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Simulating and quantifying land-surface biogeochemical, hydrological, and biogeophysical processes using the Community Land Model version 4Shi, Mingjie 08 November 2013 (has links)
Carbon and nitrogen cycles, the energy cycle, and the hydrological cycle interact with each other; all are crucial to atmosphere–land studies. Carbon and nitrogen cycle from the atmosphere to vegetation communities and soil micro-organisms through their transformation in inorganic and organic pools. Ecosystem equilibrium, which is usually disturbed by extreme events (e.g., fires or drought), depends on the speeds of carbon and nitrogen uptake and decomposition. Terrestrial biogeochemistry models typically require hundreds to thousands of years for carbon and nitrogen in various pools to reach steady-state solutions, which are generally a function of soil temperature and soil water. Hydrological processes such as the root transpiration/water removal and the cold-region infiltration with the soil ice freeze/thaw status involved affect soil water content and soil temperature, and regulate carbon- and nitrogen-stock variations. Last but not least, mineral dust, a type of atmospheric aerosol, alters surface radiation/energy balance, and may act as cloud condensation nuclei to modify precipitation rates and eventually the hydrological cycle.
Therefore, we were motivated to investigate these processes in different ecosystems. Specifically, this research aims to 1) to elucidate the carbon- and nitrogen-pool adjustment processes in different ecosystems, 2) to evaluate how the root transpiration process affects ecosystem carbon exchange patterns in Amazonia, 3) to analyze the influence of soil impermeability, which is affected by the landscape freeze/thaw status in cold regions, on hydrological cycles at high latitudes, and 4) to explore the effects of surface vegetation distribution and model resolution on surface dust emissions. The Community Land Model version 4 (CLM4) was used in this study. We did numerical experiments in three environments: forest and grassland ecosystems, river basins in cold regions, and the Arabian Peninsula. Our main scientific findings are: 1) the adjustment time of the biogeochemistry components in CLM4 is longer for boreal forests than for other ecosystems, 2) with more water is lifted from deep soil, Amazonia ecosystems start to take up carbon during dry seasons, 3) the timing of boreal spring runoff simulations is improved by reducing the impermeable area underneath the snowpack, and 4) model-simulated dust emissions increase with model resolution as a result of the heterogeneities of vegetation cover and wind speed. / text
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Role of Interactions of Boundary Conditions and Baroclinic Vorticity in the Instability of Thermally Stratified Spinup in a CylinderJanuary 2011 (has links)
abstract: A numerical study of incremental spin-up and spin-up from rest of a thermally- stratified fluid enclosed within a right circular cylinder with rigid bottom and side walls and stress-free upper surface is presented. Thermally stratified spin-up is a typical example of baroclinity, which is initiated by a sudden increase in rotation rate and the tilting of isotherms gives rise to baroclinic source of vorticity. Research by (Smirnov et al. [2010a]) showed the differences in evolution of instabilities when Dirichlet and Neumann thermal boundary conditions were applied at top and bottom walls. Study of parametric variations carried out in this dissertation confirmed the instability patterns observed by them for given aspect ratio and Rossby number values greater than 0.5. Also results reveal that flow maintained axisymmetry and stability for short aspect ratio containers independent of amount of rotational increment imparted. Investigation on vorticity components provides framework for baroclinic vorticity feedback mechanism which plays important role in delayed rise of instabilities when Dirichlet thermal Boundary Conditions are applied. / Dissertation/Thesis / M.S. Mechanical Engineering 2011
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Spin-up and spin-down in linearly stratified fluid over flat bottomRomani, Mattia 17 March 2008 (has links) (PDF)
