检索结果-内蒙古大学图书馆

International Symposium on Parallel Architectures, Algorithms and Networks (ISPAN)

作者： Tzi-Cier Chiueh Kwan-Liu Ma Computer Science Department State University of New York Stony Brook Stony Brook NY USA NASA Langley Research Center Institute for Computer Applications in Science and Engineering Hampton VA USA

ISBN: (纸本)0818682596

This paper presents a strategy for efficiently rendering time-varying volume data on a distributed-memory parallel computer. Visualizing time-varying volume data take both large storage space and long computation time. Instead of employing all processors to render one volume at a time, a pipelined rendering approach partitions processors into groups so that multiple volumes can be rendered concurrently. The overall rendering time is greatly minimized because rendering is overlapped with I/O required to load the volume data sets. Moreover, parallelization overhead may be reduced as a result of partitioning the processors. We modify an existing parallel volume renderer to exploit various levels of rendering parallelism and to study how the partitioning of processors may lead to optimal rendering performance. We find that two factors affecting the overall execution time are resource utilization efficiency and pipeline startup latency. The optimal partitioning configuration is the one that balances these two factors. Tests on Intel Paragon computers show that in general optimal partitionings do exist for a given rendering task and result in 40-50% saving in overall rendering time.

关键词： Parallel processing Animation NASA Delay computer applications Data engineering Concurrent computing Data visualization Rendering (computer graphics) computer science

来源：评论

学校读者我要写书评

暂无评论

Towards perfectly absorbing boundary conditions for euler equations 13th

Towards perfectly absorbing boundary conditions for euler eq...

引用

13th Computational Fluid Dynamics Conference, 1997

作者： Hayder, M. Ehtesham Hu, Fang Q. Hussaini, M. Yousuff Institute for Computer Applications in Science and Engineering NASA Langley Research Center Mail Stop 403 HamptonVA23681-0001 United States Department of Mathematics and Statistics Old Dominion University NorfolkVA23529 United States Florida State University TallahasseeFL32306-3075 United States

In this paper, we examine the effectiveness of absorbing layers as non-reflecting computational boundaries for the Euler equations. The absorbing-layer equations are simply obtained by splitting the governing equations in the coordinate directions and introducing absorption coefficients in each split equation. This methodology is similar to that used by Berenger for the numerical solutions of Maxwell’s equations. Specifically, we apply this methodology to three physical problems-shock-vortex interactions, a plane free shear flow and an axisymmetric jet-with emphasis on acoustic wave propagation. Our numerical results indicate that the use of absorbing layers effectively minimizes numerical reflection in all three problems considered. © 1997, American Institute of Aeronautics and Astronautics, Inc.

关键词： Euler equations

来源：评论

学校读者我要写书评

暂无评论

Constrained multipoint aerodynamic shape optimization using an adjoint formulation and parallel computers 35th

Constrained multipoint aerodynamic shape optimization using ...

引用

35th aerospace sciences Meeting and Exhibit, 1997

作者： Reuther, J. Jameson, A. Alonso, J.J. Rimlinger, M.J. Saunders, D. Research Institute for Advanced Computer Science NASA Ames Research Center MS 227-6 Moffett FieldCA94035 United States Department of Mechanical and Aerospace Engineering Princeton University PrincetonNJ08544 United States Sterling Software NASA Ames Research Center MS 227-6 Moffett FieldCA94035 United States

