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Sample records for adaptive grid code

  1. SAGE - MULTIDIMENSIONAL SELF-ADAPTIVE GRID CODE

    NASA Technical Reports Server (NTRS)

    Davies, C. B.

    1994-01-01

    SAGE, Self Adaptive Grid codE, is a flexible tool for adapting and restructuring both 2D and 3D grids. Solution-adaptive grid methods are useful tools for efficient and accurate flow predictions. In supersonic and hypersonic flows, strong gradient regions such as shocks, contact discontinuities, shear layers, etc., require careful distribution of grid points to minimize grid error and produce accurate flow-field predictions. SAGE helps the user obtain more accurate solutions by intelligently redistributing (i.e. adapting) the original grid points based on an initial or interim flow-field solution. The user then computes a new solution using the adapted grid as input to the flow solver. The adaptive-grid methodology poses the problem in an algebraic, unidirectional manner for multi-dimensional adaptations. The procedure is analogous to applying tension and torsion spring forces proportional to the local flow gradient at every grid point and finding the equilibrium position of the resulting system of grid points. The multi-dimensional problem of grid adaption is split into a series of one-dimensional problems along the computational coordinate lines. The reduced one dimensional problem then requires a tridiagonal solver to find the location of grid points along a coordinate line. Multi-directional adaption is achieved by the sequential application of the method in each coordinate direction. The tension forces direct the redistribution of points to the strong gradient region. To maintain smoothness and a measure of orthogonality of grid lines, torsional forces are introduced that relate information between the family of lines adjacent to one another. The smoothness and orthogonality constraints are direction-dependent, since they relate only the coordinate lines that are being adapted to the neighboring lines that have already been adapted. Therefore the solutions are non-unique and depend on the order and direction of adaption. Non-uniqueness of the adapted grid is

  2. The multidimensional Self-Adaptive Grid code, SAGE, version 2

    NASA Technical Reports Server (NTRS)

    Davies, Carol B.; Venkatapathy, Ethiraj

    1995-01-01

    This new report on Version 2 of the SAGE code includes all the information in the original publication plus all upgrades and changes to the SAGE code since that time. The two most significant upgrades are the inclusion of a finite-volume option and the ability to adapt and manipulate zonal-matching multiple-grid files. In addition, the original SAGE code has been upgraded to Version 1.1 and includes all options mentioned in this report, with the exception of the multiple grid option and its associated features. Since Version 2 is a larger and more complex code, it is suggested (but not required) that Version 1.1 be used for single-grid applications. This document contains all the information required to run both versions of SAGE. The formulation of the adaption method is described in the first section of this document. The second section is presented in the form of a user guide that explains the input and execution of the code. The third section provides many examples. Successful application of the SAGE code in both two and three dimensions for the solution of various flow problems has proven the code to be robust, portable, and simple to use. Although the basic formulation follows the method of Nakahashi and Deiwert, many modifications have been made to facilitate the use of the self-adaptive grid method for complex grid structures. Modifications to the method and the simple but extensive input options make this a flexible and user-friendly code. The SAGE code can accommodate two-dimensional and three-dimensional, finite-difference and finite-volume, single grid, and zonal-matching multiple grid flow problems.

  3. SAGE: The Self-Adaptive Grid Code. 3

    NASA Technical Reports Server (NTRS)

    Davies, Carol B.; Venkatapathy, Ethiraj

    1999-01-01

    The multi-dimensional self-adaptive grid code, SAGE, is an important tool in the field of computational fluid dynamics (CFD). It provides an efficient method to improve the accuracy of flow solutions while simultaneously reducing computer processing time. Briefly, SAGE enhances an initial computational grid by redistributing the mesh points into more appropriate locations. The movement of these points is driven by an equal-error-distribution algorithm that utilizes the relationship between high flow gradients and excessive solution errors. The method also provides a balance between clustering points in the high gradient regions and maintaining the smoothness and continuity of the adapted grid, The latest version, Version 3, includes the ability to change the boundaries of a given grid to more efficiently enclose flow structures and provides alternative redistribution algorithms.

  4. The multidimensional self-adaptive grid code, SAGE

    NASA Technical Reports Server (NTRS)

    Davies, Carol B.; Venkatapathy, Ethiraj

    1992-01-01

    This report describes the multidimensional self-adaptive grid code SAGE. A two-dimensional version of this code was described in an earlier report by the authors. The formulation of the multidimensional version is described in the first section of this document. The second section is presented in the form of a user guide that explains the input and execution of the code and provides many examples. Successful application of the SAGE code in both two and three dimensions for the solution of various flow problems has proven the code to be robust, portable, and simple to use. Although the basic formulation follows the method of Nakahashi and Deiwert, many modifications have been made to facilitate the use of the self-adaptive grid method for complex grid structures. Modifications to the method and the simplified input options make this a flexible and user-friendly code. The new SAGE code can accommodate both two-dimensional and three-dimensional flow problems.

  5. FLAG: A multi-dimensional adaptive free-Lagrange code for fully unstructured grids

    SciTech Connect

    Burton, D.E.; Miller, D.S.; Palmer, T.

    1995-07-01

    The authors describe FLAG, a 3D adaptive free-Lagrange method for unstructured grids. The grid elements were 3D polygons, which move with the flow, and are refined or reconnected as necessary to achieve uniform accuracy. The authors stressed that they were able to construct a 3D hydro version of this code in 3 months, using an object-oriented FORTRAN approach.

  6. An assessment of the adaptive unstructured tetrahedral grid, Euler Flow Solver Code FELISA

    NASA Technical Reports Server (NTRS)

    Djomehri, M. Jahed; Erickson, Larry L.

    1994-01-01

    A three-dimensional solution-adaptive Euler flow solver for unstructured tetrahedral meshes is assessed, and the accuracy and efficiency of the method for predicting sonic boom pressure signatures about simple generic models are demonstrated. Comparison of computational and wind tunnel data and enhancement of numerical solutions by means of grid adaptivity are discussed. The mesh generation is based on the advancing front technique. The FELISA code consists of two solvers, the Taylor-Galerkin and the Runge-Kutta-Galerkin schemes, both of which are spacially discretized by the usual Galerkin weighted residual finite-element methods but with different explicit time-marching schemes to steady state. The solution-adaptive grid procedure is based on either remeshing or mesh refinement techniques. An alternative geometry adaptive procedure is also incorporated.

  7. The development and application of the self-adaptive grid code, SAGE

    NASA Technical Reports Server (NTRS)

    Davies, Carol B.

    1993-01-01

    The multidimensional self-adaptive grid code, SAGE, has proven to be a flexible and useful tool in the solution of complex flow problems. Both 2- and 3-D examples given in this report show the code to be reliable and to substantially improve flowfield solutions. Since the adaptive procedure is a marching scheme the code is extremely fast and uses insignificant CPU time compared to the corresponding flow solver. The SAGE program is also machine and flow solver independent. Significant effort was made to simplify user interaction, though some parameters still need to be chosen with care. It is also difficult to tell when the adaption process has provided its best possible solution. This is particularly true if no experimental data are available or if there is a lack of theoretical understanding of the flow. Another difficulty occurs if local features are important but missing in the original grid; the adaption to this solution will not result in any improvement, and only grid refinement can result in an improved solution. These are complex issues that need to be explored within the context of each specific problem.

  8. Adaptive EAGLE dynamic solution adaptation and grid quality enhancement

    NASA Technical Reports Server (NTRS)

    Luong, Phu Vinh; Thompson, J. F.; Gatlin, B.; Mastin, C. W.; Kim, H. J.

    1992-01-01

    In the effort described here, the elliptic grid generation procedure in the EAGLE grid code was separated from the main code into a subroutine, and a new subroutine which evaluates several grid quality measures at each grid point was added. The elliptic grid routine can now be called, either by a computational fluid dynamics (CFD) code to generate a new adaptive grid based on flow variables and quality measures through multiple adaptation, or by the EAGLE main code to generate a grid based on quality measure variables through static adaptation. Arrays of flow variables can be read into the EAGLE grid code for use in static adaptation as well. These major changes in the EAGLE adaptive grid system make it easier to convert any CFD code that operates on a block-structured grid (or single-block grid) into a multiple adaptive code.

  9. A User's Guide to AMR1D: An Instructional Adaptive Mesh Refinement Code for Unstructured Grids

    NASA Technical Reports Server (NTRS)

    deFainchtein, Rosalinda

    1996-01-01

    This report documents the code AMR1D, which is currently posted on the World Wide Web (http://sdcd.gsfc.nasa.gov/ESS/exchange/contrib/de-fainchtein/adaptive _mesh_refinement.html). AMR1D is a one-dimensional finite element fluid-dynamics solver, capable of adaptive mesh refinement (AMR). It was written as an instructional tool for AMR on unstructured mesh codes. It is meant to illustrate the minimum requirements for AMR on more than one dimension. For that purpose, it uses the same type of data structure that would be necessary on a two-dimensional AMR code (loosely following the algorithm described by Lohner).

  10. Near-Body Grid Adaption for Overset Grids

    NASA Technical Reports Server (NTRS)

    Buning, Pieter G.; Pulliam, Thomas H.

    2016-01-01

    A solution adaption capability for curvilinear near-body grids has been implemented in the OVERFLOW overset grid computational fluid dynamics code. The approach follows closely that used for the Cartesian off-body grids, but inserts refined grids in the computational space of original near-body grids. Refined curvilinear grids are generated using parametric cubic interpolation, with one-sided biasing based on curvature and stretching ratio of the original grid. Sensor functions, grid marking, and solution interpolation tasks are implemented in the same fashion as for off-body grids. A goal-oriented procedure, based on largest error first, is included for controlling growth rate and maximum size of the adapted grid system. The adaption process is almost entirely parallelized using MPI, resulting in a capability suitable for viscous, moving body simulations. Two- and three-dimensional examples are presented.

  11. 3D Structured Grid Adaptation

    NASA Technical Reports Server (NTRS)

    Banks, D. W.; Hafez, M. M.

    1996-01-01

    Grid adaptation for structured meshes is the art of using information from an existing, but poorly resolved, solution to automatically redistribute the grid points in such a way as to improve the resolution in regions of high error, and thus the quality of the solution. This involves: (1) generate a grid vis some standard algorithm, (2) calculate a solution on this grid, (3) adapt the grid to this solution, (4) recalculate the solution on this adapted grid, and (5) repeat steps 3 and 4 to satisfaction. Steps 3 and 4 can be repeated until some 'optimal' grid is converged to but typically this is not worth the effort and just two or three repeat calculations are necessary. They also may be repeated every 5-10 time steps for unsteady calculations.

  12. TranAir: A full-potential, solution-adaptive, rectangular grid code for predicting subsonic, transonic, and supersonic flows about arbitrary configurations. Theory document

    NASA Technical Reports Server (NTRS)

    Johnson, F. T.; Samant, S. S.; Bieterman, M. B.; Melvin, R. G.; Young, D. P.; Bussoletti, J. E.; Hilmes, C. L.

    1992-01-01

    A new computer program, called TranAir, for analyzing complex configurations in transonic flow (with subsonic or supersonic freestream) was developed. This program provides accurate and efficient simulations of nonlinear aerodynamic flows about arbitrary geometries with the ease and flexibility of a typical panel method program. The numerical method implemented in TranAir is described. The method solves the full potential equation subject to a set of general boundary conditions and can handle regions with differing total pressure and temperature. The boundary value problem is discretized using the finite element method on a locally refined rectangular grid. The grid is automatically constructed by the code and is superimposed on the boundary described by networks of panels; thus no surface fitted grid generation is required. The nonlinear discrete system arising from the finite element method is solved using a preconditioned Krylov subspace method embedded in an inexact Newton method. The solution is obtained on a sequence of successively refined grids which are either constructed adaptively based on estimated solution errors or are predetermined based on user inputs. Many results obtained by using TranAir to analyze aerodynamic configurations are presented.

  13. LAPS Grid generation and adaptation

    NASA Astrophysics Data System (ADS)

    Pagliantini, Cecilia; Delzanno, Gia Luca; Guo, Zehua; Srinivasan, Bhuvana; Tang, Xianzhu; Chacon, Luis

    2011-10-01

    LAPS uses a common-data framework in which a general purpose grid generation and adaptation package in toroidal and simply connected domains is implemented. The initial focus is on implementing the Winslow/Laplace-Beltrami method for generating non-overlapping block structured grids. This is to be followed by a grid adaptation scheme based on Monge-Kantorovich optimal transport method [Delzanno et al., J. Comput. Phys,227 (2008), 9841-9864], that equidistributes application-specified error. As an initial set of applications, we will lay out grids for an axisymmetric mirror, a field reversed configuration, and an entire poloidal cross section of a tokamak plasma reconstructed from a CMOD experimental shot. These grids will then be used for computing the plasma equilibrium and transport in accompanying presentations. A key issue for Monge-Kantorovich grid optimization is the choice of error or monitor function for equi-distribution. We will compare the Operator Recovery Error Source Detector (ORESD) [Lapenta, Int. J. Num. Meth. Eng,59 (2004) 2065-2087], the Tau method and a strategy based on the grid coarsening [Zhang et al., AIAA J,39 (2001) 1706-1715] to find an ``optimal'' grid. Work supported by DOE OFES.

  14. AEST: Adaptive Eigenvalue Stability Code

    NASA Astrophysics Data System (ADS)

    Zheng, L.-J.; Kotschenreuther, M.; Waelbroeck, F.; van Dam, J. W.; Berk, H.

    2002-11-01

    An adaptive eigenvalue linear stability code is developed. The aim is on one hand to include the non-ideal MHD effects into the global MHD stability calculation for both low and high n modes and on the other hand to resolve the numerical difficulty involving MHD singularity on the rational surfaces at the marginal stability. Our code follows some parts of philosophy of DCON by abandoning relaxation methods based on radial finite element expansion in favor of an efficient shooting procedure with adaptive gridding. The δ W criterion is replaced by the shooting procedure and subsequent matrix eigenvalue problem. Since the technique of expanding a general solution into a summation of the independent solutions employed, the rank of the matrices involved is just a few hundreds. This makes easier to solve the eigenvalue problem with non-ideal MHD effects, such as FLR or even full kinetic effects, as well as plasma rotation effect, taken into account. To include kinetic effects, the approach of solving for the distribution function as a local eigenvalue ω problem as in the GS2 code will be employed in the future. Comparison of the ideal MHD version of the code with DCON, PEST, and GATO will be discussed. The non-ideal MHD version of the code will be employed to study as an application the transport barrier physics in tokamak discharges.

  15. Workshop on adaptive grid methods for fusion plasmas

    SciTech Connect

    Wiley, J.C.

    1995-07-01

    The author describes a general `hp` finite element method with adaptive grids. The code was based on the work of Oden, et al. The term `hp` refers to the method of spatial refinement (h), in conjunction with the order of polynomials used as a part of the finite element discretization (p). This finite element code seems to handle well the different mesh grid sizes occuring between abuted grids with different resolutions.

  16. Anisotropic grid adaptation in LES

    NASA Astrophysics Data System (ADS)

    Toosi, Siavash; Larsson, Johan

    2016-11-01

    The modeling errors depend directly on the grid (or filter) spacing in turbulence-resolving simulations (LES, DNS, DES, etc), and are typically at least as significant as the numerical errors. This makes adaptive grid-refinement complicated, since it prevents the estimation of the local error sources through numerical analysis. The present work attempts to address this difficulty with a physics-based error-source indicator that accounts for the anisotropy in the smallest resolved scales, which can thus be used to drive an anisotropic grid-adaptation process. The proposed error indicator is assessed on a sequence of problems, including turbulent channel flow and flows in more complex geometries. The formulation is geometrically general and applicable to complex geometries.

  17. Telescope Adaptive Optics Code

    SciTech Connect

    Phillion, D.

    2005-07-28

    The Telescope AO Code has general adaptive optics capabilities plus specialized models for three telescopes with either adaptive optics or active optics systems. It has the capability to generate either single-layer or distributed Kolmogorov turbulence phase screens using the FFT. Missing low order spatial frequencies are added using the Karhunen-Loeve expansion. The phase structure curve is extremely dose to the theoreUcal. Secondly, it has the capability to simulate an adaptive optics control systems. The default parameters are those of the Keck II adaptive optics system. Thirdly, it has a general wave optics capability to model the science camera halo due to scintillation from atmospheric turbulence and the telescope optics. Although this capability was implemented for the Gemini telescopes, the only default parameter specific to the Gemini telescopes is the primary mirror diameter. Finally, it has a model for the LSST active optics alignment strategy. This last model is highly specific to the LSST

  18. IGB grid: User's manual (A turbomachinery grid generation code)

    NASA Technical Reports Server (NTRS)

    Beach, T. A.; Hoffman, G.

    1992-01-01

    A grid generation code called IGB is presented for use in computational investigations of turbomachinery flowfields. It contains a combination of algebraic and elliptic techniques coded for use on an interactive graphics workstation. The instructions for use and a test case are included.

  19. A generic efficient adaptive grid scheme for rocket propulsion modeling

    NASA Technical Reports Server (NTRS)

    Mo, J. D.; Chow, Alan S.

    1993-01-01

    The objective of this research is to develop an efficient, time-accurate numerical algorithm to discretize the Navier-Stokes equations for the predictions of internal one-, two-dimensional and axisymmetric flows. A generic, efficient, elliptic adaptive grid generator is implicitly coupled with the Lower-Upper factorization scheme in the development of ALUNS computer code. The calculations of one-dimensional shock tube wave propagation and two-dimensional shock wave capture, wave-wave interactions, shock wave-boundary interactions show that the developed scheme is stable, accurate and extremely robust. The adaptive grid generator produced a very favorable grid network by a grid speed technique. This generic adaptive grid generator is also applied in the PARC and FDNS codes and the computational results for solid rocket nozzle flowfield and crystal growth modeling by those codes will be presented in the conference, too. This research work is being supported by NASA/MSFC.

  20. A simplified self-adaptive grid method, SAGE

    NASA Technical Reports Server (NTRS)

    Davies, C.; Venkatapathy, E.

    1989-01-01

    The formulation of the Self-Adaptive Grid Evolution (SAGE) code, based on the work of Nakahashi and Deiwert, is described in the first section of this document. The second section is presented in the form of a user guide which explains the input and execution of the code, and provides many examples. Application of the SAGE code, by Ames Research Center and by others, in the solution of various flow problems has been an indication of the code's general utility and success. Although the basic formulation follows the method of Nakahashi and Deiwert, many modifications have been made to facilitate the use of the self-adaptive grid method for single, zonal, and multiple grids. Modifications to the methodology and the simplified input options make this current version a flexible and user-friendly code.

  1. Interactive solution-adaptive grid generation procedure

    NASA Technical Reports Server (NTRS)

    Henderson, Todd L.; Choo, Yung K.; Lee, Ki D.

    1992-01-01

    TURBO-AD is an interactive solution adaptive grid generation program under development. The program combines an interactive algebraic grid generation technique and a solution adaptive grid generation technique into a single interactive package. The control point form uses a sparse collection of control points to algebraically generate a field grid. This technique provides local grid control capability and is well suited to interactive work due to its speed and efficiency. A mapping from the physical domain to a parametric domain was used to improve difficulties encountered near outwardly concave boundaries in the control point technique. Therefore, all grid modifications are performed on the unit square in the parametric domain, and the new adapted grid is then mapped back to the physical domain. The grid adaption is achieved by adapting the control points to a numerical solution in the parametric domain using control sources obtained from the flow properties. Then a new modified grid is generated from the adapted control net. This process is efficient because the number of control points is much less than the number of grid points and the generation of the grid is an efficient algebraic process. TURBO-AD provides the user with both local and global controls.

  2. An Adaptive Unstructured Grid Method by Grid Subdivision, Local Remeshing, and Grid Movement

    NASA Technical Reports Server (NTRS)

    Pirzadeh, Shahyar Z.

    1999-01-01

    An unstructured grid adaptation technique has been developed and successfully applied to several three dimensional inviscid flow test cases. The approach is based on a combination of grid subdivision, local remeshing, and grid movement. For solution adaptive grids, the surface triangulation is locally refined by grid subdivision, and the tetrahedral grid in the field is partially remeshed at locations of dominant flow features. A grid redistribution strategy is employed for geometric adaptation of volume grids to moving or deforming surfaces. The method is automatic and fast and is designed for modular coupling with different solvers. Several steady state test cases with different inviscid flow features were tested for grid/solution adaptation. In all cases, the dominant flow features, such as shocks and vortices, were accurately and efficiently predicted with the present approach. A new and robust method of moving tetrahedral "viscous" grids is also presented and demonstrated on a three-dimensional example.

  3. The fundamentals of adaptive grid movement

    NASA Technical Reports Server (NTRS)

    Eiseman, Peter R.

    1990-01-01

    Basic grid point movement schemes are studied. The schemes are referred to as adaptive grids. Weight functions and equidistribution in one dimension are treated. The specification of coefficients in the linear weight, attraction to a given grid or a curve, and evolutionary forces are considered. Curve by curve and finite volume methods are described. The temporal coupling of partial differential equations solvers and grid generators was discussed.

  4. Rapid Structured Volume Grid Smoothing and Adaption Technique

    NASA Technical Reports Server (NTRS)

    Alter, Stephen J.

    2006-01-01

    A rapid, structured volume grid smoothing and adaption technique, based on signal processing methods, was developed and applied to the Shuttle Orbiter at hypervelocity flight conditions in support of the Columbia Accident Investigation. Because of the fast pace of the investigation, computational aerothermodynamicists, applying hypersonic viscous flow solving computational fluid dynamic (CFD) codes, refined and enhanced a grid for an undamaged baseline vehicle to assess a variety of damage scenarios. Of the many methods available to modify a structured grid, most are time-consuming and require significant user interaction. By casting the grid data into different coordinate systems, specifically two computational coordinates with arclength as the third coordinate, signal processing methods are used for filtering the data [Taubin, CG v/29 1995]. Using a reverse transformation, the processed data are used to smooth the Cartesian coordinates of the structured grids. By coupling the signal processing method with existing grid operations within the Volume Grid Manipulator tool, problems related to grid smoothing are solved efficiently and with minimal user interaction. Examples of these smoothing operations are illustrated for reductions in grid stretching and volume grid adaptation. In each of these examples, other techniques existed at the time of the Columbia accident, but the incorporation of signal processing techniques reduced the time to perform the corrections by nearly 60%. This reduction in time to perform the corrections therefore enabled the assessment of approximately twice the number of damage scenarios than previously possible during the allocated investigation time.

  5. Rapid Structured Volume Grid Smoothing and Adaption Technique

    NASA Technical Reports Server (NTRS)

    Alter, Stephen J.

    2004-01-01

    A rapid, structured volume grid smoothing and adaption technique, based on signal processing methods, was developed and applied to the Shuttle Orbiter at hypervelocity flight conditions in support of the Columbia Accident Investigation. Because of the fast pace of the investigation, computational aerothermodynamicists, applying hypersonic viscous flow solving computational fluid dynamic (CFD) codes, refined and enhanced a grid for an undamaged baseline vehicle to assess a variety of damage scenarios. Of the many methods available to modify a structured grid, most are time-consuming and require significant user interaction. By casting the grid data into different coordinate systems, specifically two computational coordinates with arclength as the third coordinate, signal processing methods are used for filtering the data [Taubin, CG v/29 1995]. Using a reverse transformation, the processed data are used to smooth the Cartesian coordinates of the structured grids. By coupling the signal processing method with existing grid operations within the Volume Grid Manipulator tool, problems related to grid smoothing are solved efficiently and with minimal user interaction. Examples of these smoothing operations are illustrated for reduction in grid stretching and volume grid adaptation. In each of these examples, other techniques existed at the time of the Columbia accident, but the incorporation of signal processing techniques reduced the time to perform the corrections by nearly 60%. This reduction in time to perform the corrections therefore enabled the assessment of approximately twice the number of damage scenarios than previously possible during the allocated investigation time.

  6. Efficient Unstructured Grid Adaptation Methods for Sonic Boom Prediction

    NASA Technical Reports Server (NTRS)

    Campbell, Richard L.; Carter, Melissa B.; Deere, Karen A.; Waithe, Kenrick A.

    2008-01-01

    This paper examines the use of two grid adaptation methods to improve the accuracy of the near-to-mid field pressure signature prediction of supersonic aircraft computed using the USM3D unstructured grid flow solver. The first method (ADV) is an interactive adaptation process that uses grid movement rather than enrichment to more accurately resolve the expansion and compression waves. The second method (SSGRID) uses an a priori adaptation approach to stretch and shear the original unstructured grid to align the grid with the pressure waves and reduce the cell count required to achieve an accurate signature prediction at a given distance from the vehicle. Both methods initially create negative volume cells that are repaired in a module in the ADV code. While both approaches provide significant improvements in the near field signature (< 3 body lengths) relative to a baseline grid without increasing the number of grid points, only the SSGRID approach allows the details of the signature to be accurately computed at mid-field distances (3-10 body lengths) for direct use with mid-field-to-ground boom propagation codes.

  7. Structured adaptive grid generation using algebraic methods

    NASA Technical Reports Server (NTRS)

    Yang, Jiann-Cherng; Soni, Bharat K.; Roger, R. P.; Chan, Stephen C.

    1993-01-01

    The accuracy of the numerical algorithm depends not only on the formal order of approximation but also on the distribution of grid points in the computational domain. Grid adaptation is a procedure which allows optimal grid redistribution as the solution progresses. It offers the prospect of accurate flow field simulations without the use of an excessively timely, computationally expensive, grid. Grid adaptive schemes are divided into two basic categories: differential and algebraic. The differential method is based on a variational approach where a function which contains a measure of grid smoothness, orthogonality and volume variation is minimized by using a variational principle. This approach provided a solid mathematical basis for the adaptive method, but the Euler-Lagrange equations must be solved in addition to the original governing equations. On the other hand, the algebraic method requires much less computational effort, but the grid may not be smooth. The algebraic techniques are based on devising an algorithm where the grid movement is governed by estimates of the local error in the numerical solution. This is achieved by requiring the points in the large error regions to attract other points and points in the low error region to repel other points. The development of a fast, efficient, and robust algebraic adaptive algorithm for structured flow simulation applications is presented. This development is accomplished in a three step process. The first step is to define an adaptive weighting mesh (distribution mesh) on the basis of the equidistribution law applied to the flow field solution. The second, and probably the most crucial step, is to redistribute grid points in the computational domain according to the aforementioned weighting mesh. The third and the last step is to reevaluate the flow property by an appropriate search/interpolate scheme at the new grid locations. The adaptive weighting mesh provides the information on the desired concentration

  8. Grid adaption using Chimera composite overlapping meshes

    NASA Technical Reports Server (NTRS)

    Kao, Kai-Hsiung; Liou, Meng-Sing; Chow, Chuen-Yen

    1993-01-01

    The objective of this paper is to perform grid adaptation using composite over-lapping meshes in regions of large gradient to capture the salient features accurately during computation. The Chimera grid scheme, a multiple overset mesh technique, is used in combination with a Navier-Stokes solver. The numerical solution is first converged to a steady state based on an initial coarse mesh. Solution-adaptive enhancement is then performed by using a secondary fine grid system which oversets on top of the base grid in the high-gradient region, but without requiring the mesh boundaries to join in any special way. Communications through boundary interfaces between those separated grids are carried out using tri-linear interpolation. Applications to the Euler equations for shock reflections and to a shock wave/boundary layer interaction problem are tested. With the present method, the salient features are well resolved.

  9. Grid adaptation using chimera composite overlapping meshes

    NASA Technical Reports Server (NTRS)

    Kao, Kai-Hsiung; Liou, Meng-Sing; Chow, Chuen-Yen

    1994-01-01

    The objective of this paper is to perform grid adaptation using composite overlapping meshes in regions of large gradient to accurately capture the salient features during computation. The chimera grid scheme, a multiple overset mesh technique, is used in combination with a Navier-Stokes solver. The numerical solution is first converged to a steady state based on an initial coarse mesh. Solution-adaptive enhancement is then performed by using a secondary fine grid system which oversets on top of the base grid in the high-gradient region, but without requiring the mesh boundaries to join in any special way. Communications through boundary interfaces between those separated grids are carried out using trilinear interpolation. Application to the Euler equations for shock reflections and to shock wave/boundary layer interaction problem are tested. With the present method, the salient features are well-resolved.

  10. Grid adaptation using Chimera composite overlapping meshes

    NASA Technical Reports Server (NTRS)

    Kao, Kai-Hsiung; Liou, Meng-Sing; Chow, Chuen-Yen

    1993-01-01

    The objective of this paper is to perform grid adaptation using composite over-lapping meshes in regions of large gradient to capture the salient features accurately during computation. The Chimera grid scheme, a multiple overset mesh technique, is used in combination with a Navier-Stokes solver. The numerical solution is first converged to a steady state based on an initial coarse mesh. Solution-adaptive enhancement is then performed by using a secondary fine grid system which oversets on top of the base grid in the high-gradient region, but without requiring the mesh boundaries to join in any special way. Communications through boundary interfaces between those separated grids are carried out using tri-linear interpolation. Applications to the Euler equations for shock reflections and to a shock wave/boundary layer interaction problem are tested. With the present method, the salient features are well resolved.

  11. Adaptive Dynamic Event Tree in RAVEN code

    SciTech Connect

    Alfonsi, Andrea; Rabiti, Cristian; Mandelli, Diego; Cogliati, Joshua Joseph; Kinoshita, Robert Arthur

    2014-11-01

    RAVEN is a software tool that is focused on performing statistical analysis of stochastic dynamic systems. RAVEN has been designed in a high modular and pluggable way in order to enable easy integration of different programming languages (i.e., C++, Python) and coupling with other applications (system codes). Among the several capabilities currently present in RAVEN, there are five different sampling strategies: Monte Carlo, Latin Hyper Cube, Grid, Adaptive and Dynamic Event Tree (DET) sampling methodologies. The scope of this paper is to present a new sampling approach, currently under definition and implementation: an evolution of the DET me

  12. A Grid Sourcing and Adaptation Study Using Unstructured Grids for Supersonic Boom Prediction

    NASA Technical Reports Server (NTRS)

    Carter, Melissa B.; Deere, Karen A.

