Optimal large eddy simulation (OLES) is an approach to LES sub-grid modeling that requires multi-point correlation data as input. Until now, this has been obtained by analyzing DNS statistics. In the finite-volume OLES formulation studied here, under the assumption of small-scale homogeneity and isotropy, these correlations can be theoretically determined from Kolmogorov inertial-range theory, small-scale isotropy, along with the quasi-normal approximation. These models are expressed as generalized quadratic and linear finite volume operators that represent the convective momentum flux. These finite volume operators have been analyzed to determine their characteristics as numerical approximation operators and as models of small-scale effects. In addition, the dependence of the model operators on the anisotropy of the grid and on the size of the stencils is analyzed to develop idealized general operators that can be used on general grids. The finite volume turbulence operators developed here will be applicable in a wide range of LES problems. / text

This research explored the use of CFD simulations to study single phase flows through structured packing. Flow rates were chosen to approximate those used in the vapor phase of industrial distillation columns. The results were evaluated against experimental results obtained with the same packing model and packed height. Several novel methods were employed to quickly obtain high validity results. A high-fidelity, digital copy of an actual packing element was created in seven hours through CT scanning. The meshing strategy employed adaptive, polyhedral meshing algorithms which resulted in high quality volume meshes with 80 percent less mesh elements than would be required with traditional tetrahedral meshing. Meshing and computation were performed on the TACC clusters. The permitted meshing with up to 57 million volume cells in less than 30 hours while simulations employing a realizable k-[epsilon] model converged in approximately two days using up to 544 processors. Nitrogen simulation predictions were found to be, on average, 7 percent below experimental measurements with water simulations showing considerably more error (~40%). The error is likely attributable a discrepancy between the simulation and experimental geometries. This discrepancy is due to an oversight in sample preparation and not a flaw in the CT scanning process of geometry creation. The volume of data generated in CFD simulation was found to be very valuable for understanding and benchmarking packing performance. Streamlines and contour plots were used to analyze the variation in performance both locally and throughout the packing stack. Significant variation was observed in flow pattern, velocity distribution, and pressure profiles throughout the column. However, the joint regions were found to be most adverse to column energy efficiency. / text

I investigate mutual fund flows at the individual fund and at the fund family level. At the individual, I use SEC filings to decompose fund flows into inflows and outflows. This decomposition of net flows into its component parts provides a way to examine differences in how search costs and investor learning affect investors who are entering a fund (or adding to their investments) versus those investors who are leaving a fund (or decreasing their investments). I then examine the effect of the existence of an advertisement for the fund on these investors. At the mutual fund family level, I examine how the characteristics and performance of mutual fund families affect the flows to the family as a whole. I then examine the effects of advertising expenditures on flows to the fund family. / text

The flow and stability of co-extruded layers of different polymers in a forced assembly process is studied computationally to determine the extent of the stable process window and the types of instabilities that occur. Recent advances in layer-multiplying co-extrusion of incompatible polymers have made possible the fabrication of multilayered nanostructures with improved barrier, thermal and mechanical behavior. However, existing layering techniques are very sensitive to mismatches in viscosity and elasticity of the co-extruded polymers which often give rise to layer non-uniformity and flow instabilities, such as encapsulation. Simulations of the flows inside the feedblock and the successive multiplier dies of the multi-layering system are used to track the interface and predict instabilities and degrees of encapsulation as a function of process parameters, primarily the flow rates and rheology of the polymers. Encapsulation is found to be negligible in practice in the feedblock even for large viscosity contrasts and differences in elasticity between the two co-extruded polymers. Encapsulation or pinch-off of interfaces is more severe in the multiplier dies when there the rheologies of the polymers differ. A secondary flow due to the second normal stress differences for non-Newtonian fluids is primarily responsible for the encapsulation. A new multiplier design is proposed and simulated. The pressure drop in the proposed design is half that of the current design, which is useful for extruding highly elastic materials. Further, the degree of encapsulation is also reduced. The results of the simulations are validated with experimental measurements of pressure drop and flow visualization provided by research collaborators. / text

