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Paper is a stochastic network of fibres, water and additives, and in that sense it may be envisaged as a composite material. Since fibres are much longer than the thickness of the paper sheet, the network is planar and almost two-dimensional. The two-dimensional structure governs many paper properties but the three-dimensional porous structure is also important. Insight into the structural changes that take place when paper is compressed in the paper machine may be gained by modelling and simulation of its viscoelastoplastic behaviour. The present work describes a mathematical model based on the cellular solids theory, characterising the nonlinear rheologic behaviour of the material. This approach results in an unsteady state problem and the resulting set of ODEs is solved by means of the DLSODES subroutine, which uses an integrator based in the Gear method. Experiments were conducted on a laboratory-scale dynamic press in order to validate the mechanical model. [Copyright &y& Elsevier]

Abstract: The paper deals with modelling of hygro-thermal performance and thermo-chemical degradation of concrete exposed to high temperature. Several possible simplifications in modelling of heat and mass transport phenomena in heated concrete are considered and their effect on the results of numerical simulations is analyzed. A mathematical model of concrete at high temperature, already extensively validated with respect to experiments, is used as the reference model. It is based on mechanics of multiphase porous media and considers all important couplings and material nonlinearities, as well as different properties of water above the critical point of water, i.e. 647.3K (374.15°C). In this part of the paper, first physical phenomena, as well as heat and mass flux and sources in a concrete element are studied, both during slow and fast heating process, to examine the relative importance of different flux components. Then, the mathematical model of concrete at high temperature, developed by Authors in the last 10years, is briefly presented and for the first time all the constitutive relationships of the model are summarized and discussed in detail. Finally, the method of numerical solution of the model equations is thoroughly presented. In the companion paper (part II) a brief literature review of the existing mathematical models of concrete at high temperature and a summary of their main features and physical assumptions will be presented. Then, extensive numerical studies will be performed with several simplified models, neglecting chosen physical phenomenon or flux components, to evaluate the difference between the results obtained with the simplified models and with the reference model. The study will concern hygric, thermal and degradation performance of 1-D and 2-D axisymmetric concrete elements during fast and slow heating. The analysis will allow us to indicate which simplifications in modeling of concrete at high temperature are practically and physically possible, without generating excessive errors with respect to the full reference model. [Copyright &y& Elsevier]

In this paper we investigate the extent to which variable porosity drug-eluting coatings can provide better control over drug release than coatings where the porosity is constant throughout. In particular, we aim to establish the potential benefits of replacing a single-layer with a two-layer coating of identical total thickness and initial drug mass. In our study, what distinguishes the layers (other than their individual thickness and initial drug loading) is the underlying microstructure, and in particular the effective porosity and the tortuosity of the material. We consider the effect on the drug release profile of varying the initial distribution of drug, the relative thickness of the layers and the relative resistance to diffusion offered by each layer’s composition. Our results indicate that the contrast in properties of the two layers can be used as a means of better controlling the release, and that the quantity of drug delivered in the early stages can be modulated by varying the distribution of drug across the layers. We conclude that microstructural and loading differences between multi-layer variable porosity coatings can be used to tune the properties of the coating materials to obtain the desired drug release profile for a given application. [ABSTRACT FROM AUTHOR]

Abstract: A numerical model is developed for investigating the transport behaviour and geochemical evolution of acidic mine drainage (AMD) in discretely fractured porous media. The simulation approach is tested using a conceptual model of a reactive mine waste system in which an active source of AMD overlies a fractured silicate-rich porous host rock with a low but non-zero matrix permeability. Source composition is based on measured data from an existing mine tailings site. The numerical model includes groundwater flow, AMD infiltration, multi-component advective-dispersive transport, equilibrium geochemical speciation and water-rock pH-buffering reactions within a discrete fracture network (DFN). An analytical solution for parallel-fractures is used to verify the model, which is then applied to simulate the evolution of pH, the major aqueous species from the AMD source, as well as selected mineral buffers. As the acidic drainage water infiltrates into the initially uncontaminated fracture networks, high concentration gradients develop within the matrix along fracture interfaces inducing diffusion-limited pH buffering and precipitation of secondary minerals within the rock matrix. A comparison of AMD evolution in three fracture networks shows that even within a densely fractured network, AMD plume evolution can be significantly different from that obtained from assuming an equivalent porous medium (EPM). The paper also addresses issues of time scales and matrix diffusion. The results have implications for predicting environmental impacts of acid mine drainage in complex mining environments and for coupling of hydro-geochemical and geotechnical models. The model can also be applied to other hydrogeological systems including fractured clays and tills, to other contaminants including hydrocarbons or organic solvents, and to simulate geochemical evolution in natural flow systems. [Copyright &y& Elsevier]