Nous présentons une étude expérimentale du "spin-up" et "spin-down" en présence d'une stratification linéaire sur un fond plat. Deux comportements très différents ont été mis en évidence selon la valeur du nombre de Burger, une mesure de l'importance relative de la stratification et des effets de Coriolis. Pour des nombres de Burger supérieurs à un, l'écoulement est remarquablement axisymétrique en dehors des couches limites, et aucune instabilité n'est observée malgré le grand nombre de Reynolds. Le confinement de la circulation secondaire du à la stratification est bien décrit par la théorie de Walin (1969), qui omet la viscosité. Cependant, le "spin-up" non-uniforme de l'intérieur provoque des gradients verticaux d'écoulement sensiblesaux effets visqueux. En conséquence, la comparaison avec la théorie montre un taux plus rapide de décroissance de l'écoulement azimutal.On propose une prise en compte simplifié de la diffusion verticale de quantité de movement dans la solution analytique de Walin. Aux temps courts, l'écoulement initial est correctement décrit par l'addition d'effets diffusifs visqueux, mais l'écart entre la théorie et les mesures persiste pour des temps intermédiaires. Pour des nombres de Burger inférieurs à un, le comportement de l'écoulement est très différent. La pénétration plus profonde de la circulation secondaire réduit notamment les gradients verticaux devitesse. La décroissance de la vitesse azimutale est presque verticalement uniforme et le développement des perturbations non-axisymmetriques est observé. Le déclin initial est bien décrit par la solution analytique. Cependant, la décroissance expérimentale est plus faible que la prédiction théorique pour des temps plus longs. L'écart correspond à l'apparition d'une instabilité. Cerésultat est en contradiction avec Smirnov et al. (2005), qui affirment que la formation de tourbillons à grande échelle fournit un mécanisme supplémentaire pour transporter le moment angulaire des frontières vers l'intérieur. En revanche, le transport radial de quantité de movement des couches limites latérales vers l'intérieur expliquerait la plus forte décroissance expérimentale aux temps longs. Le modèle classique d'Eady est cohérent avec les structures expérimentales observées. En considérant une dérivation de ce modèle par Smirnov et al. (2005), ainsi que des conditions initiales pertinentes, nous trouvons une estimation raisonnable du taux de croissance de l'instabilité, ce qui n'aurait pas été le cas avec la théorieclassique d'Eady. Ainsi, le mécanisme de l'instabilité barocline est l'explication la plus plausible pour l'existence d'une instabilité à grand nombre d'onde dans les processus de "spin-up" et "spin-down".
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Effects of Model Spin-Up on Simulated Recharge Using the Hydrus-1D Vadose Zone Model / Betydelsen av spin-up för simulerad grundvattenbildning genom användning av Hydrus-1D modellen av den omättade zonenVogel, Mie January 2019 (has links)
Groundwater is a crucial part of the hydrological cycle and is an important source for drinking water, irrigation and industry, particularly during droughts. With climate change, the hydrological variability is predicted to increase, making predictions for recharge and groundwater storage even more important to implement and to maintain sustainable water use. This study examines the importance of model spin-up in simulating recharge using the Hydrus-1D computer model. The focus is on two previously made Hydrus-1D models that represent end members in climate and hydrology; one which is a natural grassland in a semi-arid climate, while the other is a low impact development (LID) bioswale site in a Mediterranean climate. The main goal of this study is to characterize the range and causes of spin-up behavior as well as to analyze the extent of the effects that the spin-up process has on the recharge simulations. Although there has been some research on spin-up behavior for surface-water models, there is still a knowledge gap regarding the effects of model spin-up on vadose zone models simulating recharge. The initial conditions varied using three parameters for each of the two models: time (3, 15 and 30 years), initial moisture (θ = 0.1, 0.2 and 0.3) and precipitation (25% drier than historical data, historical 30-year data, 25% wetter than historical data). The output from these spin-ups were then used as initial conditions in simulating recharge using the 15-year models. The study found that the impact of spin-up is significant in the natural grassland site where there is a slow response between atmospheric forcings and recharge and where there is a relatively thick vadose zone. Especially spin-up time showed great variability and there is an inverse relationship between spin-up time and magnitude of recharge, where the longer spin-ups had lower recharge rates. Initial water content and precipitation did not result in different recharge amounts for the LID model. Length of spin-up only had very small differences in recharge for the LID models, indicating they are less sensitive to changes in initial spin-up parameters.
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X-ray And Optical Observations Of High Mass X-ray BinariesBeklen, Elif 01 January 2010 (has links) (PDF)
In this thesis, X-ray and optical observations of accretion powered pulsars are presented.
By using archival RXTE observations we work on the X-ray spectral and pulse timing
analysis of 4U 1538-52, 4U 1907+09, SMC X-1 to have more detailed information about their orbital and spin parameters.
For 4U 1538-52 and SMC X-1, we determined new orbital epochs.
By using long term pulse history of 4U 1907+09, we were able to work spin-down trend of the system and also calculate the change in the spin-down rate.
