			Home About us Contact

Tracking Technique (tracking + technique)

Distribution by Scientific Domains

Engineering	40%

Selected Abstracts

Smeared crack approach: back to the original track

INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 12 2006
M. Cervera
Abstract This paper briefly reviews the formulations used over the last 40 years for the solution of problems involving tensile cracking, with both the discrete and the smeared crack approaches. The paper focuses on the smeared approach, identifying as its main drawbacks the observed mesh-size and mesh-bias spurious dependence when the method is applied ,straightly'. A simple isotropic local damage constitutive model is considered, and the (exponential) softening modulus is regularized according to the material fracture energy and the element size. The continuum and discrete mechanical problems corresponding to both the weak discontinuity (smeared cracks) and the strong discontinuity (discrete cracks) approaches are analysed and the question of propagation of the strain localization band (crack) is identified as the main difficulty to be overcome in the numerical procedure. A tracking technique is used to ensure stability of the solution, attaining the necessary convergence properties of the corresponding discrete finite element formulation. Numerical examples show that the formulation derived is stable and remarkably robust. As a consequence, the results obtained do not suffer from spurious mesh-size or mesh-bias dependence, comparing very favourably with those obtained with other fracture and continuum mechanics approaches. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Computations of two passing-by high-speed trains by a relaxation overset-grid algorithm

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 12 2004
Jenn-Long Liu
Abstract This paper presents a relaxation algorithm, which is based on the overset grid technology, an unsteady three-dimensional Navier,Stokes flow solver, and an inner- and outer-relaxation method, for simulation of the unsteady flows of moving high-speed trains. The flow solutions on the overlapped grids can be accurately updated by introducing a grid tracking technique and the inner- and outer-relaxation method. To evaluate the capability and solution accuracy of the present algorithm, the computational static pressure distribution of a single stationary TGV high-speed train inside a long tunnel is investigated numerically, and is compared with the experimental data from low-speed wind tunnel test. Further, the unsteady flows of two TGV high-speed trains passing by each other inside a long tunnel and at the tunnel entrance are simulated. A series of time histories of pressure distributions and aerodynamic loads acting on the train and tunnel surfaces are depicted for detailed discussions. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Repellency of deet to nymphs of Triatoma infestans

MEDICAL AND VETERINARY ENTOMOLOGY, Issue 1 2000
R. A. Alzogaray
Summary The repellency of N,N-diethyl-3-methylbenzamide (deet) to Triatoma infestans (Klug) (Hemiptera: Reduviidae) was evaluated using third-instar nymphs and a video tracking technique. Three experimental designs were used: (a) the test arena floor was divided into two halves, only one of which was treated with deet; (b) the arena floor was divided into an inner circle and an outer ring, only the latter treated with deet; (c) half of the test arena was covered by a filter paper roof treated with deet (out of reach of the nymphs). In all three types of experiment, a repellent effect was demonstrated proportional to the dose of deet. When a host (pigeon) was shielded by deet-treated gauze, the rate of blood-feeding by the nymphs was inhibited. Topical pre-treatment of the nymphs with N-ethylmaleimide, to block chemoreception, inhibited the repellency. [source]

Study of particle trajectories, residence times and flow behavior in kneading discs of intermeshing co-rotating twin-screw extruders

POLYMER ENGINEERING & SCIENCE, Issue 4 2004
V. L. Bravo
A three-dimensional finite element model was implemented for the solution of mass and momentum conservation equations in the kneading disc section of an intermeshing co-rotating twin-screw extruder. The polymer melt was modeled with a Carreau constitutive equation. The particle tracking technique was used to obtain residence times and analyze distributive mixing for different length to diameter ratios (L/D) of kneading discs. Previous studies from Kalyon et al. (1) and Cheng and Manas-Zloczower (2) have shown that the mixing performance of intermeshing co-rotating twin-screw extruders is highly dependent on the combination of screw configuration and operating conditions. The complexity of the geometry and the transient character of the flow demand powerful computational tools to characterize the flow and to develop a prediction tool for the analysis of relative performance between different configurations. Difficulties arise in the particle tracking technique because of the time discretization and the presence of moving boundaries. Results show the importance of particle history on the evaluation of the relative performance of different configurations of kneading blocks and suggest a reevaluation of the use of average flow characteristics for the analysis of mixing. Results also confirm the importance of an accurate description of the geometry and clearances in order to obtain information about relative mixing performance. Polym. Eng. Sci. 44:779,793, 2004. © 2004 Society of Plastics Engineers. [source]

Hydrodynamic characteristics of gas,solid fluidization at high temperature

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 1 2010
Shabnam Sanaei
Abstract Effect of temperature on the hydrodynamics of bubbling gas,solid fluidized beds was investigated in this work. Experiments were carried out at different temperatures ranged of 25,600°C and different superficial gas velocities in the range of 0.17,0.78,m/s with sand particles. The time-position trajectory of particles was obtained by the radioactive particle tracking technique at elevated temperature. These data were used for determination of some hydrodynamic parameters (mean velocity of upward and downward-moving particles, jump frequency, cycle frequency, and axial/radial diffusivities) which are representative to solids mixing through the bed. It was shown that solids mixing and diffusivity of particles increases by increasing temperature up to around 300°C. However, these parameters decrease by further increasing the temperature to higher than 300°C. This could be attributed to the properties of bubble and emulsion phases. Results of this study indicated that the bubbles grow up to a maximum diameter by increasing the temperature up to 300°C, after which the bubbles become smaller. The results showed that due to the wall effect, there is no significant change in the mean velocity of downward-moving clusters. In order to explain these trends, surface tension of emulsion between the rising bubble and the emulsion phase was introduced and evaluated in the bubbling fluidized bed. The results showed that surface tension between bubble and emulsion is increased by increasing temperature up to 300°C, however, after that it acts in oppositely. L'effet de la température sur l'hydrodynamique de lits fluidisés de gaz-solide bouillonnants a fait l'objet de l'étude de cet ouvrage. Des expériences ont été faites à différentes températures se situant entre 25 et 600°C et différentes vélocités de gaz superficiels sur une plage de 0,17 à 0,78,m/s avec particules de sable. La trajectoire temps-position des particules a été obtenue à l'aide d'une technique de repérage par particules radioactives à haute température. Ces données ont été utilisées pour déterminer certains des paramètres hydrodynamiques (vélocité moyenne des particules ascendantes et descendantes, la fréquence de sauts bonds, la fréquence de cycles et les diffusivités axiales et radiales), lesquels sont représentatifs de solides se mélangeant dans le lit. Il a été démontré que le mélange de solides et la diffusivité des particules augmentent en haussant la température à environ 300°C. Cependant, ces paramètres diminuent en accroissant davantage la température au-delà de 300°C. Cela pourrait être attribué aux propriétés des phases de bouillonnement et d'émulsion. Les résultats de cette étude indiquent que les bulles croissent pour atteindre un diamètre maximum en augmentant la température jusqu'à 300°C. Au-delà de cette température, les bulles deviennent plus petites. Les résultats démontrent qu'en raison de l'effet de paroi, il n'y a pas de changement significatif à la vélocité moyenne des grappes descendantes. Afin d'expliquer ces tendances, la tension de surface de l'émulsion entre la bulle ascendante et la phase émulsion a été introduite et évaluée dans le lit fluidisé bouillonnant. Les résultats ont démontré que la tension de surface entre la bulle et l'émulsion augmente en haussant à température jusqu'à 300°C; cependant, après cette température, elle agit inversement. [source]