An aerodynamic shape optimization method that treats the design of complex aircraft configurations subject to high fidelity computational fluid dynamics (CFD), geometric constraints and multiple design points is described. The design process will be greatly accelerated through the use of both control theory and distributed memory computer architectures. Control theory is employed to derive the adjoint differential equations whose solution allows for the evaluation of design gradient information at a fraction of the computational cost required by previous design methods [5, 4, 24, 18]. The resulting problem is implemented on parallel distributed memory architectures using a domain decomposition approach, an optimized communication schedule, and the MPI (Message Passing Interface) standard for portability and efficiency. The final result achieves very rapid aerodynamic design based on a higher order CFD method. In order to facilitate the integration of these high fidelity CFD approaches into future multi-disciplinary optimization (MDO) applications, new methods must be developed which are capable of simultaniously addressing complex geometries, multiple objective functions, and geometric design constraints. In our earlier studies [8,9,10,11, 19,15, 20,21,22, 23,1], we coupled the adjoint based design formulations with unconstrained optimization algorithms and showed that the approach was effective for the aerodynamic design of airfoils, wings, wing-bodies, and complex aircraft configurations. In many of the results presented in these earlier works, geometric constraints were satisfied either by a projection into feasible space or by posing the design space parameterization such that it automatically satisfied constraints. Furthermore, with the exception of reference [9] where the second author initially explored the use of multipoint design in conjunction with adjoint formulations, our earlier works have focused on single point design efforts. Here we demonstrate that

关键词： Computational fluid dynamics

来源：评论

学校读者我要写书评

暂无评论

Adaptive blocks: A high performance data structure 97

Adaptive blocks: A high performance data structure

引用

1997 ACM/IEEE Conference on Supercomputing, SC 1997

作者： Stout, Quentin F. De Zeeuw, Darren L. Gombosi, Tamas I. Groth, Clinton P. T. Marshall, Hal G. Powell, Kenneth G. Electrical Engineering and Computer Science Center for Parallel Computing University of Michigan Ann Arbor MI 48109-2122 United States Space Physics Research Laboratory Department of Atmospheric Oceanic and Space Sciences University of Michigan Ann Arbor MI 48109-2143 United States Laboratory for Scientific Computation Center for Parallel Computing University of Michigan Ann Arbor MI 48109-2094 United States Department of Aerospace Engineering University of Michigan Ann Arbor MI 48109-2118 United States

ISBN: (纸本)0897919858

We examine a data structure which uses flexible "adaptivity" to obtain high performance for both serial and parallel computers. The data structure is an adaptive grid which partitions a given region into regular cells. Its closest relatives are cell-based tree decompositions, but there are several important differences which lead to significant performance advantages. Using this block data structure to support adaptive mesh refinement (AMR), we were able to sustain 17 GFLOPS in ideal magnetohydrodynamic (MHD) simulations of the solar wind emanating from the base of the solar corona, using a 512 processor Cray T3D at NASA Goddard. © 1997 ACM.

关键词： Magnetohydrodynamics

来源：评论

学校读者我要写书评

暂无评论

Advances in agile manufacturing

Advances in agile manufacturing

引用

IEEE International Conference on Robotics and Automation (ICRA)

作者： F.L. Merat N.A. Barendt R.D. Quinn G.C. Causey W.S. Newman V.B. Velasco A. Podgurski Y. Kim G. Ozsoyoglu J.-Y. Jo Center for Automation and Intelligent Systems Research Department of electrical Engineeisng and Applied Physics Case Western Reserve University Cleveland OH USA Center for Automation and Intelligent Systems Research Department of Mechanical and Aerospace Engineering Case Western Reserve University Cleveland OH USA Center for Automation and Intelligent Systems Research Department of Computer Engineering and Science Case Western Reserve University Cleveland OH USA

An agile workcell has been developed for light mechanical assembly in collaboration with industrial sponsors. The workcell includes multiple Adept robots, a Bosch conveyor system, multiple flexible parts feeders at each robot's workstation, CCD cameras for parts feeding and hardware registration, and a dual VMEbus control system. Our flexible pairs feeder design uses multiple conveyors to singulate the parts and machine vision to locate them. Specialized hardware is encapsulated on modular grippers and modular worktables which can be quickly interchanged for assembly of different products. Object-oriented software (C++) running under VxWorks, a real-time operating system, is used for workcell control. An agile software architecture was developed for rapid introduction of new assemblies through code re-use. A simulation of the workcell was developed so that controller software could be written and tested off-line, enabling the rapid introduction of new products.