Abstract: The modeling and numerical simulation of char burning rate within the temperature range of 1273–1700K, which is the normal range in most boilers and furnaces, were carried out in this paper. Considering the differences in pore structure between char and non-porous carbon, several key issues were studied and discussed, including fresh char reactivity and its change during the burning process, and the effects of internal oxygen diffusion on the char burning rate. In the section of modeling, dozens of model equations were given and then implanted into the computational code. In the section of numerical simulation, the predicted values were compared with the experimental data gained from the entrained flow reactor including carbon conversion and apparent diameter change of coal char along the tube length, and good agreement was obtained. Additionally, the numerical simulation for biomass char burning was also done and the applicability of the developed model was discussed. The developed char burning model needs few empirical parameters, which can be used conveniently in the numerical simulation of actual combustion process. [Copyright &y& Elsevier]

Abstract: This paper presents a VOF-based two-phase flow model for the simulation of wave interactions with seawall supported by a porous terrace. Firstly, the model was verified against laboratory data in a simple case for wave overtopping of a vertical wall. Comparison of computed and measured wave properties showed reasonably good agreement. The model was then applied to study the interactions of waves and a seawall protected by porous structures with a permeable terrace. The application results showed that the overtopping rate was strongly related to the energy dissipation through the drag force; the porous reef and terrace were very effective to produce a low crest type seawall. It is concluded that there exist two optimum values of porosity of the submerged reef, about of 0.25 and 0.7, that give minimum overtopping rates. Whereas, there is an effective range of porosity of the permeable terrace varying from 0.4 to 0.65 for significantly reducing the overtopping rate. The verification results confirm that the VOF-based two-phase flow model is sufficient robust to simulate the wave overtopping of coastal structures with reasonable accuracy. [Copyright &y& Elsevier]

Abstract: The TalbotOgden model is a mass conservative method to simulate flow of a wetting liquid in variably-saturated porous media. The principal feature of this model is the discretization of the moisture content domain into bins. This paper gives an analysis of the relationship between the number of bins and the computed flux. Under the circumstances of discrete bins and discontinuous wetting fronts, we show that fluxes increase with the number of bins. We then apply this analysis to the continuous case and get an upper bound of the difference of infiltration rates when the number of bins tends to infinity. We also extend this model by creating a two dimensional moisture content domain so that there exists a probability distribution of the moisture content for different soil systems. With these theoretical and experimental results and using a Dynamic Data Driven Application System (DDDAS), sensors can be put in soils to detect the infiltration fluxes, which are important to compute the proper number of bins for a specific soil system and predict fluxes. Using this feedback control loop, the extended TalbotOgden model can be made more efficient for estimating infiltration into soils. [Copyright &y& Elsevier]

Abstract: In this paper, an enriched finite element method is presented for numerical simulation of saturated porous media. The arbitrary discontinuities, such as material interfaces, are encountered via the extended finite element method (X-FEM) by enhancing the standard FEM displacements. The X-FEM technique is applied to the governing equations of porous media for the spatial discretization, followed by a generalized Newmark scheme used for the time domain discretization. In X-FEM, the material interfaces are represented independently of element boundaries and the process is accomplished by partitioning the domain with some triangular sub-elements whose Gauss points are used for integration of the domain of elements. Finally, several numerical examples are analyzed, including the dynamic analysis of the failure of lower San Fernando dam, to demonstrate the efficiency of the X-FEM technique in saturated porous soils. [Copyright &y& Elsevier]

Abstract: In this paper, the authors present an efficient three-dimensional algorithm, based on the fully explicit matrix inversion free finite element version of the Characteristic Based Split (CBS) scheme, and apply it for the first time to the simulation of complex thermo-fluid-dynamic problems in domains containing simultaneously a fluid and a porous layer. The stability analysis recently developed for the two-dimensional version of the algorithm is here extended to the three-dimensional version. Unstructured grids have been successfully employed to solve complex interface problems. The present code produces an effective solution for complex 3D problems, and does not require large computing resources. The advantages deriving from the algorithm’s stability, the use of unstructured meshes and the low computing requirements make the present three-dimensional procedure a powerful and flexible tool for efficient modeling of real life problems. The present 3D code is used to solve both forced and natural convection in partially porous domains. [Copyright &y& Elsevier]

Abstract: DuMux is a free and open-source simulator for flow and transport processes in porous media, based on the Distributed and Unified Numerics Environment (DUNE). Its main intention is to provide a sustainable and consistent framework for the implementation and application of model concepts, constitutive relations, discretizations, and solvers. The paper provides an overview of DuMux with the focus on software-related aspects. Selected examples highlight the multi-scale and the parallel capabilities. [Copyright &y& Elsevier]

