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- RPI SCOREC - Technical Reports

been investigated with magnetic resonance imaging MRI Previously we have shown that the mechanical stiffness i e Young s modulus of these gels also changes with dose This finding prompted us to assess whether we can image a radiation induced stiffness distribution with quantitative ultrasound elastography and whether the stiffness distribution is correlated with the dose distribution A methacrylic acid based gel was loaded with scatterers to create ultrasound echoic signal It was irradiated to create a rod like region of increased stiffness with a 10 10 mm2 cross section The gel block was compressed in a frame that restricted the movement of the gel to planes orthogonal to the long axis of the irradiated region and ultrasonic echo data were acquired in the central plane during compression This simplified irradiation pattern and experimental setup were designed to approximate plane strain conditions and was chosen for proof of concept The movement of the gel was tracked from ultrasound images of a different compressional state using cross correlation enabling a displacement map to be created The shear modulus was reconstructed using an inverse algorithm The role of the magnitude of the regularization parameter in the inverse problem and the boundary conditions

Original URL path: http://www.scorec.rpi.edu/reports/view_report.php?id=545 (2015-07-15)

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bubbly flow for a plunging jet The derivation of this model is based on the two stage i e low and high liquid jet velocity air entrainment mechanisms suggested by Sene Sene KJ Air entrainment by plunging jets Chem Eng Sci 1988 43 10 2615 23 This model was validated against extensive experimental data for water jets in air over a wide range of liquid velocities from around 1 to

Original URL path: http://www.scorec.rpi.edu/reports/view_report.php?id=546 (2015-07-15)

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We prove that the model terms introduced by this method are dissipative under certain restrictions that are likely to be satisfied by spectral approximations of conservation laws In particular we demonstrate that the Fourier spectral approximations of Burgers equation and the incompressible Navier Stokes equations satisfy these conditions Hence we show that the residual based VMS model for these equations is dissipative even though the form of the model term

Original URL path: http://www.scorec.rpi.edu/reports/view_report.php?id=547 (2015-07-15)

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is governed by an inter atomic potential and is represented by molecular dynamics A thermo mechanical continuum defined by standard differential equations of conservation of momentum and heat transport is used The coupling is performed by an interface region where the two models overlap The phonon spectrum of the discrete region is divided into a low frequency part which is transferred to the continuum model as mechanical waves and a

Original URL path: http://www.scorec.rpi.edu/reports/view_report.php?id=560 (2015-07-15)

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mesh is distributed across a large number of processors with equal work load and minimum interpart communications A number of algorithms have been developed to meet these goals e g graph hypergraph and coordinate based methods However the global implementation of current approaches can fail on very large core counts which is resolved by combining global and local partitioning using multiple parts per processor The other limitation of graph hypergraph based partitioning is that it uses one type of mesh entity as graph nodes thus the balance of other mesh entities may not be optimal In the case of three dimensional 3 D linear finite element analysis it is common to select mesh regions elements as partition objects In current examples the regions are well balanced up to 163 840 parts for a 1 07 billion element mesh while the vertices have an imbalance which is as high as 19 52 Two methods are developed that work in conjunction with graph hypergraph based procedures to provide improved partitions Example computations executed on an IBM Blue Gene P system using up to 163 840 cores demonstrate the usefulness of the procedures particularly for time critical calculations where individual cores may be

Original URL path: http://www.scorec.rpi.edu/reports/view_report.php?id=580 (2015-07-15)

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analysis code that effectively employs advanced anisotropic adaptive algorithms and numerical models of flow physics In this paper we first describe the parallelization of PHASTA s core algorithms for an implicit solve where one of our key assumptions is that on a properly balanced supercom puter with appropriate attributes PHASTA should continue to strongly scale on high core counts until the computational workload per core becomes insufficient and inter processor communications start to dominate We then present and analyze PHASTA s parallel perfor mance across a variety of current near petascale systems including IBM BG L IBM BG P Cray XT3 and custom Opteron based supercluster this selection of systems with inherently different attributes covers a majority of potential candidates for upcoming petascale systems On one hand we achieve near perfect linear strong scaling out to 32 768 cores of IBM BG L showing that a system with desirable attributes will allow implicit solvers to strongly scale on high core counts including petascale systems On the contrary we find that the relative tipping point for strong scaling fundamentally differs among current supercomputer systems To understand the loss of scaling observed on a particular system Opteron based superclus ter we analyze

Original URL path: http://www.scorec.rpi.edu/reports/view_report.php?id=459 (2015-07-15)

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allows the user to start with subject specific data collected through clinical measurements like magnetic resonance imaging MRI data and evaluate physiological parameters of interest like flow distribution pressure variations wall shear stress in an automatic and efficient manner The process involves construction of geometric models of blood vessels specification of flow conditions and application of an adaptive flow solver The latter is based on incompressible Navier Stokes equations using

Original URL path: http://www.scorec.rpi.edu/reports/view_report.php?id=460 (2015-07-15)

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flow control via steady tangential control jet are considered A stabilized finite element method is employed to perform turbulence simulations16 using two variants of the Spalart Allmaras S A model the original S A one equation model29 in an unsteady Reynold averaged Navier Stokes simulation URANSS and a hybrid S A model30 in a Detached eddy simulation DES Furthermore computations are performed using adaptive meshing techniques developed for unstructured grids

Original URL path: http://www.scorec.rpi.edu/reports/view_report.php?id=461 (2015-07-15)

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