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  • Articles  (28)
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  • 1
    Electronic Resource
    Electronic Resource
    Kinetics of the Electrons in Striations of Spherical Glow Discharges (2000)
    Springer
    Plasma chemistry and plasma processing 20 (2000), S. 87-110 
    Details
    ISSN: 1572-8986
    Keywords: striations ; nitrogen ; spherical discharge ; spatially inhomogeneous Boltzmann equation ; electron velocity distribution function ; dc glow discharge
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract Recent observations of spherical striations in large-volume nitrogen dcdischarges with a central anode have stimulated investigations of thenonlocal electron kinetics in these striations by solving the spatiallyinhomogeneous Boltzmann equation adapted to spherical geometry. Becausethe radial course of the electric potential is largely unknown in thisdischarge, different models concerning its radial course have been developedand used. These models are based on the measured radii of the striationsand the assumption that the potential drop between successive striationsdoes not change. As a consequence, with decreasing distance between thestriations the electric field strongly increases toward the centralanode. It has been found that spherical striations are only obtained ifthe electric field is strongly modulated. In this case, a highly nonlocalbehavior of the velocity distribution function and strongly modulatedradial courses of the macroscopic quantities have been obtained.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006973911319
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  • 2
    Electronic Resource
    Electronic Resource
    Numerical Simulation of Ferrofluid Flow for Subsurface Environmental Engineering Applications (2000)
    Springer
    Transport in porous media 38 (2000), S. 319-344 
    Details
    ISSN: 1573-1634
    Keywords: ferrofluids ; magnetic fluids ; subsurface barrier verification ; magneto pressure ; numerical simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract Ferrofluids are suspensions of magnetic particles of diameter approximately 10 nm stabilized by surfactants in carrier liquids. The large magnetic susceptibility of ferrofluids allows the mobilization of ferrofluid through permeable rock and soil by the application of strong external magnetic fields. We have developed simulation capabilities for both miscible and immiscible conceptualizations of ferrofluid flow through porous media in response to magnetic forces arising from the magnetic field of a rectangular permanent magnet. The flow of ferrofluid is caused by the magnetization of the particles and their attraction toward a magnet, regardless of the orientation of the magnet. The steps involved in calculating the flow of ferrofluid are (1) calculation of the external magnetic field, (2) calculation of the gradient of the external magnetic field, (3) calculation of the magnetization of the ferrofluid, and (4) assembly of the magnetic body force term and addition of this term to the standard pressure gradient and gravity force terms. We compare numerical simulations to laboratory measurements of the magnetic field, fluid pressures, and the two‐dimensional flow of ferrofluid to demonstrate the applicability of the methods coded in the numerical simulators. We present an example of the use of the simulator for a field‐scale application of ferrofluids for barrier verification.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006611702281
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  • 3
    Electronic Resource
    Electronic Resource
    Numerical Simulations for Saltwater Intrusion by the Mixed Hybrid Finite Element Method and Discontinuous Finite Element Method (2000)
    Springer
    Transport in porous media 40 (2000), S. 171-200 
    Details
    ISSN: 1573-1634
    Keywords: flow and mass transport ; density driven flow ; numerical simulation ; Henry's problem
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract The proposed numerical code simulates the displacement of two miscible fluids through a saturated porous medium (2D configuration). Coupling between flow and transport is carried out by an equation of state. In the mixing zone, the density is assumed to vary as a function of concentration. The model uses a combination of the mixed hybrid finite element method and the discontinuous finite element method. Applied in its classical development, the mixed hybrid finite element method leads to a non-conservative formulation of the mass balance equation. However, one of the main reasons for using this technique is the ability to conserve mass cell-by-cell. Consequently, a new formulation that makes it possible to hold the conservative form of the continuity equation and so preserve the mass cell-wise is proposed. Although the pertinence of these approaches could have also been tested on other standard benchmarks, e.g., Elder's problem or salt dome problem, we have voluntarily limited ourselves to Henry's problem (1964). This choice was dictated by the possibility of a comparison with a semi-analytical solution. Contrary to previous numerical results, the comparison is made for the whole mixing zone. The very good agreement between our results and the semi-analytical solution shows the robustness and the efficiency of this approach for the seawater intrusion problems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006626230029
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  • 4
    Electronic Resource
    Electronic Resource
    Thermodynamic Automaton Simulations of Fluid Flow and Diffusion in Porous Media (1999)
    Springer
    Transport in porous media 35 (1999), S. 37-47 
