ALBERT

Description: We investigate a two-phase porous media flow model, in which dynamic effects are taken into account in phase pressure difference. We consider a one-dimensional heterogeneous case, with two adjacent homogeneous blocks separated by an interface. The absolute permeability is assumed constant, but different in each block. This may lead to the entrapment of the non-wetting phase (say, oil) when flowing from the coarse material into the fine material. We derive the interface conditions coupling the models in each homogeneous block. In doing so, the interface is approximated by a thin porous layer, and its thickness is then passed to zero. Such results have been obtained earlier for standard models, based on equilibrium relationship between the capillary pressure and the saturation. Then, oil is trapped until its saturation on the coarse material side of the interface exceeds an entry value. In the non-equilibrium case, the situation is different. Due to the dynamic effects, oil may still flow into the fine material even after the saturation drops under the entry point, and this flow may continue for a certain amount of time that is proportional to the non-equilibrium effects. This suggests that operating in a dynamic regime reduces the account of oil trapped at interfaces, leading to an enhanced oil recovery. Finally, we present some numerical results supporting the theoretical findings.

Description: The importance of gas acceleration near a wellbore in radial compressible porous media flows is quantified in terms of a dimensionless parameter, and conditions are identified under which gas acceleration is mainly responsible for the change in the pore pressure distribution and mass flux. Gas acceleration and Forchheimer drag both steepen the pressure profile and have significant impact on the pressure curve near the wellbore for a given wellbore pressure. For unchoked flows, the properties of a compressible accelerating gas flow can be modeled by a Darcy–Forchheimer flow with an upward adjusted Forchheimer drag coefficient. For choked flows, the Darcy–Forchheimer equation cannot be used to mimic the accelerating flow no matter how large the Forchheimer drag coefficient is. It is demonstrated that the value of the Forchheimer drag coefficient in some previous studies was inflated due to omission of the gas acceleration in the momentum equation.

Description: A numerical investigation is implemented on the unsteady natural convection with a temperature-dependent viscosity inside a square porous cavity. The vertical walls of the cavity are kept at constant but different temperatures, while the horizontal walls are adiabatic. The mathematical model formulated in dimensionless stream function, vorticity and temperature variables is solved using implicit finite difference schemes of the second order. The governing parameters are the Rayleigh number, Darcy number, viscosity variation parameter and dimensionless time. The effects of these parameters on the average Nusselt number along the hot wall as well as on the streamlines and isotherms are analyzed. The results show an intensification of convective flow and heat transfer with an increase in the viscosity variation parameter for the porous media, while in the case of pure fluid, the effect is opposite.

Description: The traditional advection–dispersion–reaction equation (ADRE) often meets difficulty in simulating diffusion-controlled reactive transport, because the grid-based ADRE with a laboratory-measured reaction rate overpredicts pore-scale mixing and the product concentration. In this study, we chose bimolecular reactive transport (A \(\,+\,\) B \(\,\rightarrow \,\) AB) in porous media as an example and developed a fully implicit Galerkin finite-element method with Picard’s linearization scheme for solving the ADRE considering incomplete mixing at pore scale (IM-ADRE) based on a continuum approximation by Sanchez-Vila et al. (Water Resour Res 46:W12510, 2010 ). Sensitivity analysis showed that the IM-ADRE model was most sensitive to the parameter “ m ,” which was the power index of time used to control the decline rate of the time-dependent kinetic reaction term considering effects of incomplete mixing at pore scale. We used the IM-ADRE model to interpret the column experiment reported by Raje and Kapoor (Environ Sci Technol 34(7):1234–1239, 2000 ), which studied bimolecular reactive transport of aniline (AN) +1,2-naphthoquinone-4-sulfonic acid (NQS) \(\rightarrow \) 1,2-naphthoquinone-4-aminobenzene (NQAB) in porous media. Previous studies found that the discrepancy between the simulated and observed peak product concentrations was as large as 55 % by the traditional ADRE, while the discrepancy was reduced to 5 % by the IM-ADRE model. We further conducted new reactive transport column experiments with NQS and AN to systematically understand the nature of bimolecular reactive transport in porous media and further check the validity of the IM-ADRE model. Our experiments differed from previous ones in two aspects. First, we used two different realistic porous media with six different flow velocities while previous experiments mostly involved artificial media such as glass beads under two similar flow velocities. Second, our experiment used a column (with the length of 100 cm) relatively longer than that (18 cm) in Raje and Kapoor ( 2000 ), and thus, the boundary effect of the column was minimized, and the time dependence of the effective reaction term could be further checked rigorously. Our study reveals that the IM-ADRE is a feasible tool in quantifying reactive transport at a travel distance up to 100 cm, further validating the effective, time-dependent rate coefficient proposed empirically by Sanchez-Vila et al. ( 2010 ).

Description: Groundwater tracers such as sodium chloride (NaCl) and the food color brilliant blue FCF (BBF) had been widely used to evaluate flow dynamics, but the possible discrepancy of transport dynamics between the two tracers through a same medium remains obscure. In order to fill this knowledge gap, we combined laboratory experiments and model analysis for transport of the above tracers. We first conducted three progressive experiments, including (1) transport experiments of NaCl and BBF through saturated sand columns packed with uniform glass beads; (2) transport experiments of the two tracers through silica sand columns as a function of travel distances and flow rates; and (3) a long-term adsorption experiment exploring the adsorption of the two tracers to silica sands. All laboratory results show that NaCl exhibits slower and smaller peaks in tracer breakthrough curves than BBF. Further model analysis using the standard advection-dispersion equation (with a retardation coefficient to account for equilibrium sorption) demonstrates that the NaCl plume has a larger dispersion coefficient than that of BBF. Both the laboratory and a pseudo-kinetic model also reveal that NaCl might be observed more by the medium than BBF. Therefore, although NaCl is well known to be a more conservative tracer than BBF, our laboratory and numerical experiments suggest the opposite. NaCl can be less conservative than BBF through laboratory-scale sand columns, probably due to (1) stronger sorption of NaCl to silica sand, and/or (2) relatively stronger mass exchange between mobile and immobile zones in macroscopically homogeneous porous media.

Description: The kinetics and equilibrium of water vapor adsorption/desorption isotherm (WVSI) are fundamental information for solid–moisture interaction in the microstructure of cement-based porous materials (CBPM). This paper presents firstly the experimental data for WVSI of CBPM with a ternary binder. Mass changes in specimen are recorded in sorption tests for materials with different aggregate contents and water-to-binder (w/b) ratios under controlled ambient relative humidity. Both the sorption equilibrium and sorption kinetics are investigated through some established physical models, and the corresponding intrinsic parameters of moisture sorption are determined. For sorption kinetics, the mass change during sorption is interpreted through Elovich model, power model and pseudo-first-order and pseudo-second-order models. The mass change in sorption occurs mainly in the first 40 days, and the pseudo-second-order model shows the best adaption to all adsorption/desorption processes. For sorption equilibrium, Guggenheim–Anderson–de Boer (GAB), modified Halsey and Oswin models are used to interpret the moisture sorption capacity. The hysteresis between adsorption and desorption processes is attributed, respectively, to the mechanisms of snap-through, energy instability and pore constrictivity for low, middle and high relative humidity ranges. From the analysis, it is found that (1) through the interpretation of pseudo-second-order model the moisture sorption kinetics can be controlled by the sorption between the water molecules and the pore wall in addition to vapor diffusion; (2) the sorption capacity is sensitive to aggregate content and w/b ratio; incorporating aggregates, decreasing w/b ratio and increasing humidity gradient tend to decrease the sorption capacity of CBPMs; (3) the sorption isotherm hysteresis is well described by GAB-H model, both the extent of hysteresis and the energy constant related to pore surface tension showing clear correlation with the aggregate content and w/b ratio of CBPMs.

Description: Nanoscale surface roughness and charge heterogeneity have been widely recognized to influence particle retention in porous media under unfavourable chemical conditions such as solutions of low ionic strength (IS) or high pH. However, previous researches have not appreciated the influence of nanoscale surface roughness on particle retention under favourable chemical conditions (e.g. high solution IS). This information is needed to better understand and predict particle transport and retention in such natural environments, such as enhanced oil recovery in a high-salinity reservoir. A glass-etched micro-model was employed to directly visualize retention of micro-sized particles and their spatial distribution on the glass surface under various chemical conditions. The extended DLVO calculations accounting for the effect of nanoscale surface roughness on the interaction energies were employed to quantitatively evaluate the experimental results. It was shown that nanoscale roughness on solid surfaces significantly reduced the strength of primary minimum attachment when the solution IS was high. In particular, increasing the density of roughness on the solid surface increased the strength of primary minimum, whereas increasing the roughness height decreased the strength of primary minimum interaction. Consequently, retained particles in the primary minimum are expected to be susceptible to detachment via hydrodynamic drag forces and movement of air–water interfaces during transient in water saturation (e.g. drainage or imbibition). Indeed, results obtained from the micro-model experiments demonstrated that only a fraction of solid surface was available for particle retention even at a very high IS of 0.6 M.

Description: Prospective authors are requested to submit new, unpublished manuscripts for inclusion in the upcoming event described in this call for papers.

Description: Kalyani Nair reviews "Multiscale Modeling in Biomechanics and Mechanobiology", edited by S. De, W. Hwang, and E. Kuhl, declaring it useful for anyone looking to get a quick overview of the field over a broad spectrum of areas.

Description: We consider a model problem for coupled surface–subsurface flow. The model consists of a nonlinear kinematic wave equation for the surface fluid’s height and a Brinkman model that governs fluid velocity and pressure for subsurface dynamics. For this coupled hyperbolic–elliptic model we establish the existence of weak solutions. The proof is based on a viscous approximation and the method of compensated compactness by virtue of appropriate energy estimates. To solve the coupled problem numerically, a finite volume method is applied. The numerical scheme is used to illustrate the influence of the Brinkman parameter on the coupled flow pattern for infiltration scenarios.

Description: Experimental heat transfer data for water flow in commercial, open-cell-aluminum-foam cylinder heated at the wall by a constant heat flux, are presented. The measurements include wall temperature along flow direction as well as average inlet and outlet temperatures of the water. Flow speeds were in the Darcy and non-Darcy (transitional and Forchheimer) regimes. Heat fluxes were 14,998 and \(26{,}347\,\hbox {W/m}^{2}\) for the Darcy and non-Darcy regimes, respectively. Measurements were focused on the thermally fully developed and an anticipated exit regions, with the latter region being often ignored in the literature. The experimental Nusselt number for the Darcy flow cases is compared to its analytical counterpart. A comparison shows good agreement, considering the approximations involved in the analytical solution and experimental errors. Previously unpublished phenomenon is presented in the behavior of Nusselt number for non-Darcy regimes. The experimental results and measuring technique can be used for validation of other analytical and numerical solutions, as well as in testing heat-exchange engineering designs based on metal foam.

