Numerical study of radiative heat transfer effects on a complex configuration of rack storage fire

This work describes the application and the performance of a new radiation model in CFD calculations for the simulation of thermal radiation transfer effects on a fire scenario. A 3D Cartesian coordinates radiative heat transfer procedure based on coupling of the FTn finite volume method (FTnFVM) with the bounded high-order resolution CLAM scheme is developed. The narrow-band based weighted-sum-of-gray-gases (NB-WSGG) model is applied to take account of nongray effects by CO₂, H₂O and soot. To treat irregular boundaries, the present model used the blocked-off-region procedure. This radiation code is implemented in the Fire Dynamics Simulator (FDS), a Computational-Fluid-Dynamics-based fire model, where a the combustion is represented by means of the mixture fraction with a single step chemical reaction model and the Large Eddy Simulation (LES) is used to model the dissipative processes. Computational results with and without radiation effects are compared against available experimental data and quasi-steady state law correlations of in-rack storage fire, which consists a complex configuration of double tri-wall corrugated paper cartons placed onto a wood pallet. Sensibility analyses of spatial and angular grids demonstrate the improvements due to the FTnFVM and to the CLAM scheme in the configuration studied. Results show that the simulations of the flame height, the gas temperature and the gas velocity are strongly influenced by thermal radiation. Overall, simulations predicted closer profiles to the experimental results only when the nongray-sooting radiation model was incorporated and an over-prediction of the gas temperature and the flame height is found when radiation is neglected. A sensibility analysis has shown that the flame characteristics are strongly affected by the soot yield.     

Performance analysis of Vernier slotted doubly salient permanent magnet generator for wind power

This paper presents the impact results of the variation of the rotor and the stator tooth pitches (Vernier effect), on the waveform of the back-electromotive force (EMF) generated by the low speed Doubly Salient Permanent Magnet machine (DSPM). The rotating electrical machines with and without Vernier effect are designed and optimized using genetic algorithms combined with finite element method. The optimization of machines parameters is focused on the maximization of the mass to torque ratio. The results show that the machine with Vernier effect has better performances. The obtained Vernier slotted doubly salient permanent magnet generator is then integrated into an autonomous wind energy conversion system. Simulations tests are carried out through Matlab/Simulink. The results show that the proposed machine is a valid and inexpensive alternative for directly coupled wind turbines.     

Magnetohydrodynamic co-rotating flow in a vertical cylindrical container

ABSTRACT

The effect of an external axial magnetic field on the liquid metal flow produced by co-rotation of the top and bottom disks in a vertical cylindrical container with a vertical temperature gradient is numerically analyzed. The governing Navier–Stokes, energy, and potential equations along with appropriate boundary conditions are solved using the finite-volume method. Comparisons with the previous results were performed and found to be in excellent agreement. It was observed that the Reynolds number is increased, and the axisymmetric basic state loses stability for circular patterns of axisymmetric vortices and spiral waves. In the mixed convection case the axisymmetric mode disappears, giving an asymmetric mode m = 1. It was also found that the primary thresholds, Re_cr corresponding to modes m = 1 and 2, increase with an increase in Hartmann number (Ha). We can therefore conclude that when the magnitude of the magnetic field exceeds a certain value, the instability becomes a steady bifurcation. Finally, stability diagrams were established according to the numerical results of this investigation. These diagrams show the evolution of primary thresholds as a function of Hartmann number for various values of Richardson number.     

Comments on “Some conditions on zeros to avoid step-responseextrema”. II [and reply]

The commenters give a correct version of Theorem 2 of the above-mentioned paper (Rachid, ibid., vol.40, p.1501-3, 1995). In reply Rachid accepts one of their points and gives a new statement of Theorem 2     

Un modèle générique multi-niveaux pour la recherche d’image par le contenu

In this paper we propose a generic model for content image modelling. The model is based on several levels of information. Each level is called view and relates to a class of information. We distinguish three types of views: the concept, relation and interpretation views. The view concept or relation makes it possible to define respectively the concepts or the calculable relations automatically that do not require any particular interpretation. The view interpretation relates to the interpretation of the contents of the image. The number, the nature and the contents of each view are adaptable and can vary according to the type of application. The operational model is based on the nested conceptual graphs which we extended. The model is implemented and operational and the results obtained are very encouraging.     