    2008-01-01

    NASA created the Supersonics Project as part of the NASA Fundamental Aeronautics Program to advance technology that will make a supersonic flight over land viable. Computational flow solvers have lacked the ability to accurately predict sonic boom from the near to far field. The focus of this investigation was to establish gridding and adaptation techniques to predict near-to-mid-field (<10 body lengths below the aircraft) boom signatures at supersonic speeds using the USM3D unstructured grid flow solver. The study began by examining sources along the body the aircraft, far field sourcing and far field boundaries. The study then examined several techniques for grid adaptation. During the course of the study, volume sourcing was introduced as a new way to source grids using the grid generation code VGRID. Two different methods of using the volume sources were examined. The first method, based on manual insertion of the numerous volume sources, made great improvements in the prediction capability of USM3D for boom signatures. The second method (SSGRID), which uses an a priori adaptation approach to stretch and shear the original unstructured grid to align the grid and pressure waves, showed similar results with a more automated approach. Due to SSGRID s results and ease of use, the rest of the study focused on developing a best practice using SSGRID. The best practice created by this study for boom predictions using the CFD code USM3D involved: 1) creating a small cylindrical outer boundary either 1 or 2 body lengths in diameter (depending on how far below the aircraft the boom prediction is required), 2) using a single volume source under the aircraft, and 3) using SSGRID to stretch and shear the grid to the desired length.

  13. Driver Code for Adaptive Optics

    NASA Technical Reports Server (NTRS)

    Rao, Shanti

    2007-01-01

    A special-purpose computer code for a deformable-mirror adaptive-optics control system transmits pixel-registered control from (1) a personal computer running software that generates the control data to (2) a circuit board with 128 digital-to-analog converters (DACs) that generate voltages to drive the deformable-mirror actuators. This program reads control-voltage codes from a text file, then sends them, via the computer s parallel port, to a circuit board with four AD5535 (or equivalent) chips. Whereas a similar prior computer program was capable of transmitting data to only one chip at a time, this program can send data to four chips simultaneously. This program is in the form of C-language code that can be compiled and linked into an adaptive-optics software system. The program as supplied includes source code for integration into the adaptive-optics software, documentation, and a component that provides a demonstration of loading DAC codes from a text file. On a standard Windows desktop computer, the software can update 128 channels in 10 ms. On Real-Time Linux with a digital I/O card, the software can update 1024 channels (8 boards in parallel) every 8 ms.

  14. Adaptive refinement tools for tetrahedral unstructured grids

    NASA Technical Reports Server (NTRS)

    Pao, S. Paul (Inventor); Abdol-Hamid, Khaled S. (Inventor)

    2011-01-01

    An exemplary embodiment providing one or more improvements includes software which is robust, efficient, and has a very fast run time for user directed grid enrichment and flow solution adaptive grid refinement. All user selectable options (e.g., the choice of functions, the choice of thresholds, etc.), other than a pre-marked cell list, can be entered on the command line. The ease of application is an asset for flow physics research and preliminary design CFD analysis where fast grid modification is often needed to deal with unanticipated development of flow details.

  15. TIGGERC: Turbomachinery interactive grid generator energy distributor and restart code

    NASA Technical Reports Server (NTRS)

    Miller, David P.

    1992-01-01

    A two dimensional multi-block grid generator was developed for a new design and analysis system for studying multi-blade row turbomachinery problems with an axisymmetric viscous/inviscid 'average passage' through flow code. TIGGERC is a mouse driven, fully interactive grid generation program which can be used to modify boundary coordinates and grid packing. TIGGERC generates grids using a hyperbolic tangent or algebraic distribution of grid points on the block boundaries and the interior points of each block grid are distributed using a transfinite interpolation approach. TIGGERC generates a blocked axisymmetric H grid, C grid, I grid, or O grid for studying turbomachinery flow problems. TIGGERC was developed for operation on small high speed graphic workstations.

  16. Cartesian-cell based grid generation and adaptive mesh refinement

    NASA Technical Reports Server (NTRS)

    Coirier, William J.; Powell, Kenneth G.

    1993-01-01

    Viewgraphs on Cartesian-cell based grid generation and adaptive mesh refinement are presented. Topics covered include: grid generation; cell cutting; data structures; flow solver formulation; adaptive mesh refinement; and viscous flow.

  17. Transonic airfoil calculations using solution-adaptive grids

    NASA Technical Reports Server (NTRS)

    Holst, T. L.; Brown, D.

    1981-01-01

    A new algorithm for generating solution-adaptive grids (SAG) about airfoil configurations embedded in transonic flow is presented. The present SAG approach uses only the airfoil surface solution to recluster grid points on the airfoil surface, i.e., the reclustering problem is one dimension smaller than the flow-field calculation problem. Special controls automatically built into the elliptic grid generation procedure are then used to obtain grids with suitable interior behavior. This concept of redistributing grid points greatly simplifies the idea of solution-adaptive grids. Numerical results indicate significant improvements in accuracy for SAG grids relative to standard grids using the same number of points.

  18. Elliptic Solvers for Adaptive Mesh Refinement Grids

    SciTech Connect

    Quinlan, D.J.; Dendy, J.E., Jr.; Shapira, Y.

    1999-06-03

    We are developing multigrid methods that will efficiently solve elliptic problems with anisotropic and discontinuous coefficients on adaptive grids. The final product will be a library that provides for the simplified solution of such problems. This library will directly benefit the efforts of other Laboratory groups. The focus of this work is research on serial and parallel elliptic algorithms and the inclusion of our black-box multigrid techniques into this new setting. The approach applies the Los Alamos object-oriented class libraries that greatly simplify the development of serial and parallel adaptive mesh refinement applications. In the final year of this LDRD, we focused on putting the software together; in particular we completed the final AMR++ library, we wrote tutorials and manuals, and we built example applications. We implemented the Fast Adaptive Composite Grid method as the principal elliptic solver. We presented results at the Overset Grid Conference and other more AMR specific conferences. We worked on optimization of serial and parallel performance and published several papers on the details of this work. Performance remains an important issue and is the subject of continuing research work.

  19. High Penetration, Grid Connected Photovoltaic Technology Codes and Standards: Preprint

    SciTech Connect

    Basso, T. S.

    2008-05-01

    This paper reports the interim status in identifying and reviewing photovoltaic (PV) codes and standards (C&S) and related electrical activities for grid-connected, high-penetration PV systems with a focus on U.S. electric utility distribution grid interconnection.

  20. OMEGA: The operational multiscale environment model with grid adaptivity

    SciTech Connect

    Bacon, D.P.

    1995-07-01

    This review talk describes the OMEGA code, used for weather simulation and the modeling of aerosol transport through the atmosphere. Omega employs a 3D mesh of wedge shaped elements (triangles when viewed from above) that adapt with time. Because wedges are laid out in layers of triangular elements, the scheme can utilize structured storage and differencing techniques along the elevation coordinate, and is thus a hybrid of structured and unstructured methods. The utility of adaptive gridding in this moded, near geographic features such as coastlines, where material properties change discontinuously, is illustrated. Temporal adaptivity was used additionally to track moving internal fronts, such as clouds of aerosol contaminants. The author also discusses limitations specific to this problem, including manipulation of huge data bases and fixed turn-around times. In practice, the latter requires a carefully tuned optimization between accuracy and computation speed.

  1. Cartesian Off-Body Grid Adaption for Viscous Time- Accurate Flow Simulation

    NASA Technical Reports Server (NTRS)

    Buning, Pieter G.; Pulliam, Thomas H.

    2011-01-01

    An improved solution adaption capability has been implemented in the OVERFLOW overset grid CFD code. Building on the Cartesian off-body approach inherent in OVERFLOW and the original adaptive refinement method developed by Meakin, the new scheme provides for automated creation of multiple levels of finer Cartesian grids. Refinement can be based on the undivided second-difference of the flow solution variables, or on a specific flow quantity such as vorticity. Coupled with load-balancing and an inmemory solution interpolation procedure, the adaption process provides very good performance for time-accurate simulations on parallel compute platforms. A method of using refined, thin body-fitted grids combined with adaption in the off-body grids is presented, which maximizes the part of the domain subject to adaption. Two- and three-dimensional examples are used to illustrate the effectiveness and performance of the adaption scheme.

  2. On Accuracy of Adaptive Grid Methods for Captured Shocks

    NASA Technical Reports Server (NTRS)

    Yamaleev, Nail K.; Carpenter, Mark H.

    2002-01-01

    The accuracy of two grid adaptation strategies, grid redistribution and local grid refinement, is examined by solving the 2-D Euler equations for the supersonic steady flow around a cylinder. Second- and fourth-order linear finite difference shock-capturing schemes, based on the Lax-Friedrichs flux splitting, are used to discretize the governing equations. The grid refinement study shows that for the second-order scheme, neither grid adaptation strategy improves the numerical solution accuracy compared to that calculated on a uniform grid with the same number of grid points. For the fourth-order scheme, the dominant first-order error component is reduced by the grid adaptation, while the design-order error component drastically increases because of the grid nonuniformity. As a result, both grid adaptation techniques improve the numerical solution accuracy only on the coarsest mesh or on very fine grids that are seldom found in practical applications because of the computational cost involved. Similar error behavior has been obtained for the pressure integral across the shock. A simple analysis shows that both grid adaptation strategies are not without penalties in the numerical solution accuracy. Based on these results, a new grid adaptation criterion for captured shocks is proposed.

  3. Aeroacoustic Simulation of Nose Landing Gear on Adaptive Unstructured Grids With FUN3D

    NASA Technical Reports Server (NTRS)

    Vatsa, Veer N.; Khorrami, Mehdi R.; Park, Michael A.; Lockhard, David P.

    2013-01-01

    Numerical simulations have been performed for a partially-dressed, cavity-closed nose landing gear configuration that was tested in NASA Langley s closed-wall Basic Aerodynamic Research Tunnel (BART) and in the University of Florida's open-jet acoustic facility known as the UFAFF. The unstructured-grid flow solver FUN3D, developed at NASA Langley Research center, is used to compute the unsteady flow field for this configuration. Starting with a coarse grid, a series of successively finer grids were generated using the adaptive gridding methodology available in the FUN3D code. A hybrid Reynolds-averaged Navier-Stokes/large eddy simulation (RANS/LES) turbulence model is used for these computations. Time-averaged and instantaneous solutions obtained on these grids are compared with the measured data. In general, the correlation with the experimental data improves with grid refinement. A similar trend is observed for sound pressure levels obtained by using these CFD solutions as input to a FfowcsWilliams-Hawkings noise propagation code to compute the farfield noise levels. In general, the numerical solutions obtained on adapted grids compare well with the hand-tuned enriched fine grid solutions and experimental data. In addition, the grid adaption strategy discussed here simplifies the grid generation process, and results in improved computational efficiency of CFD simulations.

  4. FUN3D Grid Refinement and Adaptation Studies for the Ares Launch Vehicle

    NASA Technical Reports Server (NTRS)

    Bartels, Robert E.; Vasta, Veer; Carlson, Jan-Renee; Park, Mike; Mineck, Raymond E.

    2010-01-01

    This paper presents grid refinement and adaptation studies performed in conjunction with computational aeroelastic analyses of the Ares crew launch vehicle (CLV). The unstructured grids used in this analysis were created with GridTool and VGRID while the adaptation was performed using the Computational Fluid Dynamic (CFD) code FUN3D with a feature based adaptation software tool. GridTool was developed by ViGYAN, Inc. while the last three software suites were developed by NASA Langley Research Center. The feature based adaptation software used here operates by aligning control volumes with shock and Mach line structures and by refining/de-refining where necessary. It does not redistribute node points on the surface. This paper assesses the sensitivity of the complex flow field about a launch vehicle to grid refinement. It also assesses the potential of feature based grid adaptation to improve the accuracy of CFD analysis for a complex launch vehicle configuration. The feature based adaptation shows the potential to improve the resolution of shocks and shear layers. Further development of the capability to adapt the boundary layer and surface grids of a tetrahedral grid is required for significant improvements in modeling the flow field.

  5. Euler Technology Assessment program for preliminary aircraft design employing SPLITFLOW code with Cartesian unstructured grid method

    NASA Technical Reports Server (NTRS)

    Finley, Dennis B.

    1995-01-01

    This report documents results from the Euler Technology Assessment program. The objective was to evaluate the efficacy of Euler computational fluid dynamics (CFD) codes for use in preliminary aircraft design. Both the accuracy of the predictions and the rapidity of calculations were to be assessed. This portion of the study was conducted by Lockheed Fort Worth Company, using a recently developed in-house Cartesian-grid code called SPLITFLOW. The Cartesian grid technique offers several advantages for this study, including ease of volume grid generation and reduced number of cells compared to other grid schemes. SPLITFLOW also includes grid adaptation of the volume grid during the solution convergence to resolve high-gradient flow regions. This proved beneficial in resolving the large vortical structures in the flow for several configurations examined in the present study. The SPLITFLOW code predictions of the configuration forces and moments are shown to be adequate for preliminary design analysis, including predictions of sideslip effects and the effects of geometry variations at low and high angles of attack. The time required to generate the results from initial surface definition is on the order of several hours, including grid generation, which is compatible with the needs of the design environment.

  6. Cosmos++: Relativistic Magnetohydrodynamics on Unstructured Grids with Local Adaptive Refinement

    SciTech Connect

    Anninos, P; Fragile, P C; Salmonson, J D

    2005-05-06

    A new code and methodology are introduced for solving the fully general relativistic magnetohydrodynamic (GRMHD) equations using time-explicit, finite-volume discretization. The code has options for solving the GRMHD equations using traditional artificial-viscosity (AV) or non-oscillatory central difference (NOCD) methods, or a new extended AV (eAV) scheme using artificial-viscosity together with a dual energy-flux-conserving formulation. The dual energy approach allows for accurate modeling of highly relativistic flows at boost factors well beyond what has been achieved to date by standard artificial viscosity methods. it provides the benefit of Godunov methods in capturing high Lorentz boosted flows but without complicated Riemann solvers, and the advantages of traditional artificial viscosity methods in their speed and flexibility. Additionally, the GRMHD equations are solved on an unstructured grid that supports local adaptive mesh refinement using a fully threated oct-tree (in three dimensions) network to traverse the grid hierarchy across levels and immediate neighbors. A number of tests are presented to demonstrate robustness of the numerical algorithms and adaptive mesh framework over a wide spectrum of problems, boosts, and astrophysical applications, including relativistic shock tubes, shock collisions, magnetosonic shocks, Alfven wave propagation, blast waves, magnetized Bondi flow, and the magneto-rotational instability in Kerr black hole spacetimes.

  7. Techniques for grid manipulation and adaptation. [computational fluid dynamics

    NASA Technical Reports Server (NTRS)

    Choo, Yung K.; Eisemann, Peter R.; Lee, Ki D.

    1992-01-01

    Two approaches have been taken to provide systematic grid manipulation for improved grid quality. One is the control point form (CPF) of algebraic grid generation. It provides explicit control of the physical grid shape and grid spacing through the movement of the control points. It works well in the interactive computer graphics environment and hence can be a good candidate for integration with other emerging technologies. The other approach is grid adaptation using a numerical mapping between the physical space and a parametric space. Grid adaptation is achieved by modifying the mapping functions through the effects of grid control sources. The adaptation process can be repeated in a cyclic manner if satisfactory results are not achieved after a single application.

  8. Comparing Anisotropic Output-Based Grid Adaptation Methods by Decomposition

    NASA Technical Reports Server (NTRS)

    Park, Michael A.; Loseille, Adrien; Krakos, Joshua A.; Michal, Todd

    2015-01-01

    Anisotropic grid adaptation is examined by decomposing the steps of flow solution, ad- joint solution, error estimation, metric construction, and simplex grid adaptation. Multiple implementations of each of these steps are evaluated by comparison to each other and expected analytic results when available. For example, grids are adapted to analytic metric fields and grid measures are computed to illustrate the properties of multiple independent implementations of grid adaptation mechanics. Different implementations of each step in the adaptation process can be evaluated in a system where the other components of the adaptive cycle are fixed. Detailed examination of these properties allows comparison of different methods to identify the current state of the art and where further development should be targeted.

  9. Automatic adaptive grid refinement for the Euler equations

    NASA Technical Reports Server (NTRS)

    Berger, M. J.; Jameson, A.

    1983-01-01

    A method of adaptive grid refinement for the solution of the steady Euler equations for transonic flow is presented. Algorithm automatically decides where the coarse grid accuracy is insufficient, and creates locally uniform refined grids in these regions. This typically occurs at the leading and trailing edges. The solution is then integrated to steady state using the same integrator (FLO52) in the interior of each grid. The boundary conditions needed on the fine grids are examined and the importance of treating the fine/coarse grid inerface conservatively is discussed. Numerical results are presented.

  10. Moving and adaptive grid methods for compressible flows

    NASA Technical Reports Server (NTRS)

    Trepanier, Jean-Yves; Camarero, Ricardo

    1995-01-01

    This paper describes adaptive grid methods developed specifically for compressible flow computations. The basic flow solver is a finite-volume implementation of Roe's flux difference splitting scheme or arbitrarily moving unstructured triangular meshes. The grid adaptation is performed according to geometric and flow requirements. Some results are included to illustrate the potential of the methodology.

  11. Perceptually-Based Adaptive JPEG Coding

    NASA Technical Reports Server (NTRS)

    Watson, Andrew B.; Rosenholtz, Ruth; Null, Cynthia H. (Technical Monitor)

    1996-01-01

    An extension to the JPEG standard (ISO/IEC DIS 10918-3) allows spatial adaptive coding of still images. As with baseline JPEG coding, one quantization matrix applies to an entire image channel, but in addition the user may specify a multiplier for each 8 x 8 block, which multiplies the quantization matrix, yielding the new matrix for the block. MPEG 1 and 2 use much the same scheme, except there the multiplier changes only on macroblock boundaries. We propose a method for perceptual optimization of the set of multipliers. We compute the perceptual error for each block based upon DCT quantization error adjusted according to contrast sensitivity, light adaptation, and contrast masking, and pick the set of multipliers which yield maximally flat perceptual error over the blocks of the image. We investigate the bitrate savings due to this adaptive coding scheme and the relative importance of the different sorts of masking on adaptive coding.

  12. Cooperative solutions coupling a geometry engine and adaptive solver codes

    NASA Technical Reports Server (NTRS)

    Dickens, Thomas P.

    1995-01-01

    Follow-on work has progressed in using Aero Grid and Paneling System (AGPS), a geometry and visualization system, as a dynamic real time geometry monitor, manipulator, and interrogator for other codes. In particular, AGPS has been successfully coupled with adaptive flow solvers which iterate, refining the grid in areas of interest, and continuing on to a solution. With the coupling to the geometry engine, the new grids represent the actual geometry much more accurately since they are derived directly from the geometry and do not use refits to the first-cut grids. Additional work has been done with design runs where the geometric shape is modified to achieve a desired result. Various constraints are used to point the solution in a reasonable direction which also more closely satisfies the desired results. Concepts and techniques are presented, as well as examples of sample case studies. Issues such as distributed operation of the cooperative codes versus running all codes locally and pre-calculation for performance are discussed. Future directions are considered which will build on these techniques in light of changing computer environments.

  13. A chimera grid scheme. [multiple overset body-conforming mesh system for finite difference adaptation to complex aircraft configurations

    NASA Technical Reports Server (NTRS)

    Steger, J. L.; Dougherty, F. C.; Benek, J. A.

    1983-01-01

    A mesh system composed of multiple overset body-conforming grids is described for adapting finite-difference procedures to complex aircraft configurations. In this so-called 'chimera mesh,' a major grid is generated about a main component of the configuration and overset minor grids are used to resolve all other features. Methods for connecting overset multiple grids and modifications of flow-simulation algorithms are discussed. Computational tests in two dimensions indicate that the use of multiple overset grids can simplify the task of grid generation without an adverse effect on flow-field algorithms and computer code complexity.

  14. Pyramidal Image-Processing Code For Hexagonal Grid

    NASA Technical Reports Server (NTRS)

    Watson, Andrew B.; Ahumada, Albert J., Jr.

    1990-01-01

    Algorithm based on processing of information on intensities of picture elements arranged in regular hexagonal grid. Called "image pyramid" because image information at each processing level arranged in hexagonal grid having one-seventh number of picture elements of next lower processing level, each picture element derived from hexagonal set of seven nearest-neighbor picture elements in next lower level. At lowest level, fine-resolution of elements of original image. Designed to have some properties of image-coding scheme of primate visual cortex.

  15. Adaptivity via mesh movement with three-dimensional block-structured grids

    SciTech Connect

    Catherall, D.

    1996-12-31

    The method described here is one in which grid nodes are redistributed so that they are attracted towards regions of high solution activity. The major difficulty in attempting this arises from the degree of grid smoothness and orthogonality required by the flow solver. These requirements are met by suitable choice of grid equations, to be satisfied by the adapted grid, and by the inclusion of certain source terms, for added control in regions where grid movement is limited by the local geometry. The method has been coded for multiblock grids, so that complex configurations may be treated. It is demonstrated here for inviscid supercritical flow with two test cases: an ONERA M6 wing with a rounded tip, and a forward-swept wing/fuselage configuration (M151).

  16. Grid-Adapted FUN3D Computations for the Second High Lift Prediction Workshop

    NASA Technical Reports Server (NTRS)

    Lee-Rausch, E. M.; Rumsey, C. L.; Park, M. A.

    2014-01-01

    Contributions of the unstructured Reynolds-averaged Navier-Stokes code FUN3D to the 2nd AIAA CFD High Lift Prediction Workshop are described, and detailed comparisons are made with experimental data. Using workshop-supplied grids, results for the clean wing configuration are compared with results from the structured code CFL3D Using the same turbulence model, both codes compare reasonably well in terms of total forces and moments, and the maximum lift is similarly over-predicted for both codes compared to experiment. By including more representative geometry features such as slat and flap brackets and slat pressure tube bundles, FUN3D captures the general effects of the Reynolds number variation, but under-predicts maximum lift on workshop-supplied grids in comparison with the experimental data, due to excessive separation. However, when output-based, off-body grid adaptation in FUN3D is employed, results improve considerably. In particular, when the geometry includes both brackets and the pressure tube bundles, grid adaptation results in a more accurate prediction of lift near stall in comparison with the wind-tunnel data. Furthermore, a rotation-corrected turbulence model shows improved pressure predictions on the outboard span when using adapted grids.

  17. An object-oriented approach for parallel self adaptive mesh refinement on block structured grids

    NASA Technical Reports Server (NTRS)

    Lemke, Max; Witsch, Kristian; Quinlan, Daniel

    1993-01-01

    Self-adaptive mesh refinement dynamically matches the computational demands of a solver for partial differential equations to the activity in the application's domain. In this paper we present two C++ class libraries, P++ and AMR++, which significantly simplify the development of sophisticated adaptive mesh refinement codes on (massively) parallel distributed memory architectures. The development is based on our previous research in this area. The C++ class libraries provide abstractions to separate the issues of developing parallel adaptive mesh refinement applications into those of parallelism, abstracted by P++, and adaptive mesh refinement, abstracted by AMR++. P++ is a parallel array class library to permit efficient development of architecture independent codes for structured grid applications, and AMR++ provides support for self-adaptive mesh refinement on block-structured grids of rectangular non-overlapping blocks. Using these libraries, the application programmers' work is greatly simplified to primarily specifying the serial single grid application and obtaining the parallel and self-adaptive mesh refinement code with minimal effort. Initial results for simple singular perturbation problems solved by self-adaptive multilevel techniques (FAC, AFAC), being implemented on the basis of prototypes of the P++/AMR++ environment, are presented. Singular perturbation problems frequently arise in large applications, e.g. in the area of computational fluid dynamics. They usually have solutions with layers which require adaptive mesh refinement and fast basic solvers in order to be resolved efficiently.

  18. Conservative treatment of boundary interfaces for overlaid grids and multi-level grid adaptations

    NASA Technical Reports Server (NTRS)

    Moon, Young J.; Liou, Meng-Sing

    1989-01-01

    Conservative algorithms for boundary interfaces of overlaid grids are presented. The basic method is zeroth order, and is extended to a higher order method using interpolation and subcell decomposition. The present method, strictly based on a conservative constraint, is tested with overlaid grids for various applications of unsteady and steady supersonic inviscid flows with strong shock waves. The algorithm is also applied to a multi-level grid adaptation in which the next level finer grid is overlaid on the coarse base grid with an arbitrary orientation.

  19. New multigrid approach for three-dimensional unstructured, adaptive grids

    NASA Technical Reports Server (NTRS)

    Parthasarathy, Vijayan; Kallinderis, Y.

    1994-01-01

    A new multigrid method with adaptive unstructured grids is presented. The three-dimensional Euler equations are solved on tetrahedral grids that are adaptively refined or coarsened locally. The multigrid method is employed to propagate the fine grid corrections more rapidly by redistributing the changes-in-time of the solution from the fine grid to the coarser grids to accelerate convergence. A new approach is employed that uses the parent cells of the fine grid cells in an adapted mesh to generate successively coaser levels of multigrid. This obviates the need for the generation of a sequence of independent, nonoverlapping grids as well as the relatively complicated operations that need to be performed to interpolate the solution and the residuals between the independent grids. The solver is an explicit, vertex-based, finite volume scheme that employs edge-based data structures and operations. Spatial discretization is of central-differencing type combined with a special upwind-like smoothing operators. Application cases include adaptive solutions obtained with multigrid acceleration for supersonic and subsonic flow over a bump in a channel, as well as transonic flow around the ONERA M6 wing. Two levels of multigrid resulted in reduction in the number of iterations by a factor of 5.

  20. New multigrid approach for three-dimensional unstructured, adaptive grids

    NASA Astrophysics Data System (ADS)

    Parthasarathy, Vijayan; Kallinderis, Y.

    1994-05-01

    A new multigrid method with adaptive unstructured grids is presented. The three-dimensional Euler equations are solved on tetrahedral grids that are adaptively refined or coarsened locally. The multigrid method is employed to propagate the fine grid corrections more rapidly by redistributing the changes-in-time of the solution from the fine grid to the coarser grids to accelerate convergence. A new approach is employed that uses the parent cells of the fine grid cells in an adapted mesh to generate successively coarser levels of multigrid. This obviates the need for the generation of a sequence of independent, nonoverlapping grids as well as the relatively complicated operations that need to be performed to interpolate the solution and the residuals between the independent grids. The solver is an explicit, vertex-based, finite volume scheme that employs edge-based data structures and operations. Spatial discretization is of central-differencing type combined with special upwind-like smoothing operators. Application cases include adaptive solutions obtained with multigrid acceleration for supersonic and subsonic flow over a bump in a channel, as well as transonic flow around the ONERA M6 wing. Two levels of multigrid resulted in reduction in the number of iterations by a factor of 5.

  1. New multigrid approach for three-dimensional unstructured, adaptive grids

    NASA Astrophysics Data System (ADS)

    Parthasarathy, Vijayan; Kallinderis, Y.

    1994-05-01

    A new multigrid method with adaptive unstructured grids is presented. The three-dimensional Euler equations are solved on tetrahedral grids that are adaptively refined or coarsened locally. The multigrid method is employed to propagate the fine grid corrections more rapidly by redistributing the changes-in-time of the solution from the fine grid to the coarser grids to accelerate convergence. A new approach is employed that uses the parent cells of the fine grid cells in an adapted mesh to generate successively coaser levels of multigrid. This obviates the need for the generation of a sequence of independent, nonoverlapping grids as well as the relatively complicated operations that need to be performed to interpolate the solution and the residuals between the independent grids. The solver is an explicit, vertex-based, finite volume scheme that employs edge-based data structures and operations. Spatial discretization is of central-differencing type combined with a special upwind-like smoothing operators. Application cases include adaptive solutions obtained with multigrid acceleration for supersonic and subsonic flow over a bump in a channel, as well as transonic flow around the ONERA M6 wing. Two levels of multigrid resulted in reduction in the number of iterations by a factor of 5.

  2. Application of a self-adaptive grid method to complex flows

    NASA Technical Reports Server (NTRS)

    Deiwert, G. S.; Venkatapathy, E.; Davies, C.; Djomehri, J.; Abrahamson, K.

    1989-01-01

    A directional-split, modular, user-friendly grid point distribution code is applied to several test problems. The code is self-adaptive in the sense that grid point spacing is determined by user-specified constants denoting maximum and minimum grid spacings and constants relating the relative influence of smoothness and orthogonality. Estimates of truncation error, in terms of flow-field gradients and/or geometric features, are used to determine the point distribution. Points are redistributed along grid lines in a specified direction in an elliptic manner over a user-specified subdomain, while orthogonality and smoothness are controlled in a parabolic (marching) manner in the remaining directions. Multidirectional adaption is achieved by sequential application of the method in each coordinate direction. The flow-field solution is redistributed onto the newly distributed grid points after each unidirectional adaption by a simple one-dimensional interpolation scheme. For time-accurate schemes such interpolation is not necessary and time-dependent metrics are carried in the fluid dynamic equations to account for grid movement.

