Dissertations / Theses: 'Eddy flux Mathematical models'

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Porumbel, Ionut. "Large Eddy Simulation of premixed and partially premixed combustion." Diss., Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/14050.

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Large Eddy Simulation (LES) of bluff body stabilized premixed and partially premixed combustion close to the flammability limit is carried out in this thesis. The LES algorithm has no ad-hoc adjustable model parameters and is able to respond automatically to variations in the inflow conditions. Algorithm validation is achieved by comparison with reactive and non-reactive experimental data. In the reactive flow, two scalar closure models, Eddy Break-Up (EBULES) and Linear Eddy Mixing (LEMLES), are used and compared. Over important regions, the flame lies in the Broken Reaction Zone regime. Here, the EBU model assumptions fail. The flame thickness predicted by LEMLES is smaller and the flame is faster to respond to turbulent fluctuations, resulting in a more significant wrinkling of the flame surface. As a result, LEMLES captures better the subtle effects of the flame-turbulence interaction. Three premixed (equivalence ratio = 0.6, 0.65, and 0.75) cases are simulated. For the leaner case, the flame temperature is lower, the heat release is reduced and vorticity is stronger. As a result, the flame in this case is found to be unstable. In the rich case, the flame temperature is higher, and the spreading rate of the wake is increased due to the higher amount of heat release Partially premixed combustion is simulated for cases where the transverse profile of the inflow equivalence ratio is variable. The simulations show that for mixtures leaner in the core the vortical pattern tends towards anti-symmetry and the heat release decreases, resulting also in instability of the flame. For mixtures richer in the core, the flame displays sinusoidal flapping resulting in larger wake spreading. More accurate predictions of flame stability will require the use of detailed chemistry, raising the computational cost of the simulation. To address this issue, a novel algorithm for training Artificial Neural Networks (ANN) for prediction of the chemical source terms has been implemented and tested. Compared to earlier methods, the main advantages of the ANN method are in CPU time and disk space and memory reduction.

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Comer, Neil Thomas. "Validation and heterogeneity investigation of the Canadian Land Surface Scheme (CLASS) for wetland landscapes." Thesis, McGill University, 2001. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=38173.

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This thesis examines the development and validation of Canadian Land Surface Scheme (CLASS) for various wetland landscapes individually, along with an evaluation of modelled results over a heterogeneous surface with airborne observations. A further statistical analysis of the effects of land surface classification procedures over the study area and their influence on modelled results is performed. CLASS is tested over individual wetland types: bog, fen and marsh in a stand-alone (non-GCM coupled) mode. Atmospheric conditions are provided for the eight site locations from tower measured data, while each surface is parameterized within the model from site specific measurements. Resulting model turbulent and radiative flux output is then statistically evaluated against observed tower data. Findings show that while CLASS models vascular dominated wetland areas (fen and marsh) quite well, non-vascular wetlands (bogs) are poorly represented, even with improved soil descriptions. At times when the water table is close to the surface, evaporation is greatly overestimated, whereas lowered water tables generate a vastly underestimated latent heat flux. Because CLASS does not include a moisture transfer scheme applicable for non-vascular vegetation, the description of this vegetation type as either a vascular plant or bare soil appears inappropriate.
CLASS was then tuned for a specific bog location found in the Hudson Bay Lowland (HBL) during the Northern Wetlands Study (NOWES). With bog surfaces better described within the model, testing of CLASS over a highly heterogeneous 169 km2 HBL region is then undertaken. The model is first modified for lake and pond surfaces and then separate runs for bog, fen, lake and tree/shrub categories is undertaken. Using a GIS, the test region under which airborne flux measurements are available is divided into 104 grid cells and proportions of each surface type are calculated within each cell. Findings indicate that although the modelled grid average radiation and flux values are reasonably well reproduced (4% error for net radiation, 10% for latent heat flux and 30% for sensible heat flux), spatial agreement between modelled and observed grid cells is disappointing. (Abstract shortened by UMI.)

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Calhoon, William Henry Jr. "On subgrid combustion modeling for large-eddy simulations." Diss., Georgia Institute of Technology, 1996. http://hdl.handle.net/1853/12336.

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Kim, Won-Wook. "A new dynamic subgrid-scale model for large-eddy simulation of turbulent flows." Diss., Georgia Institute of Technology, 1996. http://hdl.handle.net/1853/12143.

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Wong, Ching-chi, and 黃精治. "Flow and pollutant dispersion over idealized urban street canyons using large-eddy simulation." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2013. http://hdl.handle.net/10722/206698.

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Flows and pollutant dispersion over flat rural terrain have been investigated for decades. However, our understanding of their behaviours over urban areas is rather limited. Most cases have either focused on street level or in the roughness sub-layer (RSL) of urban boundary layer (UBL). Whereas, only a handful of studies have looked into the coupling between street-level and UBL-core dynamics, and their effects on pollutant dispersion. In this thesis, computational fluid dynamics (CFD) is employed to examine the flows and pollutant transport in and over urban roughness. Idealised two-dimensional (2D) street canyons are used as the basic units fabricating hypothetical urban surfaces. A ground-level passive and chemically inert pollutant source is applied to simulate the flows and pollutant dispersion over rough surfaces in isothermal condition. Large-eddy simulation (LES) with the one-equation subgrid-scale model is used to solve explicitly the broad range of scales in turbulent flows. Arrays of idealized street canyons of both uniform and non-uniform building height are used to formulate a unified theory for the flows and pollutant dispersion over urban areas of different morphology. The geometry of roughness elements is controlled by the building-height-to-street-width (aspect) ratio (0.083 ≤ AR ≤ 2) and/or the building height variability (BHV = 0.2, 0.4 and 0.6), in which the characteristic regimes of skimming flow, wake-interference and isolated roughness are covered. A detailed analysis on the roof-level turbulence structure reveals parcels of low-speed air masses in the streamwise flows and narrow high-speed down-drafts in the urban canopy layer, signifying the momentum entrainment into the street canyons. The decelerating streamwise flows in turn initiate up-drafts carrying pollutants away from the street canyons, illustrating the basic pollutant removal mechanism in 2D street canyons. Turbulent transport processes, in the form of ejection and sweep, are the key events governing the exchanges of air and pollutant of street canyon. Air exchange rate (ACH) along the roof level is dominated by turbulent transport, in particular over narrow street canyons. The LES results show that both the turbulence level and ACH increase with increasing aerodynamic resistance defined in term of the Fanning friction factor. At the same AR, BHV greatly increases the friction factor and the ACH in dense built areas (AR ≤ 0.25). The turbulence intensity is peaked on the windward side of street canyons that does not overlap with the maximum velocity gradient near the leeward building corners, suggesting the importance of background turbulence in street-level ventilation. Over the building roughness, pollutant plume dispersion after the ground-level area source in cross flows resumes the self-similar Gaussian shape in the vertical direction in which the vertical plume coverage is proportional to the square root of downwind distance in the streamwise direction. Moreover, the vertical dispersion coefficient is proportional to the one-fourth power of friction factor over idealised street canyons. Conclusively, friction factor can be used to parametrise ventilation and pollutant dispersion over urban areas.
published_or_final_version
Mechanical Engineering
Doctoral
Doctor of Philosophy

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Sreedhar, Madhu K. "Large eddy simulation of turbulent vortices and mixing layers." Diss., This resource online, 1994. http://scholar.lib.vt.edu/theses/available/etd-06062008-163324/.

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Goldin, Graham Mark. "A linear eddy model for steady-state turbulent combustion." Diss., Georgia Institute of Technology, 1996. http://hdl.handle.net/1853/12547.

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Li, Xianxiang, and 李顯祥. "Large-eddy simulation of wind flow and air pollutant transport inside urban street canyons of different aspect ratios." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2008. http://hub.hku.hk/bib/B40687326.

