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Search Results: 1 - 10 of 9098 matches for " Sassi Ben Nasrallah "
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Numerical magneto hydro dynamic flow simulation of velocity and pressure for electrically conducting, incompressible fluids
Chaabane, Raoudha;Bouras, Adam;Ben Nasrallah, Sassi;
Journal of the Brazilian Society of Mechanical Sciences and Engineering , 2007, DOI: 10.1590/S1678-58782007000300010
Abstract: in this paper, we report on numerical simulations of incompressible magnetohydroddynamic flows by a two dimensional finite difference scheme associated to an appropriate projection method performed to characterize velocity-pressure formulations along the specified mhd duct by solving the set of differential equations of magnetohydrodynamics. in the present calculation, a working electrolytic solution is considered in order to bring up the application of the magnetohydrodynamic micropump. numerical results show the characteristics of flow velocity, pressure distribution and their convergence tests. the computations aim to optimize the flow rate of a given mhd micropump regarding to its geometrical dimensions and the external electromagnetic excitation.
A new hybrid algorithm for solving transient combined conduction radiation heat transfer problems
Chaabane Raoudha,Askri Faouzi,Nasrallah Ben Sassi
Thermal Science , 2011, DOI: 10.2298/tsci100722015c
Abstract: A new algorithm based on the lattice Boltzmann method (LBM) and the Control Volume Finite Element Method (CVFEM) is proposed as an hybrid solver for two dimensional transient conduction and radiation heat transfer problems in an optically emitting, absorbing and scattering medium. The LBM was used to solve the energy equation and the CVFEM was used to compute the radiative information. The advantages of the proposed methodology is to avoid problems that confronted when previous techniques are used to predict radiative heat transfer, essentially, in complex geometries and when there is scattering and/or non-black boundaries surfaces. This method combination, which is applied for the first time to solve this unsteady combined mode of heat transfer, has been found to accurately predict the effects of various thermo-physical parameters such as the scattering albedo, the conduction-radiation parameter and the extinction coefficient on temperature distribution. The results of the LBM-CVFEM combination were found to be in excellent agreement with the LBM-CDM (Collapsed Dimension Method)this proposed numerical approach include, among others, simple implementation on a computer, accurate CPU time, and capability of stable simulation.
Evaporation of a binary liquid film by forced convection
Nasr Abdelaziz,Debbissi Chokri,Nasrallah Ben Sassi
Thermal Science , 2011, DOI: 10.2298/tsci100427076n
Abstract: This paper deals with a numerical analysis of the evaporation of a thin binary liquid film by forced convection inside a channel constituted by two parallel plates. The first plate is externally insulated and wetted by a thin water ethylene glycol film while the second is dry and isothermal. The liquid mixture consists of water (the more volatile component) and ethylene glycol while the gas mixture has three components: dry air, water vapour and ethylene-glycol vapour. The set of non linear and coupled equations expressing the conservation of mass, momentum, energy and species in the liquid and gas mixtures is solved numerically using a finite difference method. Results concerns with the effects of inlet ambience conditions and the inlet liquid concentration of ethylene glycol on the distribution of the temperature, concentrations profiles and the axial variation of the evaporation rate of species i.
Numerical simulation of sudden-expansion particle-laden flows using the Eulerian lagrangian approach
Mergheni Mohamed Ali,Sautet Jean-Charles,Ticha Ben Hmaied,Nasrallah Ben Sassi
Thermal Science , 2012, DOI: 10.2298/tsci110128036m
Abstract: A Lagrangian-Eulerian model for the dispersion of solid particles in sudden-expansion flows is reported and validated. The fluid was calculated based on the Eulerian approach by solving the Navier-Stokes equations. A Lagrangian model is also applied, using a Runge-Kutta method to obtain the particle trajectories. The effect of fluid turbulence upon particle dispersion is taken into consideration through a statistical model. The predicted axial mean velocity and turbulent kinetic energy of both phases agree well with experimental data reported by Sommerfield.
Evaporation of Water by Natural Convection in Partially Wetted Heated Vertical Plates: Effect of the Number of the Wetted Zone
Abdelaziz Nasr,Chokri Debissi,Amine Belhadj Mohamed,Jamel Orfi,Sassi Ben Nasrallah
Journal of Engineering and Applied Sciences , 2012,
Abstract: This research consists of a numerical investigation of coupled heat and mass transfers by natural convection during water evaporation in a vertical channel. The two channel walls were symmetrically heated by a uniform flux density. One wall is partially wetted by an extremely thin water film and the other is dry. The partially humid plate is divided into 2N with equal lengths being alternatively wet and dry zones. The results are reported in terms of local Sherwood number, the inlet velocity and evaporative rate for different wet zone position and for different wet number zones. However, the mass transfer is extremely influenced by the number of the wetted zones and their positions. The evaporative rate is more intense when the wetted zone is situated at the channel exit. Finally, it is observed that the evaporation is intensified by increasing the number of wetted zones.