Description: In the present work, a mathematical modeling of propagation of Love waves in dry sandy layer under initial stress above anisotropic porous half-space under gravity is reported. The equation of motion for the Love wave has been formulated following Biot, using suitably chosen boundary conditions at the interface of sandy layer and porous half-space under gravity. The dispersion equation of phase velocity of this proposed multilayer ground structure has been derived following the Whittaker function and its derivative, which is further expanded asymptotically, retaining the terms up to only the second degree for large argument due to small values of Biot’s gravity parameter (varying from 0 to 1). The study reveals that the gravity and porosity of the porous half-space play important roles on the propagation of Love waves. It is observed that with the increase in gravitation parameter and porosity of the half-space, the phase velocity of the Love wave decreases, whereas the velocity of the waves increases for the increase in the value of the sandy parameter. The effects of these above-mentioned medium parameters for isotropic and anisotropic cases are studied on the propagation of Love waves, and their numerical results have been presented graphically.

Description: X-ray microtomography is routinely used to image the three-dimensional pore space of sedimentary rocks. Flow and transport properties can then be simulated directly in such images. Advective transport in porous media is frequently simulated using streamlines. We present a novel streamline tracing algorithm based on a substantial development of the most widely used method (the Pollock algorithm) employed for macroscale (Darcy) flow, making it consistent with solutions of the Navier-Stokes equation with no flow at solid boundaries. We use this new algorithm to calculate breakthrough curves and time-of-flight distributions for advection-dominated transport in two three-dimensional images of sedimentary rocks containing up to \(10^9\) voxels: a sandstone and a carbonate. We show that our approach provides a more accurate description of flow, particularly when only a few image voxels span each pore. Therefore, it is better suited to capture anomalous (non-Fickian) transport behaviour than the standard Pollock method.

Description: Pore network modelling offers a versatile and efficient means for examining the complex interplay of a variety of microscopic processes affecting subsurface migration of \(\hbox {CO}_{2}\) injected for storage. We present a dynamic pore-to-core network model capable of simulating the full range of \(\hbox {CO}_{2}\) migration processes under the influence of capillary and gravity forces, including \(\hbox {CO}_{2}\) dissolution in brine. A parametric sensitivity study investigating four variables that define the microscopic Bond number, viz : mean pore radius, \(\hbox {CO}_{2}\) –brine interfacial tension, brine– \(\hbox {CO}_{2}\) density difference, and network height, was performed. Two broad classes of behaviours were identified—one quasi-stable and the other unstable (migratory)—and critical gas saturation \(({S}_\mathrm{gc})\) was found to change in a non-monotonic way with transition from quasi-stable to migratory regime. The model predicts strong effects of gravity at the scale typical of continuum-type simulator gridblocks, and pore size distribution variance and pore connectivity were found to have a major impact on \({S}_\mathrm{gc}\) which cannot be predicted a priori through the use of Bond number scaling. For temperatures and pressures above the \(\hbox {CO}_{2}\) critical point, \(\hbox {CO}_{2}\) and \(\hbox {CH}_{4}\) flow regimes in brine displayed generally similar characteristics, suggesting that flow coefficients (e.g. relative permeability) of \(\hbox {CH}_{4}\) and \(\hbox {CO}_{2}\) in brine could be used interchangeably in continuum-type simulators with effectively the same results.

Description: We study interfacial mass transfer between two immiscible fluids in porous media augmented with bulk reactions. A closed-form analytic approximation derived through Laplace transformation is represented for Darcy–Brinkman flow in the presence of first-order bulk reactions represented by the Damköhler number ( Da ). By comparing the residues of all the singularities, it is shown that the main contributor to the solution is the simple pole of the equations. We show that the solution holds for a range of \(Da.Pe〈2.5\times 10^{5}\) , where Pe is the Péclet number. By determining the bulk flow mass transfer coefficient, we verify our approximation compared to the previous studies and show acceptable conformity of the solutions. We find that the results are applicable for potential bulk reactions, such as biodegradation, in a typical groundwater system.

Description: Oil–water relative permeability curve constitutes important basic data in reservoir engineering. Given the influence of dead volume on experimental apparatus, the actual oil–water relative permeability curve cannot be obtained when the unsteady-state method is adopted to measure oil–water relative permeability. In this paper, on the basis of the analysis of the influence of dead volume on oil–water relative permeability, we summarize the conventional methods used to overcome dead volume and then propose the use of relationship theory between resistivity and water saturation to calibrate the oil–water relative permeability curve. This method mainly aims at to measure the resistance values at both ends of the core by using a resistance-measuring instrument. Meantime, the Archie formula is used to calibrate the relational expression of core resistivity and water saturation based on the steady-state experimental method. Therefore, the core of the actual cumulative oil production and the average water saturation can be calculated, and then oil–water relative permeability can be accurately computed without the influence of dead volume. By comparing the oil displacement process of dead volume calculated through two different methods (probability subtraction and resistivity methods), the crude oil in dead volume is found to be displaced at the beginning of the displacement. The oil–water relative permeability curve corrected through resistivity method can eliminate the influence of dead volume and iterative error in calculation, and is consistent with the law of the actual development of oilfield, which has certain theoretical and practical application values.

Description: In this paper, an unstructured grid generation algorithm is presented to produce two- and three-dimensional grids in porous media with networks of discrete fractures. The proposed grid generation algorithm considers underground contours map data to adapt unstructured grids to geological geometries. This allows construction of more realistic geometrical models. Sample two- and three-dimensional unstructured grids have been generated in complex porous media with seven intersecting fractures. Two-dimensional grids were generated within 0.17–2.37 s of CPU time. Generation of three-dimensional grids including grid quality improvement measures took 109 s of CPU time. This final grid contains 763 fracture cells and 49, 403 matrix cells. Angle distribution histograms of the three-dimensional grids show no skewed and flat angles within fracture and matrix cells. Two- and three-dimensional computational unstructured grids have been generated for geometries similar to published fractured porous media test cases. Incompressible and immiscible water–oil flow simulations were then obtained using these computational grids. Simulations gave identical results with published data which confirms the computational feature of the proposed unstructured grid generation algorithm.

Description: The Stokes flow is numerically computed in porous media based on 3D Boolean random sets of spheres. Two configurations are investigated in which the fluid flows inside the spheres or in the complementary set of the spheres. Full-field computations are carried out using the Fourier method of Wiegmann ( 2007 ). The latter is applied to large system sizes representative of the microstructure. The overall permeability of the two models as well as the representative volume element are estimated as a function of the pore volume fraction. We give numerical estimates for the asymptotic behavior of the permeability in the dilute limit for the solid phase, and close to the percolation threshold of the pores. FFT maps of the velocity field are presented, for increasing values of the pore volume fraction. The patterns of the local velocity field is analyzed using various morphological criteria. The tortuosity of the streamlines is found to be much higher than the geometrical tortuosity, for both models. The histograms of the velocity field are computed at increasing pore volume fraction. The covariance of orientation is used to characterize the spatial correlation of the velocity field.

Description: Three-dimensional visualization of dynamic water transport process in soil by computed tomography (CT) technique is still limited by its low temporal resolution. In order to monitor dynamically water transport in soil, a compromise has to be found between water flow velocity and CT acquisition time. Furthermore, an efficient image analysis method is necessary. In this work, we followed the water transport in three dimensions by CT imaging across a double-porosity media constituted of two distinct materials, i.e. sand and porous clay spheres. The CT acquisition parameters were adjusted to the water pore velocity so that we succeeded to register the water front displacement per time range of 25 min. We also used the image subtraction method to extract water distribution evolution with time with a space resolution of \(6\times 10^{-3}\hbox { cm}\) . Both time and space resolution are relatively high compared with other dynamic studies. The water content profiles showed that the clay spheres remained in their dry state during water infiltration, while the water transport only occurred in the sand matrix. These results are consistent with macroscopic experiments. The water front visualized by CT showed a non-symmetrical shape which was related to water transfer in non-equilibrium as shown by column displacement experiments.

Description: Steady-state upscaling of relative permeability is studied for a range of reservoir models. Both rate-dependent upscaling and upscaling in the capillary and viscous limits are considered. In particular, we study fluvial depositional systems, which represent a large and important class of reservoirs. Numerical examples show that steady-state upscaling is rate dependent, in accordance with previous work. In this respect we introduce a scale-dependent capillary number to estimate the balance between viscous and capillary forces. The difference between the limit solutions can be large, and we show that the intermediate flow rates can span several orders of magnitude. This substantiate the need for rate-dependent steady-state upscaling in a range of flow scenarios. We demonstrate that steady-state upscaling converges from the capillary to the viscous limit solution as the flow rate increases, and we identify a simple synthetic model where the convergence fails to be monotone. Two different sets of boundary conditions were tested, but had only minor effects on the presented reservoir models. Finally, we demonstrate the applicability of steady-state upscaling by performing dynamic flow simulation at the reservoir scale, both on fine-scaled and on upscaled models. The considered model is viscous dominated for realistic flow rates, and the simulation results indicate that viscous limit upscaling is appropriate.

Description: The transport properties of cement-based composites, including solute diffusivity, electrical conductivity and water permeability, are regarded as durability indicators of cement-based composites. These transport properties are closely related to the microstructure, or rather to the pore structure of materials. Among all the microstructural aspects, the interfacial transition zone (ITZ) between the cement paste matrix and aggregates, and the air voids are believed to play an essential role in the transport properties. However, their impacts on the transport properties are difficult to be quantified. This paper develops a closed-form four-phase micromechanical model accounting for the local properties of ITZ and the saturation states of air voids. The effects of ITZ and air voids on the transport properties of cement-based composites are addressed quantitatively in the model. The Katz–Thompson equation is reinterpreted by the model in particular. It is shown that the local properties of ITZ and volume fraction of aggregates act mutually on the overall transport properties, the influence of air voids depends significantly on the water saturation, and a critical saturation degree is found to be 1/3.

Description: A laboratory-scale tracer test has been carried out to improve the characterization of the transport properties of the concrete from the radioactive waste disposal facility at El Cabril (Spain). High entry pressure was employed in order to perform the experiment in a reasonable time span. Lithium, bromide and deuterium were used as tracers. The conceptual model considered matrix diffusion between a mobile pore domain, where water can flow, and an immobile zone without any advective transport. Three geometries have been compared, considering the immobile zone as slabs, spheres or tubes. Porosity of the mobile zone and characteristic time was estimated by calibrating the model results to the measured breakthrough curves of deuterium and bromide. The calculated values showed that the characteristic time depends on the geometry, and similar porosity of the mobile zone was estimated for all geometries. The double-porosity conservative transport model could reproduce the deuterium breakthrough curve. However, the bromide behaviour could not be reproduced even when linear retardation was applied.