  3. 3-D adaptive grid Navier-Stokes rocket plume calculations

    NASA Astrophysics Data System (ADS)

    Holcomb, J. Eric

    1991-01-01

    Three-dimensional adaptive-grid full Navier-Stokes calculations performed for the base region and plume of the Minuteman first stage and a simplified version of the Titan first stage are used to demonstrate the applicability of the Navier-Stokes flow solver, EAGLE adaptive grid generator, and k-epsilon turbulence model to rocket plume flowfields. The calculations include realistic exhaust gas thermodynamic properties, with frozen chemistry.

  4. Adaptive local grid refinement for the compressible 3-D Euler equations

    NASA Astrophysics Data System (ADS)

    Schoenfeld, Thilo

    A method is presented based on a three-dimensional Euler code, using the explicit finite volume technique and a Runge-Kutta scheme, and applied in an adaptive version for the transonic flow around wings. The method allows embedded subgrids at two levels of refinement. Computations are performed with both various fixed refined grids and in an adaptive version applying a pressure or density gradient sensor. When comparing the results of embedded grid computations with calculations on only a total coarse or fine mesh, it can be stated that the local grid refinement technique is an effective framework to obtain well-resolved solutions with, at the same time, a minimum of grid points.

  5. An adaptive Cartesian grid generation method for Dirty geometry

    NASA Astrophysics Data System (ADS)

    Wang, Z. J.; Srinivasan, Kumar

    2002-07-01

    Traditional structured and unstructured grid generation methods need a water-tight boundary surface grid to start. Therefore, these methods are named boundary to interior (B2I) approaches. Although these methods have achieved great success in fluid flow simulations, the grid generation process can still be very time consuming if non-water-tight geometries are given. Significant user time can be taken to repair or clean a dirty geometry with cracks, overlaps or invalid manifolds before grid generation can take place. In this paper, we advocate a different approach in grid generation, namely the interior to boundary (I2B) approach. With an I2B approach, the computational grid is first generated inside the computational domain. Then this grid is intelligently connected to the boundary, and the boundary grid is a result of this connection. A significant advantage of the I2B approach is that dirty geometries can be handled without cleaning or repairing, dramatically reducing grid generation time. An I2B adaptive Cartesian grid generation method is developed in this paper to handle dirty geometries without geometry repair. Comparing with a B2I approach, the grid generation time with the I2B approach for a complex automotive engine can be reduced by three orders of magnitude. Copyright

  6. Adaptive Mesh Refinement in Curvilinear Body-Fitted Grid Systems

    NASA Technical Reports Server (NTRS)

    Steinthorsson, Erlendur; Modiano, David; Colella, Phillip

    1995-01-01

    To be truly compatible with structured grids, an AMR algorithm should employ a block structure for the refined grids to allow flow solvers to take advantage of the strengths of unstructured grid systems, such as efficient solution algorithms for implicit discretizations and multigrid schemes. One such algorithm, the AMR algorithm of Berger and Colella, has been applied to and adapted for use with body-fitted structured grid systems. Results are presented for a transonic flow over a NACA0012 airfoil (AGARD-03 test case) and a reflection of a shock over a double wedge.

  7. Topology and grid adaption for high-speed flow computations

    NASA Astrophysics Data System (ADS)

    Abolhassani, Jamshid S.; Tiwari, Surendra N.

    1989-03-01

    This study investigates the effects of grid topology and grid adaptation on numerical solutions of the Navier-Stokes equations. In the first part of this study, a general procedure is presented for computation of high-speed flow over complex three-dimensional configurations. The flow field is simulated on the surface of a Butler wing in a uniform stream. Results are presented for Mach number 3.5 and a Reynolds number of 2,000,000. The O-type and H-type grids have been used for this study, and the results are compared together and with other theoretical and experimental results. The results demonstrate that while the H-type grid is suitable for the leading and trailing edges, a more accurate solution can be obtained for the middle part of the wing with an O-type grid. In the second part of this study, methods of grid adaption are reviewed and a method is developed with the capability of adapting to several variables. This method is based on a variational approach and is an algebraic method. Also, the method has been formulated in such a way that there is no need for any matrix inversion. This method is used in conjunction with the calculation of hypersonic flow over a blunt-nose body. A movie has been produced which shows simultaneously the transient behavior of the solution and the grid adaption.

  8. Topology and grid adaption for high-speed flow computations

    NASA Technical Reports Server (NTRS)

    Abolhassani, Jamshid S.; Tiwari, Surendra N.

    1989-01-01

    This study investigates the effects of grid topology and grid adaptation on numerical solutions of the Navier-Stokes equations. In the first part of this study, a general procedure is presented for computation of high-speed flow over complex three-dimensional configurations. The flow field is simulated on the surface of a Butler wing in a uniform stream. Results are presented for Mach number 3.5 and a Reynolds number of 2,000,000. The O-type and H-type grids have been used for this study, and the results are compared together and with other theoretical and experimental results. The results demonstrate that while the H-type grid is suitable for the leading and trailing edges, a more accurate solution can be obtained for the middle part of the wing with an O-type grid. In the second part of this study, methods of grid adaption are reviewed and a method is developed with the capability of adapting to several variables. This method is based on a variational approach and is an algebraic method. Also, the method has been formulated in such a way that there is no need for any matrix inversion. This method is used in conjunction with the calculation of hypersonic flow over a blunt-nose body. A movie has been produced which shows simultaneously the transient behavior of the solution and the grid adaption.

  9. Grid adaptation and remapping for arbitrary lagrangian eulerian (ALE) methods

    SciTech Connect

    Lapenta, G. M.

    2002-01-01

    Methods to include automatic grid adaptation tools within the Arbitrary Lagrangian Eulerian (ALE) method are described. Two main developments will be described. First, a new grid adaptation approach is described, based on an automatic and accurate estimate of the local truncation error. Second, a new method to remap the information between two grids is presented, based on the MPDATA approach. The Arbitrary Lagrangian Eulerian (ALE) method solves hyperbolic equations by splitting the operators is two phases. First, in the Lagrangian phase, the equations under consideration are written in a Lagrangian frame and are discretized. In this phase, the grid moves with the solution, the velocity of each node being the local fluid velocity. Second, in the Eulerian phase, a new grid is generated and the information is transferred to the new grid. The advantage of considering this second step is the possibility of avoiding mesh distortion and tangling typical of pure Lagrangian methods. The second phase of the ALE method is the primary topic of the present communication. In the Eulerian phase two tasks need to be completed. First, a new grid need to be created (we will refer to this task as rezoning). Second, the information is transferred from the grid available at the end of the Lagrangian phase to the new grid (we will refer to this task as remapping). New techniques are presented for the two tasks of the Eulerian phase: rezoning and remapping.

  10. RHALE: A 3-D MMALE code for unstructured grids

    SciTech Connect

    Peery, J.S.; Budge, K.G.; Wong, M.K.W.; Trucano, T.G.

    1993-08-01

    This paper describes RHALE, a multi-material arbitrary Lagrangian-Eulerian (MMALE) shock physics code. RHALE is the successor to CTH, Sandia`s 3-D Eulerian shock physics code, and will be capable of solving problems that CTH cannot adequately address. We discuss the Lagrangian solid mechanics capabilities of RHALE, which include arbitrary mesh connectivity, superior artificial viscosity, and improved material models. We discuss the MMALE algorithms that have been extended for arbitrary grids in both two- and three-dimensions. The MMALE addition to RHALE provides the accuracy of a Lagrangian code while allowing a calculation to proceed under very large material distortions. Coupling an arbitrary quadrilateral or hexahedral grid to the MMALE solution facilitates modeling of complex shapes with a greatly reduced number of computational cells. RHALE allows regions of a problem to be modeled with Lagrangian, Eulerian or ALE meshes. In addition, regions can switch from Lagrangian to ALE to Eulerian based on user input or mesh distortion. For ALE meshes, new node locations are determined with a variety of element based equipotential schemes. Element quantities are advected with donor, van Leer, or Super-B algorithms. Nodal quantities are advected with the second order SHALE or HIS algorithms. Material interfaces are determined with a modified Young`s high resolution interface tracker or the SLIC algorithm. RHALE has been used to model many problems of interest to the mechanics, hypervelocity impact, and shock physics communities. Results of a sampling of these problems are presented in this paper.

  11. Adaptable recursive binary entropy coding technique

    NASA Astrophysics Data System (ADS)

    Kiely, Aaron B.; Klimesh, Matthew A.

    2002-07-01

    We present a novel data compression technique, called recursive interleaved entropy coding, that is based on recursive interleaving of variable-to variable length binary source codes. A compression module implementing this technique has the same functionality as arithmetic coding and can be used as the engine in various data compression algorithms. The encoder compresses a bit sequence by recursively encoding groups of bits that have similar estimated statistics, ordering the output in a way that is suited to the decoder. As a result, the decoder has low complexity. The encoding process for our technique is adaptable in that each bit to be encoded has an associated probability-of-zero estimate that may depend on previously encoded bits; this adaptability allows more effective compression. Recursive interleaved entropy coding may have advantages over arithmetic coding, including most notably the admission of a simple and fast decoder. Much variation is possible in the choice of component codes and in the interleaving structure, yielding coder designs of varying complexity and compression efficiency; coder designs that achieve arbitrarily small redundancy can be produced. We discuss coder design and performance estimation methods. We present practical encoding and decoding algorithms, as well as measured performance results.

  12. New method adaptive to geospatial information acquisition and share based on grid

    NASA Astrophysics Data System (ADS)

    Fu, Yingchun; Yuan, Xiuxiao

    2005-11-01

    As we all know, it is difficult and time-consuming to acquire and share multi-source geospatial information in grid computing environment, especially for the data of different geo-reference benchmark. Although middleware for data format transformation has been applied by many grid applications and GIS software systems, it remains difficult to on demand realize spatial data assembly jobs among various geo-reference benchmarks because of complex computation of rigorous coordinate transformation model. To address the problem, an efficient hierarchical quadtree structure referred as multi-level grids is designed and coded to express the multi-scale global geo-space. The geospatial objects located in a certain grid of multi-level grids may be expressed as an increment value which is relative to the grid central point and is constant in different geo-reference benchmark. A mediator responsible for geo-reference transformation function with multi-level grids has been developed and aligned with grid service. With help of the mediator, a map or query spatial data sets from individual source of different geo-references can be merged into an uniform composite result. Instead of complex data pre-processing prior to compatible spatial integration, the introduced method is adaptive to be integrated with grid-enable service.

  13. Methods for prismatic/tetrahedral grid generation and adaptation

    NASA Technical Reports Server (NTRS)

    Kallinderis, Y.

    1995-01-01

    The present work involves generation of hybrid prismatic/tetrahedral grids for complex 3-D geometries including multi-body domains. The prisms cover the region close to each body's surface, while tetrahedra are created elsewhere. Two developments are presented for hybrid grid generation around complex 3-D geometries. The first is a new octree/advancing front type of method for generation of the tetrahedra of the hybrid mesh. The main feature of the present advancing front tetrahedra generator that is different from previous such methods is that it does not require the creation of a background mesh by the user for the determination of the grid-spacing and stretching parameters. These are determined via an automatically generated octree. The second development is a method for treating the narrow gaps in between different bodies in a multiply-connected domain. This method is applied to a two-element wing case. A High Speed Civil Transport (HSCT) type of aircraft geometry is considered. The generated hybrid grid required only 170 K tetrahedra instead of an estimated two million had a tetrahedral mesh been used in the prisms region as well. A solution adaptive scheme for viscous computations on hybrid grids is also presented. A hybrid grid adaptation scheme that employs both h-refinement and redistribution strategies is developed to provide optimum meshes for viscous flow computations. Grid refinement is a dual adaptation scheme that couples 3-D, isotropic division of tetrahedra and 2-D, directional division of prisms.

  14. Methods for prismatic/tetrahedral grid generation and adaptation

    NASA Astrophysics Data System (ADS)

    Kallinderis, Y.

    1995-10-01

    The present work involves generation of hybrid prismatic/tetrahedral grids for complex 3-D geometries including multi-body domains. The prisms cover the region close to each body's surface, while tetrahedra are created elsewhere. Two developments are presented for hybrid grid generation around complex 3-D geometries. The first is a new octree/advancing front type of method for generation of the tetrahedra of the hybrid mesh. The main feature of the present advancing front tetrahedra generator that is different from previous such methods is that it does not require the creation of a background mesh by the user for the determination of the grid-spacing and stretching parameters. These are determined via an automatically generated octree. The second development is a method for treating the narrow gaps in between different bodies in a multiply-connected domain. This method is applied to a two-element wing case. A High Speed Civil Transport (HSCT) type of aircraft geometry is considered. The generated hybrid grid required only 170 K tetrahedra instead of an estimated two million had a tetrahedral mesh been used in the prisms region as well. A solution adaptive scheme for viscous computations on hybrid grids is also presented. A hybrid grid adaptation scheme that employs both h-refinement and redistribution strategies is developed to provide optimum meshes for viscous flow computations. Grid refinement is a dual adaptation scheme that couples 3-D, isotropic division of tetrahedra and 2-D, directional division of prisms.

  15. Adaptive down-sampling video coding

    NASA Astrophysics Data System (ADS)

    Wang, Ren-Jie; Chien, Ming-Chen; Chang, Pao-Chi

    2010-01-01

    Down-sampling coding, which sub-samples the image and encodes the smaller sized images, is one of the solutions to raise the image quality at insufficiently high rates. In this work, we propose an Adaptive Down-Sampling (ADS) coding for H.264/AVC. The overall system distortion can be analyzed as the sum of the down-sampling distortion and the coding distortion. The down-sampling distortion is mainly the loss of the high frequency components that is highly dependent of the spatial difference. The coding distortion can be derived from the classical Rate-Distortion theory. For a given rate and a video sequence, the optimum down-sampling resolution-ratio can be derived by utilizing the optimum theory toward minimizing the system distortion based on the models of the two distortions. This optimal resolution-ratio is used in both down-sampling and up-sampling processes in ADS coding scheme. As a result, the rate-distortion performance of ADS coding is always higher than the fixed ratio coding or H.264/AVC by 2 to 4 dB at low to medium rates.

  16. Three-dimensional adaptive grid-embedding Euler technique

    NASA Astrophysics Data System (ADS)

    Davis, Roger L.; Dannenhoffer, John F., III

    1994-06-01

    A new three-dimensional adaptive-grid Euler procedure is presented that automatically detects high-gradient regions in the flow and locally subdivides the computational grid in these regions to provide a uniform, high level of accuracy over the entire domain. A tunable, semistructured data system is utilized that provides global topological unstructured-grid flexibility along with the efficiency of a local, structured-grid system. In addition, this structure data allows for the flow solution algorithm to be executed on a wide variety of parallel/vector computing platforms. An explicit, time-marching, control volume procedure is used to integrate the Euler equations to a steady state. In addition, a multiple-grid procedure is used throughout the embedded-grid regions as well as on subgrids coarser than the initial grid to accelerate convergence and properly propagate disturbance waves through refined-grid regions. Upon convergence, high flow gradient regions, where it is assumed that large truncation errors in the solution exist, are detected using a combination of directional refinement vectors that have large components in areas of these gradients. The local computational grid is directionally subdivided in these regions and the flow solution is reinitiated. Overall convergence occurs when a prespecified level of accuracy is reached. Solutions are presented that demonstrate the efficiency and accuracy of the present procedure.

  17. Parallel Implementation of an Adaptive Scheme for 3D Unstructured Grids on the SP2

    NASA Technical Reports Server (NTRS)

    Oliker, Leonid; Biswas, Rupak; Strawn, Roger C.

    1996-01-01

    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.OX speedup on 64 processors when 10% 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 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.

  18. Parallel implementation of an adaptive scheme for 3D unstructured grids on the SP2

    NASA Technical Reports Server (NTRS)

    Strawn, Roger C.; Oliker, Leonid; Biswas, Rupak

    1996-01-01

    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.

  19. An adaptive grid algorithm for one-dimensional nonlinear equations

    NASA Technical Reports Server (NTRS)

    Gutierrez, William E.; Hills, Richard G.

    1990-01-01

    Richards' equation, which models the flow of liquid through unsaturated porous media, is highly nonlinear and difficult to solve. Step gradients in the field variables require the use of fine grids and small time step sizes. The numerical instabilities caused by the nonlinearities often require the use of iterative methods such as Picard or Newton interation. These difficulties result in large CPU requirements in solving Richards equation. With this in mind, adaptive and multigrid methods are investigated for use with nonlinear equations such as Richards' equation. Attention is focused on one-dimensional transient problems. To investigate the use of multigrid and adaptive grid methods, a series of problems are studied. First, a multigrid program is developed and used to solve an ordinary differential equation, demonstrating the efficiency with which low and high frequency errors are smoothed out. The multigrid algorithm and an adaptive grid algorithm is used to solve one-dimensional transient partial differential equations, such as the diffusive and convective-diffusion equations. The performance of these programs are compared to that of the Gauss-Seidel and tridiagonal methods. The adaptive and multigrid schemes outperformed the Gauss-Seidel algorithm, but were not as fast as the tridiagonal method. The adaptive grid scheme solved the problems slightly faster than the multigrid method. To solve nonlinear problems, Picard iterations are introduced into the adaptive grid and tridiagonal methods. Burgers' equation is used as a test problem for the two algorithms. Both methods obtain solutions of comparable accuracy for similar time increments. For the Burgers' equation, the adaptive grid method finds the solution approximately three times faster than the tridiagonal method. Finally, both schemes are used to solve the water content formulation of the Richards' equation. For this problem, the adaptive grid method obtains a more accurate solution in fewer work units and

  20. ICASE/LaRC Workshop on Adaptive Grid Methods

    NASA Technical Reports Server (NTRS)

    South, Jerry C., Jr. (Editor); Thomas, James L. (Editor); Vanrosendale, John (Editor)

    1995-01-01

    Solution-adaptive grid techniques are essential to the attainment of practical, user friendly, computational fluid dynamics (CFD) applications. In this three-day workshop, experts gathered together to describe state-of-the-art methods in solution-adaptive grid refinement, analysis, and implementation; to assess the current practice; and to discuss future needs and directions for research. This was accomplished through a series of invited and contributed papers. The workshop focused on a set of two-dimensional test cases designed by the organizers to aid in assessing the current state of development of adaptive grid technology. In addition, a panel of experts from universities, industry, and government research laboratories discussed their views of needs and future directions in this field.

  1. Euler Technology Assessment for Preliminary Aircraft Design: Compressibility Predictions by Employing the Cartesian Unstructured Grid SPLITFLOW Code

    NASA Technical Reports Server (NTRS)

    Finley, Dennis B.; Karman, Steve L., Jr.

    1996-01-01

    The objective of the second phase of the Euler Technology Assessment program was to evaluate the ability of Euler computational fluid dynamics codes to predict compressible flow effects over a generic fighter wind tunnel model. This portion of the study was conducted by Lockheed Martin Tactical Aircraft Systems, using an in-house Cartesian-grid code called SPLITFLOW. The Cartesian grid technique offers several advantages, including ease of volume grid generation and reduced number of cells compared to other grid schemes. SPLITFLOW also includes grid adaption of the volume grid during the solution to resolve high-gradient regions. The SPLITFLOW code predictions of configuration forces and moments are shown to be adequate for preliminary design, including predictions of sideslip effects and the effects of geometry variations at low and high angles-of-attack. The transonic pressure prediction capabilities of SPLITFLOW are shown to be improved over subsonic comparisons. The time required to generate the results from initial surface data is on the order of several hours, including grid generation, which is compatible with the needs of the design environment.

  2. Two-layer and Adaptive Entropy Coding Algorithms for H.264-based Lossless Image Coding

    DTIC Science & Technology

    2008-04-01

    adaptive binary arithmetic coding (CABAC) [7], and context-based adaptive variable length coding (CAVLC) [3], should be adaptively adopted for advancing...Sep. 2006. [7] H. Schwarz, D. Marpe and T. Wiegand, Context-based adaptive binary arithmetic coding in the H.264/AVC video compression standard, IEEE

  3. A grid-based coulomb collision model for PIC codes

    SciTech Connect

    Jones, M.E.; Lemons, D.S.; Mason, R.J.; Thomas, V.A.; Winske, D.

    1996-01-01

    A new method is presented to model the intermediate regime between collisionless and Coulobm collision dominated plasmas in particle-in-cell codes. Collisional processes between particles of different species are treated throuqh the concept of a grid-based {open_quotes}collision field,{close_quotes} which can be particularly efficient for multi-dimensional applications. In this method, particles are scattered using a force which is determined from the moments of the distribution functions accumulated on the grid. The form of the force is such to reproduce themulti-fluid transport equations through the second (energy) moment. Collisions between particles of the same species require a separate treatment. For this, a Monte Carlo-like scattering method based on the Langevin equation is used. The details of both methods are presented, and their implementation in a new hybrid (particle ion, massless fluid electron) algorithm is described. Aspects of the collision model are illustrated through several one- and two-dimensional test problems as well as examples involving laser produced colliding plasmas.

  4. Adaptive hybrid prismatic-tetrahedral grids for viscous flows

    NASA Technical Reports Server (NTRS)

    Kallinderis, Yannis; Khawaja, Aly; Mcmorris, Harlan

    1995-01-01

    The paper presents generation of adaptive hybrid prismatic/tetrahedral grids for complex 3-D geometries including multi-body domains. The prisms cover the region close to each body's surface, while tetrahedra are created elsewhere. Two developments are presented for hybrid grid generation around complex 3-D geometries. The first is a new octree/advancing front type of method for generation of the tetrahedra of the hybrid mesh. The main feature of the present advancing front tetrahedra generator that is different from previous such methods is that it does not require the creation of a background mesh by the user for the determination of the grid-spacing and stretching parameters. These are determined via an automatically generated octree. The second development is an Automatic Receding Method (ARM) for treating the narrow gaps in between different bodies in a multiply-connected domain. This method is applied to a two-element wing case. A hybrid grid adaptation scheme that employs both h-refinement and redistribution strategies is developed to provide optimum meshes for viscous flow computations. Grid refinement is a dual adaptation scheme that couples division of tetrahedra, as well as 2-D directional division of prisms.

  5. Adaptive hybrid prismatic-tetrahedral grids for viscous flows

    NASA Astrophysics Data System (ADS)

    Kallinderis, Yannis; Khawaja, Aly; McMorris, Harlan

    1995-03-01

    The paper presents generation of adaptive hybrid prismatic/tetrahedral grids for complex 3-D geometries including multi-body domains. The prisms cover the region close to each body's surface, while tetrahedra are created elsewhere. Two developments are presented for hybrid grid generation around complex 3-D geometries. The first is a new octree/advancing front type of method for generation of the tetrahedra of the hybrid mesh. The main feature of the present advancing front tetrahedra generator that is different from previous such methods is that it does not require the creation of a background mesh by the user for the determination of the grid-spacing and stretching parameters. These are determined via an automatically generated octree. The second development is an Automatic Receding Method (ARM) for treating the narrow gaps in between different bodies in a multiply-connected domain. This method is applied to a two-element wing case. A hybrid grid adaptation scheme that employs both h-refinement and redistribution strategies is developed to provide optimum meshes for viscous flow computations. Grid refinement is a dual adaptation scheme that couples division of tetrahedra, as well as 2-D directional division of prisms.

  6. A novel hyperbolic grid generation procedure with inherent adaptive dissipation

    SciTech Connect

    Tai, C.H.; Yin, S.L.; Soong, C.Y.

    1995-01-01

    This paper reports a novel hyperbolic grid-generation with an inherent adaptive dissipation (HGAD), which is capable of improving the oscillation and overlapping of grid lines. In the present work upwinding differencing is applied to discretize the hyperbolic system and, thereby, to develop the adaptive dissipation coefficient. Complex configurations with the features of geometric discontinuity, exceptional concavity and convexity are used as the test cases for comparison of the present HGAD procedure with the conventional hyerbolic and elliptic ones. The results reveal that the HGAD method is superior in orthogonality and smoothness of the grid system. In addition, the computational efficiency of the flow solver may be improved by using the present HGAD procedure. 15 refs., 8 figs.

  7. Adaptive grids and implicit differencing applied to plasma simulation

    SciTech Connect

    Brackbill, J.U.; Forslund, D.W.; Vu, Hoanh.

    1990-01-01

    To understand the kinetic processes that determine energy confinement and impurity production in magnetic confinement experiments, we are developing methods to model kinetic effects on magnetohydrodynamic time scales in realistic geometries. We are using implicit methods and adaptive grids to achieve this goal. 9 refs., 2 figs.

  8. Adaptive discrete cosine transform based image coding

    NASA Astrophysics Data System (ADS)

    Hu, Neng-Chung; Luoh, Shyan-Wen

    1996-04-01

    In this discrete cosine transform (DCT) based image coding, the DCT kernel matrix is decomposed into a product of two matrices. The first matrix is called the discrete cosine preprocessing transform (DCPT), whose kernels are plus or minus 1 or plus or minus one- half. The second matrix is the postprocessing stage treated as a correction stage that converts the DCPT to the DCT. On applying the DCPT to image coding, image blocks are processed by the DCPT, then a decision is made to determine whether the processed image blocks are inactive or active in the DCPT domain. If the processed image blocks are inactive, then the compactness of the processed image blocks is the same as that of the image blocks processed by the DCT. However, if the processed image blocks are active, a correction process is required; this is achieved by multiplying the processed image block by the postprocessing stage. As a result, this adaptive image coding achieves the same performance as the DCT image coding, and both the overall computation and the round-off error are reduced, because both the DCPT and the postprocessing stage can be implemented by distributed arithmetic or fast computation algorithms.

  9. Rate-distortion optimized adaptive transform coding

    NASA Astrophysics Data System (ADS)

    Lim, Sung-Chang; Kim, Dae-Yeon; Jeong, Seyoon; Choi, Jin Soo; Choi, Haechul; Lee, Yung-Lyul

    2009-08-01

    We propose a rate-distortion optimized transform coding method that adaptively employs either integer cosine transform that is an integer-approximated version of discrete cosine transform (DCT) or integer sine transform (IST) in a rate-distortion sense. The DCT that has been adopted in most video-coding standards is known as a suboptimal substitute for the Karhunen-Loève transform. However, according to the correlation of a signal, an alternative transform can achieve higher coding efficiency. We introduce a discrete sine transform (DST) that achieves the high-energy compactness in a correlation coefficient range of -0.5 to 0.5 and is applied to the current design of H.264/AVC (advanced video coding). Moreover, to avoid the encoder and decoder mismatch and make the implementation simple, an IST that is an integer-approximated version of the DST is developed. The experimental results show that the proposed method achieves a Bjøntegaard Delta-RATE gain up to 5.49% compared to Joint model 11.0.

  10. Three-dimensional Navier-Stokes calculations using solution-adapted grids

    NASA Technical Reports Server (NTRS)

    Henderson, T. L.; Huang, W.; Lee, K. D.; Choo, Y. K.

    1993-01-01

    A three-dimensional solution-adaptive grid generation technique is presented. The adaptation technique redistributes grid points to improve the accuracy of a flow solution without increasing the number of grid points. It is applicable to structured grids with a multiblock topology. The method uses a numerical mapping and potential theory to modify the initial grid distribution based on the properties of the flow solution on the initial grid. The technique is demonstrated with two examples - a transonic finite wing and a supersonic blunt fin. The advantages are shown by comparing flow solutions on the adapted grids with those on the initial grids.

  11. Efficient Load Balancing and Data Remapping for Adaptive Grid Calculations

    NASA Technical Reports Server (NTRS)

    Oliker, Leonid; Biswas, Rupak

    1997-01-01

    Mesh adaption is a powerful tool for efficient unstructured- grid computations but causes load imbalance among processors on a parallel machine. We present a novel method to dynamically balance the processor workloads with a global view. This paper presents, for the first time, the implementation and integration of all major components within our dynamic load balancing strategy for adaptive grid calculations. Mesh adaption, 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. Previous results indicated that mesh repartitioning and data remapping are potential bottlenecks for performing large-scale scientific calculations. We resolve these issues and demonstrate that our framework remains viable on a large number of processors.

  12. Hierarchy-Direction Selective Approach for Locally Adaptive Sparse Grids

    SciTech Connect

    Stoyanov, Miroslav K

    2013-09-01

    We consider the problem of multidimensional adaptive hierarchical interpolation. We use sparse grids points and functions that are induced from a one dimensional hierarchical rule via tensor products. The classical locally adaptive sparse grid algorithm uses an isotropic refinement from the coarser to the denser levels of the hierarchy. However, the multidimensional hierarchy provides a more complex structure that allows for various anisotropic and hierarchy selective refinement techniques. We consider the more advanced refinement techniques and apply them to a number of simple test functions chosen to demonstrate the various advantages and disadvantages of each method. While there is no refinement scheme that is optimal for all functions, the fully adaptive family-direction-selective technique is usually more stable and requires fewer samples.

  13. HOMAR: A computer code for generating homotopic grids using algebraic relations: User's manual

    NASA Technical Reports Server (NTRS)

    Moitra, Anutosh

    1989-01-01

    A computer code for fast automatic generation of quasi-three-dimensional grid systems for aerospace configurations is described. The code employs a homotopic method to algebraically generate two-dimensional grids in cross-sectional planes, which are stacked to produce a three-dimensional grid system. Implementation of the algebraic equivalents of the homotopic relations for generating body geometries and grids are explained. Procedures for controlling grid orthogonality and distortion are described. Test cases with description and specification of inputs are presented in detail. The FORTRAN computer program and notes on implementation and use are included.

  14. HOMAR: A computer code for generating homotopic grids using algebraic relations: User's manual

    NASA Astrophysics Data System (ADS)

    Moitra, Anutosh

    1989-07-01

    A computer code for fast automatic generation of quasi-three-dimensional grid systems for aerospace configurations is described. The code employs a homotopic method to algebraically generate two-dimensional grids in cross-sectional planes, which are stacked to produce a three-dimensional grid system. Implementation of the algebraic equivalents of the homotopic relations for generating body geometries and grids are explained. Procedures for controlling grid orthogonality and distortion are described. Test cases with description and specification of inputs are presented in detail. The FORTRAN computer program and notes on implementation and use are included.