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Chung, Nga-hang, and 鍾雅行. "Large-eddy simulation of transport of inert and chemically reactive pollutants over 2D idealized street canyons." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2011. http://hub.hku.hk/bib/B47849903.

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In view of the worsening air quality in the world, more concerns are focused on the environment. This thesis uses the technique of CFD and develops the computer model to investigate the wind and pollutant transport, as well as the chemistry of reactive pollutants in idealized two-dimensional (2D) street canyons. Three scientific questions are raised in this thesis. The first task is to find out the po- sition with the most favorable pollutant removal along the ground level over 2D idealized street canyon of different building-height-to-street-width (aspect) ratios (ARs). The di- mensionless parameter, C, represents the pollutant removal performance. In the isolated roughness regime, the two local maximum C locate at the reattachment point and the windward corner. In the wake interference regime, C is peaked on the windward side. The number of vertically aligned recirculations depends on the street depth in the skimming flow regime. The sizes of the secondary recirculation upstream and downstream deter- mine how the maximum C shifts from the street centre. After identifying the position of peaked pollutant removal rate at the ground level, the emission source should be placed with the highest constant C in order to remove the pollutants upward more quickly to safeguard the street-level air quality. After understanding the best pollutant removal in the street canyon of different ARs, the second task is to find out what AR is the most favorable for the ventilation and pollutant removal across the roof level. The three parameters, namely friction factor, air exchange rate (ACH) and pollutant exchange rate (PCH), are introduced to quantify the pressure difference to sustain the mean flow, the ventilation and pollutant removal, respectively. The turbulence contributes more than 70% to the total ACH and PCH in all the three flow regimes. By increasing the atmospheric turbulence in building geometry as well as the surface roughness, the ventilation and pollutant removal performance can be improved. The linear relation between the friction factor and ACH demonstrates the larger resistance that in turn promotes the air exchange over the roof level. The physical dispersion is studied; however atmospheric pollutants are seldom in- ert but chemically reactive instead. The last task is to include the three common air pollutants, NO, NO2 and O3, in the simple NOx ?O3 mechanism in terms of the photo- stationary state and reaction rates. The Damkohler numbers of NO and O3, DaNO and DaO3, are parameterized by the concentrations of the sources NO and O3. The normalized mean and fluctuation NO, NO2 and O3 are separately considered. The integrated pho- tostationary state (PSS) in the first canyon increases with DaO3 under the same DaNO. The integrated PSS of the second to the twelveth street canyons are compared with each case, the monotonic increase in the PSS from the second to twelveth canyon is perceived in DaNO/DaO3 1, 0.03, 0.02, 0.001 and 0.000333. Further decreases the DaNO/DaO3 to 0.000143, 0.000125, 0.000118, 0.000111 and 0.0001, the PSS is found to be non-linear and the trough appears in the fourth and fifth canyons.
published_or_final_version
Mechanical Engineering
Master
Master of Philosophy

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So, Shuk-pan Ellen, and 蘇淑彬. "Large eddy simulations of wind flow and pollution dispersion in an urban street canyon." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2003. http://hub.hku.hk/bib/B29332710.

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Sánchez, Rocha Martín. "Wall-models for large eddy simulation based on a generic additive-filter formulation." Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/28086.

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Thesis (M. S.)--Aerospace Engineering, Georgia Institute of Technology, 2009.
Committee Chair: Menon, Suresh; Committee Member: Cvitanović, Predrag; Committee Member: Sankar, Lakshmi N.; Committee Member: Smith, Marilyn J.; Committee Member: Yeung, Pui-Kuen

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Moosbrugger, John C. "Numerical computation of metal/mold boundary heat flux in sand castings using a finite element enthalpy model." Thesis, Georgia Institute of Technology, 1985. http://hdl.handle.net/1853/16365.

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Klostermeier, Christian. "Investigation into the capability of large eddy simulation for turbomachinery design." Thesis, University of Cambridge, 2008. https://www.repository.cam.ac.uk/handle/1810/252106.

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Pannala, Sreekanth. "On large eddy simulations of reacting two-phase flows." Diss., Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/11978.

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Jordan, Stephen Arthur. "The large-eddy simulation of incompressible flows in simple and complex geometries." Diss., This resource online, 1994. http://scholar.lib.vt.edu/theses/available/etd-10022007-145351/.

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Heger, Walter. "Using the finite difference and the finite element method to solve an electric current diffusion problem." Thesis, McGill University, 1987. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=66150.

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Cordova, Vicente D. "Regional-scale carbon flux estimation using MODIS imagery." Virtual Press, 2005. http://liblink.bsu.edu/uhtbin/catkey/1325989.

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The National Aeronautics and Space Agency NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) platform carried by Terra and Aqua satellites, is providing systematic measurements summarized in high quality, consistent and well-calibrated satellite images and datasets ranging from reflectance in the visible and near infrared bands to estimates of leaf area index, vegetation indices and biome productivity. The objective of this research was to relate the spectral responses and derived MODIS products of ecosystems, to biogeochemical processes and trends in their physiological variables. When different sources of data were compared, discrepancies between the MODIS variables and the corresponding ground measurements were evident. Uncertainties in the input variables of MODIS products algorithms, effects of cloud cover at the studied pixel, estimation algorithm, and local variation in land cover type are considered as the cause. A simple "continuous field" model based on a physiologically-driven spectral index using two ocean-color bands of MODIS satellite sensor showed great potential to track seasonally changing photosynthetic light use efficiency and stress-induced reduction in net primary productivity of terrestrial vegetation. The model explained 88% of the variability in Flux tower-based daily Net Primary Productivity. Also a high correlation between midday gross CO2 exchange with both daily and 8-day mean gross CO2 exchange, consistent across all the studied vegetation types, was found. Although it may not be possible to estimate 8-day mean Light Use Efficiency reliably from satellite data, Light Use Efficiency models may still be useful for estimation of midday values of gross CO2 exchange which could then be related to longer term means of CO2 exchange. In addition, the MODIS enhanced vegetation index shows a high potential for estimation of ecosystem gross primary production, using respiration values from MODIS surface temperature, providing truly per-pixel estimates.
Department of Natural Resources and Environmental Management

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Wang, Yuexing, and 王越興. "Sediment nutrient flux for a pulsed organic load: mathematical modeling and experimental verfication." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2008. http://hub.hku.hk/bib/B40987826.

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Sánchez, Rocha Martín. "Wall-models for large eddy simulation based on a generic additive-filter formulation." Diss., Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/28086.

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In this work, the mathematical implications of merging two different turbulence modeling approaches are addressed by deriving the exact hybrid RANS/LES Navier-Stokes equations. These equations are derived by introducing an additive-filter, which linearly combines the RANS and LES operators with a blending function. The equations derived predict additional hybrid terms, which represent the interactions between RANS and LES formulations. Theoretically, the prediction of the hybrid terms demonstrates that the hybridization of the two approaches cannot be accomplished only by the turbulence model equations, as it is claimed in current hybrid RANS/LES models. The importance of the exact hybrid RANS/LES equations is demonstrated by conducting numerical calculations on a turbulent flat-plate boundary layer. Results indicate that the hybrid terms help to maintain an equilibrated model transition when the hybrid formulation switches from RANS to LES. Results also indicate, that when the hybrid terms are not included, the accuracy of the calculations strongly relies on the blending function implemented in the additive-filter. On the other hand, if the exact equations are resolved, results are only weakly affected by the characteristics of the blending function. Unfortunately, for practical applications the hybrid terms cannot be exactly computed. Consequently, a reconstruction procedure is proposed to approximate these terms. Results show, that the model proposed is able to mimic the exact hybrid terms, enhancing the accuracy of current hybrid RANS/LES approaches. In a second effort, the Two Level Simulation (TLS) approach is proposed as a near-wall model for LES. Here, TLS is first extended to compressible flows by deriving the small-scale equations required by the model. The full compressible TLS formulation and the hybrid TLS/LES approach is validated simulating the flow over a flat-plate turbulent boundary layer. Overall, results are found in reasonable agreement with experimental data and LES calculations.