    Details
    ISSN: 1573-1634
    Keywords: automata ; diffusion in porous media ; numerical simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract A thermodynamic automaton model of fluid flow in porous media is presented. The model is a nonrelativistic version of a Lorentz invariant lattice gas model constructed by Udey et al. (1998). In the previous model it was shown that the energy momentum tensor and the relativistic Boltzman equation can be rigorously derived from the collision and propagation rules. In the present paper we demonstrate that this nonrelativistic model can be used to accurately simulate well known results involving single phase flow and diffusion in porous media. The simulation results show that (1) one-phase flow simulations in porous media are consistent with Darcy's law; (2) the apparent diffusion coefficient decreases with a decrease in permeability; (3) small scale heterogeneity does not affect diffusion significantly in the cases considered.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006528621365
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  • 5
    Electronic Resource
    Electronic Resource
    Modeling Variable Density Flow and Solute Transport in Porous Medium: 2. Re‐Evaluation of the Salt Dome Flow Problem (1999)
    Springer
    Transport in porous media 35 (1999), S. 375-394 
    Details
    ISSN: 1573-1634
    Keywords: groundwater ; density driven flow ; numerical simulation ; salt dome.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract Case 5, Level 1 of the international HYDROCOIN groundwater flow modeling project is an example of idealized flow over a salt dome. The groundwater flow is strongly coupled to solute transport since density variations in this example are large (20%). Several independent teams simulated this problem using different models. Results obtained by different codes can be contradictory. We develop a new numerical model based on the mixed hybrid finite elements approximation for flow, which provides a good approximation of the velocity, and the discontinuous finite elements approximation to solve the advection equation, which gives a good approximation of concentration even when the dispersion tensor is very small. We use the new numerical model to simulate the salt dome flow problem. In this paper we study the effect of molecular diffusion and we compare linear and non‐linear dispersion equations. We show the importance of the discretization of the boundary condition on the extent of recirculation and the final salt distribution. We study also the salt dome flow problem with a more realistic dispersion (very small dispersion tensor). Our results are different to prior works with regard to the magnitude of recirculation and the final concentration distribution. In all cases, we obtain recirculation in the lower part of the domain, even for only dispersive fluxes at the boundary. When the dispersion tensor becomes very small, the magnitude of recirculation is small. Swept forward displacement could be reproduced by using finite difference method to compute the dispersive fluxes instead of mixed hybrid finite elements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006504326005
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  • 6
    Electronic Resource
    Electronic Resource
    Modeling Variable Density Flow and Solute Transport in Porous Medium: 1. Numerical Model and Verification (1999)
    Springer
    Transport in porous media 35 (1999), S. 345-373 
    Details
    ISSN: 1573-1634
    Keywords: groundwater ; density driven flow ; numerical simulation ; mixed finite elements ; discontinuous finite elements ; Elder problem.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract A new numerical model for the resolution of density coupled flow and transport in porous media is presented. The model is based on the mixed hybrid finite elements (MHFE) and discontinuous finite elements (DFE) methods. MHFE is used to solve the flow equation and the dispersive part of the transport equation. This method is more accurate in the calculation of velocities and ensures continuity of fluxes from one element to the adjacent one. DFE is used to solve the convective part of the transport equation. Combined with a slope limiting procedure, it avoids numerical instabilities and creates a very limited numerical dispersion, even for high grid Peclet number. Flow and transport equations are coupled by a standard iterative scheme. Residual based criterion is used to stop the iterations. Simulations of an unstable equilibrium show the effects of the criteria used to stop the iterations and the stopping criterion in the solver. The effects are more important for finer grids than for coarser grids. The numerical model is verified by the simulation of standard benchmarks: the Henry and the Elder test cases. A good agreement is found between the revised semi‐analytical Henry solution and the numerical solution. The Elder test case was also studied. The simulations were similar to those presented in previous works but with significantly less unknowns (i.e. coarser grids). These results show the efficiency of the used numerical schemes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006564309167
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  • 7
    Electronic Resource
    Electronic Resource
    Numerical Simulation of Differential Systems Displaying Rapidly Oscillating Solutions (1998)
    Springer
    Journal of engineering mathematics 34 (1998), S. 201-214 
    Details
    ISSN: 1573-2703
    Keywords: stiff differential equations ; oscillatory solutions ; numerical simulation ; systems of equations.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Technology