  15. The Quantum Workings of the Rotating 64-Grid Genetic Code

    PubMed Central

    Castro-Chavez, Fernando

    2011-01-01

    In this article, the pattern learned from the classic or conventional rotating circular genetic code is transferred to a 64-grid model. In this non-static representation, the codons for the same amino acid within each quadrant could be exchanged, wobbling or rotating in a quantic way similar to the electrons within an atomic orbit. Represented in this 64-grid format are the three rules of variation encompassing 4, 2, or 1 quadrant, respectively: 1) same position in four quadrants for the essential hydrophobic amino acids that have U at the center, 2) same or contiguous position for the same or related amino acids in two quadrants, and 3) equivalent amino acids within one quadrant. Also represented is the mathematical balance of the odd and even codons, and the most used codons per amino acid in humans compared to one diametrically opposed organism: the plant Arabidopsis thaliana, a comparison that depicts the difference in third nucleotide preferences: a C/U exchange for 11 amino acids, a G/A and a G/U exchange for 2 amino acids, respectively, and a C/A exchange for one amino acid; by studying these codon usage preferences per amino acid we present our two hypotheses: 1) A slower translation in vertebrates and 2) a faster translation in invertebrates, possibly due to the aqueous environments where they live. These codon usage preferences may also be able to determine genomic compatibility by comparing individual mRNAs and their functional third dimensional structure, transport and translation within cells and organisms. These observations are aimed to the design of bioinformatics computational tools to compare human genomes and to determine the exchange between compatible codons and amino acids, to preserve and/or to bring back extinct biodiversity, and for the early detection of incompatible changes that lead to genetic diseases. PMID:22308074

  16. ICAN Computer Code Adapted for Building Materials

    NASA Technical Reports Server (NTRS)

    Murthy, Pappu L. N.

    1997-01-01

    The NASA Lewis Research Center has been involved in developing composite micromechanics and macromechanics theories over the last three decades. These activities have resulted in several composite mechanics theories and structural analysis codes whose applications range from material behavior design and analysis to structural component response. One of these computer codes, the Integrated Composite Analyzer (ICAN), is designed primarily to address issues related to designing polymer matrix composites and predicting their properties - including hygral, thermal, and mechanical load effects. Recently, under a cost-sharing cooperative agreement with a Fortune 500 corporation, Master Builders Inc., ICAN was adapted to analyze building materials. The high costs and technical difficulties involved with the fabrication of continuous-fiber-reinforced composites sometimes limit their use. Particulate-reinforced composites can be thought of as a viable alternative. They are as easily processed to near-net shape as monolithic materials, yet have the improved stiffness, strength, and fracture toughness that is characteristic of continuous-fiber-reinforced composites. For example, particlereinforced metal-matrix composites show great potential for a variety of automotive applications, such as disk brake rotors, connecting rods, cylinder liners, and other hightemperature applications. Building materials, such as concrete, can be thought of as one of the oldest materials in this category of multiphase, particle-reinforced materials. The adaptation of ICAN to analyze particle-reinforced composite materials involved the development of new micromechanics-based theories. A derivative of the ICAN code, ICAN/PART, was developed and delivered to Master Builders Inc. as a part of the cooperative activity.

  17. An Adaptive Motion Estimation Scheme for Video Coding

    PubMed Central

    Gao, Yuan; Jia, Kebin

    2014-01-01

    The unsymmetrical-cross multihexagon-grid search (UMHexagonS) is one of the best fast Motion Estimation (ME) algorithms in video encoding software. It achieves an excellent coding performance by using hybrid block matching search pattern and multiple initial search point predictors at the cost of the computational complexity of ME increased. Reducing time consuming of ME is one of the key factors to improve video coding efficiency. In this paper, we propose an adaptive motion estimation scheme to further reduce the calculation redundancy of UMHexagonS. Firstly, new motion estimation search patterns have been designed according to the statistical results of motion vector (MV) distribution information. Then, design a MV distribution prediction method, including prediction of the size of MV and the direction of MV. At last, according to the MV distribution prediction results, achieve self-adaptive subregional searching by the new estimation search patterns. Experimental results show that more than 50% of total search points are dramatically reduced compared to the UMHexagonS algorithm in JM 18.4 of H.264/AVC. As a result, the proposed algorithm scheme can save the ME time up to 20.86% while the rate-distortion performance is not compromised. PMID:24672313

  18. BGRID: A block-structured grid generation code for wing sections

    NASA Technical Reports Server (NTRS)

    Chen, H. C.; Lee, K. D.

    1981-01-01

    The operation of the BGRID computer program is described for generating block-structured grids. Examples are provided to illustrate the code input and output. The application of a fully implicit AF (approximation factorization)-based computer code, called TWINGB (Transonic WING), for solving the 3D transonic full potential equation in conservation form on block-structured grids is also discussed.

  19. Error sensitivity to refinement: a criterion for optimal grid adaptation

    NASA Astrophysics Data System (ADS)

    Luchini, Paolo; Giannnetti, Flavio; Citro, Vincenzo

    2016-11-01

    Most indicators used for automatic grid refinement are suboptimal, in the sense that they do not really minimize the global solution error. This paper concerns with a new indicator, related to the sensitivity map of global stability problems, suitable for an optimal grid refinement that minimizes the global solution error. The new criterion is derived from the properties of the adjoint operator and provides a map of the sensitivity of the global error (or its estimate) to a local mesh refinement. Examples are presented for both a scalar partial differential equation and for the system of Navier-Stokes equations. In the last case, we also present a grid-adaptation algorithm based on the new estimator and on the FreeFem++ software that improves the accuracy of the solution of almost two order of magnitude by redistributing the nodes of the initial computational mesh.

  20. Solution adaptive grids applied to low Reynolds number flow

    NASA Astrophysics Data System (ADS)

    de With, G.; Holdø, A. E.; Huld, T. A.

    2003-08-01

    A numerical study has been undertaken to investigate the use of a solution adaptive grid for flow around a cylinder in the laminar flow regime. The main purpose of this work is twofold. The first aim is to investigate the suitability of a grid adaptation algorithm and the reduction in mesh size that can be obtained. Secondly, the uniform asymmetric flow structures are ideal to validate the mesh structures due to mesh refinement and consequently the selected refinement criteria. The refinement variable used in this work is a product of the rate of strain and the mesh cell size, and contains two variables Cm and Cstr which determine the order of each term. By altering the order of either one of these terms the refinement behaviour can be modified.

  1. On the dynamics of some grid adaption schemes

    NASA Technical Reports Server (NTRS)

    Sweby, Peter K.; Yee, Helen C.

    1994-01-01

    The dynamics of a one-parameter family of mesh equidistribution schemes coupled with finite difference discretisations of linear and nonlinear convection-diffusion model equations is studied numerically. It is shown that, when time marched to steady state, the grid adaption not only influences the stability and convergence rate of the overall scheme, but can also introduce spurious dynamics to the numerical solution procedure.

  2. Adaptive grid methods for RLV environment assessment and nozzle analysis

    NASA Technical Reports Server (NTRS)

    Thornburg, Hugh J.

    1996-01-01

    Rapid access to highly accurate data about complex configurations is needed for multi-disciplinary optimization and design. In order to efficiently meet these requirements a closer coupling between the analysis algorithms and the discretization process is needed. In some cases, such as free surface, temporally varying geometries, and fluid structure interaction, the need is unavoidable. In other cases the need is to rapidly generate and modify high quality grids. Techniques such as unstructured and/or solution-adaptive methods can be used to speed the grid generation process and to automatically cluster mesh points in regions of interest. Global features of the flow can be significantly affected by isolated regions of inadequately resolved flow. These regions may not exhibit high gradients and can be difficult to detect. Thus excessive resolution in certain regions does not necessarily increase the accuracy of the overall solution. Several approaches have been employed for both structured and unstructured grid adaption. The most widely used involve grid point redistribution, local grid point enrichment/derefinement or local modification of the actual flow solver. However, the success of any one of these methods ultimately depends on the feature detection algorithm used to determine solution domain regions which require a fine mesh for their accurate representation. Typically, weight functions are constructed to mimic the local truncation error and may require substantial user input. Most problems of engineering interest involve multi-block grids and widely disparate length scales. Hence, it is desirable that the adaptive grid feature detection algorithm be developed to recognize flow structures of different type as well as differing intensity, and adequately address scaling and normalization across blocks. These weight functions can then be used to construct blending functions for algebraic redistribution, interpolation functions for unstructured grid generation

  3. Unstructured Adaptive Grid Computations on an Array of SMPs

    NASA Technical Reports Server (NTRS)

    Biswas, Rupak; Pramanick, Ira; Sohn, Andrew; Simon, Horst D.

    1996-01-01

    Dynamic load balancing is necessary for parallel adaptive methods to solve unsteady CFD problems on unstructured grids. We have presented such a dynamic load balancing framework called JOVE, in this paper. Results on a four-POWERnode POWER CHALLENGEarray demonstrated that load balancing gives significant performance improvements over no load balancing for such adaptive computations. The parallel speedup of JOVE, implemented using MPI on the POWER CHALLENCEarray, was significant, being as high as 31 for 32 processors. An implementation of JOVE that exploits 'an array of SMPS' architecture was also studied; this hybrid JOVE outperformed flat JOVE by up to 28% on the meshes and adaption models tested. With large, realistic meshes and actual flow-solver and adaption phases incorporated into JOVE, hybrid JOVE can be expected to yield significant advantage over flat JOVE, especially as the number of processors is increased, thus demonstrating the scalability of an array of SMPs architecture.

  4. A geometry-based adaptive unstructured grid generation algorithm for complex geological media

    NASA Astrophysics Data System (ADS)

    Bahrainian, Seyed Saied; Dezfuli, Alireza Daneh

    2014-07-01

    In this paper a novel unstructured grid generation algorithm is presented that considers the effect of geological features and well locations in grid resolution. The proposed grid generation algorithm presents a strategy for definition and construction of an initial grid based on the geological model, geometry adaptation of geological features, and grid resolution control. The algorithm is applied to seismotectonic map of the Masjed-i-Soleiman reservoir. Comparison of grid results with the “Triangle” program shows a more suitable permeability contrast. Immiscible two-phase flow solutions are presented for a fractured porous media test case using different grid resolutions. Adapted grid on the fracture geometry gave identical results with that of a fine grid. The adapted grid employed 88.2% less CPU time when compared to the solutions obtained by the fine grid.

  5. DRAGON Grid: A Three-Dimensional Hybrid Grid Generation Code Developed

    NASA Technical Reports Server (NTRS)

    Liou, Meng-Sing

    2000-01-01

    Because grid generation can consume 70 percent of the total analysis time for a typical three-dimensional viscous flow simulation for a practical engineering device, payoffs from research and development could reduce costs and increase throughputs considerably. In this study, researchers at the NASA Glenn Research Center at Lewis Field developed a new hybrid grid approach with the advantages of flexibility, high-quality grids suitable for an accurate resolution of viscous regions, and a low memory requirement. These advantages will, in turn, reduce analysis time and increase accuracy. They result from an innovative combination of structured and unstructured grids to represent the geometry and the computation domain. The present approach makes use of the respective strengths of both the structured and unstructured grid methods, while minimizing their weaknesses. First, the Chimera grid generates high-quality, mostly orthogonal meshes around individual components. This process is flexible and can be done easily. Normally, these individual grids are required overlap each other so that the solution on one grid can communicate with another. However, when this communication is carried out via a nonconservative interpolation procedure, a spurious solution can result. Current research is aimed at entirely eliminating this undesired interpolation by directly replacing arbitrary grid overlapping with a nonstructured grid called a DRAGON grid, which uses the same set of conservation laws over the entire region, thus ensuring conservation everywhere. The DRAGON grid is shown for a typical film-cooled turbine vane with 33 holes and 3 plenum compartments. There are structured grids around each geometrical entity and unstructured grids connecting them. In fiscal year 1999, Glenn researchers developed and tested the three-dimensional DRAGON grid-generation tools. A flow solver suitable for the DRAGON grid has been developed, and a series of validation tests are underway.

  6. Parallel architectures for iterative methods on adaptive, block structured grids

    NASA Technical Reports Server (NTRS)

    Gannon, D.; Vanrosendale, J.

    1983-01-01

    A parallel computer architecture well suited to the solution of partial differential equations in complicated geometries is proposed. Algorithms for partial differential equations contain a great deal of parallelism. But this parallelism can be difficult to exploit, particularly on complex problems. One approach to extraction of this parallelism is the use of special purpose architectures tuned to a given problem class. The architecture proposed here is tuned to boundary value problems on complex domains. An adaptive elliptic algorithm which maps effectively onto the proposed architecture is considered in detail. Two levels of parallelism are exploited by the proposed architecture. First, by making use of the freedom one has in grid generation, one can construct grids which are locally regular, permitting a one to one mapping of grids to systolic style processor arrays, at least over small regions. All local parallelism can be extracted by this approach. Second, though there may be a regular global structure to the grids constructed, there will be parallelism at this level. One approach to finding and exploiting this parallelism is to use an architecture having a number of processor clusters connected by a switching network. The use of such a network creates a highly flexible architecture which automatically configures to the problem being solved.

  7. Adaptive grid embedding for the two-dimensional flux-split Euler equations. M.S. Thesis

    NASA Technical Reports Server (NTRS)

    Warren, Gary Patrick

    1990-01-01

    A numerical algorithm is presented for solving the 2-D flux-split Euler equations using a multigrid method with adaptive grid embedding. The method uses an unstructured data set along with a system of pointers for communication on the irregularly shaped grid topologies. An explicit two-stage time advancement scheme is implemented. A multigrid algorithm is used to provide grid level communication and to accelerate the convergence of the solution to steady state. Results are presented for a subcritical airfoil and a transonic airfoil with 3 levels of adaptation. Comparisons are made with a structured upwind Euler code which uses the same flux integration techniques of the present algorithm. Good agreement is obtained with converged surface pressure coefficients. The lift coefficients of the adaptive code are within 2 1/2 percent of the structured code for the sub-critical case and within 4 1/2 percent of the structured code for the transonic case using approximately one-third the number of grid points.

  8. Load Balancing Unstructured Adaptive Grids for CFD Problems

    NASA Technical Reports Server (NTRS)

    Biswas, Rupak; Oliker, Leonid

    1996-01-01

    Mesh adaption is a powerful tool for efficient unstructured-grid computations but causes load imbalance among processors on a parallel machine. A dynamic load balancing method is presented that balances the workload across all processors with a global view. After each parallel tetrahedral mesh adaption, the method first determines if the new mesh is sufficiently unbalanced to warrant a repartitioning. If so, the adapted mesh is repartitioned, with new partitions assigned to processors so that the redistribution cost is minimized. The new partitions are accepted only if the remapping cost is compensated by the improved load balance. Results indicate that this strategy is effective for large-scale scientific computations on distributed-memory multiprocessors.

  9. A Solution Adaptive Technique Using Tetrahedral Unstructured Grids

    NASA Technical Reports Server (NTRS)

    Pirzadeh, Shahyar Z.

    2000-01-01

    An adaptive unstructured grid refinement technique has been developed and successfully applied to several three dimensional inviscid flow test cases. The method is based on a combination of surface mesh subdivision and local remeshing of the volume grid Simple functions of flow quantities are employed to detect dominant features of the flowfield The method is designed for modular coupling with various error/feature analyzers and flow solvers. Several steady-state, inviscid flow test cases are presented to demonstrate the applicability of the method for solving practical three-dimensional problems. In all cases, accurate solutions featuring complex, nonlinear flow phenomena such as shock waves and vortices have been generated automatically and efficiently.

  10. Self-Avoiding Walks over Adaptive Triangular Grids

    NASA Technical Reports Server (NTRS)

    Heber, Gerd; Biswas, Rupak; Gao, Guang R.; Saini, Subhash (Technical Monitor)

    1998-01-01

    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.

  11. Numerical Simulation of Two-grid Ion Optics Using a 3D Code

    NASA Technical Reports Server (NTRS)

    Anderson, John R.; Katz, Ira; Goebel, Dan

    2004-01-01

    A three-dimensional ion optics code has been developed under NASA's Project Prometheus to model two grid ion optics systems. The code computes the flow of positive ions from the discharge chamber through the ion optics and into the beam downstream of the thruster. The rate at which beam ions interact with background neutral gas to form charge exchange ions is also computed. Charge exchange ion trajectories are computed to determine where they strike the ion optics grid surfaces and to determine the extent of sputter erosion they cause. The code has been used to compute predictions of the erosion pattern and wear rate on the NSTAR ion optics system; the code predicts the shape of the eroded pattern but overestimates the initial wear rate by about 50%. An example of use of the code to estimate the NEXIS thruster accelerator grid life is also presented.

  12. Preliminary Benchmarking of Plinian Eruption Simulations Using an Adaptive Grid Eulerian Technique

    NASA Astrophysics Data System (ADS)

    Peterson, A. H.; Ogden, D. E.; Wohletz, K. H.; Gisler, G.; Glatzmaier, G. A.

    2005-12-01

    The SAGE (SAIC Adaptive Grid Eulerian) code is an Eulerian hydrodynamics numerical technique employing adaptive mesh refinement at each cycle for every cell in 1-, 2-, and 3-D grids. It is primarily designed to solve high deformation flow of multiple materials and thus provides important capabilities for simulating volcanic eruption phenomena. Its multimaterial equation of state libraries includes a comprehensive coverage of water from solid ice through two-phase liquid and vapor to supercritical states approaching the Hugoniot, and extremely important aspect for simulating volcanic gases in general. In development are strength and failure rules that model non-Newtonian fluid/solid deformation. Because of the low effective sound speeds of eruptive mixtures, the facts that SAGE uses a piecewise, linear, multi-material, Gudonov numerical method to resolve shocks with second-order precision and exactly conserves mass, momentum, and energy, are a highly desirable attributes. Although this code has been previously used to simulate a volcanic eruption (i.e., eruption through a crater lake at Ruapehu volcano by Morrissey and Gisler), we are embarking in an effort to benchmark the code with CFDLib, a well-validated arbitrary Lagrangian-Eulerian code developed at Los Alamos National Laboratory. Through this effort we expect to better understand the strengths and weaknesses, the limitations, and provide direction for important enhancement of SAGE, and potentially provide the volcanological community with a powerful alternative to numerical codes currently available. At this point in our benchmarking, we demonstrate some results for fluid convection within a chamber and fluid jetting through a conduit.

  13. Grid cells: the position code, neural network models of activity, and the problem of learning.

    PubMed

    Welinder, Peter E; Burak, Yoram; Fiete, Ila R

    2008-01-01

    We review progress on the modeling and theoretical fronts in the quest to unravel the computational properties of the grid cell code and to explain the mechanisms underlying grid cell dynamics. The goals of the review are to outline a coherent framework for understanding the dynamics of grid cells and their representation of space; to critically present and draw contrasts between recurrent network models of grid cells based on continuous attractor dynamics and independent-neuron models based on temporal interference; and to suggest open questions for experiment and theory.

  14. Adaptive sparse grid expansions of the vibrational Hamiltonian

    SciTech Connect

    Strobusch, D.; Scheurer, Ch.

    2014-02-21

    The vibrational Hamiltonian involves two high dimensional operators, the kinetic energy operator (KEO), and the potential energy surface (PES). Both must be approximated for systems involving more than a few atoms. Adaptive approximation schemes are not only superior to truncated Taylor or many-body expansions (MBE), they also allow for error estimates, and thus operators of predefined precision. To this end, modified sparse grids (SG) are developed that can be combined with adaptive MBEs. This MBE/SG hybrid approach yields a unified, fully adaptive representation of the KEO and the PES. Refinement criteria, based on the vibrational self-consistent field (VSCF) and vibrational configuration interaction (VCI) methods, are presented. The combination of the adaptive MBE/SG approach and the VSCF plus VCI methods yields a black box like procedure to compute accurate vibrational spectra. This is demonstrated on a test set of molecules, comprising water, formaldehyde, methanimine, and ethylene. The test set is first employed to prove convergence for semi-empirical PM3-PESs and subsequently to compute accurate vibrational spectra from CCSD(T)-PESs that agree well with experimental values.

  15. GAMER: GPU-accelerated Adaptive MEsh Refinement code

    NASA Astrophysics Data System (ADS)

    Schive, Hsi-Yu; Tsai, Yu-Chih; Chiueh, Tzihong

    2016-12-01

    GAMER (GPU-accelerated Adaptive MEsh Refinement) serves as a general-purpose adaptive mesh refinement + GPU framework and solves hydrodynamics with self-gravity. The code supports adaptive mesh refinement (AMR), hydrodynamics with self-gravity, and a variety of GPU-accelerated hydrodynamic and Poisson solvers. It also supports hybrid OpenMP/MPI/GPU parallelization, concurrent CPU/GPU execution for performance optimization, and Hilbert space-filling curve for load balance. Although the code is designed for simulating galaxy formation, it can be easily modified to solve a variety of applications with different governing equations. All optimization strategies implemented in the code can be inherited straightforwardly.

  16. Enhancement of surface definition and gridding in the EAGLE code

    NASA Technical Reports Server (NTRS)

    Thompson, Joe F.

    1991-01-01

    Algorithms for smoothing of curves and surfaces for the EAGLE grid generation program are presented. The method uses an existing automated technique which detects undesirable geometric characteristics by using a local fairness criterion. The geometry entity is then smoothed by repeated removal and insertion of spline knots in the vicinity of the geometric irregularity. The smoothing algorithm is formulated for use with curves in Beta spline form and tensor product B-spline surfaces.

  17. A robust adaptive load frequency control for micro-grids.

    PubMed

    Khooban, Mohammad-Hassan; Niknam, Taher; Blaabjerg, Frede; Davari, Pooya; Dragicevic, Tomislav

    2016-11-01

    The goal of this study is to introduce a novel robust load frequency control (LFC) strategy for micro-grid(s) (MG(s)) in islanded mode operation. Admittedly, power generators in MG(s) cannot supply steady electric power output and sometimes cause unbalance between supply and demand. Battery energy storage system (BESS) is one of the effective solutions to these problems. Due to the high cost of the BESS, a new idea of Vehicle-to-Grid (V2G) is that a battery of Electric-Vehicle (EV) can be applied as a tantamount large-scale BESS in MG(s). As a result, a new robust control strategy for an islanded micro-grid (MG) is introduced that can consider electric vehicles׳ (EV(s)) effect. Moreover, in this paper, a new combination of the General Type II Fuzzy Logic Sets (GT2FLS) and the Modified Harmony Search Algorithm (MHSA) technique is applied for adaptive tuning of proportional-integral (PI) controller. Implementing General Type II Fuzzy Systems is computationally expensive. However, using a recently introduced α-plane representation, GT2FLS can be seen as a composition of several Interval Type II Fuzzy Logic Systems (IT2FLS) with a corresponding level of α for each. Real-data from an offshore wind farm in Sweden and solar radiation data in Aberdeen (United Kingdom) was used in order to examine the performance of the proposed novel controller. A comparison is made between the achieved results of Optimal Fuzzy-PI (OFPI) controller and those of Optimal Interval Type II Fuzzy-PI (IT2FPI) controller, which are of most recent advances in the area at hand. The Simulation results prove the successfulness and effectiveness of the proposed controller.

  18. Generating code adapted for interlinking legacy scalar code and extended vector code

    DOEpatents

    Gschwind, Michael K

    2013-06-04

    Mechanisms for intermixing code are provided. Source code is received for compilation using an extended Application Binary Interface (ABI) that extends a legacy ABI and uses a different register configuration than the legacy ABI. First compiled code is generated based on the source code, the first compiled code comprising code for accommodating the difference in register configurations used by the extended ABI and the legacy ABI. The first compiled code and second compiled code are intermixed to generate intermixed code, the second compiled code being compiled code that uses the legacy ABI. The intermixed code comprises at least one call instruction that is one of a call from the first compiled code to the second compiled code or a call from the second compiled code to the first compiled code. The code for accommodating the difference in register configurations is associated with the at least one call instruction.

  19. Anisotropic Solution Adaptive Unstructured Grid Generation Using AFLR

    NASA Technical Reports Server (NTRS)

    Marcum, David L.

    2007-01-01

    An existing volume grid generation procedure, AFLR3, was successfully modified to generate anisotropic tetrahedral elements using a directional metric transformation defined at source nodes. The procedure can be coupled with a solver and an error estimator as part of an overall anisotropic solution adaptation methodology. It is suitable for use with an error estimator based on an adjoint, optimization, sensitivity derivative, or related approach. This offers many advantages, including more efficient point placement along with robust and efficient error estimation. It also serves as a framework for true grid optimization wherein error estimation and computational resources can be used as cost functions to determine the optimal point distribution. Within AFLR3 the metric transformation is implemented using a set of transformation vectors and associated aspect ratios. The modified overall procedure is presented along with details of the anisotropic transformation implementation. Multiple two-and three-dimensional examples are also presented that demonstrate the capability of the modified AFLR procedure to generate anisotropic elements using a set of source nodes with anisotropic transformation metrics. The example cases presented use moderate levels of anisotropy and result in usable element quality. Future testing with various flow solvers and methods for obtaining transformation metric information is needed to determine practical limits and evaluate the efficacy of the overall approach.

  20. Adaptive face coding and discrimination around the average face.

    PubMed

    Rhodes, Gillian; Maloney, Laurence T; Turner, Jenny; Ewing, Louise

    2007-03-01

    Adaptation paradigms highlight the dynamic nature of face coding and suggest that identity is coded relative to an average face that is tuned by experience. In low-level vision, adaptive coding can enhance sensitivity to differences around the adapted level. We investigated whether sensitivity to differences around the average face is similarly enhanced. Converging evidence from three paradigms showed no enhancement. Discrimination of small interocular spacing differences was not better for faces close to the average (Study 1). Nor was perceived similarity reduced for face pairs close to (spanning) the average (Study 2). On the contrary, these pairs were judged most similar. Maximum likelihood perceptual difference scaling (Studies 3 and 4) confirmed that sensitivity to differences was reduced, not enhanced, around the average. We conclude that adaptive face coding does not enhance discrimination around the average face.

  1. Adaptive Quantization Parameter Cascading in HEVC Hierarchical Coding.

    PubMed

    Zhao, Tiesong; Wang, Zhou; Chen, Chang Wen

    2016-04-20

    The state-of-the-art High Efficiency Video Coding (HEVC) standard adopts a hierarchical coding structure to improve its coding efficiency. This allows for the Quantization Parameter Cascading (QPC) scheme that assigns Quantization Parameters (Qps) to different hierarchical layers in order to further improve the Rate-Distortion (RD) performance. However, only static QPC schemes have been suggested in HEVC test model (HM), which are unable to fully explore the potentials of QPC. In this paper, we propose an adaptive QPC scheme for HEVC hierarchical structure to code natural video sequences characterized by diversified textures, motions and encoder configurations. We formulate the adaptive QPC scheme as a non-linear programming problem and solve it in a scientifically sound way with a manageable low computational overhead. The proposed model addresses a generic Qp assignment problem of video coding. Therefore, it also applies to Group-Of-Picture (GOP)- level, frame-level and Coding Unit (CU)-level Qp assignments. Comprehensive experiments have demonstrated the proposed QPC scheme is able to adapt quickly to different video contents and coding configurations while achieving noticeable RD performance enhancement over all static and adaptive QPC schemes under comparison as well as HEVC default frame-level rate control. We have also made valuable observations on the distributions of adaptive QPC sets in videos of different types of contents, which provide useful insights on how to further improve static QPC schemes.

  2. Adaptive Quantization Parameter Cascading in HEVC Hierarchical Coding.

    PubMed

    Zhao, Tiesong; Wang, Zhou; Chen, Chang Wen

    2016-07-01

    The state-of-the-art High Efficiency Video Coding (HEVC) standard adopts a hierarchical coding structure to improve its coding efficiency. This allows for the quantization parameter cascading (QPC) scheme that assigns quantization parameters (Qps) to different hierarchical layers in order to further improve the rate-distortion (RD) performance. However, only static QPC schemes have been suggested in HEVC test model, which are unable to fully explore the potentials of QPC. In this paper, we propose an adaptive QPC scheme for an HEVC hierarchical structure to code natural video sequences characterized by diversified textures, motions, and encoder configurations. We formulate the adaptive QPC scheme as a non-linear programming problem and solve it in a scientifically sound way with a manageable low computational overhead. The proposed model addresses a generic Qp assignment problem of video coding. Therefore, it also applies to group-of-picture-level, frame-level and coding unit-level Qp assignments. Comprehensive experiments have demonstrated that the proposed QPC scheme is able to adapt quickly to different video contents and coding configurations while achieving noticeable RD performance enhancement over all static and adaptive QPC schemes under comparison as well as HEVC default frame-level rate control. We have also made valuable observations on the distributions of adaptive QPC sets in the videos of different types of contents, which provide useful insights on how to further improve static QPC schemes.

  3. THE PLUTO CODE FOR ADAPTIVE MESH COMPUTATIONS IN ASTROPHYSICAL FLUID DYNAMICS

    SciTech Connect

    Mignone, A.; Tzeferacos, P.; Zanni, C.; Bodo, G.; Van Straalen, B.; Colella, P.