Description: As a first step to analyze the inverse kinetic of adsorption, an inverse algorithm is developed to estimate equilibrium adsorption isotherm in a gas storage vessel by using the dynamic transient internal pressure. In the present study, no prior information is need for the functional form of the unknown isotherm equation to solve continuity equation. The conjugate gradient method is employed for optimization procedure. The incremental differential quadrature method as a computationally efficient and accurate numerical tool is applied to solve the corresponding direct, sensitivity and adjoint problems. The accuracy of the presented approach is examined by simulating the exact data of known model. Good accuracy of the obtained results validates the presented approach.

Description: We present simulations and experiments of drainage processes in a micro-model. A direct numerical simulation is introduced which is capable of describing wetting phenomena on the pore scale. A numerical smoothed particle hydrodynamics model was developed and used to simulate the two-phase flow of immiscible fluids. The experiments were performed in a micro-model which allows the visualization of interface propagation in detail. We compare the experiments and simulations of a quasistatic drainage process and pure dynamic drainage processes. For both, simulation and experiment, the interfacial area and the pressure at the inflow and outflow are tracked. The capillary pressure during the dynamic drainage process was determined by image analysis.

Description: The present work investigates the thermal aspects of a differentially heated porous square enclosure in the presence of an adiabatic block of different block sizes utilizing Darcy–Rayleigh number in the range of 1–10,000 with Darcy number \(10^{-2}\) – \(10^{-6}\) . Heatlines and Nusselt number, streamlines, and entropy generation are used for the analysis of heat transfer, flow circulation, and irreversibility production in the enclosure. The study reveals that the presence of an adiabatic block affects the heat transfer process severely, and three different zones of heat transfer are identified. These are namely the zone of heat transfer augmentation, the zone of heat transfer augmentation along with entropy generation reduction, and the zone of both heat transfer and entropy generation reduction. It is also found that the presence of an adiabatic block can enhance heat transfer up to a certain critical block size; thereafter, further increasing in block size reduces the heat transfer rate. An optimal block size where the heat transfer enhancement is maximum is observed to be smaller than the critical block size. The study demonstrates the analyses of heat transfer and entropy generation for a better thermal design of a system. This study is also extended for higher Prandtl number fluids.

Description: Scarce data and uncertainties in the spatial variation of geological properties lead to different possible models of these heterogeneities. The aim of this study is to compare the pressure results and \(\hbox {CO}_2\) behavior of different permeability field models for a large-scale \(\hbox {CO}_2\) injection in a deep saline aquifer. Five ways of representing heterogeneities are tested and compared. The simplest representation defines homogeneous equivalent properties over the entire domain. A second representation is obtained by considering homogeneous layers. Two other models represent the lateral and vertical variations in permeability in greater detail by geostatistical methods with either a continuous model or a discontinuous model (discrete values). The last model is the semi-homogeneous model combining a heterogeneous area and a homogeneous area depending on the complexity of the flow process. Highly variable predictions arise from the heterogeneities, and significant differences in estimates are obtained using the various modeling methods. The optimum resolution depends on the type of response to be estimated. Averaged properties at large scale are not adequate to estimate the critical pressure propagation far from the well. Averaged properties in the injection area are not sufficient to assess the maximum increase in pressure or the extent of \(\hbox {CO}_2\) migration. Lateral and vertical connectivities, and reservoir compartmentalization modeling are required to obtain reliable results. But the resolution requirements are not to be at the finest scale: The discontinuous model (discrete values) gives satisfactory results compared to the continuous model. The way to represent spatial variability of porosity and pore compressibility is also studied. The influence of these two properties is far lower than that of permeability.

Description: The relationship between flow properties and chemical reactions is the key to modeling subsurface reactive transport. This study develops closed-form equations to describe the effects of mineral precipitation and dissolution on multi-phase flow properties (capillary pressure and relative permeabilities) of porous media. The model accounts for the fact that precipitation/dissolution only takes place in the water-filled part of pore space. The capillary tube concept was used to connect pore-scale changes to macroscopic hydraulic properties. Precipitation/dissolution induces changes in the pore radii of water-filled pores and consequently in the pore size distribution. The updated pore size distribution is converted back to a new capillary pressure–water saturation relation from which the new relative permeabilities are calculated. Pore network modeling is conducted on a Berea sandstone to validate the new continuum-scale relations. The pore network modeling results are satisfactorily predicted by the new closed-form equations.

Description: In a lifetime of work, Dr. Olivier Coussy developed a complete theoretic framework for porous media that researchers in a broad range of fields including (but not limited to) concrete, hydrology, swelling clay, and \(\hbox {CO}_2\) -induced swelling of coal have continued to use as a foundation. However, in some of these works where a framework is developed for a deformable porous media, a dissipative inequality is assumed that implicitly results in a thermodynamical form of liquid pressure that is inconsistent with the classical thermodynamical form of pressure found in thermodynamic textbooks for a single phase. In this note, we compare this definition of pressure with those developed in other mixture-theoretic frameworks and demonstrate this inconsistency by mathematically showing that the thermodynamic quantity is most closely related to the solid pressure and explain how this inconsistency came about.

Description: The Finnish plan for the final deposition of nuclear waste is deposition deep in the crystalline bedrock. In the safety case of the final deposition, matrix diffusion, along with sorption, is considered the most important retarding factor for radionuclide transport in the geosphere. We set out to measure matrix diffusion in the gas phase for two 80 cm long drill-core samples from Olkiluoto, Finland. One sample consisted of veined gneiss and the other of pegmatitic granite. The measurements were taken in the laboratory with an advection–diffusion measurement setup that uses nitrogen as the carrier gas and helium as the tracer. The measured breakthrough curve for the veined gneiss sample could be interpreted with a homogeneous mathematical model, and the result for the effective diffusion coefficient ( \(D_{\mathrm{e}}\) ), \(4.2 \pm 0.9 \times 10^{-10}\,\frac{\mathrm {m}^2}{\mathrm {s}}\) , agreed with previous results for veined gneiss from through-diffusion experiments in the gas phase. The breakthrough curve for the pegmatitic granite sample required a three-component model because of high variations in the local transport parameters (porosity, diffusion coefficient). The spatial distributions of porosities were characterized with the \(^{14}\) C-polymethylmethacrylate-autoradiography technique. The result, \(D_{\mathrm{e}} = \left( 32 \pm 7\right) \times 10^{-10}\,\frac{\mathrm {m}^2}{\mathrm {s}}\) , for the most abundant component was also in accordance with the previous through-diffusion results. Comparison of the two measurements showed that diffusion phenomena can be very sensitive to the microstructure of rock even when macroscopic properties such as porosity remain the same. The retarding effect of matrix diffusion from flow was clearly observed for both samples, and knowledge of the sample structure, rock types, and mineralogy were concluded to be vital in analyzing and interpreting the results.

Description: Carbonate formations usually contain multi-scale fractures, cavities, and even caves within the carbonate rocks. Carbonate rocks undergo various chemical reactions with the injecting fluids during waterflooding, which may lead to the evolution of a fracture system induced by dissolution processes. This development of a natural fracture system may eventually lead to the formation of large-scale well-connected void space features, resulting in early breakthrough, unwanted production, and small increases in bottom-hole pressure. Consequently, a numerical model that accurately describes the dynamic behavior of natural fracture evolution is essential for better forecasting and optimization of production during waterflooding processes. In this paper, we have developed a mathematical model that combines the Stokes–Brinkman and reactive-transport equations to describe the coupled processes of fluid flow, solute transport, and chemical reaction. Application of the Stokes–Brinkman equation as the momentum balance model in the coupled process allows accurate modeling of the evolution process of a natural fracture system. The proposed mathematical model involves a coupled system of highly nonlinear partial differential equations. We have developed and implemented a numerical procedure that solves the Stokes–Brinkman equation by the mixed finite element method and solves the reactive-transport equation using the control volume finite difference method in a sequential fashion. Numerical validation and sensitivity studies have been performed using the proposed numerical solution procedure. The preliminary numerical results demonstrate that the fracture connectivity, flow velocity, and reaction rate are the dominant factors in fracture evolution.

Description: \(\hbox {CO}_{2}\) flood is one of the most successful and promising enhanced oil recovery technologies. However, the displacement is limited by viscous fingering, gravity segregation and reservoir heterogeneity. Foaming the \(\hbox {CO}_{2}\) and brine with a tailored surfactant can simultaneously address these three problems and improve the recovery efficiency. Commonly chosen surfactants as foaming agents are either anionic or cationic in class. These charged surfactants are insoluble in either \(\hbox {CO}_{2}\) gas phase or supercritical phase and can only be injected with water. However, some novel nonionic or switchable surfactants are \(\hbox {CO}_{2}\) soluble, thus making it possible to be injected with the \(\hbox {CO}_{2}\) phase. Since surfactant could be present in both \(\hbox {CO}_{2}\) and aqueous phases, it is important to understand how the surfactant partition coefficient influences foam transport in porous media. Thus, a 1-D foam simulator embedded with STARS foam model is developed. All test results, from different cases studied, have demonstrated that when surfactant partitions approximately equally between gaseous phase and aqueous phase, foam favors oil displacement in regard to apparent viscosity and foam propagation speed. The test results from the 1-D simulation are compared with the fractional flow theory analysis reported in the literature.

Description: The determination of the hydraulic dispersivity and effective fraction of porous medium contributing to transport on soil and rock sample in the laboratory is important to understand and model the evolution of miscible contaminant plumes in groundwater. Classical methods are based on the interpretation of the breakthrough curve, i.e., the evolution of the concentration in contaminant at the downstream end-face of a sample into which a front of contaminant is advected. Here we present an experimental device aimed at performing such measurements, but also allowing the bulk electrical conductivity of the sample to be measured. We show that the dispersivity and effective fraction can be inferred from this electrical measurement, and that the combined use of both out-flowing fluid conductivity and bulk conductivity allows the incertitude on the dispersivity and effective fraction to be significantly enhanced.

