSMC multicomponent aerosol dynamics sampling algorithms and aerosol processes /." Diss., Columbia, Mo. : University of Missouri-Columbia, 2007. http://hdl.handle.net/10355/4737.

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Thesis (Ph. D.)--University of Missouri-Columbia, 2007.
The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed Dec. 12, 2007). Vita. Includes bibliographical references.

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Palharini, Rodrigo Cassinel. "Atmospheric reentry modelling using an open-source DSMC code." Thesis, University of Strathclyde, 2014. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=24375.

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Aerothermodynamic investigations of hypersonic re-entry vehicles provides crucial information to other key disciplines as structures and materials, assisting the development of efficient and lightweight thermal protection systems (TPS). Under the transitional flow regime, where chemical and thermal nonequilibrium are predominant, the most successful numerical method for such studies has been the direct simulation Monte Carlo (DSMC) numerical technique. In the present work, the solver dsmcFoam has been benchmarked against experimental, numerical, and theoretical data found in the open literature for inert and chemically reactive flows. The Quantum-Kinetic (QK) chemistry model with a full set of 19 chemical reactions has been implemented into the code and it proved to be essential in the correct prediction of the shock wave structure and heating flux to the vehicle's surface during the re-entry phase. Having implemented the QK chemistry model, the dsmcFoam solver was employed to investigate thermal protection system discontinuities. These TPS discontinuities, representative of panel-to-panel joints or the impact of micro meteorites/ice droplets, were modelled as a family of cavities with different length-to-depth ratios. The results showed that the cavity length has a significant impact on the flowfield structure and aerodynamic surface quantities distribution inside and around the cavities. In addition, for L/D = 5, the flow separates at the cavity upstream lip and attaches to the cavity bottom surface, representing a potentially catastrophic feature under rarefied gas conditions. Furthermore, the same phenomena is only observed in the continuum regime when L/D > 14.

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Masters, Nathan Daniel. "Efficient Numerical Techniques for Multiscale Modeling of Thermally Driven Gas Flows with Application to Thermal Sensing Atomic Force Microscopy." Diss., Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/11574.

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The modeling of Micro- and NanoElectroMechanical Systems (MEMS and NEMS) requires new computational techniques that can deal efficiently with geometric complexity and scale dependent effects that may arise. Reduced feature sizes increase the coupling of physical phenomena and noncontinuum behavior, often requiring models based on molecular descriptions and/or first principles. Furthermore, noncontinuum effects are often localized to small regions of (relatively) large systemsprecluding the global application of microscale models due to computational expense. Multiscale modeling couples efficient continuum solvers with detailed microscale models to providing accurate and efficient models of complete systems. This thesis presents the development of multiscale modeling techniques for nonequilibrium microscale gas phase phenomena, especially thermally driven microflows. Much of this focuses on improving the ability of the Information Preserving DSMC (IP-DSMC) to model thermally driven flows. The IP-DSMC is a recent technique that seeks to accelerate the solution of direct simulation Monte Carlo (DSMC) simulations by preserving and transporting certain macroscopic quantities within each simulation molecules. The primary contribution of this work is the development of the Octant Splitting IP-DSMC (OSIP-DSMC) which recovers previously unavailable information from the preserved quantities and the microscopic velocities. The OSIP-DSMC can efficiently simulate flow fields induced by nonequilibrium systems, including phenomena such as thermal transpiration. The OSIP-DSMC provides an efficient method to explore rarefied gas transport phenomena which may lead to a greater understanding of these phenomena and new concepts for how these may be utilized in practical engineering systems. Multiscale modeling is demonstrated utilizing the OSIP-DSMC and a 2D BEM solver for the continuum (heat transfer) model coupled with a modified Alternating Schwarz coupling scheme. An interesting application for this modeling technique is Thermal Sensing Atomic Force Microscopy (TSAFM). TSAFM relies on gas phase heat transfer between heated cantilever probes and the scanned surface to determine the scan height, and thus the surface topography. Accurate models of the heat transfer phenomena are required to correctly interpret scan data. This thesis presents results demonstrating the effect of subcontinuum heat transfer on TSAFM operation and explores the mechanical effects of the Knudsen Force on the heated cantilevers.

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Al-Mohssen, Husain Ali 1977. "An excursion with the Boltzmann equation at low speeds : variance-reduced DSMC." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/61591.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2010.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 133-139).
The goal of the present thesis is to develop a practical method for simulating low-signal kinetic (small-scale) gaseous flows. These flows have recently received renewed attention in connection with the design and optimization of MEMS/NEMS devices operating in gaseous environments; they are typically described using the Boltzmann equation which is most efficiently solved using a stochastic particle simulation method known as direct simulation Monte Carlo (DSMC). The latter is a simple and versatile simulation method which is very efficient in producing samples of the single particle distribution function which can be used for estimating hydrodynamic properties. Unfortunately, in cases where the signal of interest is small (e.g. low-speed flows), the computational cost associated with reducing the statistical uncertainty of simulation outputs becomes overwhelming. This thesis presents a variance reduction approach for reducing the statistical uncertainty associated with low-signal flows thus making their simulation not only possible but also efficient. Variance reduction is achieved using a control variate approach based on the observation that low-signal flows are typically close to an equilibrium state. As with previous variance reduction methods, significant variance reduction is achieved making the simulation of arbitrarily small deviations from equilibrium possible. However, in contrast to previous variance-reduction methods, the method proposed, which we will refer to as VRDSMC, is able to reduce the variance with virtually no modification to the standard DSMC algorithm. This is achieved by introducing an auxiliary equilibrium simulation which, via an importance weight formulation, uses the same particle data as the non-equilibrium (DSMC) calculation; subtracting the equilibrium from the non-equilibrium hydrodynamic fields drastically reduces the statistical uncertainty of the latter because the two fields are correlated. By retaining the basic DSMC formulation, in contrast to previous approaches, the VRDSMC approach combines ease of implementation with computational efficiency and the ability to simulate all molecular interaction models available within the DSMC formulation. Our validation tests show that the proposed VRDSMC method provides considerable variance reduction for only a small increase in computational cost and approximation error compared to equivalent DSMC simulations. In other words, by addressing the major weakness associated with DSMC, VRDSMC is well suited to the solution of low-signal kinetic problems of practical interest.
by Husain Ali Al-Mohssen.
Ph.D.

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Al-Kouz, Wael G. "Investigation of Supersonic Gas Flows into Nanochannels Using an Unstructured 3D Direct Simulation Monte Carlo Method." Digital WPI, 2009. https://digitalcommons.wpi.edu/etd-dissertations/317.

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"This dissertation is devoted to the computational investigation of supersonic gas flows in rectangular nanochannels with scales between 100 nm and 1000 nm, using an unstructured three-dimensional Direct Simulation Monte Carlo (U3DSMC) methodology. This dissertation also contributes to the computational mathematics background of the U3DSMC method with validations and verifications at the micronscale and nanoscale, as well as with the investigation of the statistical fluctuations and errors associated with U3DSMC simulations at the nanoscale. The U3DSMC code is validated by comparisons with previous two dimensional DSMC simulations of flows in micron-scale rectangular channels. The simulation involves the supersonic flow of nitrogen into a microchannel with height of 1.2 m and width of 6 m. The free stream conditions correspond to a pressure of 72,450 Pa, Mach number , Knudsen number and mean free path nm. The U3DSMC centerline temperature, heat flux to the wall, and mean velocity as a function of the transverse direction are in very good agreement with previous 2D results. Statistical fluctuations and errors in U3DSMC have added significance in nanoscale domains because the number of real particles can be very small inside a computational cell. The effect of the number of samples, the number of computational particles in a Delaunay cell, and the Mach number on the fractional errors of density, velocity and temperature are investigated for uniform and pressure-driven nanoscale flows. The uniform nanoflow is implemented by applying a and free stream boundary condition with m-3, K, nm in a domain that requires resolution of a characteristic length scale nm. The pressure-driven flows consider a nanochannel of 500 nm height, 100 nm width and 4 m length. Subsonic boundary conditions are applied with inlet pressure 101,325 Pa and outlet pressure of 10132.5 Pa. The analysis shows that U3DSMC simulations at nanoscales featuring 10-30 particles per Delaunay cell result in statistical errors that are consistent with theoretical estimates. The rarefied flow of nitrogen with speed ratio of 2, 5, and 10, pressure of 10.132 kPa into rectangular nanochannels with height of 100, 500 and 1000 nm is investigated using U3DSMC. The investigation considers rarefaction effects with =0.481, 0.962, 4.81, geometric effects with nanochannel aspect ratios of (L/H) from AR=1, 10, 100 and back-pressure effects with imposed pressures from 0 to 200 kPa. The computational domain features a buffer region upstream of the inlet and the nanochannel walls are assumed to be diffusively reflecting at the free stream temperature of 273 K. The analysis is based on the phase space distributions as well as macroscopic flow variables sampled in cells along the centerline. The phase space distributions show the formation of a disturbance region ahead of the inlet due to slow particles backstreaming through the inlet and the formation of a density enhancement with its maximum inside the nanochannel. The velocity phase-space distributions show a low-speed particle population generated inside the nanochannel due to wall collisions which is superimposed with the free stream high-speed population. The mean velocity decreases, while the number density increases in the buffer region. The translational temperature increases in the buffer region and reaches its maximum near the inlet. For AR=10 and 100 nanochannels the gas reaches near equilibrium with the wall temperature. The heat transfer rate is largest near the inlet region where non-equilibrium effects are dominant. For =0.481, 0.962, 4.81, vacuum back pressure, and AR=1, the nanoflow is supersonic throughout the nanochannel, while for AR=10 and 100, the nanoflow is subsonic at the inlet and becomes sonic at the outlet. For =0.962, AR=1, and imposed back pressure of 120 kPa and 200 kPa, the nanoflow becomes subsonic at the outlet. For =0.962 and AR=10, the outlet pressure nearly matches the imposed back pressure with the nanoflow becoming sonic at 40 kPa and subsonic at 100 kPa. Heat transfer rates at the inlet and mass flow rates at the outlet are in good agreement with those obtained from theoretical free-molecular models. The flows in these nanochannels share qualitative characteristics found in microchannels ad well as continuum compressible flows in channels with friction and heat loss. The rarefied flow of nitrogen with speed ratio of 2, 5, 10, at an atmospheric pressure of 101.32 kPa into rectangular nanochannels with height of 100 and 500 nm is investigated using U3DSMC. The investigation considers rarefaction effects with =0.0962 and 4.81, geometric effects with nanochannel aspect ratios of (L/H) of AR=1 and 10 and vacuum back-pressure. Phase plots and sample-averaged macroscopic parameters are used in the analysis. Under vacuum back pressure the centerline velocity decreases in the buffer region from its free stream value. For 0.481, 0.0962 and AR=1 the Mach number is supersonic at the inlet and remains supersonic throughout the nanochannel. For 0.481, 0.0962 and AR=10, the flow becomes subsonic at the inlet and shows a sharp increase in pressure. The Mach number, subsequently, increases and reaches the sonic point at the outlet. For 0.481, 0.0962 and AR=1 the translational temperature reaches a maximum near the inlet and decreases monotonically up to the outlet. For 0.481, 0.0962 and AR=10, the translational temperature reaches a maximum near the inlet and then decreases to come in near equilibration with the wall temperature of 273 K. "

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Oh, David Y. (David Younghee). "Computational modeling of expanding plasma plumes in space using a PIC-DSMC algorithm." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/10756.