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Abareshi, Behzad. "Sensible heat flux estimation over a prairie grassland by neural networks." Thesis, McGill University, 1996. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=23765.

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Sensible heat flux, a key component of the surface energy balance, is difficult to estimate in practice. This study was conducted to see if backpropagation neural networks could estimate sensible heat flux by using horizontal wind speed, air temperature, radiometric surface temperature, net radiation, and time as input. Ground measurements from the First ISLSCP (International Satellite Land Surface Climatology Project) Field Experiment (FIFE), collected in 1987 and 1989 over a prairie grassland in Kansas, were used for network training and validation. Networks trained on part of the data from a narrow range of space-time coordinates performed well over the other part, with error (root mean square error divided by mean of observations) values as low as 0.24. This indicates the potential in neural networks for linking sensible heat flux to routinely measured meteorological variables and variables amenable to remote sensing. When the networks were tested with data from other space-times, performance varied from good to poor, with average error values around 1.26. This was mainly due to lack of input variables parameterizing canopy morphology and soil moisture, indicating that such variables should be incorporated in the design of future networks intended for large scale applications.

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MacTaggart, David. "Theoretical magnetic flux emergence." Thesis, University of St Andrews, 2011. http://hdl.handle.net/10023/1692.

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Magnetic flux emergence is the subject of how magnetic fields from the solar interior can rise and expand into the atmosphere to produce active regions. It is the link that joins dynamics in the convection zone with dynamics in the atmosphere. In this thesis, we study many aspects of magnetic flux emergence through mathematical modelling and computer simulations. Our primary aim is to understand the key physical processes that lie behind emergence. The first chapter introduces flux emergence and the theoretical framework, magnetohydrodynamics (MHD), that describes it. In the second chapter, we discuss the numerical techniques used to solve the highly non-linear problems that arise from flux emergence. The third chapter summarizes the current literature. In the fourth chapter, we consider how changing the geometry and parameter values of the initial magnetic field can affect the dynamic evolution of the emerging magnetic field. For an initial toroidal magnetic field, it is found that its axis can emerge to the corona if the tube’s initial field strength is large enough. The fifth chapter describes how flux emergence models can produce large-scale solar eruptions. A 2.5D model of the breakout model, using only dynamic flux emergence, fails to produce any large scale eruptions. A 3D model of toroidal emergence with an overlying magnetic field does, however, produce multiple large-scale eruptions and the form of these is related to the breakout model. The sixth chapter is concerned with signatures of flux emergence and how to identify emerging twisted magnetic structures correctly. Here, a flux emergence model produces signatures found in observations. The signatures from the model, however, have different underlying physical mechanisms to the original interpretations of the observations. The thesis concludes with some final thoughts on current trends in theoretical magnetic flux emergence and possible future directions.

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Parisi, Valerio. "Large Eddy Simulation of a Stagnation Point Reverse Flow Combustor." Thesis, Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/13995.

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In this study, numerical simulations of a low emission lab-scale non-premixed combustor are conducted and analyzed. The objectives are to provide new insight into the physical phenomena in the SPRF (Stagnation Point Reverse Flow) combustor built in the Georgia Tech Combustion Lab, and to compare three Large Eddy Simulation (LES) combustion models (Eddy Break-Up [EBU], Steady Flamelet [SF] and Linear Eddy Model [LEM]) for non-premixed combustion. The nominal operating condition of the SPRF combustor achieves very low NOx and CO emissions by combining turbulent mixing of exhaust gases with preheated reactants and chemical kinetics. The SPRF numerical simulation focuses on capturing the complex interaction between turbulent mixing and heat release. LES simulations have been carried out for a non-reactive case in order to analyze the turbulent mixing inside the combustor. The LES results have been compared to PIV experimental data and the code has been validated. The dominating features of the operational mode of the SPRF combustor (dilution of hot products into reactants, pre-heating and pre-mixing) have been analyzed, and results from the EBU-LES, SF-LES and LEM-LES simulations have been compared. Analysis shows that the LEM-LES simulation achieves the best agreement with the observed flame structure and is the only model that captures the stabilization processes observed in the experiments. EBU-LES and SF-LES do not predict the correct flow pattern because of the inaccurate modeling of sub-grid scale mixing and turbulence-combustion interaction. Limitations of these two models for this type of combustor are discussed.

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Murray, Michelle J. "Solar flux emergence : a three-dimensional numerical study." Thesis, University of St Andrews, 2008. http://hdl.handle.net/10023/441.

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Flux is continually emerging on the Sun, making its way from the solar interior up into the atmosphere. Emergence occurs on small-scales in the quiet Sun where magnetic fragments emerge, interact and cancel and on large-scales in active regions where magnetic fields emerge and concentrate to form sunspots. This thesis has been concerned with the large-scale emergence process and in particular the results from previous solar flux emergence modelling endeavours. Modelling uses numerical methods to evolve a domain representing simplified layers of the Sun’s atmosphere, within which the subsurface layer contains magnetic flux. The flux is initialised such that it will rises towards the surface at the start of the simulation. Once the flux reaches the solar surface, it can only emerge into the atmosphere if a magnetic buoyancy instability occurs, after which it expands rapidly both vertically and horizontally. The aim of this thesis is to test the robustness of these general findings from simulations to date upon the seed magnetic field. More explicitly, we have used three-dimensional numerical simulations to investigate how variations in the subsurface magnetic field modify the emergence process and the resulting atmospheric field. We initially consider a simple constant twist flux tube for the seed field and vary the tube’s magnetic field strength and degree of twist. Additionally, we have examined the effects of using non-constant twist flux tubes as the seed field by choosing two different profiles for the twist that are functions of the tube’s radius. Finally, we have investigated the effects of increasing the complexity of the seed field by positioning two flux tubes below the solar surface and testing two different configurations for the tubes. In both cases, the magnetic fields of the two tubes are such that, once the tubes come into contact with each other, reconnection occurs and a combined flux system is formed. From our investigations, we conclude that the general emergence results given by previous simulations are robust. However, for constant twist tubes with low field strength and twist, the buoyancy instability fails to be launched when the tubes reach the photosphere and they remain trapped in the low atmosphere. Similarly, when the non-constant twist profile results in a low tension force throughout the tube, we find that the buoyancy instability is not initialised.

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Cook, Graeme Robert. "Magnetic flux transport simulations : applications to solar and stellar magnetic fields." Thesis, University of St Andrews, 2011. http://hdl.handle.net/10023/2072.

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Magnetic fields play a key role in a wide variety of phenomena found on the Sun. One such phenomena is the Coronal Mass Ejection (CME) where a large amount of material is ejected from the Sun. CME’s may directly affect the earth, therefore understanding their origin is of key importance for space weather and the near-Earth environment. In this thesis, the nature and evolution of solar magnetic fields is considered through a combination of Magnetic Flux Transport Simulations and Potential Field Source Surface Models. The Magnetic Flux Transport Simulations produce a realistic description of the evolution and distribution of the radial magnetic field at the level of the solar photosphere. This is then applied as a lower boundary condition for the Potential Field Source Surface Models which prescribe a coronal magnetic field. Using these two techniques, the location and variation of coronal null points, a key element in the Magnetic Breakout Model of CMEs, are determined. Results show that the number of coronal null points follow a cyclic variation in phase with the solar cycle. In addition, they preferentially form at lower latitudes as a result of the complex active latitude field. Although a significant number of coronal nulls may exist at any one time (≈ 17), it is shown that only half may satisfy the necessary condition for breakout. From this it is concluded that while the Magnetic Breakout Model of CMEs is an important model in understanding the origin of the CMEs, other processes must occur in order to explain the observed number of CMEs. Finally, the Magnetic Flux Transport Simulations are applied to stellar magnetic fields and in particular to the fast rotating star HD171488. From this speculative study it is shown that the Magnetic Flux Transport Simulations constructed for the Sun may be applied in very different stellar circumstances and that for HD171488 a significantly higher rate of meridional flow (1200-1400 ms⁻¹) is required to match observed magnetic field distributions.

