Дисертації з теми "Velocity on the wall"
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1
Gresko, Lawrence Sebastian. "Characteristics of wall pressure and near-wall velocity in a flat plate turbulent boundary layer." Thesis, Massachusetts Institute of Technology, 1988. http://hdl.handle.net/1721.1/14373.
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Österberg, Klas. "Vascular wall responses to bypass grafting : studies in mice /." Göteborg : Dept. of Molecular and Clinical Medicine, Vascular Surgery, Institute of Medicine, Sahlgrenska Academy at Göteborg University, 2008. http://hdl.handle.net/2077/9437.
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3
Disotell, Kevin James. "A semi-empirical model of the wall-normal velocity induced by flow-shaping plasma actuators." Connect to resource, 2010. http://hdl.handle.net/1811/45413.
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Hurst, Edward. "A numerical study of turbulent drag reduction using streamwise travelling waves of spanwise wall velocity." Thesis, University of Warwick, 2013. http://wrap.warwick.ac.uk/67161/.
Повний текст джерелаАнотація:
A parallelisation of the fully-implicit fractional step based in-house DNS code was implemented. Utilising this, DNS of streamwise travelling waves of spanwise wall velocity in a turbulent channel flow were performed at Reτ = 200; 400; 800 and 1600, scaling the input parameters in wall units. Studying the drag reduction at varying Reynolds number showed that the maximum drag reduction decreased as Re was increased. The scaling with Reynolds number was dependent on the control parameters and therefore the optimal parameters changed with Re. An oscillation in the drag reduction over the forcing period was observed and associated with strong variations in the turbulent statistics, angling of the streaks and coherent structures, and the deterioration of the drag reduction. The conditionally averaged λ2 structures were found and behaved differently depending on the sign of the vorticity. This included a strong angling of the structure which rotated in agreement with the wall velocity, and this angle reduced over the half- period. The λ2 structures were moved away from the wall over the period, a feature also visible in the variation of the vorticity fluctuations. The relationship between the drag reduction and the extrema of the turbulent profiles were compared, and showed a good correlation between the maximum of the v rms profile and the DR achieved. This was seen to be independent of Reynolds number when the maximum v rms of the no control flow was subtracted. The variation of the power spent and net power saving with Reynolds number was also studied. The power spent scaled well with Reτ-0.16, and the net power saving scaled differently depending on the control parameters used. Although the maximum value was reduced as the Reynolds number increased.
5
Köhler, Uwe. "3D phase contrast MRI : velocity-field visualisation and wall shear rate calculation in major arteries." Thesis, University of Edinburgh, 2000. http://hdl.handle.net/1842/22384.
Повний текст джерелаАнотація:
Approximately half of all deaths in the developed world arise from cardiovascular disease, primarily caused by the deposition of atheroma within major arteries. It has been observed that atheroma is deposited preferentially in regions along the outer wall of bifurcations, and along the distal part of the inner wall of bends. These are regions associated with disturbances of the blood flow that display abnormal shear rate (spatial velocity gradient at the vessel wall). Thus, in order to facilitate clinical diagnoses, it is important to visualise the structure and haemodynamic properties of arteries and veins. Magnetic resonance imaging (MRI) is well suited for volume imaging and can be made sensitive to flow. Quantitative velocity measurements are possible using phase contrast (PC) MRI. The aim of this project was the provision of a method that provides information on wall shear rate vectors using MRI. To handle the large number of images acquired in PC MRI automated flow detection algorithms were developed. Three different algorithms were identified: one operating on magnitude MRI images only and two methods which additionally use the velocity information generated from in-vivo and in-vitro acquisitions. These algorithms are based on an edge detection method and were tested on phantoms. The post processing steps necessary to calculate wall shear stress involved the fit of smooth functions to the velocity data, the detection of walls and the calculation of the wall shear rate vector based on that information. Fitting a smooth function removed residual noise and allowed the calculation of spatial derivatives. The velocity data was satisfactorily described by a segmented fifth order polynomial fit. One method of vessel wall reconstruction was based on the fitted velocity field, while another one utilised the detected flow regions. Using the surface position and normals, the wall shear rate was calculated from the shear stress tensor. All post-processing steps were integrated in a purpose built program that enabled graphical user interactions. The calculated wall shear rate values were quantitatively verified with experiments on various phantoms and simulations, and qualitatively compared with computational fluid dynamics calculations. It is shown that a method to calculate reliably wall shear rate directly from time averaged PC MRI acquisitions has been established.
6
Loth, Francis. "Velocity and wall shear measurements inside a vascular graft model under steady and pulsatile flow conditions." Diss., Georgia Institute of Technology, 1993. http://hdl.handle.net/1853/15907.
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7
Tamtomo, Kiono Berkah Fajar. "Study of wall velocity gradient and mass transfer on rotating cylinder and finned-cylinder in crossflow." Valenciennes, 2002. https://ged.uphf.fr/nuxeo/site/esupversions/2de35dda-200e-4237-8d4b-574007c70bf2.
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Ce travail porte sur la mesure du frottement pariétal et du transfert de masse, sur un cylindre nu et sur un cylindre muni d'une ailette en rotation perpendiculairement à un écoulement, à l'aide de la méthode polarographique. Les mesures ont été réalisées pour différents nombres de Reynolds et pour différentes valeurs du paramètre α, représentant le rapport entre la vitesse périphérique du cylindre et celle de l'écoulement au loin. Une méthode inverse de transfert de masse a pemis la correction directe des signaux électrochimiques. Le frottement pariétal ainsi obtenu sur le cylindre tourne dans le sens inverse de l'écoulement moyen. La mesure du transfert de masse local autour du cylindre en rotation a permis d'établir une corrélation qui tient compte des effets combinés de la rotation du cylindre et de l'écoulement. Cette corrélation permet d'étendre celle établie dans le cas du transfert de chaleur à une gamme plus grande du nombre de Reynolds. La deuxième partie de ce travail concerne la mesure locale du frottement sur une ailette fixée au cylindre. Les valeurs locales élevées du frottement pariétal sur l'ailette sont interprétées à l'aide du modèle de tourbillon en "fer à cheval". On montre que pour les faibles valeurs de α, l'évolution du frottement instationnaire sur l'ailette est semblable à celle observée dans le cas stationnaire. Lorsque la vitesse de rotation su cylindre augmente, la distribution du frottement pariétal tend vers celle obtenue dans le cas du fluide au repos. L'analogie de Reynolds a permis d'atablir une corrélation entre le nombre de Reynolds de rotation et le nombre de Nusselt moyen calculé sur l'ailetteThis works deals with the measurement of the wall shear stress and mass transfer around a rotating cylinder alone and a rotating finned cylinder in cross flow by using the polarographic method for different Reynolds numbers and different α (peripheral speed/streamwise velocity). An inverse mass transfer method permits to correct the electronical signal. The corrected wall hear stress around the rotating cylinder show the presence of complex structures, especially in the upstream moving wall region. The mass transfer measured on the rotating cylinder leads to a correlation that takes into account the combined effects of rotation and cross flow. The second part of this work concerns the local measurement of the wall shear stress on the fin fixed to the cylinder. The high values of the wall shear stress measured on the fin are attributed to "horseshoe" vortices. It is shown that for low values of α, the distribution of the unsteady wall shear stress on the fin is similar to that observed in the steady case. Whan the rotation speed increases, the distribution of the wall shear stress tends towards that obtained in fluid at rest. A correlation between the rotation Reynolds number and mean Nusselt number on the fin is proposed by using a Reynolds analogy
8
Blake, James R. "On the assessment of blood velocity and wall shear rate in arteries with Doppler ultrasound : a validation study." Thesis, University of Edinburgh, 2008. http://hdl.handle.net/1842/4195.
Повний текст джерелаАнотація:
Cardiovascular disease, mostly atherosclerosis, is responsible for one third of all deaths globally, rising to more than 50% in the Western World. Risk factors include smoking, diet, and familial history. Doppler ultrasound can provide estimates of blood velocity and wall shear rate. Clinically, maximum velocity is used to categorise patients for surgery, although Doppler velocity measurement is prone to errors and in need of validation. Wall shear stress—which can be derived from wall shear rate—plays a role in disease initiation and progression, although its clinical utility is unclear due to difficulties associated with its measurement. This thesis investigates the use of Doppler ultrasound as a tool to estimate blood velocity and wall shear rate. A simplified method for estimation of wall shear rate in healthy arteries is developed that uses spectral Doppler ultrasound. This method is based upon the theory of oscillatory flow in rigid pipes, requiring two measurements that are readily available with clinical ultrasound machines. This method is compared to a similar method based on colour flow imaging. The spectral Doppler method underestimated the theoretic value of wall shear rate by between 7 and 22%, with results varying between phantoms. Errors for the colour method were on average 35% greater. Test measurements from one healthy volunteer demonstrated that this method can be applied in-vivo. In more advanced stages of disease, peak velocity distal to a stenosis is of clinical interest and the simplified method for wall shear rate estimation is invalid. Steady flow in a series of simplified stenosis geometries was studied using a dual-beam Doppler system to obtain velocity vectors. These measurements were compared with data from an equivalent system that used particle image velocimetry (PIV) and was considered the gold standard. For Reynolds numbers at the stenosis throat of less than 800, flow remained laminar over the region studied, although distal flow separation did occur. For higher throat Reynolds numbers—corresponding to more severe stenoses or increased flow rates—asymmetric recirculation regions developed; the transition to turbulence occurred more proximally, with a corresponding reduction in stenotic jet and recirculation length. Qualitative agreement was observed in the velocity profile shapes measured using ultrasound and PIV at throat Reynolds numbers less than 800. Above this threshold the qualitative agreement between the velocity profiles became poorer as both downstream distance and the degree of stenosis increased. Peak axial velocity distal to the stenosis was underestimated, on average, by 15% in the ultrasound system. Estimation of shear rate remained difficult with both experimental techniques. Under a Newtonian approximation, the normalised wall shear stresses agree qualitatively. Under pulsatile flow conditions using an idealised flow waveform, superior qualitative agreement was observed in the velocity profiles at diastole than at systole. Similar to the steady flow behaviour, this agreement deteriorated with stenosis severity. The current generation of clinical ultrasound machines are capable of estimating the wall shear rate in healthy arteries. In the presence of significant arterial disease, errors in the peak velocity may result in mis-selection of patients for surgery, while estimation of the wall shear stress remains extremely problematic; particularly with identifying the wall location and measuring velocities close to the wall.
