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The Himalayan orogen provides an incredible natural laboratory to test models for continent-continent collision. The highest peaks of the Himalayas are composed of the Greater Himalayan Sequence (GHS), which is bound by a north-dipping low angle detachment fault above (South Tibetan detachment; STD) and by a thrust fault below (Main Central thrust; MCT). Assuming simultaneous movement on these features, the GHS can be modeled as a southward extruding wedge or channel. Channel flow models describe the coupling between mid-crustal flow, driven by gradients in lithostatic pressure between the Tibetan Plateau and the Indian plate, and focused denudation on the range front. Although the general geometry and shear sense criteria for these bounding shear zones has been documented, prior to this investigation, relatively few attempts had been made to quantify the spatial and temporal variation in flow path history for rocks from an exhumed section of the proposed mid-crustal channel. Results from this investigation demonstrate that mid-crustal flow at high deformation temperatures was distributed throughout the proposed channel. As these rocks began to exhume to shallower crustal conditions and therefore lower temperatures, deformation began to become partitioned away from the core of the channel and into the bounding shear zones. Based on these results a new method (Rigid Grain Net) to measure the relative contributions of pure and simple shear (vorticity) is proposed. Detailed thermobarometric analysis was conducted on rocks from the highest structural level in the Khumbu region, Nepal to construct pressure-temperature-time-deformation paths during the tectonic evolution of the GHS between ~32-16 Ma. Another aspect of the project suggests that the most active feature of the region is the N-S trending Ama Drime Massif (ADM). By combining new structural interpretation with existing remote sensing data this investigation proposes that the ADM is being exhumed during extension that is coupled with denudation in the trans-Himalayan Arun River gorge. Together these data provide important insights into the dynamic links between regional-scale climate and crustal-scale tectonics. / Ph. D.

Vorticity modeling is used to simulate the flow around a surface-mounted prism. The objective is to examine whether vorticity modeling can give satisfactory information about surface pressure fluctuations which are mostly due to the outer or inviscid flow. Differences between results obtained with vorticity modeling and what one should expect from DNS and LES are pointed out. These include the difference between the governing equations, the shortcomings of having a 2-D simulation and the realization of introducing and convecting vorticity to simulate some turbulence aspects. All necessary details needed for the setup of vorticity modeling for complex flows, such as the one considered here are given. These details include choice of elements, the calculation of velocities, the application of boundary conditions and calculation of pressure. The numerical procedure and our use of parallelization in the code are explained. The results presented on velocity magnitude, vorticity and pressure show important characteristics of the flow field in terms of interaction of positive and negative vorticities and their effects on the surface pressure. The calculated peak and mean values for the pressure coefficients at the leading edge are close to those measured in separating flows over prisms. / Master of Science

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.

The flow field and forces on an isolated oscillating NACA 0012 airfoil in a uniform flow is studied using viscous vortex particle method. The simulations are carried out at very low chord (c) based Reynolds number (Re=1000), motivated by the current interest in development of Micro Air Vehicles (MAV). The airfoil is forced to oscillate in both heave and pitch at different normalized oscillation frequencies (f), which is represented by the non-dimensional reduced frequency fc/U).( From the unsteady loading on the airfoil, the net energy transfer to the airfoil is calculated to determine the propensity for the airfoil to undergo self-induced oscillations or flutter at these very low Reynolds numbers. The simulations are carried out using a viscous vortex particle method that utilizes discrete vortex elements to represent the vorticity in the flow field. After validation of the code against test cases in the literature, simulations are first carried out for the stationary airfoil at different angles of attack, which shows the stall characteristics of the airfoil at this very low Reynolds numbers. For the airfoil oscillating in heave, the airfoil is forced to oscillate at different reduced frequencies at a large angle of attack in the stall regime. The unsteady loading on the blade is obtained at different reduced frequencies. This is used to calculate the net energy transfer to the airfoil from the flow, which is found to be negative in all cases studied. This implies that stall flutter or self-induced oscillations are not possible under the given heave conditions. The wake vorticity dynamics is presented for the different reduced frequencies, which show that the leading edge vortex dynamics is progressively more complex as the reduced frequency is increased from small values. For the airfoil oscillating in pitch, the airfoil is forced to oscillate about a large mean angle of attack corresponding to the stall regime. The unsteady moment on the blade is obtained at different reduced frequencies, and this is used to calculate the net energy transfer to the airfoil from the flow, which is found to be positive in all cases studied. This implies that stall flutter or self-induced oscillations are possible in the pitch mode, unlike in the heave case. The wake vorticity dynamics for this case is found to be relatively simple compared to that in heave. The results of the present simulations are broadly in agreement with earlier stall flutter studies at higher Reynolds numbers that show that stall flutter does not occur in the heave mode, but can occur in the pitch mode. The main difference in the present very low Reynolds number case appears to be the broader extent of the excitation region in the pitch mode compared to large Re cases studied earlier. region in the pitch mode compared to large Re cases studied earlier.