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Sturrock, Zoe. "Numerical simulations of sunspot rotation driven by magnetic flux emergence." Thesis, University of St Andrews, 2017. http://hdl.handle.net/10023/10129.

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Magnetic flux continually emerges from the Sun, rising through the solar interior, emerging at the photosphere in the form of sunspots and expanding into the atmosphere. Observations of sunspot rotations have been reported for over a century and are often accompanied by solar eruptions and flaring activity. In this thesis, we present 3D numerical simulations of the emergence of twisted flux tubes from the uppermost layers of the solar interior, examining the rotational movements of sunspots in the photospheric plane. The basic experiment introduces the mechanism and characteristics of sunspot rotation by a clear calculation of rotation angle, vorticity, magnetic helicity and energy, whereby we find an untwisting of the interior portion of the field, accompanied by an injection of twist into the atmospheric field. We extend this model by altering the initial field strength and twist of the sub-photospheric tube. This comparison reveals the rotation angle, helicity and current show a direct dependence on field strength. An increase in field strength increases the rotation angle, the length of fieldlines extending into the atmosphere, and the magnetic energy transported to the atmosphere. The fieldline length is crucial as we predict the twist per unit length equilibrates to a lower value on longer fieldlines, and hence possesses a larger rotation angle. No such direct dependence is found when varying the twist but there is a clear ordering in rotation angle, helicity, and energy, with more highly twisted tubes undergoing larger rotation angles. We believe the final angle of rotation is reached when the system achieves a constant degree of twist along the length of fieldlines. By extrapolating the size of the modelled active region, we find rotation angles and rates comparable with those observed. In addition, we explore sunspot rotation caused by sub-photospheric velocities twisting the footpoints of flux tubes.

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FELIPPE, MONICA T. S. D. "Estudo de fluxo de oxido nitroso (Nsub(2)O) regional na bacia amazonica." reponame:Repositório Institucional do IPEN, 2010. http://repositorio.ipen.br:8080/xmlui/handle/123456789/9547.

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Made available in DSpace on 2014-10-09T12:27:52Z (GMT). No. of bitstreams: 0
Made available in DSpace on 2014-10-09T14:04:48Z (GMT). No. of bitstreams: 0
Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

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Sanyal, Anuradha. "Large eddy simulation of syngas-air diffusion flames with artificial neural networks based chemical kinetics." Thesis, Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/42785.

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In the present study syngas-air diffusion flames are simulated using LES with artificial neural network (ANN) based chemical kinetics modeling and the results are compared with previous direct numerical simulation (DNS) study, which exhibits significant extinction-reignition and forms a challenging problem for ANN. The objective is to obtain speed-up in chemistry computation while still having the accuracy of stiff ODE solver. The ANN methodology is used in two ways: 1) to compute the instantaneous source term in the linear eddy mixing (LEM) subgrid combustion model used within LES framework, i.e., laminar-ANN used within LEMLES framework (LANN-LEMLES), and 2) to compute the filtered source terms directly within the LES framework, i.e., turbulent-ANN used within LES (TANN-LES), which further dicreases the computational speed. A thermo-chemical database is generated from a standalone one-dimensional LEM simulation and used to train the LANN for species source terms on grid-size of Kolmogorov scale. To train the TANN coefficients the thermo-chemical database from the standalone LEM simulation is filtered over the LES grid-size and then used for training. To evaluate the performance of the TANN methodology, the low Re test case is simulated with direct integration for chemical kinetics modeling in LEM subgrid combustion model within the LES framework (DI-LEMLES), LANN-LEMLES andTANN-LES. The TANN is generated for a low range of Ret in order to simulate the specific test case. The conditional statistics and pdfs of key scalars and the temporal evolution of the temperature and scalar dissipation rates are compared with the data extracted from DNS. Results show that the TANN-LES methodology can capture the extinction-reignition physics with reasonable accuracy compared to the DNS. Another TANN is generated for a high range of Ret expected to simulate test cases with different Re and a range of grid resolutions. The flame structure and the scalar dissipation rate statistics are analyzed to investigate success of the same TANN in simulating a range of test cases. Results show that the TANN-LES using TANN generated fora large range of Ret is capable of capturing the extinction-reignition physics with a very little loss of accuracy compared to the TANN-LES using TANN generated for the specific test case. The speed-up obtained by TANN-LES is significant compared to DI-LEMLES and LANN-LEMLES.

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Cheung, Ching, and 張靜. "Effect of heat flux on wind flow and pollutant dispersion in an urban street canyon." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2006. http://hub.hku.hk/bib/B37742498.

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Marcusson, Birger. "Magnetic Leakage Fields and End Region Eddy Current Power Losses in Synchronous Generators." Doctoral thesis, Uppsala universitet, Elektricitetslära, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-331182.

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The conversion of mechanical energy to electrical energy is done mainly with synchronous generators. They are used in hydropower generators and nuclear plants that presently account for about 80% of the electric energy production in Sweden. Because of the dominating role of the synchronous generators, it is important to minimize the power losses for efficient use of natural resources and for the economies of the electric power companies and their customers. For a synchronous machine, power loss means undesired heat production. In electric machines, there are power losses due to windage, friction in bearings, resistance in windings, remagnetization of ferromagnetic materials, and induced voltages in windings, shields and parts that are conductive but ideally should be non-conductive. The subject of this thesis is prediction of end region magnetic leakage fields in synchronous generators and the eddy current power losses they cause. The leakage fields also increase the hysteresis losses in the end regions. Magnetic flux that takes paths such that eddy current power losses increase in end regions of synchronous generators is considered to be leakage flux. Although only a small fraction of the total magnetic flux is end region leakage flux, it can cause hot spots, discoloration and reduce the service life of the insulation on the core laminations. If unattended, damaged insulation could lead to electric contact and eddy currents induced by the main flux between the outermost laminations. That gives further heating and deterioration of the insulation of laminations deeper into the core. In a severe case, the core can melt locally, cause a cavity, buckling and a short circuit of the main conductors. The whole stator may have to be replaced. However, the end region leakage flux primarily causes heating close to the main stator conductors which makes the damage possible to discover by visual inspection before it has become irrepairable.

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Garrett, Joseph Lee. "A comparison of flux-splitting algorithms for the Euler equations with equilibrium air chemistry." Thesis, Virginia Tech, 1989. http://hdl.handle.net/10919/44636.

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The use of flux-splitting techniques on the Euler equations is considered for high Mach number, high temperature flows in which the fluid is assumed to be inviscid air in equilibrium. Three different versions of real gas extensions to the Stegerâ Warming and Van Leer flux-vector splitting, and four different versions of real gas extensions to the Roe flux-difference splitting, are compared with regard to general applicability and ease of implementation in existing perfect gas g algorithms. Test computations are performed for the M = 5, high temperature flow over a 10-degree wedge and the M = 24.5 flow over a blunt body. Although there were minor differences between the computed results for the three types of flux-splitting algorithms considered, little variation is observed between different versions of the same algorithm.

Master of Science

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31

Marti, Clelia Luisa. "Exchange processes between littoral and pelagic waters in a stratified lake." University of Western Australia. Centre for Water Research, 2004. http://theses.library.uwa.edu.au/adt-WU2005.0005.

