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1
Quaas, Johannes, Verena Grützun, Vera Schemann, and Torsten Weber. "Evaluating parameterisations of subgrid-scale variability." Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-189788.
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Parameterisations of fractional cloudiness in large-scale atmospheric models rely on information about the subgrid-scale variablity of the total water specific humidity, qt , provided in form of a probability density function (PDF). In this contribution, four different approaches to evaluate such total-water PDFs are discussed: (i) Satellite spectroradiometers with high spatial resolution allow to construct at the scale of model grid boxes a histogram, and subsequently to derive the moments of the PDF, of the vertical integral of qt . This can be compared to the same quantity diagnosed from the model parameterisation. Although the vertical integral mostly focuses on the boundary layer, and involves issues in grid-boxes with orographic variability, it allowed nevertheless in the example
presented to pinpoint deficiencies of a model parameterisation. (ii) Assuming a simple PDF shape and saturation within clouds, the simple “critical relative humidity” metric can be derived from infrared sounders and/or cloud lidar in combination with reanalysis data with a vertical resolution. It allows to evaluate the underlying PDF of any cloud scheme, but is sensitive to the assumptions. (iii) Supersites with a combination of ground-based lidar, radar and microwave data provide high-resolution high-quality reference data. In a “virtual reality” framework, we showed, however, that it is difficult to evaluate higher moments of a spatial PDF with this temporally-varying data. (iv) From a hierarchy of models from general circulation models to direct numerical simulations, we find
that the variance of the qt follows a power-law scaling with an exponent of about -2. This information is very useful to improve the parameterisations.
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Quaas, Johannes, Verena Grützun, Vera Schemann, and Torsten Weber. "Evaluating parameterisations of subgrid-scale variability." European Centre for Medium-Range Weather Forecasts, 2013. https://ul.qucosa.de/id/qucosa%3A13993.
Full textAbstract:
Parameterisations of fractional cloudiness in large-scale atmospheric models rely on information about the subgrid-scale variablity of the total water specific humidity, qt , provided in form of a probability density function (PDF). In this contribution, four different approaches to evaluate such total-water PDFs are discussed: (i) Satellite spectroradiometers with high spatial resolution allow to construct at the scale of model grid boxes a histogram, and subsequently to derive the moments of the PDF, of the vertical integral of qt . This can be compared to the same quantity diagnosed from the model parameterisation. Although the vertical integral mostly focuses on the boundary layer, and involves issues in grid-boxes with orographic variability, it allowed nevertheless in the example
presented to pinpoint deficiencies of a model parameterisation. (ii) Assuming a simple PDF shape and saturation within clouds, the simple “critical relative humidity” metric can be derived from infrared sounders and/or cloud lidar in combination with reanalysis data with a vertical resolution. It allows to evaluate the underlying PDF of any cloud scheme, but is sensitive to the assumptions. (iii) Supersites with a combination of ground-based lidar, radar and microwave data provide high-resolution high-quality reference data. In a “virtual reality” framework, we showed, however, that it is difficult to evaluate higher moments of a spatial PDF with this temporally-varying data. (iv) From a hierarchy of models from general circulation models to direct numerical simulations, we find
that the variance of the qt follows a power-law scaling with an exponent of about -2. This information is very useful to improve the parameterisations.
3
Candy, Adam S. "Subgrid scale modelling of transport processes." Thesis, Imperial College London, 2008. http://hdl.handle.net/10044/1/5496.
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Consideration of stabilisation techniques is essential in the development of physical models if they are to faithfully represent processes over a wide range of scales. Careful application of these techniques can significantly increase flexibility of models, allowing the computational meshes used to discretise the underlying partial differential equations to become highly nonuniform and anisotropic, for example. This exibility enables a model to capture a wider range of phenomena and thus reduce the number of parameterisations required, bringing a physically more realistic solution. The next generation of fluid flow and radiation transport models employ unstructured meshes and anisotropic adaptive methods to gain a greater degree of flexibility. However these can introduce erroneous artefacts into the solution when, for example, a process becomes unresolvable due to an adaptive mesh change or advection into a coarser region of mesh in the domain. The suppression of these effects, caused by spatial and temporal variations in mesh size, is one of the key roles stabilisation can play. This thesis introduces new explicit and implicit stabilisation methods that have been developed for application in fluid and radiation transport modelling. With a focus on a consistent residual-free approach, two new frameworks for the development of implicit methods are presented. The first generates a family of higher-order Petrov-Galerkin methods, and the example developed is compared to standard schemes such as streamline upwind Petrov-Galerkin and Galerkin least squares in accurate modelling of tracer transport. The dissipation generated by this method forms the basis for a new explicit fourth-order subfilter scale eddy viscosity model for large eddy simulation. Dissipation focused more sharply on unresolved scales is shown to give improved results over standard turbulence models. The second, the inner element method, is derived from subgrid scale modelling concepts and, like the variational multiscale method and bubble enrichment techniques, explicitly aims to capture the important under-resolved fine scale information. It brings key advantages to the solution of the Navier-Stokes equations including the use of usually unstable velocity-pressure element pairs, a fully consistent mass matrix without the increase in degrees of freedom associated with discontinuous Galerkin methods and also avoids pressure filtering. All of which act to increase the flexibility and accuracy of a model. Supporting results are presented from an application of the methods to a wide range of problems, from simple one-dimensional examples to tracer and momentum transport in simulations such as the idealised Stommel gyre, the lid-driven cavity, lock-exchange, gravity current and backward-facing step. Significant accuracy improvements are demonstrated in challenging radiation transport benchmarks, such as advection across void regions, the scattering Maynard problem and demanding source-absorption cases. Evolution of a free surface is also investigated in the sloshing tank, transport of an equatorial Rossby soliton, wave propagation on an aquaplanet and tidal simulation of the Mediterranean Sea and global ocean. In combination with adaptive methods, stabilising techniques are key to the development of next generation models. In particular these ideas are critical in achieving the aim of extending models, such as the Imperial College Ocean Model, to the global scale.
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Chakravarthy, Veerathu Kalyana. "Stochastic subgrid modeling of turbulent premixed flames." Diss., Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/12934.
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Pietarila, Graham Jonathan. "Regularizations as subgrid models for turbulent flows." Connect to online resource, 2007. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3273737.
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El-Asrag, Hossam Abd El-Raouf. "Large Eddy Simulation Subgrid Model for Soot Prediction." Diss., Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/14652.
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Soot prediction in realistic systems is one of the
most challenging problems in theoretical and applied combustion. Soot formation as a chemical process is very complicated and not fully understood up to the moment. The major difficulty stems from the chemical complexity of the soot formation processes as well as
its strong coupling with the other thermochemical and fluid processes that occur simultaneously. Soot is a major byproduct of incomplete combustion, having a strong impact on the environment, as well as the combustion efficiency. Therefore, it needs to be predicted in realistic configurations in an accurate and yet computationally efficient way.
In the current study, a new soot formation subgrid model is developed and reported here. The new
model is designed to be used within the context of the Large Eddy Simulation (LES) framework, combined with Linear Eddy Mixing (LEM)
as a subgrid combustion model. The final model can be applied equally to premixed and non-premixed flames over any required geometry and flow conditions in the free, the transition, and the
continuum regimes. The soot dynamics is predicted using a Method of Moments approach with Lagrangian Interpolative Closure (MOMIC) for the fractional moments. Since, no prior knowledge of the
particles distribution is required, the model is generally applicable. The effect of radiation is introduced as an optically thin model. As a validation the model is first applied to a
non-premixed non-sooting flame, then a set of canonically premixed flames. Finally, the model is validated against a non-premixed jet
sooting flame. Good results are predicted with reasonable accuracy.
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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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Príncipe, Ricardo Javier. "Subgrid scale stabilized finite elements for low speed flows." Doctoral thesis, Universitat Politècnica de Catalunya, 2008. http://hdl.handle.net/10803/6870.
