The objectives of this study are to revise and reformulate a previous simulation model of the Calapooia River and proposed Holley Dam project and to critically investigate the anadromous fish enhancement function of the project. The Corps of Engineers proposes a 145,000 acre-foot reservoir for the Calapooia River at Holley, Oregon. Previously, a 97,000 acre-foot reservoir was proposed. The larger project's justification is based mainly on anadromous fish enhancement. Investigation revealed that there is a great deal of uncertainty and lack of information about: (1) temperature requirements of anadromous fish in the Calapooia River and whether they can be met, (2) the affects of high streamflow discharges on spawning, incubation, and rearing of anadromous fish in the Calapooia River, (3) the affects of variability in food supply due to fluctuations in the level of the water in the reservoir, and (4) the survival rates of salmon eggs to fry, fry to smolts, and ocean survival. A simulation model in DYNAMO computer language is formulated and includes the following components: (1) hydrology generator, (2) reservoir regulation and flood control procedures, (3) freshwater life cycle of Spring Chinook and Fall Chinook Salmon, (4) supply of recreation user days, (5) supply of resident fishing angler days, and (6) supply of irrigation water. The model calculates the daily, monthly, and yearly variability of various physical, economic, and intangible outcomes. The simulation of floods and their regulation corresponds to historical data and regulation hypothesized by the Corps of Engineers. The dynamic nature of the Spring and Fall Chinook Salmon populations are modeled and computer results indicate that the likelihood of conservation and enhancement is not great enough to justify the 145,000 acre-foot reservoir. Due to the fluctuations in the reservoir level which accompany flood control regulation and reflect the variability in the hydrology, the recreational use and resident fishing angler use is highly variable and the average use is unlikely to reach the estimated supply potential. The reservoir, as simulated by the model, has sufficient capacity to supply water for the proposed irrigation project. However, it appears that uncertainty remains concerning the dollar benefits that are obtainable from irrigating soils along the Calapooia River. Further study is necessary to determine whether the 97,000 acre-foot reservoir is a feasible alternative to the proposed 145,000 acre-foot reservoir. The computer model is general in formulation and can be utilized to provide information to decision makers in determining the feasibility of further dam and reservoir construction. / Graduation date: 1972

No description available.

名古屋大学年代測定総合研究センターシンポジウム報告

No description available.

This thesis primarily concerns kinematic dynamo action by the 1:1:1 ABC flow, in the highly conducting limit of large magnetic Reynolds number Rm. The flow possesses 24 symmetries, with a symmetry group isomorphic to the group O24 of orientation-preserving transformations of a cube. These symmetries are exploited to break up the linear eigenvalue problem into five distinct symmetry classes, which we label I-V. The thesis discusses how to reduce the scale of the numerical problem to a subset of Fourier modes for a magnetic field in each class, which then may be solved independently to obtain distinct branches of eigenvalues and magnetic field eigenfunctions. Two numerical methods are employed: the first is to time step a magnetic field in a given symmetry class and obtain the growth rate and frequency by measuring the magnetic energy as a function of time. The second method involves a more direct determination of the eigenvalue using the eigenvalue solver ARPACK for sparse matrix systems, which employs an implicitly restarted Arnoldi method. The two methods are checked against each other, and compared for efficiency and reliability. Eigenvalue branches for each symmetry class are obtained for magnetic Reynolds numbers Rm up to 10^4 together with spectra and magnetic field visualisations. A sequence of branches emerges as Rm increases and the magnetic field structures in the different branches are discussed and compared. All symmetry classes are found to contain a dynamo, though dynamo effectiveness varies greatly between classes, suggesting that the symmetries play an important role in the field amplification mechanisms. A closely related problem, that of linear hydrodynamic stability, is also explored in the limit of large Reynolds number Re. As the same symmetry considerations apply, the five symmetry classes of the linear instability can be resolved independently, reducing the size of the problem and allowing exploration of the effects of the symmetries on instability growth rate. Results and visualisations are obtained for all five classes for Re up to 10^3, with comparisons drawn between the structures seen in each class and with those found in the analogous magnetic problem. For increasing Re, multiple mode crossings are observed within each class, with remarkably similar growth rates seen in all classes at Re=10^3, highlighting a lack of dependence on the symmetries of the instability, in contrast with the magnetic problem. This thesis also investigates the problem of large-scale magnetic fields in the 1:1:1 ABC flow through the introduction of Bloch waves that modify the periodicity of the magnetic field relative to the flow. Results are found for a field with increased periodicity in a single direction for Rm up to 10^3; it is established that the optimal scale for dynamo action varies as Rm increases, settling on a consistent scale for large Rm. The emerging field structures are studied and linked with those of the original dynamo problem. On contrasting this method with a previous study in which the flow is instead rescaled, it is shown that the use of Bloch waves drastically increases the range of possible scales, whilst cutting required computing time. Through a multiple-scale analysis, the contribution from the alpha-effect is calculated for the 1:1:1 ABC flow and is seen in growth rates for Rm << 1.