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[Truncated abstract] The lake boundaries are an important source of sediment, nutrients and chemicals. For life inside the lake, the exchange between the lake boundaries (littoral) and lake interior (pelagic) is of central importance to Limnology as the net flux of nutrients into the water column is both the driving force and limiting factor for most algae blooms found during the stratification period. Consequently, the understanding of the relevant processes defining such an exchange is a further step toward a sound basis for future decisions by lake managers in order to ensure high water quality. The objective of this research was to investigate the physical processes responsible for the exchange of water and particles between the lake boundaries and the lake interior. An integrated approach using field experiments and 3D modelling as applied to Lake Kinneret (Israel) is presented. The field data revealed large-scale metalimnion oscillations with amplitudes up to 10 m in response to westerly diurnal winds, the existence of a well-defined suspended particle intrusion into the metalimnion of the lake, characterized by high concentrations of organic matter, and a well-mixed benthic boundary layer (BBL). The changes in the thermal structure explained the observed vertical and horizontal movements of the suspended particle intrusion. The horizontal advective transport via the metalimnion, associated with the velocities induced by the basin-scale mode-two Poincare wave, controlled the exchange between the lake boundaries and lake interior on daily time scales. The observed BBL over the lake slope varied markedly with time and space. Detailed comparison of simulation results with field data revealed that the model captured the lake hydrodynamics for time scales from hours to days. The model could then be used to extract the residual motions in the various regions of the lake. The residual motions below the surface layer were predominantly forced by the basin-scale internal wave motions, but the residual motion in the surface layer was found to be very sensitive to the curl of the wind field. The residual circulation was responsible for redistributing mass throughout the lake basin on time scales from days to weeks. A clear connection of dynamics of the BBL with the large-scale features of the flow was addressed. The time history of the mixing in the BBL and the resulting cross-shore flux was shown to vary with the phase of the basin-scale internal waves.

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Hsu, Wei-Ching. "The variability and seasonal cycle of the Southern Ocean carbon flux." Thesis, Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/49079.

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Both physical circulation and biogeochemical characteristics are unique in the Southern Ocean (SO) region, and are fundamentally different from those of the northern hemisphere. Moreover, according to previous research, the oceanic response to the trend of the Southern Annual Mode (SAM) has profound impacts on the future oceanic uptake of carbon dioxide in the SO. In other words, the climate and circulation of the SO are strongly coupled to the overlying atmospheric variability. However, while we have understanding on the SO physical circulation and have the ability to predict the future changes of the SO climate and physical processes, the link between the SO physical processes, the air-sea carbon flux, and correlated climate variability remains unknown. Even though scientists have been studying the spatial and temporal variability of the SO carbon flux and the associated biogeochemical processes, the spatial patterns and the magnitudes of the air-sea carbon flux do not agree between models and observations. Therefore, in this study, we utilized a modified version of a general circulation model (GCM) to performed realistic simulations of the SO carbon on seasonal to interannual timescales, and focused on the crucial physical and biogeochemical processes that control the carbon flux. The spatial pattern and the seasonal cycle of the air-sea carbon dioxide flux is calculated, and is broadly consistent with the climatological observations. The variability of air-sea carbon flux is mainly controlled by the gas exchange rate and the partial pressure of carbon dioxide, which is in turn controlled by the compensating changes in temperature and dissolved inorganic carbon. We investigated the seasonal variability of dissolved inorganic carbon based on different regional processes. Furthermore, we also investigated the dynamical adjustment of the surface carbon flux in response to the different gas exchange parameterizations, and conclude that parameterization has little impact on spatially integrated carbon flux. Our simulation well captured the SO carbon cycle variability on seasonal to interannual timescales, and we will improve our model by employ a better scheme of nutrient cycle, and consider more nutrients as well as ecological processes in our future study.

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Wilson, Scott E. "Investigation of Copper Foam Coldplates as a High Heat Flux Electronics Cooling Solution." Thesis, Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/6944.

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Compact heat exchangers such as porous foam coldplates have great potential as a high heat flux cooling solution for electronics due to their large surface area to volume ratio and tortuous coolant path. The focus of this work was the development of unit cell modeling techniques for predicting the performance of coldplates with porous foam in the coolant path. Multiple computational fluid dynamics (CFD) models which predict porous foam coldplate pressure drop and heat transfer performance were constructed and compared to gain insight into how to best translate the foam microstructure into unit cell model geometry. Unit cell modeling in this study was realized by applying periodic boundary conditions to the coolant entrance and exit faces of a representative unit cell. A parametric study was also undertaken which evaluated dissimilar geometry translation recommendations from the literature. The use of an effective thermal conductivity for a representative orthogonal lattice of rectangular ligaments was compared to a porosity-matching technique of a similar lattice. Model accuracy was evaluated using experimental test data collected from a porous copper foam coldplate using deionized water as coolant. The compact heat exchanger testing facility which was designed and constructed for this investigation was shown to be capable of performing tests with coolant flow rates up to 300 mL/min and heat fluxes up to 290 W/cm2. The greatest technical challenge of the testing facility design proved to be the method of applying the heat flux across a 1 cm2 contact area. Based on the computational modeling results and experimental test data, porous foam modeling recommendations and porous foam coldplate design suggestions were generated.

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Rubaszewski, Julie. "Optimisation de la conception du stockage de déchets radioactifs HA-MAVL à l’aide de la gestion de flux." Thesis, Troyes, 2013. http://www.theses.fr/2013TROY0024/document.

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Ce projet de recherche s’inscrit dans un partenariat entre l’ANDRA (Agence Nationale pour la gestion des Déchets Radioactifs) et le LOSI de l’Institut Charles Delaunay (STMR UMR CNRS), UTT.La thèse vise à dimensionner les ouvrages de stockage vis-à-vis des divers flux industriels. Les flux concernés sont de nature variée et cela constitue l’une des caractéristiques du stockage. Les ouvrages doivent en effet être conçus pour permettre un développement progressif, à l’origine d’une coexistence de flux nucléaires (les colis de déchets nucléaires et les flux associés, telle la ventilation nucléaire) et de flux de chantiers conventionnels. Le dimensionnement des flux et la conception des ouvrages pour autoriser ces flux se trouvent donc au cœur du processus de conception du stockage.La problématique de notre partenaire industriel porte sur la conception de réseau (appelé flow path design). Notre contribution est dédiée au développement de modèles de flow path design avec de nouvelles contraintes ainsi qu’au développement de méthodes. Les extensions au modèle de base prennent en compte une flotte hétérogène, des segments interdits d’accès à certains véhicules et des coûts de construction. Différentes méthodes d'optimisation approchées ont aussi été développées et testées. Il s’agit de métaheuristiques basées sur les recherches locales, l’algorithme de colonies de fourmis ainsi que l’algorithme des abeilles. L’efficacité des méthodes est prouvée grâce à des tests sur des instances de la littérature et l’application au cas réel est faite par simulation
This research project is part of a partnership between ANDRA (National Agency for Radioactive Waste Management) and the LOSI, Institut Charles Delaunay (TSR UMR CNRS), UTT.The thesis aims to design the storage structures for various industrial flows. Flows involved are varied in nature and it is one of the characteristics of the storage. The works must be designed to effect a gradual development, from a "coactivity", that is to say, a coexistence of nuclear flux (the nuclear waste packages and the associated flow, such nuclear ventilation) and conventional flow sites. The design flow and the design of structures to allow these flows are therefore at the heart of the design process of storage.The problem of our industrial partner focuses on flow path design. Our contribution is dedicated to the development of models of flow path design with new constraints and the development of methods. Extensions to the basic model takes into account different type of vehicle, not allowed some segments and taking into account construction costs. Different optimization methods have also been developed and tested. Metaheuristics are based on local search, the ant colony algorithm and the algorithm of bees. Efficiency of methods is demonstrated through tests on literature benchmarks and application to the real case is done by simulation

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Link, Shmuel G. "Field measurements of a swell band, shore normal, flux divergence reversal." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/67625.