    Notes: Abstract The aim of this article is to describe an approximation procedure for stiff differential equations producing highly oscillating solutions. For the sake of simplicity the presentation is restricted to ordinary differential equations. The procedure and the general approximation results are presented. Then the general results are applied to a number of simple explicit systems, for which numerical simulations of the exact and approximate solutions are performed and compared.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004337014272
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  • 8
    Electronic Resource
    Electronic Resource
    On Vaporizing Water Flow in Hot Sub-Vertical Rock Fractures (1997)
    Springer
    Transport in porous media 28 (1997), S. 335-372 
    Details
    ISSN: 1573-1634
    Keywords: heterogeneous fractures ; preferential flow paths ; two-phase flow ; boiling and condensation ; vapor-dominated geothermal reservoirs ; nuclear waste disposal ; numerical simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract Water injection into unsaturated fractured rock at above-boiling temperatures gives rise to complex fluid flow and heat transfer processes. Examples include water injection into depleted vapor-dominated geothermal reservoirs, and emplacement of heat-generating nuclear wastes in unsaturated fractured rock. We conceptualize fractures as two-dimensional heterogeneous porous media, and use geostatistical techniques to generate synthetic permeability distributions in the fracture plane. Water flow in hot high-angle fractures is simulated numerically, taking into account the combined action of gravity, capillary, and pressure forces, and conductive heat transfer from the wall rocks which gives rise to strong vaporization. In heterogeneous fractures boiling plumes are found to have dendritic shapes, and to be subject to strong lateral flow effects. Fractures with spatially-averaged homogeneous permeabilities tend to give poor approximations for vaporization behavior and liquid migration patterns. Depending on water flow rates, rock temperature, and fracture permeability, liquid water can migrate considerable distances through fractured rock that is at above-boiling temperatures and be only partially vaporized.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006570702193
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  • 9
    Electronic Resource
    Electronic Resource
    Comparison of simulation results and field data on currents and density in Tokyo Bay (1996)
    Springer
    Journal of marine science and technology 1 (1996), S. 94-104 
    Details
    ISSN: 1437-8213
    Keywords: numerical simulation ; field data ; multilevel model ; Tokyo Bay
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract A multilevel model was applied to the calculation of permanent current and density variation in Tokyo Bay, and the change of the state of stratification and the accompanying current field was simulated. In the numerical simulation, the observed field data such as wind conditions and atmospheric temperature were used as input to the calculation, and the results were compared with the observed values of currents, salinity, and sea temperature. Comparison of simulation results and observed data revealed that the numerical simulation could describe well the current and density field governed by wind under stratified conditions. In particular, the long-term variations of the vertical structure of salinity and temperature from summer to autumn could be predicted qualitatively, as could the long-term variations of the vertical structure of salinity and temperature from summer to autumn. Additionally, the effects of boundary conditions on the results of numerical simulations were examined. As a result, it was clarified that the simulation results of salinity stratification were strongly affected by the boundary conditions such as river discharge and the vertical structure of salinity at the open boundary adjacent to the outer ocean.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02391165
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  • 10
    Electronic Resource
    Electronic Resource
    Slow drift damping force acting on a horizontal cylinder (1996)
    Springer
    Journal of marine science and technology 1 (1996), S. 105-113 
    Details
    ISSN: 1437-8213
    Keywords: slow drift viscous damping ; wave effect ; horizontal cylinder ; model experiment ; numerical simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract The hydrodynamic forces acting on a circular cylinder and a rectangular cylinder undergoing slow drift oscillation in regular waves were investigated experimentally and numerically. Forced oscillation tests with low frequency and large amplitude in regular waves and forced two-harmonic oscillation with combined low and high frequencies were carried out in the experimental study. In the numerical study a finite-difference method was used to simulate viscous flow around a two-dimensional oscillating cylinder. The results of experiments showed that a horizontal rectangular cylinder oscillating slowly in waves has much higher damping coefficients than one oscillating in two-harmonic mode, while the numerical study indicated that such differences in the damping coefficient arise partly from the different effects of one-direction harmonic flow and rotating flow on the vortex shedding caused by the slow drift oscillation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02391166
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  • 11
    Electronic Resource
    Electronic Resource
    The behavior of titanium, stainless steel, and copper-nickel alloys as plasma torch cathodes (1996)
    Springer
