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  • Computer Programming and Software  (12)
  • Computer Systems  (10)
  • Physics
  • Space Communications, Spacecraft Communications, Command and Tracking
  • 1995-1999  (22)
  • 1
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    Parallel implementation of an adaptive scheme for 3D unstructured grids on the SP2 (1996)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Dynamic mesh adaption on unstructured grids is a powerful tool for computing unsteady flows that require local grid modifications to efficiently resolve solution features. For this work, we consider an edge-based adaption scheme that has shown good single-processor performance on the C90. We report on our experience parallelizing this code for the SP2. Results show a 47.0X speedup on 64 processors when 10 percent of the mesh is randomly refined. Performance deteriorates to 7.7X when the same number of edges are refined in a highly-localized region. This is because almost all the mesh adaption is confined to a single processor. However, this problem can be remedied by repartitioning the mesh immediately after targeting edges for refinement but before the actual adaption takes place. With this change, the speedup improves dramatically to 43.6X.
    Keywords: Computer Programming and Software
    Type: NASA-CR-201396 , RIACS-TR-96-11 , NAS 1.26:201396
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  • 2
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    Parallel Load Balancing for Adaptive Unstructured Meshes (1998)
    In:  Other Sources
    Details
    Publication Date: 2019-07-18
    Description: Mesh adaption is a powerful tool for efficient unstructured-grid computations but causes load imbalance among processors on a parallel machine. We describe a novel method to dynamically balance the processor workloads with a global view. Mesh question, repartitioning, processor assignment, and remapping are critical components of the framework that must be accomplished rapidly and efficiently so as not to cause a significant overhead to the numerical simulation. A data redistribution model will also be presented that predicts the remapping cost. This model is required to determine whether the gain from a balanced workload distribution offsets the cost of data movement. Results presented will demonstrate that this is an effective dynamic load balancing strategy which remains viable on a large number of processors.
    Keywords: Computer Programming and Software
    Type: NEC Europe Ltd. Conference; May 04, 1998 - May 08, 1998; Sankt Augustin; Germany
    Format: text
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  • 3
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    NAS Applications and Advanced Architectures (1997)
    In:  Other Sources
    Details
    Publication Date: 2019-07-18
    Description: This paper examines the applications most commonly run on the supercomputers at the Numerical Aerospace Simulation (NAS) facility. It analyzes the extent to which such applications are fundamentally oriented to vector computers, and whether or not they can be efficiently implemented on hierarchical memory machines, such as systems with cache memories and highly parallel, distributed memory systems.
    Keywords: Computer Programming and Software
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  • 4
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    Self-Avoiding Walks over Adaptive Triangular Grids (1998)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: In this paper, we present a new approach to constructing a "self-avoiding" walk through a triangular mesh. Unlike the popular approach of visiting mesh elements using space-filling curves which is based on a geometric embedding, our approach is combinatorial in the sense that it uses the mesh connectivity only. We present an algorithm for constructing a self-avoiding walk which can be applied to any unstructured triangular mesh. The complexity of the algorithm is O(n x log(n)), where n is the number of triangles in the mesh. We show that for hierarchical adaptive meshes, the algorithm can be easily parallelized by taking advantage of the regularity of the refinement rules. The proposed approach should be very useful in the run-time partitioning and load balancing of adaptive unstructured grids.
    Keywords: Computer Programming and Software
    Type: 39th Symposium on Foundations of Computer Science; Nov 08, 1998 - Nov 11, 1998; Palo Alto, CA; United States
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  • 5
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    A New Approach to Parallel Dynamic Partitioning for Adaptive Unstructured Meshes (1999)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Classical mesh partitioning algorithms were designed for rather static situations, and their straightforward application in a dynamical framework may lead to unsatisfactory results, e.g., excessive data migration among processors. Furthermore, special attention should be paid to their amenability to parallelization. In this paper, a novel parallel method for the dynamic partitioning of adaptive unstructured meshes is described. It is based on a linear representation of the mesh using self-avoiding walks.
    Keywords: Computer Systems
    Type: IPPS''99; Apr 12, 1999 - Apr 16, 1999; San Juan; Puerto Rico
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  • 6
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    Dynamic Load Balancing for Adaptive Unstructured Grids (1998)
    In:  Other Sources
    Details
    Publication Date: 2019-07-18
    Description: Dynamic mesh adaptation on unstructured grids is a powerful tool for computing unsteady three-dimensional problems that require grid modifications to efficiently resolve solution features. By locally refining and coarsening the mesh to capture phenomena of interest, such procedures make standard computational methods more cost effective. Highly refined meshes are required to accurately capture shock waves, contact discontinuities, vortices, and shear layers in fluid flow problems. Adaptive meshes have also proved to be useful in several other areas of computational science and engineering like computer vision and graphics, semiconductor device modeling, and structural mechanics. Local mesh adaptation provides the opportunity to obtain solutions that are comparable to those obtained on globally-refined grids but at a much lower cost. Additional information is contained in the original extended abstract.