Abstract: In this paper, a three-dimensional model is presented to study the geo-temperature variation with the porous theory. The simulation is validated in comparison with experiment that carried out on the mode of heating. The model was used to predict the geo-temperature distribution in operation and recovery period of ground-source heat pump system. Moreover, the influencing factors including thermal conductivity, porosity, backfill material, air temperature, solar radiation energy and velocity of wind on the soil recovery process were calculated. The results show that the soil temperature recovers more quickly when heat conductivity increases and soil porosity decreases. Under the heating mode, the soil temperature recovers more quickly when the solar radiation and air temperature increase and the wind reduces. Furthermore, the results indicate that the soil properties have great effect on the soil recovery, however the environment factors have little effect. [Copyright &y& Elsevier]

Summary: Detailed geological models of a reservoir may contain many more cells that can be handled by reservoir simulators due to computer hardware limitations. Upscaling is introduced as an effective way to overcome this problem. However, recovery predictions performed on a coarser upscaled mesh are inevitably less accurate than those performed on the initial fine mesh. Dual mesh method is an approach that uses both coarse and fine grid information during simulation. In the reconstruction step of this method, the equations should be solved numerically within each coarse block, which is a time consuming process. Recently, a new coarse-grid generation technique based on the vorticity preservation concept has been applied successfully in the upscaling field. Relaying on this technique for coarse-grid generation, a novel method is introduced in this paper, which replaces the time-consuming reconstruction step in the dual mesh method with a fast analytical solution. This method is tested on challenging test cases regarding upscaling, in order to examine its accuracy and speed. The results show that the simulation time is decreased noticeably with respect to the conventional simulation methods. It is also 2–4 times faster than the original dual mesh method with almost the same accuracy. [ABSTRACT FROM AUTHOR]

Abstract: In foam EOR, complex dynamics of bubble creation and destruction controls foam properties. Here we reconsider whether and when non-equilibrium effects are important, focusing specifically on the entrance region, where injected gas and liquid are transformed into foam. We solve for water saturation and foam texture in the entrance region using the population-balance foam model of Kam (2008), which features three steady states (no foam, strong foam, and an unstable intermediate state) at some injection rates, as seen in experiments. We derive and solve equations for water saturation and foam properties along the entrance region at steady state. Mathematical conditions on the entrance region itself can control which of the several possible steady states is ultimately taken downstream by foam. For instance, if foam is not pre-generated, and capillary-pressure gradients are neglected, as in many published simulation studies, the final steady state downstream is the one with highest water saturation – the weakest foam. Simulations neglecting capillary pressure therefore may lead to inference of the wrong foam state in the formation or core. In some cases, in the presence of capillary pressure, analysis of the asymptotic dynamic behavior in the vicinity of possible downstream steady states may rule out some possible steady states. We show that the apparent length of entrance region can be quite different if one measures water saturation or pressure gradient. Finally, we fit foam kinetic parameters to the length of the entrance region seen in some experiments; a companion paper investigates the effect of these parameters on the traveling wave at the shock front downstream. [Copyright &y& Elsevier]

Abstract: This paper focuses on the investigation of the 3D mathematical model to simulate the coupled heat and liquid moisture transfer in hygroscopic porous fibrous media. The flow of the liquid moisture, the water vapor sorption/desorption by fibers and the diffusion of the water vapor are taken into account in this 3D model. Prediction-corrector method is used to solve the 3D governing equations. A series of computational results of the coupled heat and moisture transfer are obtained with the specific initial conditions and boundary conditions. The distribution of the water vapor concentration in the void spaces, the volume fraction of the liquid water in the void spaces, the distribution of the water content in fibers and the changes of the temperature in porous fibrous media are computed. It is shown that the effects of the gravity and capillary actions are significant in hygroscopic porous fibrous media. The comparison with the experimental measurements shows the reasonable agreement between the two. The results illustrate that the 3D model of the coupled heat and liquid moisture transfer in hygroscopic porous fibrous media is satisfactory. [Copyright &y& Elsevier]

Abstract: In the first three parts of this series a three-dimensional (3D) model was developed for transport and reaction of gaseous mixtures in a landfill. An optimization technique was also utilized in order to determine a landfill''s spatial distributions of the permeability, porosity, the tortuosity factors, and the total gas generation potential, given a limited amount of experimental data. In the present paper we develop the model further by including the flow of both the leachate and the gases. A 3D dynamic model is developed that accounts for the generation of the four main gases of a landfill, along with the dissolved organic acids and the carbon in the presence of the leachate. The model is then utilized, through extensive numerical simulations, to study the effect of the various factors on the concentrations of the gases and the micro-organism. In particular, we demonstrate the strong effect of the heterogeneities of a landfill, represented by the spatial distribution of the local porosities, as well as an anisotropic distribution of the local permeabilities, on the behavior of a landfill, and in particular pressure buildup in it. [Copyright &y& Elsevier]