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.

La dynamique instable des jets tournants est étudiée, en tenant compte des variations de masse volumique au sein de l'écoulement. Un code de simulation numérique directe permettant de résoudre les équations de Navier-Stokes à masse volumique variable a été développé, en utilisant une méthode originale et efficace pour résoudre le champs de pression. Analytiquement, deux modes instables bidimensionnels ont été mis en évidence, et sont identifiés comme des modes de Couette-Taylor et de Rayleigh-Taylor, ainsi qu'un troisième mode tridimensionnel, du à un couplage de vitesse. La dynamique instable de cet écoulement résulte d'une compétition entre ces trois modes, et les simulations numériques montrent que ces modes perdurent non linéairement. Ensuite, le comportement spatio-temporel de cette instabilité est étudiée par simulation numérique directe, et il a été montré qu'il existe une transition vers des modes absolument instables, sous l'effet du rapport de densité s ainsi que du taux de rotation q. Cette dynamique est également étudiée expérimentalement au travers de plusieurs méthodes de mesures, et la présence de mode globaux auto-entretenus est mise en évidence qui sont en bon accord avec les résultats numériques. Finalement, le phénomène de l'éclatement tourbillonnaire est étudié, et montre le rôle prépondérant de la viscosité réelle. En effet, l'éclatement tourbillonnaire est un mécanisme permettant de soulager le système de l'intensification de la vorticité, au travers de la viscosité, alors qu'il n'apparaît pas en traitant les équations d'Euler tronquées. / The unstable dynamics of a swirling jet flow is studied, including density variations within the flow. A direct numerical simulation method was developed to solve variable density Navier-Stokes equations, using an accurate and efficient pressure solver. Analitically, two unstable bi-dimensionnal modes are highlighted, and are identified as Couette-Taylor and Rayleigh-Taylor modes. A three-dimensionnal mode is also highlighted, wich is created by the shear. Numerical simulations show that those modes are nonlinearly persistant. Then, the spatio-temporal instability behaviour is studied numerically, and show that the instability undergoes to a convective/absolute transition with density ratio s and rotation rate q. This dynamic is also studied experiementally through different methods, and Global selfsustained modes are highlighted wich are in ggod agreement with numerical results. Finally, the vortex breakdown phenomenon is studied, and show the crucial role of real viscosity. Indeed, the vorticity intensification is relaxed through the viscosity effect, while it is not treating the truncated Euler Equations.