Description: This study reports a numerical simulation of the natural convection combined with thermal radiation in a square porous cavity with a thin isothermally heated plate placed horizontally or vertically at its center. The vertical walls of the cavity are cooled while the horizontal ones are adiabatic. The governing equations were solved using a finite volume method on a uniformly staggered grid system. The computational results are presented in the form of isotherm and streamline plots and Nusselt numbers. The effects of the Darcy number ( \(10^{-5} \le \mathrm{Da} \le ~10^{-2})\) , plate length ( \(0.25\le D \le 0.75\) ) and the radiation parameter ( \(0 \le R_{d} \le 2\) ) are investigated for the Rayleigh number Ra =  \(10^{7}\) . It is found that the Darcy number, the plate length and the radiation parameter enhance the overall heat transfer rate across the cavity.

Description: Although pressure-pulse-decay permeametry has been in wide use for the past 50 years, its standard configuration and design have remained largely intact. To date, almost all implementations of this approach involve the analysis of a pressure response, in either an upstream or downstream reservoir or both, to a disturbance applied to one of the planar faces of a cylindrical sample, which induces a unidirectional flow along its axial coordinate. For characterizing ultra-low permeability materials like shales or caprocks, where this methodology often becomes problematic, many have turned to unsteady-state analyses on crushed particles. A paucity of models exists in the public literature for the latter scenario, most of which are analytical approximations of very simple cases. This study addresses both issues by proposing analytical flow models for alternative experimental schemes. First, new unidimensional flow scenarios are considered as substitutes for the classical pulse-decay techniques for core plugs. These models involve flow along the axial and radial directions of cylindrical core samples, which are shown to decrease testing times by a factor of 7.5 and 17.5, respectively, as compared to conventional pressure-pulse-decay strategies. Monte Carlo analyses are performed on these approaches, which demonstrate comparable accuracy and reliability to the conventional unidirectional strategy under realistic experimental conditions. Second, a model is presented that relaxes a key simplifying assumption inherent to publicly available models for crushed media, namely that the entire collection of particles is of uniform size. Rather, an analytical model for a discrete distribution of sizes is presented that more accurately represents the broad range of particle sizes that are typically seen in crushed materials.

Description: The dual-medium approach is convenient for simulating flows within two interacting continua such as fractured reservoirs, because it greatly simplifies the apparent complexity of the flow problem while offering a conceptual representation of flows within and between the two continua that helps the understanding of flow responses. Considerable work has been achieved during the last decades to model the coupling term of such models, that is, matrix-fracture transfers. Whereas pseudo-steady-state transfers taking place at late times can be fairly well predicted, the simulation of transient, i.e. early-time, transfers still encounters difficulties due to intrinsically complex transfer mechanisms that the resolution of diffusion equations entails. Those difficulties are emphasized for tight porous media where transient flow behaviour persists over a durable period of time, for compressible fluids that increase inaccuracy of linear approximations of transfers, and also because of the multi-directionality of transfers. Starting from analytical solutions of diffusivity equations, the present paper proposes a methodology to account for transient effects and for non-linearities in matrix-fracture transfer formulas of dual-porosity simulators in order that they can predict the production of unconventional low-permeability hydrocarbon reservoirs. Validation of these formulas for the production of very tight fractured media is shown at the matrix block scale and at the scale of a stimulated reservoir volume.

Description: Variations of the cross-sectional area of a conduit embedded within a porous medium have two effects on flow and transport. First, the hydraulic gradient required to convey a specified flux of water is increased. Second, local exchanges of water and pollutants between the conduit and surrounding porous medium are induced, forming a hyporheic zone. Both these effects are quantified in the case that the variations are periodic and the fractional change of conduit flux induced by the variations is small. The resistance to flow increases dramatically as the variations increase in amplitude. The volume of the hyporheic zone is proportional to the square of the wavelength of the variations. If the wavelength is large, the volume of the hyporheic zone can be far larger than that of the conduit, permitting the sequestration of contaminants for long periods of time.

Description: A new data analyzing method to characterize pore size distribution (PSD) of porous media was recently presented in the context of an international consensus on the need to develop alternatives to toxic mercury porosimetry. It consists in measuring the flow rate Q at several pressure gradients \(\nabla \textit{P}\) during flow experiments of yield stress fluids through porous media. In the present work, the PSD of different types of porous media is determined with this new technique and the obtained results are compared with those provided by mercury porosimetry. A series of experiments using a given yield stress fluid with different porous media were carried out in order to study the relevance of the obtained PSD. Besides, the critical aspects conditioning the experimental performance of the method were also identified and assessed.

Description: This special issue of CiSE magazine deals with the application of discrete modeling and simulation tools to problems from different fields, including physics, engineering, environment science, social science, and life sciences. Many of the authors highlighted here examine the computing abilities and principles of discrete models with a focus on their expressive dynamics, their emergent computation, and their inherent parallelism, making them suitable for high-performance computing. Such models can also successfully tackle the computational bottleneck in terms of the complexity inherent in so many mesh-based and analytical numerical simulations.

Description: In this article, the dependence of tortuosity on the geometrical structure of a porous medium is studied. In particular, the considered porous media have anisotropic structures, being composed by a collection of object of similar shape, with a well-defined orientation. Geometrical expressions for the tortuosity as a function of the porosity, of shape factors characterizing the geometry of the solid objects and of the orientation of the flow with respect to the object axes are derived. Besides the general case, two simpler expressions are derived for 2D porous media and for media composed by axisymmetric objects. The expressions for the two particular cases are validated through a series of numerical simulations of diffusion phenomena, finding a good agreement. The model is also compared with experimental data from literature, showing its possible use in the prediction of the transport properties of a porous medium made by assembling similar solid particles, by a simple geometrical characterization of its components. Finally, a parametric analysis is performed, showing a strong dependence of the tortuosity on the objects shape and on their orientation with respect to the flow. The capability of the presented model to predict such effects can be used to design materials with particular non-isotropic transport characteristics.

Description: Computationally efficient microscale models designed to simulate multi-phase flow and characterize low-porosity media are challenged in thin, highly porous materials, primarily due to large, irregular pore spaces and inability to satisfy representative elementary volume requirements. In this article, we describe the pore topology method (PTM) and explore its capabilities to characterize a set of isotropic fibrous materials and to simulate multi-phase flow. PTM is a fast, algorithmically simple method that reduces the complexity of the 3-D void space geometry to its topologically consistent medial surface and uses it as a solution domain for single- and multi-phase flow simulations. Our results in permeability calculations, pore size distribution, and quasi-static drainage and imbibition simulations are in very good agreement with other numerical methods and analytical solutions. We expect that incorporating detailed spatial information about the porous media structure into the medial surface will enable a more accurate representation of the void space structure and of physical phenomena involved in multi-phase flow, thus expanding the applicability of PTM to a broader range of porous media, including non-fibrous materials.

Description: In this paper we present new methods to estimate the effective permeability ( \(k_\mathrm{eff}\) ) of heterogeneous porous media with a wide distribution of permeabilities and various underlying structures, using percolation concepts. We first set a threshold permeability ( \(k_\mathrm{th}\) ) on the permeability density function and use standard algorithms from percolation theory to check whether the high permeable grid blocks (i.e., those with permeability higher than \(k_\mathrm{th}\) ) with occupied fraction of “ p ” first forms a cluster connecting two opposite sides of the system in the direction of the flow (high permeability flow pathway). Then we estimate the effective permeability of the heterogeneous porous media in different ways: a power law ( \(k_\mathrm{eff} =k_\mathrm{th} p^{m}\) ), a weighted power average ( \(k_\mathrm{eff} =\left[ {p\cdot k_\mathrm{th}^m +\left( {1-p} \right) \cdot k_\mathrm{g}^m } \right] ^{1/m}\) with \(k_\mathrm{g}\) the geometric average of the permeability distribution) and a characteristic shape factor multiplied by the permeability threshold value. We found that the characteristic parameters (i.e., the exponent “ m ”) can be inferred either from the statistics and properties of percolation subnetworks at the threshold point (i.e., high and low permeable regions corresponding to those permeabilities above and below the threshold permeability value) or by comparing the system properties with an uncorrelated random field having the same permeability distribution. These physically based approaches do not need fitting to the experimental data of effective permeability measurements to estimate the model parameter (i.e., exponent m ) as is usually necessary in empirical methods. We examine the order of accuracy of these methods on different layers of \(10{\mathrm{th}}\) SPE model and found very good estimates as compared to the values determined from the commercial flow simulators.

Description: In this paper, a unit-cell model for determination of the effective thermal and electrical conductivity, respectively, of highly porous, closed-cell metal foams is presented. Hereby, (i) a large contrast between the transport properties of the conducting, solid material phase and the pore space is assumed, and (ii) thin, interconnected spherical shells of the solid material phase in a simple cubic arrangement are considered as a geometrical model. The unit-cell model prediction is compared to (i) literature data and (ii) well-established homogenization schemes from the effective medium theory.

Description: The field of computing is rapidly developing, requiring a strong and diverse labor force. The authors' work assessed the relationship between lesbian, gay, bisexual, transgender, and queer (LGBTQ) students' sense of belonging in computing and thoughts about leaving the field. The results of two studies indicated that among undergraduate students (study 1) and graduate students (study 2), thoughts about leaving a computing program were associated with feeling a low sense of belonging in the computing community. Importantly, women LGBTQ students reported the lowest sense of belonging among all student groups in the samples. These findings suggest in order to capitalize on talent and perspective offered by the LGBTQ community, the field of computing should be especially attentive to LGBTQ students' sense of fit in the computing community.

Description: Associate editor in chief Doug Post describes how the periodic table of elements is an example of big data as we know it today.

Description: Using funding from the National Science Foundation, DePauw University launched a program for low-income, first-generation scholars in science, technology, engineering, and math (STEM) fields called Julian Scholars. All but one of the undergraduate students in the program began college expressing interest in medical careers, yet over half of the STEM graduates now pursue computer science graduate degrees or computing careers, which is an important statistic because little research about recruiting and retaining underrepresented low-income, first-generation computing students exists. Cornerstones of the program include a week-long summer research experience bridging high school and college, common classes for each cohort, mentoring, one-on-one resume and internship/research counseling, and scholarships. Rockman et al surveyed the Julian Scholars about the bridge program and additional program components to provide quantitative data and also held focus groups to collect qualitative data to augment graduation rates and postgraduation career information.

Description: The guest editors introduce best papers on broadening participation in computing from the RESPECT'15 conference. The five articles presented here are part two of a two-part series representing research on broadening participation in computing. These articles study participation in intersectional ways, through the perceptions and experiences of African-American middle school girls, the sense of belonging in computing for LGBTQ students, the impact of a STEM scholarship and community development program for low-income and first-generation college students, a leadership development program, and how African-American women individually take leadership to enable their success in computing.

Description: Kevin Thielen and Vivienne Tien review J.M. Kinder and P. Nelson's "A Student's Guide to Python for Physical Modeling", declaring that readers can expect to not only know how to write and read Python but also to develop a thorough understanding for developing complex physical models and calculations.