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La descripción del flujo de fluidos involucra la solución de las ecuaciones de Navier-Stokes compresible, un problema muy complejo cuya estructura matemática no es del todo comprendida. Por lo tanto, mediante análisis asintótico, se pueden derivar modelos simplificados bajo ciertas hipótesis sobre el problema hechas en términos de parámetros adimensionales que miden la importancia relativa de los diferentes procesos físicos. Los flujos a baja velocidad se pueden describir por diferentes modelos que incluyen las ecuaciones de Navier Stokes incompresible cuya matemática es mucho mas conocida. Sin embargo, algunos flujos importantes no se pueden considerar incompresibles debido a la presencia de efectos térmicos. En esta clase de problemas se pueden derivar otra clase de ecuaciones simplificadas: las ecuaciones de Boussinesq y las ecuaciones de bajo numero de Mach.La complejidad de estos problemas matemáticos hace que su solución numérica sea muy difícil. En estos problemas el método de los elementos finitos es inestable, lo que en la práctica implica soluciones numéricas que presentan oscilaciones nodo a nodo de naturaleza no física. En las ecuaciones de Navier Stokes incompresible, dos fuentes bien conocidas de inestabilidad son la condición de incompresibilidad y la presencia del término convectivo. Muchas técnicas de estabilización utilizadas hoy en día se basan en la separación de escalas, descomponiendo la incógnita en una parte gruesa inducida por la discretización del domino y una parte fina de subescala. Modelar la subescala y su influencia conduce a un problema modificado para la escala gruesa que resulta estable.
Aunque las técnicas de estabilización son ampliamente utilizadas hoy en día, importantes problemas permanecen abiertos. Contribuyendo a su comprensión, en este trabajo se analizan varios aspectos del modelado de las subescalas. Para problemas escalares de segundo orden, se encuentra la dependencia de la subescala con el tamaño de la malla en el caso general de mallas anisótropas. Estas ideas son extendidas a sistemas de ecuaciones para considerar el problema de Oseen. También se analiza el modelado de las subescalas en problemas transitorios, obteniendo un mejor esquema de integración temporal para el problema de escala gruesa. Para considerar flujos a baja velocidad, se presenta la extensión de estas técnicas a problemas no lineales acoplados, lo que esta íntimamente relacionado con el problema del modelado de la turbulencia, que es un tema en si mismo.
Los flujos acoplados térmicamente, aparte del interés intrínseco que merecen, son importantes desde un punto de vista ingenieril. Una solución precisa del problema de flujo es necesaria para definir las cargas térmicas sobre las estructuras, que en muchos casos responden fuertemente, haciendo el problema acoplado. Esta clase de problemas, que motivaron este trabajo, incluyen la respuesta estructural en el caso de un incendio.
A general description of a fluid flow involves the solution of the compressible Navier-Stokes equations, a very complex problem whose mathematical structure is not well understood. Therefore, simplified models can be derived by asymptotic analysis under some assumptions on the problem, made in terms of dimensionless parameters that measure the relative importance of different physical processes. Low speed flows can be described by several models including the incompressible Navier Stokes equations whose mathematical structure is much better understood. However many important flows cannot be considered as incompressible, even at low speed, due to the presence of thermal effects. In such kind of problems another class of simplified equations can be derived: the Boussinesq equations and the Low Mach number equations.
The complexity of these mathematical problems makes their numerical solution very difficult. For these problems the standard finite element method is unstable, what in practice means that node to node oscillations of non physical nature may appear in the numerical solution. In the incompressible Navier Stokes equations, two well known sources of numerical instabilities are the incompressibility constraint and the presence of the convective terms. Many stabilization techniques used nowadays are based on scale separation, splitting the unknown into a coarse part induced by the discretization of the domain and a fine subgrid part. The modelling of the subgrid scale and its influence leads to a modified coarse scale problem that now can be shown to be stable.
Although stabilization techniques are nowadays widely used, important problems remain open. Contributing to their understanding, several aspects of the subgrid scale modelling are analyzed in this work. For second order scalar problems, the dependence of the subgrid scale on the mesh size, in the general anisotropic case, is clarified. These ideas are extended to systems of equations to consider the Oseen problem. The modelling of the subgrid scales in transient problems is also analyzed, leading to an improved time discretization scheme for the coarse scale problem. To consider low speed flow models, the extension of these techniques to nonlinear and coupled problems is presented, something that is intimately related to the problem of turbulence modelling, which a entire subject on its own right.
Thermally coupled flow problems, despite the intrinsic interest they deserve, are important from an engineering point of view. An accurate solution of a flow problem is needed to define thermal loads on structures which, in many cases have a strong response, making the problem coupled. This kind of problems, that motivated this work, include the problem of a structural response in the case of fires.
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Hinneburg, Detlef, and Nicole Mölders. "Dry deposition by an atmospheric model with horizontal subgrid." Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-215342.
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Two modules have been developed which qualify mesoscale atmospheric models for simulating the chemical transport at resolutions much higher than the model grid. Compared with total fine-grid application this method proves to be nearly so efficient but more economic. The modules solve the chemical transport equations (a) and submit the horizontal subgrid (b) for the meteorological and chemical calculations: (a) The chemical transport module considers the triad NO-N02-03 together with a simplified hydrocarbon chemistry. Involved are chemical reactions, anthropogenic and biogenic emission, dry deposition, passive transport, and turbulent diffusion. For these calculations a special vertical subgrid was introduced within the lowest atmospheric model layer. lt eliminates the frequently used approach of constant vertical particle fluxes near the surface. (b) The horizontal-subgrid module splits the horizontal model grid equidistantly into subgrid cells. The vertical surface fluxes of momentum, sensible and latent heat, radiation, soil heat and wetness, and chemical components are explicitly treated on this subgrid. The subgrid-averaged surface fluxes are employed for the (coarser) normal-grid calculations of the atmospheric meteorological variables. In contrast to the meteorological quantities, the chemical components and processes are perf ormed at all model layers on the horizontal subgrid. Several results are compared to conventional simulations of variable model resolutionZwei Programm-Module für mesoskalige Atmosphärenmodelle sind entwickelt worden, die Chemie-Transport-Vorgänge in höherer als der normalen Modellgitter-Auflösung simulieren. Im Vergleich zu hochaufgelösten Standardmodell-Anwendungen erweist sich diese Methode als effizienter. Die Module lösen die Chemie-Transport-Gleichungen (a) und schaffen das horizontale Untergitter für die meteorologischen und chemischen Berechnungen (b): (a) Im Chemie-Transport-Modul wird die Triade NO-N02-03 gemeinsam mit einer vereinfachten Kohlenwasserstoff-Chemie betrachtet. Berücksichtigt werden chemische Reaktionen, anthropogene und biogene Emissionen, trockene Deposition, passiver Transport und turbulente Diffusion. Für diese Berechnungen wurde innerhalb der untersten Modellschicht ein spezielles vertikales Untergitter eingeführt, um die in Oberflächennähe häufig angewendete Näherung konstanter Stoffflüsse zu eliminieren. (b) Das Untergitter-Modul unterteilt das horizontale Modellgitter in Unterzellen, auf welche die Berechnung der Boden- und Oberflächenflüsse bezogen wird. Die vertikalen Oberflächenflüsse von Impuls, sensibler und latenter Wärme, Strahlung, Bodenwärme und -feuchte sowie der chemischen Komponenten werden explizit im Untergitter bestimmt. Die über die Unterzellen gemittelten Flüsse werden für die im (gröberen) Modellgitter ablaufenden Berechnungen der meteorologischen Größen genutzt. Im Gegensatz dazu werden die chemischen Komponenten und Prozesse in allen Modellschichten vollständig auf dem Untergitter behandelt. Einige Ergebnisse dieser Methode werden im Vergleich mit Standard-Simulationen unterschiedlichen Auflösungsgrades gezeigt
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Hinneburg, Detlef, and Nicole Mölders. "Dry deposition by an atmospheric model with horizontal subgrid." Wissenschaftliche Mitteilungen des Leipziger Instituts für Meteorologie ; 17 = Meteorologische Arbeiten aus Leipzig ; 5 (2000), S. 18-28, 2000. https://ul.qucosa.de/id/qucosa%3A15146.