    2012-01-01

    We present a description of the adaptive mesh refinement (AMR) implementation of the PLUTO code for solving the equations of classical and special relativistic magnetohydrodynamics (MHD and RMHD). The current release exploits, in addition to the static grid version of the code, the distributed infrastructure of the CHOMBO library for multidimensional parallel computations over block-structured, adaptively refined grids. We employ a conservative finite-volume approach where primary flow quantities are discretized at the cell center in a dimensionally unsplit fashion using the Corner Transport Upwind method. Time stepping relies on a characteristic tracing step where piecewise parabolic method, weighted essentially non-oscillatory, or slope-limited linear interpolation schemes can be handily adopted. A characteristic decomposition-free version of the scheme is also illustrated. The solenoidal condition of the magnetic field is enforced by augmenting the equations with a generalized Lagrange multiplier providing propagation and damping of divergence errors through a mixed hyperbolic/parabolic explicit cleaning step. Among the novel features, we describe an extension of the scheme to include non-ideal dissipative processes, such as viscosity, resistivity, and anisotropic thermal conduction without operator splitting. Finally, we illustrate an efficient treatment of point-local, potentially stiff source terms over hierarchical nested grids by taking advantage of the adaptivity in time. Several multidimensional benchmarks and applications to problems of astrophysical relevance assess the potentiality of the AMR version of PLUTO in resolving flow features separated by large spatial and temporal disparities.

  4. A novel bit-wise adaptable entropy coding technique

    NASA Technical Reports Server (NTRS)

    Kiely, A.; Klimesh, M.

    2001-01-01

    We present a novel entropy coding technique which is adaptable in that each bit to be encoded may have an associated probability esitmate which depends on previously encoded bits. The technique may have advantages over arithmetic coding. The technique can achieve arbitrarily small redundancy and admits a simple and fast decoder.

  5. A wavelet-optimized, very high order adaptive grid and order numerical method

    NASA Technical Reports Server (NTRS)

    Jameson, Leland

    1996-01-01

    Differencing operators of arbitrarily high order can be constructed by interpolating a polynomial through a set of data followed by differentiation of this polynomial and finally evaluation of the polynomial at the point where a derivative approximation is desired. Furthermore, the interpolating polynomial can be constructed from algebraic, trigonometric, or, perhaps exponential polynomials. This paper begins with a comparison of such differencing operator construction. Next, the issue of proper grids for high order polynomials is addressed. Finally, an adaptive numerical method is introduced which adapts the numerical grid and the order of the differencing operator depending on the data. The numerical grid adaptation is performed on a Chebyshev grid. That is, at each level of refinement the grid is a Chebvshev grid and this grid is refined locally based on wavelet analysis.

  6. Three-dimensional adaptive grid generation for body-fitted coordinate system

    NASA Technical Reports Server (NTRS)

    Chen, S. C.

    1988-01-01

    This report describes a numerical method for generating 3-D grids for general configurations. The basic method involves the solution of a set of quasi-linear elliptic partial differential equations via pointwise relaxation with a local relaxation factor. It allows specification of the grid spacing off the boundary surfaces and the grid orthogonality at the boundary surfaces. It includes adaptive mechanisms to improve smoothness, orthogonality, and flow resolution in the grid interior.

  7. Adaptive 3D single-block grids for the computation of viscous flows around wings

    SciTech Connect

    Hagmeijer, R.; Kok, J.C.

    1996-12-31

    A robust algorithm for the adaption of a 3D single-block structured grid suitable for the computation of viscous flows around a wing is presented and demonstrated by application to the ONERA M6 wing. The effects of grid adaption on the flow solution and accuracy improvements is analyzed. Reynolds number variations are studied.

  8. Grid and basis adaptive polynomial chaos techniques for sensitivity and uncertainty analysis

    SciTech Connect

    Perkó, Zoltán Gilli, Luca Lathouwers, Danny Kloosterman, Jan Leen

    2014-03-01

    The demand for accurate and computationally affordable sensitivity and uncertainty techniques is constantly on the rise and has become especially pressing in the nuclear field with the shift to Best Estimate Plus Uncertainty methodologies in the licensing of nuclear installations. Besides traditional, already well developed methods – such as first order perturbation theory or Monte Carlo sampling – Polynomial Chaos Expansion (PCE) has been given a growing emphasis in recent years due to its simple application and good performance. This paper presents new developments of the research done at TU Delft on such Polynomial Chaos (PC) techniques. Our work is focused on the Non-Intrusive Spectral Projection (NISP) approach and adaptive methods for building the PCE of responses of interest. Recent efforts resulted in a new adaptive sparse grid algorithm designed for estimating the PC coefficients. The algorithm is based on Gerstner's procedure for calculating multi-dimensional integrals but proves to be computationally significantly cheaper, while at the same it retains a similar accuracy as the original method. More importantly the issue of basis adaptivity has been investigated and two techniques have been implemented for constructing the sparse PCE of quantities of interest. Not using the traditional full PC basis set leads to further reduction in computational time since the high order grids necessary for accurately estimating the near zero expansion coefficients of polynomial basis vectors not needed in the PCE can be excluded from the calculation. Moreover the sparse PC representation of the response is easier to handle when used for sensitivity analysis or uncertainty propagation due to the smaller number of basis vectors. The developed grid and basis adaptive methods have been implemented in Matlab as the Fully Adaptive Non-Intrusive Spectral Projection (FANISP) algorithm and were tested on four analytical problems. These show consistent good performance both

  9. Weighted adaptively grouped multilevel space time trellis codes

    NASA Astrophysics Data System (ADS)

    Jain, Dharmvir; Sharma, Sanjay

    2015-05-01

    In existing grouped multilevel space-time trellis codes (GMLSTTCs), the groups of transmit antennas are predefined, and the transmit power is equally distributed across all transmit antennas. When the channel parameters are perfectly known at the transmitter, adaptive antenna grouping and beamforming scheme can achieve the better performance by optimum grouping of transmit antennas and properly weighting transmitted signals based on the available channel information. In this paper, we present a new code designed by combining GMLSTTCs, adaptive antenna grouping and beamforming using the channel state information at transmitter (CSIT), henceforth referred to as weighted adaptively grouped multilevel space time trellis codes (WAGMLSTTCs). The CSIT is used to adaptively group the transmitting antennas and provide a beamforming scheme by allocating the different powers to the transmit antennas. Simulation results show that WAGMLSTTCs provide improvement in error performance of 2.6 dB over GMLSTTCs.

  10. GPU accelerated cell-based adaptive mesh refinement on unstructured quadrilateral grid

    NASA Astrophysics Data System (ADS)

    Luo, Xisheng; Wang, Luying; Ran, Wei; Qin, Fenghua

    2016-10-01

    A GPU accelerated inviscid flow solver is developed on an unstructured quadrilateral grid in the present work. For the first time, the cell-based adaptive mesh refinement (AMR) is fully implemented on GPU for the unstructured quadrilateral grid, which greatly reduces the frequency of data exchange between GPU and CPU. Specifically, the AMR is processed with atomic operations to parallelize list operations, and null memory recycling is realized to improve the efficiency of memory utilization. It is found that results obtained by GPUs agree very well with the exact or experimental results in literature. An acceleration ratio of 4 is obtained between the parallel code running on the old GPU GT9800 and the serial code running on E3-1230 V2. With the optimization of configuring a larger L1 cache and adopting Shared Memory based atomic operations on the newer GPU C2050, an acceleration ratio of 20 is achieved. The parallelized cell-based AMR processes have achieved 2x speedup on GT9800 and 18x on Tesla C2050, which demonstrates that parallel running of the cell-based AMR method on GPU is feasible and efficient. Our results also indicate that the new development of GPU architecture benefits the fluid dynamics computing significantly.

  11. A time-accurate adaptive grid method and the numerical simulation of a shock-vortex interaction

    NASA Technical Reports Server (NTRS)

    Bockelie, Michael J.; Eiseman, Peter R.

    1990-01-01

    A time accurate, general purpose, adaptive grid method is developed that is suitable for multidimensional steady and unsteady numerical simulations. The grid point movement is performed in a manner that generates smooth grids which resolve the severe solution gradients and the sharp transitions in the solution gradients. The temporal coupling of the adaptive grid and the PDE solver is performed with a grid prediction correction method that is simple to implement and ensures the time accuracy of the grid. Time accurate solutions of the 2-D Euler equations for an unsteady shock vortex interaction demonstrate the ability of the adaptive method to accurately adapt the grid to multiple solution features.

  12. Three-dimensional self-adaptive grid method for complex flows

    NASA Technical Reports Server (NTRS)

    Djomehri, M. Jahed; Deiwert, George S.

    1988-01-01

    A self-adaptive grid procedure for efficient computation of three-dimensional complex flow fields is described. The method is based on variational principles to minimize the energy of a spring system analogy which redistributes the grid points. Grid control parameters are determined by specifying maximum and minimum grid spacing. Multidirectional adaptation is achieved by splitting the procedure into a sequence of successive applications of a unidirectional adaptation. One-sided, two-directional constraints for orthogonality and smoothness are used to enhance the efficiency of the method. Feasibility of the scheme is demonstrated by application to a multinozzle, afterbody, plume flow field. Application of the algorithm for initial grid generation is illustrated by constructing a three-dimensional grid about a bump-like geometry.

  13. Analysis of a Major Electric Grid -- Stability and Adaptive Protection

    NASA Astrophysics Data System (ADS)

    Alanzi, Sultan

    Protective systems of the electric grid are designed to detect and mitigate the effects of faults and other disturbances that may occur. Distance relays are used extensively for the detection of faults on transmission lines. Out-of-step relays are used for generator protection to detect loss of synchronism conditions that result from disturbances on the electric grid. Also, when a disturbance occurs and generators may tend to lose synchronism with each other, it is beneficial to separate the overall system into several independent systems that can remain stable. Unfortunately there have been cases, such as the 2003 Northeast blackout where the operation of protective relays, namely the zone 3 distance relay used for transmission line protection, contributed to the cascading effect of the blackout. It is the objective of this dissertation to propose adaptive relays for both distance protection of transmission lines and out-of-step protection of generators. By being adaptive, the relays are made aware of the system operating conditions and can adjust its settings accordingly. Inputs to the adaptive logic can come from system or environmental conditions. As a result of this effort, a new distance relay operating characteristic is proposed, referred to as a mushroom relay, which is a combination of a quadrilateral relay and a Mho relay. Also, a new criterion for determining if a power swing following a disturbance is stable or unstable is proposed. Distance protection of transmission lines is very important when discussing system responses to faults and disturbances. Distance relays are very common worldwide and although they offer great protection, there are limitations that need to be addressed. Parallel line operations (infeed effect) and the loadability limits are among the limitations that lead to improper response of relays. An Adaptive Distance Relays (ADR) offer great benefits to the protection scheme as their settings can be changed in accordance with prefault

  14. Adaptive Modulation and Coding for LTE Wireless Communication

    NASA Astrophysics Data System (ADS)

    Hadi, S. S.; Tiong, T. C.

    2015-04-01

    Long Term Evolution (LTE) is the new upgrade path for carrier with both GSM/UMTS networks and CDMA2000 networks. The LTE is targeting to become the first global mobile phone standard regardless of the different LTE frequencies and bands use in other countries barrier. Adaptive Modulation and Coding (AMC) is used to increase the network capacity or downlink data rates. Various modulation types are discussed such as Quadrature Phase Shift Keying (QPSK), Quadrature Amplitude Modulation (QAM). Spatial multiplexing techniques for 4×4 MIMO antenna configuration is studied. With channel station information feedback from the mobile receiver to the base station transmitter, adaptive modulation and coding can be applied to adapt to the mobile wireless channels condition to increase spectral efficiencies without increasing bit error rate in noisy channels. In High-Speed Downlink Packet Access (HSDPA) in Universal Mobile Telecommunications System (UMTS), AMC can be used to choose modulation types and forward error correction (FEC) coding rate.

  15. Adaptive image coding based on cubic-spline interpolation

    NASA Astrophysics Data System (ADS)

    Jiang, Jian-Xing; Hong, Shao-Hua; Lin, Tsung-Ching; Wang, Lin; Truong, Trieu-Kien

    2014-09-01

    It has been investigated that at low bit rates, downsampling prior to coding and upsampling after decoding can achieve better compression performance than standard coding algorithms, e.g., JPEG and H. 264/AVC. However, at high bit rates, the sampling-based schemes generate more distortion. Additionally, the maximum bit rate for the sampling-based scheme to outperform the standard algorithm is image-dependent. In this paper, a practical adaptive image coding algorithm based on the cubic-spline interpolation (CSI) is proposed. This proposed algorithm adaptively selects the image coding method from CSI-based modified JPEG and standard JPEG under a given target bit rate utilizing the so called ρ-domain analysis. The experimental results indicate that compared with the standard JPEG, the proposed algorithm can show better performance at low bit rates and maintain the same performance at high bit rates.

  16. More About Vector Adaptive/Predictive Coding Of Speech

    NASA Technical Reports Server (NTRS)

    Jedrey, Thomas C.; Gersho, Allen

    1992-01-01

    Report presents additional information about digital speech-encoding and -decoding system described in "Vector Adaptive/Predictive Encoding of Speech" (NPO-17230). Summarizes development of vector adaptive/predictive coding (VAPC) system and describes basic functions of algorithm. Describes refinements introduced enabling receiver to cope with errors. VAPC algorithm implemented in integrated-circuit coding/decoding processors (codecs). VAPC and other codecs tested under variety of operating conditions. Tests designed to reveal effects of various background quiet and noisy environments and of poor telephone equipment. VAPC found competitive with and, in some respects, superior to other 4.8-kb/s codecs and other codecs of similar complexity.

  17. Automated Grid Disruption Response System: Robust Adaptive Topology Control (RATC)

    SciTech Connect

    2012-03-01

    GENI Project: The RATC research team is using topology control as a mechanism to improve system operations and manage disruptions within the electric grid. The grid is subject to interruption from cascading faults caused by extreme operating conditions, malicious external attacks, and intermittent electricity generation from renewable energy sources. The RATC system is capable of detecting, classifying, and responding to grid disturbances by reconfiguring the grid in order to maintain economically efficient operations while guaranteeing reliability. The RATC system would help prevent future power outages, which account for roughly $80 billion in losses for businesses and consumers each year. Minimizing the time it takes for the grid to respond to expensive interruptions will also make it easier to integrate intermittent renewable energy sources into the grid.

  18. Preprocessor that Enables the Use of GridProTM Grids for Unsteady Reynolds-Averaged Navier-Stokes Code TURBO

    NASA Technical Reports Server (NTRS)

    Shyam, Vikram

    2010-01-01

    A preprocessor for the Computational Fluid Dynamics (CFD) code TURBO has been developed and tested. The preprocessor converts grids produced by GridPro (Program Development Company (PDC)) into a format readable by TURBO and generates the necessary input files associated with the grid. The preprocessor also generates information that enables the user to decide how to allocate the computational load in a multiple block per processor scenario.

  19. A multigrid method for steady Euler equations on unstructured adaptive grids

    NASA Technical Reports Server (NTRS)

    Riemslagh, Kris; Dick, Erik

    1993-01-01

    A flux-difference splitting type algorithm is formulated for the steady Euler equations on unstructured grids. The polynomial flux-difference splitting technique is used. A vertex-centered finite volume method is employed on a triangular mesh. The multigrid method is in defect-correction form. A relaxation procedure with a first order accurate inner iteration and a second-order correction performed only on the finest grid, is used. A multi-stage Jacobi relaxation method is employed as a smoother. Since the grid is unstructured a Jacobi type is chosen. The multi-staging is necessary to provide sufficient smoothing properties. The domain is discretized using a Delaunay triangular mesh generator. Three grids with more or less uniform distribution of nodes but with different resolution are generated by successive refinement of the coarsest grid. Nodes of coarser grids appear in the finer grids. The multigrid method is started on these grids. As soon as the residual drops below a threshold value, an adaptive refinement is started. The solution on the adaptively refined grid is accelerated by a multigrid procedure. The coarser multigrid grids are generated by successive coarsening through point removement. The adaption cycle is repeated a few times. Results are given for the transonic flow over a NACA-0012 airfoil.

  20. A trellis-searched APC (adaptive predictive coding) speech coder

    SciTech Connect

    Malone, K.T. ); Fischer, T.R. . Dept. of Electrical and Computer Engineering)

    1990-01-01

    In this paper we formulate a speech coding system that incorporates trellis coded vector quantization (TCVQ) and adaptive predictive coding (APC). A method for optimizing'' the TCVQ codebooks is presented and experimental results concerning survivor path mergings are reported. Simulation results are given for encoding rates of 16 and 9.6 kbps for a variety of coder parameters. The quality of the encoded speech is deemed excellent at an encoding rate of 16 kbps and very good at 9.6 kbps. 13 refs., 2 figs., 4 tabs.

  1. Adaptive feature extraction using sparse coding for machinery fault diagnosis

    NASA Astrophysics Data System (ADS)

    Liu, Haining; Liu, Chengliang; Huang, Yixiang

    2011-02-01

    In the signal processing domain, there has been growing interest in sparse coding with a learned dictionary instead of a predefined one, which is advocated as an effective mathematical description for the underlying principle of mammalian sensory systems in processing information. In this paper, sparse coding is introduced as a feature extraction technique for machinery fault diagnosis and an adaptive feature extraction scheme is proposed based on it. The two core problems of sparse coding, i.e., dictionary learning and coefficients solving, are discussed in detail. A natural extension of sparse coding, shift-invariant sparse coding, is also introduced. Then, the vibration signals of rolling element bearings are taken as the target signals to verify the proposed scheme, and shift-invariant sparse coding is used for vibration analysis. With the purpose of diagnosing the different fault conditions of bearings, features are extracted following the proposed scheme: basis functions are separately learned from each class of vibration signals trying to capture the defective impulses; a redundant dictionary is built by merging all the learned basis functions; based on the redundant dictionary, the diagnostic information is made explicit in the solved sparse representations of vibration signals; sparse features are formulated in terms of activations of atoms. The multiclass linear discriminant analysis (LDA) classifier is used to test the discriminability of the extracted sparse features and the adaptability of the learned atoms. The experiments show that sparse coding is an effective feature extraction technique for machinery fault diagnosis.

  2. GAMER: A GRAPHIC PROCESSING UNIT ACCELERATED ADAPTIVE-MESH-REFINEMENT CODE FOR ASTROPHYSICS

    SciTech Connect

    Schive, H.-Y.; Tsai, Y.-C.; Chiueh Tzihong

    2010-02-01

    We present the newly developed code, GPU-accelerated Adaptive-MEsh-Refinement code (GAMER), which adopts a novel approach in improving the performance of adaptive-mesh-refinement (AMR) astrophysical simulations by a large factor with the use of the graphic processing unit (GPU). The AMR implementation is based on a hierarchy of grid patches with an oct-tree data structure. We adopt a three-dimensional relaxing total variation diminishing scheme for the hydrodynamic solver and a multi-level relaxation scheme for the Poisson solver. Both solvers have been implemented in GPU, by which hundreds of patches can be advanced in parallel. The computational overhead associated with the data transfer between the CPU and GPU is carefully reduced by utilizing the capability of asynchronous memory copies in GPU, and the computing time of the ghost-zone values for each patch is diminished by overlapping it with the GPU computations. We demonstrate the accuracy of the code by performing several standard test problems in astrophysics. GAMER is a parallel code that can be run in a multi-GPU cluster system. We measure the performance of the code by performing purely baryonic cosmological simulations in different hardware implementations, in which detailed timing analyses provide comparison between the computations with and without GPU(s) acceleration. Maximum speed-up factors of 12.19 and 10.47 are demonstrated using one GPU with 4096{sup 3} effective resolution and 16 GPUs with 8192{sup 3} effective resolution, respectively.

  3. SIMULATION OF DISPERSION OF A POWER PLANT PLUME USING AN ADAPTIVE GRID ALGORITHM

    EPA Science Inventory

    A new dynamic adaptive grid algorithm has been developed for use in air quality modeling. This algorithm uses a higher order numerical scheme?the piecewise parabolic method (PPM)?for computing advective solution fields; a weight function capable of promoting grid node clustering ...

  4. Peripheral adaptation codes for high odor concentration in glomeruli.

    PubMed

    Lecoq, Jérôme; Tiret, Pascale; Charpak, Serge

    2009-03-11

    Adaptation is a general property of sensory receptor neurons and has been extensively studied in isolated cell preparation of olfactory receptor neurons. In contrast, little is known about the conditions under which peripheral adaptation occurs in the CNS during odorant stimulation. Here, we used two-photon laser-scanning microscopy and targeted extracellular recording in freely breathing anesthetized rats to investigate the correlate of peripheral adaptation at the first synapse of the olfactory pathway in olfactory bulb glomeruli. We find that during sustained stimulation at high concentration, odorants can evoke local field potential (LFP) postsynaptic responses that rapidly adapt with time, some within two inhalations. Simultaneous measurements of LFP and calcium influx at olfactory receptor neuron terminals reveal that postsynaptic adaptation is associated with a decrease in odorant-evoked calcium response, suggesting that it results from a decrease in glutamate release. This glomerular adaptation was concentration-dependent and did not change the glomerular input-output curve. In addition, in situ application of antagonists of either ionotropic glutamate receptors or metabotropic GABA(B) receptors did not affect this adaptation, thus discarding the involvement of local presynaptic inhibition. Glomerular adaptation, therefore, reflects the response decline of olfactory receptor neurons to sustained odorant. We postulate that peripheral fast adaptation is a means by which glomerular output codes for high concentration of odor.

  5. Adaptive Grid Generation for Numerical Solution of Partial Differential Equations.

    DTIC Science & Technology

    1983-12-01

    RETURN 65 Bibliography 1. Thompson , J . F ., "A Survey of Grid Generation Tecniques in Computational Fluid Dynamics," AIAA Paper No. 83-0447, 1-36...edited by K. N. Ghia and U. Ghia. ASME FED, 5: 35-47 (1983). 3. Thompson , J . F ., Thames, F. C., and Mastin, C. W., "Automated Numerical Generation...Equations," Numerical Grid Generation, Edited by J. F. Thompson. New York: North Holland, 1982. 10. Thompson , J . F ., and Mastin, C. W., "Grid Generation

  6. Adaptive Energy Forecasting and Information Diffusion for Smart Power Grids

    SciTech Connect

    Simmhan, Yogesh; Agarwal, Vaibhav; Aman, Saim; Kumbhare, Alok; Natarajan, Sreedhar; Rajguru, Nikhil; Robinson, Ian; Stevens, Samuel; Yin, Wei; Zhou, Qunzhi; Prasanna, Viktor

    2012-05-16

    Smart Power Grids exemplify an emerging class of Cyber Physical Applications that exhibit dynamic, distributed and data intensive (D3) characteristics along with an always-on paradigm to support operational needs. Smart Grids are an outcome of instrumentation, such as Phasor Measurement Units and Smart Power Meters, that is being deployed across the transmission and distribution network of electric grids. These sensors provide utilities with improved situation awareness on near-realtime electricity usage by individual consumers, and the power quality and stability of the transmission network.

  7. Adaptive EZW coding using a rate-distortion criterion

    NASA Astrophysics Data System (ADS)

    Yin, Che-Yi

    2001-07-01

    This work presents a new method that improves on the EZW image coding algorithm. The standard EZW image coder uses a uniform quantizer with a threshold (deadzone) that is identical in all subbands. The quantization step sizes are not optimized under the rate-distortion sense. We modify the EZW by applying the Lagrange multiplier to search for the best step size for each subband and allocate the bit rate for each subband accordingly. Then we implement the adaptive EZW codec to code the wavelet coefficients. Two coding environments, independent and dependent, are considered for the optimization process. The proposed image coder retains all the good features of the EZW, namely, embedded coding, progressive transmission, order of the important bits, and enhances it through the rate-distortion optimization with respect to the step sizes.

  8. Overview of the NASA Glenn Flux Reconstruction Based High-Order Unstructured Grid Code

    NASA Technical Reports Server (NTRS)

    Spiegel, Seth C.; DeBonis, James R.; Huynh, H. T.

    2016-01-01

    A computational fluid dynamics code based on the flux reconstruction (FR) method is currently being developed at NASA Glenn Research Center to ultimately provide a large- eddy simulation capability that is both accurate and efficient for complex aeropropulsion flows. The FR approach offers a simple and efficient method that is easy to implement and accurate to an arbitrary order on common grid cell geometries. The governing compressible Navier-Stokes equations are discretized in time using various explicit Runge-Kutta schemes, with the default being the 3-stage/3rd-order strong stability preserving scheme. The code is written in modern Fortran (i.e., Fortran 2008) and parallelization is attained through MPI for execution on distributed-memory high-performance computing systems. An h- refinement study of the isentropic Euler vortex problem is able to empirically demonstrate the capability of the FR method to achieve super-accuracy for inviscid flows. Additionally, the code is applied to the Taylor-Green vortex problem, performing numerous implicit large-eddy simulations across a range of grid resolutions and solution orders. The solution found by a pseudo-spectral code is commonly used as a reference solution to this problem, and the FR code is able to reproduce this solution using approximately the same grid resolution. Finally, an examination of the code's performance demonstrates good parallel scaling, as well as an implementation of the FR method with a computational cost/degree- of-freedom/time-step that is essentially independent of the solution order of accuracy for structured geometries.

  9. Link-Adaptive Distributed Coding for Multisource Cooperation

    NASA Astrophysics Data System (ADS)

    Cano, Alfonso; Wang, Tairan; Ribeiro, Alejandro; Giannakis, Georgios B.

    2007-12-01

    Combining multisource cooperation and link-adaptive regenerative techniques, a novel protocol is developed capable of achieving diversity order up to the number of cooperating users and large coding gains. The approach relies on a two-phase protocol. In Phase 1, cooperating sources exchange information-bearing blocks, while in Phase 2, they transmit reencoded versions of the original blocks. Different from existing approaches, participation in the second phase does not require correct decoding of Phase 1 packets. This allows relaying of soft information to the destination, thus increasing coding gains while retaining diversity properties. For any reencoding function the diversity order is expressed as a function of the rank properties of the distributed coding strategy employed. This result is analogous to the diversity properties of colocated multi-antenna systems. Particular cases include repetition coding, distributed complex field coding (DCFC), distributed space-time coding, and distributed error-control coding. Rate, diversity, complexity and synchronization issues are elaborated. DCFC emerges as an attractive choice because it offers high-rate, full spatial diversity, and relaxed synchronization requirements. Simulations confirm analytically established assessments.

  10. An adaptive remeshing scheme for vortex dominated flows using three-dimensional unstructured grids

    NASA Astrophysics Data System (ADS)

    Parikh, Paresh

    1995-10-01

    An adaptive remeshing procedure for vortex dominated flows is described, which uses three-dimensional unstructured grids. Surface grid adaptation is achieved using the static pressure as an adaptation parameter, while entropy is used in the field to accurately identify high vorticity regions. An emphasis has been placed in making the scheme as automatic as possible so that a minimum user interaction is required between remeshing cycles. Adapted flow solutions are obtained on two sharp-edged configurations at low speed, high angle-of-attack flow conditions. The results thus obtained are compared with fine grid CFD solutions and experimental data, and conclusions are drawn as to the efficiency of the adaptive procedure.

  11. ALEGRA -- A massively parallel h-adaptive code for solid dynamics

    SciTech Connect

    Summers, R.M.; Wong, M.K.; Boucheron, E.A.; Weatherby, J.R.

    1997-12-31

    ALEGRA is a multi-material, arbitrary-Lagrangian-Eulerian (ALE) code for solid dynamics designed to run on massively parallel (MP) computers. It combines the features of modern Eulerian shock codes, such as CTH, with modern Lagrangian structural analysis codes using an unstructured grid. ALEGRA is being developed for use on the teraflop supercomputers to conduct advanced three-dimensional (3D) simulations of shock phenomena important to a variety of systems. ALEGRA was designed with the Single Program Multiple Data (SPMD) paradigm, in which the mesh is decomposed into sub-meshes so that each processor gets a single sub-mesh with approximately the same number of elements. Using this approach the authors have been able to produce a single code that can scale from one processor to thousands of processors. A current major effort is to develop efficient, high precision simulation capabilities for ALEGRA, without the computational cost of using a global highly resolved mesh, through flexible, robust h-adaptivity of finite elements. H-adaptivity is the dynamic refinement of the mesh by subdividing elements, thus changing the characteristic element size and reducing numerical error. The authors are working on several major technical challenges that must be met to make effective use of HAMMER on MP computers.

  12. Application of adaptive hierarchical sparse grid collocation to the uncertainty quantification of nuclear reactor simulators

    SciTech Connect

    Yankov, A.; Downar, T.

    2013-07-01

    Recent efforts in the application of uncertainty quantification to nuclear systems have utilized methods based on generalized perturbation theory and stochastic sampling. While these methods have proven to be effective they both have major drawbacks that may impede further progress. A relatively new approach based on spectral elements for uncertainty quantification is applied in this paper to several problems in reactor simulation. Spectral methods based on collocation attempt to couple the approximation free nature of stochastic sampling methods with the determinism of generalized perturbation theory. The specific spectral method used in this paper employs both the Smolyak algorithm and adaptivity by using Newton-Cotes collocation points along with linear hat basis functions. Using this approach, a surrogate model for the outputs of a computer code is constructed hierarchically by adaptively refining the collocation grid until the interpolant is converged to a user-defined threshold. The method inherently fits into the framework of parallel computing and allows for the extraction of meaningful statistics and data that are not within reach of stochastic sampling and generalized perturbation theory. This paper aims to demonstrate the advantages of spectral methods-especially when compared to current methods used in reactor physics for uncertainty quantification-and to illustrate their full potential. (authors)

  13. A well-balanced numerical scheme for shallow water simulation on adaptive grids

    NASA Astrophysics Data System (ADS)

    Zhang, H. J.; Zhou, J. Z.; Bi, S.; Li, Q. Q.; Fan, Y.