Description: The number of women in computing is significantly lower than the number of men in the discipline, with African-American women making up an even smaller segment of this population. Related literature accredits this phenomenon to multiple sources, including background, stereotypes, discrimination, a lack of self-confidence, and a lack of self-efficacy. However, a majority of the literature fails to represent African-American females in research studies. The purpose of this study is to understand the factors that influence the attitudes of African-American middle school girls toward computer science. The results reveal that the African-American middle school girls in the sample generally have negative attitudes toward computer science. However, after participating in a computer science intervention, perceptions become more positive due to four factors: engaging in the intervention, the intervention content domain, the facilitation of performance accomplishments, and participant characteristics.

Description: Research on marginalized groups in science, technology, engineering, and mathematics (STEM) commonly overlooks those who persist and succeed, positioning groups such as women of color as passive victims instead of active agents in their own achievements. Focusing on women of color who are successfully staying in STEM, particularly in a field like computer science where women and minorities are severely underrepresented, lets researchers pay attention to the ways the women enact agency. This articles examines the agentic strategies women of color in computing use to ensure their own success. The authors present stories of agency from women of color who describe their approaches for actively persisting in computing. Such approaches include being motivated by challenges and finding inspiration from failure; drawing on unique experiences as marginalized persons; and developing and using "soft"' skills.

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Description: In this article, the authors examine the impact of participation in a national community for broadening participation in computing that engages college students in computing-related service projects. Results of their study show many benefits for undergraduate computing students who engage in such projects, including academic, career, and personal benefits, with students who are underrepresented in computing benefitting more than others. Results also suggest that that an annual conference centered on training and reflection on service learning projects can help build a strong sense of community among students who otherwise wouldn't have access to a similar group of peers. These findings establish empirical support for the Students & Technology in Academia, Research, and Service Computing Corps model of engagement, a flexible approach that can be applied across a variety of institutional types to positively impact underrepresented students in computing.

Description: The influence of the moisture capacity of cell walls on liquid transport in wood is studied using neutron imaging in combination with precision weighing. The time-dependent and spatial distribution of two liquids, one polar, water, and one nonpolar, decane, is documented during liquid uptake in the three orthotropic directions for samples of three softwood species: spruce and fir heartwood, and pine sapwood. Polar and nonpolar liquid uptake versus time is compared, the spatial distribution of the liquids within the samples is discussed, and the liquid volume and swelling profiles along the height of the samples are described in details. Water uptake is shown to be slower than decane uptake, due to water being adsorbed by the cells walls. Decane, due to its very low contact angle and high wettability compared to water, does not face much resistance from wood cellular features.

Description: Several sorption nonequilibrium models have been developed to gain a better understanding of solute transport in porous media, among which are those that assume a single-rate behavior. In this study, two commonly used single-rate models were fitted to computer-simulated breakthrough data from hypothetical column experiments in which multirate sorption kinetics exist at the pore scale. The objective was to determine how the sorption distribution coefficient ( K ) predicted using these models depends on the conditions under which the data were obtained. Simulated cases covered a range of experimental conditions and involved compounds with different sorption characteristics and different degrees of sorption rate heterogeneity. Results revealed that, for a system with a multirate sorption behavior, the true K value is under-predicted if the parameter estimation is determined by curve fitting a single-rate model. The extent of deviation between the fitted and true K increases with the decrease in residence time and increase in sorption rate heterogeneity. Functional relationships were developed between the relative reduction in K and solute residence time. Analysis using the relationships developed suggests that a major potential cause of the previously reported discrepancy between batch- and column-determined K could be attributed to the use of single-rate models for parameter prediction.

Description: Quantitative validation of numerical simulations of percolation in porous media has always been challenging due to the stochastic nature of the material structure and morphology regardless of the numerical technique being used. In this article, we present a technique that allows for a quantitative comparison between numerical and experimental percolation. The experimental observations are of injection pressure and liquid intrusion within thin porous materials in a Hele-Shaw style test. The thin porous materials tested had a surface treatment such the contact angle was larger than \(90^{\circ }\) resulting drainage percolation. Flow rates were adjusted to encompass the range of capillary numbers for drainage flow patterns between the stable displacement and capillary fingering. In parallel to the experimental observations, a series of numerical simulations using a two-dimensional pore network model were performed mimicking the Hele-Shaw experiments. The material properties of the pore network realizations, pore size distribution, contact angle, and representative volume for the pore space were based on measurements of the porous materials tested. Boundary and initial conditions were matched between numerical simulations and experiments. To compare and validate the numerical simulation against the experiments, a new scaling of the dissipated energy during percolation in thin porous media was used. This scaling has been recently used to identify the transition between capillary fingering and stable displacement for drainage in different thin porous materials and provides a unique method for characterizing percolation in thin porous materials. Though the experiments and simulations presented in this article are for drainage, the technique described is equally applicable to imbibition. Excellent agreement is obtained between experiment and simulation with clear delineation between different types of thin porous materials.

Description: We formulate a problem describing the onset of multi-diffusive convection in a horizontal porous layer. Our formulation collapses to a clear fluid case in a special limit. We study this problem, analytically and numerically, for the case of two diffusing components. We concentrate on the case when the boundary conditions at the two horizontal walls approach isoflux conditions and thus the critical wave number approaches zero. We investigate how the reduction in the critical wave number affects oscillatory instability.

Description: Subsurface simulation of multiphase extraction from wells is notoriously difficult. Explicit representation of well geometry requires small grid resolution, potentially leading to large computational demands. To reduce the problem dimensionality, multiphase extraction is mostly modeled using vertically averaged approaches. In this paper, a multiphase well model approach is presented as an alternative to simplify the application. The well model, a multiphase extension of the classic Peaceman model, has been implemented in the STOMP simulator. The numerical solution approach accounts for local conditions and gradients in the exchange of fluids between the well and the aquifer. Advantages of this well model implementation include the option to simulate the effects of well characteristics and operation. Simulations were conducted investigating the effects of extraction location, applied vacuum pressure, and a number of hydraulic properties. The obtained results were all consistent and logical. A major outcome of the test simulations is that, in contrast to common recommendations to extract from either the gas–NAPL or the NAPL–aqueous phase interface, the optimum extraction location should be in between these two levels. The new model implementation was also used to simulate extraction at a field site in Brazil. The simulation shows a good match with the field data, suggesting that the new STOMP well module may correctly represent oil removal. The field simulations depend on the quality of the site conceptual model, including the porous media and contaminant properties and the boundary and extraction conditions adopted. The new module may potentially be used to design field applications and analyze extraction data.

Description: Simple, yet accurate representation of cell structure is essential when conducting a multidimensional thermo-fluid simulation on porous medium in microscopic scale. Presented in this paper is a study of the fluid dynamic simulation of the nickel metal foam’s unit cell domain using idealized cell structure. Commercially available multi-physics package, COMSOL, was utilized to conduct numerical simulation. Simplified methodology to create an idealized cell structure of metal foam is presented, and simulation results on pressure drop are discussed. Nonlinear solver in COMSOL was utilized to solve the unidirectional pressure drop and permeability across the cell structure. Obtained results showed confirmed agreement to the data obtained from the experiment and previous researchers, verifying the practicality and applicability of the proposed unit cell structure.

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Description: Here, Konrad Hinsen talks about how one aspect of validating a piece of software is to check that it does what it's expected to do. But how do you write down your expectations?

Description: A Matlab tool called Gide allows user-aided deblurring of images. Gide helps practitioners restore a blurred grayscale image using their knowledge or intuition about the true image. At the same time, it safeguards from possible bias by validating the choice using statistical diagnostics, based on an assumption of Gaussian added noise. Gide also allows practitioners (or students) to visually explore the range of statistically likely solutions resulting from any of three regularization methods: Tikhonov, truncated SVD, and total variation.

Description: A multi-institutional team led by researchers at the US Department of Energy's (DoE) Argonne National Laboratory has achieved high scalability and sustained performance on three of the most powerful systems in the world: IBM Blue Gene/Q supercomputers Mira at Argonne and Sequoia at Lawrence Livermore National Laboratory, and the Cray XK7 system Titan at Oak Ridge National Laboratory. The team set benchmarks for the largest cosmological simulations to date on different high-performance computing architectures on the massively parallel, CPU-only system Sequoia and on the hybrid accelerated Titan. This article takes a closer look at a recent Titan run and the team that's currently pushing the state of the art in precision cosmology with the goal of better understanding cosmic acceleration.

Description: EIC George Thiruvathukal describes the magazine's digital future and the importance of archives--being able to access digital content in the years to come will be an important challenge for both publishers and readers.

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Description: The cosmic microwave background (CMB) consists of photons created in the Big Bang and cooled by the subsequent expansion of the universe to an almost perfectly uniform 3-Kelvin sky signal today. These photons experience the entire history of the universe, and each epoch has left its imprint as tiny fluctuations in their temperature and polarization. Decoding these provides unique insight into the history of the universe, constraining the fundamental parameters of both cosmology and high-energy physics. The faintness of these fluctuations requires us "researchers" to gather huge datasets and analyze them on supercomputers. For 15 years, the National Energy Research Scientific Computing Center (NERSC) has provided the resources for the CMB community's most computationally challenging analyses. In this article, the authors describe how their analysis algorithms and implementations have evolved over this time, driven by both the growth in CMB data volumes and the changes in high-performance computing architectures.

Description: Public funding bodies in the UK and the US have published documents laying out a broadly similar vision for funding the development of e-infrastructures to support scientific collaborations. Analyzing these documents reveals much to commend in them as well as some weaknesses that could lead to failure to achieve their aims. One such weakness is lack of adequate recognition of the effect of the academic reward structure on the development and deployment of e-infrastructures.

Description: Two evolutionary algorithms are introduced as universal approaches for the identification of water transport characteristics of inorganic porous materials in both absorption and desorption phases. At first, genetic algorithm and genetic programming are applied for the inverse analysis of water content profiles measured in an absorption experiment. A comparison of results with the output of the commonly used Boltzmann–Matano approach shows that the calculated diffusivities can reproduce experimental data with a similarly good or even slightly better accuracy. In the second part of investigations, a water desorption experiment is realized for autoclaved aerated concrete, a typical representative of inorganic porous materials used in the construction sector. The genetic algorithm and genetic programming exhibit an excellent performance also in this case. Both approaches can thus be considered as viable, more universal alternatives to the traditional methods.