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Cave, Hadley Mervyn. "Development of Modelling Techniques for Pulsed Pressure Chemical Vapour Deposition (PP-CVD)." Thesis, University of Canterbury. Mechanical Engineering, 2008. http://hdl.handle.net/10092/1572.

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In this thesis, a numerical and theoretical investigation of the Pulsed Pressure Chemical Vapour Deposition (PP-CVD) progress is presented. This process is a novel method for the deposition of thin films of materials from either liquid or gaseous precursors. PP-CVD operates in an unsteady manner whereby timed pulsed of the precursor are injected into a continuously evacuated reactor volume. A non-dimensional parameter indicating the extent of continuum breakdown under strong temporal gradients is developed. Experimental measurements, supplemented by basic continuum simulations, reveal that spatio-temporal breakdown of the continuum condition occurs within the reactor volume. This means that the use of continuum equation based solvers for modelling the flow field is inappropriate. In this thesis, appropriate methods are developed for modelling unsteady non-continuum flows, centred on the particle-based Direct Simulation Monte Carlo (DSMC) method. As a first step, a basic particle tracking method and single processor DSMC code are used to investigate the physical mechanisms for the high precursor conversion efficiency and deposition uniformity observed in experimental reactors. This investigation reveals that at soon after the completion of the PP-CVD injection phase, the precursor particles have an approximately uniform distribution within the reactor volume. The particles then simply diffuse to the substrate during the pump-down phase, during which the rate of diffusion greatly exceeds the rate at which particles can be removed from the reactor. Higher precursor conversion efficiency was found to correlate with smaller size carrier gas molecules and moderate reactor peak pressure. An unsteady sampling routine for a general parallel DSMC method called PDSC, allowing the simulation of time-dependent flow problems in the near continuum range, is then developed in detail. Nearest neighbour collision routines are also implemented and verified for this code. A post-processing procedure called DSMC Rapid Ensemble Averaging Method (DREAM) is developed to improve the statistical scatter in the results while minimising both memory and simulation time. This method builds an ensemble average of repeated runs over small number of sampling intervals prior to the sampling point of interest by restarting the flow using either xi a Maxwellian distribution based on macroscopic properties for near equilibrium flows (DREAM-I) or output instantaneous particle data obtained by the original unsteady sampling of PDSC for strongly non-equilibrium flows (DREAM-II). The method is validated by simulating shock tube flow and the development of simple Couette flow. Unsteady PDSC is found to accurately predict the flow field in both cases with significantly reduced run-times over single processor code and DREAM greatly reduces the statistical scatter in the results while maintaining accurate particle velocity distributions. Verification simulations are conducted involving the interaction of shocks over wedges and a benchmark study against other DSMC code is conducted. The unsteady PDSC routines are then used to simulate the PP-CVD injection phase. These simulations reveal the complex flow phenomena present during this stage. The initial expansion is highly unsteady; however a quasi-steady jet structure forms within the reactor after this initial stage. The simulations give additional evidence that the collapse of the jet at the end of the injection phase results in an approximately uniform distribution of precursor throughout the reactor volume. Advanced modelling methods and the future work required for development of the PP-CVD method are then proposed. These methods will allow all configurations of reactor to be modelled while reducing the computational expense of the simulations.

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Rose, Martin. "Untersuchungen zur Oberflächenchemie der Atomlagenabscheidung und deren Einfluss auf die Effizienz von Prozessen." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-63111.

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In dieser Arbeit werden verschiedene Prozesse zur Atomlagenabscheidung (ALD) von TiO2 und HfO2 experimentell untersucht. Die Untersuchungen schließen eine experimentelle Charakterisierung des Schichtwachstums sowie eine massenspektrometrische Analyse der Reaktionsprodukte ein. Im Detail wurden der ALD-Prozess mit Cp*Ti(OMe)3 und Ozon zur Abscheidung von TiO2 sowie der ALD-Prozess mit TEMAHf und Ozon zur Abscheidung von HfO2 untersucht. Der theoretische Teil der Arbeit beginnt mit einer Methode zur Bestimmung des absoluten Haftkoeffizienten. Anschließend werden numerische Modelle entwickelt, welche die Adsorption von Präkursormolekülen durch strukturierte Substrate beschreiben. Diese Modelle enthalten die Substratstruktur und den absoluten Haftkoeffizienten. Es wird eine statistische numerische Methode entwickelt, mit der der Gastransport in dem ALD-Reaktor statistisch beschrieben wird. Die statistischen Größen, welche die Gasdynamik im Reaktor beschreiben, werden mit der Discrete Simulation Monte Carlo (DSMC) Methode bestimmt. Mit dieser Methode und den Modellen der Adsorption kann der komplette ALD-Prozess simuliert werden. Die neu entwickelte Methode wird verwendet um die Effizienz verschiedener ALD-Reaktoren in Abhängigkeit des absoluten Haftkoeffizienten, der Substratstruktur sowie der Prozessbedingungen zu untersuchen. Die Geometrie des Reaktors wird variiert und mit der Referenzgeometrie verglichen
This dissertation is divided into an experimental part and a theoretical part. The experimental part describes the atomic layer deposition (ALD) of TiO2 and HfO2. TDMAT and Cp*Ti(OMe)3 were used as titanium precursors, while TEMAHf was used as the hafnium precursor. Ozone was used as the oxygen source. The self limiting film growth and the temperature window of these ALD processes were investigated. The reaction by-products of the Cp*Ti(OMe)3/O3 process were identified by quadrupol mass spectrometry (QMS). The QMS analysis of the TEMAHf/O3 process revealed that water is formed during the metal precursor pulse. The theoretical part of this thesis describes the development of models and numerical methods to simulate the ALD as a whole. First of all, a model for the adsorption of precursor molecules by planar substrates was developed. This model was extended to describe the adsorption of precursor molecules inside a cylindrical hole with an aspect ratio of 20, 40 and 80. The adsorption of precursor molecules is dominated by the absolute sticking coefficient (SC), i.e., the reactivity of the precursor molecules. From the numerical model the saturation profiles along the wall of a cylindrical hole can be determined. From the comparison of the simulated profile with an experimentally determined thickness profile the SC can be determined. This method was used to determine the SC of the precursors examined in the experimental part. The SC of TEMAHf increases exponentially with the substrate temperature. A discrete particle method (DSMC) was used to derive a statistical description of the gas kinetics inside an ALD reactor. Combining the statistical description of the gas transport and the numerical models of the adsorption, it is possible to simulate the ALD for any combination of reactor, substrate and SC. It is possible to distinguish the contribution of the reactor geometry, the process parameters and the process chemistry (SC) to the process efficiency. Therefore, the ALD reactor geometry can be optimized independently of the process chemistry. This method was used to study a shower head ALD reactor. The reactor geometry, the composition of the gas at the inlet and the position of the inlet nozzles was varied in order to find more efficient ALD reactors. The efficiency of the reference geometry is limited by the inlet nozzles close to the exhaust and the decrease of the pressure on the substrate near the exhaust. The efficiency of ALD processes with different SCs was simulated for planar and structured substrates with a diameter of 300 mm and 450 mm

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Si, Hadj Mohand Hacene. "Micro-vélocimétrie par marquage moléculaire adaptée aux écoulements gazeux confinés." Thesis, Toulouse, INSA, 2015. http://www.theses.fr/2015ISAT0039.

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Nous présentons dans cette thèse une adaptation de la technique de vélocimétrie par marquage moléculaire (MTV) aux micro-écoulements gazeux. Les effets de luminescence de l’acétone gazeuse excitée par un rayonnement UV, mis en jeu dans la MTV, ont été analysés en vue d’une application en vélocimétrie à basse pression. La phosphorescence de l’acétone diminue fortement avec la pression, pour devenir non détectable à des pressions de l’ordre du kPa. En revanche, la fluorescence reste détectable à des pressions de l’ordre de la dizaine de Pa. L’analyse des déplacements de molécules luminescentes au sein de l’écoulement porteur a montré que les effets de la diffusion moléculaire sont importants et augmentent avec la raréfaction du gaz. Une méthode de reconstruction, basée sur l’équation d’advection diffusion, a été développée. Elle permet d’extraire le profil de vitesse à partir de l’analyse du déplacement et de la déformation de la zone marquée, en prenant en compte la diffusion des molécules luminescentes. L’analyse d’un écoulement de Poiseuille dans un canal de section rectangulaire et de dimensions millimétriques, sous des pressions de l’ordre de 100 kPa, a montré la capacité de la MTV à extraire avec précision la vitesse locale en écoulements confinés, lorsque la méthode de reconstruction est appliquée. Une feuille de route pour l’analyse future par MTV des écoulements raréfiés, notamment dans le régime glissant, est finalement proposée
In the present thesis we present an adaptation of Molecular Tagging Velocimetry (MTV) to gas microflows. The photo-luminescence effects of gaseous acetone excited by UV light, implemented in MTV, have been analyzed in various pressure conditions. The acetone phosphorescence shows a drastic decrease with pressure and becomes non measurable for pressures lower than 1 kPa. On the other hand, fluorescence shows a slower decrease and remains clearly detectible at pressures as low as 10 Pa. The motion of tracer molecules within the carrier flow has been studied. The analysis of the displacement of the tagged molecules has shown the strong influence of molecular diffusion, this influence being increased with the gas rarefaction. A reconstruction method based on the advection-diffusion equation has been developed. It allows to extract the velocity profile from the analysis of the displacement and deformation of the tagged region, taking into account the diffusion of tracer molecules. This reconstruction method has been successfully implemented to analyse a Poiseuille flow in a rectangular millimetric channel, under atmospheric pressure conditions, and the capability of MTV to accurately extract the local velocity in confined gas flows has been demonstrated. Finally, some short term perspectives have been proposed with the aim to help achieving rarefied flows analysis by MTV

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Chen, Jie. "Numerical and experimental analysis of flows generated by temperature fields in rarefied gas : application to the design of Knudsen micropumps." Thesis, Toulouse, INSA, 2016. http://www.theses.fr/2016ISAT0009/document.