Accurate models for the mixing of fuel and oxidizer at small, unresolved flow length scales are critical to the predictive skill of large eddy simulation (LES) of turbulent combustion. Subfilter scalar variance and subfilter scalar dissipation rate are important parameters in combustion modeling approaches based on a conserved scalar, but are prone to numerical and modeling errors due to the nature of practical LES computations. This work examines the errors incurred in these models using a novel method that couples LES scalar modeling with direct numerical simulation (DNS) of homogeneous isotropic turbulence and offers modeling and numerical techniques to address these errors. In the coupled DNS-LES method, DNS velocity fields are evolved simultaneously with LES scalar fields. The filtered DNS velocities are supplied to the LES scalar equations, instead of solving the LES momentum equations. This removes the effect of errors in the filtered scalar evolution from the scalar modeling analysis. Results obtained using the coupled DNS-LES approach, which permits detailed study of physics-related and numerical errors in scalar modeling, show that widely used algebraic dynamic models for subfilter scalar variance lack accuracy due to faulty equilibrium modeling assumptions and sensitivity to numerical error. Transport equation models for variance show superior performance, provided that the scalar dissipation rate model coefficient is set appropriately. For this purpose, a new dynamic approach for nonequilibrium modeling of subfilter scalar dissipation rate is developed and validated through a priori tests in an inhomogeneous jet flow and using the coupled DNS-LES method for assessment of numerical error effects. Explicit filtering is assessed as means to control numerical error in LES scalar modeling and the scalar equations are reformulated to account for the explicit filtering technique. Numerical convergence of the mean subfilter scalar variance prediction with increasing grid resolution is demonstrated. / text

Modifications were made to the turbulent channel flow facility to allow for fully developed rough quasi-2D Poiseuille flow with flow injection through one surface and flow suction through the opposing surface. The combination of roughness and flow injection is designed to be analogous to the flow field over a thermal protection system which produces ablative pyrolysis gases during ablation. It was found that the additional momentum through the surface acted to reduce skin friction to a point below smooth-wall behavior. This effect was less significant with increasing Reynolds number. It was also found that the momentum injection modified the wake region of the flow.

This thesis is an assessment of the dynamics of trade affinities and how they have influenced trade flows in the European continent. The focus is how trade affinities have altered over a time span of four time periods stretching from the 1970s up to today and how these alterations have influenced globalization. A total of 41 countries belonging to the European continent have been selected. Furthermore four variables were selected to represent trade affinities; distance, border, colony, and language. These have been selected as they are generally believed to be static and thus should not change over time. Also, this thesis aims to show the separate influence of each trade affinity as other papers usually estimate trade affinities as one collective variable. By the use of a gravity model 9 variables are tested in order to determine their influence on trade flows. This is done through a regression with a log-log equation where the dependent variable is Export and the affinity variables are estimated as dummy variables. The regression is divided into four time periods in order to more easily determine how the trade affinity variables have altered in influence on trade flows in Europe. The first time period represent an average of the time period 1974-1976, the second 1984-1986, the third 1994-1996 and the fourth 2004-2006. The regression results illustrate that the majority of the selected variables are significant but most importantly that the trade affinity variables are proven to have altered over the time periods. The performance of a Wald estimation gives an indication that trade affinities are in fact dynamic although the results are not entirely significant for all variables. Based on the results, it is apparent that trade affinities still have a significant effect on trade flows in the European continent. Although, their effects have altered to become less significant in some cases while others have become stronger they all jointly share the attributes of affecting trade. These alterations can in turn be interpreted as dependent on the globalization process of the European continent. As globalization has progressed some affinities have decreased in influence while others have regained new importance.

The increase in the availability and power of computational resources over the last fifteen years has contributed to the development of many different types of numerical optimization methods and created a large area of research focussed on numerical aerodynamic shape optimization and, more recently, high-fidelity multidisciplinary optimization. Numerical optimization provides dramatic savings when designing new aerodynamic configurations, as it allows the designer to focus more on the development of a well-posed design problem rather than on performing an exhaustive search of the design space via the traditional cut-and-try approach, which is expensive and time-consuming. It also reduces the dependence on the designer’s experience and intuition, which can potentially lead to more optimal designs. Numerical optimization methods are particularly attractive when designing novel, unconventional aircraft for which the designer has no pre-existing studies or experiences from which to draw; these methods have the potential to discover new designs that might never have been arrived at without optimization. This work presents an extension of an efficient gradient-based numerical aerodynamic shape optimization algorithm to enable optimization in turbulent flow. The algorithm includes an integrated geometry parameterization and mesh movement scheme, an efficient parallel Newton-Krylov-Schur algorithm for solving the Reynolds-Averaged Navier-Stokes (RANS) equations, which are fully coupled with the one-equation Spalart-Allmaras turbulence model, and a discrete-adjoint gradient evaluation. In order to develop an efficient methodology for optimization in turbulent flows, the viscous and turbulent terms in the ii governing equations were linearized by hand. Additionally, a set of mesh refinement tools was introduced in order to obtain both an acceptable control volume mesh and a sufficiently refined computational mesh from an initial coarse mesh. A series of drag minimization studies was carried out which show that the algorithm is able to maintain robustness in the mesh movement and flow analysis in the presence of large shape changes, an important requirement for performing exploratory optimizations aiming to discover novel configurations and for multidisciplinary optimization. Additionally, the algorithm is able to find incremental improvements when given well-designed initial planar and nonplanar geometries. A comparison of Euler-based and RANS-based optimizations highlights the importance of considering viscous and turbulent effects. A multi-point optimization demonstrates that the algorithm is able to address practical aerodynamic design problems.

