Nadia Martaj

Réseaux de neurones

Les neurones, au nombre d’une centaine de milliards, sont les cellules de base du systeme nerveux central. Chaque neurone recoit des influx nerveux a travers ses dendrites (recepteurs), les integre pour en former un nouvel influx nerveux qu’il transmet a un neurone voisin par le biais de son axone (emetteur).

An engineer–oriented optimisation of Stirling engine cycle with finite–size finite–speed of revolution thermodynamics

Finite–time thermodynamics takes into account exo–irreversibilities which are not managed by reversible thermodynamics, especially reservoir–to–gas temperature gaps. In todays works, thermodynamicists use the working gas mass as the main imposed parameter. In this paper, the study of the Stirling engine cycle is carried out with a motorist–oriented viewpoint: instead of the working gas mass, the reference parameters are those linked to engineering constraints; they are the maximum pressure, the maximum volume, the extreme temperatures and the overall thermal conductance; the adjustable parameters are the volumetric compression ratio, the hot–to–cold conductance ratio and the regenerator efficiency. Analytical normalised expressions of the operating characteristics of the engine, such as power, work, efficiency, speed and their optima are set up. Classical results of analytical optimisation are found back and new ones are established, leading to new conclusions. Some dimensionless and dimensional numbers are put into evidence.

Modeling of a Building System and its Parameter Identification

This study proposes a low order dynamic model of a building system in order to predict thermal behavior within a building and its energy consumption. The building system includes a thermally well-insulated room and an electric heater. It is modeled by a second order lumped RC thermal network based on the thermal-electrical analogy. In order to identify unknown parameters of the model, an experimental procedure is firstly detailed. Then, the different linear parametric models (ARMA, ARX, ARMAX, BJ, and OE models) are recalled. The parameters of the parametric models are obtained by the least square approach. The obtained parameters are interpreted to the parameters of the physically based model in accordance with their relationship. Afterwards, the obtained models are implemented in Matlab/Simulink® and are evaluated by the mean of the sum of absolute error (MAE) and the mean of the sum of square error (MSE) with the variable of indoor temperature of the room. Quantities of electrical energy and converted thermal energy are also compared. This study will permit a further study on Model Predictive Control adapting to the proposed model in order to reduce energy consumption of the building.

Study of improving the thermal response of a construction material containing a phase change material

The use of phase change materials (PCMs) for improving the thermal comfort in buildings has become an attractive application. This solution contributes to increasing the thermal inertia of the building envelope and reducing power consumption. A building element filled with a PCM and equipped with ventilation tubes is proposed, both for increasing inertia and contributing to refreshing building envelope. A numerical simulation is conducted by the finite element method in COMSOL Multiphysics, which aims to test the thermal behaviour of the developed solution. An experimental study is carried out on a concrete block containing a PCM with ventilation tubes. The objective is to see the effect of PCM coupled with ventilation on increasing the inertia of the block. The results show the ability of this new solution to ensure an important thermal inertia of a building.

Traitement numérique des signaux aléatoires

Nous considerons un filtre a reponse impulsionnelle finie (FIR) de fonction de transfert:\( F(z^{-1})=\frac{1}{2}(1+z{-1})\) Ce filtre peut aussi etre defini par cette equation aux differences : \(y(k)=\frac{1}{2}[x(k)+x(k-1)]\) Le filtre n’etant pas recursif, sa sortie y(k) ne depend que des echantillons du signal d’entree x(k).

Statistiques et probabilités

Les statistiques et les probabilités occupent une place importante dans l’enseignement de certaines classes préparatoires. Les principales fonctions nécessaires pour travailler dans ce domaine se trouvent dans les applications Calculs et Tableur & listes. L’application Données & statistiques permet d’effectuer des représentations graphiques de données statistiques, l’application Graphiques & géométrie ne permettant que la représentation de nuages de points. Des fonctions définies dans ce chapitre vous permettront d’étendre les possibilités de votre unité nomade.

Thermoacoustic Effect Under the Influence of Resonator Curvature

The present work deals with a CFD simulation of thermoacoustic engine composed of two heat exchangers, stack and resonator. The simulation is based on a numerical model based on coupled compressible Navier-Stokes and heat transfer equations that govern the working gas using COMSOL Multiphysics. The objective of this work is to investigate the effect of different bent resonators (30°, 60°, 90°) and the effect of varying the length over which a constant curvature angle (90°) on acoustic pressure and the operating frequency of thermoacoustic engine.

2D simulation of the oscillating flow in the thermoacoustic engine Swift Backhaus

This work is devoted to the study of a thermoacoustic Swift-Backhaus engine, composed of a porous medium regenerator and a resonator consisting of an annular loop and of a linear portion. This machine has finally attracted the attention of researchers to create industrial applications of renewable energies. This last stage can only be done after an improvement and an optimization of certain components of the machine, in order to reduce the losses of heat by convection, due to nonlinear phenomena. The simulation is based on solving the coupled Navier-Stokes and heat equations for a compressible fluid. The COMSOL Multiphysics software provides the numerical tools to solve the strong coupling of transient transitional fluid flow and heat transfer using the iLES (implicit Large Eddy Simulation) method.

Energy efficiency of thermoacoustic systems — Study of acoustic streaming in standing wave resonator

The acoustic streaming is a time-averaged flow that can generate in the thermoacoustic devices. The origin of the slow phenomena is the interaction between the acoustic oscillation in the fluid and thermal and mechanical conditions on the solid walls. This mean flow leads to mean convective heat transport that can have a large impact on the performance of thermoacoustic devices. This paper reports on the acoustic streaming in a standing wave resonator. We have carried out a study of acoustic streaming, firstly experimentally using LDV technique, secondly theoretically using DeltaEC based on linear theory, and finally numerically with Fluent software. Results of three methods are compared and analyzed.

Flow and heat transfer in thermoacoustic resonators implicit 2D large eddy simulations

In this study, we have devised a numerical 2D model (plane symmetry) of a linear thermoacoustic machine composed of two heat exchangers, stack and a resonator. It solves the coupled compressible Navier-Stokes and heat transfer equations using COMSOL Multiphysics software, using an ideal gas model for air, and P2-P1 finite elements. Implicit Large Eddy Simulation (iLES) has been used to simulate the transitional flow and thermoacoustic dynamics in this device. It is an effective method for transitional flows, especially when coupled with heat transfer [10]. These techniques are numerically efficient, since they require only a moderate refinement of the spatial mesh and time-stepping sequence, without any additional terms or equations. They have the advantage of using dissipation properties of existing numerical schemes, when they have certain properties that make them equivalent, from a dynamic and energetic point of view, to the effect of turbulence on the large scales of the flow.