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Cette thèse présente une étude numérique et expérimentale d’écoulements gazeux raréfiés confinés, induits par gradients thermiques. L’écoulement d’un gaz raréfié peut en effet être généré en appliquant uniquement un gradient tangentiel de température le long d'une paroi. Ainsi, sans gradient initial de pression, le gaz peut se déplacer de la région froide vers la région chaude. Ce phénomène, appelé transpiration thermique, est à la base du fonctionnement des pompes dites de Knudsen, capables de générer un pompage du gaz sans utiliser de pièces mécaniques mobiles. L’apport principal de ce travail est relatif à l’investigation numérique de l’écoulement de transpiration thermique dans trois nouvelles configurations de pompe Knudsen. Dans ce but, une méthode numérique de simulation d’écoulements dans le régime de glissement a été développée ; elle implémente des conditions aux limites de saut de vitesse et de température spécifiques dans un code CFD commercial. Parallèlement, un code DSMC a été mis en œuvre pour étudier des écoulements plus fortement raréfiés dans les géométries les plus complexes. Des écoulements de transpiration thermique générés dans des canaux courbés, dans des canaux convergents/divergents ou entre deux surfaces spécialement micro-texturées ont ainsi été étudiés. D’autre part, l’analyse expérimentale d’un écoulement de transpiration thermique dans un microtube de section circulaire a été réalisée sur un nouveau banc d’essais conçu pour être adaptable à diverses géométries de canaux ou de pompes Knudsen
This thesis presents a numerical and experimental analysis of internal rarefied gas flows induced by temperature fields. In rarefied gases, a flow can be generated by solely applying a tangential temperature gradient along a wall: without any initial pressure gradient, the gas macroscopically moves from the cold toward the hot region. This phenomenon is the so-called thermal creep or thermal transpiration effect. It is the main operating principle of the Knudsen pump, which can generate gas pumping without the need of any moving parts. The main aspect of this work is centered on numerical investigations of thermal transpiration flows in three new possible configurations of Knudsen pumps. For that goal, a numerical model for slip flows has been developed in which the appropriate slip boundary conditions are implemented in a commercial CFD code and a DSMC code has been adapted for studying transition flows in complex geometries. The pumping effect of curved-channel Knudsen pumps, the thermal transpiration flows through tapered channels and between two ratchets surfaces at different uniform temperatures have been investigated. In addition, an experimental study of thermal transpiration flow through a single micro-tube has been carried out on a new experimental set-up designed to be adaptable for testing thermally driven flows through various kinds of microchannels or generated by autonomous Knudsen compressors

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Wang, Ye. "Ecoulement dans une pompe à vide turbomoléculaire : modélisation et analyse par voie numérique." Thesis, Grenoble, 2013. http://www.theses.fr/2013GRENI062/document.

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La thèse est consacrée à la modélisation et à l'analyse par voie numérique de l'écoulement dans une pompe à vide turbomoléculaire hybride, combinant une succession d'étages de type rotor et stator et un Holweck. Une approche de type Test Particle Monte Carlo 3D a été développée pour des configurations de pompes industrielles (géométries complexes d'aubes, gestion des étages rotor et stator) dans un souci d'optimisation des coûts de simulation. L'outil numérique développé a été validé pour des configurations académiques et industrielles, en s'appuyant notamment sur des résultats expérimentaux obtenus grâce au banc d'essai de l'entreprise aVP. L'apport de l'approche TPMC3D par rapport aux méthodes de design disponibles en début de thèse a été clairement démontré pour le régime moléculaire libre. Quelques préconisations de design ont également pu être formulées en utilisant le code développé. Le potentiel d'une approche de type Direct Simulation Monte Carlo, prenant en compte les interactions entre molécules du gaz, a également été établi en 2D pour le régime de transition
The thesis is devoted to the modeling and the numerical analysis of the flow in a turbomolecular vacuum pump of hybrid type, that is combining a succession of rotor and stator stages with an Holweck. A 3D Test Particle Monte Carlo approach has been developed for simulating industrial pump configurations (complex blade geometries, management of rotor and stator stages), with attention paid to the optimization of the computational cost. The numerical tool developed in the thesis has been validated for academic and industrial test cases, relying in particular on reference experimental results obtained on the test rig of the aVP company. The prediction improvement brought by the TPMC 3D approach with respect to the design tools available at the start of the thesis has been clearly demonstrated for the free molecular flow regime. Some design recommendations have also been formulated using the developed solver. The potential of a Direct Simulation Monte Carlo approach, taking into account the interactions between gas molecules, has also been established in 2D for the transition regime

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Damazo, Graciliano Antonio. "Controle com modos deslizantes aplicado em sistemas com atraso e acesso somente à saída /." Ilha Solteira : [s.n.], 2008. http://hdl.handle.net/11449/87264.

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Orientador: José Paulo Fernandes Garcia
Banca: Laurence Duarte Colvara
Banca: Ivan Nunes da Silva
Resumo: O enfoque principal do trabalho foi dado ao Controle Discreto com Modos Deslizantes(CDMD) aplicado em sistemas que possuem atraso no processamento do sinal de controle e acesso somente à saída do sistema. A estratégia de controle tem por objetivo a utilização de técnicas de controle com modos deslizantes para a elaboração de uma lei de controle simples e robusta às incertezas da planta e ao atraso. O observador de estados apresentado possui características de modo deslizante, o qual realiza a estimação robusta do vetor de estados que na maioria dos casos práticos não é totalmente acessível. Os métodos de projetos propostos podem ser aplicados no controle de plantas estáveis ou instáveis com atraso no sinal de controle e acesso somente à saída da planta. Para comprovar a eficiência dos projetos apresentados neste trabalho, analisou-se o controlador atuando com acesso a todos estados e o controlador atuando juntamente com o observador robusto para a estimação dos estados. Os resultados foram obtidos através de simulações no Sistema Bola e Viga, Sistema Pêndulo Invertido Linear e Sistema Pêndulo Invertido Rotacional que são exemplos de plantas de natureza instável.
Abstract: The main focus was placed on the Discrete Sliding Mode Control (DSMC) applied to systems that have a delay in the processing of the control signal and access to the system output only. The control strategy is intended to use control techniques of sliding modes to elaborate a simple and robust control law against the uncertainties of the plant and the delay. The states observer presented has the characteristics of a sliding mode, which performs the robust estimation of the states vector that, in most practical cases, is not fully accessible. The design methods proposed may be applied to the control of stable or unstable plants with delay on the control signal and access to the plant output only. In order to attest the efficiency of the design presented in this work, the controller was analyzed at work with access to all states and jointly with the robust observer to estimate the states. The results were obtained by means of simulations in the Ball and Beam System, Linear Inverted Pendulum System, and Rotational Inverted Pendulum System, which are examples of plants of unstable nature.
Mestre

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15

Reyhanian, Mashhadi Mehrnaz. "Simulation numérique par la méthode Monte Carlo (DSMC) et modélisation analytique d'un mélange gazeux dans un micro canal." Paris 6, 2011. http://www.theses.fr/2011PA066396.

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Ce travail porte sur des simulations numériques par la méthode DSMC (Direct Simulation Monte Carlo) de l'écoulement raréfié d'un mélange de deux gaz entrant, soit séparément, soit déjà mélangés, dans un micro canal. Dans le cas de deux gaz déjà mélangés, les paramètres permettant de retrouver les valeurs d'initialisation sont étudiés. En tenant compte de ces résultats pour l'étude de l'écoulement de deux gaz séparés et leur mélange, des facteurs influant sur la longueur de mélange sont analysés. On a tenté de diminuer cette longueur en étudiant les effets de quelques paramètres géométriques, comme ajouter deux bosses de manière symétrique dans le canal, ou des conditions aux limites d'initialisation, comme diminuer la vitesse d'entrée. Les résultats des simulations DSMC pour le gaz mélangé sont comparés avec des résultats théoriques connus dans deux cas : avec des bosses et sans bosses. On obtient un bon accord entre les résultats théoriques et ceux des simulations. Enfin, une étude analytique à partir des équations de Navier-Stokes avec les conditions aux limites du glissement à la paroi et les termes du couplage du modèle BGK pour le mélange, est faite pour modéliser un mélange binaire gazeux isotherme dans un micro canal. Le système asymptotique obtenu pour les pressions et les vitesses de chaque espèce dans le mélange, est analysé numériquement avec MATLAB. Pour finir, pour un problème identique, les résultats asymptotiques sont comparés avec ceux de la simulation DSMC pour les pressions

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16

Wishart, Stuart Jackson. "A Parallel Solution Adaptive Implementation of the Direct Simulation Monte Carlo Method." University of Sydney. School of Aerospace, Mechanical and Mechatronic Engineering, 2005. http://hdl.handle.net/2123/619.

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This thesis deals with the direct simulation Monte Carlo (DSMC) method of analysing gas flows. The DSMC method was initially proposed as a method for predicting rarefied flows where the Navier-Stokes equations are inaccurate. It has now been extended to near continuum flows. The method models gas flows using simulation molecules which represent a large number of real molecules in a probabilistic simulation to solve the Boltzmann equation. Molecules are moved through a simulation of physical space in a realistic manner that is directly coupled to physical time such that unsteady flow characteristics are modelled. Intermolecular collisions and moleculesurface collisions are calculated using probabilistic, phenomenological models. The fundamental assumption of the DSMC method is that the molecular movement and collision phases can be decoupled over time periods that are smaller than the mean collision time. Two obstacles to the wide spread use of the DSMC method as an engineering tool are in the areas of simulation configuration, which is the configuration of the simulation parameters to provide a valid solution, and the time required to obtain a solution. For complex problems, the simulation will need to be run multiple times, with the simulation configuration being modified between runs to provide an accurate solution for the previous run�s results, until the solution converges. This task is time consuming and requires the user to have a good understanding of the DSMC method. Furthermore, the computational resources required by a DSMC simulation increase rapidly as the simulation approaches the continuum regime. Similarly, the computational requirements of three-dimensional problems are generally two orders of magnitude more than two-dimensional problems. These large computational requirements significantly limit the range of problems that can be practically solved on an engineering workstation or desktop computer. The first major contribution of this thesis is in the development of a DSMC implementation that automatically adapts the simulation. Rather than modifying the simulation configuration between solution runs, this thesis presents the formulation of algorithms that allow the simulation configuration to be automatically adapted during a single run. These adaption algorithms adjust the three main parameters that effect the accuracy of a DSMC simulation, namely the solution grid, the time step and the simulation molecule number density. The second major contribution extends the parallelisation of the DSMC method. The implementation developed in this thesis combines the capability to use a cluster of computers to increase the maximum size of problem that can be solved while simultaneously allowing excess computational resources to decrease the total solution time. Results are presented to verify the accuracy of the underlying DSMC implementation, the utility of the solution adaption algorithms and the efficiency of the parallelisation implementation.