Using Fermi/GBM observations we can monitor bright accreting pulsar systems. We are producing long term
histories of pulse frequency and
flux of 20 continuosly monitoring systems.
Adding Swift/BAT observations to GBM observations, for 4U 1626-67, we did reveal the characteristics belong to spin-down trend before and
spin-up behaviour after torque reversal seen in 2008 February.
Two newly discovered IGRJ06074+2205 and IGRJ01583+6713 sources are identified as X-ray binary systems and we found
parameters of them like distance, magnitudes, by using both optical photometric and spectroscopic observations.
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Fluid Agitation Studies for Drug Product Containers Using Computational Fluid DynamicsIchinose, Matthew Hiroki 01 December 2018 (has links) (PDF)
At Amgen, the Automated Vision Inspection (AVI) systems capture the movement of unwanted particles in Amgen's drug product containers. For quality inspection, the AVI system must detect these undesired particles using a high speed spin-stop agitation process. To better understand the fluid movements to swirl the particles away from the walls, Computational Fluid Dynamics (CFD) is used to analyze the nature of the two phase flow of air and a liquid solution.
Several 2-D and 3-D models were developed using Fluent to create simulations of Amgen's drug product containers for a 1 mL syringe, 2.25 mL syringe, and a 5 mL cartridge. Fluid motion and potential bubble formations were studied within the liquid/gas domain inside the container by varying parameters such as viscosity, angular velocity, and surface tension. Experiments were conducted using Amgen's own equipment to capture the images of the spin-stop process and validate the models created in Fluent. Observations were made to see the effects of bubble formation or splashing during spin-down to rest.
The numerical and experimental results showed favorable comparison when measuring the meniscus height or the surface profile between the air and liquid. Also, at high angular velocity and dynamic viscosity, the container experiences instabilities and bubble formations. These studies indicate that CFD can be used as an useful and important tool to study fluid movement during agitation and observe any undesirable results for quality inspection.
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Étude et modèles effectifs d'écoulements quasi-2DPotherat, Alban 07 September 2000 (has links) (PDF)
Les écoulement confinés soumis à un fort champ magnétique vertical et les écoulements en rotation autour d'un axe vertical présentent au moins deux caractéristiques communes marquantes : d'une part, le champ de vitesse est quasi-bidimensionnel loin des parois, et d'autre part, une couche limite de structure simple se développe le long des parois perpendiculaires à la direction du champ magnétique (couche de Hartmann) ou à l'axe de rotation (couche d'Ekman). Nous présentons ici une étude de ces propriétés remarquables dans des cas où les autres forces qui agissent sur l'écoulement (inertie, viscosité,...) ne sont plus négligeables devant la force de Laplace ou de Coriolis. Il est montré que la combinaison des couplages verticaux et horizontaux conduit d'une part, à une dépendance quadratique du champ de vitesse en fonction de la verticale (effet tonneau), et d'autre part à la présence de jet dans les couches de Hartmann ou d'Ekman. Une loi de paroi analytique pour diverses configurations des couches de Hartmann est construite (présence d'effets inertiels, présence d'une composante horizontale du champ magnétique, parois conductrices...) dans le but d'éviter le maillage fin que requiert le calcul numérique direct d'une telle couche. Les propriétés remarquables des écoulements quasi-2D sont ensuite utilisées pour construire trois modèles 2D différents, à partir de la moyenne verticale des équations du mouvement. Ces modèles simples, ne reposent que sur les hypothèses physiques et ne nécessitent en particulier aucun étalonnage numérique. Le modèle PSM2000 pour les écoulements MHD avec inertie et sous fort champ vertical conduit à des résultats très proches de l'expérience et met notamment en évidence le fait que le pompage d'Ekman dans les couches de Hartmann se traduit approximativement par une diffusion du champ de vorticité le long des lignes de courant de l'écoulement moyen. Un modèle analogue, mais sans effets inertiels et avec un champ non homogène et instationnaire permet en premier lieu de déterminer dans quel cas les couches de Hartmann contrôlent l'écoulement global et en second lieu, d'étudier la possibilité de contrôler un écoulement d'acier liquide par un champ glissant dans un procédé de coulée continue. Finalement, un modèle quasi-géostrophique modifié fournit une base théorique pour l'étude du comportement des couches parallèles lors des expériences de Spin-Up et Spin-Down d'une cuve tournante.
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