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Two modules have been developed which qualify mesoscale atmospheric models for simulating the chemical transport at resolutions much higher than the model grid. Compared with total fine-grid application this method proves to be nearly so efficient but more economic. The modules solve the chemical transport equations (a) and submit the horizontal subgrid (b) for the meteorological and chemical calculations: (a) The chemical transport module considers the triad NO-N02-03 together with a simplified hydrocarbon chemistry. Involved are chemical reactions, anthropogenic and biogenic emission, dry deposition, passive transport, and turbulent diffusion. For these calculations a special vertical subgrid was introduced within the lowest atmospheric model layer. lt eliminates the frequently used approach of constant vertical particle fluxes near the surface. (b) The horizontal-subgrid module splits the horizontal model grid equidistantly into subgrid cells. The vertical surface fluxes of momentum, sensible and latent heat, radiation, soil heat and wetness, and chemical components are explicitly treated on this subgrid. The subgrid-averaged surface fluxes are employed for the (coarser) normal-grid calculations of the atmospheric meteorological variables. In contrast to the meteorological quantities, the chemical components and processes are perf ormed at all model layers on the horizontal subgrid. Several results are compared to conventional simulations of variable model resolution.Zwei Programm-Module für mesoskalige Atmosphärenmodelle sind entwickelt worden, die Chemie-Transport-Vorgänge in höherer als der normalen Modellgitter-Auflösung simulieren. Im Vergleich zu hochaufgelösten Standardmodell-Anwendungen erweist sich diese Methode als effizienter. Die Module lösen die Chemie-Transport-Gleichungen (a) und schaffen das horizontale Untergitter für die meteorologischen und chemischen Berechnungen (b): (a) Im Chemie-Transport-Modul wird die Triade NO-N02-03 gemeinsam mit einer vereinfachten Kohlenwasserstoff-Chemie betrachtet. Berücksichtigt werden chemische Reaktionen, anthropogene und biogene Emissionen, trockene Deposition, passiver Transport und turbulente Diffusion. Für diese Berechnungen wurde innerhalb der untersten Modellschicht ein spezielles vertikales Untergitter eingeführt, um die in Oberflächennähe häufig angewendete Näherung konstanter Stoffflüsse zu eliminieren. (b) Das Untergitter-Modul unterteilt das horizontale Modellgitter in Unterzellen, auf welche die Berechnung der Boden- und Oberflächenflüsse bezogen wird. Die vertikalen Oberflächenflüsse von Impuls, sensibler und latenter Wärme, Strahlung, Bodenwärme und -feuchte sowie der chemischen Komponenten werden explizit im Untergitter bestimmt. Die über die Unterzellen gemittelten Flüsse werden für die im (gröberen) Modellgitter ablaufenden Berechnungen der meteorologischen Größen genutzt. Im Gegensatz dazu werden die chemischen Komponenten und Prozesse in allen Modellschichten vollständig auf dem Untergitter behandelt. Einige Ergebnisse dieser Methode werden im Vergleich mit Standard-Simulationen unterschiedlichen Auflösungsgrades gezeigt.
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Misra, Ashish Pullin Dale Ian. "Large-eddy simulation using a vortex-based subgrid stress model /." Diss., Pasadena, Calif. : California Institute of Technology, 1998. http://resolver.caltech.edu/CaltechETD:etd-08102005-134328.
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Nilsen, Christopher. "Fractal modelling of turbulent flows : Subgrid modelling for the Burgers equation." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for energi- og prosessteknikk, 2011. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-13916.
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The stochastically forced Burgers equation shares some of the same characteristics as the three-dimensional Navier-Stokes equations. Because of this it is sometimes used as a model equation for turbulence. Simulating the stochastically forced Burgers equation with low resolution can be considered as a one dimensional model of a three-dimensional large eddy simulation, and can be used to evaluate subgrid models. Modified versions of subgrid models using the fractal interpolation technique are presented here and tested in low resolution simulations of the stochastically forced Burgers equations. The results are compared with high resolution simulations, then low resolution simulations first using the dynamic Smagorinsky model and then using no subgrid model other than the numerical dissipation of the convective flux discretisation scheme. The fractal models perform reasonably well and most of the large scale features from the high resolution simulations are reproduced by corresponding simulations with low resolution. The performance of the fractal models is not, however, better than the performance of the dynamic Smagorinsky model. Therefore one might say that although the fractal models give promising results, it is not obvious that they are in any way superior to the traditional models. Also the low resolution simulation with the dissipative convective scheme performs well, suggesting that numerical dissipation can be sufficient as a subgrid model in one dimension.The solutions to the stochastically forced Burgers equation follow a k^(-5/3) energy spectrum, but high order statistics are not similar to real turbulence, due to the complete domination of shocks. Thus the stochastically forced Burgers equation might not be a suitable model for turbulence. It is not likely that the complexity of three-dimensional subgrid modelling is sufficiently represented by the one-dimensional case either.
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Cassisa, Cyril. "Optical flow estimation with subgrid model for study of turbulent flow." Phd thesis, Ecole Centrale de Lyon, 2011. http://tel.archives-ouvertes.fr/tel-00674772.
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The objective of this thesis is to study the evolution of scalar field carried by a flow from a temporal image sequence. The estimation of the velocity field of turbulent flow is of major importance for understanding the physical phenomenon. Up to now the problem of turbulence is generally ignored in the flow equation of existing methods. An information given by image is discrete at pixel size. Depending on the turbulent rate of the flow, pixel and time resolutions may become too large to neglect the effect of sub-pixel small-scales on the pixel velocity field. For this, we propose a flow equation defined by a filtered concentration transport equation where a classic turbulent sub-grid eddy viscosity model is introduced in order to account for this effect. To formulate the problem, we use a Markovian approach. An unwarping multiresolution by pyramidal decomposition is proposed which reduces the number of operations on images. The optimization coupled with a multigrid approach allows to estimate the optimal 2D real velocity field. Our approach is tested on synthetic andreal image sequences (PIV laboratory experiment and remote sensing data of dust storm event) with high Reynolds number. Comparisons with existing approaches are very promising.
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Zidikheri, Meelis Juma, and m. zidikheri@bom gov au. "Dynamical Subgrid-scale Parameterizations for Quasigeostrophic Flows using Direct Numerical Simulations." The Australian National University. Research School of Physical Sciences and Engineering, 2008. http://thesis.anu.edu.au./public/adt-ANU20090108.112027.
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In this thesis, parameterizations of non-linear interactions in quasigeostrophic (QG) flows for severely truncated models (STM) and Large Eddy Simulations (LES) are studied.
Firstly, using Direct Numerical Simulations (DNS), atmospheric barotropic flows over topography
are examined, and it is established that such flows exhibit multiple equilibrium states for a wide range of parameters. A STM is then constructed, consisting of the large
scale zonal flow and a topographic mode. It is shown that, qualitatively, this system behaves similarly to the DNS as far as the interaction between the zonal flow and topography
is concerned, and, in particular, exhibits multiple equilibrium states. By fitting the analytical form of the topographic stationary wave amplitude, obtained from the STM,
to the results obtained from DNS, renormalized dissipation and rotation parameters are obtained. The usage of renormalized parameters in the STM results in better quantitative
agreement with the DNS.¶
In the second type of problem, subgrid-scale parameterizations in LES are investigated with both atmospheric and oceanic parameters. This is in the context of two-level QG flows on the sphere, mostly, but not exclusively, employing a spherical harmonic triangular truncation at wavenumber 63 (T63) or higher. The methodology that is used is spectral, and is motivated by the stochastic representation of statistical closure theory, with the damping and forcing covariance, representing backscatter, determined from the statistics
of DNS. The damping and forcing covariance are formulated as 2 × 2 matrices for each wavenumber. As well as the transient subgrid tendency, the mean subgrid tendency is needed in the LES when the energy injection region is unresolved; this is also calculated from the statistics of the DNS. For comparison, a deterministic parameterization scheme consisting of 2×2 damping parameters, which are calculated from the statistics of DNS,
has been constructed. The main difference between atmospheric and oceanic flows, in this thesis, is that the atmospheric LES completely resolves the deformation scale, the energy and enstrophy injection region, and the truncation scale is spectrally distant from it, being well in the enstrophy cascade inertial range. In oceanic flows, however, the truncation scale is in the vicinity of the injection scale, at least for the parameters chosen, and is therefore not in an inertial range. A lower resolution oceanic LES at T15 is also examined, in which case the injection region is not resolved at all.¶
For atmospheric flows, it is found that, at T63, the matrix parameters are practically diagonal so that stratified atmospheric flows at these resolutions may be treated as uncoupled
layers as far as subgrid-scale parameterizations are concerned. It is also found that the damping parameters are relatively independent of the (vertical) level, but the
backscatter parameters are proportional to the subgrid flux in a given level. The stochastic
and deterministic parameterization schemes give comparably good results relative to the DNS. For oceanic flows, it is found that the full matrix structure of the parameters must be used. Furthermore, it is found that there is a strong injection of barotropic energy
from the subgrid scales, due to the unresolved, or partially resolved, baroclinic instability injection scales. It is found that the deterministic parameterization is too numerically unstable to be of use in the LES, and instead the stochastic parameterization must be used to obtain good agreement with the DNS. The subgrid tendency of the ensemble mean flow is also needed in some problems, and is found to reduce the available potential energy of
the flow.
