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8:45am

Science: Massively parallel
    Thursday July 19, 2012 8:45am - 9:15am @ King Arthur 3rd Floor

    Science: Massively parallel direct numerical simulations of forced compressible turbulence: a hybrid MPI/OpenMP approach

    Abstract: A highly scalable simulation code for turbulent flowswhich solves the fully compressible Navier-Stokesequations is presented. The code, which supports one, twoand three dimensional domain decompositionsis shown to scale well on up to 262,144cores. Introducing multiple levels of parallelism based ondistributed message passing and shared-memory paradigms results in areductionof up to 33\% of communication time at large core counts.The code has been used to generate a large database ofhomogeneous isotropic turbulence in a stationary state created by forcingthe largest scales in the flow.The scaling of spectra of velocity and density fluctuationsare presented. While the former follow classical theories strictly validfor incompressible flows, the latter presents a more complicated behavior.Fluctuations in velocity gradients and derived quantitiesexhibit extreme though rare fluctuations, a phenomenon known as intermittency.The simulations presented provide data to disentangle Reynolds andMach number effects.

     



    Speakers

    Type Science Track
    Session Titles Astrophysics
    Tags File Systems


9:15am

Science: High Accuracy
    Thursday July 19, 2012 9:15am - 9:45am @ King Arthur 3rd Floor

    Science: High Accuracy Gravitational Waveforms from Black Hole Binary Inspirals Using OpenCL

    Abstract: There is a strong need for high-accuracy and efficient modeling of extreme-mass-ratio binary black hole systems (EMRIs) because these are strong sources of gravitational waves that would be detected by future observatories. In this article, we present sample results from our Teukolsky EMRI code: a time-domain Teukolsky equation solver (a linear, hyperbolic, partial differential equation solver using finite-differencing), that takes advantage of several mathematical and computational enhancements to efficiently generate long-duration and high-accuracy EMRI waveforms. 

     We emphasize here the computational advances made in the context of this code. Currently there is considerable interest in making use of many-core processor architectures, such as Nvidia and AMD graphics processing units (GPUs) for scientific computing. Our code uses the Open Computing Language (OpenCL) for taking advantage of the massive parallelism offered by modern GPU architectures. We present the performance of our Teukolsky EMRI code on multiple modern processors architectures and demonstrate the high level of accuracy and performance it is able to achieve. We also present the code's scaling performance on a large supercomputer i.e. NSF's XSEDE resource, Keeneland.

     



    Speakers

    Type Science Track
    Session Titles Astrophysics
    Tags File Systems


9:45am

Science: A High throughput
    Thursday July 19, 2012 9:45am - 10:15am @ King Arthur 3rd Floor

    Science: A High throughput workflow environment for cosmological simulations

    Abstract: The cause of cosmic acceleration remains an important unanswered question in cosmology. The Dark Energy Survey (DES) is a joint DoE-NSF project that will perform a sensitive survey of cosmic structure traced by galaxies and quasars across 5000 sq deg of sky. DES will be the first project to combine four different methods (supernova brightness, the acoustic scale of galaxy clustering, the population of groups and clusters of galaxies, and weak gravitational lensing) to study dark matter, dark energy, and departures from general relativistic gravity via evolution of the cosmic expansion rate and growth rate of linear density perturbations. Realizing the full statistical power of this and complementary surveys requires support from cosmological simulations to address the many potential sources of systematic error, particularly errors that are shared jointly across the tests of cosmic acceleration using cosmic structure. 

    We are coordinating a Blind Cosmology Challenge (BCC) process for DES, in which a variety of synthetic sky realizations in different cosmologies will be analyzed, in a blind manner, by DES science teams. The BCC process requires us to generate a suite of roughly 50 2048^3-particle N-body simulations that sample the space-time structure in a range of cosmic volumes. These simulations are dressed with galaxies, and the resulting catalog-level truth tables are then processed with physical (e.g., gravitational lensing) and telescope/instrument effects (e.g., survey mask) before their release to science teams. We describe here our efforts to embed control of the catalog production process within a workflow engine that employs a service-oriented architecture to manage XSEDE job requests. We describe the approach, including workflow tests and extensions, and present first production results for the N-body portion of the workflow. We propose future extensions aimed toward a science gateway service for astronomical sky

     



    Speakers

    Type Science Track
    Session Titles Astrophysics
    Tags File Systems


 

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