    Plasma chemistry and plasma processing 16 (1996), S. 577-603 
    Details
    ISSN: 1572-8986
    Keywords: Cathode erosion ; electrode materials ; argon ; nitrogen ; hydrogen
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract Cathode erosion continues to be a problem hindering the widespread application of plasma technology. In this work, cathode erosion was studied on titanium, stainless steel 314, copper-nickel 10% and 30%, and copper 122 for magnetically rotated arcs operating in argon, nitrogen, and argon/hydrogen mixtures at a constant magnetic flux density of 0.1 T Titanium and stainless steel gave very low erosion rates in argon (0.2 and 0.3, μg/C respectively). Cupronickels were shown to be suitable for nitrogen and hydrogen plasmas. The slope of hydrogen solubility versus temperature in the cathode material was found to be important in determining hydrogen plasma erosion characteristics. When the plasma gas has a high solubility in the cathode material, or can react with the cathode, a negative erosion rate may result. When gas solubility in the cathode is low, oxide stability and mode of electron emission may govern the erosion rate. A high gas solubility in the cathode material, as with hydrogen, can result in mechanical erosion due to micro-explosions near the cathode surface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01447010
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  • 12
    Electronic Resource
    Electronic Resource
    Upscaling permeability: Error analysis for renormalization (1996)
    Springer
    Transport in porous media 23 (1996), S. 337-354 
    Details
    ISSN: 1573-1634
    Keywords: numerical simulation ; upscaling ; renormalisation ; error analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract In this paper we briefly discuss the background to the problems of finding effective flow properties when moving from a detailed representation of reservoir geology to a coarse gridded model required for reservoir performance simulation. The basic requirements for the upscaled properties are also discussed. We then consider one technique, renormalization, that in recent years has shown promise as an accurate, yet fast, method. The mathematical background of the renormalization approach is examined. A rigorous formalism is developed that allows an explicit calculation of the error terms to be made. In a very simple case use of the correction terms is shown to produce a dramatic improvement in accuracy of the method.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00167102
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  • 13
    Electronic Resource
    Electronic Resource
    Influence of capillary pressure, adsorption and dispersion on chemical flood transport phenomena (1996)
    Springer
    Transport in porous media 24 (1996), S. 275-296 
    Details
    ISSN: 1573-1634
    Keywords: chemical flooding ; ternary ; immiscible ; surfactant ; numerical simulation ; interfacial tension ; phase behavior ; miscibility ; capillarity ; numerical grid ; adsorption ; dispersion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract This is the second of two joint papers which study the influence of several physical properties on the transport phenomena in chemical flooding. To that aim, we use a previously reported ternary two-phase model into which representative physical properties have been incorporated as concentration-dependent functions. Physical properties such as phase behavior, interfacial tensions, residual saturations, relative permeabilities, phase viscosities and wettability have been analyzed in the first paper. In this paper, we discuss the influence of capillary pressure, adsorption of the chemical component onto the rock and dispersion. Although arising from different phenomenological sources, these transport mechanisms show some similar effects on concentration profiles and on oil recovery. They are studied for systems with different phase behavior. A numerical analysis is also presented in order to determine the relevance of the number of grid blocks taken in the discretization of the differential equations. This numerical analysis provides useful guidelines for the selection of the appropriate numerical grid in each type of displacement.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00154094
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  • 14
    Electronic Resource
    Electronic Resource
    Moisture transport in initially fully saturated concrete during drying (1996)
    Springer
    Transport in porous media 24 (1996), S. 81-106 
    Details
    ISSN: 1573-1634
    Keywords: concrete ; drying ; moisture content distribution ; gravimetric method ; numerical simulation ; Darcy flow ; heat and mass transport
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract Moisture content changes during drying were investigated in the present work. Particular emphasis was placed on the initial stage of drying of saturated concrete, where moisture contents are high. For this stage of drying, experimental data are lacking, and no comprehensive theory exists to describe it. The present investigation was performed experimentally and numerically for drying of cylinders with one exposed end, made of normal weight and lightweight concrete with varying water to cement ratio (w/c). The gravimetric technique was employed to obtain the spatial distribution of moisture content. The experimental results obtained indicate that drying of concrete becomes diffusion controlled when the average moisture content decreases below 70 to 80% of the initial saturation. Typical drying rates are in the order of magnitude of 0.18 kg/day/m2 and 0.02 kg/day/m2 for the first and the second stage of drying, respectively. The lightweight concrete cylinders as compared to those made of normal weight concrete exhibited higher levels of moisture content throughout the process. At high w/c ratios, the moisture profiles for both types of cylinders, as expected, show steeper changes with time. Large, constant drying rates were observed both experimentally and numerically in the beginning of the drying. The numerical model developed is based on a generalized mathematical formulation for mass and heat transfer in porous media, and its predictions are in agreement with the experimental data within the uncertainty range of the input data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00175604
