Search results for: Marwan Fahs

Items from 1 to 20 out of 20 results

article

Algorithms for activity correction models for geochemical speciation and reactive transport modeling

Jérôme Carrayrou, Caroline Bertagnolli, Marwan Fahs

Reactive transport softwares are today one of the cornerstones of environmental research. They contain multiphysics with very complex algorithms, including flow, transport, chemical, and sometimes heat transport, mechanical, and/or biological algorithms. Because of this complexity, some parts of these algorithms still have not been sufficiently studied. In this work, we focus on algorithms for activity...

article

A new efficient Bayesian parameter inference strategy: Application to flow and pesticide transport through unsaturated porous media

Anis Younes, Thierry A. Mara, Marc Voltz, Lamia Guellouz, more

Journal of Hydrology > 2018 > 563 > C > 887-899

Statistical calibration of flow and transport models in unsaturated porous media is often carried out with Markov Chain Monte Carlo (MCMC) methods. However, the practicality of these methods is limited by their computational requirement, particularly when large prior intervals are assigned to the model parameters. In this work, a new operational strategy is investigated to alleviate the computational...

article

An Efficient ELLAM Implementation for Modeling Solute Transport in Fractured Porous Media

Fanilo Ramasomanana, Marwan Fahs, Husam Musa Baalousha, Nicolas Barth, more

Water, Air, & Soil Pollution > 2018 > 229 > 2 > 1-22

The goal of this study is to introduce an adaptation of the Eulerian-Lagrangian localized adjoint method (ELLAM) for the simulation of mass transport in fractured porous media, and to evaluate the performance of ELLAM in such a case. The fractures are represented explicitly using the discrete fracture model. The velocity field was calculated using the mixed hybrid finite element method. A sound ELLAM...

article

A comparison of discrete versus continuous adjoint states to invert groundwater flow in heterogeneous dual porosity systems

Frederick Delay, Hamid Badri, Marwan Fahs, Philippe Ackerer

Advances in Water Resources > 2017 > 110 > C > 1-18

Dual porosity models become increasingly used for simulating groundwater flow at the large scale in fractured porous media. In this context, model inversions with the aim of retrieving the system heterogeneity are frequently faced with huge parameterizations for which descent methods of inversion with the assistance of adjoint state calculations are well suited. We compare the performance of discrete...

article

Analyzing natural convection in porous enclosure with polynomial chaos expansions: Effect of thermal dispersion, anisotropic permeability and heterogeneity

Noura Fajraoui, Marwan Fahs, Anis Younes, Bruno Sudret

International Journal of Heat and Mass Transfer > 2017 > 115 > PA > 205-224

In this paper, global sensitivity analysis (GSA) and uncertainty quantification (UQ) have been applied to the problem of natural convection (NC) in a porous square cavity. This problem is widely used to provide physical insights into the processes of fluid flow and heat transfer in porous media. It introduces however several parameters whose values are usually uncertain. We herein explore the effect...

article

Analytical solution and Bayesian inference for interference pumping tests in fractal dual-porosity media

Mohamed Hayek, Anis Younes, Jabran Zouali, Noura Fajraoui, more

Computational Geosciences > 2018 > 22 > 1 > 413-421

A new analytical solution is developed for interference hydraulic pumping tests in fractal fractured porous media using the dual-porosity concept. Heterogeneous fractured reservoirs are considered with hydrodynamic parameters assumed to follow power-law functions in radial distance. The developed analytical solution is verified by comparison against a finite volume numerical solution. The comparison...

article

Bayesian sparse polynomial chaos expansion for global sensitivity analysis

Qian Shao, Anis Younes, Marwan Fahs, Thierry A. Mara

Computer Methods in Applied Mechanics and Engineering > 2017 > 318 > C > 474-496

Polynomial chaos expansions are frequently used by engineers and modellers for uncertainty and sensitivity analyses of computer models. They allow representing the input/output relations of computer models. Usually only a few terms are really relevant in such a representation. It is a challenge to infer the best sparse polynomial chaos expansion of a given model input/output data set. In the present...

article

Extension of the Henry semi-analytical solution for saltwater intrusion in stratified domains

Anis Younes, Marwan Fahs

Computational Geosciences > 2015 > 19 > 6 > 1207-1217

The Henry semi-analytical solution is developed for stratified aquifers with exponential and Gaussian permeability–depth relationships and small dispersion. The semi-analytical solution is sought by expanding the stream function and the concentration in an infinite Fourier series truncated at given orders. Due to the heterogeneity, the semi-analytical solution contains additional terms and quickly...

article

A new benchmark with high accurate solution for hot–cold fluids mixing

Anis Younes, Marwan Fahs, Ali Zidane, Peter Huggenberger, more

Heat and Mass Transfer > 2015 > 51 > 9 > 1321-1336

A new benchmark is proposed for the verification of buoyancy-driven flow codes. The benchmark deals with mixing hot and cold fluids from the opposite boundaries of an open channel. A high accurate solution is developed using the Fourier–Galerkin (FG) method and compared to the results of an advanced finite element (FE) model. An excellent agreement is observed between the FG and FE solutions for different...

article

A new benchmark semi-analytical solution for density-driven flow in porous media

Marwan Fahs, Anis Younes, Thierry Alex Mara

Advances in Water Resources > 2014 > 70 > Complete > 24-35

A new benchmark semi-analytical solution is proposed for the verification of density-driven flow codes. The problem deals with a synthetic square porous cavity subject to different salt concentrations at its vertical walls. A steady state semi-analytical solution is investigated using the Fourier–Galerkin method. Contrarily to the standard Henry problem, the cavity benchmark allows high truncation...