Description: Electroosmotic flow and dispersion in open and closed packed beds were investigated using Nuclear Magnetic Resonance (NMR) spectroscopy and pore-scale simulation. A series of NMR spectroscopy experiments were conducted to measure the effect of electroosmotic pressure on dispersion in packed spheres as a function of diameter and electric field strength. The experiments confirm earlier observations by others of superdiffusive transport in closed media. However, superdiffusive behavior is observed even at small pore sizes, contrary to earlier results and simulations in fixed sphere packs, and is conjectured to result from pressure-induced rearrangement of the particles. Simulations also support the existence of pore size-independent velocity distributions in closed media. The distribution of reverse velocities is also similar, apart from a difference in sign, to pressure-driven flow in open porous media.

Description: The present work deals with the propagation of Rayleigh-type surface waves in a swelling porous elastic half-space consisting of three phases, namely solid matrix, liquid (viscous) and gas (inviscid). Using Eringen’s theory of swelling porous media, the governing equations are first solved by potential method. Frequency equation of Rayleigh-type waves has been derived, which is found to be irrational due to the presence of radicals in it. This irrational equation has been rationalized into a polynomial, which is then solved numerically for a specific porous model consisting of sandstone, water (viscous) and carbon dioxide as solid, liquid and gas phases, respectively. The nature of Rayleigh-type surface waves in the considered swelling porous medium is found to be inhomogeneous. Two modes of Rayleigh-type surface waves are noticed: One of them is the counterpart of the classical Rayleigh wave, while the second mode of Rayleigh-type surface waves arises due to the presence of either liquid or gas phases of the swelling porous medium. The variation of phase speeds and the corresponding attenuations of Rayleigh-type surface waves are depicted graphically against frequency parameter for the selected model. In the considered model, the swelling parameter has negligible effect on the propagation speeds of Rayleigh-type surface modes. It is also observed that in the absence of swelling, there still exist two modes of Rayleigh-type waves. The effect of the viscosity of the liquid constituent present in the pores is also examined on the phase speeds and attenuations. The results of Gales (Eur J Mech A Solids, 23:345–357 2004 ) for the cases of fluid saturation alone and gas saturation alone have also been deduced analytically as special cases from the present formulation.

Description: An overview of spectroscopic methods to investigate physical processes specific to the water-based ink/substrate interaction is made in this work. Optical techniques (as VIS reflectometry, IR-ATR and spectroellipsometry) and electrical impedance spectroscopy have been employed to study physical phenomena that describe the interaction between water-based mixtures and the substrate for printing; the latter can be absorbent (porous) or non-absorbent of liquid. Therefore, evaporation of aqueous mixtures and/or liquid penetration in porous paper are the main subjects of these studies. After brief introduction in each method, examples of various particular cases are presented and analyzed: evaporation of pure liquids and mixtures, water penetration into paper of various thicknesses, the penetration of different liquids into plain paper. The method of spectroellipsometry was used to characterize the coating of the coated paper for printing industry.

Description: In this article, we present fundamental transport property relations incorporating direct descriptors of the pore structure. The pore structure descriptors are defined from streamline decomposition of the numerical solutions of the transport equations. These descriptors have been introduced earlier, while the calculations are extended to voxel-based microstructures in this article. The pore structure descriptors for the respective transport equations are used in turn to obtain rigorous cross-property relations for porous media. We derive such cross-property relations exemplarily for computed tomography (CT) data and digital rock models of Fontainebleau sandstone, and CT data of two reservoir sandstone facies. Pore structure parameterizations of these porous media are given for electrical conductance and fluid permeability in the microstructure, yielding correlations for the transport property-dependent descriptors of effective porosity, tortuosity and constriction. These relations are shown to be well-correlated functions over the range of sample porosities for the Fontainebleau sandstone. Differences between the outcrop Fontainebleau sandstone and the reservoir samples are observed mainly in the derived hydraulic length descriptor. A quantitative treatment of the obtained cross-property functions is provided that could be applied for porous medium characterization. It is suggested that such cross-property investigation honoring the detailed microstructure will lead to more fundamental relations between porous medium properties, which could be exploited for example in rock typing or wire-line log interpretation.

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Description: An in-depth study of two decades of data from the IPEDS database examines trends in the participation of women in postsecondary academic computing programs at the bachelor's, master's, and doctoral levels. Emphasis is placed on determining differences among the various disciplines within the computing field and differences based on institutional and citizenship/ethnicity characteristics.

Description: Helical flow can occur in porous media if the hydraulic conductivity tensor is anisotropic. We study the structure of steady-state flow fields in three-dimensional anisotropic porous media formed by two homogeneous layers, one of which is anisotropic. We simulate transient transport of a conservative scalar in such flow fields by a hybrid streamline/smoothed particle hydrodynamics method and analyze dilution. We use stretching and folding metrics to characterize the flow field and the dilution index of a conservative scalar divided by the volume of the domain to quantify plume dilution. Based on the results of detailed numerical simulations, we conclude that nonlinear deformation triggers dilution and that plume dilution is controlled by two parameters: the contrast between the principal directions of the anisotropic layer, and the orientation of the hydraulic conductivity tensor with respect to the main flow direction. Furthermore, we show that in this kind of flow fields transverse dispersion is responsible for an increase in plume dilution, while the effect of longitudinal dispersion is negligible.

Description: We have used linear instability theory to determine the condition for the onset of convection in an internally heated horizontal layer, occupied by a porous medium, when the source strength varies in the vertical direction. Some paradigmatic special cases are investigated. In particular, we investigated linear, quadratic and concentrated source strength distributions. Stability is increased in those situations in which the region where the basic temperature gradient is destabilizing is of small extent.

Description: Biogrout is a method for reinforcement of granular soil. In the Biogrout process, calcium carbonate is produced. This solid connects the grains, and therefore the strength of the soil is increased. The calcium carbonate is formed with the use of micro-organisms. Experiments and numerical simulations have been performed to demonstrate the process under various conditions. In this paper, it has been examined whether a reactive transport model can be used to describe a Biogrout experiment that was performed in a column with a length of 5 m. Four different models for the course of the reaction rate are considered. The concentration of micro-organisms and the reaction rate are fine-tuned in order to find a description of the experiment that is a best fit for the particular model. This is done by minimizing the error between the experimental and numerical results for the concentration of calcium carbonate and the by-product of the reaction.

Description: Motivated by observations of saturation overshoot, this article investigates generic classes of smooth travelling wave solutions of a system of two coupled nonlinear parabolic partial differential equations resulting from a flux function of high symmetry. All boundary resp. limit value problems of the travelling wave ansatz, which lead to smooth travelling wave solutions, are systematically explored. A complete, visually and computationally useful representation of the five-dimensional manifold connecting wave velocities and boundary resp. limit data is found by using methods from dynamical systems theory. The travelling waves exhibit monotonic, non-monotonic or plateau-shaped behaviour. Special attention is given to the non-monotonic profiles. The stability of the travelling waves is studied by numerically solving the full system of the partial differential equations with an efficient and accurate adaptive moving grid solver.

Description: A major challenge of \(\hbox {CO}_{2}\) injection into saline aquifers is the risk of formation clogging due to salt precipitation. Capillary-driven flow of brine can provide a continuous transport of dissolved salt toward the dry zone around the injection well where it ultimately precipitates due to evaporation. In this study, core flooding experiments were performed in homogeneous coarse-textured cores and in layered cores consisting of a coarse-textured layer overlying a fine-textured layer. \(\hbox {CO}_{2}\) was injected through a well in the upper part of the cores, and the bottom parts functioned as brine sources. Impairment in injectivity was found due to accumulation of precipitated salt caused by capillary-driven flow from the brine sources to the upper dryer region. Compared to flow domains without a brine source, we found that capillary-driven upward flow at first prevents complete clogging because the porous medium remains wet, but eventually leads to a more severe clogging of the entire domain. The results show that after sufficient dry-out, a coarse-textured injection layer can draw brine from an underlying fine-textured layer by capillary forces. A connected fine-textured layer can therefore contribute to salt precipitation and clogging of the injection layer.

Description: A sequence of drainage and imbibition shocks within the traditional theory of two-phase immiscible displacement can give rise to shallow non-monotone saturation profiles as shown in Hilfer and Steinle (Eur Phys J Spec Top 223:2323, 2014 ). This phenomenon depends sensitively on model parameters and initial conditions. The dependence of saturation overshoot on initial conditions is investigated more systematically in this article. The results allow to determine regions in the parameter space for the observation of saturation overshoot and to explore limitations of the underlying idealized hysteresis model. Numerical solutions of the nonlinear partial differential equations of motion reveal a strong dependence of the overshoot phenomenon on the boundary and initial conditions. Overshoot solutions with experimentally detectable height are shown to exist numerically. Extensive parameter studies reveal different classes of initial conditions for which the width of the overshoot region can decrease, increase or remain constant.

Description: There is a gap between direct discrete fracture network numerical model and conceptual multi-linear/porosity analytical model for simulating production performance from fractured unconventional reservoirs. The principle focus of this work is on proposing a hybrid model of complexly fractured reservoir by associating fractal theory with multiple-fractured configuration. The formulation is established on the trilinear-flow idealization presented by Brown et al. ( 2009 ). Our model could account for the heterogeneity of fracture network in stimulated reservoir volume (SRV) and the arbitrary properties of multiple hydraulic fractures. Furthermore, a semi-analytical solution is correspondingly presented by incorporating Laplace–Fourier transformation and Stehfest numerical inversion based on the principle of pressure superposition. The new algorithm integrates multiple trilinear-flow solutions for single-fracture hypothesis into a general solution for multi-fractured horizontal well. The second focus is put on verification of the semi-analytical solution by comparing with alternative analytical/numerical simulations for two cases: (a) multi-fractures solution in homogeneity media; (b) multi-fractures solution in heterogeneity media with fractal characteristic. Excellent agreement between alternative simulations and our solutions is achieved. Finally, several synthetic examples are introduced to illustrate the application of semi-analytical solution in the field of pressure transient analysis and discuss the effects of the parameters on transient pressure behavior, including fracture number/spacing, conductivity, fractal characteristic constant and associated anomalous-diffusion constant. The model provides a new knowledge and insight into understanding flow behavior in fractured unconventional reservoirs.