    2014-04-01

    The efficiency of solving two-dimensional shallow-water equations (SWEs) is vital for simulation of large-scale flood inundation. For flood flows over real topography, local high-resolution method, which uses adaptable grids, is required in order to prevent the loss of accuracy of the flow pattern while saving computational cost. This paper introduces an adaptive grid model, which uses an adaptive criterion calculated on the basis of the water lever. The grid adaption is performed by manipulating subdivision levels of the computation grids. As the flow feature varies during the shallow wave propagation, the local grid density changes adaptively and the stored information of neighbor relationship updates correspondingly, achieving a balance between the model accuracy and running efficiency. In this work, a well-balanced (WB) scheme for solving SWEs is introduced. In reconstructions of Riemann state, the definition of the unique bottom elevation on grid interfaces is modified, and the numerical scheme is pre-balanced automatically. By the validation against two idealist test cases, the proposed model is applied to simulate flood inundation due to a dam-break of Zhanghe Reservoir, Hubei province, China. The results show that the presented model is robust and well-balanced, has nice computational efficiency and numerical stability, and thus has bright application prospects.

  14. Adaptive directional lifting-based wavelet transform for image coding.

    PubMed

    Ding, Wenpeng; Wu, Feng; Wu, Xiaolin; Li, Shipeng; Li, Houqiang

    2007-02-01

    We present a novel 2-D wavelet transform scheme of adaptive directional lifting (ADL) in image coding. Instead of alternately applying horizontal and vertical lifting, as in present practice, ADL performs lifting-based prediction in local windows in the direction of high pixel correlation. Hence, it adapts far better to the image orientation features in local windows. The ADL transform is achieved by existing 1-D wavelets and is seamlessly integrated into the global wavelet transform. The predicting and updating signals of ADL can be derived even at the fractional pixel precision level to achieve high directional resolution, while still maintaining perfect reconstruction. To enhance the ADL performance, a rate-distortion optimized directional segmentation scheme is also proposed to form and code a hierarchical image partition adapting to local features. Experimental results show that the proposed ADL-based image coding technique outperforms JPEG 2000 in both PSNR and visual quality, with the improvement up to 2.0 dB on images with rich orientation features.

  15. Motion-compensated wavelet video coding using adaptive mode selection

    NASA Astrophysics Data System (ADS)

    Zhai, Fan; Pappas, Thrasyvoulos N.

    2004-01-01

    A motion-compensated wavelet video coder is presented that uses adaptive mode selection (AMS) for each macroblock (MB). The block-based motion estimation is performed in the spatial domain, and an embedded zerotree wavelet coder (EZW) is employed to encode the residue frame. In contrast to other motion-compensated wavelet video coders, where all the MBs are forced to be in INTER mode, we construct the residue frame by combining the prediction residual of the INTER MBs with the coding residual of the INTRA and INTER_ENCODE MBs. Different from INTER MBs that are not coded, the INTRA and INTER_ENCODE MBs are encoded separately by a DCT coder. By adaptively selecting the quantizers of the INTRA and INTER_ENCODE coded MBs, our goal is to equalize the characteristics of the residue frame in order to improve the overall coding efficiency of the wavelet coder. The mode selection is based on the variance of the MB, the variance of the prediction error, and the variance of the neighboring MBs' residual. Simulations show that the proposed motion-compensated wavelet video coder achieves a gain of around 0.7-0.8dB PSNR over MPEG-2 TM5, and a comparable PSNR to other 2D motion-compensated wavelet-based video codecs. It also provides potential visual quality improvement.

  16. Adaptive Grid Techniques for Elliptic Fluid-Flow Problems,

    DTIC Science & Technology

    1985-12-01

    J . F . (1984), "Grid Generation Techniques in Computational Fluid Dynamics," AIAA Jnl., Vol. 22, No. 11, pp. 1505-1523. Thompson , J . F . (1983...Procedure," Ph.D. Thesis, Dept. of Computer Science, Stanford University, Calif. Tang, W. P., W. Skamarock, and J. Oliger (1985). To appear. Thompson

  17. Locally adapted space-wise grids from GOCE data

    NASA Astrophysics Data System (ADS)

    Reguzzoni, Mirko; Gatti, Andrea; De Gaetani, Carlo; Migliaccio, Federica; Sansò, Fernando

    2014-05-01

    GOCE data are usually translated into a spherical harmonic global model that can be used to generate various functionals of the Earth's gravitational field. An alternative representation of the information coming from GOCE is to project the observed along-track gradients onto a spherical grid at mean satellite altitude. This is the solution pursued in this work by exploiting the so called space-wise approach. In particular, once the data are filtered along the orbit in order to reduce variance and correlation of the observation noise, a gridding procedure is implemented by least-squares collocation on local data patches. Crucial points are the new way in which data are subdivided and local covariances are modeled. Basically the idea is to consider clouds of observation points around each grid knot reducing as much as possible the data undersampling in order to catch their local information. Inside the point cloud a signal covariance model based on local degree variances is used. The method has been applied on a subset of GOCE data. The resulting grid values are compared with those synthesized from a global model based on the same observation time span, showing the differences between the two representations.

  18. Grid noise in moving mesh codes: fixing the volume inconsistency problem

    NASA Astrophysics Data System (ADS)

    Steinberg, Elad; Yalinewich, Almog; Sari, Re'em

    2016-06-01

    Current Voronoi-based moving mesh hydro codes suffer from `grid noise'. We identify the cause of this noise as the volume inconsistency error, where the volume that is transferred between cells is inconsistent with the hydrodynamical calculations. As a result, the codes do not achieve second-order convergence. In this paper we describe how a simple fix allows Voronoi-based moving mesh codes to attain second-order convergence. The fix is based on the understanding that the volume exchanged between cells should be consistent with the hydrodynamical calculations. We benchmark our fix with three test problems and show that it can significantly improve the computational accuracy. We also examine the effect of initial mesh initialization and present an improved model for the Green-Gauss-based gradient estimator.

  19. Adaptive coded aperture imaging: progress and potential future applications

    NASA Astrophysics Data System (ADS)

    Gottesman, Stephen R.; Isser, Abraham; Gigioli, George W., Jr.

    2011-09-01

    Interest in Adaptive Coded Aperture Imaging (ACAI) continues to grow as the optical and systems engineering community becomes increasingly aware of ACAI's potential benefits in the design and performance of both imaging and non-imaging systems , such as good angular resolution (IFOV), wide distortion-free field of view (FOV), excellent image quality, and light weight construct. In this presentation we first review the accomplishments made over the past five years, then expand on previously published work to show how replacement of conventional imaging optics with coded apertures can lead to a reduction in system size and weight. We also present a trade space analysis of key design parameters of coded apertures and review potential applications as replacement for traditional imaging optics. Results will be presented, based on last year's work of our investigation into the trade space of IFOV, resolution, effective focal length, and wavelength of incident radiation for coded aperture architectures. Finally we discuss the potential application of coded apertures for replacing objective lenses of night vision goggles (NVGs).

  20. Adaptive Unstructured Grid Generation for Modeling of Coastal Margins

    DTIC Science & Technology

    1999-09-30

    applied to the 2+1D simulations of the barotropic circulation in the Tagus estuary (Fortunato et al. 1997). The approach, denoted localized sigma...analysis. Application to the Tagus does not appear to have produced new pathologies relative to a conventional sigma-coordinate discretization, and reduced...particular, adopt and provide additional testbeds and technical feedback for our grid generation software. The Columbia River estuary and plume have provided

  1. Grid-enhanced X-ray coded aperture microscopy with polycapillary optics.

    PubMed

    Sowa, Katarzyna M; Last, Arndt; Korecki, Paweł

    2017-03-21

    Polycapillary devices focus X-rays by means of multiple reflections of X-rays in arrays of bent glass capillaries. The size of the focal spot (typically 10-100 μm) limits the resolution of scanning, absorption and phase-contrast X-ray imaging using these devices. At the expense of a moderate resolution, polycapillary elements provide high intensity and are frequently used for X-ray micro-imaging with both synchrotrons and X-ray tubes. Recent studies have shown that the internal microstructure of such an optics can be used as a coded aperture that encodes high-resolution information about objects located inside the focal spot. However, further improvements to this variant of X-ray microscopy will require the challenging fabrication of tailored devices with a well-defined capillary microstructure. Here, we show that submicron coded aperture microscopy can be realized using a periodic grid that is placed at the output surface of a polycapillary optics. Grid-enhanced X-ray coded aperture microscopy with polycapillary optics does not rely on the specific microstructure of the optics but rather takes advantage only of its focusing properties. Hence, submicron X-ray imaging can be realized with standard polycapillary devices and existing set-ups for micro X-ray fluorescence spectroscopy.

  2. Grid-enhanced X-ray coded aperture microscopy with polycapillary optics

    NASA Astrophysics Data System (ADS)

    Sowa, Katarzyna M.; Last, Arndt; Korecki, Paweł

    2017-03-01

    Polycapillary devices focus X-rays by means of multiple reflections of X-rays in arrays of bent glass capillaries. The size of the focal spot (typically 10–100 μm) limits the resolution of scanning, absorption and phase-contrast X-ray imaging using these devices. At the expense of a moderate resolution, polycapillary elements provide high intensity and are frequently used for X-ray micro-imaging with both synchrotrons and X-ray tubes. Recent studies have shown that the internal microstructure of such an optics can be used as a coded aperture that encodes high-resolution information about objects located inside the focal spot. However, further improvements to this variant of X-ray microscopy will require the challenging fabrication of tailored devices with a well-defined capillary microstructure. Here, we show that submicron coded aperture microscopy can be realized using a periodic grid that is placed at the output surface of a polycapillary optics. Grid-enhanced X-ray coded aperture microscopy with polycapillary optics does not rely on the specific microstructure of the optics but rather takes advantage only of its focusing properties. Hence, submicron X-ray imaging can be realized with standard polycapillary devices and existing set-ups for micro X-ray fluorescence spectroscopy.

  3. Grid-enhanced X-ray coded aperture microscopy with polycapillary optics

    PubMed Central

    Sowa, Katarzyna M.; Last, Arndt; Korecki, Paweł

    2017-01-01

    Polycapillary devices focus X-rays by means of multiple reflections of X-rays in arrays of bent glass capillaries. The size of the focal spot (typically 10–100 μm) limits the resolution of scanning, absorption and phase-contrast X-ray imaging using these devices. At the expense of a moderate resolution, polycapillary elements provide high intensity and are frequently used for X-ray micro-imaging with both synchrotrons and X-ray tubes. Recent studies have shown that the internal microstructure of such an optics can be used as a coded aperture that encodes high-resolution information about objects located inside the focal spot. However, further improvements to this variant of X-ray microscopy will require the challenging fabrication of tailored devices with a well-defined capillary microstructure. Here, we show that submicron coded aperture microscopy can be realized using a periodic grid that is placed at the output surface of a polycapillary optics. Grid-enhanced X-ray coded aperture microscopy with polycapillary optics does not rely on the specific microstructure of the optics but rather takes advantage only of its focusing properties. Hence, submicron X-ray imaging can be realized with standard polycapillary devices and existing set-ups for micro X-ray fluorescence spectroscopy. PMID:28322316

  4. Cellular Adaptation Facilitates Sparse and Reliable Coding in Sensory Pathways

    PubMed Central

    Farkhooi, Farzad; Froese, Anja; Muller, Eilif; Menzel, Randolf; Nawrot, Martin P.

    2013-01-01

    Most neurons in peripheral sensory pathways initially respond vigorously when a preferred stimulus is presented, but adapt as stimulation continues. It is unclear how this phenomenon affects stimulus coding in the later stages of sensory processing. Here, we show that a temporally sparse and reliable stimulus representation develops naturally in sequential stages of a sensory network with adapting neurons. As a modeling framework we employ a mean-field approach together with an adaptive population density treatment, accompanied by numerical simulations of spiking neural networks. We find that cellular adaptation plays a critical role in the dynamic reduction of the trial-by-trial variability of cortical spike responses by transiently suppressing self-generated fast fluctuations in the cortical balanced network. This provides an explanation for a widespread cortical phenomenon by a simple mechanism. We further show that in the insect olfactory system cellular adaptation is sufficient to explain the emergence of the temporally sparse and reliable stimulus representation in the mushroom body. Our results reveal a generic, biophysically plausible mechanism that can explain the emergence of a temporally sparse and reliable stimulus representation within a sequential processing architecture. PMID:24098101

  5. Adaptively-refined overlapping grids for the numerical solution of systems of hyperbolic conservation laws

    NASA Technical Reports Server (NTRS)

    Brislawn, Kristi D.; Brown, David L.; Chesshire, Geoffrey S.; Saltzman, Jeffrey S.

    1995-01-01

    Adaptive mesh refinement (AMR) in conjunction with higher-order upwind finite-difference methods have been used effectively on a variety of problems in two and three dimensions. In this paper we introduce an approach for resolving problems that involve complex geometries in which resolution of boundary geometry is important. The complex geometry is represented by using the method of overlapping grids, while local resolution is obtained by refining each component grid with the AMR algorithm, appropriately generalized for this situation. The CMPGRD algorithm introduced by Chesshire and Henshaw is used to automatically generate the overlapping grid structure for the underlying mesh.

  6. Unstructured Grid Adaptation: Status, Potential Impacts, and Recommended Investments Toward CFD Vision 2030

    NASA Technical Reports Server (NTRS)

    Park, Michael A.; Krakos, Joshua A.; Michal, Todd; Loseille, Adrien; Alonso, Juan J.

    2016-01-01

    Unstructured grid adaptation is a powerful tool to control discretization error for Computational Fluid Dynamics (CFD). It has enabled key increases in the accuracy, automation, and capacity of some fluid simulation applications. Slotnick et al. provides a number of case studies in the CFD Vision 2030 Study: A Path to Revolutionary Computational Aerosciences to illustrate the current state of CFD capability and capacity. The authors forecast the potential impact of emerging High Performance Computing (HPC) environments forecast in the year 2030 and identify that mesh generation and adaptivity continue to be significant bottlenecks in the CFD work flow. These bottlenecks may persist because very little government investment has been targeted in these areas. To motivate investment, the impacts of improved grid adaptation technologies are identified. The CFD Vision 2030 Study roadmap and anticipated capabilities in complementary disciplines are quoted to provide context for the progress made in grid adaptation in the past fifteen years, current status, and a forecast for the next fifteen years with recommended investments. These investments are specific to mesh adaptation and impact other aspects of the CFD process. Finally, a strategy is identified to diffuse grid adaptation technology into production CFD work flows.

  7. A self-adaptive-grid method with application to airfoil flow

    NASA Technical Reports Server (NTRS)

    Nakahashi, K.; Deiwert, G. S.

    1985-01-01

    A self-adaptive-grid method is described that is suitable for multidimensional steady and unsteady computations. Based on variational principles, a spring analogy is used to redistribute grid points in an optimal sense to reduce the overall solution error. User-specified parameters, denoting both maximum and minimum permissible grid spacings, are used to define the all-important constants, thereby minimizing the empiricism and making the method self-adaptive. Operator splitting and one-sided controls for orthogonality and smoothness are used to make the method practical, robust, and efficient. Examples are included for both steady and unsteady viscous flow computations about airfoils in two dimensions, as well as for a steady inviscid flow computation and a one-dimensional case. These examples illustrate the precise control the user has with the self-adaptive method and demonstrate a significant improvement in accuracy and quality of the solutions.

  8. A 3D finite-volume scheme for the Euler equations on adaptive tetrahedral grids

    SciTech Connect

    Vijayan, P.; Kallinderis, Y. )

    1994-08-01

    The paper describes the development and application of a new Euler solver for adaptive tetrahedral grids. Spatial discretization uses a finite-volume, node-based scheme that is of central-differencing type. A second-order Taylor series expansion is employed to march the solution in time according to the Lax-Wendroff approach. Special upwind-like smoothing operators for unstructured grids are developed for shock-capturing, as well as for suppression of solution oscillations. The scheme is formulated so that all operations are edge-based, which reduces the computational effort significantly. An adaptive grid algorithm is employed in order to resolve local flow features. This is achieved by dividing the tetrahedral cells locally, guided by a flow feature detection algorithm. Application cases include transonic flow around the ONERA M6 wing and transonic flow past a transport aircraft configuration. Comparisons with experimental data evaluate accuracy of the developed adaptive solver. 31 refs., 33 figs.

  9. Adaptive Local Grid Refinement in Computational Fluid Mechanics.

    DTIC Science & Technology

    1987-11-01

    Adaptive mesh refinements in reservoir simulation applications (R.E. Ew- ing), Proceedings Intl. Conference on Accuracy Est. and Adaptive Refine... reservoir simulation (R.E. Ewing and .J.V. 1{oebbe), Innovati’ve Numerical Mlethods in Engineering, (R.P. Shaw, J. Pc- riaux, A. Chaudouet, J. Wu...Universities, Cheyenne, Wyoming, February 21, 1986, O 9. Finite element techniques for reservoir simulation , Fourth International Sym- posium on Numerical

  10. Adaptive shape coding for perceptual decisions in the human brain

    PubMed Central

    Kourtzi, Zoe; Welchman, Andrew E.

    2015-01-01

    In its search for neural codes, the field of visual neuroscience has uncovered neural representations that reflect the structure of stimuli of variable complexity from simple features to object categories. However, accumulating evidence suggests an adaptive neural code that is dynamically shaped by experience to support flexible and efficient perceptual decisions. Here, we review work showing that experience plays a critical role in molding midlevel visual representations for perceptual decisions. Combining behavioral and brain imaging measurements, we demonstrate that learning optimizes feature binding for object recognition in cluttered scenes, and tunes the neural representations of informative image parts to support efficient categorical judgements. Our findings indicate that similar learning mechanisms may mediate long-term optimization through development, tune the visual system to fundamental principles of feature binding, and optimize feature templates for perceptual decisions. PMID:26024511

  11. Adaptive neural coding: from biological to behavioral decision-making

    PubMed Central

    Louie, Kenway; Glimcher, Paul W.; Webb, Ryan

    2015-01-01

    Empirical decision-making in diverse species deviates from the predictions of normative choice theory, but why such suboptimal behavior occurs is unknown. Here, we propose that deviations from optimality arise from biological decision mechanisms that have evolved to maximize choice performance within intrinsic biophysical constraints. Sensory processing utilizes specific computations such as divisive normalization to maximize information coding in constrained neural circuits, and recent evidence suggests that analogous computations operate in decision-related brain areas. These adaptive computations implement a relative value code that may explain the characteristic context-dependent nature of behavioral violations of classical normative theory. Examining decision-making at the computational level thus provides a crucial link between the architecture of biological decision circuits and the form of empirical choice behavior. PMID:26722666

  12. Adaptive grid finite element model of the tokamak scrapeoff layer

    SciTech Connect

    Kuprat, A.P.; Glasser, A.H.

    1995-07-01

    The authors discuss unstructured grids for application to transport in the tokamak edge SOL. They have developed a new metric with which to judge element elongation and resolution requirements. Using this method, the authors apply a standard moving finite element technique to advance the SOL equations while inserting/deleting dynamically nodes that violate an elongation criterion. In a tokamak plasma, this method achieves a more uniform accuracy, and results in highly stretched triangular finite elements, except near separatrix X-point where transport is more isotropic.

  13. A general hybrid radiation transport scheme for star formation simulations on an adaptive grid

    SciTech Connect

    Klassen, Mikhail; Pudritz, Ralph E.; Kuiper, Rolf; Peters, Thomas; Banerjee, Robi; Buntemeyer, Lars

    2014-12-10

    Radiation feedback plays a crucial role in the process of star formation. In order to simulate the thermodynamic evolution of disks, filaments, and the molecular gas surrounding clusters of young stars, we require an efficient and accurate method for solving the radiation transfer problem. We describe the implementation of a hybrid radiation transport scheme in the adaptive grid-based FLASH general magnetohydrodyanmics code. The hybrid scheme splits the radiative transport problem into a raytracing step and a diffusion step. The raytracer captures the first absorption event, as stars irradiate their environments, while the evolution of the diffuse component of the radiation field is handled by a flux-limited diffusion solver. We demonstrate the accuracy of our method through a variety of benchmark tests including the irradiation of a static disk, subcritical and supercritical radiative shocks, and thermal energy equilibration. We also demonstrate the capability of our method for casting shadows and calculating gas and dust temperatures in the presence of multiple stellar sources. Our method enables radiation-hydrodynamic studies of young stellar objects, protostellar disks, and clustered star formation in magnetized, filamentary environments.

  14. A General Hybrid Radiation Transport Scheme for Star Formation Simulations on an Adaptive Grid

    NASA Astrophysics Data System (ADS)

    Klassen, Mikhail; Kuiper, Rolf; Pudritz, Ralph E.; Peters, Thomas; Banerjee, Robi; Buntemeyer, Lars

    2014-12-01

    Radiation feedback plays a crucial role in the process of star formation. In order to simulate the thermodynamic evolution of disks, filaments, and the molecular gas surrounding clusters of young stars, we require an efficient and accurate method for solving the radiation transfer problem. We describe the implementation of a hybrid radiation transport scheme in the adaptive grid-based FLASH general magnetohydrodyanmics code. The hybrid scheme splits the radiative transport problem into a raytracing step and a diffusion step. The raytracer captures the first absorption event, as stars irradiate their environments, while the evolution of the diffuse component of the radiation field is handled by a flux-limited diffusion solver. We demonstrate the accuracy of our method through a variety of benchmark tests including the irradiation of a static disk, subcritical and supercritical radiative shocks, and thermal energy equilibration. We also demonstrate the capability of our method for casting shadows and calculating gas and dust temperatures in the presence of multiple stellar sources. Our method enables radiation-hydrodynamic studies of young stellar objects, protostellar disks, and clustered star formation in magnetized, filamentary environments.

  15. 3-D grid refinement using the University of Michigan adaptive mesh library for a pure advective test

    NASA Astrophysics Data System (ADS)

    Oehmke, R.; Vandenberg, D.; Andronova, N.; Penner, J.; Stout, Q.; Zubov, V.; Jablonowski, C.

    2008-05-01

    The numerical representation of the partial differential equations (PDE) for high resolution atmospheric dynamical and physical features requires division of the atmospheric volume into a set of 3D grids, each of which has a not quite rectangular form. Each location on the grid contains multiple data that together represent the state of Earth's atmosphere. For successful numerical integration of the PDEs the size of each grid box is used to define the Courant-Friedrichs-Levi criterion in setting the time step. 3D adaptive representations of a sphere are needed to represent the evolution of clouds. In this paper we present the University of Michigan adaptive mesh library - a library that supports the production of parallel codes with use of adaptation on a sphere. The library manages the block-structured data layout, handles ghost cell updates among neighboring blocks and splits blocks as refinements occur. The library has several modules that provide a layer of abstraction for adaptive refinement: blocks, which contain individual cells of user data; shells — the global geometry for the problem, including a sphere, reduced sphere, and now a 3D sphere; a load balancer for placement of blocks onto processors; and a communication support layer which encapsulates all data movement. Users provide data manipulation functions for performing interpolation of user data when refining blocks. We rigorously test the library using refinement of the modeled vertical transport of a tracer with prescribed atmospheric sources and sinks. It is both a 2 and a 3D test, and bridges the performance of the model's dynamics and physics needed for inclusion of cloud formation.

  16. Grid-based Parallel Data Streaming Implemented for the Gyrokinetic Toroidal Code

    SciTech Connect

    S. Klasky; S. Ethier; Z. Lin; K. Martins; D. McCune; R. Samtaney

    2003-09-15

    We have developed a threaded parallel data streaming approach using Globus to transfer multi-terabyte simulation data from a remote supercomputer to the scientist's home analysis/visualization cluster, as the simulation executes, with negligible overhead. Data transfer experiments show that this concurrent data transfer approach is more favorable compared with writing to local disk and then transferring this data to be post-processed. The present approach is conducive to using the grid to pipeline the simulation with post-processing and visualization. We have applied this method to the Gyrokinetic Toroidal Code (GTC), a 3-dimensional particle-in-cell code used to study microturbulence in magnetic confinement fusion from first principles plasma theory.

  17. Interim storage of spent and disused sealed sources: optimisation of external dose distribution in waste grids using the MCNPX code.

    PubMed

    Paiva, I; Oliveira, C; Trindade, R; Portugal, L

    2005-01-01

    Radioactive sealed sources are in use worldwide in different fields of application. When no further use is foreseen for these sources, they become spent or disused sealed sources and are subject to a specific waste management scheme. Portugal does have a Radioactive Waste Interim Storage Facility where spent or disused sealed sources are conditioned in a cement matrix inside concrete drums and following the geometrical disposition of a grid. The gamma dose values around each grid depend on the drum's enclosed activity and radionuclides considered, as well as on the drums distribution in the various layers of the grid. This work proposes a method based on the Monte Carlo simulation using the MCNPX code to estimate the best drum arrangement through the optimisation of dose distribution in a grid. Measured dose rate values at 1 m distance from the surface of the chosen optimised grid were used to validate the corresponding computational grid model.

  18. Adaptive zero-tree structure for curved wavelet image coding

    NASA Astrophysics Data System (ADS)

    Zhang, Liang; Wang, Demin; Vincent, André

    2006-02-01

    We investigate the issue of efficient data organization and representation of the curved wavelet coefficients [curved wavelet transform (WT)]. We present an adaptive zero-tree structure that exploits the cross-subband similarity of the curved wavelet transform. In the embedded zero-tree wavelet (EZW) and the set partitioning in hierarchical trees (SPIHT), the parent-child relationship is defined in such a way that a parent has four children, restricted to a square of 2×2 pixels, the parent-child relationship in the adaptive zero-tree structure varies according to the curves along which the curved WT is performed. Five child patterns were determined based on different combinations of curve orientation. A new image coder was then developed based on this adaptive zero-tree structure and the set-partitioning technique. Experimental results using synthetic and natural images showed the effectiveness of the proposed adaptive zero-tree structure for encoding of the curved wavelet coefficients. The coding gain of the proposed coder can be up to 1.2 dB in terms of peak SNR (PSNR) compared to the SPIHT coder. Subjective evaluation shows that the proposed coder preserves lines and edges better than the SPIHT coder.

  19. Radiation Coupling with the FUN3D Unstructured-Grid CFD Code

    NASA Technical Reports Server (NTRS)

    Wood, William A.

    2012-01-01

    The HARA radiation code is fully-coupled to the FUN3D unstructured-grid CFD code for the purpose of simulating high-energy hypersonic flows. The radiation energy source terms and surface heat transfer, under the tangent slab approximation, are included within the fluid dynamic ow solver. The Fire II flight test, at the Mach-31 1643-second trajectory point, is used as a demonstration case. Comparisons are made with an existing structured-grid capability, the LAURA/HARA coupling. The radiative surface heat transfer rates from the present approach match the benchmark values within 6%. Although radiation coupling is the focus of the present work, convective surface heat transfer rates are also reported, and are seen to vary depending upon the choice of mesh connectivity and FUN3D ux reconstruction algorithm. On a tetrahedral-element mesh the convective heating matches the benchmark at the stagnation point, but under-predicts by 15% on the Fire II shoulder. Conversely, on a mixed-element mesh the convective heating over-predicts at the stagnation point by 20%, but matches the benchmark away from the stagnation region.

  20. Optimizations of the energy grid search algorithm in continuous-energy Monte Carlo particle transport codes

    NASA Astrophysics Data System (ADS)

    Walsh, Jonathan A.; Romano, Paul K.; Forget, Benoit; Smith, Kord S.

    2015-11-01

    In this work we propose, implement, and test various optimizations of the typical energy grid-cross section pair lookup algorithm in Monte Carlo particle transport codes. The key feature common to all of the optimizations is a reduction in the length of the vector of energies that must be searched when locating the index of a particle's current energy. Other factors held constant, a reduction in energy vector length yields a reduction in CPU time. The computational methods we present here are physics-informed. That is, they are designed to utilize the physical information embedded in a simulation in order to reduce the length of the vector to be searched. More specifically, the optimizations take advantage of information about scattering kinematics, neutron cross section structure and data representation, and also the expected characteristics of a system's spatial flux distribution and energy spectrum. The methods that we present are implemented in the OpenMC Monte Carlo neutron transport code as part of this work. The gains in computational efficiency, as measured by overall code speedup, associated with each of the optimizations are demonstrated in both serial and multithreaded simulations of realistic systems. Depending on the system, simulation parameters, and optimization method employed, overall code speedup factors of 1.2-1.5, relative to the typical single-nuclide binary search algorithm, are routinely observed.

  1. Composite-Grid Techniques and Adaptive Mesh Refinement in Computational Fluid Dynamics

    DTIC Science & Technology

    1990-01-01

    the equations govern- ing the flow. The patched adaptive mesh refinement technique, devised at Stanford by Oliger, et al ., copes with these sources of...patched adaptive mesh refinement technique, devised at Stanford by Oliger et al . [OL184], copes with these sources of error efficiently by refining...differential equation, as in the numerical grid generation methods proposed by Thompson et al . [THO85], or simply a list of pairs of points in

  2. Generalized Monge-Kantorovich optimization for grid generation and adaptation in LP

    SciTech Connect

    Delzanno, G L; Finn, J M

    2009-01-01

    The Monge-Kantorovich grid generation and adaptation scheme of is generalized from a variational principle based on L{sub 2} to a variational principle based on L{sub p}. A generalized Monge-Ampere (MA) equation is derived and its properties are discussed. Results for p > 1 are obtained and compared in terms of the quality of the resulting grid. We conclude that for the grid generation application, the formulation based on L{sub p} for p close to unity leads to serious problems associated with the boundary. Results for 1.5 {approx}< p {approx}< 2.5 are quite good, but there is a fairly narrow range around p = 2 where the results are close to optimal with respect to grid distortion. Furthermore, the Newton-Krylov methods used to solve the generalized MA equation perform best for p = 2.