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Hammel, Jeffrey Robert. "Development of an unstructured 3-D direct simulation Monte Carlo/particle-in-cell code and the simulation of microthruster flows." Link to electronic thesis, 2002. http://www.wpi.edu/Pubs/ETD/Available/etd-0510102-153614.

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18

Wishart, Stuart Jackson. "A Parallel Solution Adaptive Implementation of the Direct Simulation Monte Carlo Method." Thesis, The University of Sydney, 2004. http://hdl.handle.net/2123/619.

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This thesis deals with the direct simulation Monte Carlo (DSMC) method of analysing gas flows. The DSMC method was initially proposed as a method for predicting rarefied flows where the Navier-Stokes equations are inaccurate. It has now been extended to near continuum flows. The method models gas flows using simulation molecules which represent a large number of real molecules in a probabilistic simulation to solve the Boltzmann equation. Molecules are moved through a simulation of physical space in a realistic manner that is directly coupled to physical time such that unsteady flow characteristics are modelled. Intermolecular collisions and moleculesurface collisions are calculated using probabilistic, phenomenological models. The fundamental assumption of the DSMC method is that the molecular movement and collision phases can be decoupled over time periods that are smaller than the mean collision time. Two obstacles to the wide spread use of the DSMC method as an engineering tool are in the areas of simulation configuration, which is the configuration of the simulation parameters to provide a valid solution, and the time required to obtain a solution. For complex problems, the simulation will need to be run multiple times, with the simulation configuration being modified between runs to provide an accurate solution for the previous run's results, until the solution converges. This task is time consuming and requires the user to have a good understanding of the DSMC method. Furthermore, the computational resources required by a DSMC simulation increase rapidly as the simulation approaches the continuum regime. Similarly, the computational requirements of three-dimensional problems are generally two orders of magnitude more than two-dimensional problems. These large computational requirements significantly limit the range of problems that can be practically solved on an engineering workstation or desktop computer. The first major contribution of this thesis is in the development of a DSMC implementation that automatically adapts the simulation. Rather than modifying the simulation configuration between solution runs, this thesis presents the formulation of algorithms that allow the simulation configuration to be automatically adapted during a single run. These adaption algorithms adjust the three main parameters that effect the accuracy of a DSMC simulation, namely the solution grid, the time step and the simulation molecule number density. The second major contribution extends the parallelisation of the DSMC method. The implementation developed in this thesis combines the capability to use a cluster of computers to increase the maximum size of problem that can be solved while simultaneously allowing excess computational resources to decrease the total solution time. Results are presented to verify the accuracy of the underlying DSMC implementation, the utility of the solution adaption algorithms and the efficiency of the parallelisation implementation.

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19

Mertz, Helene. "Modélisation des réactions chimiques dans un code de simulation par la méthode Monte Carlo." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLV012/document.

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Les méthodes Direct Simulation Monte Carlo (DSMC) sont utilisées par Ariane group pour calculer les torseurs d'efforts aérodynamiques et les flux thermiques sur les engins spatiaux pour des écoulements hypersoniques en milieu raréfié.Afin de pouvoir caractériser la dislocation des étages de lanceurs et donc l'empreinte de retombée de débris, une modélisation précise des mécanismes générateurs de flux thermiques est nécessaire. Les réactions chimiques étant dimensionnantes pour le calcul du flux thermique, l'objectif de cette thèse est de développer l'outil de calcul avec la méthode DSMC nommé IEMC de manière à pouvoir prendre en compte les écoulements réactifs.Deux modèles de chimie sont mis en place pour pouvoir prendre en compte la totalité des réactions. Après leur vérifications sur des cas élémentaires, ils sont appliqués et validés sur des cas tests de rentrée pour différentes atmosphères. Les différents modèles considérés sont testés afin d'évaluer leur influence. Les modèles de chimie dépendent de nouveaux paramètres d'entrée, dont les valeurs numériques sont incertaines. Une étude de quantification de leur incertitude est menée et a permis de vérifier que les grandeurs de sorties de la simulation avec un écoulement réactif, notamment le flux thermique, n'est que peu impacté par ces paramètres incertains
Direct Simulation Monte Carlo (DSMC) methods are used in Ariane group to compute aerodynamic forces and moments and heat fluxes on space objects for hypersonic flows in rarefied regimes.To caracterise the dislocation of the stages and the debris footprints, a precise modelisation of the mechanism that contribute to the heat flux is necessary. The contribution of the chemical reactions is important for the determination of the heat flux. The purpose of this thesis is to develop the in house IEMC tool using the DSMC method so that it can compute reactive flows.The different steps of the developments are presented in this work. The first step is the presentation, implementation and verification of two different chemistry models. They are validated for simulations on real test cases. Different models are tested in order to evaluate their effect. Chemical models implemented in the code depend on new input parameters, whose numerical data are uncertain. Using a uncertainty quantification study, it is shown that the output data of the reactive simulation, especially the heat flux, is weakly impacted by the tested uncertain parameters

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20

Rojas, cardenas Marcos javier. "Temperature gradient induced rarefied gas flow." Thesis, Aix-Marseille, 2012. http://www.theses.fr/2012AIXM4797.

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Ce manuscrit présente l'étude et l'analyse d'écoulements de gaz raréfiés, induits par la transpiration thermique. Le terme de transpiration thermique désigne le mouvement macroscopique d'un gaz raréfié engendré par l'effet du seul gradient de température. L'aspect principal de ce travail est centré autour de la mesure du débit stationnaire déclenché en soumettant un micro tube à un gradient de température appliqué le long de son axe. On a développé à cet effet un appareillage expérimental original ainsi qu'une méthodologie expérimentale innovatrice basée sur la dépendance du phénomène, analysé dans son ensemble, à l'égard du temps. Les résultats obtenus pour le débit stationnaire initial de transpiration thermique et pour les paramètres thermo-moléculaires caractérisant l'équilibre final de débit nul, ont été comparés aux résultats obtenus numériquement par la résolution de l'équation cinétique modèle de Shakhov et par la méthode de simulation directe de Monte-Carlo
This thesis presents the study and analysis of rarefied gas flows induced by thermal transpiration. Thermal transpiration refers to the macroscopic movement of rarefied gas generated by a temperature gradient. The main aspect of this work is centered around the measurement of the mass flow rate engendered by subjecting a micro-tube to a temperature gradient along its axis. In this respect, an original experimental apparatus and an original time-dependent experimental methodology was developed. The experimental results for the initial stationary thermal transpiration mass flow rate and for the final zero- flow thermal molecular parameters were compared with the results obtained from the numerical solution of the Shakhov model kinetic equation and the direct simulation Monte Carlo method

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21

Gokaltun, Seckin. "Lattice Boltzmann Method for Flow and Heat Transfer in Microgeometries." FIU Digital Commons, 2008. http://digitalcommons.fiu.edu/etd/64.

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Recent technological developments have made it possible to design various microdevices where fluid flow and heat transfer are involved. For the proper design of such systems, the governing physics needs to be investigated. Due to the difficulty to study complex geometries in micro scales using experimental techniques, computational tools are developed to analyze and simulate flow and heat transfer in microgeometries. However, conventional numerical methods using the Navier-Stokes equations fail to predict some aspects of microflows such as nonlinear pressure distribution, increase mass flow rate, slip flow and temperature jump at the solid boundaries. This necessitates the development of new computational methods which depend on the kinetic theory that are both accurate and computationally efficient. In this study, lattice Boltzmann method (LBM) was used to investigate the flow and heat transfer in micro sized geometries. The LBM depends on the Boltzmann equation which is valid in the whole rarefaction regime that can be observed in micro flows. Results were obtained for isothermal channel flows at Knudsen numbers higher than 0.01 at different pressure ratios. LBM solutions for micro-Couette and micro-Poiseuille flow were found to be in good agreement with the analytical solutions valid in the slip flow regime (0.01 < Kn < 0.1) and direct simulation Monte Carlo solutions that are valid in the transition regime (0.1 < Kn < 10) for pressure distribution and velocity field. The isothermal LBM was further extended to simulate flows including heat transfer. The method was first validated for continuum channel flows with and without constrictions by comparing the thermal LBM results against accurate solutions obtained from analytical equations and finite element method. Finally, the capability of thermal LBM was improved by adding the effect of rarefaction and the method was used to analyze the behavior of gas flow in microchannels. The major finding of this research is that, the newly developed particle-based method described here can be used as an alternative numerical tool in order to study non-continuum effects observed in micro-electro-mechanical-systems (MEMS).

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22

Torres, Erik [Verfasser], and Stefanos [Akademischer Betreuer] Fasoulas. "Ab initio quantum-chemistry database for N2 (v, J) + N in a state-to-state implementation of the DSMC method / Erik Torres ; Betreuer: Stefanos Fasoulas." Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2017. http://d-nb.info/1143597060/34.

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23

Damazo, Graciliano Antonio [UNESP]. "Controle com modos deslizantes aplicado em sistemas com atraso e acesso somente à saída." Universidade Estadual Paulista (UNESP), 2008. http://hdl.handle.net/11449/87264.