La magnétohydrodynamique (MHD) est la science et le formalisme qui décrivent les mouvements d'un fluide conducteur d'électricité. Il est possible que de tels mouvements donnent lieu à l'effet dynamo qui consiste en la génération d'un champ magnétique stable et de grande échelle. Ce phénomène est vraisemblablement à l'origine des champs magnétiques des planètes, des étoiles et des galaxies. Il est surprenant qu'alors que les mouvements fluides à l'intérieur de ces objets célestes sont turbulents, les champs magnétiques généré soient de grande échelle spatiale et stables sur de longues périodes de temps. De plus, ils peuvent présenter une dynamique temporelle régulière comme c'est le cas pour le champ magnétique solaire dont la polarité s'inverse tous les onze ans. Décrire et prédire les mouvements d'un fluide turbulent reste l'un des problèmes les plus difficiles de la mécanique classique. %La description aussi bien analytique que numérique d'un fluide hautement turbulent est d'une effroyable complexité, si pas tout simplement impraticable. Dans cette situation, Il est donc utile de construire des modèles aussi proches que possible du système de départ mais de moindre complexité de sorte que des études théoriques et numériques deviennent envisageables. Deux approches ont été considérées ici. D'une part, nous avons développé des modèles présentant un très petit nombre de degrés de liberté (de l'ordre de la dizaine). Une étude analytique est alors possible. Ces modèles ont une dépendance en les paramètres physiques - nombres de Reynolds cinétique et magnétique et injection d'hélicité - qualitativement similaire aux dynamos célestes et expérimentales. D'autre part, les modèles en couches permettent de caractériser les transferts d'énergie entre les structures de différentes tailles présentes au sein du champ de vitesse. Nous avons développé un nouveau formalisme qui permet d'étudier aussi les échanges avec le champ magnétique. De plus, nous proposons une étude de la MHD dans le cadre de la décomposition hélicoïdale des champs solénoïdaux - une idée similaire à la décomposition de la lumière en composantes polarisées et que nous sommes les premiers à appliquer à la MHD. Nous avons montré comment exploiter cette approche pour déduire systématiquement des modèles simplifiés de la MHD. En particulier, nos méthodes multiplient le nombre de situations descriptibles par les modèles en couche comme par exemple le problème anisotrope de la turbulence en rotation. Elles permettent aussi de construire des modèles à basse dimension en calquant les résultats de simulations numériques directes. Ces modèles peuvent alors être étudiés à moindre coûts. _______________ Magnetohydrodynamics (MHD) is both the science and the formalism that describe the motion of an electro-conducting fluid. Such motion may yield the dynamo effect consisting in the spontaneous generation of a large scale stationary magnetic field. This phenomenon is most likely the reason behind the existence of planetary, stellar and galactic magnetic fields. It is quite surprising that also the fluid motion within these objects is turbulent, the generated magnetic fields present large spatial structures evolving over long time scales. Moreover these fields can present a very regular non trivial dynamics like in the case of the Sun, the magnetic field of which switches polarity every eleven years. To describe and predict the motion of a turbulent flow remains one of the most challenging problem of classical mechanics. It is therefore useful to build models as close to the initial system as possible but of a lesser complexity so that their theoretical and numerical analysis become tractable. Two approaches have been considered here. Low dimensional models have been developed that present about ten degrees of freedom. An analytical study of the resulting dynamical system is then possible. Interestingly, the dependance of these models on the physical parameters - kinetic and magnetic Reynolds number as well as injection of kinetic helicity - qualitatively matches that of the cosmic and experimental dynamos. On the other hand, shell models allow to characterise the energy transfers between structures of different sizes within the velocity field. A new formalism is presented which makes possible to also study the exchanges with the magnetic field. Furthermore, a description of MHD in the helical decomposition is proposed. I show how to use this decomposition to build new shell and low dimensional models. The methods developed here allow to broaden the scope of possible applications of the models. In particular, shell models are generalised in such a way that they can now describe anisotropic situations like that of rotating turbulence.