  3. Stability of a modified Peaceman-Rachford method for the paraxial Helmholtz equation on adaptive grids

    NASA Astrophysics Data System (ADS)

    Sheng, Qin; Sun, Hai-wei

    2016-11-01

    This study concerns the asymptotic stability of an eikonal, or ray, transformation based Peaceman-Rachford splitting method for solving the paraxial Helmholtz equation with high wave numbers. Arbitrary nonuniform grids are considered in transverse and beam propagation directions. The differential equation targeted has been used for modeling propagations of high intensity laser pulses over a long distance without diffractions. Self-focusing of high intensity beams may be balanced with the de-focusing effect of created ionized plasma channel in the situation, and applications of grid adaptations are frequently essential. It is shown rigorously that the fully discretized oscillation-free decomposition method on arbitrary adaptive grids is asymptotically stable with a stability index one. Simulation experiments are carried out to illustrate our concern and conclusions.

  4. A Hyperspherical Adaptive Sparse-Grid Method for High-Dimensional Discontinuity Detection

    SciTech Connect

    Zhang, Guannan; Webster, Clayton G.; Gunzburger, Max D.; Burkardt, John V.

    2015-06-24

    This study proposes and analyzes a hyperspherical adaptive hierarchical sparse-grid method for detecting jump discontinuities of functions in high-dimensional spaces. The method is motivated by the theoretical and computational inefficiencies of well-known adaptive sparse-grid methods for discontinuity detection. Our novel approach constructs a function representation of the discontinuity hypersurface of an N-dimensional discontinuous quantity of interest, by virtue of a hyperspherical transformation. Then, a sparse-grid approximation of the transformed function is built in the hyperspherical coordinate system, whose value at each point is estimated by solving a one-dimensional discontinuity detection problem. Due to the smoothness of the hypersurface, the new technique can identify jump discontinuities with significantly reduced computational cost, compared to existing methods. In addition, hierarchical acceleration techniques are also incorporated to further reduce the overall complexity. Rigorous complexity analyses of the new method are provided as are several numerical examples that illustrate the effectiveness of the approach.

  5. SIMULATION OF DISPERSION OF A POWER PLANT PLUME USING AN ADAPTIVE GRID ALGORITHM. (R827028)

    EPA Science Inventory

    A new dynamic adaptive grid algorithm has been developed for use in air quality modeling. This algorithm uses a higher order numerical scheme––the piecewise parabolic method (PPM)––for computing advective solution fields; a weight function capable o...

  6. Algebraic grid adaptation method using non-uniform rational B-spline surface modeling

    NASA Technical Reports Server (NTRS)

    Yang, Jiann-Cherng; Soni, B. K.

    1992-01-01

    An algebraic adaptive grid system based on equidistribution law and utilized by the Non-Uniform Rational B-Spline (NURBS) surface for redistribution is presented. A weight function, utilizing a properly weighted boolean sum of various flow field characteristics is developed. Computational examples are presented to demonstrate the success of this technique.

  7. Integration of hp-Adaptivity and a Two Grid Solver. II. Electromagnetic Problems

    DTIC Science & Technology

    2005-01-01

    for lower order FE spaces. More precisely, let T be a grid,M the associated lowest order Nedelec subspaces ofHD(curl; Ω) of the first kind [24], and W... Nedelec , Mixed finite elements in IR3., Numer. Math., 35 (1980), pp. 315–341. [25] D. Pardo and L. Demkowicz, Integration of hp-adaptivity with a two

  8. White Light Schlieren Optics Using Bacteriorhodopsin as an Adaptive Image Grid

    NASA Technical Reports Server (NTRS)

    Peale, Robert; Ruffin, Boh; Donahue, Jeff; Barrett, Carolyn

    1996-01-01

    A Schlieren apparatus using a bacteriorhodopsin film as an adaptive image grid with white light illumination is demonstrated for the first time. The time dependent spectral properties of the film are characterized. Potential applications include a single-ended Schlieren system for leak detection.

  9. Re-architecting flow-control adaptation for grid environments

    SciTech Connect

    Engelhart, A.; Gardner, M. K.; Feng, W. C.

    2004-01-01

    The performance of TCP in wide-area networks (WANs) is becoming increasingly important with the deployment of computational and data grids. At WAN speeds, TCP does not provide good performance for data-intensive applications without the tuning of flow-control buffer sizes. Manual adjustment of buffer sizes is tedious even for network experts. For scientists, tuning is often an impediment to getting work done. Thus, buffer tuning should be automated. Existing techniques for automatic buffer tuning only measure the bandwidth-delay product (BDP) during connection establishment. This ignores the (large) fluctuation of the BDP over the lifetime of the connection. In contrast, the Dynamic Right-Sizing algorithm dynamically changes buffer sizes in response to changing network conditions. In this paper, we describe a new user-space implementation of Dynamic Right-Sizing in FTP (drsFTP) that supports third-party data transfers, a mainstay of scientific computing. In addition to comparing the performance of the new implementation with the old, we give performance results over a live WAN. The new implementation gives transfer rates of up to five times higher than untuned FTP.

  10. Long non-coding RNAs in innate and adaptive immunity

    PubMed Central

    Aune, Thomas M.; Spurlock, Charles F.

    2015-01-01

    Long noncoding RNAs (lncRNAs) represent a newly discovered class of regulatory molecules that impact a variety of biological processes in cells and organ systems. In humans, it is estimated that there may be more than twice as many lncRNA genes than protein-coding genes. However, only a handful of lncRNAs have been analyzed in detail. In this review, we describe expression and functions of lncRNAs that have been demonstrated to impact innate and adaptive immunity. These emerging paradigms illustrate remarkably diverse mechanisms that lncRNAs utilize to impact the transcriptional programs of immune cells required to fight against pathogens and maintain normal health and homeostasis. PMID:26166759

  11. Emergent Adaptive Noise Reduction from Communal Cooperation of Sensor Grid

    NASA Technical Reports Server (NTRS)

    Jones, Kennie H.; Jones, Michael G.; Nark, Douglas M.; Lodding, Kenneth N.

    2010-01-01

    In the last decade, the realization of small, inexpensive, and powerful devices with sensors, computers, and wireless communication has promised the development of massive sized sensor networks with dense deployments over large areas capable of high fidelity situational assessments. However, most management models have been based on centralized control and research has concentrated on methods for passing data from sensor devices to the central controller. Most implementations have been small but, as it is not scalable, this methodology is insufficient for massive deployments. Here, a specific application of a large sensor network for adaptive noise reduction demonstrates a new paradigm where communities of sensor/computer devices assess local conditions and make local decisions from which emerges a global behaviour. This approach obviates many of the problems of centralized control as it is not prone to single point of failure and is more scalable, efficient, robust, and fault tolerant

  12. Global error estimation based on the tolerance proportionality for some adaptive Runge-Kutta codes

    NASA Astrophysics Data System (ADS)

    Calvo, M.; González-Pinto, S.; Montijano, J. I.

    2008-09-01

    Modern codes for the numerical solution of Initial Value Problems (IVPs) in ODEs are based in adaptive methods that, for a user supplied tolerance [delta], attempt to advance the integration selecting the size of each step so that some measure of the local error is [similar, equals][delta]. Although this policy does not ensure that the global errors are under the prescribed tolerance, after the early studies of Stetter [Considerations concerning a theory for ODE-solvers, in: R. Burlisch, R.D. Grigorieff, J. Schröder (Eds.), Numerical Treatment of Differential Equations, Proceedings of Oberwolfach, 1976, Lecture Notes in Mathematics, vol. 631, Springer, Berlin, 1978, pp. 188-200; Tolerance proportionality in ODE codes, in: R. März (Ed.), Proceedings of the Second Conference on Numerical Treatment of Ordinary Differential Equations, Humbold University, Berlin, 1980, pp. 109-123] and the extensions of Higham [Global error versus tolerance for explicit Runge-Kutta methods, IMA J. Numer. Anal. 11 (1991) 457-480; The tolerance proportionality of adaptive ODE solvers, J. Comput. Appl. Math. 45 (1993) 227-236; The reliability of standard local error control algorithms for initial value ordinary differential equations, in: Proceedings: The Quality of Numerical Software: Assessment and Enhancement, IFIP Series, Springer, Berlin, 1997], it has been proved that in many existing explicit Runge-Kutta codes the global errors behave asymptotically as some rational power of [delta]. This step-size policy, for a given IVP, determines at each grid point tn a new step-size hn+1=h(tn;[delta]) so that h(t;[delta]) is a continuous function of t. In this paper a study of the tolerance proportionality property under a discontinuous step-size policy that does not allow to change the size of the step if the step-size ratio between two consecutive steps is close to unity is carried out. This theory is applied to obtain global error estimations in a few problems that have been solved with

  13. RAM: a Relativistic Adaptive Mesh Refinement Hydrodynamics Code

    SciTech Connect

    Zhang, Wei-Qun; MacFadyen, Andrew I.; /Princeton, Inst. Advanced Study

    2005-06-06

    The authors have developed a new computer code, RAM, to solve the conservative equations of special relativistic hydrodynamics (SRHD) using adaptive mesh refinement (AMR) on parallel computers. They have implemented a characteristic-wise, finite difference, weighted essentially non-oscillatory (WENO) scheme using the full characteristic decomposition of the SRHD equations to achieve fifth-order accuracy in space. For time integration they use the method of lines with a third-order total variation diminishing (TVD) Runge-Kutta scheme. They have also implemented fourth and fifth order Runge-Kutta time integration schemes for comparison. The implementation of AMR and parallelization is based on the FLASH code. RAM is modular and includes the capability to easily swap hydrodynamics solvers, reconstruction methods and physics modules. In addition to WENO they have implemented a finite volume module with the piecewise parabolic method (PPM) for reconstruction and the modified Marquina approximate Riemann solver to work with TVD Runge-Kutta time integration. They examine the difficulty of accurately simulating shear flows in numerical relativistic hydrodynamics codes. They show that under-resolved simulations of simple test problems with transverse velocity components produce incorrect results and demonstrate the ability of RAM to correctly solve these problems. RAM has been tested in one, two and three dimensions and in Cartesian, cylindrical and spherical coordinates. they have demonstrated fifth-order accuracy for WENO in one and two dimensions and performed detailed comparison with other schemes for which they show significantly lower convergence rates. Extensive testing is presented demonstrating the ability of RAM to address challenging open questions in relativistic astrophysics.

  14. Hybrid Adaptive Ray-Moment Method (HARM2): A highly parallel method for radiation hydrodynamics on adaptive grids

    NASA Astrophysics Data System (ADS)

    Rosen, A. L.; Krumholz, M. R.; Oishi, J. S.; Lee, A. T.; Klein, R. I.

    2017-02-01

    We present a highly-parallel multi-frequency hybrid radiation hydrodynamics algorithm that combines a spatially-adaptive long characteristics method for the radiation field from point sources with a moment method that handles the diffuse radiation field produced by a volume-filling fluid. Our Hybrid Adaptive Ray-Moment Method (HARM2) operates on patch-based adaptive grids, is compatible with asynchronous time stepping, and works with any moment method. In comparison to previous long characteristics methods, we have greatly improved the parallel performance of the adaptive long-characteristics method by developing a new completely asynchronous and non-blocking communication algorithm. As a result of this improvement, our implementation achieves near-perfect scaling up to O (103) processors on distributed memory machines. We present a series of tests to demonstrate the accuracy and performance of the method.

  15. Operational adaptability evaluation index system of pumped storage in UHV receiving-end grids

    NASA Astrophysics Data System (ADS)

    Yuan, Bo; Zong, Jin; Feng, Junshu

    2017-01-01

    Pumped storage is an effective solution to deal with the emergency reserve shortage, renewable energy accommodating and peak-shaving problems in ultra-high voltage (UHV) transmission receiving-end grids. However, governments and public opinion in China tend to evaluate the operational effectiveness of pumped storage using annual utilization hour, which may result in unreasonable and unnecessary dispatch of pumped storage. This paper built an operational adaptability evaluation index system for pumped storage in UHV-receiving end grids from three aspects: security insurance, peak-shaving and renewable energy accommodating, which can provide a comprehensive and objective way to evaluate the operational performance of a pumped storage station.

  16. Parallel computation of three-dimensional flows using overlapping grids with adaptive mesh refinement

    NASA Astrophysics Data System (ADS)

    Henshaw, William D.; Schwendeman, Donald W.

    2008-08-01

    This paper describes an approach for the numerical solution of time-dependent partial differential equations in complex three-dimensional domains. The domains are represented by overlapping structured grids, and block-structured adaptive mesh refinement (AMR) is employed to locally increase the grid resolution. In addition, the numerical method is implemented on parallel distributed-memory computers using a domain-decomposition approach. The implementation is flexible so that each base grid within the overlapping grid structure and its associated refinement grids can be independently partitioned over a chosen set of processors. A modified bin-packing algorithm is used to specify the partition for each grid so that the computational work is evenly distributed amongst the processors. All components of the AMR algorithm such as error estimation, regridding, and interpolation are performed in parallel. The parallel time-stepping algorithm is illustrated for initial-boundary-value problems involving a linear advection-diffusion equation and the (nonlinear) reactive Euler equations. Numerical results are presented for both equations to demonstrate the accuracy and correctness of the parallel approach. Exact solutions of the advection-diffusion equation are constructed, and these are used to check the corresponding numerical solutions for a variety of tests involving different overlapping grids, different numbers of refinement levels and refinement ratios, and different numbers of processors. The problem of planar shock diffraction by a sphere is considered as an illustration of the numerical approach for the Euler equations, and a problem involving the initiation of a detonation from a hot spot in a T-shaped pipe is considered to demonstrate the numerical approach for the reactive case. For both problems, the accuracy of the numerical solutions is assessed quantitatively through an estimation of the errors from a grid convergence study. The parallel performance of the

  17. Parallel Computation of Three-Dimensional Flows using Overlapping Grids with Adaptive Mesh Refinement

    SciTech Connect

    Henshaw, W; Schwendeman, D

    2007-11-15

    This paper describes an approach for the numerical solution of time-dependent partial differential equations in complex three-dimensional domains. The domains are represented by overlapping structured grids, and block-structured adaptive mesh refinement (AMR) is employed to locally increase the grid resolution. In addition, the numerical method is implemented on parallel distributed-memory computers using a domain-decomposition approach. The implementation is flexible so that each base grid within the overlapping grid structure and its associated refinement grids can be independently partitioned over a chosen set of processors. A modified bin-packing algorithm is used to specify the partition for each grid so that the computational work is evenly distributed amongst the processors. All components of the AMR algorithm such as error estimation, regridding, and interpolation are performed in parallel. The parallel time-stepping algorithm is illustrated for initial-boundary-value problems involving a linear advection-diffusion equation and the (nonlinear) reactive Euler equations. Numerical results are presented for both equations to demonstrate the accuracy and correctness of the parallel approach. Exact solutions of the advection-diffusion equation are constructed, and these are used to check the corresponding numerical solutions for a variety of tests involving different overlapping grids, different numbers of refinement levels and refinement ratios, and different numbers of processors. The problem of planar shock diffraction by a sphere is considered as an illustration of the numerical approach for the Euler equations, and a problem involving the initiation of a detonation from a hot spot in a T-shaped pipe is considered to demonstrate the numerical approach for the reactive case. For both problems, the solutions are shown to be well resolved on the finest grid. The parallel performance of the approach is examined in detail for the shock diffraction problem.

  18. The implementation of the graphics of program EAGLE: A numerical grid generation code on NASA Langley SNS computer system

    NASA Technical Reports Server (NTRS)

    Houston, Johnny L.

    1989-01-01

    Program EAGLE (Eglin Arbitrary Geometry Implicit Euler) Numerical Grid Generation System is a composite (multi-block) algebraic or elliptic grid generation system designed to discretize the domain in and/or around any arbitrarily shaped three dimensional regions. This system combines a boundary conforming surface generation scheme and includes plotting routines designed to take full advantage of the DISSPLA Graphics Package (Version 9.0). Program EAGLE is written to compile and execute efficiently on any Cray machine with or without solid state disk (SSD) devices. Also, the code uses namelist inputs which are supported by all Cray machines using the FORTRAN compiler CFT77. The namelist inputs makes it easier for the user to understand the inputs and operation of Program EAGLE. EAGLE's numerical grid generator is constructed in the following form: main program, EGG (executive routine); subroutine SURFAC (surface generation routine); subroutine GRID (grid generation routine); and subroutine GRDPLOT (grid plotting routines). The EAGLE code was modified to use on the NASA-LaRC SNS computer (Cray 2S) system. During the modification a conversion program was developed for the output data of EAGLE's subroutine GRID to permit the data to be graphically displayed by IRIS workstations, using Plot3D. The code of program EAGLE was modified to make operational subroutine GRDPLOT (using DI-3000 Graphics Software Packages) on the NASA-LaRC SNS Computer System. How to implement graphically, the output data of subroutine GRID was determined on any NASA-LaRC graphics terminal that has access to the SNS Computer System DI-300 Graphics Software Packages. A Quick Reference User Guide was developed for the use of program EAGLE on the NASA-LaRC SNS Computer System. One or more application program(s) was illustrated using program EAGLE on the NASA LaRC SNS Computer System, with emphasis on graphics illustrations.

  19. COLLABORATIVE RESEARCH: CONTINUOUS DYNAMIC GRID ADAPTATION IN A GLOBAL ATMOSPHERIC MODEL: APPLICATION AND REFINEMENT

    SciTech Connect

    Gutowski, William J.; Prusa, Joseph M.; Smolarkiewicz, Piotr K.

    2012-05-08

    This project had goals of advancing the performance capabilities of the numerical general circulation model EULAG and using it to produce a fully operational atmospheric global climate model (AGCM) that can employ either static or dynamic grid stretching for targeted phenomena. The resulting AGCM combined EULAG's advanced dynamics core with the "physics" of the NCAR Community Atmospheric Model (CAM). Effort discussed below shows how we improved model performance and tested both EULAG and the coupled CAM-EULAG in several ways to demonstrate the grid stretching and ability to simulate very well a wide range of scales, that is, multi-scale capability. We leveraged our effort through interaction with an international EULAG community that has collectively developed new features and applications of EULAG, which we exploited for our own work summarized here. Overall, the work contributed to over 40 peer-reviewed publications and over 70 conference/workshop/seminar presentations, many of them invited. 3a. EULAG Advances EULAG is a non-hydrostatic, parallel computational model for all-scale geophysical flows. EULAG's name derives from its two computational options: EULerian (flux form) or semi-LAGrangian (advective form). The model combines nonoscillatory forward-in-time (NFT) numerical algorithms with a robust elliptic Krylov solver. A signature feature of EULAG is that it is formulated in generalized time-dependent curvilinear coordinates. In particular, this enables grid adaptivity. In total, these features give EULAG novel advantages over many existing dynamical cores. For EULAG itself, numerical advances included refining boundary conditions and filters for optimizing model performance in polar regions. We also added flexibility to the model's underlying formulation, allowing it to work with the pseudo-compressible equation set of Durran in addition to EULAG's standard anelastic formulation. Work in collaboration with others also extended the demonstrated range of

  20. An adaptive grid/Navier-Stokes methodology for the calculation of nozzle afterbody base flows with a supersonic freestream

    NASA Technical Reports Server (NTRS)

    Williams, Morgan; Lim, Dennis; Ungewitter, Ronald

    1993-01-01

    This paper describes an adaptive grid method for base flows in a supersonic freestream. The method is based on the direct finite-difference statement of the equidistribution principle. The weighting factor is a combination of the Mach number, density, and velocity first-derivative gradients in the radial direction. Two key ideas of the method are to smooth the weighting factor by using a type of implicit smoothing and to allow boundary points to move in the grid adaptation process. An AGARD nozzle afterbody base flow configuration is used to demonstrate the performance of the adaptive grid methodology. Computed base pressures are compared to experimental data. The adapted grid solutions offer a dramatic improvement in base pressure prediction compared to solutions computed on a nonadapted grid. A total-variation-diminishing (TVD) Navier-Stokes scheme is used to solve the governing flow equations.

  1. Parallel Domain Connectivity Algorithm for Unsteady Flow Computations using Overlapping and Adaptive Grids

    DTIC Science & Technology

    2010-01-01

    ARC3DC code employs third-order temporal discretizations using a multi-stage Runge – Kutta time-stepping framework and is capable of up to fifth-order...lean cache-friendly data structure and flow solution procedures for isotropic Carte- sian grids and (2) explicit time stepping (using 3-stage Runge ...fringes and holes (termed hole-cutting) can be done in one of two ways, explicitly or implicitly. Explicit hole cutting means the hole boundaries are

  2. Euler technology assessment for preliminary aircraft design employing OVERFLOW code with multiblock structured-grid method

    NASA Technical Reports Server (NTRS)

    Treiber, David A.; Muilenburg, Dennis A.

    1995-01-01

    The viability of applying a state-of-the-art Euler code to calculate the aerodynamic forces and moments through maximum lift coefficient for a generic sharp-edge configuration is assessed. The OVERFLOW code, a method employing overset (Chimera) grids, was used to conduct mesh refinement studies, a wind-tunnel wall sensitivity study, and a 22-run computational matrix of flow conditions, including sideslip runs and geometry variations. The subject configuration was a generic wing-body-tail geometry with chined forebody, swept wing leading-edge, and deflected part-span leading-edge flap. The analysis showed that the Euler method is adequate for capturing some of the non-linear aerodynamic effects resulting from leading-edge and forebody vortices produced at high angle-of-attack through C(sub Lmax). Computed forces and moments, as well as surface pressures, match well enough useful preliminary design information to be extracted. Vortex burst effects and vortex interactions with the configuration are also investigated.

  3. The Volume Grid Manipulator (VGM): A Grid Reusability Tool

    NASA Technical Reports Server (NTRS)

    Alter, Stephen J.

    1997-01-01

    This document is a manual describing how to use the Volume Grid Manipulation (VGM) software. The code is specifically designed to alter or manipulate existing surface and volume structured grids to improve grid quality through the reduction of grid line skewness, removal of negative volumes, and adaption of surface and volume grids to flow field gradients. The software uses a command language to perform all manipulations thereby offering the capability of executing multiple manipulations on a single grid during an execution of the code. The command language can be input to the VGM code by a UNIX style redirected file, or interactively while the code is executing. The manual consists of 14 sections. The first is an introduction to grid manipulation; where it is most applicable and where the strengths of such software can be utilized. The next two sections describe the memory management and the manipulation command language. The following 8 sections describe simple and complex manipulations that can be used in conjunction with one another to smooth, adapt, and reuse existing grids for various computations. These are accompanied by a tutorial section that describes how to use the commands and manipulations to solve actual grid generation problems. The last two sections are a command reference guide and trouble shooting sections to aid in the use of the code as well as describe problems associated with generated scripts for manipulation control.

  4. Wing tip vortex calculations with an unstructured adaptive-grid Euler solver

    NASA Technical Reports Server (NTRS)

    Strawn, Roger C.

    1991-01-01

    A solution-adaptive grid method has been developed for computing tip-vortex flowfields around rectangular wings. This method uses subdivision in order to locally refine the grid in regions with high vorticity. Two different flow solvers are used. Each solves the three-dimensional Euler equations on unstructured grids. Computed results are compared to experimentally measured surface pressures and vortex velocities on a NACA 0015 rectangular wing. Predicted results for surface pressures and integrated lift agree well with the experimental data. The predicted size of the rotational vortex core is larger than the experimentally-measured value and the peak velocities are less. This discrepancy appears to be caused by deficiencies in the inviscid Euler-equation model. This model cannot capture the complex viscous effects at the tip that determine the detailed structure of the resulting vortex. In spite of this limitation, the present Euler unstructured adaptive-grid method demonstrates the ability to convert vortical flows with low numerical diffusion. Applications for modeling helicopter rotor wake systems are discussed.

  5. Adaptive Distributed Video Coding with Correlation Estimation using Expectation Propagation

    PubMed Central

    Cui, Lijuan; Wang, Shuang; Jiang, Xiaoqian; Cheng, Samuel

    2013-01-01

    Distributed video coding (DVC) is rapidly increasing in popularity by the way of shifting the complexity from encoder to decoder, whereas no compression performance degrades, at least in theory. In contrast with conventional video codecs, the inter-frame correlation in DVC is explored at decoder based on the received syndromes of Wyner-Ziv (WZ) frame and side information (SI) frame generated from other frames available only at decoder. However, the ultimate decoding performances of DVC are based on the assumption that the perfect knowledge of correlation statistic between WZ and SI frames should be available at decoder. Therefore, the ability of obtaining a good statistical correlation estimate is becoming increasingly important in practical DVC implementations. Generally, the existing correlation estimation methods in DVC can be classified into two main types: pre-estimation where estimation starts before decoding and on-the-fly (OTF) estimation where estimation can be refined iteratively during decoding. As potential changes between frames might be unpredictable or dynamical, OTF estimation methods usually outperforms pre-estimation techniques with the cost of increased decoding complexity (e.g., sampling methods). In this paper, we propose a low complexity adaptive DVC scheme using expectation propagation (EP), where correlation estimation is performed OTF as it is carried out jointly with decoding of the factor graph-based DVC code. Among different approximate inference methods, EP generally offers better tradeoff between accuracy and complexity. Experimental results show that our proposed scheme outperforms the benchmark state-of-the-art DISCOVER codec and other cases without correlation tracking, and achieves comparable decoding performance but with significantly low complexity comparing with sampling method. PMID:23750314

  6. Adaptive Distributed Video Coding with Correlation Estimation using Expectation Propagation.

    PubMed

    Cui, Lijuan; Wang, Shuang; Jiang, Xiaoqian; Cheng, Samuel

    2012-10-15

    Distributed video coding (DVC) is rapidly increasing in popularity by the way of shifting the complexity from encoder to decoder, whereas no compression performance degrades, at least in theory. In contrast with conventional video codecs, the inter-frame correlation in DVC is explored at decoder based on the received syndromes of Wyner-Ziv (WZ) frame and side information (SI) frame generated from other frames available only at decoder. However, the ultimate decoding performances of DVC are based on the assumption that the perfect knowledge of correlation statistic between WZ and SI frames should be available at decoder. Therefore, the ability of obtaining a good statistical correlation estimate is becoming increasingly important in practical DVC implementations. Generally, the existing correlation estimation methods in DVC can be classified into two main types: pre-estimation where estimation starts before decoding and on-the-fly (OTF) estimation where estimation can be refined iteratively during decoding. As potential changes between frames might be unpredictable or dynamical, OTF estimation methods usually outperforms pre-estimation techniques with the cost of increased decoding complexity (e.g., sampling methods). In this paper, we propose a low complexity adaptive DVC scheme using expectation propagation (EP), where correlation estimation is performed OTF as it is carried out jointly with decoding of the factor graph-based DVC code. Among different approximate inference methods, EP generally offers better tradeoff between accuracy and complexity. Experimental results show that our proposed scheme outperforms the benchmark state-of-the-art DISCOVER codec and other cases without correlation tracking, and achieves comparable decoding performance but with significantly low complexity comparing with sampling method.

  7. An adaptive grid for graph-based segmentation in retinal OCT

    PubMed Central

    Lang, Andrew; Carass, Aaron; Calabresi, Peter A.; Ying, Howard S.; Prince, Jerry L.

    2016-01-01

    Graph-based methods for retinal layer segmentation have proven to be popular due to their efficiency and accuracy. These methods build a graph with nodes at each voxel location and use edges connecting nodes to encode the hard constraints of each layer’s thickness and smoothness. In this work, we explore deforming the regular voxel grid to allow adjacent vertices in the graph to more closely follow the natural curvature of the retina. This deformed grid is constructed by fixing node locations based on a regression model of each layer’s thickness relative to the overall retina thickness, thus we generate a subject specific grid. Graph vertices are not at voxel locations, which allows for control over the resolution that the graph represents. By incorporating soft constraints between adjacent nodes, segmentation on this grid will favor smoothly varying surfaces consistent with the shape of the retina. Our final segmentation method then follows our previous work. Boundary probabilities are estimated using a random forest classifier followed by an optimal graph search algorithm on the new adaptive grid to produce a final segmentation. Our method is shown to produce a more consistent segmentation with an overall accuracy of 3.38 μm across all boundaries. PMID:27773959

  8. A user`s guide for BREAKUP: A computer code for parallelizing the overset grid approach

    SciTech Connect

    Barnette, D.W.

    1998-04-01

    In this user`s guide, details for running BREAKUP are discussed. BREAKUP allows the widely used overset grid method to be run in a parallel computer environment to achieve faster run times for computational field simulations over complex geometries. The overset grid method permits complex geometries to be divided into separate components. Each component is then gridded independently. The grids are computationally rejoined in a solver via interpolation coefficients used for grid-to-grid communications of boundary data. Overset grids have been in widespread use for many years on serial computers, and several well-known Navier-Stokes flow solvers have been extensively developed and validated to support their use. One drawback of serial overset grid methods has been the extensive compute time required to update flow solutions one grid at a time. Parallelizing the overset grid method overcomes this limitation by updating each grid or subgrid simultaneously. BREAKUP prepares overset grids for parallel processing by subdividing each overset grid into statically load-balanced subgrids. Two-dimensional examples with sample solutions, and three-dimensional examples, are presented.

  9. New laser driver for physics modeling codes using unstructured 3d grids

    SciTech Connect

    Kaiser, T; Milovich, J L; Prasad, M K; Shestakov, A I

    1999-02-01

    We present a status report on the current state of development, testing and application of a new scheme for laser beam evolution and power deposition on three-dimensional unstructured grids. The scheme is being encapsulated in a C++ library for convenient porting to existing modeling codes. We have added a new ray propagator that is second order in time, allowing rays to refract within computational zones as well as at zone interfaces. In a globally constant free-electron density gradient on a randomized hexahedral mesh,the new integrator produces ray trajectories that agree with analytic results to within machine roundoff. A new method for computing the inverse-bremmstrahlung energy deposition rate that captures its highly non-uniform spatial dependence within a zone has also been added. This allows accurate trajectories without the necessity of sub-stepping in time. Other enhancements (not discussed) include multiple user-configurable beams, computation of the electron oscillation velocity in the laser electric field and energy-deposition accounting. Results of laser-driven simulations are presented in a companion paper.