9
Lunt, Tilmann. "Experimental investigation of the plasma-wall transition." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2008. http://dx.doi.org/10.18452/15837.
Повний текст джерелаАнотація:
In der vorliegenden Arbeit wurde das Strömungsverhalten eines magnetisierten Argonplasmas beim Auftreffen auf eine neutralisierende Oberfläche untersucht. Mit Hilfe der Laserinduzierten Fluoreszenz wurde dazu nicht-invasiv die Geschwindigkeitsverteilung der Ionen mit einer Ortsauflösung von standardmäßig dz=0.5 mm als Funktion des Abstandes zur Oberfläche gemessen. Zwei Situationen wurden untersucht (a): praktisch das ganze Plasma strömt auf ein großes Target (Durchmesser 100 mm) und (b) die Größe des Targets ist wesentlich kleiner (Durchmesser 15 mm) als der Durchmesser der Plasmasäule. Unmittelbar vor der Oberfläche war in beiden Fällen die Strömungsgeschwindigkeit u mindestens so groß wie die Ionenschallgeschwindigkeit cs, genau wie von Bohm bereits 1949 vorhergesagt[]. Unter fusionsrelevanten Bedingungen ist dies die erste direkte Beobachtung des Bohmkriteriums. Bei Annäherung an die Oberfläche steigt die Machzahl M=u/cs von 0.5 auf 1 auf typischen Skalenlängen lambda_a=30 mm bzw. lambda_b=5 mm an. Um diese kurzen Längen erklären zu können wurden die Messdaten in (a) mit einem Stoß-Diffusionsmodell und im Falle von (b) mit dem Modell von Hutchinson[] verglichen. Eine gute Übereinstimmung in (a) wurde erzielt, wenn eine sehr niedrige Neutralgastemperatur von etwa 400 K angenommen wird. Die Messdaten in (b) werden sehr gut durch das Modell wiedergegeben, wenn ein Transportkoeffizient von D=20 m²/s angenommen wird. Ein derartig hoher Transport kann unmöglich allein durch Diffusion verursacht werden. Teilweise kann dieser Transport anhand der endlichen Gyroradien erklärt werden, vermutlich aber spielen auch zeitabhängige Phänomene, wie z.B. Driftwellen eine wichtige Rolle. Weiterhin wurde die Abhängigkeit von dem Winkel zwischen Flächennormalen und B-Feld untersucht. Die unmittelbar vor der Oberfläche auftretenden Überschallströmungen werden verhältnismäßig gut von dem Modell von Chodura[] beschrieben. Im Gegensatz dazu ist die Größe der Zone in der Machzahlen größer eins auftreten deutlich kleiner, als vom Modell vorhergesagt.In the present work the streaming behavior of a magnetized argon plasma impinging on a neutralizing surface was investigated. For that purpose the ion velocity distribution was measured non-invasively as a function of the distance to the surface by means of Laser Induced Fluorescence. The spatial resolution was typically dz=0.5 mm. Two situations are investigated, (a): when practically the whole plasma streams onto a large target (diameter 100 mm), and (b): when the size of the target (diameter 15 mm) is significantly smaller than the diameter of the plasma column. In both cases the streaming velocity u was at least as high as the ion acoustic sound speed, as already predicted by Bohm in 1949. Under fusion relevant conditions this is the first direct observation of the Bohm criterion. Approaching the target surface the Mach number M=u/c_s increases from values of around 0.5 to 1 on typical scales of lambda_a=30 mm and lambda_b=5 mm, respectively. In order to explain these very short scale lengths the measured data were compared with a collisional-diffusive model in the case of (a) and with Hutchinson''s model[] in the case of (b). A good agreement was achieved in (a) by assuming a very low neutral gas temperature of about 400 K. In (b) the model fits the data excellently when the transport coefficient is chosen as high as D=20 m²/s. Such a high transport cannot be caused solely by diffusion. Partly it is explained by finite gyro-radii effects, but presumably time dependent phenomena, like drift waves, play an important role. In addition the dependence on the angle between surface normal and B-field was investigated. The supersonic fluxes found in the immediate vicinity of the surface are described fairly well by the model developed by Chodura[]. By contrast the size of the region, where Mach numbers greater one appear is significantly smaller than predicted.
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Bermuske, Mike, Lars Büttner, and Jürgen Czarske. "Measurement uncertainty budget of an interferometric flow velocity sensor." SPIE, 2017. https://tud.qucosa.de/id/qucosa%3A35151.
Повний текст джерелаАнотація:
Flow rate measurements are a common topic for process monitoring in chemical engineering and food industry. To achieve the requested low uncertainties of 0:1% for flow rate measurements, a precise measurement of the shear layers of such flows is necessary. The Laser Doppler Velocimeter (LDV) is an established method for measuring local flow velocities. For exact estimation of the flow rate, the flow profile in the shear layer is of importance. For standard LDV the axial resolution and therefore the number of measurement points in the shear layer is defined by the length of the measurement volume. A decrease of this length is accompanied by a larger fringe distance variation along the measurement axis which results in a rise of the measurement uncertainty for the flow velocity (uncertainty relation between spatial resolution and velocity uncertainty). As a unique advantage, the laser Doppler profile sensor (LDV-PS) overcomes this problem by using two fan-like fringe systems to obtain the position of the measured particles along the measurement axis and therefore achieve a high spatial resolution while it still offers a low velocity uncertainty. With this technique, the flow rate can be estimated with one order of magnitude lower uncertainty, down to 0:05% statistical uncertainty.1 And flow profiles especially in film flows can be measured more accurately. The problem for this technique is, in contrast to laboratory setups where the system is quite stable, that for industrial applications the sensor needs a reliable and robust traceability to the SI units, meter and second. Small deviations in the calibration can, because of the highly position depending calibration function, cause large systematic errors in the measurement result. Therefore, a simple, stable and accurate tool is needed, that can easily be used in industrial surroundings to check or recalibrate the sensor. In this work, different calibration methods are presented and their in uences to the measurement uncertainty budget of the sensor is discussed. Finally, generated measurement results for the film flow of an impinging jet cleaning experiment are presented.
11
Garg, Chirag [Verfasser], Stuart S. P. [Gutachter] Parkin, Georg [Gutachter] Woltersdorf, and Christian [Gutachter] Back. "Investigating the effect of curvature on chiral domain wall velocity / Chirag Garg ; Gutachter: Stuart S. P. Parkin, Georg Woltersdorf, Christian Back." Halle (Saale) : Universitäts- und Landesbibliothek Sachsen-Anhalt, 2019. http://d-nb.info/1210731932/34.
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Awasthi, Manuj. "High Reynolds Number Turbulent Boundary Layer Flow over Small Forward Facing Steps." Thesis, Virginia Tech, 2012. http://hdl.handle.net/10919/33820.
Повний текст джерелаАнотація:
Measurements were made on three forward steps with step height to boundary layer ratio of approximately 3.8%, 15% and 60% and Reynolds number based on step height ranging from 6640 to 213,000. The measurements included mean wall pressure, single and 2 point wall pressure fluctuations, single and 2 point velocity fluctuations and, oil flow visualization. Pressure fluctuation measurements were made 5 boundary layer thicknesses upstream of step to 22 boundary layer thickness (or 600 step heights for smallest step size) downstream of the step. The results show that the steps remarkably enhance the wall pressure fluctuations that scale on the step height in the vicinity of the step and far downstream of the step. The decay of wall pressure fluctuations post reattachment is a slow process and elevated levels can be seen as far as 150 step heights downstream for the mid step size. The enhanced pressure fluctuations come from the unsteady reattachment region on top face of the step which was found to be a strong function of flow geometry and flow parameters such as Reynolds number. The 2 point pressure and velocity space-time correlations show a quasi-periodic structure which begins to develop close to the reattachment and grows in intensity and scale further downstream of reattachment and is responsible for the elevated pressure fluctuations downstream of the step. However, the velocity correlations lack in scale reflecting the fact that large scales reflected in pressure are masked by smaller scales that exist within them.Master of Science
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Castagna, Marco. "An in vitro method for the error assessment of Phase Contrast Magnetic Resonance lmaging based velocity measurements and calculation of derived Wall Shear Stress." Thesis, Nantes, 2020. http://www.theses.fr/2020NANT1012.