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Zidikheri, Meelis Juma. "Dynamical subgrid-scale parameterizations for quasigeostrophic flows using direct numerical simulations /." View thesis entry in Australian Digital Theses, 2007. http://thesis.anu.edu.au/public/adt-ANU20090108.112027/index.html.
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Nelson, Christopher C. "Simulations of spatially evolving compressible turbulence using a local dynamic subgrid model." Diss., Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/12002.
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Sen, Baris Ali. "Artificial neural networks based subgrid chemistry model for turbulent reactive flow simulations." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/31757.
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Thesis (Ph.D)--Aerospace Engineering, Georgia Institute of Technology, 2010.Committee Chair: Menon, Suresh; Committee Member: Lieuwen, Timothy C.; Committee Member: Sankar, Lakshmi; Committee Member: Stoesser, Thorsten; Committee Member: Syed, Saadat; Committee Member: Walker, Mitchell. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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Chen, Qinglin. "Investigation of the effects of subgrid-scale turbulence on resolvable-scale statistics." Connect to this title online, 2006. http://etd.lib.clemson.edu/documents/1175016121/.
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Cotter, Colin John. "Model reducation for shallow water dynamics : balance adiabatic invariance and subgrid modelling." Thesis, Imperial College London, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.415125.
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Bhushan, Shanti. "Development of a nonlinear model for subgrid scale turbulence and it's applications." Master's thesis, Mississippi State : Mississippi State University, 2003. http://library.msstate.edu/etd/show.asp?etd=etd-04062003-124906.
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Koster, Randal Dean. "Tracer water transport and subgrid precipitation variation within atmospheric general circulation models." Thesis, Massachusetts Institute of Technology, 1988. http://hdl.handle.net/1721.1/14673.
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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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Zhou, Ye. "Renormalization group theory technique and subgrid scale closure for fluid and plasma turbulence." W&M ScholarWorks, 1987. https://scholarworks.wm.edu/etd/1539623774.
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Renormalization group theory is applied to incompressible three-dimension Navier-Stokes turbulence so as to eliminate unresolvable small scales. The renormalized Navier-Stokes equation includes a triple nonlinearity with the eddy viscosity exhibiting a mild cusp behavior, in qualitative agreement with the test-field model results of Kraichnan. For the cusp behavior to arise, not only is the triple nonlinearity necessary but the effects of pressure must be incorporated in the triple term.;Renormalization group theory is also applied to a model Alfven wave turbulence equation. In particular, the effect of small unresolvable subgrid scales on the large scales is computed. It is found that the removal of the subgrid scales leads to a renormalized response function. (i) This response function can be calculated analytically via the difference renormalization group technique. Strong absorption can occur around the Alfven frequency for sharply peaked subgrid frequency spectra. (ii) With the {dollar}\epsilon{dollar} - expansion renormalization group approach, the Lorenzian wavenumber spectrum of Chen and Mahajan can be recovered for finite {dollar}\epsilon{dollar}, but the nonlinear coupling constant still remains small, fully justifying the neglect of higher order nonlinearities introduced by the renormalization group procedure.
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Wheadon, Andrew John. "Wave-turbulence interaction in shallow water numerical models : asymptotic limits, and subgrid interactions." Thesis, University of Exeter, 2018. http://hdl.handle.net/10871/34333.
Full textAbstract:
The ability to directly simulate all atmospheric motion is currently well beyond the limits of the computers available to us. As such techniques must be developed that accurately model important processes in an affordable manner. Large-scale balanced motion is well understood, but as affordable resolution increases, models are able to resolve scales where large-scale turbulence and small-scale waves are important. This requires a new set of techniques that respect the interactions between these different kinds of motion. In this thesis we look at two ways of assessing the accuracy of models capable of representing the scales at which these interactions occur. The first approach uses asymptotic limit solutions to derive a set of terms whose scale is known. These terms can then be evaluated as the model approaches a relevant asymptotic regime, and a `good' model should reproduce the expected rate of scaling. We apply this method of asymptotic limit solutions to an Eulerian and a Lagrangian shallow water model. The former is based upon ENDGame, the model currently in use at the Met Office, and the latter is based upon a candidate model from GungHo which is seeking a replacement for ENDGame. In addition, the Eulerian model is evaluated with both small and large timesteps and the results confirm the ability of the semi-implicit scheme to retain accuracy at large timesteps. Errors in the higher-order diagnostics used in this section highlight the need to make these analytic diagnostics consistent with the discretisations of the model in question. The second method involves looking at the exchanges of energy in a spectral shallow water model in order to inform the design of subgrid models. By running a high-resolution simulation and truncating the energy at a certain wavenumber, comparing the result to a run without truncation shows the contribution of the scales below the truncation limit. We extend this by separating the total energy into separate components that may be truncated and evaluated individually in order to give a more complete picture of energy exchanges at the subgrid scale.
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Rasam, Amin. "Anisotropy-resolving subgrid-scale modelling using explicit algebraic closures for large eddy simulation." Doctoral thesis, KTH, Turbulens, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-142401.
Full textAbstract:
The present thesis deals with the development and performance analysis ofanisotropy-resolving models for the small, unresolved scales (”sub-grid scales”,SGS) in large eddy simulation (LES). The models are characterised by a descriptionof anisotropy by use of explicit algebraic models for both the subgridscale(SGS) stress tensor (EASSM) and SGS scalar flux vector (EASSFM). Extensiveanalysis of the performance of the explicit algebraic SGS stress model(EASSM) has been performed and comparisons made with the conventionalisotropic dynamic eddy viscosity model (DEVM). The studies include LES ofplane channel flow at relatively high Reynolds numbers and a wide range ofresolutions and LES of separated flow in a channel with streamwise periodichill-shaped constrictions (periodic hill flow) at coarse resolutions. The formersimulations were carried out with a pseudo-spectral Navier–Stokes solver, whilethe latter simulations were computed with a second-order, finite-volume basedsolver for unstructured grids. The LESs of channel flow demonstrate that theEASSM gives a good description of the SGS anisotropy, which in turn gives ahigh degree of resolution independence, contrary to the behaviour of LES predictionsusing the DEVM. LESs of periodic hill flow showed that the EASSMalso for this case gives significantly better flow predictions than the DEVM.In particular, the reattachment point was much better predicted with the EASSMand reasonably well predicted even at very coarse resolutions, where theDEVM is unable to predict a proper flow separation.The explicit algebraic SGS scalar flux model (EASSFM) is developed toimprove LES predictions of complex anisotropic flows with turbulent heat ormass transfer, and can be described as a nonlinear tensor eddy diffusivity model.It was tested in combination with the EASSM for the SGS stresses, and itsperformance was compared to the conventional dynamic eddy diffusivity model(DEDM) in channel flow with and without system rotation in the wall-normaldirection. EASSM and EASSFM gave predictions of high accuracy for meanvelocity and mean scalar fields, as well as stresses and scalar flux components.An extension of the EASSM and EASSFM, based on stochastic differentialequations of Langevin type, gave further improvements. In contrast to conventionalmodels, these extended models are able to describe intermittent transferof energy from the small, unresolved scales, to the resolved large ones.The present study shows that the EASSM/EASSFM gives a clear improvementof LES of wall-bounded flows in simple, as well as in complex geometriesin comparison with simpler SGS models. This is also shown to hold for a widerange of resolutions and is particularly accentuated for coarse resolution. The advantages are also demonstrated both for high-order numerical schemes andfor solvers using low-order finite volume methods. The models therefore havea clear potential for more applied computational fluid mechanics.QC 20140304
Explicit algebraic sub-grid scale modelling for large-eddy simulations
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Chung, Daniel Pullin Dale Ian Pullin Dale Ian. "Numerical simulation and subgrid-scale modeling of mixing and wall-bounded turbulent flows." Diss., Pasadena, Calif. : California Institute of Technology, 2009. http://resolver.caltech.edu/CaltechETD:etd-05292009-123828.