    Keywords: Computer Programming and Software
    Type: MASCOTS 1998; Jul 19, 1998 - Jul 24, 1998; Montreal; Canada
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  • 7
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    Communication Studies of DMP and SMP Machines (1997)
    In:  CASI
    Details
    Publication Date: 2019-07-10
    Description: Understanding the interplay between machines and problems is key to obtaining high performance on parallel machines. This paper investigates the interplay between programming paradigms and communication capabilities of parallel machines. In particular, we explicate the communication capabilities of the IBM SP-2 distributed-memory multiprocessor and the SGI PowerCHALLENGEarray symmetric multiprocessor. Two benchmark problems of bitonic sorting and Fast Fourier Transform are selected for experiments. Communication-efficient algorithms are developed to exploit the overlapping capabilities of the machines. Programs are written in Message-Passing Interface for portability and identical codes are used for both machines. Various data sizes and message sizes are used to test the machines' communication capabilities. Experimental results indicate that the communication performance of the multiprocessors are consistent with the size of messages. The SP-2 is sensitive to message size but yields a much higher communication overlapping because of the communication co-processor. The PowerCHALLENGEarray is not highly sensitive to message size and yields a low communication overlapping. Bitonic sorting yields lower performance compared to FFT due to a smaller computation-to-communication ratio.
    Keywords: Computer Systems
    Type: NAS-96-005
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  • 8
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    The Feasibility of Adaptive Unstructured Computations On Petaflops Systems (1999)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: This viewgraph presentation covers the advantages of mesh adaptation, unstructured grids, and dynamic load balancing. It illustrates parallel adaptive communications, and explains PLUM (Parallel dynamic load balancing for adaptive unstructured meshes), and PSAW (Proper Self Avoiding Walks).
    Keywords: Computer Programming and Software
    Type: Petaflops II; Feb 15, 1999 - Feb 19, 1999; Santa Barbara, CA; United States
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  • 9
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    Load Balancing Sequences of Unstructured Adaptive Grids (1997)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Mesh adaption is a powerful tool for efficient unstructured grid computations but causes load imbalance on multiprocessor systems. To address this problem, we have developed PLUM, an automatic portable framework for performing adaptive large-scale numerical computations in a message-passing environment. This paper makes several important additions to our previous work. First, a new remapping cost model is presented and empirically validated on an SP2. Next, our load balancing strategy is applied to sequences of dynamically adapted unstructured grids. Results indicate that our framework is effective on many processors for both steady and unsteady problems with several levels of adaption. Additionally, we demonstrate that a coarse starting mesh produces high quality load balancing, at a fraction of the cost required for a fine initial mesh. Finally, we show that the data remapping overhead can be significantly reduced by applying our heuristic processor reassignment algorithm.
    Keywords: Computer Programming and Software
    Type: NASA-CR-205229 , NAS 1.26:205229 , RIACS-TR-97.08 , High Performance Computing; Dec 18, 1997 - Dec 21, 1997; Bangalore; India
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  • 10
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    Performance Analysis and Portability of the PLUM Load Balancing System (1998)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The ability to dynamically adapt an unstructured mesh is a powerful tool for solving computational problems with evolving physical features; however, an efficient parallel implementation is rather difficult. To address this problem, we have developed PLUM, an automatic portable framework for performing adaptive numerical computations in a message-passing environment. PLUM requires that all data be globally redistributed after each mesh adaption to achieve load balance. We present an algorithm for minimizing this remapping overhead by guaranteeing an optimal processor reassignment. We also show that the data redistribution cost can be significantly reduced by applying our heuristic processor reassignment algorithm to the default mapping of the parallel partitioner. Portability is examined by comparing performance on a SP2, an Origin2000, and a T3E. Results show that PLUM can be successfully ported to different platforms without any code modifications.
    Keywords: Computer Programming and Software
    Type: NASA/CR-1998-208235 , NAS 1.26:208235 , RIACS-TR-98-02 , Sep 01, 1998 - Sep 04, 1998; Southampton; United Kingdom
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