Origin and symmetry of the observed global magnetic fields in galaxies are not fully understood. We intend to clarify the question of the magnetic field origin and investigate the global action of the magneto-rotational instability (MRI) in galactic disks with the help of 3D global magneto-hydrodynamical (MHD) simulations. The calculations were done with the time-stepping ZEUS 3D code using massive parallelization. The alpha-Omega dynamo is known to be one of the most efficient mechanisms to reproduce the observed global galactic fields. The presence of strong turbulence is a pre-requisite for the alpha-Omega dynamo generation of the regular magnetic fields. The observed magnitude and spatial distribution of turbulence in galaxies present unsolved problems to theoreticians. The MRI is known to be a fast and powerful mechanism to generate MHD turbulence and to amplify magnetic fields. <br><br> We find that the critical wavelength increases with the increasing of magnetic fields during the simulation, transporting the energy from critical to larger scales. The final structure, if not disrupted by supernovae explosions, is the structure of `thin layers' of thickness of about 100 pcs. An important outcome of all simulations is the magnitude of the horizontal components of the Reynolds and Maxwell stresses. The result is that the MRI-driven turbulence is magnetic-dominated: its magnetic energy exceeds the kinetic energy by a factor of 4. The Reynolds stress is small and less than 1% of the Maxwell stress. <br><br> The angular momentum transport is thus completely dominated by the magnetic field fluctuations. The volume-averaged pitch angle is always negative with a magnitude of about -30. The non-saturated MRI regime is lasting sufficiently long to fill the time between the galactic encounters, independently of strength and geometry of the initial field. Therefore, we may claim the observed pitch angles can be due to MRI action in the gaseous galactic disks. The MRI is also shown to be a very fast instability with e-folding time proportional to the time of one rotation. Steep rotation curves imply a stronger growth for the magnetic energy due to MRI. The global e-folding time is from 44 Myr to 100 Myr depending on the rotation profile. Therefore, MRI can explain the existence of rather large magnetic field in very young galaxies. We also have reproduced the observed rms values of velocities in the interstellar turbulence as it was observed in NGC 1058. We have shown with the simulations that the averaged velocity dispersion of about 5 km/s is a typical number for the MRI-driven turbulence in galaxies, which agrees with observations. The dispersion increases outside of the disk plane, whereas supernovae-driven turbulence is found to be concentrated within the disk. In our simulations the velocity dispersion increases a few times with the heights. <br><br> An additional support to the dynamo alpha-effect in the galaxies is the ability of the MRI to produce a mix of quadrupole and dipole symmetries from the purely vertical seed fields, so it also solves the seed-fields problem of the galactic dynamo theory. The interaction of magneto-rotational instability and random supernovae explosions remains an open question. It would be desirable to run the simulation with the supernovae explosions included. They would disrupt the calm ring structure produced by global MRI, may be even to the level when we can no longer blame MRI to be responsible for the turbulence. / Die Beobachtung polarisierter Synchrotronstrahlung mit modernen Radioteleskopen zeigen die Existenz von großskaligen Magnetfeldern in Galaxien. Mit den ständig verbesserten Beobachtungsinstrumenten findet man Magnetfelder in immer mehr Galaxien, so dass man annehmen kann, Magnetfelder treten mehr oder weniger in allen Galaxien auf. Selbst in sehr jungen Galaxien (damit weit entfernten) wurden schon Magnetfelder von einigen mikroG gefunden.<br> Eine mögliche Erklärung für die Entstehung der Magnetfeldern ist die Wirkung eines turbulenten Dynamos. Neben Supernova-Explosionen können magnetische Instabilitäten eine Quelle für die Turbulenz im interstellaren Medium sein. So werden Galaxien bei Anwesenheit eines schwachen Magnetfeldes auf Grund der &quot;Magneto-Rotations-Instabilität&quot; (MRI) turbulent. Die globale Entwicklung des interstellaren Gases in Galaxien unter Wirkung der MRI ist in der vorliegenden Arbeit betrachtet worden.