A interação entre troposfera e estratosfera tem grande influência e é de grande importância nos processos de ciclogênese em superfície. Entretanto, não se conhece exatamente a frequência destas interações e nem como podem influenciar na intensidade de ciclones em geral. Este trabalho tem como objetivo geral estudar como os altos níveis da atmosfera afetam o desenvolvimento de ciclones em superfície na América do Sul e Oceano Atlântico Sul, utilizando o conceito de vorticidade potencial (VP). Através de dados de ciclones rastreados em superfície e VP em 300 hPa desenvolveu-se um algoritmo que associa automaticamente os ciclones em superfície com anomalias de vorticidade potencial (AVP). Para o período 1998-2003, fez-se então a separação dos ciclones em associados (AAVP) e não-associados (NAVP) a AVP. De forma geral, observou-se que a maior parte dos ciclones AAVP concentra-se na região oceânica extratropical e os NAVP preferencialmente na região continental próximo de 30°S e em latitudes subtropicais. Para todo o período analisado, o número total de ciclones AAVP (55%) superou o número de NAVP (45%), sendo o ano de 2002 o único que apresentou número maior de eventos NAVP. Quanto à distribuição sazonal, os ciclones AAVP são mais frequentes nos meses de inverno e primavera, enquanto que os NAVP nos meses de verão. O tempo de vida dos NAVP é menor que dos AAVP, além de possuírem menor intensidade (de acordo com a pressão central média). Além destes fatores, a distância percorrida e a velocidade médias dos ciclones NAVP são menores do que dos AAVP. As composições dos campos sinóticos mostram que nos eventos NAVP, independente da estação do ano, a troposfera é mais quente que nos AAVP. Nos NAVP a forçante térmica é essencial para a formação do ciclone, enquanto que nos AAVP a AVP induz vorticidade ciclônica primeiro em altos níveis, que então se propaga para baixos níveis. Através da análise dos campos sinóticos, notou-se maior baroclinia nos casos NAVP, pois tanto os cavados em altos e médios níveis quanto a corrente de jato permanecem favorecendo o desenvolvimento do ciclone em superfície, enquanto que nos AAVP o centro do ciclone em superfície está verticalmente quase alinhado ao cavado. Centros de vorticidade relativa ciclônica em 500 hPa desprendem-se do escoamento de oeste em todas as estações para os casos AAVP, porém, no verão, isto também é visto nos NAVP. / The process of troposphere-stratosphere interaction has influence and is very important on surface cyclogenesis. However, the frequency of these interactions and how they influence the intensity of cyclones is not known exactly. The main objective of this work is to study how the upper levels affect the development of surface cyclones in South America and South Atlantic Ocean using the concept of potential vorticity (PV). Cyclone tracking data and 300 hPa PV were used to develop an algorithm that automatically associates the surface cyclones with potential vorticity anomaly (PVA). For the period 1998-2003, the cyclones were separated as associated (APVA) and non-associated (NPVA) with PVA. In general, it was observed that most of the APVA cyclone was concentrated in extratropical oceanic region, while NPVA cyclones form over the continent preferably around 30°S and subtropics. The total number of APVA cyclones (55%) exceeds the number of NPVA (45%), except for 2002. In regard to seasonal distribution, the APVA cyclones are more frequent in winter and spring months while NPVA in summer months. The lifetime of NPVA cyclones is shorter and they are less intense than APVA (according to the average central pressure). In addition to these factors, the mean traveled distance and mean velocity are smaller in the NPVA than in APVA. The composites of the synoptic fields show that in NPVA events, regardless of the season, the troposphere is warmer than in APVA. In NPVA cases the thermal forcing is essential to the cyclogenesis, while in the APVA the cyclonic vorticity induced by PVA at upper levels propagating to low levels is more important. The NPVA cases present more baroclinic characteristics which the upper and mid-level troughs accompanied by the jet stream favoring the surface cyclone development, whereas in the APVA the surface cyclone center remains almost vertically aligned with these troughs. For APVA cases, the centers of cyclonic vorticity at 500 hPa detach from westerly flow in all seasons however in summer this is also seen in NPVA.