Full textAbstract:
Thesis (Ph.D.) -- California Institute of Technology,2009.Advisor name found in the Acknowledgments pages of the thesis. Title from home page (viewed 05/04/2010). Includes bibliographical references.
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Rasam, Amin. "Explicit algebraic subgrid-scale stress and passive scalar flux modeling in large eddy simulation." Licentiate thesis, KTH, Linné Flow Center, FLOW, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-34453.
Full textAbstract:
The present thesis deals with a number of challenges in the field of large eddy simulation (LES). These include the performance of subgrid-scale (SGS) models at fairly high Reynolds numbers and coarse resolutions, passive scalar and stochastic modeling in LES. The fully-developed turbulent channel flow is used as the test case for these investigations. The advantage of this particular test case is that highly accurate pseudo-spectral methods can be used for the discretization of the governing equations. In the absence of discretization errors, a better understanding of the subgrid-scale model performance can be achieved. Moreover, the turbulent channel flow is a challenging test case for LES, since it shares some of the common important features of all wall-bounded turbulent flows. Most commonly used eddy-viscosity-type models are suitable for moderately to highly-resolved LES cases, where the unresolved scales are approximately isotropic. However, this makes simulations of high Reynolds number wall-bounded flows computationally expensive. In contrast, explicit algebraic (EA) model takes into account the anisotropy of SGS motions and performs well in predicting the flow statistics in coarse-grid LES cases. Therefore, LES of high Reynolds number wall-bounded flows can be performed at much lower number of grid points in comparison with other models. A demonstration of the resolution requirements for the EA model in comparison with the dynamic Smagorinsky and its high-pass filtered version for a fairly high Reynolds number is given in this thesis. One of the shortcomings of the commonly used eddy diffusivity model arises from its assumption of alignment of the SGS scalar flux vector with the resolved scalar gradients. However, better SGS scalar flux models that overcome this issue are very few. Using the same methodology that led to the EA SGS stress model, a new explicit algebraic SGS scalar flux model is developed, which allows the SGS scalar fluxes to be partially independent of the resolved scalar gradient. The model predictions are verified and found to improve the scalar statistics in comparison with the eddy diffusivity model. The intermittent nature of energy transfer between the large and small scales of turbulence is often not fully taken into account in the formulation of SGS models both for velocity and scalar. Using the Langevin stochastic differential equation, the EA models are extended to incorporate random variations in their predictions which lead to a reasonable amount of backscatter of energy from the SGS to the resolved scales. The stochastic EA models improve the predictions of the SGS dissipation by decreasing its length scale and improving the shape of its probability density function.QC 20110615
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Häggblad, Jon. "Modified Stencils for Boundaries and Subgrid Scales in the Finite-Difference Time-Domain Method." Doctoral thesis, KTH, Numerisk analys, NA (stängd 2012-06-30), 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-95510.
Full textAbstract:
This thesis centers on modified stencils for the Finite-Difference Time-Domain method (FDTD), or Yee scheme, when modelling curved boundaries, obstacles and holes smaller than the discretization length. The goal is to increase the accuracy while keeping the structure of the standard method, enabling improvements to existing implementations with minimal effort. We present an extension of a previously developed technique for consistent boundary approximation in the Yee scheme. We consider both Maxwell's equations and the acoustic equations in three dimensions, which require separate treatment, unlike in two dimensions. The stability properties of coefficient modifications are essential for practical usability. We present an analysis of the requirements for time-stable modifications, which we use to construct a simple and effective method for boundary approximations. The method starts from a predetermined staircase discretization of the boundary, requiring no further data on the underlying geometry that is being approximated. Not only is the standard staircasing of curved boundaries a poor approximation, it is inconsistent, giving rise to errors that do not disappear in the limit of small grid lengths. We analyze the standard staircase approximation by deriving exact solutions of the difference equations, including the staircase boundary. This facilitates a detailed error analysis, showing how staircasing affects amplitude, phase, frequency and attenuation of waves. To model obstacles and holes of smaller size than the grid length, we develop a numerical subgrid method based on locally modified stencils, where a highly resolved micro problem is used to generate effective coefficients for the Yee scheme at the macro scale. The implementations and analysis of the developed methods are validated through systematic numerical tests.QC 20120530
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Balasubramanian, Sivaramakrishnan. "A Novel Approach for the Direct Simulation of Subgrid-Scale Physics in Fire Simulations." NCSU, 2010. http://www.lib.ncsu.edu/theses/available/etd-12212009-122246/.
Full textAbstract:
A Lagrangian framework for computing subgrid-scale combustion physics in Large Eddy Simulations (LES) of fire is formulated and validated. The framework is based on coupling LES formulation, based on the Fire Dynamic Simulator (FDS) with the One-Dimensional Turbulence (ODT) model. The ODT model involves reaction-diffusion and turbulent transport along one-dimensional domains. The one-dimensional domains are attached to the flame brush positions, computed in LES, and are allowed to propagate along its surface. The Lagrangian LES-ODT framework involves various implementations including a) momentum, energy, and species solution along one-dimensional ODT domain, b) Tracking of ODT domains through their anchor points, c) Filtering of ODT solutions on the LES grid, d) Inverse filtering (interpolation) of LES velocity fields in ODT domains, and e) The management of ODT domains at the flow inlets and as they reach the flame tip. Comparison of LES-ODT solutions with FDS solutions shows that the LES-ODT implementation reproduces reasonably well the flame topology and structure.
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Myers, Seth. "A One-Dimensional Subgrid Near-Wall Treatment for Reynolds Averaged Computational Fluid Dynamics Simulations." MSSTATE, 2006. http://sun.library.msstate.edu/ETD-db/theses/available/etd-04122006-110804/.
Full textAbstract:
Prediction of the near wall region is crucial to the accuracy of turbulent flow computational fluid dynamics (CFD) simulation. However, sufficient near-wall resolution is often prohibitive for high Reynolds number flows with complex geometries, due to high memory and processing requirements. A common approach in these cases is to use wall functions to bridge the region from the first grid node to the wall. This thesis presents an alternative method that relaxes the near wall resolution requirement by solving one dimensional transport equations for velocity and turbulence across a locally defined subgrid contained within wall adjacent grid cells. The addition of the subgrid allows for wall adjacent primary grid sizes to vary arbitrarily from low-Re model sizing (y+ ~ 1) to wall function sizing without significant loss of accuracy or increase in computational cost.
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Hong, Zhao. "Adaptive subgrid scale modelling and multiple mesh simulation of low Reynolds number channel flow." Thesis, University of Surrey, 1994. http://epubs.surrey.ac.uk/843196/.