<br> Mit drei-dimensionalen numerischen Simulationen auf großen Clusterrechnern wurde die zeitliche Entwicklung des Geschwindigkeitsfeldes und der Magnetfelder untersucht. Für die extrem rechenintensiven globalen Modelle wurde ein hochgradig parallelisierbares Rechenprogramm zur Lösung der MHD-Gleichungen an die Problemstellung angepasst, in der Rechenzeit optimiert und ausführlich getestet. <br> Es konnte erstmalig die zeitliche Entwicklung des interstellaren Gases unter dem Einfluss eines schwachen Magnetfeldes über mehrere Milliarden Jahre verfolgt werden. In der galaktischen Scheibe entwickelt sich Turbulenz mit einer Geschwindigkeitsdispersion von einigen km/s und großskalige Magnetfelder von einigen mikroG, genau wie in realen Galaxien beobachtet. Damit konnte der Nachweis erbracht werden, dass das interstellare Gas durch Wirkung der MRI auch bei geringer Sternaktivität Turbulenz entwickelt, wie es in einigen ruhigen Galaxien auch beobachtet wird.<br> Ein anderes wichtiges Resultat ist die Entstehung großskaliger Magnetfelder aus kleinskaligen Strukturen in der Art eines turbulenten Dynamos. Die Wachstumsrate der magnetischen Energie geht bei diesem Prozess mit der Umlaufzeit, schnell genug um auch Magnetfelder mit einigen mikroG in sehr jungen Galaxien zu erreichen.<br> Die Entstehung von Magnetfeldern aus der MRI löst auch die bisher ungeklärte Frage nach der Geometrie der Saatfelder für turbulente Dynamos.

Ce travail de thèse s’articule autour de plusieurs questions relatives à l’instabilité dynamo dans des écoulements turbulents en métaux liquides. Cette instabilité de conversion d’énergie cinétique en énergie magnétique dans les fluides électriquement conducteurs est à l’origine, par exemple, des champs magnétiques terrestre et solaire. En particulier, nous abordons l’estimation du seuil de l’instabilité, l’influence de l’écoulement et des conditions aux limites ainsi que les mécanismes de saturation du champ magnétique. Ces travaux expérimentaux s’appuient sur deux écoulements turbulents de type von Kármán : en sodium liquide à Cadarache (collaboration VKS) et en gallium liquide à l’ENS de Lyon.Dans un premier temps, l’étude est consacrée à l’analyse de critères permettant d’estimer la distance au seuil de l’instabilité dynamo, à travers la mesure de la réponse magnétique du système à une excitation pour la dynamo auto-entretenue VKS. Ces critères ont été validés dans les configurations dynamos de l’expérience puis appliquées aux configurations non-dynamo.Ensuite, nous illustrons l’influence de l’écoulement sur le champ dynamo à travers l’étude de bifurcations globales. Une bistabilité hydrodynamique, pilotant deux branches dynamos d’amplitude différentes, est décrite ainsi que les liens entre les états magnétiques et hydrodynamiques.Nous portons notre attention sur l’étude des mécanismes de saturation à travers la dynamo semi- synthétique de Bullard-von Karman mettant en jeu un mécanisme d’induction turbulente et un mécanisme de bouclage artificiel permettant l’observation d’une dynamo à faible nombre de Reynolds magnétique. L’instabilité démarre à travers un régime intermittent et sature par la rétroaction des forces de Lorentz sur l’écoulement. Nous donnons les lois d’échelle et le bilan de puissance de ce régime. Un régime d’instabilité sous-critique est aussi introduit et caractérisé.Nous détaillons dans une dernière partie, les techniques de mesure spécifiques aux métaux liquides utilisées et développées au cours de la thèse. / This PhD thesis deals with several problems relative to the dynamo instability in liquid metals turbulent flows. This instability converts kinetic energy into magnetic one in electrically conductive flows. It is the root of the magnetic field of the Earth and the Sun.We address the estimation of threshold of the instability, the influence of the flow configuration and of the electromagnetic boundary conditions as well as the saturation mechanism of the magnetic field. This experimental work rely on two turbulent flows of von Kármán type: in liquid sodium located in Cadarache (VKS collaboration) and in liquid gallium in ENS de Lyon.First we analyze several criteria about the estimation of the distance to threshold of the dynamo instability with the magnetic response of the system to a magnetic excitation for the self sustained dynamo in the VKS experiment. These method have been checked for dynamo configurations and then applied for non-dynamo configurations. Then, we study the influence of the flow on the dynamo field under the action of global hydrodynamic bifurcations. We describe a bistability of the flow which triggers two dynamo branches of different amplitude and the dynamics of the transitions between both hydrodynamic and magnetic states.We then focus on the saturation mechanism with the semi-synthetic Bullard-von Karman dynamo, involving a turbulent induction mechanism and an artificial electronic feedback. This setup allows to observe dynamo action for very low magnetic Reynolds number, far below the natural threshold of the instability.We observe an intermittent regime close to threshold and a fluid saturation by Lorentz force feedback on the flow. We specify the scaling laws and a power budget estimation of this regime. A sub-critical regime is also introduced and characterized.In the last section we detailed several measurement techniques in liquid metals developed and used during the PhD.