Diese Dissertation befasst sich mit Beobachtungen von konvektiven Strömungen in der Sonne, und insbesondere mit den Auswirkungen der Rotation auf diese Strömungen auf der Längenskala von Supergranulation und größeren Skalen (>30 Mm). Die Rotation der Sonne verursacht durch die Corioliskraft Wirbelströmungen und bewirkt anisotrope Korrelationen der Geschwindigkeitskomponenten. Man nimmt an, dass diese Korrelationen die Dynamik der Sonne auf großen Längenskalen beeinflussen. Um horizontale Strömungen zu messen, untersuchen wir photosphärische Aufnahmen der Doppler-Geschwindigkeit und der Kontinuumsintensität des ``Helioseismic and Magnetic Imagers'' (HMI) an Bord der Raumsonde ``Solar Dynamics Observatory'' (SDO) mit Hilfe der Methoden Time-Distance-Helioseismologie (TD) und Local Correlation Tracking (LCT) von Granulen. Im Rahmen der Time-Distance-Helioseismologie kann die lokale vertikale Vortizität gemessen werden, indem die Differenz von Wellenlaufzeiten entlang eines geschlossenen Weges ermittelt wird (Laufzeiten gegen den Uhrzeigersinn minus Laufzeiten im Uhrzeigersinn). Die Ergebnisse von TD und LCT stimmen bis zu den höchsten studierten Breitengraden (+/-60°) hervorragend überein, nachdem eine Korrektur für so genannte Center-to-Limb-Effekte angewandt wurde. Nach dem Mitteln in Ost-West-Richtung messen wir abseits des Äquators eine schwache, aber signifikante Korrelation zwischen der horizontalen Komponente der Divergenz und der vertikalen Komponente der Vortizität von supergranularen Strömungen. Ein Vergleich der Messungen mit einem Modell für das Rauschen offenbart, dass die TD-Methode verwendet werden kann, um die vertikale Vortizität von Strömungen auf Längenskalen größer als 15 Mm zu messen. Damit können mit dieser Methode nicht nur Strömungen in Supergranulen, sondern auch in Riesenzellen gemessen werden. Wir stellen außerdem fest, dass das Signal in Messungen der vertikalen Vortizität mit Hilfe von Aufnahmen von SDO/HMI sehr viel leichter detektiert werden kann als mit Hilfe von früheren Aufnahmen. Um den Einfluss der Sonnenrotation auf die Supergranulation im Detail zu studieren, kartieren wir die vertikale Vortizität der Strömungen in der durchschnittlichen Supergranule. Die durchschnittliche Supergranule wird konstruiert, indem Tausende von einzelnen Supergranulen in einem bestimmten Breitengradbereich durch räumliche Verschiebungen zur Deckung gebracht werden. Damit lösen wir zum ersten Mal die vertikale Vortizität in Aus- und Einströmungen räumlich auf. In nördlichen Breiten sind Ausströmungen im Mittel mit einer Zirkulation im Uhrzeigersinn verbunden. Das Signal verschwindet am Äquator und hat in südlichen Breiten das umgekehrte Vorzeichen. Aus- und Einströmungen besitzen eine vertikale Vortizität mit entgegengesetzten Vorzeichen, wie es von Vorhersagen erwartet wird, die sich auf die Corioliskraft stützen. Es wird offenbar, dass der Vortizitätspeak in der durchschnittlichen supergranularen Ausströmung vergleichsweise ausgedehnt und schwach ist (Halbwertsbreite von 13 Mm und Spitzenwert von 4 x 10^{-6}/s im Uhrzeigersinn bei 40° nördlicher Breite), verglichen mit der durchschnittlichen Einströmung (Halbwertsbreite von 8 Mm und Spitzenwert von 8 x 10^{-6}/s gegen den Uhrzeigersinn). Darüberhinaus untersuchen wir mit SDO/HMI-Daten das Magnetfeld in den Einströmungen um die durchschnittliche Supergranule am Äquator herum. Die mittlere Stärke des Magnetfelds stellt sich als richtungsabhängig heraus: In westlicher Richtung (prograd) ist das Netzwerkfeld ungefähr 10% stärker als in östlicher Richtung. Dieses überraschende Ergebnis fügt dem Rätsel um die Supergranulation einen weiteren Aspekt hinzu. Ob ein Zusammenhang mit anderen bekannten Eigenschaften der Supergranulation besteht (beispielsweise zur Superrotation des supergranularen Strömungsmusters oder zu wellenartigen Eigenschaften), ist nicht geklärt.

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