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Thesis (S.M.)--Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Mechanical Engineering; and the Woods Hole Oceanographic Institution), June 2011.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 55-56).
Throughout this thesis we will discuss the theoretical background and empirical observation of a swell band shore normal flux divergence reversal. Specifically, we will demonstrate the existence and persistence of the energy flux divergence reversal in the nearshore region of Atchafalaya Bay, Gulf of Mexico, across storms during the March through April 2010 deployment. We will show that the swell band offshore component of energy flux is rather insignificant during the periods of interest, and as such we will neglect it during the ensuing analysis. The data presented will verify that the greatest flux divergence reversal is seen with winds from the East to Southeast, which is consistent with theories which suggest shoreward energy flux as well as estuarine sediment transport and resuspension prior to passage of a cold front. Employing the results of theoretical calculations and numerical modeling we will confirm that a plausible explanation for this phenomena can be found in situations where temporally varying wind input may locally balance or overpower bottom induced dissipation, which may also contravene the hypothesis that dissipation need increase shoreward due to nonlinear wave-wave interactions and maturation of the spectrum. Lastly, we will verify that the data presented is consistent with other measures collected during the same deployment in the Atchafalaya Bay during March - April 2010.
by Shmuel G. Link.
S.M.

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36

Hodges, Christopher Sean. "Theory and practice of near-field thermal probes for microscopy and thermal analysis." Thesis, Lancaster University, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.322519.

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Kolandaivelu, Kannikha Parameswari. "Hydrothermal Transport in the Panama Basin and in Brothers Volcano using Heat Flow, Scientific Deep Sea Drilling and Mathematical Models." Diss., Virginia Tech, 2019. http://hdl.handle.net/10919/99631.

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Two-thirds of submarine volcanism in the Earth's ocean basins is manifested along mid-ocean ridges and the remaining one-third is revealed along intraoceanic arcs and seamounts. Hydrothermal systems and the circulation patterns associated with these volcanic settings remove heat from the solid Earth into the deep ocean. Hydrothermal circulation continues to remove and redistribute heat in the crust as it ages. The heat and mass fluxes added to the deep ocean influence mixing in the abyssal ocean thereby affecting global thermohaline circulation. In addition to removing heat, hydrothermal processes extract chemical components from the oceanic and carry it to the surface of the ocean floor, while also removing certain elements from seawater. The resulting geochemical cycling has ramifications on the localized mineral deposits and also the biota that utilize these chemical fluxes as nutrients. In this dissertation, I analyze observed conductive heat flow measurements in the Panama Basin and borehole thermal measurements in Brothers Volcano and use mathematical models to estimate advective heat and mass fluxes, and crustal permeability. In the first manuscript, I use a well-mixed aquifer model to explain the heat transport in a sediment pond in the inactive part of the Ecuador Fracture Zone. This model yields mass fluxes and permeabilities similar to estimates at young upper oceanic crust suggesting vigorous convection beneath the sediment layer. In the second manuscript, I analyze the conductive heat flow measurements made in oceanic between 1.5 and 5.7 Ma on the southern flank of the Costa Rica Rift. These data show a mean conductive heat deficit of 70%, and this deficit is explained by various hydrothermal advective transport mechanisms, including outcrop to outcrop circulation, transport through faults, and redistribution of heat by flow of hydrothermal fluids in the basement. In the third manuscript, I analyze the borehole temperature logs for two sites representative of recharge and discharge areas of hydrothermal systems in the Brothers Volcano. I develop upflow and downflow models for fluids in the borehole and formation resulting in estimated of flow rates and permeabilities. All three independent research works are connected by the common thread of utilizing relatively simple mathematical concepts to get new insights into hydrothermal processes in oceanic crust.
PHD

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Gu, Chao. "Création d'un modèle inductifs de croissance de clusters industriels à flux optimisés, pour réduire leur impact sur l'environnement." Thesis, Le Havre, 2015. http://www.theses.fr/2015LEHA0013/document.

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L’écologie industrielle a pour objectif de résoudre les questions liées à l'utilisation des ressources technologiques dans les sociétés, dans le but d'ajouter à la partie des connaissances nécessaires pour commencer à évaluer les problèmes de qualité liés à l'environnement et les questions de disponibilité des ressources. Le concept d’écologie industrielle peut être réalisé et pratiqué à travers d’établissement des parcs éco-industriels. Un parc éco-industriel est une communauté de fabrication et de service des entreprises situées ensemble sur une propriété commune. Les membres cherchent la performance environnementale, économique et sociale accrue grâce à la collaboration dans la gestion des questions environnementales et de ressource. L’objectif principal de la thèse est de créer des modèles mathématiques d’optimisation pour maximiser des flux des échanges dans un parc éco-industriel et pour réduire les impacts négatifs des industries sur l’environnement. Les sept parcs éco-industriels symboliques et emblématiques dans le monde ont été étudiés durant la thèse pour obtenir une vision pratique de la problématique et pour acquérir les informations du développement des éco-parcs de la réalité. Les dix outils informatiques et les modèles d’optimisation pour les parcs éco-industriels ont été étudiés. Trois modélisations d’optimisation sont proposées avec les simulations numériques effectuées
Industrial ecology aims to resolve issues related to the use of technological resources in societies in order to add to the party the knowledge to begin to assess quality issues related to the environment and resource availability issues. The concept of industrial ecology can be realized and practiced through the establishment of eco-industrial parks. An eco-industrial park is a manufacturing community and service businesses located together on a common property. Members seek environmental performance, increased economic and social through collaboration in managing environmental and resource. The main aim of this thesis is to create mathematical optimization models to maximize trade flows in an eco-industrial park and to reduce the negative impacts of industry on the environment. The seven symbolic eco-industrial parks have been studied in this thesis in order to get a practical view of the issues and to acquire information from the development of eco-parks in reality. The numerical tools and optimization models for eco-industrial parks were studied. Three optimization models have been proposed with numerical simulations in this thesis

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Hu, Chih-Chieh. "Mechanistic modeling of evaporating thin liquid film instability on a bwr fuel rod with parallel and cross vapor flow." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/28148.

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Thesis (M. S.)--Mechanical Engineering, Georgia Institute of Technology, 2009.
Committee Chair: Abdel-Khalik, Said; Committee Member: Ammar, Mostafa H.; Committee Member: Ghiaasiaan, S. Mostafa; Committee Member: Hertel, Nolan E.; Committee Member: Liu, Yingjie.

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Gustafsson, David. "Land surface heat exchange over snow and frozen soil." Licentiate thesis, KTH, Land and Water Resources Engineering, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-1231.

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The energy exchange in the soil-snow-vegetation-atmospheresystem was studied to improve the quantitative knowledge of thegoverning processes. The lack of such knowledge contributes tothe uncertainty in the applicability of many existing modelsindependent of the temporal or spatial scale. The theoreticalbackground and available methods for measurements and numericalsimulations were reviewed. Numerical simulation models andavailable data sets representing open land and boreal forestwere evaluated in both diurnal and seasonal time-scales.Surface heat fluxes, snow depth, soil temperatures andmeteorological conditions were measured at an agriculturalfield in central Sweden over two winters, 1997-1999. Twoone-dimensional simulation models of different complexity wereused to simulate the heat and water transfer in thesoil-snow-atmosphere system and compared with the measurements.Comparison of simulated and observed heat fluxes showed thatparameter values governing the upper boundary condition weremore important than the formulation of the internal mass andheat balance of the snow cover. The models were useful toevaluate the lack of energy balance closure in the observedsurface heat fluxes, which underlined the importance ofimproved accuracy in eddy correlation measurements of latentflow during winter conditions.