Full textAbstract:
The present study is aimed at enhancing the effectiveness of the large eddy simulation (LES) approach to the computation of turbulent flows by these two methods: i) developing a superior subgrid scale (SGS) model and ii) improving the economy of LES. First of all, the various existing SGS models are extensively investigated, and their advangages and disadvantages are addressed to highlight the areas requiring improvements. This study leads to the construction of a modified SGS dynamic model. In addition, a detailed derivation of the second-order velocity structure function SGS model is made, correcting an error found in that model. A new multiple mesh method is also designed to accelerate LES. After the above theoretical studies, several low-Reynolds-number channel flow simulations have been performed. Firstly, simulations with varying model constants are carried out, and the results agree with those of Deardorff [14], showing that a model constant of about 0.1 is optimum for channel flows. Secondly, simulations with varying numerical resolutions have been carried out. They reveal that the refinement of the mesh in the direction normal to the wall improves all the turbulence statistics, both higher- and lower-order statistics, over the whole channel, while the refinement of the resolution in the streamwise and spanwise directions improves lower-order statistics over the whole channel, but only improves higher-order turbulence statistics in the central region of the channel. Thirdly, a dissipation-range SGS model (i.e. the Smagorinsky model with low- Reynolds-number modification [67]) is, for the first time, tested and compared with the standard Smagorinsky model. The results obtained show some promise for automatically adjusting the SGS model with Reynolds number. Fourthly, the performance of the modified dynamic SGS model is assessed through a comparison of length scales computed respectively by this modified model, the Germano- Lilly dynamic SGS model and two empirical wall damping functions in conjunction with an optimum model coefficient, which have been successfully used in many simulations of channel flows. Two values of the ratio of filter widths are set for each of the dynamic models. The results have confirmed that the modified dynamic SGS model can be successfully extended to simulate low-Reynolds-number channel flows. Of great promise is that the modified SGS dynamic model gives the correct behaviour of the subgrid eddy viscosity in the region of a plane wall to an accuracy that exceeds the best-tuned wall damping function, and almost collapses with the theoretical behaviour of the length scale near the wall without any tuning and adjustment. In addition, the impact of the choice of the ratio of filter widths on the modified dynamic SGS model is much less than that on the Germano-Lilly model. Finally, simulations using the new and old multiple mesh methods are performed. The instantaneous results just after the interpolation of the coarse mesh velocity field onto the fine mesh show that the fine mesh velocity field created by the new multiple mesh method contains the information of the residual field. In contrast, there is no difference between the fine mesh results obtained by the old method and those from a simulation on the coarse mesh.
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Marstorp, Linus. "Subgrid-scale modelling for large-eddy simulation including scalar mixing in rotating turbulent shear flows." Licentiate thesis, KTH, Mekanik, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3916.
Full textAbstract:
The aim of the present study is to develop subgrid-scale models that are relevant for complex flows and combustion. A stochastic model based on a stochastic Smagorinsky constant with adjustable variance and time scale is proposed. The stochastic model is shown to provide for backscatter of both kinetic energy and scalar variance without causing numerical instabilities. A new subgrid-scale scalar flux model is developed using the same kind of methodology that leads to the explicit algebraic scalar flux model, EASFM, for RANS. The new model predicts the anisotropy of the subgrid-scales in a more realistic way than the eddy diffusion model. Both new models were tested in rotating homogeneous shear flow with a passive scalar. Rogallo’s method of moving the frame with the mean flow to enable periodic boundary conditions was used to simulate homogeneous shear flow.QC 20101119
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Avila, Matías. "Nonlinear subgrid finite element models for low Mach number flows coupled with radiative heat transfer." Doctoral thesis, Universitat Politècnica de Catalunya, 2012. http://hdl.handle.net/10803/285809.
Full textAbstract:
The general description of a fluid flow involves the solution of the compressible Navier-Stokes equations, a very complex problem whose mathematical structure is not well understood. It is widely accepted that these equations provide an accurate description of any problem in fluid mechanics which may present many different nonlinear physical mechanisms. Depending on the physics of the problem under consideration, different simplified models neglecting some physical mechanisms can be derived from asymptotic analysis. On the other hand, radiative heat transfer can strongly interact with convection in high temperature flows, and neglecting its effects may have significant consequences in the overall predictions. Problems as fire scenarios emphasized the need for an evaluation of the effect of radiative heat transfer. This work is directed to strongly thermally coupled low Mach number flows with radiative heat transfer.
The complexity of these mathematical problem makes their numerical solution very difficult. Despite the important difference in the treatment of the incompressibility, the low Mach number equations present the same mathematical structure as the incompressible Navier-Stokes equations, in the sense that the mechanical pressure is determined from the mass conservation constraint. Consequently the same type of numerical instabilities can be found, namely, the problem of compatibility conditions between the velocity and pressure finite element spaces, and the instabilities due to convection dominated flows. These instabilities can be avoided by the use of stabilization techniques. Many stabilization techniques used nowadays are based on the variational multiscale method, in which a decomposition of the approximating space into a coarse scale resolvable part and a fine scale subgrid part is performed. The modeling of the subgrid scale and its influence leads to a modified coarse scale problem providing stability. The quality of the final approximation (accuracy, efficiency) depends on the particular model.
The extension of these techniques to nonlinear and coupled problems is presented. The distinctive features of our approach are to consider the subscales as transient and to keep the scale splitting in all the nonlinear terms appearing in the finite element equations and in the subgrid scale model. The first ingredient permits to obtain an improved time discretization scheme(higher accuracy, better stability). The second ingredient permits to prove global conservation properties, being also responsible of the higher accuracy of the method. This ingredient is intimately related to the problem of thermal turbulence modeling from a strictly numerical point of view. The capability for the simulation of turbulent flows is a measure of the ability of modeling the effect of the subgrid flow structures over the coarser ones. The performance of the model in predicting the behavior of turbulent flows is demonstrated.
The radiation transport equation has been also approximated within the variational multiscale framework, the design and analysis of stabilized finite element methods is presented.La descripción general del movimiento de un flujo implica la solución de las ecuaciones de Navier-Stokes compresibles, un problema de muy compleja estructura matemática. Estas ecuaciones proporcinan una descripción detallada de cualquier problema en mecánica de fluidos, que puede presentar distintos mecanismos no lineales que interactúan entre si. En función de la física del problema que se esté considerando, pueden derivarse modelos simplificados de las ecuaciones de Navier-Stokes mediante analisis dimensional, que ignoran algunos fenómenos físicos. Por otro lado, la transferencia de calor por radiación puede interactuar con el movimiento de un fluido, e ignorar sus efectos puede tener consecuencias importantes en las predicciones del flujo. Problemas donde hay fuego implican la evaluacion del efecto del calor por radiación. El presente trabajo está dirigido a flujos a bajo número de Mach térmicamente acoplados, donde el calor por radiación afecta al flujo. Debido a la complejidad del problema matemático, la solución numérica es muy complicada. A pesar de las diferencia en el tratamiento de la incompresibilidad, las ecuaciones de flujo a bajo número de Mach poseen una estructura matemática similar a la de flujo incompresible, en el sentido que la presión mecánica se determina a partir de la ecuación de conservación de la masa. En consecuencia poseen el mismo tipo de inestabilidades numéricas, que son el problema de condiciones de compatibilidad entre los espacios de elementos finitos de velocidad y presión, y las inestabilidades debidas a flujos con convección dominante. Estas inestabilidades pueden evitarse mediante técnicas de estabilización numérica. Muchos métodos de estabilización utilizados hoy día se basan en el método de multiscalas variacionales, donde el espacio funcional de la solucion se divide en un espacio discreto y resolubre y un espacio infinito de subscalas. El modelado de las subescalas y su influencia modifican el problema discreto proporcionando estabilidad. La calidad de la aproximación numérica final (precisión, eficiencia) depende del modelo particular de subescalas. En este trabajo se extienden estas técnicas de estabilización a problemas no lineales y acoplados. Las características que distinguen a nuestra aproximación son considerar las subsecalas como transitorias y mantener la división de escalas en todos los términos no lineales que aparecen en las ecuaciones de elementros finitos y en las del modelo de subescalas. La primera característica permite obtener mayor precisión y mejor estabilidad en la solución, la segunda característica permite obtener esquemas donde las propiedades se conservan globalmente, y mayor precisión del método. El hecho de mantener la división de escalas en todos los términos no lineales está intimamemte relacionado con el modelado de turbulencia en flujos térmicamente acoplados desde un punto de vista estrictamente numérico. La capacidad de simulación de flujo turbulento es una medida de la habilidad de modelar el efecto de las estructuras de escala fina sobre las estructuras de escala gruesa. Se muestra en esta tesis el desempeño del método para de predecir flujo turbulento. La ecuación de transporte de radiación también se aproxima numéricamente en el marco de multiscala variacional. El diseño y análisis de este método se presenta en detalle en esta tesis
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Marstorp, Linus. "Subgrid-scale modelling for large-eddy simulation invluding scalar mixing in rotating turbulent shear flows." Licentiate thesis, KTH, Mechanics, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3916.
Full textAbstract:
The aim of the present study is to develop subgrid-scale models that are relevant for complex flows and combustion. A stochastic model based on a stochastic Smagorinsky constant with adjustable variance and time scale is proposed. The stochastic model is shown to provide for backscatter of both kinetic energy and scalar variance without causing numerical instabilities. A new subgrid-scale scalar flux model is developed using the same kind of methodology that leads to the explicit algebraic scalar flux model, EASFM, for RANS. The new model predicts the anisotropy of the subgrid-scales in a more realistic way than the eddy diffusion model. Both new models were tested in rotating homogeneous shear flow with a passive scalar. Rogallo’s method of moving the frame with the mean flow to enable periodic boundary conditions was used to simulate homogeneous shear flow.
