共查询到20条相似文献,搜索用时 15 毫秒
1.
We propose a model for porous sandstone formation from unconsolidated sand based on a series of restructuring events where the local pressure difference due to flow in the sand is the largest. We investigate the local and global permeability distributions after steady state has been reached. Whereas we find no spatial correlations in the local permeability distribution, the distribution of inverse permeability shows spatial correlations consistent with a fractional Brownian noise characterized by a Hurst exponent of 0.88(9). The global permeability of the system shows time fluctuations as restructuring proceeds consistent with self-affinity characterized by a Hurst exponent of 0.25(3), crossing over to white noise at larger time scales. 相似文献
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《Physics letters. A》2014,378(30-31):2308-2311
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In this Letter, a difference-fractal model for the permeability of viscous flow through fibrous porous media is proposed. Since fractal objects have well-defined geometric properties, and are discrete and discontinuous, we apply the difference approach to developing the fractal model. The model of non-dimensional permeability is expressed as a function of porosity and fractal dimension. To verify the validity of the proposed model, the predicted permeability values are compared with those of experimental measurements. A good agreement between the prediction of the fractal model and the existing experimental data from the literature is found. 相似文献
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A fermionic version of Dyson's hierarchical model is defined. An exact renormalization group transformation is given as a rational transformation of two-dimensional parameter space. Two branches of nontrivial fixed points are described, one of which bifurcates from the trivial Gaussian branch. The existence of the thermodynamic limit for these branches of fixed points is investigated. 相似文献
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A volume averaging approach is used to estimate the porous media permeability. Contrary to traditional methods that rely on solving the Navier-Stokes equations for laminar flow, this approach has the advantage that it does not require the specification of some physical conditions and parameters (pressure drop and viscosity). Numerical results on synthetic models of porous media showed that (i) the local porous medium configuration has an important effect on the permeability value, and (ii) the Carman-Kozeny equation cannot describe the permeability behavior as a function of porosity and characteristic lengths. In turn, our results indicate that simple empirical equations, commonly used in practice, are unable to describe the permeability functionalities over a broad range of porous media configurations. 相似文献
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Krutyeva M Yang X Vasenkov S Kärger J 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2007,185(2):300-307
A new method to determine the surface permeability of nanoporous particles is proposed. It is based on the comparison of experimental data on tracer exchange and intracrystalline molecular mean square displacements as obtained by the PFG NMR tracer desorption technique with the corresponding solutions of the diffusion equation via dynamical Monte Carlo simulations. The method is found to be particularly sensitive in the "intermediate" regime, when the influence of intracrystalline diffusion and surface resistances of the nanoporous crystal on molecular transport are comparable and the conventional method fails. As an example, the surface permeabilities of two samples of zeolite NaCaA with different crystal sizes are determined with methane, as a probe molecule, at room temperature. 相似文献
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G. A. Kohring 《Journal of statistical physics》1991,63(1-2):411-418
The permeability of two-dimensional porous media is calculated numerically as a function of porosity using the hydrodynamic cellular automata (lattice gas) approach. Results are presented for systems with up to 22 million sites (8192×2688). For randomly distributed solid obstacles whose macroscopic dimensions are much longer than the mean free path of particles in the fluid, the permeability varies with porosity as (–0.6)/(1–) for>0.7. When the solid obstacles are much smaller than the mean free path of particles in the fluid, i.e., when they form a dust of point objects, then such a relationship no longer holds and the permeability is more than an order of magnitude smaller than for the former case. The program used for the simulations is discussed and a listing is presented in the Appendix which achieved a sustained speed of 185 million sites updated per second on a single processor of the Cray-YMP. (On a Sun Sparc Workstation, the same program ran about 100 times slower.) 相似文献
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Heterogeneity, as it occurs in porous media, is characterized in terms of a scaling exponent, or fractal dimension. A feature of primary interest for two-phase flow is the mixing length. This paper determines the relation between the scaling exponent for the heterogeneity and the scaling exponent which governs the mixing length. The analysis assumes a linear transport equation and uses random fields first in the characterization of the heterogeneity and second in the solution of the flow problem, in order to determine the mixing exponents. The scaling behavior changes from long-length-scale dominated to short-length-scale dominated at a critical value of the scaling exponent of the rock heterogeneity. The long-length-scale-dominated diffusion is anomalous. 相似文献
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An analysis of the radial flow in the heterogeneous porous media based on fractal and constructal tree networks 总被引:1,自引:0,他引:1
In this paper, an analysis of the radial flow in the heterogeneous porous media based on fractal and constructal tree networks is presented. A dual-domain model is applied to simulate the heterogeneous porous media embedded with a constructal tree network based on the fractal distribution of pore space and tortuosity nature of flow paths. The analytical expressions for seepage velocity, pressure drop, local and global permeability of the network and binary system are derived, and the transport properties for the optimal branching structure are discussed. Notable is that the global permeability (Kn) of the network and the volume fraction (fn) occupied by the network exhibit linear scaling law with the fractal dimension (Dp) of channel diameter bylogKn∼0.46Dp and logfn∼1.03Dp, respectively. Our analytical results are in good agreement with the available numerical results for steady-state soil vapor extraction and indicate that the fractal dimension for pore space has significant effect on the permeable properties of the media. The proposed dual-domain model may capture the characteristics of heterogeneous porous media and help understanding the transport mechanisms of the radial flow in the media. 相似文献
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A. D'Onofrio V.M. Freytes M. Rosen C. Allain J.P. Hulin 《The European physical journal. E, Soft matter》2002,7(3):251-259
Tracer dispersion in Newtonian and shear-thinning fluids (scleroglucan-water polymer solutions) flowing through single and
double porosity grain packings has been studied experimentally using both classical transmission dispersion and echo dispersion
(in the latter, the concentration variation front is pumped back through a detector at the inlet after penetrating for a chosen
distance into the sample). Transmission dispersion increases markedly in both types of samples with the shear thinning index
of the fluid at all Péclet numbers (except when molecular diffusion is dominant). Echo and transmission experiments give nearly
identical dispersivity values for Newtonian fluids while echo dispersivity is lower than transmission for shear thinning ones.