关键词： Agile manufacturing Robotic assembly Service robots Hardware Control systems Collaborative work Electrical equipment industry Manufacturing industries Workstations Charge coupled devices

来源：评论

学校读者我要写书评

暂无评论

Developing a prototype concurrent design tool for composite topside structures

引用

NAVAL ENGINEERS JOURNAL 1997年第3期109卷 279-290页

作者： Dirlik, S Hambric, S Azarm, S Marquardt, M Hellman, A Bartlett, S Castelli, V Steve Dirlik:began his career at the Naval Surface Warfare Center Carderock Division in 1981 as an aerospace engineer co-op student. He completed his bachelor of science degree in aeropace and ocean engineering from Virginia Polytechnic Institute and State University in 1985 and his master of science degree in aerospace engineering from the University of Maryland in 1990. Mr. Dirlik recently completed a master of science program in applied physics at The Johns Hopins University and currently works in the Radar Cross Section and Target Physics Branch of the Signatures Directorate at the Naval Surface Warfare Center Corderoke Division. He has worked on Navy low observable programs since 1990. Stephen Hambric:is a research associate at the Applied Research Laboratory at The Pennsylvania State University. He received his B. S. and M.S. degree in mechanical engineering from Virginia Polytechnic Institute and State University and his D. Sc. in mechnical engineering from the George Washington University. He has worked on several computer aided multidiscikplinary design and optimization projects over the years including an automated propeller design system and a structural acoustic optimization capability. Dr. Shpour Azarm:is currently working as an associate professor with the Design and Manufacturing Group of the Department of Mechanical Engineering at the University of maryland at College Park. Dr Azarm's expertise is in the areas of optimization-based designed and concurrent design and optimization of multidisciplinary systems. He was a consultant at Black & Decker Corporation (summer 1996) and worked as a Navy senior summer faculty fellow (summer 1995) and a NASA summer faculty fellow (summer 1994). He was a visiting scientist at NASA Langley Research Center for Multidisciplinary Analysis and Applied Structural Optimzatiom at the University of Siegen in Germany (spring 1992) and the Design Institute of the Technical University of Denmark (summer 1990). Dr Azarm was an associate technical editor of the ASME Jour

A prototype concurrent engineering tool has been developed for the preliminary design of composite topside structures for modern navy warships. This tool, named GELS for the Concurrent engineering of Layered Structures, provides designers with an immediate assessment of the impacts of their decisions on several disciplines which are important to the performance of a modern naval topside structure, including electromagnetic interference effects (EMI), radar cross section (RCS), structural integrity, cost, and weight. Preliminary analysis modules in each of these disciplines are integrated to operate from a common set of design variables and a common materials database. Performance in each discipline and an overall fitness function for the concept are then evaluated. A graphical user interface (GUI) is used to define requirements and to display the results from the technical analysis modules. Optimization techniques, including feasible sequential quadratic programming (FSQP) and exhaustive search are used to modify the design variables to satisfy all requirements simultaneously. The development of this tool, the technical modules, and their integration are discussed noting the decisions and compromises required to develop and integrate the modules into a prototype conceptual design tool.

关键词： Warships

来源：评论

学校读者我要写书评

暂无评论

Analysis and modeling of subgrid scalar mixing using numerical data

引用

PHYSICS OF FLUIDS 1996年第5期8卷 1224-1236页

作者： Girimaji, SS Zhou, Y Institute for Computer Applications in Science and Engineering NASA Langley Research Center Hampton Virginia 23681

Direct numerical simulations (DNS) of passive scalar mixing in isotropic turbulence is used to study, analyze, and, subsequently, model the role of small (subgrid) scales in the mixing process. In particular, we attempt to model the dissipation of the large-scale (supergrid) scalar fluctuations caused by the subgrid scales by decomposing it into two parts: (i) the effect due to the interaction among the subgrid scales, E(phi)(>);and, (ii) the effect due to interaction between the supergrid and the subgrid scales, E(phi)(><). Model comparison with DNS data shows good agreement. (C) 1996 American Institute of Physics.

