Physical experiments are used to investigate the influence of the Coriolis forces on flow structures in channelized turbidity currents, and their implication for the evolution of straight and sinuous submarine channels. Initial tests were used to determine whether or not saline density currents are a good surrogate for particle-laden currents. Results imply that this assumption is valid when turbidity currents are weakly-depositional and have similar velocity and turbulence structures to saline density currents. Second, the controls of Coriolis forces on flow structures in straight channel sections are compared with two mathematical models: Ekman boundary layer dynamics and the theory of Komar [1969]. Ekman boundary layer dynamics prove to be a more suitable description of flow structures in rotating turbidity currents and should be used to derive flow parameters from submarine channels systems that are subjected to Coriolis forces. The significance of Coriolis forces for submarine channel systems were determined by evaluating the dimensionless Rossby number RoW. The Rossby number is defined as the ratio of the flow velocity, U, of a turbidity current to the channel width, W, and the rotation rate of the Earth represented by the Coriolis parameter, f. Coriolis forces are very significant for channel systems with RoW ≤ O(1). Third, the effect of Coriolis forces on the internal flow structure in sinuous submarine channels is considered. Since previous studies have only considered pressure gradient and centrifugal forces, the Coriolis force provides a crucial contribution to the lateral momentum balance in channel bends. In a curved channel, both the Rossby number RoW and the ratio of the channel curvature radius R to the channel width W, determine whether Coriolis forces affect the internal flow structure. The results demonstrate that Coriolis forces can cause a significant shift of the density interface and the downstream velocity core of channelized turbidity currents. The sediment transport regime in high-latitude channel systems, which have RoW << R/W, is therefore strongly influenced by Coriolis forces. Finally, these findings are incorporated into a conceptual model describing the evolution of submarine channels at different latitudes. For instance, the Northern Hemisphere channels have a distinctly higher right levee system and migrate predominantly to the left side and generally exhibit a low sinuosity. In contrast, low latitude channel systems have RoW >> R/W so that centrifugal forces are more dominant. This results in more sinuous submarine channel systems with varying levee asymmetries in subsequent channel bends. In conclusion, Coriolis forces are negligible around the equator but should be considered in high latitude systems, particularly when RoW ~ O(1) and RoW << R/W.

We consider the solidification of a binary alloy in a mushy layer subject to Coriolis effects. A near-eutectic approximation and large far-field temperature is employed in order to study the dynamics of the mushy layer in the form of small deviations from the classical case of convection in a horizontal porous layer of homogenous permeability. The linear stability theory is used to investigate analytically the Corio lis effect in a rotating mushy layer for, a diffusion time scale used by Amberg & Homsey (1993) and Anderson & Worster (1996), and for a new diffusion time scale proposed in the current study. As such, it is found that in contrast to the problem of a stationary mushy layer, rotating the mushy layer has a stabilising effect on convection. For the case of the new diffusion time scale proposed by the author, it is established that the viscosity at high rotation rates has a destabilising effect on the onset of stationary convection, ie. the higher the viscosity, the less stable the liquid. Finite amplitude results obtained by using a weak non-linear analysis provide differential equations for the amplitude, corresponding to both stationary and overstable convection. These amplitude equations permit one to identify from the post-transient conditions that the fluid is subject to a pitchfork bifurcation in the stationary case and to a Hopf bifurcation associated with the overstable convection. Heat transfer results were evaluated from the amplitude solution and are presented in terms of the Nusselt number for both stationary and overstable convection. They show that rotation enhances the convective heat transfer in the case of stationary convection and retards convective heat transfer in the oscillatory case, but only for low values of the parameter X I = 8 Pr ~ 0 So· The parameter 1/ X I represents the coefficient of the time derivative term in the Darcy equation. For high X I values, the contribution from the time derivative term is small (and may be neglected), whilst for small X I values the time derivative term may be retained. / Thesis (Ph.D.)-University of Durban-Westville, 2000.

Thesis (M.Sc.)--Memorial University of Newfoundland, 2002. / Restricted until May 2003. Bibliography: leaves 98-101.

No description available.

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.

Strong coherence in quasi-resonant laser driven system interferes with effective relaxations, resulting in behaviors like, coherent population trapping and Electromagnetically induced transparency. The Raman system can optimize this utilizing excited coherence in the lambda system when exposed to counter- intuitive pump-stokes pulses. The phenomenon can result in complete population transfer between vibrational levels called Stimulated Raman adiabatic passage(STIRAP). STIRAP and CHIRAP have been studied with Gaussian and chirped pulses. The optical propagation effects in dense medium for these phenomenon is studied to calculate the limitations and induced coherences. Further, the effect of rotational levels has been investigated. The molecular vibrational coherence strongly depends on the effect of rotational levels. The change in coherence interaction for ro-vibrational levels are reported and explained. We have considered the effects on the phase of radiation related to rotational mechanical motion of quantum system by taking advantages in ultra strong dispersion medium provided by quantum coherence in lambda system. The enhanced Fizeau effect on a single atom is observed.

The aim of this thesis has been to provide the reader with an intuitive insight into the mechanisms of the Coriolis effect. Apart from thoroughly describing the phenomenon, the essay attempts to eliminate as many myths prevailing around the Coriolis effect as possible. To get there, only a few mathematical derivations and calculations have been presented – the focus has been on a pure conceptual level. Furthermore, delusive textbook explanations have been examined and discussed in case studies. In the conclusion, the goal is reached by summarising the sought intuitive description of the Coriolis effect into one single sentence.

