共查询到20条相似文献,搜索用时 31 毫秒
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The performance of radiosity algorithms has been improved in recent years by means of using coherence when evaluating the visibility function for form factor computation. We present here a brief characterization of the uses of coherence for this goal. The characterization includes both previously proposed techniques and unexplored ones. Afterwards we propose new uses of coherence for visibility computation in form factor determination and we discuss the results of its implementation. 相似文献
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R. Schneiders 《Engineering with Computers》1996,12(3-4):168-177
An algorithm for the generation of hexahedralelement meshes is presented. The algorithm works in two steps: first the interior of the volume is filled with a regular grid; then the boundary region is meshed by using basically twodimensional operations.The algorithm was designed for use in the fem-simulation of metal forming processes where a remeshing must be done very often. In principle, it can be used for meshing any geometry with hexahedral elements and examples of meshes for geometries arising from various applications are given. The algorithm is checked against the criteria proposed by Sabin [1] (Advances in Engineering Software, 13, 220–225). 相似文献
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Progress in grid generation via the advancing front technique 总被引:8,自引:0,他引:8
R. Löhner 《Engineering with Computers》1996,12(3-4):186-210
We describe recent extensions and improvements to the advancing front grid generation technique. These improvements target a range of applicability, speed and user friendliness. The range of applicability is enlarged by the ability to produce volumetric grids around thin surfaces (such as shells, membranes, fabrics or surfaces with cusps), the generation of high aspect ratio grids for Navier-Stokes applications, the generation of higher order triangular and tetrahedral elements, and the generation of quadrilateral and hexahedral elements. Speed improvements are the result of reduced search overheads, as well as vectorization and parallelization. User friendliness is enhanced by the ability to grid directly discrete data and simpler ways of specifying the desired element size and shape in space. Numerous examples are included that demonstrate the versatility and maturity that advancing front grid generators have achieved. 相似文献
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Published online: 15 March 2002 相似文献
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O (n) for n subsystems. Moreover, the data necessary for each subsystem computation is completely localized, which allows the database
to be stored on disk. The algorithm can easily be implemented with a slight modification of the hierarchical radiosity algorithm.
Experiments demonstrate the efficiency of the algorithm. 相似文献
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In this paper, we present an efficient global illumination technique, and then we discuss the results of its extensive experimental
validation. The technique is a hybrid of cluster-based hierarchical and progressive radiosity techniques, which does not require
storing links between interacting surfaces and clusters. We tested our technique by applying a multistage validation procedure,
which we designed specifically for global illumination solutions. First, we experimentally validate the algorithm against
analytically derived and measured real-world data to check how calculation speed is traded for lighting simulation accuracy
for various clustering and meshing scenarios. Then we test the algorithm performance and rendering quality by directly comparing
the virtual and real-world images of a complex environment. 相似文献
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G. Foucault J.-C. Cuillière V. François J.-C. Léon R. Maranzana 《Computer aided design》2013,45(11):1408-1425
Being able to automatically mesh composite geometry is an important issue in the context of CAD–FEA integration. In some specific contexts of this integration, such as using virtual topology or meshing constraints topology (MCT), it is even a key requirement. In this paper, we present a new approach to automatic mesh generation over composite geometry. The proposed mesh generation approach is based on a generalization of the advancing front method (AFM) over curved surfaces. The adaptation of the AFM to composite faces (composed of multiple boundary representation (B-Rep) faces) involves the computation of complex paths along these B-Rep faces, on which progression of the advancing front is based. Each mesh segment or mesh triangle generated through this progression on composite geometry is likely to lie on multiple B-Rep faces and consequently, it is likely to be associated with a composite definition across multiple parametric spaces. Collision tests between new front segments and existing mesh elements also require specific and significant adaptations of the AFM, since a given front segment is also likely to lie on multiple B-Rep faces. This new mesh generation approach is presented in the context of MCT, which requires being able to handle composite geometry along with non-manifold boundary configurations, such as edges and vertices lying in the interior domain of B-Rep faces. 相似文献
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We present algorithms for rendering realistic images of large terrains and their implementation on a parallel computer for
rapid production of terrain-animation sequences. “Large” means datasets too large for RAM. A hybrid ray-casting and projection
technique incorporates quadtree subdivision techniques and filtering using precomputed bit masks. Hilbert space-filling curves
determine the imagepixel rendering order. A parallel version of the algorithm is based on a Meiko parallel computer architecture,
designed to relieve dataflow bottlenecks and exploit temporal image coherence. Our parallel system, incorporating 26 processors,
can generate a full color-terrain image at video resolution (without noticable aliasing artifacts) every 2 s, including I/O