关键词： TURBULENT FLOW SCALAR FIELDS MIXING CHEMICAL REACTIONS DIFFUSION computerIZED SIMULATION ENERGY LOSSES ISOTROPY

来源：评论

学校读者我要写书评

暂无评论

Perspective on unstructured grid flow solvers

引用

AIAA JOURNAL 1996年第3期34卷 533-547页

作者： Venkatakrishnan, V Institute for Computer Applications in Science and Engineering NASA Langley Research Center Hampton Virginia 23681-0001

Unstructured grid flow solvers for the compressible Navier-Stokes equations are surveyed. Significant progress are made in the areas of spatial and temporal discretization and adaptative and parallel algorithms. Newly developed field equation turbulence models seem to mesh nicely with the unstructured grid framework. Based on these developments, it is safe to say that unstructured grid technology is almost on par with structured grid technology, although encumbered with additional memory andcomputational costs.

关键词： Unstructured Grid Compressible Fluid Parallel Computing NASA Langley Research center Total Variation Diminishing Roe Approximate Riemann Solver Galerkin Finite Element Approach Velocity Profiles Parallel Algorithm Navier Stokes Equations

来源：评论

学校读者我要写书评

暂无评论

A relaxation approximation for time-dependent second-order effects in shear turbulence

引用

THEORETICAL AND COMPUTATIONAL FLUID DYNAMICS 1996年第5期8卷 377-386页

作者： Rubinstein, R Institute for Computer Applications in Science and Engineering NASA Langley Research Center Hampton USA

The Crow constraint on time-dependent turbulence models is generalized to effects of second order in the strain rate. For simple shear flow, this generalization requires agreement of the time-dependent normal stress deviators with the short-time rapid distortion limit and with long-time equilibrium data. A model consistent with these requirements is proposed based on a perturbative solution of the equations of the direct interaction approximation for shear flow. It requires a decomposition of the Reynolds stress into tensor components which satisfy coupled linear relaxation equations. This approach to time-dependent turbulence modeling based on analytical theories offers an alternative to the standard ones, in which various hypotheses are introduced to close correlations in the exact transport equation for second-order single-point moments.

关键词：

来源：评论

学校读者我要写书评

暂无评论

Analytical theory of the destruction terms in dissipation rate transport equations

引用

PHYSICS OF FLUIDS 1996年第11期8卷 3172-3178页

作者： Rubinstein, R Zhou, Y Institute for Computer Applications in Science and Engineering MS 403 NASA Langley Research Center Hampton Virginia 23681

Modeled dissipation rate transport equations are often derived by invoking various hypotheses to close correlations in the corresponding exact equations. D. C. Leslie [Modern Developments in the Theory of Turbulence (Oxford University, Oxford, 1972)] suggested that these models might be derived instead from Kraichnan's [J. Fluid Mech. 47 (1971)] wavenumber space integrals for inertial range transport Stower. This suggestion is applied to the destruction terms in the dissipation rate equations for incompressible turbulence, buoyant turbulence, rotating incompressible turbulence, and rotating buoyant turbulence. Model constants like C-epsilon 2 are expressed as integrals;convergence of these integrals implies the absence of Reynolds number dependence ii the corresponding destruction term. The dependence of C-epsilon 2 on rotation rate emerges naturally;sensitization of the modeled dissipation rats equation to rotation is not required. A buoyancy related effect which is absent in the exact transport equation for temperature variance dissipation, but which sometimes improves computational predictions;also arises naturally, The time scale in the modeled transport equation depends on whether Bolgiano or Kulmogorov inertial range scaling applies. A simple extension af these methods leads to a preliminary dissipation rate equation for rotating buoyant turbulence. (C) 1996 American Institute of Physics.

关键词： TURBULENT FLOW ENERGY LOSSES INCOMPRESSIBLE FLOW BUOYANCY TRANSPORT THEORY SCALING LAWS CORRELATION FUNCTIONS VISCOUS FLOW REYNOLDS NUMBER

来源：评论

学校读者我要写书评

暂无评论

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

请选择保存的检索档案：

请选择收藏分类：

通借通还

建议与咨询 留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

请选择保存的检索档案： 新增检索档案 确定 取消

请选择收藏分类： 新增自定义分类 确定 取消

通借通还

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

请选择保存的检索档案：

请选择收藏分类：