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  • 15
    Electronic Resource
    Electronic Resource
    Influence of phase behavior on chemical flood transport phenomena (1996)
    Springer
    Transport in porous media 24 (1996), S. 247-273 
    Details
    ISSN: 1573-1634
    Keywords: chemical flooding ; ternary ; immiscible ; surfactant ; numerical simulation ; wettability ; interfacial tension ; mobility control ; phase behavior ; miscibility
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract A one-dimensional ternary two-phase simulator has been extended to include improved physical properties. These physical properties - such as phase behavior, interfacial tension, residual saturations, relative permeabilities, phase viscosities, wettability, capillary pressure, adsorption and dispersion - are modeled as concentration dependent functions. Their functionality completely controls the chemical flood transport phenomena. In this paper, the influence of phase behavior, interfacial tension reduction, mobility control and wettability alteration on chemical flooding are analyzed. In a subsequent paper the influence of capillary pressure, adsorption, and physical and numerical dispersion will be presented. The main application of the simulator here presented is to describe enhanced oil recovery processes. It may also be applied to describe oil spill cleaning and groundwater contamination.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00154093
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  • 16
    Electronic Resource
    Electronic Resource
    Study of the dynamic and static behavior of de vortex plasma torches: Part II: Well-tye cathode (1995)
    Springer
    Plasma chemistry and plasma processing 15 (1995), S. 257-277 
    Details
    ISSN: 1572-8986
    Keywords: Vortex plasma torch ; arc characteristic ; dimensionless analysis ; electrical measurements ; acoustical measurements ; optical measurements ; signal treatment ; numerical simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract This work was devoted to the study of the dynamic and static behavior of de vortex plasma torch with a well-type cathode (power level below 100 kW). The dynamic behavior of the torch was characterized by the fulctuations of arc voltage and current, plasma jet radiation, and acoustic pressure. Characteristic frequencies of the arc root movement inside the torch were observed. By numerical simulation (with the numerical codeMelodie, it was shown that the position of the erosion diameter) of the axial velocity along the cathode channel near the wall. The static behavior of the torch was inverstigated for different cathode designs. The variations of voltage U with arc current I, gas flow rate G nature of the gas and cathode design were represented by semiempirical relationships established between dimensionless numbers. By dimensional analysis, the behavior of this torch was compared with that of two powerful torches: the Aerospatiale and the Plasma Energy Corporation torches.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01459699
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  • 17
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    Transport coefficients of air, argon-air, nitrogen-air, and oxygen-air plasmas (1995)
    Springer
    Plasma chemistry and plasma processing 15 (1995), S. 279-307 
    Details
    ISSN: 1572-8986
    Keywords: Transport coefficients ; transport properties ; viscosity ; thermal conductivity ; electrical conductivity ; diffusion coefficient ; Chapman-Etskog method ; air ; argon ; nitrogen ; oxygen ; plasma
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract Calculated values of the viscosity, thermal conductivity and electrical conductivity of air and mixtures of air and argon, air and nitrogen, and air and oxygen at high temperatures are presented. In addition, combined ordinary, pressure, and thermal diffusion coefficients are given for the gas mixtures. The calculations, which assione local thermodynamic equilibrium, are performed for atmospheric pressure plasmas in the temperature range from 300 to 30,000 K. The results for air plasmas are compared with those of published theoretical and experimental studies. Significant discrepancies are found with the other theoretical studies; these are attributed to differences in the collision integrals used in calculating the transport coefficients. A number of the collision integrals used here are significantly more accurate than values used previously, resulting in more reliable values of the transport coefficients.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01459700
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  • 18
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    Transport coefficients of argon, nitrogen, oxygen, argon-nitrogen, and argon-oxygen plasmas (1994)
    Springer
    Plasma chemistry and plasma processing 14 (1994), S. 451-490 
    Details
    ISSN: 1572-8986
