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TOM: totally ordered mesh. A multiresolution data structure for time-critical graphics applications
Get PDFTridimensional interactive applications are confronted to situations where very large databases have to be animated, transmitted and displayed in very short bounded times. As it is generally impossible to handle the complete graphics description while meeting timing constraint, techniques enabling the extraction and manipulation of a significant part of the geometric database have been the focus of many research works in the field of computer graphics. Multiresolution representations of 3D models provide access to 3D objects at arbitrary resolutions while minimizing appearance degradation. We describe the TOM (Totally Ordered Mesh), a multiresolution triangle mesh structure tailored to the support of time-critical adaptive rendering. The structure grants high speed access to the continuous levels of detail of a mesh and allows very fast traversal of the list of triangles at arbitrary resolution so that bottlenecks in the graphic pipeline are avoided. Moreover, and without specific compression, the memory footprint of the TOM is small (about 108% of the single resolution object in face-vertex form) so that large scenes can be handled effectively. The TOM structure also supports storage per vertex (or per corner of triangle) attributes such as colors, normals, texture coordinates or dynamic properties. Implementation details are presented along with the results of tests for memory needs, approximation quality, timing and efficacy.Pubblicat
CFD simulation of an isothermal water flow in the EADF-target geometry in dynamical similarity (COULI experiment)
Get PDFThe results of the numerical simulation of an isothermal water-flow in a geometry typical of the spallation target of the Energy Amplifier Demonstration Facility (EADF) are presented, and compared with the experimental results obtained at CEA-Cadarache (COULI experiment). All the calculations were performed with the Star-CD finite-volume commercial code. Basically, a 2D axisymmetric model was adopted, although a full 3D simulation was carried out as well, as explained below. The Chen k-ε high-Reynolds model was used, joined with a Norris & Reynolds Two-Layer model for the simulation of the near-wall turbulence. The grid-independence of the solution has been verified, and the results obtained with two different convection schemes (QUICK and MARS) has been compared, in order to minimise numerical uncertainties. No appreciable differences were found in the results. Because of the fact that experimental measurements revealed a high non-axisymmetric and non stationary flow behaviour, the possible presence of instabilities intrinsic in the flow topology has been analysed through a full 3D simulation, obtained with the circumferential extrusion of the 2D model. The simulation yielded a steady solution, with results in perfect agreement with the 2D case. It is worth to notice that it was possible to obtain a converged solution in the 3D case only using the MARS scheme, while the QUICK scheme had numerical problems. In spite of the above-mentioned lack of axial symmetry in the experimental set-up, the comparison with computational results showed the capability of Star-CD to correctly simulate the main flow characteristics
Implementation of a catchment hydrologic model for the Brisy subcatchment of the Ourthe watershed, and generation of a dataset for a 240-day storm-interstorm sequence
Get PDFThis report describes the generation of a synthetic dataset needed for testing and verification of more simplified modeling approaches which aim to develop models applicable at large catchment and river basin scales. The work is carried out within the framework of a European project (DAUFIN) on developing data assimilation methodologies and a unified framework for hydrological modeling of catchment and river basin flow processes
Modeling coupled surface and subsurface flow at the catchment scale
Get PDFWe will describe a physically-based distributed catchment-scale model for the simulation of coupled surface runoff and subsurface flow. The model is based on coupling Richard’s equation for variably saturated porous media and a diffusion wave approximation for surface water dynamics. The numerical scheme uses a finite element Richard’s equation solver, FLOW3D and a surface DEM-based finite difference module, SURF-ROUTE. Retardation and storage effects due to lakes or depressions are also implemented, to give a complete description of the catchment flow dynamics
Montecarlo wavefield imaging of 3D prestack data
Get PDFWe present a new imaging methodology based on the depth extrapolation of a single dataset obtained by randomly compressing sources and shot-gathers. In this work a Monte Carlo imaging condition was implemented with a Phase Shift Plus Interpolation (PSPI) extrapolating kernel and tested on the SEG-EAGE salt model. This study demonstrates that wavefield 3D prestack depth migration is possible for industrial applications, providing high quality results in reasonable computational times
SITAI WEB: analisi degli accessi al sito (maggio 2000-maggio 2001)
Get PDFIl SITAI WEB, versione on-line del Sistema Informativo territoriale delle Aree Industriali della Sardegna (SITAI), sviluppato dal CRS4 per conto dell’Osservatorio Industriale della Sardegna è stato presentato al pubblico all'inizio del mese di maggio 2000 (http://www.crs4.it/sitai). Il presente rapporto offre un'analisi degli accessi al sito registrati sino nel corso di 13 mesi di esercizio del sistema, valutando non solo l'accesso alle pagine, ma fornendo anche una visione più dettagliata della ripartizione tra la fruizione delle varie sezioni e, in merito alla parte di selezione dei lotti, alcune statistiche sulle richieste inoltrate al sistema
A windowless design for the target of the EADF
Get PDFIn this note, we review the main features of the windowless target requirement. Then, we derive some necessary characteristics of the flow. We also make some comments hopefully useful for an eventual design optimisation process. From a first analysis, it seems that the requirements imposed on the maximum temperature and the pressure losses can be met but care must be taken to avoid a buoyancy induced flow critical instability
Exploring virtual prototypes using time-critical rendering techniques
Get PDFScientists at CRS4, the Center for Advanced Studies, Research and Development in Cagliari, Sardinia, Italy, have developed a time-critical rendering algorithm that relies upon a scene description in which objects are represented as multiresolution meshes. In collaboration with other European partners, this technique has been applied to the visual and collaborative exploration of large digital mock-ups.Pubblicat
An integrated environment for steroscopic acquisition, off-line 3D elaboration, and visual presentation of biological actions
Get PDFWe present an integrated environment for stereoscopic acquisition, off-line 3D elaboration, and visual presentation of biological hand actions. The system is used in neurophysiological experiments aimed at the investigation of the parameters of the external stimuli that mirror neurons visually extract and match on their movement related activity.23-2
Gradient, counter-gradient transport and their transition in turbulent premixed flames
Get PDFWe theoretically and numerically analyze the phenomena of counter-gradient transport in open premixed turbulent flames. The focus is on the transition from counter-gradient to gradient transport obtained when reducing the turbulence intensity/laminar flame speed ratio, a phenomenon recently found in open laboratory flames experiments by Frank at el. The analysis is based on the TFC combustion model for the simulation of turbulent premixed flames at strong turbulence (u`>>sι). In this case earlier work suggests that turbulent premixed flames have increasing flame brush with controlled in the model only by turbulence and independent from the counter-gradient transport phenomenon which has gasdynamics nature, and a turbulent flame speed which quickly adapts to a local equilibrium value, i. e. Intermediate Steady Propagation (ISP) flames. According to the present analysis transport in turbulent premixed flames is in fact composed by two contributions: real physical gradient turbulent diffusion, which is responsible for the growth of flame brush thickness, and counter-gradient pressure-driven convective transport related to the differential acceleration of burnt and unburnt gases subject to the average pressure variation across the turbulent flame. The novel gas dynamics model for the pressure-driven transport which is developed here, shows that in open turbulent premixed flames the overall transport may be of gradient or counter-gradient nature according to which of these contributions is dominant and that along the flame a transformation from gradient to counter-gradient transport takes place. Reasonable agreement with the mentioned laboratory experimental data, strongly support the validity of the present modeling ideas. Finally, the model predicts existence of this phenomenon also in large-scale industrial burners at much higher Reynolds number