Повний текст джерелаАнотація:
L’athérosclérose représente environ 21 % des décès dans le monde. Elle se développe principalement dans des sites spécifiques du système cardiovasculaire où le Wall Shear Stress (WSS) peut s’écarter plus facilement de ses valeurs de référence. Les applications cliniques potentielles du WSS comme biomarquer reposent sur une évaluation précise de la vitesse du sang, car il dépend de la dérivée de la vitesse à la paroi artérielle. Le présent travail vise à concevoir et à développer un banc d’essai hydraulique pour valider les acquisitions de vitesse obtenues par la Phase Contrast Magnetic Resonance Imaging (PC MRI) et le calcul du WSS dérivé. Pour ce faire, des profils de vitesse de référence ont été obtenus avec la Vélocimétrie Laser à effet Doppler (LDV) utilisés pour comparaison directe avec les résultats de la PC MRI. L’installation expérimentale développée est composée d’une pompe compatible avec l’IRM, de tuyaux de raccordement flexibles, d’une section d’essai, d’un réservoir, d’un fluide et d’un débitmètre. Une séquence standard 2D PC MRI et une séquence standard 4D Flow MRI ont été utilisées pour obtenir des profils de vitesse IRM, en ajustant leurs paramètres comme dans la pratique clinique. Ensuite, la résolution spatiale et temporelle des acquisitions 4D Flow MRI a été raffinée. Le WSS a été calculé avec les méthodes 2D et 3D proposées respectivement par Stalder et al. et Potters et al. Les résultats indiquaient un excellent accord entre les données de vitesse et WSS obtenues par PC MRI et LDV. Cette étude constitue une base fiable pour toute validation avec LDV des méthodes IRM 4D Flow pour le calcul WSSAtherosclerosis accounts for about 21% of deaths worldwide. It develops primarily in specific locations of the cardiovascular system where the Wall Shear Stress (WSS) can deviate more easily from its baseline values. Potential clinical applications of WSS as a biomarker rely on an accurate assessment of blood velocity in patients since it is defined from the derivative of blood velocity at the arterial wall. The present work aims to design and develop a hydraulic test rig to validate Phase Contrast Magnetic Resonance Imaging (PC MRI) velocity acquisitions and the computation of derived WSS. To do that, reference velocity profiles were obtained with Laser Doppler Velocimetry (LDV) and employed as a standard for direct comparison with PC MRI results. The experimental set-up was composed of an MRI compatible pump, flexible connection pipes, a test section, a reservoir, a working fluid, and a flowmeter. One standard 2D PC MRI and one standard 4D Flow MRI sequences were employed to obtain MRI velocity profiles, adjusting their parameters as in clinical practice. The WSS was calculated with the 2D and 3D methods proposed respectively by Stalder et al. and Potter et al. A second experimental campaign was performed with the refinement of the data spatial and temporal resolution, employing only the 4D Flow MRI sequence. Results indicated an excellent agreement between MRI and LDV velocity and WSS data. This study represents a reliable basis for any validation with LDV of 4D Flow MRI based methods for WSS calculation
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Gliah, Omemah Rajab. "In Vitro Investigation of Cell-Free Layer Formation in Microchannels: Dependency on the Red Blood Cell Aggregation and Field of Shear." Thesis, Université d'Ottawa / University of Ottawa, 2018. http://hdl.handle.net/10393/37211.
Повний текст джерелаАнотація:
Red blood cells (RBCs) form approximately 40 to 45% of the human blood volume, and their behaviour and characteristics are the main determinant of blood properties, such as viscosity. RBCs are deformable species and stack together under low shear rate to form aggregates or rouleaux. Flowing RBCs migrate away from the wall leaving a cell-depleted layer known as the cell-free layer (CFL). This layer contributes to the blood viscosity and exchange between the RBCs and the target cells: a thinner CFL enhances the exchange process by reducing the diffusion distance. The formation of this CFL, however, is not yet completely understood.
The goal of this study is to improve the understanding of the formation of the CFL in the micro-flow. This was accomplished by studying the effects of changing both the flow rate and the microchannel geometry on blood flow in microchannels.
In this work, 10% hematocrit human blood suspensions were prepared in native plasma and flowed through poly-dimethylsiloxane (PDMS) microchannels of 100 μm x 34 μm cross-section. Investigation of the flowing cells was performed by using micro particle image velocimetry (μPIV) coupled with a high-speed camera. First, the high-speed camera images were processed with customized Matlab programs to detect and measure the CFL thickness and the RBC aggregates sizes. Second, the blood flow velocity profiles were measured using μPIV in order to determine the actual flow rate, the RBCs’ centerline velocity, and the shear rate.
The results showed that the increase in both flow rate and shear rate significantly reduced the CFL thickness and RBC aggregates size. Comparison of the upstream and downstream measurements in the bifurcating microchannel showed that the change in microchannel geometry did not significantly influence CFL thickness and RBC aggregate size, while within the daughter branches, RBCs tended to flow close to the inner wall resulting in an undetectable CFL at the inner wall and in a larger CFL at the outer wall of the branch. These in vitro results quantitatively relate CFL thickness and RBC aggregate size at different shear rates. The findings are of immediate interest regarding the understanding of microcirculation and improved designs of microchips.
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Halama, Lukáš. "Studium chování nenewtonských kapalin ve slit-flow reometru za podmínek nestabilního toku." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2019. http://www.nusl.cz/ntk/nusl-399291.
Повний текст джерелаАнотація:
The thesis deals with the description of the unstable flow of non-Newtonian fluid in a slit-flow rheometer, which negatively affects its behaviour. The initiators of unstable fluid flow are the roughness of the rheometer slit walls, the slip on the rheometer walls, and the influence of the inlet and outlet region geometry of the rheometer slit. The work contains methodical procedures for mathematical consideration of individual unstable fluid flow initiators and design of change of slit geometry of slit-flow rheometer. Part of the work is also a comparison of the most commonly used rheological models, derivation of general relations for the creation of the velocity profile of individual rheological models and their subsequent implementation in the rheological application, which significantly simplifies the process of evaluation of measured data when measured on slit-flow rheometer. This application can be used to determine basic parameters in CFD simulations or as a teaching aid.
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Jang, Jun-keun. "Study on the Application of Shear-wave Elastography to Thin-layered Media and Tubular Structure: Finite-element Analysis and Experiment Verification." 京都大学 (Kyoto University), 2016. http://hdl.handle.net/2433/217145.
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Ma, Jieyan. "Development of numerical tools for hemodynamics and fluid structure interactions." Thesis, University of Manchester, 2014. https://www.research.manchester.ac.uk/portal/en/theses/development-of-numerical-tools-for-hemodynamics-and-fluid-structure-interactions(f7e72de2-c1f8-4d7a-aa2c-f2a4d239187f).html.
Повний текст джерелаАнотація:
The aim of this study is to create CFD tools and models capable of simulating pulsatile blood flow in abdominal aortic aneurysm (AAA) and stent graft. It helps to increase the current physiological understanding of rupture risk of AAA and stent graft fixation or migration. Firstly, in order to build a general solver for the AAA modeling with reasonable accuracy, a third/fourth order modified OCI scheme is originally developed for general numerical simulation. The modified OCI scheme has a wider cell Reynolds number limitation. This high order scheme performs well with general rectangular mesh for incompressible fluid. Second, a velocity based finite volume method is originally developed to calculate the stress field for solid in order to capture the transient changes of the blood vessel since the artery is a rubber like material. All one, two and three dimensional classical cases for solid are tested and good results are obtained. The velocity based finite volume method show good potential to calculate the stress field for solid and easy to blend with the finite volume fluid solver. It has been recognized that fluid structure interaction (FSI) is very crucial in biomechanics. In this regard, the velocity based finite volume method is then further developed for FSI application. A well known one dimensional piston problem is studied to understand the feasibility of the fluid structure coupling. The numerical prediction matches the analytical solution very well. The velocity based method introduces less numerical damping compared with a stagger method and a monolithic method. Finally, the work focuses on practical pulsatile boundary conditions, non-Newtonian blood viscous properties and bifurcating geometry, and provides an overview of the hemodynamic within the AAA model. A modified Womersley inlet and imbalance pressure outlet boundary conditions are originally used in this study. The Womersley inlet boundary represents better approximation for pulsatile flow compared with the parabolic inlet condition. Numerical results are presented providing comparison between different boundary conditions using different viscous models in both 2D and 3D aneurysms. Good agreement between the numerical predictions and the experimental data is achieved for 2D case. 3D stent models with different bifurcation angles are also tested. The Womersley inlet boundary condition improves the existing inlet conditions significantly and it can reduce the Aneurysm neck computation domain. The influence of the non-Newtonian model to the wall shear stress (WSS) and strain-rate is also studied. The non-Newtonian model tends to produce higher WSS at both proximal and distal end of the aneurysm as compared with the Newtonian model (both 2D and 3D cases). The computed strain-rate distribution at the centre of the aneurysm is different between these two models. The influence of imbalance outlet pressure at the iliac arteries to the blood flow is originally investigated. The imbalance outlet pressure boundary conditions affect the computed wall shear stress significantly near the bifurcation point. All the pulsatile Womersley inlet, non-Newtonian viscosity properties and the imbalance pressure outlet need to be considered in blood flow simulation of AAA.
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Bjarnegård, Niclas. "Aspects on wall properties of the brachial artery in man : with special reference to SLE and insulin-dependent diabetes mellitus." Doctoral thesis, Linköpings universitet, Institutionen för medicin och hälsa, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-11273.