    Keywords: Transport coefficients ; transport properties ; viscosity ; thermal conductivity ; electrical conductivity ; diffusion coefficient ; Chapman Enskog method ; argon ; nitrogen ; oxygen ; plasma
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract Calculated values of the viscosity, thermal conductivity, and electrical conductivity of argon, nitrogen, and oxygen plasmas, and mixtures of argon anti nitrogen and of argon anti oxygen, are presented. In addition, combined ordinary, pressure, and thermal diffusion coefficients are given for the gas mixtures. These three combined diffusion coefficients fully describe di fusion of the two gases, irrespective of their degree of dissociation or ionizati on. The calculations, which assume local thermodynamic equilibrium, are performed! for atmospheric-pressure plasmas in the temperature range /torn 300 to 30,000 K. A number of the collision integrals used in calculating the transport coefficients are significantly more accurate than values used in previous theoretical studies, resulting in more reliable values of the transport coefficients. The results are compared with those of published theoretical and experimental studies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01570207
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  • 19
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    The use of standard deviation and skewness for estimating apparent permeability in a two-dimensional, heterogeneous medium (1994)
    Springer
    Transport in porous media 15 (1994), S. 1-14 
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    ISSN: 1573-1634
    Keywords: Apparent permeability ; heterogeneity ; numerical simulation ; probability density function ; skewness ; standard deviation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract In this theoretical study, characteristic or effective permeabilities (referred to as ‘apparent permeability’) of a radial/parallel flow system in a heterogeneous medium are calculated by the Monte Carlo method and the finite element method. The permeability distribution in the radial and parallel flow systems are not the same, as going from Cartesian to cylindrical coordinates changes the probability measure. The Bernoulli trials, the normal distribution or the log-normal distribution, is assumed to be the probability density function of permeability. The results are summarized as follows: (1) when the skewness of the distribution function is equal to zero or nearly equal to zero (that is, when the permeability distribution is regarded to be symmetric), the apparent permeability depends on the standard deviation, but not on the kind of distribution function, (2) when the skewness is not equal to zero, the apparent permeability depends not only on the standard deviation, but also on the skewness, (3) the above facts appeared in the radial and the parallel flow systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01046155
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  • 20
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    A geometrical model for numerical simulation of capillary imbibition in sedimentary rocks (1993)
    Springer
    Transport in porous media 12 (1993), S. 125-141 
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    ISSN: 1573-1634
    Keywords: Capillary imbibition kinetics ; tube model ; spherical pore shape ; numerical simulation ; sedimentary rocks ; specific surface area ; surface roughness
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract The cylindrical model is discussed and a new tube model is proposed to describe capillary imbibition kinetics in porous sedimentary rocks. The tube consists of a periodic succession of a single hollow spherical element of which the geometry is defined by the sphere radius and the sphere access radius. These two parameters are estimated experimentally for four rock types from their specific surface areas. Introducing those parameters in the model capillary imbibition kinetics, parameters are calculated and compared with the experimental ones. A direct relation between imbibition kinetics and specific surface area has been pointed out.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00616976
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  • 21
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    Modelling fluid flow in cross-bedded sections (1993)
    Springer
    Transport in porous media 12 (1993), S. 143-159 
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    ISSN: 1573-1634
    Keywords: Heterogeneity ; layers ; displacement ; numerical simulation ; flow in porous media ; dispersion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract Beadpack experiments and numerical simulations have been carried out to study flow displacements, effluent profiles and streamline patterns for layered systems with flow not parallel to the layers. The effects of layer thickness, permeability contrast, angle of layer to flow direction, mobility ratio and flood rate have been examined. Each of these parameters influence the displacement profiles, and disperse the flood front. Such real effects must be considered when subsuming reservoir heterogeneities in average reservoir parameters in simulation studies, or interpreting core tests.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00616977
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    Upscaling of conductivity of heterogeneous formations: General approach and application to isotropic media (1993)
    Springer
    Transport in porous media 12 (1993), S. 161-183 
    Details
    ISSN: 1573-1634