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Made available in DSpace on 2014-06-11T19:22:36Z (GMT). No. of bitstreams: 0 Previous issue date: 2008-06-11Bitstream added on 2014-06-13T20:09:52Z : No. of bitstreams: 1 damazo_ga_me_ilha.pdf: 760851 bytes, checksum: d1a0f2a22e4917da6787ce545199a696 (MD5)
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
O enfoque principal do trabalho foi dado ao Controle Discreto com Modos Deslizantes(CDMD) aplicado em sistemas que possuem atraso no processamento do sinal de controle e acesso somente à saída do sistema. A estratégia de controle tem por objetivo a utilização de técnicas de controle com modos deslizantes para a elaboração de uma lei de controle simples e robusta às incertezas da planta e ao atraso. O observador de estados apresentado possui características de modo deslizante, o qual realiza a estimação robusta do vetor de estados que na maioria dos casos práticos não é totalmente acessível. Os métodos de projetos propostos podem ser aplicados no controle de plantas estáveis ou instáveis com atraso no sinal de controle e acesso somente à saída da planta. Para comprovar a eficiência dos projetos apresentados neste trabalho, analisou-se o controlador atuando com acesso a todos estados e o controlador atuando juntamente com o observador robusto para a estimação dos estados. Os resultados foram obtidos através de simulações no Sistema Bola e Viga, Sistema Pêndulo Invertido Linear e Sistema Pêndulo Invertido Rotacional que são exemplos de plantas de natureza instável.
The main focus was placed on the Discrete Sliding Mode Control (DSMC) applied to systems that have a delay in the processing of the control signal and access to the system output only. The control strategy is intended to use control techniques of sliding modes to elaborate a simple and robust control law against the uncertainties of the plant and the delay. The states observer presented has the characteristics of a sliding mode, which performs the robust estimation of the states vector that, in most practical cases, is not fully accessible. The design methods proposed may be applied to the control of stable or unstable plants with delay on the control signal and access to the plant output only. In order to attest the efficiency of the design presented in this work, the controller was analyzed at work with access to all states and jointly with the robust observer to estimate the states. The results were obtained by means of simulations in the Ball and Beam System, Linear Inverted Pendulum System, and Rotational Inverted Pendulum System, which are examples of plants of unstable nature.

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24

Zachreson, Matthew R. "Comparing Theory and Experiment for Analyte Transport in the First Vacuum Stage of the Inductively Coupled Plasma Mass Spectrometer." BYU ScholarsArchive, 2012. https://scholarsarchive.byu.edu/etd/3538.

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The Direct Simulation Monte Carlo algorithm as coded in FENIX is used to model the transport of trace ions in the first vacuum stage of the inductively coupled plasma mass spectrometer. Haibin Ma of the Farnsworth group at Brigham Young University measured two radial trace density profiles: one 0.7 mm upstream of the sampling cone and the other 10 mm downstream. We compare simulation results from FENIX with the experimental results. We find that gas dynamic convection and diffusion are unable to account for the experimentally-measured profile changes from upstream to downstream. Including discharge quenching and ambipolar electric fields, however, makes it possible to account for the way the profiles change.

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25

Kohen, Nicolas. "Physique et modélisation d'une source d'ions négatifs pour l'injection du faisceau de neutres sur ITER." Thesis, Toulouse 3, 2015. http://www.theses.fr/2015TOU30035/document.

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La source d'ions des injecteurs de neutres d'ITER devra produire un fort courant d'ions négatifs de deutérium qui seront accélérés puis neutralisés afin d'obtenir un faisceau d'atomes qui chauffera le plasma thermonucléaire. Un plasma froid d'hydrogène à basse pression et forte puissance est généré par induction dans la source et les ions négatifs sont produits par des réactions en volume et en surface et extraits à travers une série de grilles électrostatiques. Cette thèse est consacrée à la modélisation de ce plasma, afin d'étudier des phénomènes peu abordés à ce jour : aspect hors équilibre des espèces neutres, déplétion et chauffage du gaz, génération et transport des atomes, et génération des ions négatifs sur les parois. Un code fluide bidimensionnel de simulation plasma a pour cela été modifié afin de simuler la cinétique des espèces neutres au moyen d'un module Direct Simulation Monte-Carlo et a été utilisé pour simuler le plasma de manière auto-cohérente
The ion source of the ITER neutral beam injectors will have to deliver a high current of negative deuterium ions which will be accelerated and neutralized, and the resulting atom beam will heat the thermonuclear plasma. A low pressure and high power cold hydrogen plasma is inductively generated in the source and negative ions are produced by volume and surface reactions and are extracted through a set of electrostatic grids. This thesis aims at modelling this plasma, and focuses on topics that haven't been studied much before : out of equilibrium neutral kinetics, gas heating and depletion, atoms production and transport, and negative ions generation on the walls. To this end, a two-dimensional fluid plasma code has been modified to simulate the neutrals kinetics with a Direct Simulation Monte Carlo module and has been used to perform self-consistent simulations of the plasma

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26

Chamberlin, Ryan Earl. "A three-dimensional direct simulation Monte Carlo methodology on unstructured Delaunay grids with applications to micro and nanoflows." Worcester, Mass. : Worcester Polytechnic Institute, 2007. http://www.wpi.edu/Pubs/ETD/Available/etd-032907-092912/.

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27

Somers, William R. "Testing Direct Simulation Monte Carlo Methods Against the Fluid Equations in the Inductively Coupled Plasma Mass Spectrometer." Diss., CLICK HERE for online access, 2008. http://contentdm.lib.byu.edu/ETD/image/etd2621.pdf.

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28

Nanson, III Richard A. "Navier/Stokes/Direct Simulation Monte Carlo Modeling of Small Cold Gas Thruster Nozzle and Plume Flows." Digital WPI, 2002. https://digitalcommons.wpi.edu/etd-theses/254.

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This study involves the modeling of small cold-gas (N2) thrusters nozzle and plume flows, their interactions with spacecraft surfaces and the induced pressure environment. These small cold-gas thrusters were used for pitch, yaw and roll control and were mounted on the bottom of the conical Environmental Monitor Payload (EMP) suborbital spacecraft. The pitch and yaw thrusters had 0.906 mm throat diameter and 4.826 mm exit diameter, while the roll thrusters had 1.6 mm throat diameter and 5.882 mm exit diameter. During thruster firing, at altitudes between 670 km and 1200 km, pressure measurements exhibited non-periodic pulses (Gatsonis et al., 1999). The pressure sensor was located inside the EMP and was connected to it's sidewall with a 0.1-m long, 0.022-m diameter tube and the pressure pulses appeared instantaneously with the firings for thrusters without a direct line-of-sight with the sensor entrance. Preliminary analysis showed that the plume of these small EMP thrusters undergoes transition from continuous to rarefied. Therefore, nozzle and plume simulations are performed using a combination of Navier-Stokes and Direct Simulation Monte Carlo codes. This study presents first a validation of the Navier-Stokes code Rampant used for the continuous EMP nozzle and plume simulations. The first Rampant validation example involves a two-dimensional axisymetric freejet expansion and is used to demonstrate the use of Bird's breakdown parameter. Results are compared favorably with those of Bird (1980) obtained through the method of characteristics. The second validation example involves three-dimensional plume simulations of a NASA thruster. This nitrogen nozzle has a throat diameter of 3.18 mm, an exit diameter of 31.8 mm, half-angle of 20 degrees, stagnation temperature of 699 K, stagnation pressure of 6,400 Pa. Simulation results are compared favorably with previous Navier-Stokes and Direct Simulation Monte Carlo numerical work. The third validation example involves three-dimensional simulations of Rothe's (1970) nozzle that has a throat diameter of 2.5 mm, an exit diameter of 20.3 mm, half-angle of 20 degrees, operating at stagnation temperature of 300 K and pressure of 1975 Pa. Numerical results also compared favorably to experimental data. The combined Navier-Stokes/DSMC approach and the EMP simulation results are presented and discussed. The continuous part of the EMP nozzle and plume flow is modeled using the three-dimensional Navier-Stokes Rampant code. The Navier-Stokes domain includes the geometry of the nozzle and the EMP base until transition of the continuous flow established by Bird's breakdown parameter. The rarefied part of the plume flow is modeled using the Direct Simulation Monte Carlo code DAC. Flowfield data obtained inside the breakdown surface from the Navier-Stokes simulation are used as inputs to the DSMC simulations. The DSMC domain includes the input surface and the EMP spacecraft geometry. The combined Navier-Stokes/DSMC simulations show the complex structure of the plume flow as it expands over the EMP surfaces. Plume reflection and backflow are demonstrated. The study also summarizes findings presented by Gatsonis et al. (2000), where the DSMC predictions at the entrance of the pressure sensor are used as inputs to a semi-analytical model to predict the pressure inside the sensor. It is shown that the pressure predictions for the pitch/yaw thrusters are close to the measurements. The plume of a pitch or yaw thruster reaches the pressure sensor after expanding on the EMP base. The pressure predicted for the roll thruster is larger that the measured. This is attributed to the uncertainty in the roll thruster location on the EMP base resulting, in the simulation, in a component of direct flow to the sensor.

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29

Ameur, Djilali. "Modélisation analytique et simulation numérique par la méthode de Monte-Carlo d'un écoulement de gaz dans des micro-canaux." Paris 6, 2008. http://www.theses.fr/2008PA066102.

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L’objectif de la thèse est de modéliser l’écoulement d’un gaz (azote) dans des micro-filtres. La région du filtrage est une membrane qui contient des orifices, en fait des micro-canaux, dont le diamètre est de quelques micromètres. Au voisinage de chaque orifice, l’écoulement du gaz supposé normal à la membrane, est en régime de raréfaction dit de ‘transition’, intermédiaire entre le régime continu relevant des équations de Navier-Stokes et le régime moléculaire libre où les molécules du gaz évoluent sans interactions entre elles. Deux approches sont utilisées pour analyser l’écoulement dans un micro-canal. La première, théorique, est basée sur une analyse adimensionnelle des équations de Navier-Stokes avec des conditions de glissement à la paroi. La seconde, numérique, est statistique et est basée sur une simulation de Monte Carlo (DSMC). Une étude paramétrique sur différentes géométries de micro-canaux est faite dans le cas d’un écoulement isotherme. Le comportement d’écoulement gazeux à travers un micro-canal est ensuite étudié en appliquant un gradient de température entre son entrée et sa sortie. Cette analyse permet de mettre en évidence le phénomène de transpiration thermique. En s’appuyant sur les résultats numériques, un modèle analytique est proposé. L’effet du coefficient d’accommodation à la paroi sur l’écoulement est aussi étudié. En fin, les effets de compressibilité sont étudiés dans un micro-canal, puis les relations liant le débit et les gradients de pression. Une simulation numérique d’écoulement au travers d’une série de micro-canaux est aussi présentée

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Zachreson, Matthew R. "Comparing Theory and Experiment for Analyte Transport in the First Vacuum Stage of the Inductively Coupled Plasma Mass Spectrometer." BYU ScholarsArchive, 2015. https://scholarsarchive.byu.edu/etd/5610.