Повний текст джерелаАнотація:
The mechanical properties of the arterial wall are of great importance for blood pressure regulation and cardiac load. With increasing age, large arteries are affected by increased wall stiffness. Furthermore, atherosclerotic manifestations may increase the stiffness even further, both processes acting as independent cardiovascular risk factors affecting the arterial system in a heterogeneous way. The aims of this thesis was to characterize the local mechanical properties of brachial artery (BA) with the aid of ultrasound technique and to evaluate the influence of 1) age, gender, sympathetic stimulation and examination site; 2) type 1 diabetes (DM) and its association to circulatory biomarkers; and 3) to evaluate the general properties of the arterial system with the aid of pulse wave velocity (PWV) as well as pulse wave analysis (PWA) in systemic lupus erythematosus (SLE) and correlate the findings to disease activity and circulatory biomarkers. In the most proximal arterial segment of the upper arm a pronounced age-related decrease in wall distensibility, increase in intima-media thickness (IMT), and a slight increase in diameter were seen. Sympathetic stimulation had no influence on wall mechanics. More distally in BA, no change in diameter, and only minor increase in IMT and decrease in distensibility were seen. No gender differences were found. These findings suggest that the principle transit zone between elastic and muscular artery behaviour is located in the proximal part of the upper arm. Women with uncomplicated insulin-dependent DM had similar diameter, IMT and distensibility in their distal BA as controls, whereas flow-mediated dilatation (FMD) was slightly, and nitrate mediated dilatation (NMD) markedly reduced. NMD was negatively correlated with higher HbA1c levels. Vascular smooth muscle cell function seems to be an early manifestation of vascular disease in women with DM, influenced by long-term hyperglycaemia. Women with SLE had increased aortic PWV compared to controls, a finding positively associated with increased levels of complement factor 3 (C3), but not with disease activity. The increased stiffness of central arteries may be one factor contributing to the increased cardiovascular risk seen in SLE.
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Івіцький, Ігор Ігорович. "Пристінні ефекти в процесах течії полімерів у каналах переробного обладнання". Thesis, НТУУ "КПІ", 2016. https://ela.kpi.ua/handle/123456789/16117.
Повний текст джерелаАнотація:
Дисертаційна робота присвячена дослідженню наявності, характеру та
величини пристінних ефектів, що виникають при течії розплаву полімерних
матеріалах у каналах переробного обладнання.
Розроблено метод визначення наявності пристінних ефектів у полімерному
матеріалі та природи цих ефектів. В залежності від природи пристінних ефектів
розроблено методики визначення величини цих ефектів у матеріалі. Математичну
модель течії полімерних матеріалів доповнено врахуванням пристінних ефектів в
залежності від їх природи та матеріалу, що дозволило створити універсальний
підхід до визначення параметрів процесу течії під час числового моделювання.
Проведено числові дослідження впливу геометричних параметрів каналу на
розбіжності перепаду тиску між умовами відсутності швидкості на стінці та
врахування пристінних ефектів. На основі проведених досліджень виведено
емпіричні рівняння, що дозволяють враховувати пристінні ефекти при проектуванні
переробного обладнання без додаткового проведення числових досліджень.The dissertation is devoted to research presence, the nature and value of wall effects arising from the melt flow channels in polymer materials processing equipment. The method of determining the presence of wall effects polymeric material and the nature of these effects. Depending of the nature of wall effects developed methodology for determining the value of these effects in the material. Mathematical model of current polymer materials supplemented into account the effects of wall, depending on their nature and the material allowed us to create a universal approach to determining process parameters during the current numerical modeling. It was examine a numerical study of the influence of geometrical parameters of channel differences pressure between the absence of speed on the wall and consideration of wall effects. On the basis of empirical studies deduce equations to take into account when designing shelving effects without additional processing equipment of numerical studies.
Диссертация посвящена исследованию наличия, характера и величины пристенных эффектов, возникающих при течении расплава полимерных материалов в каналах перерабатывающего оборудования. Проведенный аналитический анализ современного состояния исследований течения полимера показал, что ранее рассматриваются отдельные вопросы пристенных эффектов при течении расплава полимера, однако они имеют ряд недостатков: не учитывают природу и характер возникновения пристенных эффектов в различных материалах, позволяют определить величину эффекта не во всем диапазоне сечений каналов, не позволяют использовать полученные данные для численного расчета с использованием систем автоматизированного проектирования. Разработан метод определения наличия пристенных эффектов в полимерном материале и природы этих эффектов. В зависимости от природы пристенных эффектов разработаны методики определения величины этих эффектов в материале, которые учитывают неньютоновские свойства материалов. Разработана методика проведения экспериментальных исследований на базе созданной экспериментальной установки для исследования пристенных эффектов. Проведены экспериментальные исследования с использованием трех типов полимерных материалов: полиэтилен низкого давления, полистирол, севилен. Также проведены эксперименты с использованием смазывающего агента для определения величины его влияния на пристенные эффекты. Установлены зависимости напряжения сдвига от скорости расплава материала на стенке, что позволило получить исходные данные для задания граничных условий при численном моделировании процесса Математическая модель течения полимерных материалов дополнена учетом пристенных эффектов в зависимости от их природы и материала, что позволило создать универсальный подход к определению параметров процесса течения при численном моделировании. Адекватность математической модели и граничных условий подтверждается сопоставлением результатов численного моделирования и экспериментальных данных, а также сопоставлением с существующими результатами исследований. Адекватность изотермического предположения проверялась числовым расчетом для изотермического режима и с учетом диссипации при постоянной температуре стенок. Адекватность экстраполяции результатов, полученных в экспериментальных исследованиях с цилиндрическими каналами на другие типы каналов, подтверждается проведением дополнительного опыта с капилляром прямоугольной формы, гидравлический диаметр которого совпадал с одним из исследуемых капилляров.Численное моделирование проводилось на каналах цилиндрической, конической и прямоугольной геометрии, а также на геометрии формующей головки экструдера. Граничными условиями на стенке каналов послужили данные, полученные в результате проведения экспериментальных исследований. Проведены численные исследования влияния геометрических параметров каналов на разность перепадов давления между условиями отсутствия скорости на стенке и учетом пристенных эффектов, а также влияния смазывающего агента. Установлено, что характер влияния геометрических параметров на разность перепадов давления имеет, в основном, нелинейный характер. Исследования показали, что при численном моделировании течения полимерного материала по геометрии формующей головки пренебрежение пристенными эффектами приводит к погрешности в полученных результатах от 11% до 22% в зависимости от материала. Для определения степени влияния параметров и создания регресивной модели процесса был проведен полный факторный эксперимент, который позволил вывести эмпирические уравнения, позволяющие учитывать пристенные эффекты при проектировании перерабатывающего оборудования без дополнительного проведения численных исследований. Разработаны конструкции экструзионных головок, позволяющих компенсировать влияние пульсаций расплава, которые возникают в результате действия пристенных эффектов, а также конструкция червяка экструдера, которая позволяет обеспечить поглощение пульсаций давления, возникающих в результате действия пристенных эффектов.Проведены численные исследования влияния геометрических параметров каналов на разность перепадов давления между условиями отсутствия скорости на стенке и учетом пристенных эффектов, а также влияния смазывающего агента. Установлено, что характер влияния геометрических параметров на разность перепадов давления имеет, в основном, нелинейный характер. Исследования показали, что при численном моделировании течения полимерного материала по геометрии формующей головки пренебрежение пристенными эффектами приводит к погрешности в полученных результатах от 11% до 22% в зависимости от материала. Для определения степени влияния параметров и создания регресивной модели процесса был проведен полный факторный эксперимент, который позволил вывести эмпирические уравнения, позволяющие учитывать пристенные эффекты при проектировании перерабатывающего оборудования без дополнительного проведения численных исследований. Разработаны конструкции экструзионных головок, позволяющих компенсировать влияние пульсаций расплава, которые возникают в результате действия пристенных эффектов, а также конструкция червяка экструдера, которая позволяет обеспечить поглощение пульсаций давления, возникающих в результате действия пристенных эффектов.Проведены численные исследования влияния геометрических параметров каналов на разность перепадов давления между условиями отсутствия скорости на стенке и учетом пристенных эффектов, а также влияния смазывающего агента. Установлено, что характер влияния геометрических параметров на разность перепадов давления имеет, в основном, нелинейный характер. Исследования показали, что при численном моделировании течения полимерного материала по геометрии формующей головки пренебрежение пристенными эффектами приводит к погрешности в полученных результатах от 11% до 22% в зависимости от материала. Для определения степени влияния параметров и создания регресивной модели процесса был проведен полный факторный эксперимент, который позволил вывести эмпирические уравнения, позволяющие учитывать пристенные эффекты при проектировании перерабатывающего оборудования без дополнительного проведения численных исследований. Разработаны конструкции экструзионных головок, позволяющих компенсировать влияние пульсаций расплава, которые возникают в результате действия пристенных эффектов, а также конструкция червяка экструдера, которая позволяет обеспечить поглощение пульсаций давления, возникающих в результате действия пристенных эффектов.
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Soukup, Lubomír. "Analýza proudění v potrubí kruhového i nekruhového průřezu metodou využívající rozložení hustoty vířivosti po průřezu." Doctoral thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2016. http://www.nusl.cz/ntk/nusl-256580.
Повний текст джерелаАнотація:
The doctoral thesis deals with the analysis of the flow in the circular and not circular cross-section pipes by methods using the distribution of the vorticity density. This analysis is particularly focused on the derivation of the new velocity profiles formulas using the above mentioned method. In this work is presented a historical overview of the derived velocity profiles. This overview of already derived velocity profiles will be a fundamental benchmark for newly derived velocity profiles. These new velocity profiles are derived for the circular and not circular cross-section pipes and the derivation is based on the analogy of electromagnetic induction by using Biot-Savart law. It is necessary to apply this analogy at first on solitary vortex filament. By taking this step is possible to get the value of the induced velocity from one solitary vortex filament. Subsequently it is possible to obtain the value of the induced velocity from the vorticity wall and afterwards from the vorticity density distribution over the cross section. This work contains also the results of the experimental measurements of the velocity profiles, and of the CFD simulations. Experimentally measured results are used besides other for the selecting of the most suitable CFD computational model. Selected CFD model will be subsequently declared as a reference model and the valid velocity profiles for this model will serve with the experimentally measured data as a benchmark for the newly derived velocity profiles.