    Keywords: Heterogeneous porous media ; homogenization ; upscaling ; numerical simulation ; stochastic modeling ; effective conductivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract The numerical simulation of flow through heterogeneous formations requires the assignment of the conductivity value to each numerical block. The conductivity is subjected to uncertainty and is modeled as a stationary random space function. In this study a methodology is proposed to relate the statistical moments of the block conductivity to the given moments of the continuously distributed conductivity and to the size of the numerical blocks. After formulating the necessary conditions to be satisfied by the flow in the upscaled medium, it is found that they are obeyed if the mean and the two-point covariance of the space averaged energy disspation function over numerical elements in the two media, of point value and of upscaled conductivity, are identical. This general approach leads to a systematic upscaling procedure for uniform average flow in an unbounded domain. It yields the statistical moments of upscaled logconductivity that depend only on those of the original one and on the size and shape of the numerical elements. The approach is applied to formations of isotropic heterogeneity and to isotropic partition elements. After a general discussion based on dimensional analysis, the procedure is illustrated by using a first-order approximation in the logconductivity variance. The upscaled logconductivity moments (mean, two-point covariance) are computed for two and three dimensional flows, isotropic heterogeneous media and elements of circular or spherical shape. The asymptotic cases of elements of small size, which preserve the point value conductivity structure on one hand, and of large blocks for which the medium can be replaced by one of deterministic effective properties, on the other hand, are analyzed in detail. The results can be used in order to generate the conductivity of numerical elements in Monte Carlo simulations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00616978
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  • 23
    Electronic Resource
    Electronic Resource
    Synthesis of aluminum nitride in transferred arc plasma furnaces (1993)
    Springer
    Plasma chemistry and plasma processing 13 (1993), S. 613-632 
    Details
    ISSN: 1572-8986
    Keywords: Aluminum nitride ; aluminum ; nitrogen ; hydrogen ; ammonia ; thermal plasma ; transferred plasma ; emission spectroscopy ; sintering ; ultrafine powder ; nanophase ; composite
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract Ultrafine particles of aluminum tnitride (AIN) arc produced by a transferred an plasma. Two devices are used: a transferred arc plasma on aluminum natal in nitrogen or nitrogenlammonia atmospheres, and a item concept of transferred arc plasma when, DC anode and cathode ares are coupled together above an alumintun melt. Equilibrium chemical compositions mere calculated. The temperature distributions in the plasma are measured hr emission spectroscopy Flit, powder, made from 99.8%, aluminum ingot, it as analyzed and confirmed to be 99.3%, of hexagonal phase aluminum nitride. In othertests, from 99.99% aluminum ingot, a translucent AIN vinter was obtained. The densification behavior was assessed by hot pressing and by pressureless sintering, with and without additives. The thermal conductivities are given.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01570134
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  • 24
    Electronic Resource
    Electronic Resource
    Numerical simulation and homogenization of two-phase flow in heterogeneous porous media (1991)
    Springer
    Transport in porous media 6 (1991), S. 519-547 
    Details
    ISSN: 1573-1634
    Keywords: Heterogeneous porous media ; two-phase flow ; numerical simulation ; finite element method
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract A mathematically rigorous method of homogenization is presented and used to analyze the equivalent behavior of transient flow of two incompressible fluids through heterogeneous media. Asymptotic expansions and H-convergence lead to the definition of a global or effective model of an equivalent homogeneous reservoir. Numerical computations to obtain the homogenized coefficients of the entire reservoir have been carried out via a finite element method. Numerical experiments involving the simulation of incompressible two-phase flow have been performed for each heterogeneous medium and for the homogenized medium as well as for other averaging methods. The results of the simulations are compared in terms of the transient saturation contours, production curves, and pressure distributions. Results obtained from the simulations with the homogenization method presented show good agreement with the heterogeneous simulations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00137848
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  • 25
    Electronic Resource
    Electronic Resource
    Simulation of multiphase flows in porous media (1991)
    Springer
    Transport in porous media 6 (1991), S. 479-499 
    Details
    ISSN: 1573-1634
    Keywords: Multiphase flow ; numerical simulation ; viscous fingering