article

An efficient numerical model for hydrodynamic parameterization in 2D fractured dual-porosity media

Hassane Fahs, Mohamed Hayek, Marwan Fahs, Anis Younes, more

Advances in Water Resources > 2014 > 63 > Complete > 179-193

This paper presents a robust and efficient numerical model for the parameterization of the hydrodynamic in fractured porous media. The developed model is based upon the refinement indicators algorithm for adaptive multi-scale parameterization. For each level of refinement, the Levenberg–Marquardt method is used to minimize the difference between the measured and predicted data that are obtained by...

article

A semi-analytical solution for saltwater intrusion with a very narrow transition zone

Anis Younes, Marwan Fahs

Hydrogeology Journal > 2014 > 22 > 2 > 501-506

The Henry saltwater intrusion problem provides a semi-analytical solution that is largely used for benchmarking density-dependent groundwater flow models. The major drawback of this problem arises from the high dispersion value used by Henry (represented by the dimensionless parameter b = 0.1). Finding a stable semi-analytical solution for small values of b is challenging due to the low convergence...

article

On equivalent hydraulic conductivity for oscillation–free solutions of Richard’s equation

Benjamin Belfort, Anis Younes, Marwan Fahs, François Lehmann

Journal of Hydrology > 2013 > 505 > Complete > 202-217

The estimation of numerical equivalent conductivity remains a crucial issue for the accuracy and stability of the solution of the non-linear Richards’ equation (RE) when modeling variably saturated flow. In the literature, it appears that this topic has been typically considered for one-dimensional discretization despite the growing interest in multidimensional problems. After reviewing different...

article

Monotonicity of the cell-centred triangular MPFA method for saturated and unsaturated flow in heterogeneous porous media

Anis Younes, Marwan Fahs, Benjamin Belfort

Journal of Hydrology > 2013 > 504 > Complete > 132-141

In this work, the monotonicity of the symmetric cell-centred Multi-Point Flux Approximation (MPFA) method on triangular grids is studied for saturated and unsaturated flow in heterogeneous porous media. For the linear saturated flow, we derive necessary conditions on the triangulation to satisfy the Positive Transmissibility (PT) condition which ensures monotonicity of the discrete scheme. For the...

article

A Semi-Analytical Solution for the Reactive Henry Saltwater Intrusion Problem

Anis Younes, Marwan Fahs

Water, Air, & Soil Pollution > 2013 > 224 > 11 > 1-11

Because of the existence of a semi-analytical solution, the Henry saltwater intrusion problem has been widely used for benchmarking non-reactive density-driven flow models. In this work, we extend the semi-analytical solution of Henry to reactive transport in variable-density fluid flow. Accurate semi-analytical solutions are provided for three test cases dealing with saltwater transport including...

article

An Efficient Implementation of the Method of Lines for Multicomponent Reactive Transport Equations

Marwan Fahs, Anis Younes, Philippe Ackerer

Water, Air, & Soil Pollution > 2011 > 215 > 1-4 > 273-283

Modeling reactive transport with chemical equilibrium reactions requires solution of coupled partial differential and algebraic equations. In this work, two formulations are developed to combine the method of lines (MOL) with the global implicit approach. The first formulation has a non-conservative form and leads to a nonlinear system of ordinary differential equations with a reduced number of unknowns...

article

An efficient geometric approach to solve the slope limiting problem with the Discontinuous Galerkin method on unstructured triangles

Anis Younes, Marwan Fahs, Philippe Ackerer

International Journal for Numerical Methods in Biomedical Engineering > 26 > 12 > 1824 - 1835

The Discontinuous Galerkin method requires the use of an appropriate slope limiter to avoid unphysical oscillations near sharp fronts. Standard limiters, based on the resolution of a minimization problem with linear constraints, are usually solved using an iterative procedure. In this work, an efficient geometric approach is developed to solve the minimization problem on a general triangular mesh...

article

An easy and efficient combination of the Mixed Finite Element Method and the Method of Lines for the resolution of Richards’ Equation

Marwan Fahs, Anis Younes, François Lehmann

Environmental Modelling and Software > 2009 > 24 > 9 > 1122-1126

In this work, the Mixed Hybrid Finite Element (MHFE) method is combined with the Method Of Lines (MOL) for an accurate resolution of the Richard's Equation (RE). The combination of these methods is often complicated since hybridization requires a discrete approximation of the time derivative whereas with the MOL, it should remain continuous. In this paper, we use the new mass lumping technique developed...

article

Solving density driven flow problems with efficient spatial discretizations and higher-order time integration methods

Anis Younes, Marwan Fahs, Selim Ahmed

Advances in Water Resources > 2009 > 32 > 3 > 340-352

Modelling density driven flow problems requires an excessive computational time and/or heavy equipments due to the non-linear coupling between flow and transport equations. In this work, we develop a robust numerical model with efficient advanced approximations for both spatial and temporal discretizations in order to reduce the excessive computational requirement while maintaining accuracy.The spatial...

article

On the Efficiency of the Direct Substitution Approach for Reactive Transport Problems in Porous Media

Marwan Fahs, Jérôme Carrayrou, Anis Younes, Philippe Ackerer

Water, Air, & Soil Pollution > 2008 > 193 > 1-4 > 299-308

Nonlinear reactive transport problems can be solved using the Operator Splitting (OS) approach, where transport and reaction processes are separated or the Direct Substitution Approach (DSA) where chemical and transport equations are solved simultaneously. The OS techniques can be very attractive, but are known to introduce splitting errors with SNIA (Non Iterative OS) and have low convergence rate...

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