Abstract: This paper presents experimental and numerical studies of the pressure drop in ceramic foams for solar air receiver applications. There are three main aims in this study. The first is to measure the pressure drop in the studied ceramic foams, and to build an empirical model based on the experimental results and a parametric numerical simulation. The second aim is to study flow field characteristics in the ceramic foams, especially in the vicinity of the interface. The third is to study the pressure drop characteristics of two modified structures (by manufacturing holes on the ceramic foams) that are expected to decrease the pressure drop in ceramic foams, but maintain good heat transfer properties. The experimental results from the samples, including two modified structures, along with the simulation results, show that the pressure drop in the ceramic foams follows a modified Darcy relationship. The experimental results also show that the two modified structures dramatically decrease the pressure drop (with pressure drop decreases up to 70% at a superficial velocity of 5m/s). Based on both the experimental and the simulation results, a generalized model for predicting the pressure drop in ceramic foams was proposed. [Copyright &y& Elsevier]

Abstract: A novel technique has been developed to fabricate uranium-ceramic nuclear fuel using the depleted uranium (DU), U3O8 powder, and allylhydridopolycarbosilane (AHPCS) polymer precursor. This process involves a continuous change of the composition, porosity, and material properties. To fabricate nuclear fuel with a uniform structure/volume ratio, it is important to understand the transport phenomena during high temperature processing and at different length scales. In our prior work, a system-level model based on the reactive porous medium theory was developed to account for pyrolysis process during the uranium-ceramic fuel fabrication. In this paper, a mesoscopic model based on the smoothed particle hydrodynamics (SPH) is developed to simulate the synthesis of filler U3O8 particles and SiC matrix. The system-level model provides the necessary thermal boundary conditions for the mesoscopic simulation. The evolution of the particle concentration and the structure as well as the composition of the composite produced is investigated. Since the process heat flux plays an important role in the material quality and uniformity, the effect of the heating rate, filler particle size and distribution on the uniformity and the structure of the final product are investigated. The uncertainty issue is also discussed. [Copyright &y& Elsevier]

• Water-alternating-gas (WAG) process is systematically studied through a modeling work. • The developed model includes proper three-phase capillary pressure, relative permeability, and hysteresis effects. • There is a great match between experimental data and modeling outputs. • A lower fixed injection slug size results in less oil recovery in each cycle. • Optimal operating conditions for WAG are determined based on sensitivity analysis. Mathematical modeling and simulation of three-phase flow in porous media involves complexities related to the three-phase relative permeability, capillary pressure, and hysteresis effects that are cycle-dependent. Extensive theoretical studies are available in the literature, simulating immiscible and miscible water-alternating-gas (WAG) processes; however, the simulation of recovery behaviors and mechanisms of near-miscible WAG is overlooked. Also, a majority of WAG simulation studies lack the cycle-dependent three-phase hysteresis that appears in the relative permeability and capillary pressure models. In this paper, we study a three-phase flow modeling of near-miscible WAG process for EOR implication, using implicit pressure explicit saturation (IMPES) method. The mathematical model simulates a WAG case study in a strongly water-wet Berea sandstone core, using synthetic oil and brine at 38 °C and 12.7 MPa. Three cycles of water flooding (WF) and gas injection (GI) are used in the WAG operation. The recovery data from our mathematical model is in excellent agreement with the corresponding experimental data. The absolute relative error is less than 1.7%, while estimating the ultimate oil recovery factor in the WF and GI stages of all three cycles. We also study the effects of influential variables such as injection rate, WAG ratio, slug size, crude oil viscosity, and core absolute permeability on the WAG performance. The WAG ratio of 1 is found to be better than 0.5 and 2 cases. Although the absolute permeability changes the breakthrough recovery performance of the individual stages, it does not significantly affect the ultimate recovery of near-miscible WAG. Increasing the injection rate decreases the recovery factor. This effect is more pronounced in the GI cycles. Also, the ultimate recovery factor is reduced by 20% upon an increase in the viscosity of the in-situ oil. The findings of this research work can help to better understand the near-miscible WAG injection at various scenarios/conditions in terms of operational conditions and rock and fluid characteristics for the purposes of WAG design, operation, and optimization. [ABSTRACT FROM AUTHOR]