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract The ability to numerically simulate single phase and multiphase flow of fluids in porous media is extremely important in developing an understanding of the complex phenomena governing the flow. The flow is complicated by the presence of heterogeneities in the reservoir and by phenomena such as diffusion, dispersion, and viscous fingering. These effects must be modeled by terms in coupled systems of nonlinear partial differential equations which form the basis of the simulator. The simulator must be able to handle both single and multiphase flows and the transition regimes between the two. A discussion of some of the aspects of modeling dispersion and viscous fingering is presented along with directions for future work. The partial differential equation models are convection-dominated and contain important local effects. An operator-splitting technique is used to address these different effects accurately. Convection is treated by time stepping along the characteristics of the associated pure convection problem, and diffusion is modeled via a Galerkin method for single phase flow and a Petrov-Galerkin technique for multiphase regimes. ELLAM (Eulerian-Lagrangian Localized Adjoint Methods) are discussed to effectively treat the advection-dominated processes. Accurate approximations of the fluid velocities needed in the Eulerian-Lagrangian time-stepping procedure are obtained by mixed finite element methods. Adaptive local grid refinement techniques are then indicated to resolve important local phenomena around wells and large heterogeneities or to resolve the moving internal boundary layers which often govern the mass transfer between phases.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00137846
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  • 26
    Electronic Resource
    Electronic Resource
    Nonlinear stability analysis of miscible displacements (1990)
    Springer
    Transport in porous media 5 (1990), S. 49-69 
    Details
    ISSN: 1573-1634
    Keywords: Stability ; nonlinear stability analysis ; miscible displacement ; numerical simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract A simulator for three-dimensional horizontal miscible displacements in porous media is developed. Using this simulator, we examine the initiation and development of instabilities, viscous fingers and gravity tongues. With the only perturbations to the system being truncation and round-off errors, a density ratio (the ratio of the density of the displacing fluid to that of the displaced fluid) different from one is responsible for the initiation of the instabilities, and an unfavorable mobility ratio (the ratio of the viscosity of the displaced fluid to that of the displacing fluid) is responsible for the growth of the instabilities. When macroscopic perturbations attributable to initially imperfect contact between the displaced fluid and the displacing fluid at the injection boundary are introduced, an unfavorable mobility ratio is again responsible for the growth of instabilities. Macroscopic perturbations play the same role as a density ratio different from one in initiation of the instabilities, although the manner in which instabilities develop is different.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00714628
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  • 27
    Electronic Resource
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    Numerical experiments on convective heat transfer in water-saturated porous media at near-critical conditions (1990)
    Springer
    Transport in porous media 5 (1990), S. 299-323 
    Details
    ISSN: 1573-1634
    Keywords: Supercritical convection ; heat transfer ; numerical simulation ; porous media ; geothermal systems ; water ; critical point
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract Fluid and heat flow at temperatures approaching or exceeding that at the critical point (374 °C for pure water, higher for saline fluids) may be encountered in deep zones of geothermal systems and above cooling intrusives. In the vicinity of the critical point the density and internal energy of fluids show very strong variations for small temperature and pressure changes. This suggests that convective heat transfer from thermal buoyancy flow would be strongly enhanced at near-critical conditions. This has been confirmed in laboratory experiments. We have developed special numerical techniques for modeling porous flow at near-critical conditions, which can handle the extreme nonlinearities in water properties near the critical point. Our numerical simulations show strong enhancements of convective heat transfer at near-critical conditions; however, the heat transfer rates obtained in the simulations are considerably smaller than data reported from laboratory experiments by Dunn and Hardee. We discuss possible reasons for this discrepancy and develop suggestions for additional laboratory experiments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00140018
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  • 28
    Electronic Resource
    Electronic Resource
    A finite element simulator for incompressible two-phase flow (1987)
    Springer
    Transport in porous media 2 (1987), S. 465-478 
    Details
    ISSN: 1573-1634
    Keywords: Two-phase flow ; numerical simulation ; finite elements ; Godunov methods ; slope limiter ; nonlinear convection ; heterogeneity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract This paper describes a finite element simulator for incompressible two-phase flow. This simulator is based on numerical techniques which are novel to the field of reservoir simulation. It uses irregular meshes, discontinuous high-order finite elements for the approximation of saturations (including Riemann solvers and slope limiters), and the mixed-hybrid formulation of mixed finite elements for an efficient and precise approximation of pressures and velocities. Each injection or production well is simulated by a few one-dimensional implicit models arranged to form a macroelement. This simulator is able to handle gravity, capillary pressures, porosity and permeability (both absolute and relative), and heterogeneity. Numerical results are shown which illustrate the capabilities of the code.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00211103
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