Автоматизация проектирования несущих конструкций – одно из стремительно развивающихся направлений в области BIM моделирования. В работе рассмотрены методики армирования железобетонных конструкций с применением информационной модели здания. По результатам исследования написаны два скрипта для среды визуального программирования Dynamo для автоматизации расчета на продавливание. / Automation of the design of load-bearing structures is one of the rapidly developing areas in the field of BIM modeling. The paper considers methods of reinforcing reinforced concrete structures using an information model of a building. According to the results of the study, two scripts were written for the Dynamo visual programming environment to automate the calculation for punching.

Our Sun is a variable star. The magnetic fields in the Sun play an important role for the existence of a wide variety of phenomena on the Sun. Among those, sunspots are the slowly evolving features of the Sun but solar ares and coronal mass ejections are highly dynamic phenomena. Hence, the solar magnetic fields could affect the Earth directly or indirectly through the Sun's open magnetic flux, solar wind, solar are, coronal mass ejections and total solar irradiance variations. These large scale magnetic fields originate due to Magnetohydrodynamic dynamo process inside the solar convection zone converting the kinetic energy of the plasma motions into the magnetic energy. Currently the most promising model to understand the large scale magnetic fields of the Sun is the Flux Transport Dynamo (FTD) model. FTD models are mostly axisymmetric models, though the non-axisymmetric 3D FTD models are started to develop recently. In these models, we assume the total magnetic fields of the Sun consist of poloidal and toroidal components and solve the magnetic induction equation kinematicaly in the sense that velocity fields are invoked motivated from the observations. Differential rotation stretches the poloidal field to generate the toroidal field. When toroidal eld near the bottom of the convection zone become magnetically buoyant, it rises through the solar convection zone and pierce the surface to create bipolar sunspots. While rising through the solar convection zone, the Coriolis force keeps on acting on the flux tube, which introduces a tilt angle between bipolar sunspots. Since the sunspots are the dense region of magnetic fields, they diffuse away after emergence. The leading polarity sunspots (close to equator) from both the hemisphere cancel each other across the equator and trailing polarity sunspots migrate towards the pole to generate effective poloidal fields. This mechanism for generation of poloidal field from the decay of sunspots is known as Babcock-Leighton process. After the poloidal field is generated, the meridional flow carries this field to the pole and further to the bottom of the convection zone where differential rotation again acts on it to generate toroidal field. Hence the solar dynamo goes on by oscillation between the poloidal field and toroidal field, where they can sustain each other through a cyclic feedback process. Just like other physical models, FTD models have various assumptions and approximations to incorporate these different processes. Some of the assumptions are observationally verified and some of them are not. Considering the availability of observed data, many approximations have been made in these models on the theoretical basis. In this thesis, we present various studies leading to better understanding of the different processes and parameters of FTD models, which include magnetic buoyancy, meridional circulation and Babcock-Leighton process. In the introductory Chapter 1, we first present the observational features of the solar magnetic fields, theoretical background of the FTD models and motivation for investigating different processes. Most of the results of our work are presented in Chapters 2 - 7. In the Chapters 2 - 5, we explain various important issues regarding the treatment of magnetic buoyancy, irregularities of the solar cycle during descending