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The inductively coupled plasma mass spectrometer (ICP-MS) has been used in laboratories for many years. The majority of the improvements to the instrument have been done empirically through trial and error. A few fluid models have been made, which have given a general description of the flow through the mass spectrometer interface. However, due to long mean free path effects and other factors, it is very difficult to simulate the flow details well enough to predict how changing the interface design will change the formation of the ion beam. Towards this end, Spencer et al. developed FENIX, a direct simulation Monte Carlo algorithm capable of modeling this transitional flow through the mass spectrometer interface, the transitional flow from disorganized plasma to focused ion beam. Their previous work describes how FENIX simulates the neutral ion flow. While understanding the argon flow is essential to understanding the ICP-MS, the true goal is to improve its analyte detection capabilities. In this work, we develop a model for adding analyte to FENIX and compare it to previously collected experimental data. We also calculate how much ambipolar fields, plasma sheaths, and electron-ion recombination affect the ion beam formation. We find that behind the sampling interface there is no evidence of turbulent mixing. The behavior of the analyte seems to be described simply by convection and diffusion. Also, ambipolar field effects are small and do not significantly affect ion beam formation between the sampler and skimmer cones. We also find that the plasma sheath that forms around the sampling cone does not significantly affect the analyte flow downstream from the skimmer. However, it does thermally insulate the electrons from the sampling cone, which reduces ion-electron recombination. We also develop a model for electron-ion recombination. By comparing it to experimental data, we find that significant amounts of electron-ion recombination occurs just downstream from the sampling interface.

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Sade, Asli. "Interaction Of The Non Steroidal Anti-inflammatory Drug Celecoxib With Pure And Cholesterol-containing Model Membranes." Master's thesis, METU, 2009. http://etd.lib.metu.edu.tr/upload/3/12610749/index.pdf.

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The interactions of the non steroidal anti-inflammatory drug celecoxib with pure and cholesterol containing distearoyl phosphatidylcholine multilamellar vesicles were studied using Fourier transform infrared spectroscopy, differential scanning calorimetry and turbidity technique at 440 nm. The results reveal that celecoxib exerts opposing effects on membrane order in a concentration dependent manner while cholesterol disorders and orders the membrane in the gel and liquid crystalline phase, respectively. Ternary mixtures of DSPC/Cholesterol/celecoxib behave similar to cholesterol with a small effect of celecoxib. While celecoxib decreases fluidity of the DSPC membranes, cholesterol shows an opposite effect, and in ternary mixtures, a dominant effect of cholesterol is observed. Celecoxib induces opposite effects on the hydration status of the carbonyl groups in the binary system whereas
cholesterol induces hydrogen bonding around this group. An evidence of phase separation has also been observed for all three systems (DSPC/celecoxib, DSPC/Chol, and DSPC/Chol/celecoxib). In addition, a possible location of celecoxib in the interfacial region of the membrane has been proposed. Finally, penetration of celecoxib into the hydrophobic core of the ternary system at high cholesterol concentrations and formation of a new phase has also been suggested. Thus, depending on the concentration used, celecoxib induces significant changes in the biophysical properties of membranes that may aid in understanding its mechanism of action. Furthermore, highly complex interactions take place in ternary membrane systems and further investigations are needed to explore them in detail.

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Shabani, Shahpar. "Pure Java interface to a DSMS : Pure Java interface to a DSMS." Thesis, Uppsala universitet, Institutionen för informationsteknologi, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-423975.

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SCSQ (Scalable Stream Query processor) is a data stream management system (DSMS) that allows different kinds of distributed high-volume infinite streams to be queried. The current Java interface to SCSQ usesC libraries to communicate between Java and a SCSQ server. Therefore, a pure Java client-server interface to SCSQ is needed. Unlike regular databases, DSMS can process queries over infinite streams. Such continuous queries (CQs) are running until they are explicitlyterminated. The interface must be able to process infinite scans of continuous query results. This master thesis implements a pure Java client-server interface to SCSQ which can handle CQs.

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Varum, Tiago Miguel Valente. "Antena para comunicações DSRC." Master's thesis, Universidade de Aveiro, 2010. http://hdl.handle.net/10773/4482.

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Mestrado em Engenharia Electrónica e Telecomunicações
Dadas as suas características, a utilização das antenas microstrip tem aumentado nos sistemas de comunicações sem fio, em diferentes projectos. A sua simplicidade aliada ao baixo custo permitem desenvolver quer antenas quer agregados de antenas com elevada qualidade e eficiência, que podem ser usadas nas mais diversas aplicações do dia-a-dia. Uma das aplicações possíveis das antenas microstrip são as comunicações dedicadas de curto alcance (DSRC) muito usadas no controlo de veículos nas estradas. No âmbito desta temática, foi projectada, simulada, construída e medida uma antena com características que respeitam a norma europeia para as comunicações DSRC. A antena desenvolvida é um agregado planar cujo diagrama de radiação se adequa ás comunicações rodoviárias e possui polarização circular imposta pela norma. Uma tecnologia que tem crescido nos últimos tempos no âmbito das antenas de forma a potenciar o seu desempenho são o uso de estruturas EBG (Electromagnetic Band Gap) em redor das antenas de forma a eliminar as não desejadas ondas superficiais. Posteriormente foi estudado o impacto do uso de estruturas EBG na antena dimensionada, com o objectivo de melhorar o desempenho global desta. Foram adicionadas estruturas EBG em redor da antena, e analisado impacto destas nas características de radiação da antena.
Given its characteristics, the use of microstrip antennas has increased in wireless communications systems, in di erent projects. Its simplicity coupled with the low cost allow to develop antennas or arrays of antennas with high quality and e ciency, that can be used in diverse applications in day-to-day. One of the possible applications of microstrip antennas is the dedicated short range communications (DSRC) widely used to communicate with vehicles on the roads. Under this theme an antenna, was designed, simulated, built and measured with features that meet the European standard for DSRC communications. The developed antenna is a planar array whose radiation pattern and circular polarization ts the european standard. A technology that has grown, in recent times, in the antennas, to maximize their performance are the EBG structures (Electromagnetic Band Gap) around the radiating elements to eliminate the unwanted surface waves. Subsequently the impact of using EBG structures in the antenna proposed, as been studied in order to improve its overall performance. Some EBG structures were added around the antenna, and their impact analysed on the antenna radiation characteristics.

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Rito, Pedro Filipe Vieira. "Recetor SDR para comunicações DSRC." Master's thesis, Universidade de Aveiro, 2011. http://hdl.handle.net/10773/8614.

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Mestrado em Engenharia Electrónica e Telecomunicações
Nos ultimos anos, um dos focos de investigação tem sido a conceção e inclusão de sistemas inteligentes no tráfego rodoviário. Chamados Intelli- gent Transportation Systems (ITS), têm como nalidade minimizar o tempo perdido em congestionamentos, consumo de energia e danos ambientais, humanos e materiais, tentando assim contribuir para a sustentabilidade do setor. Um dos exemplos mais conhecidos e a cobrança eletrónica de taxas, Electronic Fee Collection (EFC). O EFC usa comunicações sem os de curto alcance, normalmente definidas por Dedicated Short-Range Communicati- ons (DSRC). Atualmente, existem algumas questões que precisam de ser ultrapassadas para ser possível o desenvolvimento efetivo destes sistemas. Por estarmos perante sistemas que estão em constante evolução são necessárias novas tecnologias de implementação dos terminais que tornem possível a sua atualização frequente. A melhor solução para satisfazer este tipo de requisitos e recorrer a utilização do conceito de Software De ned Radio (SDR), isto e, tratar os sinais de rádio tanto quanto possível no domínio digital e, eventualmente, com recurso a software. Esta dissertação tem como objetivo o desenvolvimento de parte de um recetor BPSK para DSRC recorrendo aos conceitos de SDR. O recetor de rádio inclui a conversão de analógico para digital dos sinais recebidos e de seguida a desmodulação em FPGA. Para isso, é feita inicialmente uma apresentação dos standards que envolvem as comunicações DSRC a nível europeu, tal como as vantagens da aplicação de SDR neste projeto. Com vista a conceptualização do projeto, são estudadas e simuladas algumas das arquiteturas mais importantes na receção de sinais BPSK. Partindo da análise das vantagens e desvantagens de cada uma destas, é escolhida a melhor para utilizar na implementação. Essa arquitetura utiliza o Costas loop. Seguidamente, é efetuada a apresentação de forma detalhada dos dois principais módulos implementados para o recetor: a construção da placa de amplificação, filtragem e conversão analógico-digital dos sinais recebidos, e a realização do desmodulador BPSK em FPGA. Numa última fase, recorrendo a alguns testes de validação e avaliação do sistema, são apresentados vários resultados que ilustram o funcionamento do sistema. Conclui-se que o recetor é capaz de desmodular os sinais recebidos. A dissertação termina com algumas sugestões com vista à evolução do equipamento no futuro.
Recently, a focus by the research teams has been the conception and inclusion of intelligent systems in road tra c. Called Intelligent Transportation Systems (ITS), they are intended to minimize the time lost in congestion, energy consumption and environmental, human and material damage, thus trying to contribute to the sustainability of the setor. One of the known examples is the Electronic Fee Collection (EFC). EFC uses Dedicated Short- Range Communications (DSRC). Currently, there are some issues that need to be achieved to the e ective development of these systems. Because we are dealing with systems that have constant evolution, new technologies are needed for design of these terminals that make possible to be frequently updated. The best solution to meet such requirements is to use Software De ned Radio (SDR), that is, handle the radio signals as much as possible by digital domain and, eventually, using software. This dissertation aims to develop part of a BPSK receiver for DSRC using SDR. The radio receiver includes conversion of received signals from analog to digital and then the demodulation in FPGA. Therefore, it is initially made a presentation of communications involving DSRC standards at European level, such as the advantages of using SDR in this project. For the conceptualization of the project to be implemented, they are studied and simulated some of the most important architectures in the reception of BPSK signals. Analyzing the advantages and disadvantages of each one, the demodulation method chosed for the implementation was the Costas loop. Next, it is made a detailed presentation of the two main modules of receiver implementation: the construction of the ampli cation, ltering and analog to digital conversion board, and the realization of BPSK demodulator in FPGA. In a last phase, using validation and evaluation tests, several results are presented that illustrate the operation of the system. It was concluded that the receiver can demodulate the received signals. The dissertation ends with some suggestions for a maybe future evolution of the equipment.

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Bæren, Mats Møller. "Antenne til bruk i DSRC-brikke." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for elektronikk og telekommunikasjon, 2012. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-19062.