and communication overheads. 相似文献
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Gerhard Globisch 《Parallel Computing》1995,21(12):1979-1995
A program for the efficient parallel generation of tetrahedral meshes in a wide class of three-dimensional domains having a generalized cylindrical shape is presented. The applied mesh generation strategy is based on the decomposition of some 2D-reference domain into simply connected subdomains. By means of the reference triangulations of these subdomains the tetrahedral layers are built up in parallel. Adaptive grid controlling as well as nodal renumbering algorithms are involved. In the paper several examples are included to demonstrate both the capabilities of the program and the adequate handling with the implemented method of parallelization. 相似文献
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A comprehensive modeling environment for the simulation of groundwater flow and transport 总被引:2,自引:0,他引:2
A comprehensive graphical modeling environment has been developed to address the needs of the computer simulation of groundwater flow and transport. The Department of Defense Groundwater Modeling Systems (GMS), developed at the Engineering Computer Graphics Laboratory at Brigham Young University, is part of a multi-year project funded through the Department of Defense, Department of Energy and Environmental Protection Agency. GMS is a graphically based software tool providing facility through all aspects of the groundwater flow and transport modeling process. Facilities include geometric modeling of hydrostratigraphy, two- and three-dimensional mesh generation, graphically based model input for specific flow and transport codes, interpolation and geostatistics as well as complete three-dimensional scientific visualization. 相似文献
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Jung-Hong Chuang Christoph M. Hoffmann Kun-Ming Ko Wei-Chung Hwang 《The Visual computer》1998,14(10):455-470
n -dimensional space, where n>3. This definition can be used for given surfaces that are implicit or parametric. This paper presents a robust, adaptive
polygonization algorithm for evaluating and visualizing geometrically constrained surfaces. Let be the constrained surface, a 2-surface in n-space, and let π() be its projection into the subspace spanned by the first three coordinates. Our polygonization algorithm computes π(). The method works directly with the n-space representation, but performs all major computations in 3-space. Techniques for triangulation, polygon decimation, and
local refinement are also presented. 相似文献
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Published online: 14 February 2003 相似文献
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Operator and parameter adaptation in genetic algorithms 总被引:6,自引:1,他引:6
J. E. Smith T. C. Fogarty 《Soft Computing - A Fusion of Foundations, Methodologies and Applications》1997,1(2):81-87
Genetic Algorithms are a class of powerful, robust search techniques based on genetic inheritance and the Darwinian metaphor
of “Natural Selection”. These algorithms maintain a finite memory of individual points on the search landscape known as the
“population”. Members of the population are usually represented as strings written over some fixed alphabet, each of which
has a scalar value attached to it reflecting its quality or “fitness”. The search may be seen as the iterative application
of a number of operators, such as selection, recombination and mutation, to the population with the aim of producing progressively
fitter individuals.
These operators are usually static, that is to say that their mechanisms, parameters, and probability of application are fixed
at the beginning and constant throughout the run of the algorithm. However, there is an increasing body of evidence that not
only is there no single choice of operators which is optimal for all problems, but that in fact the optimal choice of operators
for a given problem will be time-variant i.e. it will depend on such factors as the degree of convergence of the population.
Based on theoretical and practical approaches, a number of authors have proposed methods of adaptively controlling one or
more of the operators, usually invoking some kind of “meta-learning” algorithm, in order to try and improve the performance
of the Genetic Algorithm as a function optimiser.
In this paper we describe the background to these approaches, and suggest a framework for their classification, based on the
learning strategy used to control them, and what facets of the algorithm are susceptible to adaptation. We then review a number
of significant pieces of work within the context of this setting, and draw some conclusions about the relative merits of various
approaches and promising directions for future work. 相似文献
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J. B. Cavalcante Neto P. A. Wawrzynek M. T. M. Carvalho L. F. Martha A. R. Ingraffea 《Engineering with Computers》2001,17(1):75-91
An algorithm for generating unstructured tetrahedral meshes of arbitrarily shaped three-dimensional regions is described.
The algorithm works for regions without cracks, as well as for regions with one or multiple cracks. The algorithm incorporates
aspects of well known meshing procedures, but includes some original steps. It uses an advancing front technique, along with
an octree to develop local guidelines for the size of generated elements. The advancing front technique is based on a standard
procedure found in the literature, with two additional steps to ensure valid volume mesh generation for virtually any domain.
The first additional step is related to the generation of elements only considering the topology of the current front, and
the second additional step is a back-tracking procedure with face deletion, to ensure that a mesh can be generated even when
problems happen during the advance of the front. To improve mesh quality (as far as element shape is concerned), an a posteriori local mesh improvement procedure is used. The performance of the algorithm is evaluated by application to a number of realistically
complex, cracked geometries. 相似文献