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Pieroth, Martin [Verfasser], Ulrich [Gutachter] Achatz, and Andrey [Gutachter] Gritsun. "On the climate dependence of subgrid-scale parameterizations / Martin Pieroth ; Gutachter: Ulrich Achatz, Andrey Gritsun." Frankfurt am Main : Universitätsbibliothek Johann Christian Senckenberg, 2019. http://d-nb.info/1197127992/34.
Full text
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Montecchia, Matteo. "Testing of subgrid scale (SGS) models for large-eddy simulation (LES) of turbulent channel flow." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2015. http://amslaurea.unibo.it/8423/.
Full textAbstract:
Sub-grid scale (SGS) models are required in order to model the influence of the unresolved small scales on the resolved scales in large-eddy simulations (LES),
the flow at the smallest scales of turbulence.
In the following work two SGS models are presented and deeply analyzed in terms of accuracy through several LESs with different spatial resolutions, i.e. grid spacings.
The first part of this thesis focuses on the basic theory of turbulence, the governing equations of fluid dynamics and their adaptation to LES. Furthermore, two important SGS models
are presented:
one is the Dynamic eddy-viscosity model (DEVM), developed by \cite{germano1991dynamic}, while the other is the Explicit Algebraic SGS model (EASSM), by \cite{marstorp2009explicit}.
In addition, some details about the implementation of the EASSM in a Pseudo-Spectral Navier-Stokes code \cite{chevalier2007simson} are presented.
The performance of the two aforementioned models will be investigated in the following chapters, by means of LES of a channel flow, with friction Reynolds numbers
$Re_\tau=590$ up to $Re_\tau=5200$, with relatively coarse resolutions.
Data from each simulation will be compared to baseline DNS data.
Results have shown that, in contrast to the DEVM, the EASSM has promising potentials for flow predictions at high friction Reynolds numbers: the higher the friction Reynolds number
is the better the EASSM will behave and the worse the performances of the DEVM will be.
The better performance of the EASSM is contributed to the ability to capture flow anisotropy at the small scales through a correct formulation for the SGS stresses.
Moreover, a considerable reduction in the required computational resources can be achieved using the EASSM compared to DEVM. Therefore, the EASSM combines accuracy and computational
efficiency, implying that it has a clear potential for industrial CFD usage.
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Weber, Torsten, and Johannes Quaas. "Incorporating the subgrid-scale variability of clouds in the autoconversion parameterization using a PDF-scheme." Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-186356.
Full textAbstract:
An investigation of the impact of the subgrid-scale variability of cloud liquid water on the autoconversion process as parameterized in a general circulation model is presented in this paper. For this purpose, a prognostic statistical probability density distribution (PDF) of the subgrid scale variability of cloud water is incorporated in a continuous autoconversion parameterization. Thus, the revised autoconversion rate is calculated by an integral of the autoconversion equation over the PDF of total water
mixing ratio from the saturation vapor mixing ratio to the maximum of total water mixing ratio. An evaluation of the new autoconversion parameterization is carried out by means of one year simulations with the ECHAM5 climate model. The results indicate that the new autoconversion scheme causes an increase of the frequency of occurrence of high autoconversion rates and a decrease of low ones compared to the
original scheme. This expected result is due to the emphasis on areas of high cloud liquid water in the new approach, and the non-linearity of the autoconversion with respect to liquid water mixing ratio. A similar trend as in the autoconversion is observed in the accretion process resulting from the coupling of both processes. As a consequence of the altered autoconversion, large-scale surface precipitation also shows a shift of occurrence from lower to higher rates. The vertically integrated cloud
liquid water estimated by the model shows slight improvements compared to satellite data. Most importantly, the artificial tuning factor for autoconversion in the continuous parameterization could be reduced by almost an order of magnitude using the revised parameterization.
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Weber, Torsten, and Johannes Quaas. "Incorporating the subgrid-scale variability of clouds in the autoconversion parameterization using a PDF-scheme." American Geophysical Union (AGU), 2012. https://ul.qucosa.de/id/qucosa%3A13851.
Full textAbstract:
An investigation of the impact of the subgrid-scale variability of cloud liquid water on the autoconversion process as parameterized in a general circulation model is presented in this paper. For this purpose, a prognostic statistical probability density distribution (PDF) of the subgrid scale variability of cloud water is incorporated in a continuous autoconversion parameterization. Thus, the revised autoconversion rate is calculated by an integral of the autoconversion equation over the PDF of total water
mixing ratio from the saturation vapor mixing ratio to the maximum of total water mixing ratio. An evaluation of the new autoconversion parameterization is carried out by means of one year simulations with the ECHAM5 climate model. The results indicate that the new autoconversion scheme causes an increase of the frequency of occurrence of high autoconversion rates and a decrease of low ones compared to the
original scheme. This expected result is due to the emphasis on areas of high cloud liquid water in the new approach, and the non-linearity of the autoconversion with respect to liquid water mixing ratio. A similar trend as in the autoconversion is observed in the accretion process resulting from the coupling of both processes. As a consequence of the altered autoconversion, large-scale surface precipitation also shows a shift of occurrence from lower to higher rates. The vertically integrated cloud
liquid water estimated by the model shows slight improvements compared to satellite data. Most importantly, the artificial tuning factor for autoconversion in the continuous parameterization could be reduced by almost an order of magnitude using the revised parameterization.
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Chevrier, Solène. "Development of subgrid models for a periodic circulating fluidized bed of binary mixture of particles." Phd thesis, Toulouse, INPT, 2017. http://oatao.univ-toulouse.fr/19905/1/CHEVRIER_Solene.pdf.
Full textAbstract:
Detailed sensitivity numerical studies have shown that the mesh cell-size may have a drastic effect on the modelling of circulating fluidized bed with small particles. Typically, the cell-size must be of the order of few particle diameters to predict accurately the dynamical behaviour of a fluidized bed. Hence, the Euler-Euler numerical simulations of industrial processes are generally performed with grids too coarse to allow the prediction of the local segregation effects. Appropriate modelling, which takes into account the influence of unresolved structures, have been already proposed for monodisperse simulations. In this work, the influence of unresolved structures on a binary mixture of particles is investigated and models are proposed to account for those effect on bidisperse simulations of bidisperse gas-solid fluidized bed. To achieve this goal, Euler-Euler reference simulations are performed with grid refinement up to reach a mesh independent solution. Such kind of numerical simulation is very expensive and is restricted to very simple configurations. In this work, the configuration consists of a 3D periodical circulating fluidized bed, that could represent the established zone of an industrial circulating fluidized bed. In parallel, a filtered approach is developed where the unknown terms, called sub-grid contributions, appear. They correspond to the difference between filtered terms, which are calculated with the reference results then filtered, and resolved contributions, calculated with the filtered fields. Then spatial filters can be applied to reference simulation results to measure each sub-grid contribution appearing in the theoretical filtered approach. A budget analysis is carried out to understand and model the sub-grid term. The analysis of the filtered momentum equation shows that the resolved fluid-particle drag and inter-particle collision are overestimating the momentum transfer effects. The analysis of the budget of the filtered random kinetic energy shows that the resolved production by the mean shear and by the mean particle relative motion are underestimating the filtered ones. Functional models are proposed for the subgrid contributions of the drag and the inter-particle collision.
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Fang, Le. "Applying the Kolmogorov equation to the problem of subgrid modeling for Large-Eddy Simulation of turbulence." Phd thesis, Ecole Centrale de Lyon, 2009. http://tel.archives-ouvertes.fr/tel-00446447.