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Jegede, Olaseinde. "Dual-axis fluidic thrust vectoring of high-aspect ratio supersonic jets." Thesis, University of Manchester, 2016. https://www.research.manchester.ac.uk/portal/en/theses/dualaxis-fluidic-thrust-vectoring-of-highaspect-ratio-supersonic-jets(6d6a5867-8281-4dfd-ac45-105ff4e73e39).html.
Повний текст джерелаАнотація:
A dual-axis fluidic thrust vectoring (FTV) system is proposed where the supersonic propulsive jet of an aircraft is exhausted over a scarfed (swept), curved surface to produce flight control moments in both the pitch and yaw axes. This work contributes towards practical dual-axis FTV through expansion of fundamental curved-wall jet (CWJ) understanding, development of the novel Superimposed Characteristics technique for supersonic nozzle design, and performance evaluation of an experimental scarfed curved wall FTV configuration. Previous work has suggested that the use of a sheared exhaust velocity profile improves the attachment of supersonic jets to curved surfaces; however, evidence to support this is limited. To address this, an inviscid numerical CWJ model was developed using the two-dimensional method of characteristics. A major outcome is improved understanding of the effect of exhaust velocity profile on CWJ wave structure and subsequent jet attachment. A sheared velocity exhaust is shown to generate a wave structure that diminishes adverse streamwise pressure gradients within a supersonic curved-wall jet. This reduces the likelihood of boundary layer separation and as a result, a sheared exhaust velocity CWJ is expected to be less readily separated compared to other exhaust velocity profiles. A novel method termed Superimposed Characteristics was developed for the low-order design of supersonic nozzles with rectangular exits. The technique is capable of generating 3D nozzle geometries based on independent exit plane orientation and exhaust velocity distribution requirements. The Superimposed Characteristics method was used to design scarfed rectangular exit nozzles with sheared velocity exhaust profiles. These nozzles were then evaluated using finite volume computational methods and experimental methods. From the analysis, the Superimposed Characteristics method is shown to be valid for preliminary nozzle design. Experimental methods were used to study the on- and off-design attachment qualities of uniform and sheared velocity exhaust jets for a FTV configuration with an external curved wall termination angle of 90 degrees and scarf angle of 30 degrees. Experiments at the on-design nozzle pressure ratio (NPR) of 3.3 demonstrated pitch and yaw jet deflection angles of 78 degrees and 23 degrees respectively for the uniform exhaust velocity CWJ. The sheared exhaust velocity CWJ achieved lower pitch and yaw deflection angles of 34 degrees and 14 degrees respectively at the same on-design NPR. The lower jet deflection angles observed for sheared exhaust velocity jets is inconsistent with the CWJ model prediction of reduced adverse streamwise pressure gradients; however, there was insufficient experimental instrumentation to identify the cause. In the off-design experiments, the uniform exhaust velocity CWJ was observed to detach at an NPR of 3.6, whilst the sheared exhaust velocity CWJ remained attached at NPRs in excess of 4. The capability of sheared exhaust velocity CWJs to remain attached at higher NPRs is consistent with the analytical theory and the CWJ model predictions. An actuation study was carried out to achieve controlled jet detachment using secondary blowing injected normal to the curved wall. Full separation of the wall jets was achieved downstream of the injection point. This provided vectoring angles of more than 20 degrees in pitch and 10 degrees in yaw, exceeding expected vectoring requirements for practical aircraft control. At the on-design NPR, the uniform and sheared exhaust velocity jets required secondary blowing mass flow rates of 2.1% and 3.8% of the primary mass flow respectively to achieve full separation.
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Wong, William Chiu-Kit. "CFD Flame Spread Model Validation: Multi-Component Data Set Framework." Digital WPI, 2012. https://digitalcommons.wpi.edu/etd-theses/918.
Повний текст джерелаАнотація:
"Review of the literature shows that the reported correlation between predictions and experimental data of flame spread vary greatly. The discrepancies displayed by the models are generally attributed to inaccurate input parameters, user effects, and inadequacy of the model. In most experiments, the metric to which the model is deemed accurate is based on the prediction of the heat release rate, but flame spread is a highly complex phenomenon that should not be simplified as such. Moreover, fire growth models are usually made up of distinctive groups of calculation on separate physical phenomena to predict processes that drive fire growth. Inaccuracies of any of these “sub-models” will impact the overall flame spread prediction, hence identifying the sources of error and sensitivity of the subroutines may aid in the development of more accurate models. Combating this issue required that the phenomenon of flame spread be decomposed into four components to be studied separately: turbulent fluid dynamics, flame temperature, flame heat transfer, and condensed phase pyrolysis. Under this framework, aspects of a CFD model may be validated individually and cohesively. However, a lack of comprehensive datasets in the literature hampered this process. Hence, three progressively more complex sets of experiments, from free plume fires to fires against an inert wall to combustible wall fires, were conducted in order to obtain a variety of measurements related to the four inter-related components of flame spread. Multiple permutations of the tests using different source fuels, burner size, and source fire heat release rate allowed a large amount of comparable data to be collected for validation of different fire configurations. FDS simulations using mostly default parameters were executed and compared against the experimental data, but found to be inaccurate. Parametric study of the FDS software shows that there are little definitive trends in the correlation between changes in the predicted quantities and the modeling parameters. This highlights the intricate relationships shared between the subroutines utilized by FDS for calculations related to the four components of flame spread. This reveals a need to examine the underlying calculation methods and source code utilized in FDS."
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Goudot, Guillaume. "Applications innovantes des ultrasons en pathologie vasculaire : utilisation de l'imagerie ultrarapide dans l'analyse de la rigidité artérielle et des ultrasons pulsés en thérapie Arterial stiffening assessed by ultrafast ultrasound imaging gives new insight into arterial phenotype of vascular Ehlers–Danlos mouse models Aortic wall elastic properties in case of bicuspid aortic valve Segmental aortic stiffness in bicuspid aortic valve patients compared to first-degree relatives Wall shear stress measurement by ultrafast vector flow imaging for atherosclerotic carotid stenosis Pulsed cavitational therapy using high-frequency ultrasound for the treatment of deep vein thrombosis in an in vitro model of human blood clot." Thesis, Sorbonne Paris Cité, 2018. https://wo.app.u-paris.fr/cgi-bin/WebObjects/TheseWeb.woa/wa/show?t=2215&f=13951.
Повний текст джерела
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Li, Ling [Verfasser], Puits Ronald [Akademischer Betreuer] Du, Jörg [Akademischer Betreuer] Schumacher, and Christoph [Akademischer Betreuer] Egbers. "Experimental investigation of the velocity and temperature fields near the walls in turbulent Rayleigh-Bénard convection / Ling Li. Betreuer: Ronald Du Puits. Gutachter: Jörg Schumacher ; Christoph Egbers." Ilmenau : Universitätsbibliothek Ilmenau, 2013. http://d-nb.info/1077774451/34.
Повний текст джерела
25
Faye, El Alioune. "Cisaillement pariétal et tourbillons en écoulement Taylor-Couette." Thesis, La Rochelle, 2013. http://www.theses.fr/2013LAROS393.
Повний текст джерелаАнотація:
Ce travail est une étude expérimentale permettant de mettre en évidence la cartographie générale de l’ensemble des états d’écoulement obtenus entre le régime laminaire de Couette et la turbulence. L’ensemble des expériences a été réalisé dans un dispositif appelé système Taylor-Couette (STC), composé de deux cylindres concentriques avec le cylindre intérieur tournant. Ces différentes instabilités (SPI, TVF, WVF, MWVF, TTVF), qui dépendent principalement du nombre de Taylor (Ta), seront obtenues avec ou sans débit axial dans le STC selon des protocoles d’analyse bien définis et nous notons que le nombre de Reynolds axial (Reax) a un effet de stabilisation de l’écoulement. Les vortex de Taylor toroïdaux, ondulés ou ondulés modulés, ont été caractérisés en termes de gradient pariétal de vitesse, de nombre d’ondes, de longueur d’ondes axiales et azimutales, de la vitesse de déplacement axial, de fréquence et de la vitesse de révolution ; la polarographie sera utilisée comme technique de mesure. La vitesse du cylindre intérieur (Ta) est essentiellement le seul phénomène agissant sur l’évolution de ces paramètres. L’utilisation de la sonde tri-segmentée dans la caractérisation des structures tourbillonnaires a contribué à la compréhension des mécanismes d’interaction vortex-paroi et à la détermination des composantes azimutale et axiale du gradient pariétal de vitesseThis work is an experimental study to highlight general mapping of the set of states obtained from the Couette laminar flow to turbulence. All experiments were performed in a device called Taylor-Couette system (TCS) which consists of two concentric cylinders with the inner cylinder rotating. The flow regimes (SPI, TVF, WVF, MWVF, TTVF), which depend mainly on the Taylor number (Ta), were obtained with or without axial flow in the TCS according to well-defined experimental protocols. We noted that the axial Reynolds number (Reax) has astabilizing effect on the flow. Using electrodiffusion method and analysis of films, the toroidal Taylor vortices, wavy or wavy modulated flow, were characterized in terms of the wall velocity gradients, wave number, axial and azimuthal wavelength, the axial velocity of vortex displacement, and there frequencies. The Taylor number has substantial effect on the evolution of these parameters in the investigated range. The use of three-segment electrodiffusion has contributed to the understanding of the mechanisms of vortex-wall interaction and the determination of the azimuthal and axial components of the wall velocity gradient
26
Vičan, Martin. "Modelování obrazů proudění." Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2014. http://www.nusl.cz/ntk/nusl-226818.