phase, effect of different spatial structure of meridional flow on the dynamo and how dynamo generated fields would a ect the meridional ow using 2D axisymmetric Flux Transport Dynamo model. In the Chapters 6 & 7, the build up of polar fields from the decay of sunspots and a proper treatment of Babcock-Leighton process by invoking realistic convective flows, are presented using 3D Flux Transport Dynamo model. Finally the conclusions and future works are given in the Chapter 8. In 2D axisymmetric Flux Transport Dynamo models, the rise of the toroidal magnetic field through the convection zone due to magnetic buoyancy and then the generation of the poloidal magnetic field from these bipolar sunspots, has been treated mainly in two ways|a non-local method and a local method. In Chapter 2, we have analyzed the advantages and disadvantages of both the methods. We find that none of them are satisfactory to depict the correct picture of magnetic buoyancy because it is an inherently 3D process. Unless we go to the 3D framework of Flux Transport Dynamo models, we have to treat the magnetic buoyancy in such simplistic way. We find that the non-local treatment of magnetic buoyancy is very robust for a large span of parameter space but it does not take into account the depletion of flux from the bottom of the convection zone which has a significant importance in irregularity study of the solar cycle. The local treatment of magnetic buoyancy includes the flux depletion from the bottom of the convection zone and treats the magnetic buoyancy much realistically than the non-local treatment. But this local treatment of magnetic buoyancy is not so robust. We also pointed out that the long-standing issue about appearance of sunspots in the low-latitudes needs to be studied carefully. In Chapter 3, we have studied various irregularities of the solar cycle during its decaying phase. We have reported that the decay rate of the cycle is strongly correlated with amplitude of the same cycle as well as the amplitude of the next cycle from different sunspot proxies like sunspot number, sunspot area and 10.7 cm radio flux data. We explain these correlation from flux transport dynamo models. We nd that the correlations can only be reproduced if we introduce stochastic fluctuations in the meridional circulations. We also reproduced most of the correlation found in ascending and descending phase of the solar cycle from century long sunspot area data (Mandal et al., 2017) from Kodaikanal observatory, India which are in great agreement with the correlations found earlier from Greenwich sunspots data. In most of the FTD models, a single cell meridional circulation is assumed within the solar convection zone, with the equatorward return flow at its bottom. But with recent development in helioseismology, plenty of results have come out about various spatial structure of meridional circulation (Zhao et al., 2013; Schad et al., 2013; Rajaguru & Antia, 2015; Jackiewicz et al., 2015). Some helioseismology group (Zhao et al., 2013) reported that the meridional circulation has a double cell structure in solar convection zone and some groups (Schad et al., 2013; Jackiewicz et al., 2015) have reported a multi-cellular structure of meridional circulation in the convection zone. By probing the supergranular motion Hathaway (2012) estimated that the meridional ow has an equatorward return ow at the upper convection zone 70 Mm below the surface. In view of the above observed results, we have discussed in Chapter 4 what would happen to Flux Transport Dynamo model if we consider other structure of meridional circulation instead of single cell meridional circulation encompassing whole convection zone. We nd that the our dynamo model works perfectly ne as long as there is an equatorward propagation at the bottom of the convection zone. Our model also works with shallow meridional circulation as found by Hathaway (2012), if we consider the latitudinal pumping in our model. The temporal variation of meridional circulation on the surface is also observed from various measurement techniques. Chou & Dai (2001) rst observed a variation of meridional circulation with the solar cycle from their helioseismic measurements. Hathaway & Rightmire (2010) also found a variation up to 5 m s 1 for the solar cycle 23 by measuring the magnetic elements on the surface of the Sun. Recently Komm et al. (2015) have analyzed MDI and HMI Dopplergram data and reported a solar cyclic variation with detail latitudinal dependence. To explain this variation of the meridional circulation with the solar cycle, we construct a theoretical model by coupling the equation of the