The representation of boreal forest in the land surfacescheme used within a weather forecast model was tested with athree-year data set from the NOPEX forest site in centralSweden. The formulation with separate energy balances forvegetation and the soil/snow beneath tree cover improvedsimulation of the seasonal and diurnal variations of latent andsensible heat flux compared with an older model version.Further improvements of simulated surface heat fluxes could beexpected if the variation of vegetation properties within andbetween years and a new formulation of the boundary conditionsfor heat flux into the soil is included.

Keywords: Surface energy balance, Snow, Boreal forest,SVAT models, Eddy-correlation Measurements, Latent heat flux,Sensible heat flux, Net radiation, Soil temperature,Aerodynamic roughness, Surface resistance

QC 20100614

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Munoz, Esparza Domingo. "Multiscale modelling of atmospheric flows: towards improving the representation of boundary layer physics." Doctoral thesis, Universite Libre de Bruxelles, 2013. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/209363.

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Atmospheric boundary layer flows are characterized by the coexistence of a broad range of scales. These scales cover from synoptic- (100-5000 km) and meso-scales (1-100 km) up to three-dimensional micro-scale turbulence (less than a few kilometers). This multiscale nature inherent to atmospheric flows clearly determines the behaviour of the atmospheric boundary layer, whose structure and evolution are of major importance for the wind energy community. This PhD thesis is focused on the development of a numerical methodology that allows to include contribution from all the above mentioned scales, with the purpose of improving the representation of boundary layer processes. The multiscale numerical methodology is developed based on a numerical weather prediction (NWP) model, the Weather Research and Forecasting (WRF) model.

Prior to the development of the multiscale numerical methodology, one-year of sonic anemometer and wind LiDAR measurements from the FINO1 offshore platform are analyzed. A comprehensive database of offshore measurements in the lowest 250 m of the boundary layer is developed after quality data check and correction for flow distortion effects by the measurement mast, allowing the characterization of the offshore conditions at FINO1. Spectral analysis of high frequency sonic anemometer measurements is used to estimate a robust averaing time for the turbulent fluxes that minimizes non-universal contributions from mesoscale structures but captures the contribution from boundary layer turbulence, employing the Ogive function concept. A stability classification of the measurements is carried out based on the Obukhov length. Results compare well to other surface layer observational studies while vertical wind speed profiles exhibit the expected stability-dependency.

Although NWP models have been extensively used for weather forecasting purposes, a comprehensive analysis of its suitability to meet the wind energy requirements needs to be carried out. The applicability of the WRF mesoscale model to reproduce offshore boundary layer characteristics is evaluated and validated against field measurements from FINO1. The ability of six planetary boundary layer (PBL) parameterizations to account for stability effects is analyzed. Overall, PBL parameterizations are rather accurate in reproducing the vertical structure of the boundary layer for convective and neutral stabilities. However, difficulties are found under stable stratifications, due to the general tendency of PBL formulations to be overdiffusive and therefore, not capable to develope the strong vertical gradients found in the observations. A low-level jet and a very shallow boundary layer cases are simulated to provide further insights into the limits of the parameterizations.

Large-eddy simulations (LES) based on averaged conditions from a convective episode at FINO1 are conducted to understand the mechanisms of transition and equilibration that occur in turbulent one-way nested simulations. The nonlinear backscatter and anisotropy subgrid scale model with a prognostic turbulent kinetic energy equation is found to be capable of providing similar results when performing one-way nested large-eddy simulations to a reference stand-alone domain using periodic lateral boundary conditions. A good agreement is obtained in terms of velocity shear and turbulent fluxes of heat and momentum, while velocity variances are overestimated. A considerable streamwise fetch is needed following each domain transition for appropriate energy levels to be reached at high wavelengths and for the solution to reach quasi-stationary results. A pile-up of energy is observed at low wavelengths on the first nested domain, mitigated by the inclusion of a second nested domain with higher resolution that allows the development of an appropriate turbulent energy cascade.

As the final step towards developing the multiscale capabilities of WRF, the specific problem of the transition from meso- to micro-scales in atmospheric models is addressed. The challenge is to generate turbulence on inner LES domain from smooth mesoscale inflow. Several new methods are proposed to trigger the development of turbulent features. The inclusion of adequate potential temperature perturbations near the inflow boundaries of the LES domain results in a very good agreement of mean velocity profiles, variances and turbulent fluxes, as well as velocity spectra, when compared to periodic stand-alone simulations. This perturbation method allows an efficient generation of fully developed turbulence and is tested under a broad range of atmospheric stabilities: convective, neutral and stable conditions, showing successful results in all the regimes.
Doctorat en Sciences de l'ingénieur
info:eu-repo/semantics/nonPublished

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Albano, Gustavo Doratioto. "Integração de um modelo matemático de quantidade de água em rede de fluxo (ACQUANET) com um modelo matemático de qualidade de água em represas (CE-QUAL-R1) - Estudo de Caso: Represa Jaguari-Jacareí - Sistema Cantareira." Universidade de São Paulo, 2004. http://www.teses.usp.br/teses/disponiveis/3/3147/tde-24112004-112750/.

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Desenvolveu-se uma metodologia para integração de dois modelos matemáticos, um de quantidade de água, em rede de fluxo, denominado ACQUANET com outro de qualidade de água, de uma dimensão, aplicado a represas, denominado CE-QUAL-R1. Para tanto, foi elaborada uma INTERFACE em linguagem de programação possibilitando que as vazões resultantes, simuladas pelo ACQUANET, servissem como dados de entrada ao CE-QUAL-R1 para simular a distribuição vertical das variáveis de qualidade de água em uma represa. Essa metodologia foi aplicada à Represa Jaguari-Jacareí no Sistema Cantareira em São Paulo, Brasil, como alternativa de gerenciamento quali-quantitativo, além de possibilitar o uso de retirada de água em diferentes profundidades, através da operação de tomadas dágua seletivas existentes.
A methodology was developed for the integration of two mathematical models, one of water quantity in network named ACQUANET with other of water quality, in one dimension, applied in revervoirs, named CE-QUAL-R1. In order to achieve this goal, an INTERFACE was developed to link the CE-QUAL-R1 with ACQUANET outflow results. It should be highlighted that ACQUANET has been used for beginning values of CE-QUAL-R1 and to simulate the vertical distribution of water quality variables in a reservoir. This methodology was applied to Jaguari-Jacarei Reservoir, of Cantareira System in Sao Paulo, Brazil, as a management quality and quantity tool of the system and it showed the use possibility of withdrawal of outflowing waters from different depths, through existing selective withdrawals ports operation.

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Brown, Steven Richard. "A design of experiments approach for engineering carbon metabolism in the yeast Saccharomyces cerevisiae." Thesis, University of Exeter, 2016. http://hdl.handle.net/10871/26158.

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The proven ability to ferment Saccharomyces cerevisiae on a large scale presents an attractive target for producing chemicals and fuels from sustainable sources. Efficient and predominant carbon flux through to ethanol is a significant engineering issue in the development of this yeast as a multi-product cell chassis used in biorefineries. In order to evaluate diversion of carbon flux away from ethanol, combinatorial deletions were investigated in genes encoding the six isozymes of alcohol dehydrogenase (ADH), which catalyse the terminal step in ethanol production. The scarless, dominant and counter- selectable amdSYM gene deletion method was optimised for generation of a combinatorial ADH knockout library in an industrially relevant strain of S. cerevisiae. Current understanding of the individual ADH genes fails to fully evaluate genotype-by-genotype and genotype-by-environment interactions: rather, further research of such a complex biological process requires a multivariate mathematical modelling approach. Application of such an approach using the Design of Experiments (DoE) methodology is appraised here as essential for detailed empirical evaluation of complex systems. DoE provided empirical evidence that in S. cerevisiae: i) the ADH2 gene is not associated with producing ethanol under anaerobic culture conditions in combination with 25 g l-1 glucose substrate concentrations; ii) ADH4 is associated with increased ethanol production when the cell is confronted with a zinc-limited [1 μM] environment; and iii) ADH5 is linked with the production of ethanol, predominantly at pH 4.5. A successful metabolic engineering strategy is detailed which increases the product portfolio of S. cerevisiae, currently used for large-scale production of bioethanol. Heterologous expression of the cytochrome P450 fatty acid peroxygenase from Jeotgalicoccus sp., OleTJE, fused to the RhFRED reductase from Rhodococcus sp. NCIMB 978 converted free fatty acid precursors to C13, C15 and C17 alkenes (3.81 ng μl-1 total alkene concentration).