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The aim of the current work is to investigate a series of new subgrid models by employing the Kolmogorov equation of ltered quantities (KEF), which is an exact relation of turbulence in physical space. Different formulations of KEF are derived, including the forms in velocity eld (homogeneous isotropic turbulence, inhomogeneous anisotropic turbulence, homogeneous shear turbulence, homogeneous rotating turbulence), in scalar turbulence and in magnetohydrodynamic turbulence. The corresponding subgrid models are then formulated, for example: - The multi-scale improvement of CZZS model. - A new anisotropic eddy-viscosity model in homogeneous shear turbulence. - The improved velocity increment model (IVI). - The rapid-slow analysis and model application in inhomogeneous anisotropic scalar turbulence. - The attempt in magnetohydrodynamic (MHD) turbulence. Besides, there are also other important conclusions in this thesis: - The anisotropic effect of mean shear in physical space is analyzed. - Analytical corrections to the scaling of the second-order structure function in isotropic turbulence in introduced. - It is shown that the two-point distance of velocity increment must be much larger than the lter size, in order to satisfy the classical scaling law. Otherwise, the classical scaling law can not be directly applied in subgrid modeling. - A thought-experiment is described to analyse the time-reversibility problem of subgrid models. - A rapid algorithm for Tophat lter operator in discrete eld is introduced.
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Lee, Haksu. "Development and performance analysis of a physically based hydrological model incorporating the effects of subgrid heterogeneity." University of Western Australia. School of Environmental Systems Engineering, 2007. http://theses.library.uwa.edu.au/adt-WU2007.0129.
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[Truncated abstract] The balance equations of mass and momentum, defined at the scale of what has been defined as a Representative Elementary Watershed (REW) has been proposed by Reggiani et al. (1998, 1999). While it has been acknowledged that the REW approach and the associated balance equations can be the basis for the development of a new generation of distributed physically based hydrological models, four building blocks have been identified as necessary to transform the REW approach into, at the very least least, a workable modelling framework beyond the theoretical achievements. These are: 1) the development of reasonable closure relations for the mass exchange fluxes within and between various REW sub-regions that effectively parameterize the effects of sub-REW heterogeneity of climatic and landscape properties, 2) the design of numerical algorithms capable of generating numerical solutions of the REW-scale balance equations composed of a set of coupled ordinary differential and algebraic equations for the number of REWs constituting a study catchment and the sub-regions within the REWs, 3) applications of the resulting numerical model to real catchments to assess its performance in the prediction of any specified hydrological variables, and 4) the assessment of the model reliability through estimation of model predictive uncertainty and parameter uncertainty. This thesis is aimed at making substantial progress in developing each of these building blocks. Chapter 1 presents the background and motivation for the thesis, while Chapter 2 summarizes its main contributions. Chapter 3 presents a description of the closure problem that the REW approach faces, and presents and implements various approaches to develop closure relations needed for the completeness of balance equations of the REW approach. ... In addition, Chapter 4 also shows an initial application of CREW to a small catchment, Susannah Brook in the south-west of Western Australia. Chapter 5 presents the application of CREW to two meso-scale catchments in Australia, namely Collie and Howard Springs, located in contrasting climates. Chapter 6 presents results of the estimation of predictive uncertainty and parameter sensitivity through the application of CREW to two catchments in Australia, namely Susannah Brook and Howard Springs, by using the Generalized Likelihood Uncertainty Estimation (GLUE) methodology. Finally, Chapter 7 presents recommendations for future work for the further advancement of the REW approach. Through these exercises this PhD thesis has successfully transformed the REW-scale coupled balance equations derived by Reggiani et al. (1998, 1999) into a new, well tested numerical model blueprint for the development and implementation of distributed, physically based models applicable at the catchment, or REW scale.
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Fang, Le Bertoglio Jean-Pierre. "Applying the Kolmogorov equation to the problem of subgrid modeling for Large-Eddy Simulation of turbulence." [S.l.] : [s.n.], 2009. http://bibli.ec-lyon.fr/exl-doc/lfang.pdf.
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Foster, Justin. "A priori analysis of subgrid scalar phenomena and mass diffusion vectors in turbulent hydrogen-oxygen flames." Connect to this title online, 2009.
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Kemenov, Konstantin A. "A New Two-Scale Decomposition Approach for Large-Eddy Simulation of Turbulent Flows." Diss., Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/11520.
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A novel computational approach, Two Level Simulation (TLS), was developed based on the explicit reconstruction of the small-scale velocity by solving the small-scale governing equations on the domain with reduced dimension representing a collection of one-dimensional lines
embedded in the three-dimensional flow domain. A coupled system of equations, that is not based on an eddy-viscosity hypothesis, was derived based on the decomposition of flow variables into the large-scale and the small-scale components without introducing the concept of filtering. Simplified treatment of the small-scale equations was proposed based on modeling of the small-scale advective derivatives and the small-scale dissipative terms in the directions orthogonal to the lines. TLS approach was tested to simulate benchmark cases of turbulent flows, including forced isotropic turbulence, mixing layers and well-developed channel flow, and demonstrated good capabilities to capture turbulent flow features using relatively coarse grids.
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Faridhosseini, Alireza. "Evaluation of Summer Rainfall Estimation by Satellite Data using the ANN Model for the GCM Subgrid Distribution." Thesis, The University of Arizona, 1998. http://etd.library.arizona.edu/etd/GetFileServlet?file=file:///data1/pdf/etd/azu_etd_hy0021_m_sip1_w.pdf&type=application/pdf.
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Yano, Jun-Ichi, Jean-François Geleyn, Martin Köller, Dmitrii Mironov, Johannes Quaas, Pedro M. M. Soares, Vaughan T. J. Phillips, et al. "Basic concepts for convection parameterization in weather forecast and climate models." Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-177427.
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The research network “Basic Concepts for Convection Parameterization in Weather Forecast and Climate Models” was organized with European funding (COST Action ES0905) for the period of 2010–2014. Its extensive brainstorming suggests how the
subgrid-scale parameterization problem in atmospheric modeling, especially for convection, can be examined and developed from the point of view of a robust theoretical basis. Our main cautions are current emphasis on massive observational data analyses and process studies. The closure and the entrainment–detrainment problems are identified as the two highest priorities for convection parameterization under the mass–flux formulation. The need for
a drastic change of the current European research culture as concerns policies and funding in order not to further deplete the visions of the European researchers focusing on those basic issues is emphasized.
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Marstorp, Linus. "Modelling of subgrid-scale stress and passive scalar flux in large eddy simulations of wall bounded turbulent flows." Doctoral thesis, KTH, Mekanik, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4809.
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The aim of the thesis is to develop and validate subgrid-scale models that are relevant for large eddy simulations of complex flows including scalar mixing. A stochastic Smagorinsky model with adjustable variance and time scale is developed by adding a stochastic component to the Smagorinsky constant. The stochastic model is shown to provide for backscatter of both kinetic energy and scalar variance without causing numerical instabilities. In addition, new models for the subgrid-scale stress and passive scalar flux are derived from modelled subgrid scale transport equations. These models properly account for the anisotropy of the subgrid scales and have potentials wall bounded flows. The proposed models are validated in wall bounded flows with and without rotation and show potential or significantly improve predictions for such cases.QC 20100826
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Morar, Dejan [Verfasser], and X. [Akademischer Betreuer] Cheng. "Subgrid-scale heat flux modeling for large eddy simulation of turbulent mixed convection / Dejan Morar. Betreuer: X. Cheng." Karlsruhe : KIT-Bibliothek, 2014. http://d-nb.info/1065732139/34.
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Marstorp, Linus. "Modelling of subgrid-scale stress and passive scalar flux in large eddy simulaitons of wall bounded turbulent flows /." Stockholm : Mekanik, Kungliga Tekniska högskolan, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4809.
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Veloudis, Ioannis. "A study of subgrid scale modelling and inflow boundary conditions for large eddy simulation of wall-bounded flows." Thesis, Loughborough University, 2006. https://dspace.lboro.ac.uk/2134/7966.
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The complicated turbulence structures in wall-bounded flows require accurate subgrid scale, SGS, modelling and realistic inlet boundary conditions for Large Eddy Simulation, LES. The present study focused on the investigation and development of transport equation SGS models and on the development of inlet conditions generation algorithms specialised for LES of wall-bounded flows. The investigation of SGS models has been carried out in two stages. In the first stage, models based on resolved scales and models based on subgrid scales were tested on a series of channel flow cases. Among the second group of models, there was a new SGS model whose development was based on the concept of dissipation calculated from the energy spectrum. The results indicated the superiority of the models based on subgrid scales, with the new model providing the most accurate flow field in general. (Continues...).