Numerical Analysis of the Evaporation of Water by Forced Convection into Humid Air in Partially Wetted Vertical Plates
Chokri Debissi Hfaiedh,Abdelaziz Nasr,Jamel Orfi,Amine Belhadj Mohamed,Sassi Ben Nasrallah
Journal of Engineering and Applied Sciences , 2012,
Abstract: The present study focuses on a numerical investigation of steady conjugated heat and mass transfers by forced convection in an externally heated or insulated channel. One wall is partially wetted by an extremely thin water film, while the other is dry and impermeable. The partially humid plate is divided into 2.n equal regions, which are alternately humid and dry zones. The effect of the number of wetted zones and their positions on the flow, on the heat and mass transfers is analysed. The results are reported in terms of axial distribution of wall temperature, relative heat fluxes and evaporative rate for different wetted zone positions. It is noticed that the change of the wetted zone position has no significant effect on the moist air flow. However, the heat and mass transfers are extremely influenced by the presence of the wetted zones and their positions. As the condition of an insulated channel, the evaporative rate is more intense when the wetted zone is situated at the channel entrance. In case of the condition of a heated wall channel, the situation is generally inversed. It is also shown that there exists a critical value for the density heat flux from which the behaviour of the evaporative rate is reversed. Finally, it is noticed that the evaporation is intensified by increasing the number of humid zones.
Mycobacterium abscessus multispacer sequence typing
Sassi Mohamed,Ben Kahla Imen,Drancourt Michel
BMC Microbiology , 2013, DOI: 10.1186/1471-2180-13-3
Abstract: Background Mycobacterium abscessus group includes antibiotic-resistant, opportunistic mycobacteria that are responsible for sporadic cases and outbreaks of cutaneous, pulmonary and disseminated infections. However, because of their close genetic relationships, accurate discrimination between the various strains of these mycobacteria remains difficult. In this report, we describe the development of a multispacer sequence typing (MST) analysis for the simultaneous identification and typing of M. abscessus mycobacteria. We also compared MST with the reference multilocus sequence analysis (MLSA) typing method. Results Based on the M. abscessus CIP104536T genome, eight intergenic spacers were selected, PCR amplified and sequenced in 21 M. abscessus isolates and analysed in 48 available M. abscessus genomes. MST and MLSA grouped 37 M. abscessus organisms into 12 and nine types, respectively; four formerly “M. bolletii” organisms and M. abscessus M139 into three and four types, respectively; and 27 formerly “M. massiliense” organisms grouped into nine and five types, respectively. The Hunter-Gaston index was off 0.912 for MST and of 0.903 for MLSA. The MST-derived tree was similar to that based on MLSA and rpoB gene sequencing and yielded three main clusters comprising each the type strain of the respective M. abscessus sub-species. Two isolates exhibited discordant MLSA- and rpoB gene sequence-derived position, one isolate exhibited discordant MST- and rpoB gene sequence-derived position and one isolate exhibited discordant MST- and MLSA-derived position. MST spacer n°2 sequencing alone allowed for the accurate identification of the different isolates at the sub-species level. Conclusions MST is a new sequencing-based approach for both identifying and genotyping M. abscessus mycobacteria that clearly differentiates formerly “M. massiliense” organisms from other M. abscessus subsp. bolletii organisms.
Computation of Polytopic Invariants for Polynomial Dynamical Systems using Linear Programming
Mohamed Amin Ben Sassi,Antoine Girard
Mathematics , 2010,
Abstract: This paper deals with the computation of polytopic invariant sets for polynomial dynamical systems. An invariant set of a dynamical system is a subset of the state space such that if the state of the system belongs to the set at a given instant, it will remain in the set forever in the future. Polytopic invariants for polynomial systems can be verified by solving a set of optimization problems involving multivariate polynomials on bounded polytopes. Using the blossoming principle together with properties of multi-affine functions on rectangles and Lagrangian duality, we show that certified lower bounds of the optimal values of such optimization problems can be computed effectively using linear programs. This allows us to propose a method based on linear programming for verifying polytopic invariant sets of polynomial dynamical systems. Additionally, using sensitivity analysis of linear programs, one can iteratively compute a polytopic invariant set. Finally, we show using a set of examples borrowed from biological applications, that our approach is effective in practice.
Controller Synthesis for Robust Invariance of Polynomial Dynamical Systems using Linear Programming
Mohamed Amin Ben Sassi,Antoine Girard
Mathematics , 2011,
Abstract: In this paper, we consider a control synthesis problem for a class of polynomial dynamical systems subject to bounded disturbances and with input constraints. More precisely, we aim at synthesizing at the same time a controller and an invariant set for the controlled system under all admissible disturbances. We propose a computational method to solve this problem. Given a candidate polyhedral invariant, we show that controller synthesis can be formulated as an optimization problem involving polynomial cost functions over bounded polytopes for which effective linear programming relaxations can be obtained. Then, we propose an iterative approach to compute the controller and the polyhedral invariant at once. Each iteration of the approach mainly consists in solving two linear programs (one for the controller and one for the invariant) and is thus computationally tractable. Finally, we show with several examples the usefulness of our method in applications.
Bernstein Polynomial Relaxations for Polynomial Optimization Problems
Mohamed Amin Ben Sassi,Sriram Sankaranarayanan
Mathematics , 2015,
Abstract: In this paper, we examine linear programming (LP) relaxations based on Bernstein polynomials for polynomial optimization problems (POPs). We present a progression of increasingly more precise LP relaxations based on expressing the given polynomial in its Bernstein form, as a linear combination of Bernstein polynomials. The well-known bounds on Bernstein polynomials over the unit box combined with linear inter-relationships between Bernstein polynomials help us formulate "Bernstein inequalities" which yield tighter lower bounds for POPs in bounded rectangular domains. The results can be easily extended to optimization over polyhedral and semi-algebraic domains. We also examine techniques to increase the precision of these relaxations by considering higher degree relaxations, and a branch-and-cut scheme
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