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Belhaj H.,Petroleum Institute | Dhabi A.,Ecole Polytechnique de Tunisie | Mnejja M.,Ecole Polytechnique de Tunisie
Society of Petroleum Engineers - SPE Reservoir Characterisation and Simulation Conference and Exhibition 2011, RCSC 2011 | Year: 2011

Hydraulic fracturing is a technique commonly used to mitigate formation damage and improve well productivity. This stimulation technique is frequently used to improve oil and gas recoveries from tight reservoirs by virtue of squeezing fracturing fluid under high pressure exceeding formation fracture and propagation pressures. However, the prediction of the production performance of hydraulically-fractured wells, an essential step during hydraulic fracture design, uses analytical solutions that cannot reproduce the complexities associated with flow from the near-wellbore area into the well with both matrix and fracture flow contributions. A sophisticated numerical model, which is based on Computational Fluid Dynamics (CFD), has been used to simulate the fluid flow near the wellbore with the presence of an induced fracture perpendicular to the well trajectory at the pay zone. We used the DFM (Discrete Fracture Model) where the hydraulic fracture is explicitly represented in the model. In this modeling proposal, the fracture is presented as an interface through the rock matrix domain with nonlocal transmission conditions. This allows for communication between flow through the fracture and flow into the matrix systems. Therefore, it will not be necessary to use mesh refinement around the fracture. This is considered a big advantage over most currently used modeling techniques. It is emphasized in this modeling scheme that the fracture is discretized as a 1-D entity to account for fracture aperture by an integral form of the flow equations. Following this, the discrete fracture model is implemented using the MFEM (Mixed Finite Element Method). A case study is presented to support the field application of this unique modeling approach. Copyright 2011, Society of Petroleum Engineers.

Gharbi M.,University of Houston | Sun Z.H.,University of Houston | Sharma P.,University of Houston | White K.,University of Houston | El-Borgi S.,Ecole Polytechnique de Tunisie
International Journal of Solids and Structures | Year: 2011

Recent works have established the critical role of flexoelectricity in a variety of size-dependent physical phenomena related to ferroelectrics including giant piezoelectricity at the nanoscale, dead-layer effect in nanocapacitors, dielectric properties of nanostructures among others. Flexoelectricity couples strain gradients to polarization in both ordinary and piezoelectric dielectrics. Relatively few experimental works exist that have determined flexoelectric properties and they all generally involve some sort of bending tests on micro-specimens. In this work, we present a straightforward method based on nanoindentation that allows the evaluation of flexoelectric properties in a facile manner. The key contribution is the development of an analytical model that, in conjunction with indentation load-displacement data, allows an estimate of the flexoelectric constants. In particular, we confirm the experimental results of other groups on BaTiO3 which differ by three orders of magnitude from atomistic predictions. Our analytical model predicts (duly confirmed by our experiments) a strong indentation size-effect due to flexoelectricity. © 2010 Elsevier Ltd. All rights reserved.

Jaffre J.,French Institute for Research in Computer Science and Automation | Mnejja M.,Ecole Polytechnique de Tunisie | Roberts J.E.,French Institute for Research in Computer Science and Automation
Procedia Computer Science | Year: 2011

This article introduces a model for incompressible, two-phase flow in a porous medium with a fracture. The model is an extension to the case of two-phase flow of the model for single phase flow described in [1]. The model is a discrete fracture model in which the fractures are treated as interfaces of dimension n - 1 but in which there is fluid exchange between the fracture and the surrounding rock matrix. The matrix domain is effected by the fracture flow through a Robin type boundary condition along both sides of the fracture, while the fracture takes into account the flow in the matrix by means of a source term representing the discontinuity across the fracture of the flux. Two-phase flow is modeled using the global pressure formulation in which the unknowns are the global pressure and the wetting phase saturation; see [2]. The case of different rock types in the (n - 1)-dimensional fracture domain and in the n-dimensional matrix rock domain is considered. © 2011 Published by Elsevier Ltd.