Description: Transitions between liquid and gaseous phases of a fluid material are characterised by a jump in density and the coexistence of both phases during the phase change process. The jump occurs at the interface between the fluid phases and can be handled numerically by the introduction of a singular surface. This allows for a thermodynamically consistent description of mass transfer across the interface and the transition of the interfacial term towards the mass production term included in the mass balance equations. In the present article, a multicomponent and multiphasic porous aggregate is treated in a non-isothermal environment, while accounting for the thermodynamics of the fluid-phase transitions. Based on the Theory of Porous Media, this approach provides a well-founded continuum mechanical basis for the description of deformable, fluid-saturated porous solid aggregates. In particular, a bicomponent, triphasic model is proposed consisting of a thermoelastic porous solid, which is percolated by compressible gaseous and liquid fluid phases. The thermodynamical behaviour, i.e. the dependency of the fluid densities on temperature and pressure, is governed by the van der Waals equation of state and the Antoine equation for the vaporisation–condensation line. Moreover, the interface between the fluid phases is represented by a singular surface and results in jump conditions included in the balance relations of the components of the overall aggregate. The evaluation of the jump conditions leads to a formulation of the interfacial mass transfer, which basically relates the energy added to the system to the latent heat needed for the phase change in a certain amount of a substance. The mass transfer itself or the mass production, respectively, furthermore depends on interfacial areas introduced as a function of porosity and saturation. Thus, geometrical and fluid-flow-dependent parameters are included into the phase change process. Finally, this allows for the numerical simulation of evaporation or condensation of, for example, \({\hbox {CO}}_2\) in a deformable porous solid with heat transfer.

Description: Mixing is a scale-dependent phenomenon that has been shown to increase with increasing heterogeneity, mobility ratio, longitudinal correlation length, aspect ratio and distance traveled. The interface between miscible fluids may be dilated by velocity variations, which are promoted by certain characteristics of a porous medium, or by a high mobility ratio. Here we use a high-resolution numerical scheme to compute local dispersivities by fitting grid-block concentration histories to the 1D convection–diffusion equation. We provide new insights on the scale dependence of local dispersivity in heterogeneous porous media. We explain that irreversible mixing only increases monotonically with increasing longitudinal correlation length (layering) for unit mobility ratio displacements. The combination of an adverse mobility ratio and reservoir layering causes mixing to increase, peak and then decline with distance traveled by the injectant. We show that mixing evolves non-monotonically in layered porous media due to the effect of channeling (and not viscous fingering) at adverse mobility ratios. We also examine the effect of diffusion on local dispersivity as modeled in Eulerian simulation. The level of dispersivity is increased when diffusion is explicitly modeled, although molecular diffusion is much smaller than numerical diffusion, even in our high-resolution simulations. Diffusion is more important to consider when sharp concentration gradients exist, as is the case when mobility ratio is large and permeabilities are highly correlated in the longitudinal direction (i.e., layered). This combination gives rise to pronounced channelized flow in which a sharp concentration gradient drives diffusion over a large area of contact between fluids.