Повний текст джерелаАнотація:
The master thesis explores modelling fluid dynamics images in simulation software Star-CCM+ Version 8.04.007. Three proposed variants are modelled. The first variant describes modelling swirl diffusers, the second and third variant describe modelling wall diffusers. The results of modelling are processed in the form of scalar and vector arrays, which depict the velocity of flowing air, temperature and the age of air.
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Perkins, Richard Mark. "PIV Measurements of Turbulent Flow in a Rectangular Channel over Superhydrophobic Surfaces with Riblets." BYU ScholarsArchive, 2014. https://scholarsarchive.byu.edu/etd/5547.
Повний текст джерелаАнотація:
In this thesis I investigate characteristics of turbulent flow in a channel where one of the walls has riblets, superhydrophobic microribs, or a hybrid surface with traditional riblets built on a superhydrophobic microrib surface. PIV measurements are used to find the velocity profile, the turbulent statistics, and shear stress profile in the rectangular channel with one wall having a structured test surface. Both riblets and superhydrophobic surfaces can each provide a reduction in the wall shear stress in a turbulent channel flow. Characterizing the features of the flow using particle image velocimetry (PIV) is the focus of this research. Superhydrophobicity results from the combination of a hydrophobic coating applied to a surface with microrib structures, resulting in a very low surface energy, such that the fluid does not penetrate in between the structures. The micro-rib structures are aligned in the streamwise flow direction. The riblets are larger than the micro-rib structure by an order of magnitude and protrude into the flow. All the test surfaces were produced on silicon wafers using photolithographic techniques. Pressure in the channel is maintained below the Laplace pressure for all testing, creating sustainable air pockets between the microribs. Velocity profiles, turbulent statistics, shear stress profiles, and friction factors are presented. Measurements were acquired for Reynolds numbers ranging from 4.5x10^3 to 2.0x10^4. Modest drag reductions were observed for the riblet surfaces. Substantial drag increase occurred over the superhydrophobic surfaces. The hybrid surfaces showed the greatest drag reduction. Turbulence production was strongly reduced during riblet and hybrid tests.
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Al-Faesly, Taofiq Qassim. "Extreme Hydrodynamic Loading on Near-Shore Structures." Thesis, Université d'Ottawa / University of Ottawa, 2016. http://hdl.handle.net/10393/34179.
Повний текст джерелаАнотація:
The main objective of this study was to investigate and quantify the impact of extreme hydrodynamic forces, similar to those generated by tsunami-induced inundation, on structural elements. As part of a comprehensive experimental program and analytical study, pressures, base shear forces, and base overturning moments generated by hydraulic bores on structural models of various shapes were studied. In addition, the impact force induced by waterborne wooden debris of different shapes and masses on the structural models was also investigated. Two structural models, one with circular and the other with square cross-section, were installed individually downstream of a dam-break wave in a high-discharge flume. Three impounding water heights (550, 850 and 1150 mm) were used to produce dam-break waves, which have been shown to be analogous to tsunami-induced coastal inundation in the form of highly turbulent hydraulic bores. Time-history responses of the structural models were recorded, including: pressures, base shear forces, base overturning moments, lateral displacements, and accelerations. In addition, the flow depth-time histories were recorded at various locations along the length of the flume. Regular and high-speed video cameras were used to monitor the bore-structure interaction. The effect of initial flume bed condition (“wet” or “dry” bed) on the forces and pressures exerted on the structural models were also investigated. Moreover, the vertical distribution of pressure around the models was captured. Simple low-height walls with various geometries were installed upstream from the structural models to investigate their efficiency as tsunami mitigation measures. The experimentally recorded data were compared with those estimated from currently available formulations.
The results and analysis of the simulated tsunami-induced bore presented in this study will be of significant use to better estimate forces exerted on structures by tsunami-induced turbulent bores. It is expected that this work will contribute to the new ASCE7 Chapter 6 - Tsunami Loads and Effects in which two of this author’s academic supervisors, Drs. Ioan Nistor and Dan Palermo, are members.
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Thuesen, Anna Helena, and Benjamin Lindahl. "Comparison of oxygen consumption while walking on treadmill wearing MBT Shoes versus Orthopedic Shoes : A treatise on shoe mass." Thesis, Hälsohögskolan, Högskolan i Jönköping, HHJ, Avd. för rehabilitering, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:hj:diva-13695.
Повний текст джерелаАнотація:
Purpose: The purpose of this study was to investigate if there was any difference in energy expenditure (kcal/min) and oxygen consumption (VO2) between subjects walking with Masai Barefoot Technology ® (MBT) shoes and regular orthopedic shoes. The research hypothesis was that MBT shoes demand more energy expenditure than regular orthopedic shoes. Methods: Seven women aged 49-65 were recruited for the study. The subjects were tested in two sessions, with a minimum of two weeks in between each sesssion. On each test session the subjects walked with both MBT shoes and orthopedic shoes which were adjusted in mass (g) to match the mass of the MBT shoes. While the subjects walked on a treadmill, the oxygen consumption (VO2), heart rate (min-1) and self selected velocity (m/s) for each of the shoe types was measured. Results: Results showed that there is no significant difference in oxygen consumption (VO2) between the MBT and orthopedic shoes. Energy expenditure (kcal/min) was also calculated from the data and the results revealed that there is no significant differ-ence between MBT and orthopedic shoes in energy expenditure (kcal/min) either. The self selected velocity (m/s) between the two shoe types was also found to be insignificant. Conclusion: The results showed no significant difference between the shoes. This could indicate that the specific construction of the MBT shoe has no effect on the energy expenditure (kcal/min) of its user. This lack of difference may be due to the equal mass of the shoes, but since oxygen consumption (VO2) was not investigated in orthopedic shoes with different shoe masses, this conclusion cannot be confirmed. The self selected velocity (m/s) was found to be insignificant and this finding could suggest to that prolonged usage of the MBT shoe may diminish gait parameters dissimilarities during ambulation. This study should therefore be seen as a pilot study and further investigation in this area should be pursued.
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Taan, Aly H. "A wall within a wall." Thesis, Virginia Polytechnic Institute and State University, 1990. http://hdl.handle.net/10919/53277.
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Saez, Manuel. "Contribution à l'étude expérimentale de la convection mixte." Université Joseph Fourier (Grenoble), 1998. http://www.theses.fr/1998GRE10197.
Повний текст джерелаАнотація:
Les travaux presentes dans cette these concernent plusieurs aspects d'un programme experimental dont l'objectif est de fournir des donnees pour la validation et l'aide au developpement des modeles de turbulence dans les codes de calculs thermohydrauliques, pour des situations d'etudes allant de la convection forcee a la convection naturelle (nombre de reynolds : 10#3 a 6. 10#4 et nombre de richardson : 10#-#4 a 1). La configuration etudiee est celle d'un ecoulement ascendant d'air entre deux parois verticales a temperatures differentes. Dans le premier chapitre, nous avons extrait de la bibliographie les donnees disponibles pour les ecoulements en canal plan et en couches limites. Le second chapitre presente les caracteristiques de l'installation et du banc d'etalonnage ainsi que la methode de positionnement des sondes pour atteindre la precision de l'ordre du centieme de millimetre requise en paroi. Le troisieme chapitre presente les techniques de mesure mises en uvre ainsi que les developpements apportes a certaines techniques experimentales. Les lois classiques de refroidissement d'un fil chaud sont verifiees jusqu'a des vitesses de quelques centimetres par seconde. En prealable aux resultats de convection forcee et mixte, nous presentons une methode que nous avons developpee pour permettre la realisation de mesures tres proches de la paroi. Notre procedure de correction des mesures est elaboree grace a une evaluation numerique de l'erreur basee sur une modelisation thermohydraulique. Les mesures en convection forcee ont permis de retrouver les lois de paroi. En convection mixte, les profils moyens de vitesse et de temperature, obtenus avec une sonde a fil chaud simple, montrent nettement l'effet des forces de volume sur le champ de vitesses. Concernant les lois de paroi en convection mixte, une piste proposee consiste a trouver des lois algebriques qui prennent en compte les effets des forces de volume, a partir de la base de donnees issue de notre experience en convection mixte. La recherche de l'existence de lois de paroi en situation de convection mixte montre que les representations des profils dimensionnels de vitesse et de temperature moyenne peut se faire suivant des lois du meme type que celles de convection forcee avec des constantes d'integration qui sont des fonctions lineaires du nombre de richardson.
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Makin, Alexis David James. "Velocity memory." Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/velocity-memory(c5c1c28d-0a23-44a5-93bc-21f993d2e7ad).html.