Khaled N.,Ecole Polytechnique de Tunisie | Rouissi K.,Ecole Polytechnique de Tunisie | Krarti M.,University of Colorado at Boulder
Journal of Solar Energy Engineering, Transactions of the ASME | Year: 2012

This paper presents an analytical solution associated with the steady-periodic heat transfer for a typical slab-on-grade floor building foundation in contact with a nonhomogeneous soil medium. In particular, the solution accounts for the impact of the above-grade wall thickness on the ground-coupled heat transfer. The interzone temperature estimation profile (ITPE) technique is utilized to obtain the analytical solution to determine soil temperature distributions and to estimate foundation heat loss/gain from slab-on-grade floors. In this paper, the impact of the nonhomogeneous soil properties on the transient foundation heat transfer is investigated for various slab configurations and soil thermal properties. The presented solution presents the first ITPE analytical solution for building foundation coupled with layered soil medium. The results indicate that nonhomogeneous soil properties have a significant effect on soil temperature distribution and on total slab heat loss. In particular, it is found that an error of up to 20 in estimating total slab heat transfer can be incurred if homogeneous soil medium is considered instead of a two-layered ground. © 2012 American Society of Mechanical Engineers.

Rouissi K.,Ecole Polytechnique de Tunisie | Krarti M.,University of Colorado at Boulder | McCartney J.S.,University of Colorado at Boulder
Journal of Solar Energy Engineering, Transactions of the ASME | Year: 2012

This paper presents a heat transfer model for thermo-active drilled-shaft foundations used for heating and cooling buildings. Specifically, this paper presents a numerical approach to evaluate the unsteady temperature distribution within the ground medium surrounding the foundation as well as indoor/outdoor heat fluxes. In particular, a 2D numerical solution was obtained using the finite difference technique with a purely implicit solution scheme. The results of the sensitivity analysis indicate that the efficiency of the thermo-active foundation can be significantly improved with a proper selection of design parameters including heat exchanger fluid flow velocity, foundation depth, and foundation materials. © 2012 American Society of Mechanical Engineers.

Bichiou Y.,Ecole Polytechnique de Tunisie | Krarti M.,University of Colorado at Boulder
Energy and Buildings | Year: 2011

In this paper, a comprehensive energy simulation environment is developed and presented to optimally select both building envelope features and heating and air conditioning system design and operation settings. The simulation environment is able to determine the building design features that minimize the life cycle costs. Three optimization algorithms are considered in the simulation environment including Genetic Algorithm, the Particle Swarm Algorithm and the Sequential Search algorithm. The robustness and the effectiveness of the three algorithms are compared to assess the performance of the simulation environment for various design applications and climatic conditions. In particular, the simulation environment has been applied to design single family homes in five US locations: Boulder, CO; Chicago, IL; Miami, FL; Phoenix, AZ; and San Francisco, CA. Optimal designs are determined to reduce life cycle costs with and without budget constraints. It is found that the optimal selection can reduce life cycle costs by 10-25% depending on the climate and type of homes. © 2011 Elsevier B.V.

Khlifi A.,Ecole Polytechnique de Tunisie | Krarti M.,University of Colorado at Boulder
Journal of Building Performance Simulation | Year: 2012

In this article, the Interzone Temperature Profile Estimation solutions are first utilized to carry out a frequency analysis for the foundation heat transfer to determine the effect of indoor air and ambient air temperature fluctuations on the variation of the foundation heat loss/gain. Then, a frequency-domain regression-based method is used to develop transfer functions for ground-coupled surfaces. The regression frequency-domain method is tested and validated using one-dimensional heat transfer for above-grade walls. It is found that the proposed method provides a more effective alternative than numerical methods to estimate conduction transfer function coefficients for building foundations and thus can be easily implemented in whole-building simulation programs. © 2012 Taylor and Francis Group, LLC.

Ennejah T.,Ecole Polytechnique de Tunisie | Bahloul F.,Ecole Polytechnique de Tunisie | Attia R.,Ecole Polytechnique de Tunisie
Journal of Optical Communications | Year: 2010

A simple actively microstructured optical fiber laser is proposed in order to generate regular pulse bursts at the round trip frequency, with a very high repetition rate. The principle of the scheme is described and demonstrated. We tried to study the output shape of pulses by varying the different linear and non linear parameters of the cavity. An accordable repetition rate fiber laser was obtained. The repetition rate and the width of pulses can be adjusted till 320GHz and 750 fs.

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