meridional circulation (the component of the vorticity equation within the solar convection zone) with the equations of the flux transport dynamo model in Chapter 5. We consider the back reaction due to the Lorentz force of the dynamo-generated magnetic fields and study the perturbations produced in the meridional circulation due to it. This enables us to model the variations of the meridional circulation without developing a full theory of the meridional circulation itself. We obtain results which reproduce the observational data of solar cycle variations of the meridional circulation reasonably well. We get the best results on assuming the turbulent viscosity acting on the velocity field to be comparable to the magnetic diffusivity (i.e. on assuming the magnetic Prandtl number to be close to unity). We have to assume an appropriate bottom boundary condition to ensure that the Lorentz force cannot drive a flow in the sub-adiabatic layers below the bottom of the tachocline. Our results are sensitive to this bottom boundary condition. We also suggest a hypothesis how the observed inward flow towards the active regions may be produced. In Chapter 6 and Chapter 7, we have studied some of the aspects of solar magnetic eld generation process using 3D dynamo model that were not possible to study earlier using axisymmetric 2D Flux Transport dynamo models. We have used the 3D dynamo model developed by Mark Miesch (Miesch & Dikpati, 2014; Miesch & Teweldebirhan, 2016) and study how polar fields build up from the decay of sunspots more realistically in Chapter 6. We first reproduce the observed butter y diagram and periodic solution considering higher diffusivity value than earlier reported results and use it as a reference model to study the build up polar fields by putting a single sunspot pair in one hemisphere and two sunspot pairs in both the hemispheres. The build up of the polar fields from the decay of sunspots are studied earlier using Surface Flux Transport model (Wang et al., 1989; Baumann et al., 2004; Cameron et al., 2010) which solve only radial component of the induction equation on the surface of the Sun ( | plane). But these 2D SFT models have some inherent limitation for not considering the 3D vectorial nature of the magnetic fields and subsurface processes. We have shown that not considering the vectorial nature and subsurface process has an important effect on the development of the polar fields. We have also studied the effect of a few large sunspot pairs violating Hale's law on the strength of the polar field in this Chapter. We nd that such ant-Hale sunspot pairs do produce some effect on the polar fields, if they appear at higher latitudes during the mid-phase of the solar cycle|but the effect is not dramatic. In Chapter 7, we have incorporated observed surface convective ows directly in our 3D dynamo model. As we know that the observed convective flows on the photosphere (e.g., supergranulation, granulation) play a key role in the Babcock-Leighton (BL) process to generate large scale polar fields from sunspots fields. In most surface flux transport (SFT) and BL dynamo models, the dispersal and migration of surface fields is modeled as an effective turbulent diffusion. Recent SFT models have incorporated explicit, realistic convective flows in order to improve the fidelity of convective transport but, to our knowledge, this has not yet been implemented in previous BL models. Since most Flux-Transport (FT)/BL models are axisymmetric, they do not have the capacity to include such flows. We present the first kinematic 3D FT/BL model to explicitly incorporate realistic convective flows based on solar observations. Though we describe a means to generalize these flows to 3D, we find that the kinematic small-scale dynamo action they produce disrupts the operation of the cyclic dynamo. Cyclic solution is found by limiting the convective flow to surface flux transport. The results obtained are generally in good agreement with the observed surface flux evolution and with non-convective models that have a turbulent diffusivity on the order of 3 1012 cm 2 s 1 (300 km2 s 1). However, we nd that the use of a turbulent diffusivity underestimates the dynamo efficiency, producing weaker mean fields than in the convective models. Also, the convective models exhibit mixed polarity bands in the polar regions that have no counterpart in solar observations. Also, the explicitly computed turbulent electromotive force (emf) bears little resemblance to a diffusive flux. We also find that the poleward migration speed of poloidal flux is determined mainly by the meridional flow and the vertical diffusion.