Search results for "Computer simulation"
showing 10 items of 1054 documents
Time-dependent simulation of Czochralski silicon crystal growth
1997
We have developed a detailed mathematical model and numerical simulation tools based on the streamline upwind/Petrov-Galerkin (SUPG) finite element formulation for the Czochralski silicon crystal growth. In this paper we consider the mathematical modeling and numerical simulation of the time-dependent melt flow and temperature field in a rotationally symmetric crystal growth environment. Heat inside the Czochralski furnace is transferred by conduction, convection and radiation, Radiating surfaces are assumed to be opaque, diffuse and gray. Hence the radiative heat exchange can be modeled with a non-local boundary condition on the radiating part of the surface. The position of the crystal-me…
Simulation of turbulent metal flows
2007
Comprehensive knowledge of the heat and mass transfer processes in turbulent metal flows is required to realize efficient and reliable melting and casting processes. Experimental and numerical studies of the melt flow in induction furnaces show that the flow pattern, which comprise several vortexes of the mean flow, and the temperature distribution in the melt are significantly influenced by low-frequency large scale flow oscillations. Two- and three-dimensional hydrodynamic calculations of the melt flow, using two-equation turbulence models based on Reynolds Averaged Navier-Stokes approach, do not predict the large scale periodic flow instabilities obtained from the experimental data. That…
Detection of vortex tubes in solar granulation from observations with Sunrise
2010
We have investigated a time series of continuum intensity maps and corresponding Dopplergrams of granulation in a very quiet solar region at the disk center, recorded with the Imaging Magnetograph eXperiment (IMaX) on board the balloon-borne solar observatory Sunrise. We find that granules frequently show substructure in the form of lanes composed of a leading bright rim and a trailing dark edge, which move together from the boundary of a granule into the granule itself. We find strikingly similar events in synthesized intensity maps from an ab initio numerical simulation of solar surface convection. From cross sections through the computational domain of the simulation, we conclude that th…
Convective phenomena in large melts including magnetic fields
2007
The set of characteristic parameters which describe modern large industrial CZ silicon single crystal growth systems is introduced. The main melt flow driving mechanisms are considered, and the characteristic density values of various in the melt acting forces are estimated. The analysis is illustrated with examples of numerical simulation and comparisons with experiments.
What makes learning and understanding in virtual teams so difficult?
2004
The ideas presented in this article are especially challenged by critical questions raised by the other authors in this special issue. One of the core questions throughout the different studies is whether participants in distributed learning groups are able to successfully work on a common task and achieve a type of interaction that leads them to educationally relevant higher-level discussion and learning. This article discusses the central findings of these studies in light of the recent research on computer-supported collaborative learning. At the beginning of the article, typical problems and challenges related to learning in virtual teams are described. In the end of the discussion, som…
Granulometric analysis of corneal endothelium specular images by using a germ–grain model
2007
Specular microscopy is widely used to study the human corneal endothelium status in vivo. In this paper, the corneal endothelium is represented as a binary image composed of the cell inscribed circles. The granulometric distribution function of the complement of this image is used as a functional descriptor, which provides information about the shape, size and spatial arrangement of cells. Experimental evaluation using bootstrap techniques shows its ability to discriminate between controls and pathological cases. It represents a reliable and graphical alternative to the classical indices (cell density, hexagonality and coefficient of variation of cell areas), which behave poorly when detect…
Numerical Simulation of Thermal Effects in Electric Circuits via Energy Transport equations
2006
In this work we present the coupling of stationary energy-transport (ET) equations with Modified Nodal Analysis (MNA)-equations to model electric circuits containing semiconductor devices. The one-dimensional ET-equations are discretised in space by an exponential fitting mixed hybrid finite element approach to ensure current continuity and positivity of charge carriers. The discretised ET-equations are coupled to MNA-equations and the resulting system is solved with backwarddifference formulas. Numerical examples are shown for a test circuit containing a pn-diode, and the results are compared to those achieved using the drift-diffusion model to describe the semiconductor devices in the cir…
Kerr Optical Frequency Combs With Multi-FSR Mode Spacing in Silica Microspheres
2021
We experimentally demonstrate Kerr optical frequency combs (OFCs) with mode spacing of 1, 2, 3, 5, 6, and 8 free spectral ranges (FSRs) corresponding to 0.4, 0.8, 1.2, 2, 2.4, and 3.2 THz, respectively, in silica microspheres pumped by CW C-band lasers in the anomalous dispersion range. Experimental realizations are based on using standard telecom equipment and components such as SMF-28e fiber for producing microspheres and fiber tapers for pump coupling and OFC outcoupling. Numerical simulation is performed to support the experimental results and explain the observed spectral asymmetry in OFCs by the influence of the 3rd-order dispersion.
Numerical analysis of composite plates with multiple delaminations subjected to uniaxial buckling load
2006
Abstract In this paper the buckling and post-buckling behaviour of unidirectional and cross-ply composite laminated plates with multiple delaminations has been studied. Finite elements analyses have been performed, using a linear buckling model, based on the solution of the eigenvalues problem, and a non-linear one, based on an incremental-iterative method. With non-linear method large displacements have been taken into account and also contact constraints between sublaminates have been added to avoid their interpenetration. It has been found that both delamination length and position and stacking sequence of the plies influence the critical load of the plate; furthermore, linear and non-li…
Interpretation of epicardial mapping by means of computer simulations: Applications to calcium, lidocaine and to BRL 34915
1992
The aim of this work was to compare experimental investigations on effects of lidocaine, calcium and, BRL 34915 on reentries to simulated data obtained by use of a model of propagation based on the Huygens' construction method already described in previous works. Calcium and lidocaine effects are investigated on anisotropic conduction conditions. In both cases, reduction in conduction velocities are observed. In lidocaine case, a refractory area is located along the longitudinal axis. In agreement with experimental electrical mapping, the simulations show that the stabilization of reentrant excitation is mainly due to the existence of this refractory area around which the reentrant circuit …