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DSRC er et system for enveis eller toveis trådløs kommunikasjon med kort til medium rekkevidde,som blant annet brukes til å automatisere innkreving av bompenger i de største byene i Norge.Systemet benytter en interrogator og en DSRC-brikke populært kalt bompengebrikke. DSRCbrikkenmodulerer inn en unik identifikasjon på signalet den får fra interrogatoren, som foreksempel kan brukes til å identifisere brukeren som passerer igjennom en bompengering.NORBIT er et firma lokalisert i Trondheim som utvikler og produserer DSRC-produkter, blandtannet til det norske AutoPASS-systemet. NORBIT produserer et stort antall DSRC-brikkerhvert år, derfor er det viktig å ta hensynet til produksjonenskostnader. DSRC-brikkene kangjøres rimeligere ved bruk av andre substrat og ved å integrere komponenter som en del avgeometrien til antennen. Aluminiumsoksid er et substrat på markedet som er rimeligere, har godegenskaper for høye frekvenser, og kan fungere like godt som det substratet som brukes i dagensproduksjon. Dette substratet har høyere dielektrisitetskonstant, som fører til at antennen ogtilhørende matenettverk må redesignes.Studiet har da omhandlet hvordan antennen til DSRC-brikken kan designes med aluminiumsoksidsubstrat og fortsatt fungere like godt som antennen til dagens DSRC-brikke. I simuleringene gikkbruken av aluminiumsoksid gikk på bekostning antenneforsterkningen, men det viste seg imidlertidmulig å kompensere for denne nedgangen ved å eksitere andre og litt utradisjonelle TM-moder iantennen. Dagens DSRC-brikker bruker ortogonale spalter for å oppnå sirkulær polarisasjon, mendet viste seg også mulig i simuleringene å bruke geometrien til selve antenneelementet for å oppnådet samme.Det ble utarbeidet to forslag til antennedesign, desverre viste det seg at det var stor forskjell mellomsimulering og målinger på fysiske antenner. Testantennene tilfredsstillte ikke kravene tilundertrykkelse av krysspolarisasjon og konversjons forsterkning til en DSRC-brikke. Det er ganskevanlig at det må flere revisjoner til for å få et optimalt antennedesign. Derfor er det også forslåttvidereføring og forbedringer av antennedesignet.

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36

Thorsrud, Einar. "Programvaredefinert radio : Mulige hyllevareløsninger for DSRC-anvendelser." Thesis, Norwegian University of Science and Technology, Department of Electronics and Telecommunications, 2009. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-10507.

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Utviklingen innen radiokommunikasjon går i retning av rekonfigurerbare programvaredefinerte radioer, der funksjonaliteten og signalbehandlingen er implementert i programvare. Fremveksten av standardiserte maskinvareplattformer og programvarerammeverk, som gjør det mulig å utvikle nye og fleksible radioer ved hjelp av hyllevarer, er et resultat av dette. To sentrale frie rammeverk for programvaredefinert radio er: GNU Radio, et selvstendig rammeverk; og «Open Source SCA Implementation::Embedded», en fri implementering av «Software Communications Architecture». Denne masteroppgaven undersøker hvordan radioplattformen «Universal Software Radio Peripheral» (USRP) kan brukes sammen med de to frie rammeverkene til å realisere en veikantenhet for elektronisk bompengeinnkreving. Det innledende litteraturstudiet viser at GNU Radio er best egnet til realiseringen på grunn av lav interkomponentlatens, et stort utvalg ferdige signalbehandlingsblokker og god støtte for USRP. Gjennom arbeidet med denne oppgaven ble det implementert en sender og en koherent mottaker til en veikantenhet ved hjelp av GNU Radio og USRP. Realiseringene fungerer delvis, men det oppsto betydelige problemer under testing. Beregningskompleksiteten er lav nok til at det vil være mulig å pakke radiofunksjonaliteten inn i en integrert enhet basert på datamaskinkomponenter og USRP.

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Shiue, Gueng-Shuen, and 薛光舜. "DSMC Simulation of 2D Convergent Micronozzle Flow." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/88811217048227124250.

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碩士
國防大學理工學院
航空太空工程碩士班
99
In this study, it uses Direct Simulation Monte Carlo (DSMC) method with trapezoidal meshes to simulate characteristics of flows field for two-dimensional convergent micronozzle. The influence of the micro/nanoscale rarefied gas effects on flow characteristics were investigated and analyzed. First, real three-dimensional micronozzle flow field use simplified to a two–dimensional convergent micronozzle. Modified no time counter (M-NTC) rule is applied on the selection of representative collision pairs. Different reflect boundary conditions, such as specular/diffuse/isotropic reflection an adopted as wall boundary conditions. Finally the effects of back pressure, reflection conditions, and rarefaction on the flow field characteristics in two-dimensional convergent micronozzle are studied.

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38

Le, Minmin. "DSMC simulation of flows in multiple microchannel geometries." Thesis, 2006. http://spectrum.library.concordia.ca/8880/1/MR16251.pdf.

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The direct simulation Monte Carlo method was applied to simulate the flows in uniform, parallel, series, and T-shape microchannels. For the uniform microchannel case, both the supersonic and subsonic flows have been considered. The effect of the Knudsen number (Kn) on the flow properties and the heat transfer characteristics were investigated. Some significant flow features, such as the flow acceleration along the channel, the nonlinear pressure distribution, and the velocity slip near the wall, due to the compressibility and the rarefaction of the microflow were specified. Most of the wall heat flux occurs within the channel entrance region when the wall temperature is higher than the bulk flow temperature. Furthermore, in supersonic flow case, the wall heat flux is mainly caused by the deceleration of the flow due to the wall friction.

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39

Soo, Jar Nan, and 蘇嘉南. "Three Dimensional DSMC Analysis of Supersonic Microchannel Flow." Thesis, 2000. http://ndltd.ncl.edu.tw/handle/36413675929940833373.

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碩士
國立成功大學
機械工程學系
88
The microchannel is a very important element in Microelectro- mechanical system, and the gas flow in the channel will affect the performance of microsystem directly. Hence, the regime of interaction between microchannel and working gas becomes a serious topic. Because of the approach of characteristic length of microchannel to the mean free path of working gas, the thesis takes advantage of the concept of probability and statistics to simulate the behavior of molecules in the system with the theory of molecular gas dynamics, and then show the profiles of flow fields finally. This method is well-known as Direct Simulation of Monte Carlo Method. The thesis have simulated five different cases of supersonic square microchannel flows with different channel sizes and got the regimes handling the flow field of microchannels. The regimes include the effect of inertia, viscous effect and effect of relaxation. The effects are caused respectively from the gas injected from the inlet, walls of the channel, and the outlet and channel length. The obvious shack waves in the local region of the center of inlet, the non-zero flow velocity and the temperature jump in the region close to walls of channel are also found. After the comparison of three dimensional simulated results and the two dimensional results done by other researchers, the deviation will be great if two dimensional simulated result is used to explain square microchannel flow field. Many physical phenomena, such as shock waves in the region of the inlet, will be far away from the channel inlet in the direction to channel outlet. This resulted from the ignorance of one side of channel walls. Hence, the simulate model must be built very carefully when DSMC is used to analyse the flow field of microsystem.

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40

Hung, Nien-Tzu, and 洪念慈. "DSMC Simulation of 3-D Micro-channel Flows." Thesis, 2004. http://ndltd.ncl.edu.tw/handle/79689220045967791712.

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碩士
淡江大學
機械與機電工程學系
92
In this paper, the direct simulation Monte Carlo has been applied to compute 3-D Low-speed Micro-channel Flows, then compare with the difference in 2-D and 3-D flows. Variation of the Knudsen number is obtained by change the inlet pressure while keeping the pressure ratio. The effects of varying Knudsen number on flow property were investigated. The VHS model and Nitrogen has been applied. The result shows that simulation of 3-D differs a lot from 2-D. In the velocity distribution, the result of the 3-D is lower than 2-D,about only 65% of 2-D,because the friction of the wall. In addition, compare to the different inlet pressure case, wall slip velocity increase and inner velocity decrease along the enhanced rarefaction. On the analysis of heat flux, the result of 3-D is larger then 2-D, but not distinct with high Knudsen number.

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Luo, Wen-Bin, and 羅文彬. "DSMC Simulation of 2-D Micro-channel Flows." Thesis, 2004. http://ndltd.ncl.edu.tw/handle/82193636833952538195.

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碩士
淡江大學
機械與機電工程學系
92
In this paper, the DSMC method was employed to investigate the flow properties in microchannels with different wall temperature and the heat transfer phenomenon between the fluid and the channel walls. The molecular collisions are simulated using the variable hard sphere (VHS) molecular model. The results of supersonic flows in microchannels show that the temperature increases near the entrance and decreases as the flow develops downstream. The subsonic flows in microchannels are simulated by different wall temperature. The higher wall temperature increases the rarefaction of the flow field. The subsonic flows in microchannels are also simulated by varying inlet pressure for a range of slip to transition regime flows. It is found that the slip velocity increases with the increase of Kn.

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42

Lo, Chung-Yeu, and 羅仲禹. "DSMC of Gaseous Flow and Heat Transfer in Microchannel." Thesis, 2001. http://ndltd.ncl.edu.tw/handle/86644974844481757793.

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碩士
國防大學中正理工學院
兵器系統工程研究所
89
The study of micro-channel flow is partly in response to the need for thermal control in the operation of MEMS in which the range of gas flow is from slip flow to transition regime. It will lead to incorrect results if we consider gas flow in micro-channel as continuum phenomena. In this paper, molecular approach DSMC has been used to study the flow and heat transfer characteristic of rarefied gas in micro-channel. In one-dimensional simulation, a constant acceleration body force is applied to the system and the flow is restricted in laminar and subsonic state. The simulation results show that the discrepancies of hydrodynamic prediction are widening as indicated from velocity and temperature profiles when the flow in continuum regime transfers to slip flow regime, then low transition regime by increasing Knudsen number（Kn）. The data predicted by VHS model differ quantitatively from HS model, but it exists qualitative consistency between them. The macroscopic flow phenomena could be related to and described by the microscopic molecular motion based on simulation results. Pressure-driven flows in micro-channel are simulated by varying inlet/exit pressure for a range of slip to transition regime flows. Both ambient and hot wall temperature cases are investigated. The simulation results of the former case show that the temperature in the flow field is lower than that of the channel wall. It is opposite to one-dimensional flow because of the difference of driving force. It is found that pressure distribution along the channel and streamwise velocity distribution in the transverse direction become more linear and flatter respectively with the increase of the Kn. In addition, the slip velocity increases along the streamwise direction. In hot surface case, the heat flux through the channel wall is more pronounced than in the cold surface case. The flow properties such as temperature, density and pressure are strongly dependent on Kn and heat transfer. The effect of heat transfer from hot wall increases the rarefaction of the flow field and the inlet influence at the same boundary condition. Additionally, the pressure ratio in the flow field is higher than that without heat transfer.