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Chumakov, Sergei G. "Subgrid models for large eddy simulation : scalar flux, scalar dissipation and energy dissipation /." 2005. http://www.library.wisc.edu/databases/connect/dissertations.html.

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Jayanti, Shekhar. "Modeling tracers and contaminant flux in heterogeneous aquifers." Thesis, 2003. http://wwwlib.umi.com/cr/utexas/fullcit?p3116345.

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46

Davis, Ian M. (Ian Mack). "Neutron transport benchmarks for binary stochastic multiplying media : planar geometry, two energy groups." Thesis, 2005. http://hdl.handle.net/1957/29748.

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Benchmark calculations are performed for neutron transport in a two material (binary) stochastic multiplying medium. Spatial, angular, and energy dependence are included. The problem considered is based on a fuel assembly of a common pressurized water nuclear reactor. The mean chord length through the assembly is determined and used as the planar geometry system length. According to assumed or calculated material distributions, this system length is populated with alternating fuel and moderator segments of random size. Neutron flux distributions are numerically computed using a discretized form of the Boltzmann transport equation employing diffusion synthetic acceleration. Average quantities (group fluxes and k-eigenvalue) and variances are calculated from an ensemble of realizations of the mixing statistics. The effects of varying two parameters in the fuel, two different boundary conditions, and three different sets of mixing statistics are assessed. A probability distribution function (PDF) of the k-eigenvalue is generated and compared with previous research. Atomic mix solutions are compared with these benchmark ensemble average flux and k-eigenvalue solutions. Mixing statistics with large standard deviations give the most widely varying ensemble solutions of the flux and k-eigenvalue. The shape of the k-eigenvalue PDF qualitatively agrees with previous work. Its overall shape is independent of variations in fuel cross-sections for the problems considered, but its width is impacted by these variations. Statistical distributions with smaller standard deviations alter the shape of this PDF toward a normal distribution. The atomic mix approximation yields large over-predictions of the ensemble average k-eigenvalue and under-predictions of the flux. Qualitatively correct flux shapes are obtained, however. These benchmark calculations indicate that a model which includes higher statistical moments of the mixing statistics is needed for accurate predictions of binary stochastic media k-eigenvalue problems. This is consistent with previous findings.
Graduation date: 2005

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Nes, Razvan. "An advanced nodal discretization for the quasi-diffusion low-order equations." Thesis, 2002. http://hdl.handle.net/1957/30335.

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The subject of this thesis is the development of a nodal discretization of the low-order quasi-diffusion (QDLO) equations for global reactor core calculations. The advantage of quasi-diffusion (QD) is that it is able to capture transport effects at the surface between unlike fuel assemblies better than the diffusion approximation. We discretize QDLO equations with the advanced nodal methodology described by Palmtag (Pal 1997) for diffusion. The fast and thermal neutron fluxes are presented as 2-D, non-separable expansions of polynomial and hyperbolic functions. The fast flux expansion consists of polynomial functions, while the thermal flux is expanded in a combination of polynomial and hyperbolic functions. The advantage of using hyperbolic functions in the thermal flux expansion lies in the accuracy with which hyperbolic functions can represent the large gradients at the interface between unlike fuel assemblies. The hyperbolic expansion functions proposed in (Pal 1997) are the analytic solutions of the zero-source diffusion equation for the thermal flux. The specific form of the QDLO equations requires the derivation of new hyperbolic basis functions which are different from those proposed for the diffusion equation. We have developed a discretization of the QDLO equations with node-averaged cross-sections and Eddington tensor components, solving the 2-D equations using the weighted residual method (Ame 1992). These node-averaged data are assumed known from single assembly transport calculations. We wrote a code in "Mathematica" that solves k-eigenvalue problems and calculates neutron fluxes in 2-D Cartesian coordinates. Numerical test problems show that the model proposed here can reproduce the results of both the simple diffusion problems presented in (Pal 1997) and those with analytic solutions. While the QDLO calculations performed on one-node, zero-current, boundary condition diffusion problems and two-node, zero-current boundary condition problems with UO₂-UO₂ assemblies are in excellent agreement with the benchmark and analytic solutions, UO₂-MOX configurations show more important discrepancies that are due to the single-assembly homogenized cross-sections used in the calculations. The results of the multiple-node problems show similar discrepancies in power distribution with the results reported in (Pal 1997). Multiple-node k-eigenvalue problems exhibit larger discrepancies, but these can be diminished by using adjusted diffusion coefficients (Pal 1997). The results of several "transport" problems demonstrate the influence of Eddington functionals on homogenized flux, power distribution, and multiplication factor k.
Graduation date: 2003

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Eckerle, Kate. "Capriccio For Strings: Collision-Mediated Parallel Transport in Curved Landscapes and Conifold-Enhanced Hierarchies Among Mirror Quintic Flux Vacua." Thesis, 2017. https://doi.org/10.7916/D85H7TH2.

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This dissertation begins with a review of Calabi-Yau manifolds and their moduli spaces, flux compactification largely tailored to the case of type IIb supergravity, and Coleman-De Luccia vacuum decay. The three chapters that follow present the results of novel research conducted as a graduate student. Our first project is concerned with bubble collisions in single scalar field theories with multiple vacua. Lorentz boosted solitons traveling in one spatial dimension are used as a proxy to the colliding 3-dimensional spherical bubble walls. Recent work found that at sufficiently high impact velocities collisions between such bubble vacua are governed by "free passage" dynamics in which field interactions can be ignored during the collision, providing a systematic process for populating local minima without quantum nucleation. We focus on the time period that follows the bubble collision and provide evidence that, for certain potentials, interactions can drive significant deviations from the free passage bubble profile, thwarting the production of a new patch with different field value. However, for simple polynomial potentials a fine-tuning of vacuum locations is required to reverse the free passage kick enough that the field in the collision region returns to the original bubble vacuum. Hence we deem classical transitions mediated by free passage robust. Our second project continues with soliton collisions in the limit of relativistic impact velocity, but with the new feature of nontrivial field space curvature. We establish a simple geometrical interpretation of such collisions in terms of a double family of field profiles whose tangent vector fields stand in mutual parallel transport. This provides a generalization of the well-known limit in flat field space (free passage). We investigate the limits of this approximation and illustrate our analytical results with numerical simulations. In our third and final project we investigate the distribution of field theories that arise from the low energy limit of flux vacua built on type IIb string theory compactified on the mirror quintic. For a large collection of these models, we numerically determine the distribution of Taylor coefficients in a polynomial expansion of each model's scalar potential to fourth order. We provide an analytic explanation of the proncounced hierarchies exhibited by the random sample of masses and couplings generated numerically. The analytic argument is based on the structure of masses in no scale supergravity and the divergence of the Yukawa coupling at the conifold point in the moduli space of the mirror quintic. Our results cast the superpotential vev as a random element whose capacity to cloud structure vanishes as the conifold is approached.

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Dissertations / Theses on the topic 'Eddy flux Mathematical models'

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