The increase in the availability and power of computational resources over the last fifteen years has contributed to the development of many different types of numerical optimization methods and created a large area of research focussed on numerical aerodynamic shape optimization and, more recently, high-fidelity multidisciplinary optimization. Numerical optimization provides dramatic savings when designing new aerodynamic configurations, as it allows the designer to focus more on the development of a well-posed design problem rather than on performing an exhaustive search of the design space via the traditional cut-and-try approach, which is expensive and time-consuming. It also reduces the dependence on the designer’s experience and intuition, which can potentially lead to more optimal designs. Numerical optimization methods are particularly attractive when designing novel, unconventional aircraft for which the designer has no pre-existing studies or experiences from which to draw; these methods have the potential to discover new designs that might never have been arrived at without optimization. This work presents an extension of an efficient gradient-based numerical aerodynamic shape optimization algorithm to enable optimization in turbulent flow. The algorithm includes an integrated geometry parameterization and mesh movement scheme, an efficient parallel Newton-Krylov-Schur algorithm for solving the Reynolds-Averaged Navier-Stokes (RANS) equations, which are fully coupled with the one-equation Spalart-Allmaras turbulence model, and a discrete-adjoint gradient evaluation. In order to develop an efficient methodology for optimization in turbulent flows, the viscous and turbulent terms in the ii governing equations were linearized by hand. Additionally, a set of mesh refinement tools was introduced in order to obtain both an acceptable control volume mesh and a sufficiently refined computational mesh from an initial coarse mesh. A series of drag minimization studies was carried out which show that the algorithm is able to maintain robustness in the mesh movement and flow analysis in the presence of large shape changes, an important requirement for performing exploratory optimizations aiming to discover novel configurations and for multidisciplinary optimization. Additionally, the algorithm is able to find incremental improvements when given well-designed initial planar and nonplanar geometries. A comparison of Euler-based and RANS-based optimizations highlights the importance of considering viscous and turbulent effects. A multi-point optimization demonstrates that the algorithm is able to address practical aerodynamic design problems.

Pasaulio ekonomikos augimas, spartėjantis globalizacijos procesas, technologijų pažanga didina atstumus tarp žaliavų gavimo, gamybos ir pagamintų prekių naudojimo taškų. Gausėjant prekybinių ryšių bei plečiantis jų geografijai, didėja reikalavimai transporto ir logistikos paslaugas teikiančiam sektoriui. Regionų ekonominis augimas priklauso nuo to, kaip transporto sistema geba patenkinti žaliavų tiekėjų, gamintojų, prekybininkų ir vartotojų logistikos poreikius laiko, greičio, saugumo, sąnaudų prasmėmis. Transporto srautai ilgainiui prisitaiko prie kintamų regiono logistikos poreikių, tačiau dėl transporto sistemos inertiškumo tam sugaištama laiko. Lietuvoje reikšminga dalis bendrojo nacionalinio produkto sukuriama transporto ir logistikos sektoriuje, kadangi šalis yra stambių tranzitinių krovinių srautų kryžkelėje. Lietuvai tapus Europos Sąjungos nare, atsiveria tarptautinės prekybos augimo galimybes, Lietuva tampa Europos Sąjungos buferine zona prekybai su Rytų bloko šalimis, taigi teisinga Lietuvos transporto sistemos plėtros strategija gali suteikti Lietuvai didžiulį ekonominį potencialą, bendrojo vidaus produkto ir darbo vietų skaičiaus augimo perspektyvas. Transporto srautams užtikrinti būtina transporto infrastruktūra, kurios plėtrai yra labai svarbu nustatyti potencialius krovinių srautus. Transporto infrastruktūra labai imli kapitalui, todėl jos plėtros kryptys turi tiksliai atitikti logistikos poreikius, priešingu atveju milžiniškos investicijos nepateisinamos... [to full text] / Relevance of the dissertation is determined by the object of research – the influence of logistical factors on transport flows distribution. The growth of world economics, business globalization, progress in technology skills extends the distances between geographical points of raw materials resources, manufacturers and consumers. Due to the membership in the European Union (EU) Lithuania has got new opportunities for international trade growth, and all the Eastern Baltic countries have become the buffer region for the EU trading with the countries of the Eastern Europe and Asia. A proper transport policy and infrastructure development would increase significantly the GNP in warehousing, transport and distribution sectors. Forecasting of potential transport flows according to logistical requirements of freight suppliers is most important for transport network optimization. Scientific problem. Contemporary transport engineering theory approaches the peculiarities of transport flows formation too narrowly, only as an analysis of internal factors determining freight flows. There is no analysis of external factors. Many researchers assume that transport flows are determined only by the existing transport network and its characteristics. Other researchers consider transport flows as a result of logistic elements only. The estimating of internal and external logistical factors provides a possibility to forecast the transport flows. Aim of the research is to create a model of... [to full text]