The normalized dispersivity difference has same order of magnitude for single and double porosity samples and increases with
the shear thinning exponent α (by a factor of 2 between α = 0.35 and α = 0.60). This difference may be due to heterogeneities
inducing permeability variations of small amplitude over distances of the order of the sample section : their influence on
tracer dispersion is partly reversible with respect to a change of the flow direction and is only detectable if it is amplified
by the shear-thinning properties of the fluid.
Received 19 September 2001 相似文献
13.
Exact renormalization group equations are derived for a position-space renormalization of spin systems with weak long-range forces. It is shown how an apparent dependence of the critical exponents on the choice of the renormalization group can be resolved via the mechanism of dangerous irrelevant variables and that this same mechanism is responsible for the breakdown of hyperscaling. The dimensiond=4 can be seen to be a borderline dimension above which classical critical exponents are expected. 相似文献
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J.A. Mydosh 《物理学进展》2017,66(4):263-314
Magnetic fields are now available to 100?T (pulsed), 45?T (static) at temperatures below 0.3?K. Such technical developments allow the study and tuning of (quantum) phase transitions, unusual magnetic structures and (high-temperature) superconductors in a variety of quantum materials. An especially important class of strongly correlated electron materials is the heavy Fermi liquids (HFLs) displaying numerous reduced-moment antiferromagnets, quantum critical points, unconventional superconductivity, hidden order (HO) and other mysterious ground states. Among the ‘heavy fermions’, the duality of 5f electrons in uranium-based compounds introduces interesting behavior that can be affected by large magnetic fields. I list a few such heavy fermion materials to be considered: URu2Si2 and its tunable hidden state, UBe13 and UPt3 as very HFL paramagnets that become superconducting, the magnetic superconductors UPd2Al3 and UNi2Al3, and the ferromagnetic s UGe2, URhGe and UCoGe. There are also the suggested metamagnetic Fermi-surface reconstructed intermetallic compounds such as UPt2Si2 and UCo2Si2. Present research attention focuses on the high-field behavior (30–40?T) of URu2Si2 and its destruction of HO. These and other U-based systems, e.g. UAu2Si2, UIrGe, etc., expand the opportunities of high magnetic field studies far into the future. 相似文献
17.
R.E. Lee DeVille Anthony Harkin Matt Holzer Kreimir Josi Tasso J. Kaper 《Physica D: Nonlinear Phenomena》2008,237(8):1029-1052
For singular perturbation problems, the renormalization group (RG) method of Chen, Goldenfeld, and Oono [Phys. Rev. E. 49 (1994) 4502–4511] has been shown to be an effective general approach for deriving reduced or amplitude equations that govern the long time dynamics of the system. It has been applied to a variety of problems traditionally analyzed using disparate methods, including the method of multiple scales, boundary layer theory, the WKBJ method, the Poincaré–Lindstedt method, the method of averaging, and others. In this article, we show how the RG method may be used to generate normal forms for large classes of ordinary differential equations. First, we apply the RG method to systems with autonomous perturbations, and we show that the reduced or amplitude equations generated by the RG method are equivalent to the classical Poincaré–Birkhoff normal forms for these systems up to and including terms of , where is the perturbation parameter. This analysis establishes our approach and generalizes to higher order. Second, we apply the RG method to systems with nonautonomous perturbations, and we show that the reduced or amplitude equations so generated constitute time-asymptotic normal forms, which are based on KBM averages. Moreover, for both classes of problems, we show that the main coordinate changes are equivalent, up to translations between the spaces in which they are defined. In this manner, our results show that the RG method offers a new approach for deriving normal forms for nonautonomous systems, and it offers advantages since one can typically more readily identify resonant terms from naive perturbation expansions than from the nonautonomous vector fields themselves. Finally, we establish how well the solution to the RG equations approximates the solution of the original equations on time scales of . 相似文献
18.
Using the principle of diffusion-limited aggregation(DLA),a new model is introduced to simulate the displacement of one fluid by another in porous media.The results agree with experiments.apparently they do not leave out film-flow phenomena.Simultaneously,we also present a new numerical method to treat our results by the lattice Boltzmann method(LBM),All these will be helpful for analysing similar subjects. 相似文献
19.
Development of a new correlation to calculate permeability for flows with high Knudsen number 下载免费PDF全文
Esmaeil Dehdashti 《中国物理 B》2016,25(2):24702-024702
Flows with high Knudsen number play a prominent role in many engineering applications. The present study is an effort toward the simulation of flow with high Knudsen number using modified lattice Boltzmann method(LBM) through a porous medium in a channel. The effect of collision between molecules and solid walls, which is required to accurately simulate transition flow regime, is taken into account using a modified relaxation time. Slip velocity on the wall, which is another significant difficulty in simulating transition flow regime, is captured using the slip reflection boundary condition(SRBC). The geometry of porous medium is considered as in-line and staggered. The results are in good agreement with previous works. A new correlation is obtained between permeability, Knudsen number and porosity for flows in transition flow regimes. 相似文献