Ce travail de thèse porte sur l’étude et la réalisation de micro-capteurs dédiés à la mesure de vitesse angulaire par des principes basés sur des échanges thermiques. Deux types de gyromètres ont été développés dont la principale différence est liée au principe qui permet la mise en mouvement du gaz : convection forcée pour l’un et expansion thermique pour l’autre. Le principe est basé sur la modification par la force de Coriolis des échanges thermiques dans un fluide chauffé localement lorsque le dispositif est soumis à une vitesse de rotation. L’utilisation d’un fluide comme masse sismique est en rupture avec les concepts de gyromètres dits traditionnels. Cet avantage a pour conséquence la possibilité d’une utilisation dans des conditions environnementales sévères telles que de fortes accélérations (> 10 000 g) et de fortes vibrations. Les objectifs de ce travail consistent à étudier, à développer et à caractériser ces deux types de gyromètres. Pour cela, des études numériques ont été menées afin de mieux appréhender les phénomènes physiques et thermiques mis en jeu dans la cavité. On a pu aussi étudier l’effet des paramètres thermo-physiques du fluide, des différentes dimensions géométriques et de la vitesse d’écoulement du gaz sur la sensibilité et l’étendue de mesure. Par ailleurs, des prototypes des deux types de gyromètres ont été réalisés puis caractérisés. Les résultats sont très encourageants et les principes validés, mais leur confrontation avec ceux de la simulation montre que des améliorations sont à apporter sur le modèle numérique. / This PhD thesis deals with both study and fabrication of micro-sensors dedicated to the measurement of angular velocity, these devices are based on heat exchanges. Two types of gyroscopes have been developed, one using a jet of gas being deflected by the rotation, the other one using thermal expansion of a gas. Under rotation, heat transfers in a locally heated fluid is modified by the Coriolis force and induces a change in temperature distribution. Using a fluid as seismic mass enhances performances in terms shock (> 10 000g) and vibration resistances compared with standard mechanical gyroscopes.The aim of this work has been to study, develop and characterize these two gyroscopes. For this purpose, numerical studies have been carried out in order to improve our understanding of physical and thermal phenomena involved in the device. Effects of thermo-physical parameters, sensor size and gas flow velocity on both sensitivity and measuring range were analyzed.On the other hand, prototypes of both gyroscopes were manufactured and characterized. The proof of concept has been validated and encouraging results have been found. Comparison of measure and simulation have shown that improvements have to be made on the numerical model.

No description available.

In this thesis, the ribbed ducts of the internal cooling passage in turbine blading are investigated to demonstrate the effects of high speed rotation. Rotation coupled with high temperature operating conditions alters the mean flow, turbulence, and heat transfer augmentation due to Coriolis and centrifugal buoyancy forces that arises from density stratification in the domain. Gas turbine engines operate in particle laden environments (sand, volcanic ash), and particulate matter ingested by the engine can make their way into the blade internal cooling passages over thousands of operating hours. These particulates can deposit on the walls of these cooling passages and degrade performance of the turbine blade. Large-Eddy Simulations (LES) with temperature dependent properties is used for turbulent flow and heat transfer in the ribbed cooling passages and Lagrangian tracking is used to calculate the particle trajectories together with a wall deposition model. The conditions used are Re=100,000, Rotation number, Ro = 0.0 and 0.2, and centrifugal Buoyancy parameters of Bo=0, 0.5, and 1.0. First, the independent effects of Coriolis and centrifugal buoyancy forces are investigated, with a focus on the additional augmentation obtained in heat transfer with the addition of centrifugal buoyancy. Coriolis forces are known to augment heat transfer at the trailing wall and attenuate the same at the leading wall. Phenomenological arguments stated that centrifugal buoyancy augments the effects of Coriolis forces in outward flow in the first pass while opposing the effect of Coriolis forces during inward flow in the second pass. In this study, it was found that in the first pass, centrifugal buoyancy had a greater effect in augmenting heat transfer at the trailing wall than in attenuating heat transfer at the leading wall. On the contrary, it aided heat transfer in the second half of the first pass at the leading wall by energizing the flow near the wall. Also, contrary to phenomenological arguments, inclusion of centrifugal buoyancy augmented heat transfer over Coriolis forces alone on both the leading and trailing walls of the second pass. Sand ingestion is then investigated, by injecting 200,000 particles in the size range of 0.5-175μm with 65% of the particles below 10 μm. Three duct wall temperatures are investigated, 950, 1000 and 1050 °C with an inlet temperature of flow and particles at 527 °C . The impingement, deposition levels, and impact characteristics are recorded as the particles move through the domain. It was found that the Coriolis force greatly increases deposition. This was made prevalent in the first pass, as 84% of the deposits in the domain occurred in the first pass for the rotating case, whereas only 27% of deposits occurred in the first pass for the stationary case with the majority of deposits occurring in the bend region. This was due to an increased interaction with the trailing wall in the rotating case whereas particles in the stationary case were allowed to remain in the mean flow and gain momentum, making rebounding from a wall during collision more likely than deposition. In contrast, the variation of wall temperatures caused little to no change in deposition levels. This was concluded to be a result of the high Reynolds number used in the flow. At high Reynolds numbers, the particles have a short residence times in the internal cooling circuit not allowing the flow and particles to heat up to the wall temperature. Overall, 87% of the injected particles deposited in the rotating duct whereas 58% deposited in the stationary duct. / Master of Science