Vector-valued image regularization with PDEs: a common framework for different applications

In this paper, we focus on techniques for vector-valued image regularization, based on variational methods and PDE. Starting from the study of PDE-based formalisms previously proposed in the literature for the regularization of scalar and vector-valued data, we propose a unifying expression that gathers the majority of these previous frameworks into a single generic anisotropic diffusion equation. On one hand, the resulting expression provides a simple interpretation of the regularization process in terms of local filtering with spatially adaptive Gaussian kernels. On the other hand, it naturally disassembles any regularization scheme into the smoothing process itself and the underlying geometry that drives the smoothing. Thus, we can easily specialize our generic expression into different regularization PDE that fulfill desired smoothing behaviors, depending on the considered application: image restoration, inpainting, magnification, flow visualization, etc. Specific numerical schemes are also proposed, allowing us to implement our regularization framework with accuracy by taking the local filtering properties of the proposed equations into account. Finally, we illustrate the wide range of applications handled by our selected anisotropic diffusion equations with application results on color images.     

Synthesis of Biodegradable Diblock Copolymers of Glycolide and Poly(oxyethylene) Using a Montmorillonite Clay as Catalyst

Biodegradable diblock copolymers were prepared from glycolide and poly(oxyethylene) of M_n=600 (POE 600), 1500 (POE 1500) and 2000 (POE 2000). The copolymerization of glycolide and POE was induced in heterogeneous phase by “Maghnite-H⁺” under suitable conditions. Maghnite-H⁺ is a montmorillonite sheet silicate clay exchanged with protons. Various techniques, including ¹H NMR, ¹³C NMR, IR, DSC and Ubbelohde viscometer were used to elucidate structural characteristics and thermal properties of the resulting copolymers. The effect of the [glycolide]/[POE] molar ratio on the rate of copolymerization and on intrinsic viscosity of the resulting copolymers was studied. Data showed that the rate of copolymerization and intrinsic viscosity of copolymers increase with increasing [glycolide]/[POE] molar ratio.     

Cationic Ring Opening Polymerization of Glycolide Catalysed by a Montmorillonite Clay Catalyst

The ring opening bulk polymerization of glycolide catalyzed by Maghnite-H⁺ was reported. Maghnite-H⁺ is a montmorillonite sheet silicate clay, exchanged with protons. The effect of the amount of Maghnite-H⁺ and the temperature on polymerisation was studied. Increasing Maghnite-H⁺ proportion and temperature produced the increase in glycolide conversion. The kinetics indicated that the polymerization rate is first order with respect to monomer concentration. Mechanism studies showed that monomer inserted into the growing chains with the acyl–oxygen bond scission rather than the break of alkyl–oxygen bond.     

Information contained in the motion field of lines and the cooperation between motion and stereo

We investigate the relationships that exist between the three-dimensional structure and kinematics of a line moving rigidly in space and the two-dimensional structure and kinematics (motion field) of its image in one or two cameras. We establish the fundamental equations that relate its three-dimensional motion to its observed image motion. We show how this motion field can be estimated from a line-based token tracker. We then assume that stereo matches have been established between image segments and show how the estimation of the motion field in the two images can be used to compute part of the kinematic screw of the corresponding 3D line. The equations are linear and if several lines belong to the same object provide a very simple way to estimate the full kinematic screw of that object. Finally, we show how the motion field can constrain the stereo matches by establishing necessary conditions that must be satisfied by the motion field of segments which are images of lines belonging to the same object. Only part of this theory has been implemented yet. This part uses Kalman filtering. Several experimental results using synthetic and real data are presented.     

A bounding surface model for concrete

A rate-independent, three-dimensional bounding surface model for concrete is developed. The model adopts a scalar representation of the damage related to the strain and stress states of the material. The salient features of the model are: (1) a bounding surface in stress space that shrinks uniformly as damage accumulates, and (2) material parameters that depend on damage and the distance between the current stress point and the bounding surface. Satisfactory prediction is obtained of the multiaxial compression behavior of concrete in monotonic and cyclic loadings. The model is relatively simple and incrementally linear, and its finite element implementation appears promising.