Повний текст джерелаАнотація:
It is known that primates are sensitive to the velocity of moving objects. We can also remember velocity information after moving objects disappear. This cognitive faculty has been investigated before, however, the literature on velocity memory to date has been fragmented. For example, velocity memory has been disparately described as a system that controls eye movements and delayed discrimination. Furthermore, velocity memory may have a role in motion extrapolation, i.e. the ability to judge the position of a moving target after it becomes occluded. This thesis provides a unifying account of velocity memory, and uses electroencephalography (EEG) to explore its neural basis. In Chapter 2, the relationship between oculomotor control and motion extrapolation was investigated. Two forms of motion extrapolation task were presented. In the first, participants observed a moving target disappear then reappear further along its path. Reappearance could be at the correct time, too early or too late. Participants discriminated reappearance error with a two-alternative forced choice button press. In the second task, participants saw identical targets travel behind a visible occluder, and they attempted to press a button at the exact time that it reached the other side. Tasks were completed under fixation and free viewing conditions. The accuracy of participant's judgments was reduced by fixation in both tasks. In addition, eye movements were systematically related to behavioural responses, and small eye movements during fixation were affected by occluded motion. These three results imply that common velocity memory and pre-motor systems mediate eye movements and motion extrapolation. In Chapter 3, different types of velocity representation were explored. Another motion extrapolation task was presented, and targets of a particular colour were associated with fast or slow motion. On identical-velocity probe trials, colour still influenced response times. This indicates that long-term colour-velocity associations influence motion extrapolation. In Chapter 4, interference between subsequently encoded velocities was explored. There was robust interference between motion extrapolation and delayed discrimination tasks, suggesting that common processes are involved in both. In Chapter 5, EEG was used to investigate when memory-guided tracking begins during motion extrapolation. This study compared conditions where participants covertly tracked visible and occluded targets. It was found that a specific event related potential (ERP) appeared around 200 ms post occlusion, irrespective of target location or velocity. This component could delineate the onset of memory guided tracking during occlusion. Finally, Chapter 6 presents evidence that a change in alpha band activity is associated with information processing during motion extrapolation tasks. In light of these results, it is concluded that a common velocity memory system is involved a variety of tasks. In the general discussion (Chapter 7), a new account of velocity memory is proposed. It is suggested that a velocity memory reflects persistent synchronization across several velocity sensitive neural populations after stimulus offset. This distributed network is involved in sensory-motor integration, and can remain active without visual input. Theoretical work on eye movements, delayed discrimination and motion extrapolation could benefit from this account of velocity memory.
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Seligman, Joshua R. "Power development through low velocity isotonic, or combined low velocity isotonic-high velocity isokinetic training /." Thesis, University of Hawaii at Manoa, 2003. http://hdl.handle.net/10125/7046.
Повний текст джерела
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Bellec, Morgane. "Études du couplage entre turbulence et gradient de température pour l'intensification des transferts de chaleur dans les récepteurs solaires à haute température." Thesis, Perpignan, 2017. http://www.theses.fr/2017PERP0005/document.
Повний текст джерелаАнотація:
Une voie prometteuse pour améliorer le rendement des centrales solaires à tour consiste à chauffer de l'air pressurisé à haute température afin d'alimenter un cycle thermodynamique de Brayton. Pour cela, il est indispensable de concevoir des récepteurs solaires performants,permettant de forts transferts de chaleur vers le fluide. Le développement de tels récepteurs passe par une compréhension fine de leurs écoulements internes. Il s'agit d'écoulements complexes, combinant de hauts niveaux de turbulence et un fort gradient de température entre la paroi irradiée par le flux solaire concentré et la paroi arrière isolée. On se propose dans ce travail de réaliser une étude amont numérique et expérimentale de ce type d'écoulements.D'une part, des mesures de vitesse par SPIV (vélocimétrie par images de particules stéréoscopique) sont effectuées dans une soufflerie de canal plan turbulent lisse dont la cellule de mesure est représentative d'un récepteur solaire surfacique. On observe en particulier l'influence d'un chauffage asymétrique sur les statistiques de la turbulence. Ces mesures sont d'autre part complétées par des simulations fines LES (simulation des grandes échelles)menées dans les conditions de la soufflerie. Pour finir, une simulation LES d'un canal plan texturé sur une paroi par une géométrie innovante est conduite. Cette architecture interne du récepteur combine des générateurs de tourbillon et des riblets afin d'intensifier les échanges de chaleur vers le fluideA promising line of research to increase the efficiency of solar tower power plants consists in heating pressurized air to high temperatures in order to fuel a Brayton thermodynamic cycle. This requires to design effective solar receivers that allow for intense heat transfers toward the fluid. To develop such receivers, an in-depth understanding of their internal flows is needed. These are complex flows, combining strong turbulence and strong temperature gradient between the concentrated sun irradiated wall and the back insulated wall.The aim of this work is to investigate numerically and experimentally such flows.On one hand, velocities are measured by SPIV (Stereoscopic Particle Image Velocimetry) in a turbulent channel flow wind tunnel whom measurement cell is similar to a surface solar receiver. The influence of an asymmetric heating on the turbulence statistics are especially investigated. These measurements are supplemented by Large Eddy Simulations run under the same conditions as the wind tunnel. Finally, a Large Eddy Simulation is run in a channel flow textured on one wall by an innovative geometry. This internal receiver design combines vortex generators and riblets in order to enhance the heat transfers
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Stratmann, Jochen. "Droplet wall and spray wall interaction at increased ambient pressure and wall temperature." Aachen Shaker, 2009. http://d-nb.info/995684472/04.
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Nordblad, Amanda. "Wall-Couture." Thesis, Högskolan i Borås, Akademin för textil, teknik och ekonomi, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:hb:diva-692.
Повний текст джерелаАнотація:
Wall-Couture is a project within the textile design field, which aims to explore methods for surface design in digitally printed wallpaper. Through a practice based working method, textile after-treatment techniques have been used to manipulate digitally printed wallpaper with hand-painted motives. Practices borrowed from haute couture have influenced the working method. The result is a range of design examples displaying various expressions of the techniques. The project shows that several surface materials could be applied in ways that enhance tactility and visual depth to digitally printed wallpaper, and also that methods from craftsmanship could be use to design contemporary wallpaper. The combination of techniques increases the designer’s opportunities to design wallpaper by using alternative approaches to material and surfaces. The work also strives to higher the value of handicraft, decoration and ornamentation in the design field. Another value is to strengthen the position of digital printing in the textile industry; the work encourages technical progress for creating digital print in combination with surface treatments.
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Brunstorp, Jimmi. "Gallery Wall." Thesis, Konstfack, Inredningsarkitektur & Möbeldesign, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:konstfack:diva-4763.
Повний текст джерелаАнотація:
För vissa är graffiti konst, för andra är det ett tecken på förlorad kontroll. För mig är det ett redskap för att mötas. Jag har delat in mitt examensarbete i två delar. Den första behandlar visionen jag baserat mitt arbete på. Den andra handlar om design och placering av de fysiska paviljongerna. I den första delen har jag utgått ifrån ett scenario där den fysiska arkitekturen återspeglas i ett virtuellt gallerisystem jag get namnet Gallery Wall. Denna del finns bara på idébasis men har varit utgångspunkt då jag formgivit mina paviljonger. Jag har skapat fem olika paviljongstyper som tillsammans på ett teoretiskt plan utgör en och samma virtuella huvudform. I, eller rättare sagt på, paviljongerna ges tillfälle för vem som helst att måla och presenteras sin gatukonst. Min förhoppning är att mina paviljongtyper skall inspirera andra att bygga egna varianter som alla är del av Gallery Wall. Systemet är tänkt att vara open source. Jag vill också med mitt arbete ifrågasätta och belysa vad som får visas upp och värdesätts inom konstvärlden och i samhället. Mitt examensarbete är baserat på en dröm som förhoppningsvis i framtiden blir verklighet.
38
Arrieta, Concha José Luis, and Huamán Glendha Falconí. "Video Wall." Bachelor's thesis, Universidad Peruana de Ciencias Aplicadas (UPC), 2013. http://hdl.handle.net/10757/273539.
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Setright, E. Helen. "Moses Wall." Thesis, University of Leicester, 2003. http://hdl.handle.net/2381/30278.
Повний текст джерелаАнотація:
My purpose has been to discover and present all that is known of Moses Wall (1606?-1664+). In approximately 62,000 words this study addresses the three main aspects of his work. 1 HOUSE OF LORDS DEPOSITIONS. These documents were officially destroyed but secretly copied. I found and examined them in the House of Lords archive. I present detailed considerations of the material and the implications of Moses Wall's close involvement with Sir Harry Vane, as messenger and as spy for the Independents. 2 TRANSLATION OF SPES ISRAELIS. As a scholar and millennial idealist Moses Wall was the anonymous translator for the first English edition of Spes Israelis by the Dutch Rabbi Menasseh ben Israel. Responding to MP Edward Spencer's reply, the second edition contained a cogent and well-argued Discourse by Wall, establishing a rational and religious case for readmitting the Jews as citizens of England. I establish the context and consequences of this work. 3 CORRESPONDENCE with SAMUEL HARTLIB and JOHN MILTON. Fourteen letters written by Moses Wall between 1652 and 1660 are available from the Hartlib archive. They offer political, personal and practical information, with rare insights into daily survival under the Commonwealth. In my work these letters are edited and examined as a body for the first time. Together with supporting detail from other sources I show how these offer a living record of the man Moses Wall and his achievement. I offer the possibility that these letters conveyed more than their immediate meaning. One single letter from Moses Wall to John Milton survives, well known and discussed by Milton scholars. In the context of other material here presented, this is perceived as a source of inspiration and influence from 1659 to1980.
40
Stratmann, Jochen [Verfasser]. "Droplet-Wall and Spray-Wall Interaction at Increased Ambient Pressure and Wall Temperature / Jochen Stratmann." Aachen : Shaker, 2009. http://d-nb.info/1159832323/34.
Повний текст джерела
41
Kokkalis, Efstratios. "Fluid dynamic assessments of spiral flow induced by vascular grafts." Thesis, University of Dundee, 2014. https://discovery.dundee.ac.uk/en/studentTheses/5b96492f-983f-4baa-8e48-20da6939e65c.