Description: 〈h3〉Abstract〈/h3〉 〈p〉To assess salt damage risks in building materials and geomaterials, the key components to identify are the accumulation of salts and the damage propagation. Experimental data combining both are scarce but offer an additional richness for understanding the coupling between transport and mechanics in the context of salt crystallization in porous media. Here, we quantify the drying of sodium sulfate and sodium chloride solutions from Savonnières limestone together with the damaging character of anhydrous sodium sulfate and halite precipitation, respectively. Repeated wetting–drying cycles are performed, by using salt solutions in the rewetting phase and by drying at an elevated temperature of 45 °C. The drying and deformation dynamics are characterized by means of high-resolution neutron radiography, with a moisture content resolution of 0.04 kg/m〈sup〉3〈/sup〉 and a spatial resolution of 13.5 μm/pixel. Precipitation occurs inside the specimen by treating the upper volume of the specimen hydrophobically. High Peclet numbers are found, representing a long first drying stage leading to salt accumulation in a localized zone, increasing the damage risk. In-pore crystallization of halite during drying of 5.8 molal sodium chloride solutions is particularly damaging for our type of samples. Large deformations are observed already during the first cycle, indicative of crack formation. With 1.4 molal sodium sulfate solutions, no damage is observed upon precipitating the anhydrous sodium sulfate crystal, but the drying rate decreases with every cycle due to augmented pore clogging.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉The stress dependency of the porosity and permeability of porous rocks is described theoretically by representing the preferential flow paths in heterogeneous porous rocks by a bundle of tortuous cylindrical elastic tubes. A Lamé-type equation is applied to relate the radial displacement of the internal wall of the cylindrical elastic tubes and the porosity to the variation of the pore fluid pressure. The variation of the permeability of porous rocks by effective stress is determined by incorporating the radial displacement of the internal wall of the cylindrical elastic tubes into the Kozeny–Carman relationship. The fully analytical solutions of the mechanistic elastic pore-shell model developed by combining the Lamé and Kozeny–Carman equations are shown to lead to very accurate correlations of the stress dependency of both the porosity and the permeability of porous rocks.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉Gas bubbles can be generated naturally or introduced artificially in porous media. Gas bubble migration through porous media governs the rate of gas emission to the atmosphere as well as the hydraulic and mechanical properties of sediments. The migration of air bubbles through water-wet porous media of uniform geometry was studied using a glass micromodel. Experiments were conducted to measure the velocity of bubbles of various lengths rising in a glass micromodel saturated with different test liquids and varying elevation angles. The results showed a linear dependency of the average bubble velocity on the bubble length and the sine of inclination angle of the micromodel. Comparisons were made using experimental data for air bubbles rising in kerosene, Soltrol 170 and dyed white oil. The effective permeability of the micromodel for the gas bubble, 〈em〉K〈/em〉〈sub〉g〈/sub〉, was calculated for different systems at different inclination angles, assuming that the effective length for viscous dissipation is equal to the initial static bubble length. It was found that the calculated permeability of the medium for gas bubbles had an increasing trend with increasing the bubble length. To visualize the periodic nature of the flow of rising bubbles in a porous medium, the motion of the air bubbles in white oil was video recorded by a digital camera, reviewed and analyzed using PowerDVDTM11 software. The bubble shape, exact positions of the bubble front and bubble tail during motion and, hence, the dynamic bubble length were determined through image analysis. Numerical simulation was performed by modifying an existing simulation code for the rise velocity of a gas bubble and the induced pressure field while it migrates through the pore network. The results showed that the rise velocity of a gas bubble is affected by the grid size of the pore network in the direction perpendicular to the bubble migration. The findings of this study can have important implications for studies on the migration of injected gas bubbles in geoenvironmental applications, as well as fundamental studies on bubble transport and behavior in porous media.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉To celebrate the tenth anniversary of InterPore, we present an interdisciplinary review of colloid transport through porous media. This review aims to explore both classical colloid transport and topics that fall outside that purview and thus offer transformative insights into the physics governing transport behavior. First, we discuss the unique colloid characteristics relative to molecules and larger particles. Then, the classical advection–dispersion–filtration models (both conceptual and mathematical) of colloid transport are introduced as well as anomalous transport behaviors. Next, the forces of interaction between colloids and porous media surfaces are discussed. Fourth, applications that are interested in maximizing the transport of colloids through porous media are considered. Then the concept of motile, active biocolloids is introduced, and finally, colloid swarming as a newly recognized mode of transport is summarized.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉Natural convection in a porous enclosure in the presence of thermal dispersion is investigated. The Fourier–Galerkin (FG) spectral element method is adapted to solve the coupled equations of Darcy’s flow and heat transfer with a full velocity-dependent dispersion tensor, employing the stream function formulation. A sound implementation of the FG method is developed to obtain accurate solutions within affordable computational costs. In the spectral space, the stream function is expressed analytically in terms of temperature, and the spectral system is solved using temperature as the primary unknown. The FG method is compared to finite element solutions obtained using an in-house code (TRACES), OpenGeoSys and COMSOL Multiphysics〈sup〉®〈/sup〉. These comparisons show the high accuracy of the FG solution which avoids numerical artifacts related to time and spatial discretization. Several examples having different dispersion coefficients and Rayleigh numbers are tested to analyze the solution behavior and to gain physical insight into the thermal dispersion processes. The effect of thermal dispersion coefficients on heat transfer and convective flow in a porous square cavity has not been investigated previously. Here, taking advantage of the developed FG solution, a detailed parameter sensitivity analysis is carried out to address this gap. In the presence of thermal dispersion, the Rayleigh number mainly affects the convective velocity and the heat flux to the domain. At high Rayleigh numbers, the temperature distribution is mainly controlled by the longitudinal dispersion coefficient. Longitudinal dispersion flux is important along the adiabatic walls while transverse dispersion dominates the heat flux toward the isothermal walls. Correlations between the average Nusselt number and dispersion coefficients are derived for three Rayleigh number regimes.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉Estimating the fluid imbibition flow in natural system composed of nanopores is challenging due to the strong fluid/rock molecular scale interaction and the invalidation of the macroscopic thermodynamics treatment. We develop an analytical model for Lennard-Jones fluid imbibition into an organic nanopore considering the phase transition and fluid/rock intermolecular interactions. In addition, we apply the proposed model on octane molecules imbibition into 1–10 nm slit-shape graphite nanopores under the standard and shale reservoir condition. Predicted velocity and density profiles of 2 nm model at the standard condition show that octane molecules first imbibe as vapor phase at around 200–300 m/s and form adsorbed layers near the pore wall. Velocity and density profiles are compared with the molecular dynamic simulation results. Calculated mean velocities of the analytical model and simulation are around 10〈sup〉3〈/sup〉–10〈sup〉4〈/sup〉 of those predicted by classical models, which are similar with previous experimental results. Reservoir condition results show octane can fast flow only when the driving pressure is greater than 0.12 MPa when the initial reservoir pressure is 5.72 MPa. Particularly, the impact of the fluid phase transition on the imbibition rate is significant in organic nanopores.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉The first experimental evidence of polymer adsorption in natural carbonates obtained from streaming potential measurements is presented. The surface probing of the Estaillades core was realized in a highly saline environment with 〈em〉I〈/em〉 ~ 3 M similar to formation water naturally found in some oil reservoirs, which are typical target for enhanced oil recovery (EOR) by Smart Water Injection Methods (SWIM) and Hybrid SWIM. A highly sensitive setup with an exceptional signal-to-noise ratio even at high salinity, allowing to discriminate voltage fluctuations below 0.1 mV, was used to probe the streaming potential coupling coefficient. The injection of partially hydrolyzed polyacrylamide Flopaam 3130S was followed by chase flooding with formation water for several pore volumes, to assure that any changes measured after the polymer flooding are due to the retained polymer. We show that the streaming potential coupling coefficient changes sign after polymer adsorption. This result not only is an unambiguous evidence for polymer adsorption but has implications on chemical EOR scenarios that need to consider wettability changes due to inversion of surface charge.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉Understanding mechanism of transmitted and stored heat in porous materials was extremely important for improving thermal protective performance of clothing. A coupled heat and moisture transfer model in a three-layer fabric system while exposing to a low-level thermal radiation was developed in this study. The model simulated the transmitted and stored heat in porous materials, and considered the effect of moisture transport on the transmitted and stored heat. The predicted results from the coupled model were validated with the experimental results, and compared with the predicted results from the previous model without considering the moisture effect. It was found that the prediction accuracies in skin burn and skin temperature through the coupled model were further improved. The coupled model was used to examine the moisture effect on heat transport and storage in porous materials. The results demonstrated that the moisture within porous materials increased the heat storage and discharge, but decreased the heat transport. The increases in initial moisture content and fiber moisture regain, while increasing the thermal hazardous effect, greatly enhanced the thermal protective performance of clothing. Therefore, it suggested that the moisture management in porous materials was a key consideration for thermal functional design of fabric.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉A high-fidelity physics-based model of mixed-gas transport coupled with kinetic and equilibrium adsorption is derived, and experiments were performed in order to calibrate and exercise the model. In the literature, a continuum-scale model that couples Fickian diffusion with Henry’s law absorption, and kinetic Langmuir adsorption was previously developed to describe the diffusion and sorption of moisture in porous materials. Here, we expand the model to gases, rather than moisture, derive, and implement a competitive adsorption mechanism into the model to enable mixed-gas sorption. This model facilitates a mechanistic-based understanding of the sorption and diffusion processes of mixed gases in polymeric materials. Diffusion and sorption experiments were conducted for a range of partial pressures; model validation and calibration were carried out by comparing modeled mass uptake and experimental data considering the uncertainties of conceptualized (or assumed) physical processes and system parameters. Uncertainty quantification and sensitivity analysis methods are described and exercised here to demonstrate the capability of this predictive model.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉The RANS modelling of turbulence across fluid-porous interface regions within ribbed channels has been investigated by applying double (both volume and Reynolds) averaging to the Navier–Stokes equations. In this study, turbulence is represented by using the Launder and Sharma (Lett Heat Mass Transf 1:131–137, 1974) low-Reynolds-number 〈span〉 〈span〉\(k-\varepsilon \)〈/span〉 〈/span〉 turbulence model, modified via proposals by either Nakayama and Kuwahara (J Fluids Eng 130:101205, 2008) or Pedras and de Lemos (Int Commun Heat Mass Transf 27:211–220, 2000), for extra source terms in turbulent transport equations to account for the porous structure. One important region of the flow, for modelling purposes, is the interface region between the porous medium and clear fluid regions. Here, corrections have been proposed to the above porous drag/source terms in the 〈em〉k〈/em〉 and 〈span〉 〈span〉\(\varepsilon \)〈/span〉 〈/span〉 transport equations that are designed to account for the effective increase in porosity across a thin near-interface region of the porous medium, and which bring about significant improvements in predictive accuracy. These terms are based on proposals put forward by Kuwata and Suga (Int J Heat Fluid Flow 43:35–51, 2013), for second-moment closures. Two types of porous channel flows have been considered. The first case is a fully developed turbulent porous channel flow, where the results are compared with DNS predictions obtained by Breugem et al. (J Fluid Mech 562:35–72, 2006) and experimental data produced by Suga et al. (Int J Heat Fluid Flow 31:974–984, 2010). The second case is a turbulent solid/porous rib channel flow to examine the behaviour of flow through and around the solid/porous rib, which is validated against experimental work carried out by Suga et al. (Flow Turbul Combust 91:19–40, 2013). Cases are simulated covering a range of porous properties, such as permeability and porosity. Through the comparisons with the available data, it is demonstrated that the extended model proposed here shows generally satisfactory accuracy, except for some predictive weaknesses in regions of either impingement or adverse pressure gradients, associated with the underlying eddy-viscosity turbulence model formulation. 〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉Various processes such as heterogeneous reactions or biofilm growth alter a porous medium’s underlying geometric structure. This significantly affects its hydrodynamic parameters, in particular the medium’s effective permeability. An accurate, quantitative description of the permeability is, however, essential for predictive flow and transport modeling. Well-established relations such as the Kozeny–Carman equation or power law approaches including fitting parameters relate the porous medium’s porosity to a scalar permeability coefficient. Opposed to this, upscaling methods directly enable calculating the full, potentially anisotropic, permeability tensor. As input, only the geometric information in terms of a representative elementary volume is needed. To compute the porosity–permeability relations, supplementary cell problems must be solved numerically on this volume and their solutions must be integrated. We apply this approach to provide easy-to-use quantitative porosity–permeability relations that are based on representative single grain, platy, blocky, prismatic soil structures, porous networks, and real geometries obtained from CT-data. As a discretization method, we use discontinuous Galerkin method on structured grids. To make the relations explicit, interpolation of the obtained data is used. We compare the outcome with the well-established relations and investigate the ranges of the validity. From our investigations, we conclude whether Kozeny–Carman-type or power law-type porosity–permeability relations are more reasonable for various prototypic representative elementary volumes. Finally, we investigate the impact of a microporous solid matrix onto the permeability.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉Growing plants under microgravity conditions in a space ship is essential for future long-term missions to supply needs for food and oxygen. Although plant growth modules for microgravity have been developed and tested for more than 40 years, creating optimal saturation conditions for plant growth in the absence of gravity still remains a challenge. In this study, we present results from a series of spontaneous imbibition experiments designed to approximate microgravity conditions by using density-matched fluid pairs. Porous media with patterned wettability characteristics are used to manipulate macroscopic fluid saturation and microscopic fluid interfacial configurations. These are compared to an additional experiment under Earth gravity, wherein we observe spontaneous imbibition of water into common potting soil. Patterning grains of different wettabilities under microgravity conditions proves to be an effective method to manipulate spatial distributions and saturations of fluids. These wettability patterns can be optimised to fine-tune residual fluid characteristics, e.g. non-wetting phase saturation, connectivity and interfacial area. Furthermore, we present tomographic evidence supporting previous work which was suggesting enhanced snap-off and disconnection of the gas phase in porous media under microgravity. 〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉Suspension flow through porous medium was studied using the Stokesian dynamics simulation method. Stokesian dynamics is an efficient tool to carry out numerical simulations for suspension of rigid particles interacting through hydrodynamic and non-hydrodynamic forces. After validating the simulation method for a single particle flowing through an array of fixed grain particles, we have analysed the suspension transport through porous medium. It was observed that the hydrodynamic interactions and the inter-particle non-hydrodynamic forces between the moving and fixed grain particles have a strong influence on the particle trajectories. This was apparent from the change in particle flux with the fractional channel width in the presence of non-hydrodynamic forces. Hydrodynamic interaction between the suspension and grain particles was also studied for large-scale porous system that was generated by a random arrangement of the particles in a periodic cell. It was found that the change in porosity leads to change in the average fluctuation velocity of the suspension. The fluctuation velocity was observed to vary linearly with the particle concentration and average suspension velocity. Finally, a comparative study was performed with suspension flow in a straight channel and it was observed that the shear-induced particle migration in porous medium is altered by the presence of grain particles.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉The onset of convection in a porous layer saturated by a power-law fluid is here investigated. The walls are considered to be isothermal, isobaric and permeable in such a way that a vertical throughflow is described. The threshold for a buoyancy-driven cellular flow is investigated by means of a linear stability analysis. This study consists in introducing disturbances with small amplitude. The disturbances are plane waves, i.e. a normal modes stability analysis of the basic stationary solution is performed. The resulting problem is an ordinary differential equation eigenvalue problem which is solved numerically by coupling the Runge–Kutta method with the shooting method. Results are presented in the form of marginal stability curves and their critical points representing the values of the control parameters such that the growth rate of the disturbances is zero. It is found that, among roll disturbances, the most unstable modes are stationary and uniform with infinite wavelength. For this reason, an asymptotic analysis for vanishing wave numbers is carried out. The results of this asymptotic analysis are obtained analytically displaying a very good agreement with the numerical solution. It is found that vertical throughflow plays a destabilising role for pseudoplastic fluids and a stabilising role for dilatant fluids.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉We review fundamental aspects of linear poro-elasticity. In contrast to most available textbooks and review articles, our treatment of poro-elastic media is based on the continuum Mixture Theory. Kinematic state variables and dynamic variables are introduced and formally linearized before the fundamental constitutive relations, between pairs of these, are extensively discussed. The role of porosity in linear poro-elasticity is highlighted, and it is shown that porosity is one of the possible choices for one of the two kinematic state variables, and therefore, relations to alternative pairs of kinematic variables can be formulated. The treatment is concluded by the formulation of the governing set of partial differential equations that constitute the basis for analytical or numerical investigations of boundary value problems.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉Capillary pressure saturation (〈em〉P〈/em〉〈sub〉c〈/sub〉–〈em〉S〈/em〉〈sub〉w〈/sub〉) relationship plays a central role in the description of fluid flow in porous media. In this research, the light transmission visualization (LTV) technique was applied to characterize the 〈em〉P〈/em〉〈sub〉c〈/sub〉–〈em〉S〈/em〉〈sub〉w〈/sub〉 relationship in a double-porosity medium. Four experiments were conducted in two-dimensional (2-D) flow chambers packed with a double-porosity medium composed of a mixture of silica sand and sintered kaolin clay spheres. In each experiment, a different volumetric fraction of macropores and micropores was used. The experiment was also repeated by compacting the flow chamber with silica sand only to represent single-porosity medium. Variable saturations of water across the height of the system were applied by controlling the capillary pressure. Images of the 2-D model were collected using a digital camera and analyzed pixel by pixel to determine water saturation in the double-porosity medium. Results from the LTV technique showed that the 〈em〉P〈/em〉〈sub〉c〈/sub〉–〈em〉S〈/em〉〈sub〉w〈/sub〉 relationships for all experiments in double-porosity soil medium were similar in shape but varied depending on the porous media composition. Comparison with the pressure cell test results showed that the 〈em〉P〈/em〉〈sub〉c〈/sub〉–〈em〉S〈/em〉〈sub〉w〈/sub〉 curves for all experiments consistent comparable to those obtained by the LTV technique. The 〈em〉P〈/em〉〈sub〉c〈/sub〉–〈em〉S〈/em〉〈sub〉w〈/sub〉 curves were also fit to van Genuchten model for comparison and validation. For double-porosity media, the best-fit parameters were consistent with published data for sandy clay. Moreover, little variability was observed in the best-fit 〈em〉α〈/em〉 and 〈em〉n〈/em〉 values for the different double porosity. Overall, this study proves that the LTV technique is a noninvasive laboratory tool that can provide high-resolution spatial data for water saturation distribution in different types of porous media and is capable of producing highly resolved 〈em〉P〈/em〉〈sub〉c〈/sub〉–〈em〉S〈/em〉〈sub〉w〈/sub〉 relationships. 〈/p〉