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Shing, Cheng Tine, and 鄭廷訓. "The Design of Turbo Molecular Pump by DSMC Method." Thesis, 2004. http://ndltd.ncl.edu.tw/handle/54819278991906241790.

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碩士
國立屏東科技大學
機械工程系
92
Turbo molecular pump can provide good air-removal effect in free molecular flow to the ultra high vacuum status. The blade geometries and arrangement have a great influence on pump speed and compression ratio. In this research, direct simulation of Monte Carlo method is adopted to check to specific parameters influence on the pump speed and compression ratio. Parameters need include: blade geometries, rotor blade angle and stator blade angle , blade spacing ratio and blade chord (s/b ratio), and rotational speed. Also the blade geometry is optimized by the Taguchi method. Following the result of Taguchi method, rotor blade angle, blade s/b ratio, and rotational speed are the main (key) issues which affect the pump speed. With the Taguchi optimization, the signal-to-interference ratio is 0.8db higher than the best result from the experiment orthogonal table, and the pump speed also increased from 34.23% to 36.67%.

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Cheng, Chun-Chang, and 陳均彰. "Mixing Analysis of a Scramjet engine via DSMC method." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/41993388924996868161.

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碩士
淡江大學
機械與機電工程學系碩士班
100
Supersonic combustion ramjet engine work flow field are thin. Therefore, We have to use micro particle to analyze. The macro continuum hypothesis is no longer suitable. This article use one of the Numerical Solution to simulate DSMC. It is precise and used a lot of analyze recently. This article adopted the variety of Scramjet inner flow field by DSMC. We consider the situation of fuel ignition and air mixing. How to achieve good mixing efficiency has become concerned about the direction of the research, therefore, for a variety of different the combustion chamber configuration calculation and analysis its mixing efficiency.

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45

Hsu, Che-Kang, and 許哲綱. "Parametric Study of Spiral Drag Pump Using The DSMC Method." Thesis, 2003. http://ndltd.ncl.edu.tw/handle/79417308048265918726.

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碩士
國立交通大學
機械工程系
91
Numerical simulations of rarefied gas flows in spiral drag pump (SDP) channel are carried out by using the three-dimensional unstructured direct simulation Monte Carlo (DSMC) method. Using Variable Hard Sphere (VHS) molecular model, No Time Counter (NTC) collision sample and variable time-step method (VTS) to simulate the molecular collision kinetics and use Cell-By-Cell particle tracing method complete the part of molecular move. According to Nanbu et al. (1991) experiment condition, to simulate a real three-dimension model on SDP geometry parameter (include depth of groove, gap size, screw angle) and rotation speed directly, use the pump performance parameter are volumetric flow rate (pumping speed), mass flow rate (throughput), compression ratio, and pressure different (between discharge and inlet) to analysis the flow field in the pump channel. The flow occurring in the pumping channel develops from the molecular transition to slip flow traveling downstream. Results show that to increase the depth of groove, molecules mass, screw angle and rotation speed can raise the pumping speed and the mass flow rate. As the gap value increases, pumping speed and the mass flow rate will be decreased.

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46

Shih, Chang-Chieh, and 施長杰. "DSMC Analysis of Rarefied Gas Flow Over a Flat Plate." Thesis, 1997. http://ndltd.ncl.edu.tw/handle/89243114582690735457.

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碩士
大同工學院
機械工程學系
85
The present study is concerned with the flow behaviors of the rarefied gas over a flat plate. The Direct Simulation of Monte Carlo Method (DSMC) is employed to examine the effects of the physical parameters, such as the Knudsen number, Mach number, angle of attack of the incoming flow, and the plate length, on the flow patterns as well as the pressure and the skin friction coefficients. In order to ensure the validity ofthe numerical method, comparison between the present solution and the existing information has been made. For low-speed flows, the present study also presents the continuum-model solution to study the conversion process from the molecular flows to the continuous. The present analysis includes both the subsonic and the supersonics flow. The parameter ranges considered here are :Knudsen number is between 0.01 and 1, Mach number is between 0.15 and 5, angle of attack of the incoming flow is between 0 and 90.

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47

Titov, Evgeny V. "Application of the DSMC method to high density micro-flows /." 2007. http://etda.libraries.psu.edu/theses/approved/WorldWideIndex/ETD-2105/index.html.

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Lin, Shin-Chieh, and 林士傑. "DSMC Simulation of the Subsonic Flow Past a Vertical Plate." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/36965453204015601503.

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碩士
國立交通大學
機械工程系所
96
The phenomena of vortex shedding associated with the subsonic external flow problems in different length scales are visible everywhere in fluid dynamics. For example, aviation of fruit flies and birds, driving car in the wind, flowing river through piers under a bridge, and the air current interaction with an island and so forth. A large number of experimental and numerical studies have been reported on the vortex-shedding flows in the continuum limit, while there have been very few studies focusing on similar flows in the rarefied gas regime. Major obstacle of the investigation in rarefied regime mostly came from the difficulties of experiments and also numerical simulations for unsteady flows in this regime. In the present paper, a general-purpose Parallel Direct Simulation Monte Carlo Code, named PDSC, is used to simulate the subsonic flow pasts a 2D vertical plate for studying the vortex-shedding phenomena. An unsteady time-averaging with temporal variable time step sampling method, called TVTS. Parametric studies, including temporal variable time step (TVTS) factor, particles per cell, number of temporal nodes, domain size and Reynolds number, are conducted to obtain the Strouhal number and aerodynamics coefficients. The results are compared to experimental data in the continuum region and simulations from the literature wherever they are available. Results of TVTS=100 and 150 has oscillation phenomenon, but results of TVTS=100 has results clear vortex shedding. Both the Strouhal number (0.174, 0.188, and 0.21) and the average drag coefficients (1.05, 1.14, 1.35, and 1.4) are increased with respect to Re=73, 126, 287 and 412 respectively, expect that the Strouhal value of Re=73 case is unavailable because the vortex is steady.

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Strand, James Stephen. "Statistical methods for the analysis of DSMC simulations of hypersonic shocks." Thesis, 2012. http://hdl.handle.net/2152/ETD-UT-2012-05-5384.

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In this work, statistical techniques were employed to study the modeling of a hypersonic shock with the Direct Simulation Monte Carlo (DSMC) method, and to gain insight into how the model interacts with a set of physical parameters. Direct Simulation Monte Carlo (DSMC) is a particle based method which is useful for simulating gas dynamics in rarefied and/or highly non-equilibrium flowfields. A DSMC code was written and optimized for use in this research. The code was developed with shock tube simulations in mind, and it includes a number of improvements which allow for the efficient simulation of 1D, hypersonic shocks. Most importantly, a moving sampling region is used to obtain an accurate steady shock profile from an unsteady, moving shock wave. The code is MPI parallel and an adaptive load balancing scheme ensures that the workload is distributed properly between processors over the course of a simulation. Global, Monte Carlo based sensitivity analyses were performed in order to determine which of the parameters examined in this work most strongly affect the simulation results for two scenarios: a 0D relaxation from an initial high temperature state and a hypersonic shock. The 0D relaxation scenario was included in order to examine whether, with appropriate initial conditions, it can be viewed in some regards as a substitute for the 1D shock in a statistical sensitivity analysis. In both analyses sensitivities were calculated based on both the square of the Pearson correlation coefficient and the mutual information. The quantity of interest (QoI) chosen for these analyses was the NO density profile. This vector QoI was broken into a set of scalar QoIs, each representing the density of NO at a specific point in time (for the relaxation) or a specific streamwise location (for the shock), and sensitivities were calculated for each scalar QoI based on both measures of sensitivity. The sensitivities were then integrated over the set of scalar QoIs to determine an overall sensitivity for each parameter. A weighting function was used in the integration in order to emphasize sensitivities in the region of greatest thermal and chemical non-equilibrium. The six parameters which most strongly affect the NO density profile were found to be the same for both scenarios, which provides justification for the claim that a 0D relaxation can in some situations be used as a substitute model for a hypersonic shock. These six parameters are the pre-exponential constants in the Arrhenius rate equations for the N2 dissociation reaction N2 + N ⇄ 3N, the O2 dissociation reaction O2 + O ⇄ 3O, the NO dissociation reactions NO + N ⇄ 2N + O and NO + O ⇄ N + 2O, and the exchange reactions N2 + O ⇄ NO + N and NO + O ⇄ O2 + N. After identification of the most sensitive parameters, a synthetic data calibration was performed to demonstrate that the statistical inverse problem could be solved for the 0D relaxation scenario. The calibration was performed using the QUESO code, developed at the PECOS center at UT Austin, which employs the Delayed Rejection Adaptive Metropolis (DRAM) algorithm. The six parameters identified by the sensitivity analysis were calibrated successfully with respect to a group of synthetic datasets.
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Huang, Ying-Hsiang, and 黃盈翔. "DSMC Simulation of 3-D backward-facing step flow at microscale." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/53wmm9.

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碩士
淡江大學
機械與機電工程學系碩士班
94
The Direct Simulation Monte Carlo (DSMC) method has been employed to analyze the rationality of the 2-D simplification for a 3-D backward-facing step flow. An mass flux treatment for low-speed inflow and outflow boundaries for the DSMC of the microchannel flow is employed. The VHS model and Nitrogen was employed in the simulation. The 3-D microchannel flows is simulated with the cross aspect ratio in the range of 1 and 5. The calculated flow properties in the 3-D cases are compared with the results of the 2-D case. It shows that when the aspect ratio < 3, the two extra side walls in the 3-D case have significant effects on the heat transfer and flow properties. When the aspect ratio increases, the flow pattern and heat transfer characteristics tend to approach that of 2-D results. The 2-D simplification is found to be reasonable only when the cross aspect ratio is larger than 5. In this paper, the effects of rarefaction on flow characteristics are also analyzed and discussed. It is found that flow separation, recirculation, and reattachment will disappear as Knudsen number, Kn, exceeds 0.1 for 2-D case, and will disappear as Kn exceeds 0.02 for 3-D case.

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