Повний текст джерелаАнотація:
Peripheral vascular grafts are used for the treatment of peripheral arterial disease and arteriovenous grafts for vascular access in end stage renal disease. The development of neo-intimal hyperplasia and thrombosis in the distal anastomosis remains the main reason for occlusion in that region. The local haemodynamics produced by a graft in the host vessel is believed to significantly affect endothelial function. Single spiral flow is a normal feature in medium and large sized vessels and it is induced by the anatomical structure and physiological function of the cardiovascular system. Grafts designed to generate a single spiral flow in the distal anastomosis have been introduced in clinical practice and are known as spiral grafts. In this work, spiral peripheral vascular and arteriovenous grafts were compared with conventional grafts using ultrasound and computational methods to identify their haemodynamic differences. Vascular-graft flow phantoms were developed to house the grafts in different surgical configurations. Mimicking components, with appropriate acoustic properties, were chosen to minimise ultrasound beam refraction and distortion. A dual-beam two-dimensional vector Doppler technique was developed to visualise and quantify vortical structures downstream of each graft outflow in the cross-flow direction. Vorticity mapping and measurements of circulation were acquired based on the vector Doppler data. The flow within the vascular-graft models was simulated with computed tomography based image-guided modelling for further understanding of secondary flow motions and comparison with the experimental results. The computational assessments provided a three-dimensional velocity field in the lumen of the models allowing a range of fluid dynamic parameters to be predicted. Single- or double-spiral flow patterns consisting of a dominant and a smaller vortex were detected in the outflow of the spiral grafts. A double- triple- or tetra-spiral flow pattern was found in the outflow of the conventional graft, depending on model configuration and Reynolds number. These multiple-spiral patterns were associated with increased flow stagnation, separation and instability, which are known to be detrimental for endothelial behaviour. Increased in-plane mixing and wall shear stress, which are considered atheroprotective in normal vessels, were found in the outflow of the spiral devices. The results from the experimental approach were in agreement with those from the computational approach. This study applied ultrasound and computational methods to vascular-graft phantoms in order to characterise the flow field induced by spiral and conventional peripheral vascular and arteriovenous grafts. The results suggest that spiral grafts are associated with advanced local haemodynamics that may protect endothelial function and thereby may prevent their outflow anastomosis from neo-intimal hyperplasia and thrombosis. Consequently this work supports the hypothesis that spiral grafts may decrease outflow stenosis and hence improve patency rates in patients.
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Zhu, Weijia. "A new instrumentation for particle velocity and velocity related measurements under water /." View online ; access limited to URI, 2006. http://0-wwwlib.umi.com.helin.uri.edu/dissertations/fullcit/3239913.
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Beg, Sarena. "The determinants of velocity." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp04/mq20781.pdf.
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Saeed, Khizer. "Laminar burning velocity measurements." Thesis, University of Oxford, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.270733.
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Kopp, Robert William. "Determination of the velocity." Thesis, Monterey, California. Naval Postgraduate School, 1989. http://hdl.handle.net/10945/25837.
Повний текст джерелаАнотація:
Hypervelocity flows for velocities is excess of 1.4 km/sec (Mach 5) require very high stagnation temperature to avoid liquefaction. The arc heater wind tunnel has been designed to provide such flows. The electric-are driven wind tunnel can develop stagnation temperatures up to 13,000 K which will produce hypervelocity flows up to 7 km/sec (earth orbital speed). The nature of the flow, however, is such that the high temperature source flow may cause severe gradients at the nozzle exit. In order to perform aero-thermodynamic tests the characterization of the flow in the test section is required. This paper experimentally determines the stream profiles for an arcjet wind tunnel conical nozzle directly from calorimetry and pitot probe surveys. Keywords: Arcjet flow; Hypervelocity flow; High enthalpy flow; Flow characteristics; Characteristic profile of the flow;
46
Teng, Xiaoqing. "High velocity impact fracture." Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/32118.
Повний текст джерелаАнотація:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, 2005.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Includes bibliographical references (p. 315-330).
An in-depth understanding of dynamic ductile fracture is one of the most important steps to improve the survivability of critical structures such as the lost Twin Towers. In the present thesis, the macroscopic fracture modes and the fracture mechanisms of ductile structural components under high velocity impact are investigated numerically and theoretically. Attention is focused on the formation and propagation of through-thickness cracks, which is difficult to experimentally track down using currently available instruments. Studied are three typical and challenging types of impact problems: (i) rigid mass-to beam impact, (ii) the Taylor test, and (iii) dynamic compression tests on an axisymmetric hat specimen. Using an existing finite element code (ABAQUS/Explicit) implemented with the newly developed Bao-Wierzbicki's (BW) fracture criterion, a number of distinct failure modes including fragmentation, shear plugging, tensile tearing in rigid mass-to-beam impact, confined fracture, petalling, and shear cracking in the Taylor test, are successfully recreated for the first time in the open literature. All of the present predictions are in qualitative agreement with experimental observations.
(cont.) This investigation convincingly demonstrates the applicability of the BW's fracture criterion to high velocity impact problems and at the same time provides an insight into deficiencies of existing fracture loci. Besides void growth, the adiabatic shear banding is another basic failure mechanism often encountered in high velocity impact. This failure mechanism and subsequent fracture is studied through numerical simulation of a recently conducted compression test on a hat specimen. The periodical occurrence of hot spots in the propagating adiabatic shear bands is successfully captured. The relation between hot spots and crack formation is revealed. The numerical predictions correlate well with experimental results. An explicit expression controlling through-thickness crack growth is proposed and verified by performing an extensive parametric study in a wide range of input variables. Using this expression, a two-stage analytical model is formulated for shear plugging of a beam/plate impacted by a flat-nosed projectile. Obtained theoretical solutions are compared with experimental results published in the literature showing very good agreement.
(cont.) Three theoretical models for rigid mass-to-beam impact, the single, double, and multiple impact of beam-to-beam are derived from the momentum conservation principle. The obtained closed-form solutions, which are applicable to the axial stretching dominated case, are validated by finite element analysis.
by Xiaoqing Teng.
Ph.D.
47
Stober, Gunter, and Christoph Jacobi. "Meteor head velocity determination." Universität Leipzig, 2007. https://ul.qucosa.de/id/qucosa%3A15571.
Повний текст джерелаАнотація:
Meteore, die in die Atmosphäre eindringen, bilden bei hohen Oberflächentemperaturen, die durch Kollisionen mit der umgebenden Luft hervorgerufen werden, einen mehrere Kilometer langen Plasmaschweif aus. An diesem Schweif werden ausgesandte Radarwellen reflektiert und zurückgestreut. Dies führt zu einem charakteristischen Schwingungsverhalten, auch Fresnel Zonen genannt, am Empfänger. Die Überlagerung dieser Wellen ist verantwortlich für die typische Signalform eines Meteors, mit dem abrupten Anstieg und dem exponentiellen Abfall für \'underdense\' Meteore. Mit Hilfe einer Simulation wird der theoretische Zusammenhang zwischen Geschwindigkeit und Signalverlauf demonstriert. Des weiteren wird gezeigt, das die Methode von Baggaley et al. [1997] zur Bestimmung von Meteoreintrittsgeschwindigkeiten auch auf ein Radarinterferometer (SKiYMET) anwendbar ist. Abschliessend werden die gewonnen Ergebnisse mit einem anderen Verfahren sowie der Literatur verglichen.Meteors, penetrating the earths atmosphere, creating at high surface temperatures, which are caused by collisions with the surrounding air molecules, a several kilometer long plasma trail. The ionized plasma backscatters transmitted radar waves. This leads to characteristic oscillations, called Fresnel zones, at the receiver. The interference of these waves entails the typical signal shape of a underdense meteor with the sudden rise of the signal and the exponential decay. By means of a simulation the theoretical connection between velocity and signal shape is demonstrated. Furthermore it is presented, that the method from Baggaley et al. [1997] for determination of meteor entry velocities is applicable for a radar interferometer (SKiYMET). Finally the results are compared to other radar methods on similar equipment and to other experiments.
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Johansson, Torneus Daniel, and Alexander Kotoglou. "Velocity of plasma flow." Thesis, KTH, Skolan för elektro- och systemteknik (EES), 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-199363.
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Stober, Gunter, and Christoph Jacobi. "Meteor head velocity determination." Universitätsbibliothek Leipzig, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-223206.
Повний текст джерелаАнотація:
Meteore, die in die Atmosphäre eindringen, bilden bei hohen Oberflächentemperaturen, die durch Kollisionen mit der umgebenden Luft hervorgerufen werden, einen mehrere Kilometer langen Plasmaschweif aus. An diesem Schweif werden ausgesandte Radarwellen reflektiert und zurückgestreut. Dies führt zu einem charakteristischen Schwingungsverhalten, auch Fresnel Zonen genannt, am Empfänger. Die Überlagerung dieser Wellen ist verantwortlich für die typische Signalform eines Meteors, mit dem abrupten Anstieg und dem exponentiellen Abfall für \"underdense\" Meteore. Mit Hilfe einer Simulation wird der theoretische Zusammenhang zwischen Geschwindigkeit und Signalverlauf demonstriert. Des weiteren wird gezeigt, das die Methode von Baggaley et al. [1997] zur Bestimmung von Meteoreintrittsgeschwindigkeiten auch auf ein Radarinterferometer (SKiYMET) anwendbar ist. Abschliessend werden die gewonnen Ergebnisse mit einem anderen Verfahren sowie der Literatur verglichenMeteors, penetrating the earths atmosphere, creating at high surface temperatures, which are caused by collisions with the surrounding air molecules, a several kilometer long plasma trail. The ionized plasma backscatters transmitted radar waves. This leads to characteristic oscillations, called Fresnel zones, at the receiver. The interference of these waves entails the typical signal shape of a underdense meteor with the sudden rise of the signal and the exponential decay. By means of a simulation the theoretical connection between velocity and signal shape is demonstrated. Furthermore it is presented, that the method from Baggaley et al. [1997] for determination of meteor entry velocities is applicable for a radar interferometer (SKiYMET). Finally the results are compared to other radar methods on similar equipment and to other experiments
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Widhe, Björn. "Chest wall sarcomas." Stockholm, 2010. http://diss.kib.ki.se/2010/978-91-7409-810-5/.
Повний текст джерела