  10. Adjoint-Based, Three-Dimensional Error Prediction and Grid Adaptation

    NASA Technical Reports Server (NTRS)

    Park, Michael A.

    2002-01-01

    Engineering computational fluid dynamics (CFD) analysis and design applications focus on output functions (e.g., lift, drag). Errors in these output functions are generally unknown and conservatively accurate solutions may be computed. Computable error estimates can offer the possibility to minimize computational work for a prescribed error tolerance. Such an estimate can be computed by solving the flow equations and the linear adjoint problem for the functional of interest. The computational mesh can be modified to minimize the uncertainty of a computed error estimate. This robust mesh-adaptation procedure automatically terminates when the simulation is within a user specified error tolerance. This procedure for estimating and adapting to error in a functional is demonstrated for three-dimensional Euler problems. An adaptive mesh procedure that links to a Computer Aided Design (CAD) surface representation is demonstrated for wing, wing-body, and extruded high lift airfoil configurations. The error estimation and adaptation procedure yielded corrected functions that are as accurate as functions calculated on uniformly refined grids with ten times as many grid points.

  11. Staggered grid lagrangian method with local structured adaptive mesh refinement for modeling shock hydrodynamics

    SciTech Connect

    Anderson, R W; Pember, R B; Elliot, N S

    2000-09-26

    A new method for the solution of the unsteady Euler equations has been developed. The method combines staggered grid Lagrangian techniques with structured local adaptive mesh refinement (AMR). This method is a precursor to a more general adaptive arbitrary Lagrangian Eulerian (ALE-AMR) algorithm under development, which will facilitate the solution of problems currently at and beyond the boundary of soluble problems by traditional ALE methods by focusing computational resources where they are required. Many of the core issues involved in the development of the ALE-AMR method hinge upon the integration of AMR with a Lagrange step, which is the focus of the work described here. The novel components of the method are mainly driven by the need to reconcile traditional AMR techniques, which are typically employed on stationary meshes with cell-centered quantities, with the staggered grids and grid motion employed by Lagrangian methods. These new algorithmic components are first developed in one dimension and are then generalized to two dimensions. Solutions of several model problems involving shock hydrodynamics are presented and discussed.

  12. A Hyperspherical Adaptive Sparse-Grid Method for High-Dimensional Discontinuity Detection

    DOE PAGES

    Zhang, Guannan; Webster, Clayton G.; Gunzburger, Max D.; ...

    2015-06-24

    This study proposes and analyzes a hyperspherical adaptive hierarchical sparse-grid method for detecting jump discontinuities of functions in high-dimensional spaces. The method is motivated by the theoretical and computational inefficiencies of well-known adaptive sparse-grid methods for discontinuity detection. Our novel approach constructs a function representation of the discontinuity hypersurface of an N-dimensional discontinuous quantity of interest, by virtue of a hyperspherical transformation. Then, a sparse-grid approximation of the transformed function is built in the hyperspherical coordinate system, whose value at each point is estimated by solving a one-dimensional discontinuity detection problem. Due to the smoothness of the hypersurface, the newmore » technique can identify jump discontinuities with significantly reduced computational cost, compared to existing methods. In addition, hierarchical acceleration techniques are also incorporated to further reduce the overall complexity. Rigorous complexity analyses of the new method are provided as are several numerical examples that illustrate the effectiveness of the approach.« less

  13. A hyper-spherical adaptive sparse-grid method for high-dimensional discontinuity detection

    SciTech Connect

    Zhang, Guannan; Webster, Clayton G; Gunzburger, Max D; Burkardt, John V

    2014-03-01

    This work proposes and analyzes a hyper-spherical adaptive hi- erarchical sparse-grid method for detecting jump discontinuities of functions in high-dimensional spaces is proposed. The method is motivated by the the- oretical and computational inefficiencies of well-known adaptive sparse-grid methods for discontinuity detection. Our novel approach constructs a func- tion representation of the discontinuity hyper-surface of an N-dimensional dis- continuous quantity of interest, by virtue of a hyper-spherical transformation. Then, a sparse-grid approximation of the transformed function is built in the hyper-spherical coordinate system, whose value at each point is estimated by solving a one-dimensional discontinuity detection problem. Due to the smooth- ness of the hyper-surface, the new technique can identify jump discontinuities with significantly reduced computational cost, compared to existing methods. Moreover, hierarchical acceleration techniques are also incorporated to further reduce the overall complexity. Rigorous error estimates and complexity anal- yses of the new method are provided as are several numerical examples that illustrate the effectiveness of the approach.

  14. Was Wright right? The canonical genetic code is an empirical example of an adaptive peak in nature; deviant genetic codes evolved using adaptive bridges.

    PubMed

    Seaborg, David M

    2010-08-01

    The canonical genetic code is on a sub-optimal adaptive peak with respect to its ability to minimize errors, and is close to, but not quite, optimal. This is demonstrated by the near-total adjacency of synonymous codons, the similarity of adjacent codons, and comparisons of frequency of amino acid usage with number of codons in the code for each amino acid. As a rare empirical example of an adaptive peak in nature, it shows adaptive peaks are real, not merely theoretical. The evolution of deviant genetic codes illustrates how populations move from a lower to a higher adaptive peak. This is done by the use of "adaptive bridges," neutral pathways that cross over maladaptive valleys by virtue of masking of the phenotypic expression of some maladaptive aspects in the genotype. This appears to be the general mechanism by which populations travel from one adaptive peak to another. There are multiple routes a population can follow to cross from one adaptive peak to another. These routes vary in the probability that they will be used, and this probability is determined by the number and nature of the mutations that happen along each of the routes. A modification of the depiction of adaptive landscapes showing genetic distances and probabilities of travel along their multiple possible routes would throw light on this important concept.

  15. Damping of spurious numerical reflections off of coarse-fine adaptive mesh refinement grid boundaries

    NASA Astrophysics Data System (ADS)

    Chilton, Sven; Colella, Phillip

    2010-11-01

    Adaptive mesh refinement (AMR) is an efficient technique for solving systems of partial differential equations numerically. The underlying algorithm determines where and when a base spatial and temporal grid must be resolved further in order to achieve the desired precision and accuracy in the numerical solution. However, propagating wave solutions prove problematic for AMR. In systems with low degrees of dissipation (e.g. the Maxwell-Vlasov system) a wave traveling from a finely resolved region into a coarsely resolved region encounters a numerical impedance mismatch, resulting in spurious reflections off of the coarse-fine grid boundary. These reflected waves then become trapped inside the fine region. Here, we present a scheme for damping these spurious reflections. We demonstrate its application to the scalar wave equation and an implementation for Maxwell's Equations. We also discuss a possible extension to the Maxwell-Vlasov system.

  16. Enhancing adaptive sparse grid approximations and improving refinement strategies using adjoint-based a posteriori error estimates

    DOE PAGES

    Jakeman, J. D.; Wildey, T.

    2015-01-01

    In this paper we present an algorithm for adaptive sparse grid approximations of quantities of interest computed from discretized partial differential equations. We use adjoint-based a posteriori error estimates of the interpolation error in the sparse grid to enhance the sparse grid approximation and to drive adaptivity. We show that utilizing these error estimates provides significantly more accurate functional values for random samples of the sparse grid approximation. We also demonstrate that alternative refinement strategies based upon a posteriori error estimates can lead to further increases in accuracy in the approximation over traditional hierarchical surplus based strategies. Throughout this papermore » we also provide and test a framework for balancing the physical discretization error with the stochastic interpolation error of the enhanced sparse grid approximation.« less

  17. Enhancing adaptive sparse grid approximations and improving refinement strategies using adjoint-based a posteriori error estimates

    SciTech Connect

    Jakeman, J. D.; Wildey, T.

    2015-01-01

    In this paper we present an algorithm for adaptive sparse grid approximations of quantities of interest computed from discretized partial differential equations. We use adjoint-based a posteriori error estimates of the interpolation error in the sparse grid to enhance the sparse grid approximation and to drive adaptivity. We show that utilizing these error estimates provides significantly more accurate functional values for random samples of the sparse grid approximation. We also demonstrate that alternative refinement strategies based upon a posteriori error estimates can lead to further increases in accuracy in the approximation over traditional hierarchical surplus based strategies. Throughout this paper we also provide and test a framework for balancing the physical discretization error with the stochastic interpolation error of the enhanced sparse grid approximation.

  18. Parallel level-set methods on adaptive tree-based grids

    NASA Astrophysics Data System (ADS)

    Mirzadeh, Mohammad; Guittet, Arthur; Burstedde, Carsten; Gibou, Frederic

    2016-10-01

    We present scalable algorithms for the level-set method on dynamic, adaptive Quadtree and Octree Cartesian grids. The algorithms are fully parallelized and implemented using the MPI standard and the open-source p4est library. We solve the level set equation with a semi-Lagrangian method which, similar to its serial implementation, is free of any time-step restrictions. This is achieved by introducing a scalable global interpolation scheme on adaptive tree-based grids. Moreover, we present a simple parallel reinitialization scheme using the pseudo-time transient formulation. Both parallel algorithms scale on the Stampede supercomputer, where we are currently using up to 4096 CPU cores, the limit of our current account. Finally, a relevant application of the algorithms is presented in modeling a crystallization phenomenon by solving a Stefan problem, illustrating a level of detail that would be impossible to achieve without a parallel adaptive strategy. We believe that the algorithms presented in this article will be of interest and useful to researchers working with the level-set framework and modeling multi-scale physics in general.

  19. Adaptive Hierarchical Voltage Control of a DFIG-Based Wind Power Plant for a Grid Fault

    SciTech Connect

    Kim, Jinho; Muljadi, Eduard; Park, Jung-Wook; Kang, Yong Cheol

    2016-11-01

    This paper proposes an adaptive hierarchical voltage control scheme of a doubly-fed induction generator (DFIG)-based wind power plant (WPP) that can secure more reserve of reactive power (Q) in the WPP against a grid fault. To achieve this, each DFIG controller employs an adaptive reactive power to voltage (Q-V) characteristic. The proposed adaptive Q-V characteristic is temporally modified depending on the available Q capability of a DFIG; it is dependent on the distance from a DFIG to the point of common coupling (PCC). The proposed characteristic secures more Q reserve in the WPP than the fixed one. Furthermore, it allows DFIGs to promptly inject up to the Q limit, thereby improving the PCC voltage support. To avert an overvoltage after the fault clearance, washout filters are implemented in the WPP and DFIG controllers; they can prevent a surplus Q injection after the fault clearance by eliminating the accumulated values in the proportional-integral controllers of both controllers during the fault. Test results demonstrate that the scheme can improve the voltage support capability during the fault and suppress transient overvoltage after the fault clearance under scenarios of various system and fault conditions; therefore, it helps ensure grid resilience by supporting the voltage stability.

  20. Adaptive finite-volume WENO schemes on dynamically redistributed grids for compressible Euler equations

    NASA Astrophysics Data System (ADS)

    Pathak, Harshavardhana S.; Shukla, Ratnesh K.

    2016-08-01

    A high-order adaptive finite-volume method is presented for simulating inviscid compressible flows on time-dependent redistributed grids. The method achieves dynamic adaptation through a combination of time-dependent mesh node clustering in regions characterized by strong solution gradients and an optimal selection of the order of accuracy and the associated reconstruction stencil in a conservative finite-volume framework. This combined approach maximizes spatial resolution in discontinuous regions that require low-order approximations for oscillation-free shock capturing. Over smooth regions, high-order discretization through finite-volume WENO schemes minimizes numerical dissipation and provides excellent resolution of intricate flow features. The method including the moving mesh equations and the compressible flow solver is formulated entirely on a transformed time-independent computational domain discretized using a simple uniform Cartesian mesh. Approximations for the metric terms that enforce discrete geometric conservation law while preserving the fourth-order accuracy of the two-point Gaussian quadrature rule are developed. Spurious Cartesian grid induced shock instabilities such as carbuncles that feature in a local one-dimensional contact capturing treatment along the cell face normals are effectively eliminated through upwind flux calculation using a rotated Hartex-Lax-van Leer contact resolving (HLLC) approximate Riemann solver for the Euler equations in generalized coordinates. Numerical experiments with the fifth and ninth-order WENO reconstructions at the two-point Gaussian quadrature nodes, over a range of challenging test cases, indicate that the redistributed mesh effectively adapts to the dynamic flow gradients thereby improving the solution accuracy substantially even when the initial starting mesh is non-adaptive. The high adaptivity combined with the fifth and especially the ninth-order WENO reconstruction allows remarkably sharp capture of

  1. Time-dependent grid adaptation for meshes of triangles and tetrahedra

    NASA Technical Reports Server (NTRS)

    Rausch, Russ D.

    1993-01-01

    This paper presents in viewgraph form a method of optimizing grid generation for unsteady CFD flow calculations that distributes the numerical error evenly throughout the mesh. Adaptive meshing is used to locally enrich in regions of relatively large errors and to locally coarsen in regions of relatively small errors. The enrichment/coarsening procedures are robust for isotropic cells; however, enrichment of high aspect ratio cells may fail near boundary surfaces with relatively large curvature. The enrichment indicator worked well for the cases shown, but in general requires user supervision for a more efficient solution.

  2. Evaluating two sparse grid surrogates and two adaptation criteria for groundwater Bayesian uncertainty quantification

    NASA Astrophysics Data System (ADS)

    Zeng, Xiankui; Ye, Ming; Burkardt, John; Wu, Jichun; Wang, Dong; Zhu, Xiaobin

    2016-04-01

    Sparse grid (SG) stochastic collocation methods have been recently used to build accurate but cheap-to-run surrogates for groundwater models to reduce the computational burden of Bayesian uncertainty analysis. The surrogates can be built for either a log-likelihood function or state variables such as hydraulic head and solute concentration. Using a synthetic groundwater flow model, this study evaluates the log-likelihood and head surrogates in terms of the computational cost of building them, the accuracy of the surrogates, and the accuracy of the distributions of model parameters and predictions obtained using the surrogates. The head surrogates outperform the log-likelihood surrogates for the following four reasons: (1) the shape of the head response surface is smoother than that of the log-likelihood response surface in parameter space, (2) the head variation is smaller than the log-likelihood variation in parameter space, (3) the interpolation error of the head surrogates does not accumulate to be larger than the interpolation error of the log-likelihood surrogates, and (4) the model simulations needed for building one head surrogate can be recycled for building others. For both log-likelihood and head surrogates, adaptive sparse grids are built using two indicators: absolute error and relative error. The adaptive head surrogates are insensitive to the error indicators, because the ratio between the two indicators is hydraulic head, which has small variation in the parameter space. The adaptive log-likelihood surrogates based on the relative error indicators outperform those based on the absolute error indicators, because adaptation based on the relative error indicator puts more sparse-grid nodes in the areas in the parameter space where the log-likelihood is high. While our numerical study suggests building state-variable surrogates and using the relative error indicator for building log-likelihood surrogates, selecting appropriate type of surrogates and

  3. Fair Energy Scheduling for Vehicle-to-Grid Networks Using Adaptive Dynamic Programming.

    PubMed

    Xie, Shengli; Zhong, Weifeng; Xie, Kan; Yu, Rong; Zhang, Yan

    2016-08-01

    Research on the smart grid is being given enormous supports worldwide due to its great significance in solving environmental and energy crises. Electric vehicles (EVs), which are powered by clean energy, are adopted increasingly year by year. It is predictable that the huge charge load caused by high EV penetration will have a considerable impact on the reliability of the smart grid. Therefore, fair energy scheduling for EV charge and discharge is proposed in this paper. By using the vehicle-to-grid technology, the scheduler controls the electricity loads of EVs considering fairness in the residential distribution network. We propose contribution-based fairness, in which EVs with high contributions have high priorities to obtain charge energy. The contribution value is defined by both the charge/discharge energy and the timing of the action. EVs can achieve higher contribution values when discharging during the load peak hours. However, charging during this time will decrease the contribution values seriously. We formulate the fair energy scheduling problem as an infinite-horizon Markov decision process. The methodology of adaptive dynamic programming is employed to maximize the long-term fairness by processing online network training. The numerical results illustrate that the proposed EV energy scheduling is able to mitigate and flatten the peak load in the distribution network. Furthermore, contribution-based fairness achieves a fast recovery of EV batteries that have deeply discharged and guarantee fairness in the full charge time of all EVs.

  4. A numerical study of 2D detonation waves with adaptive finite volume methods on unstructured grids

    NASA Astrophysics Data System (ADS)

    Hu, Guanghui

    2017-02-01

    In this paper, a framework of adaptive finite volume solutions for the reactive Euler equations on unstructured grids is proposed. The main ingredients of the algorithm include a second order total variation diminishing Runge-Kutta method for temporal discretization, and the finite volume method with piecewise linear solution reconstruction of the conservative variables for the spatial discretization in which the least square method is employed for the reconstruction, and weighted essentially nonoscillatory strategy is used to restrain the potential numerical oscillation. To resolve the high demanding on the computational resources due to the stiffness of the system caused by the reaction term and the shock structure in the solutions, the h-adaptive method is introduced. OpenMP parallelization of the algorithm is also adopted to further improve the efficiency of the implementation. Several one and two dimensional benchmark tests on the ZND model are studied in detail, and numerical results successfully show the effectiveness of the proposed method.

  5. Parallel grid library with adaptive mesh refinement for development of highly scalable simulations

    NASA Astrophysics Data System (ADS)

    Honkonen, I.; von Alfthan, S.; Sandroos, A.; Janhunen, P.; Palmroth, M.

    2012-04-01

    As the single CPU core performance is saturating while the number of cores in the fastest supercomputers increases exponentially, the parallel performance of simulations on distributed memory machines is crucial. At the same time, utilizing efficiently the large number of available cores presents a challenge, especially in simulations with run-time adaptive mesh refinement. We have developed a generic grid library (dccrg) aimed at finite volume simulations that is easy to use and scales well up to tens of thousands of cores. The grid has several attractive features: It 1) allows an arbitrary C++ class or structure to be used as cell data; 2) provides a simple interface for adaptive mesh refinement during a simulation; 3) encapsulates the details of MPI communication when updating the data of neighboring cells between processes; and 4) provides a simple interface to run-time load balancing, e.g. domain decomposition, through the Zoltan library. Dccrg is freely available for anyone to use, study and modify under the GNU Lesser General Public License v3. We will present the implementation of dccrg, simple and advanced usage examples and scalability results on various supercomputers and problems.

  6. Parallelization of GeoClaw code for modeling geophysical flows with adaptive mesh refinement on many-core systems

    USGS Publications Warehouse

    Zhang, S.; Yuen, D.A.; Zhu, A.; Song, S.; George, D.L.

    2011-01-01

    We parallelized the GeoClaw code on one-level grid using OpenMP in March, 2011 to meet the urgent need of simulating tsunami waves at near-shore from Tohoku 2011 and achieved over 75% of the potential speed-up on an eight core Dell Precision T7500 workstation [1]. After submitting that work to SC11 - the International Conference for High Performance Computing, we obtained an unreleased OpenMP version of GeoClaw from David George, who developed the GeoClaw code as part of his PH.D thesis. In this paper, we will show the complementary characteristics of the two approaches used in parallelizing GeoClaw and the speed-up obtained by combining the advantage of each of the two individual approaches with adaptive mesh refinement (AMR), demonstrating the capabilities of running GeoClaw efficiently on many-core systems. We will also show a novel simulation of the Tohoku 2011 Tsunami waves inundating the Sendai airport and Fukushima Nuclear Power Plants, over which the finest grid distance of 20 meters is achieved through a 4-level AMR. This simulation yields quite good predictions about the wave-heights and travel time of the tsunami waves. ?? 2011 IEEE.

  7. An Adaptive Integration Model of Vector Polyline to DEM Data Based on Spherical Degeneration Quadtree Grids

    NASA Astrophysics Data System (ADS)

    Zhao, X. S.; Wang, J. J.; Yuan, Z. Y.; Gao, Y.

    2013-10-01

    Traditional geometry-based approach can maintain the characteristics of vector data. However, complex interpolation calculations limit its applications in high resolution and multi-source spatial data integration at spherical scale in digital earth systems. To overcome this deficiency, an adaptive integration model of vector polyline and spherical DEM is presented. Firstly, Degenerate Quadtree Grid (DQG) which is one of the partition models for global discrete grids, is selected as a basic framework for the adaptive integration model. Secondly, a novel shift algorithm is put forward based on DQG proximity search. The main idea of shift algorithm is that the vector node in a DQG cell moves to the cell corner-point when the displayed area of the cell is smaller or equal to a pixel of screen in order to find a new vector polyline approximate to the original one, which avoids lots of interpolation calculations and achieves seamless integration. Detailed operation steps are elaborated and the complexity of algorithm is analyzed. Thirdly, a prototype system has been developed by using VC++ language and OpenGL 3D API. ASTER GDEM data and DCW roads data sets of Jiangxi province in China are selected to evaluate the performance. The result shows that time consumption of shift algorithm decreased about 76% than that of geometry-based approach. Analysis on the mean shift error from different dimensions has been implemented. In the end, the conclusions and future works in the integration of vector data and DEM based on discrete global grids are also given.

  8. APSARA: A multi-dimensional unsplit fourth-order explicit Eulerian hydrodynamics code for arbitrary curvilinear grids

    NASA Astrophysics Data System (ADS)

    Wongwathanarat, A.; Grimm-Strele, H.; Müller, E.

    2016-10-01

    We present a new fourth-order, finite-volume hydrodynamics code named Apsara. The code employs a high-order, finite-volume method for mapped coordinates with extensions for nonlinear hyperbolic conservation laws. Apsara can handle arbitrary structured curvilinear meshes in three spatial dimensions. The code has successfully passed several hydrodynamic test problems, including the advection of a Gaussian density profile and a nonlinear vortex and the propagation of linear acoustic waves. For these test problems, Apsara produces fourth-order accurate results in case of smooth grid mappings. The order of accuracy is reduced to first-order when using the nonsmooth circular grid mapping. When applying the high-order method to simulations of low-Mach number flows, for example, the Gresho vortex and the Taylor-Green vortex, we discover that Apsara delivers superior results to codes based on the dimensionally split, piecewise parabolic method (PPM) widely used in astrophysics. Hence, Apsara is a suitable tool for simulating highly subsonic flows in astrophysics. In the first astrophysical application, we perform implicit large eddy simulations (ILES) of anisotropic turbulence in the context of core collapse supernova (CCSN) and obtain results similar to those previously reported.

  9. A Programmable Liquid Collimator for Both Coded Aperture Adaptive Imaging and Multiplexed Compton Scatter Tomography

    DTIC Science & Technology

    2012-03-01

    Assessment of COMSCAN, A Compton Backscatter Imaging Camera , for the One-Sided Non-Destructive Inspection of Aerospace Compo- nents. Technical report...A PROGRAMMABLE LIQUID COLLIMATOR FOR BOTH CODED APERTURE ADAPTIVE IMAGING AND MULTIPLEXED COMPTON SCATTER TOMOGRAPHY THESIS Jack G. M. FitzGerald, 2d...LIQUID COLLIMATOR FOR BOTH CODED APERTURE ADAPTIVE IMAGING AND MULTIPLEXED COMPTON SCATTER TOMOGRAPHY THESIS Presented to the Faculty Department of

  10. Application study of piecewise context-based adaptive binary arithmetic coding combined with modified LZC

    NASA Astrophysics Data System (ADS)

    Su, Yan; Jun, Xie Cheng

    2006-08-01

    An algorithm of combining LZC and arithmetic coding algorithm for image compression is presented and both theory deduction and simulation result prove the correctness and feasibility of the algorithm. According to the characteristic of context-based adaptive binary arithmetic coding and entropy, LZC was modified to cooperate the optimized piecewise arithmetic coding, this algorithm improved the compression ratio without any additional time consumption compared to traditional method.

  11. Adaptive Mesh Refinement Algorithms for Parallel Unstructured Finite Element Codes

    SciTech Connect

    Parsons, I D; Solberg, J M

    2006-02-03

    This project produced algorithms for and software implementations of adaptive mesh refinement (AMR) methods for solving practical solid and thermal mechanics problems on multiprocessor parallel computers using unstructured finite element meshes. The overall goal is to provide computational solutions that are accurate to some prescribed tolerance, and adaptivity is the correct path toward this goal. These new tools will enable analysts to conduct more reliable simulations at reduced cost, both in terms of analyst and computer time. Previous academic research in the field of adaptive mesh refinement has produced a voluminous literature focused on error estimators and demonstration problems; relatively little progress has been made on producing efficient implementations suitable for large-scale problem solving on state-of-the-art computer systems. Research issues that were considered include: effective error estimators for nonlinear structural mechanics; local meshing at irregular geometric boundaries; and constructing efficient software for parallel computing environments.

  12. A solution-adaptive mesh algorithm for dynamic/static refinement of two and three dimensional grids

    NASA Technical Reports Server (NTRS)

    Benson, Rusty A.; Mcrae, D. S.

    1991-01-01

    An adaptive grid algorithm has been developed in two and three dimensions that can be used dynamically with a solver or as part of a grid refinement process. The algorithm employs a transformation from the Cartesian coordinate system to a general coordinate space, which is defined as a parallelepiped in three dimensions. A weighting function, independent for each coordinate direction, is developed that will provide the desired refinement criteria in regions of high solution gradient. The adaptation is performed in the general coordinate space and the new grid locations are returned to the Cartesian space via a simple, one-step inverse mapping. The algorithm for relocation of the mesh points in the parametric space is based on the center of mass for distributed weights. Dynamic solution-adaptive results are presented for laminar flows in two and three dimensions.

  13. Real-space grids and the Octopus code as tools for the development of new simulation approaches for electronic systems

    NASA Astrophysics Data System (ADS)

    Andrade, Xavier; Strubbe, David; De Giovannini, Umberto; Larsen, Ask Hjorth; Oliveira, Micael J. T.; Alberdi-Rodriguez, Joseba; Varas, Alejandro; Theophilou, Iris; Helbig, Nicole; Verstraete, Matthieu J.; Stella, Lorenzo; Nogueira, Fernando; Aspuru-Guzik, Alán; Castro, Alberto; Marques, Miguel A. L.; Rubio, Angel

    Real-space grids are a powerful alternative for the simulation of electronic systems. One of the main advantages of the approach is the flexibility and simplicity of working directly in real space where the different fields are discretized on a grid, combined with competitive numerical performance and great potential for parallelization. These properties constitute a great advantage at the time of implementing and testing new physical models. Based on our experience with the Octopus code, in this article we discuss how the real-space approach has allowed for the recent development of new ideas for the simulation of electronic systems. Among these applications are approaches to calculate response properties, modeling of photoemission, optimal control of quantum systems, simulation of plasmonic systems, and the exact solution of the Schr\\"odinger equation for low-dimensionality systems.

  14. A Freestream-Preserving High-Order Finite-Volume Method for Mapped Grids with Adaptive-Mesh Refinement

    SciTech Connect

    Guzik, S; McCorquodale, P; Colella, P

    2011-12-16

    A fourth-order accurate finite-volume method is presented for solving time-dependent hyperbolic systems of conservation laws on mapped grids that are adaptively refined in space and time. Novel considerations for formulating the semi-discrete system of equations in computational space combined with detailed mechanisms for accommodating the adapting grids ensure that conservation is maintained and that the divergence of a constant vector field is always zero (freestream-preservation property). Advancement in time is achieved with a fourth-order Runge-Kutta method.

  15. The use of the spectral method within the fast adaptive composite grid method

    SciTech Connect

    McKay, S.M.

    1994-12-31

    The use of efficient algorithms for the solution of partial differential equations has been sought for many years. The fast adaptive composite grid (FAC) method combines an efficient algorithm with high accuracy to obtain low cost solutions to partial differential equations. The FAC method achieves fast solution by combining solutions on different grids with varying discretizations and using multigrid like techniques to find fast solution. Recently, the continuous FAC (CFAC) method has been developed which utilizes an analytic solution within a subdomain to iterate to a solution of the problem. This has been shown to achieve excellent results when the analytic solution can be found. The CFAC method will be extended to allow solvers which construct a function for the solution, e.g., spectral and finite element methods. In this discussion, the spectral methods will be used to provide a fast, accurate solution to the partial differential equation. As spectral methods are more accurate than finite difference methods, the ensuing accuracy from this hybrid method outside of the subdomain will be investigated.

  16. An Adaptive Reputation-Based Algorithm for Grid Virtual Organization Formation

    NASA Astrophysics Data System (ADS)

    Cui, Yongrui; Li, Mingchu; Ren, Yizhi; Sakurai, Kouichi

    A novel adaptive reputation-based virtual organization formation is proposed. It restrains the bad performers effectively based on the consideration of the global experience of the evaluator and evaluates the direct trust relation between two grid nodes accurately by consulting the previous trust value rationally. It also consults and improves the reputation evaluation process in PathTrust model by taking account of the inter-organizational trust relationship and combines it with direct and recommended trust in a weighted way, which makes the algorithm more robust against collusion attacks. Additionally, the proposed algorithm considers the perspective of the VO creator and takes required VO services as one of the most important fine-grained evaluation criterion, which makes the algorithm more suitable for constructing VOs in grid environments that include autonomous organizations. Simulation results show that our algorithm restrains the bad performers and resists against fake transaction attacks and badmouth attacks effectively. It provides a clear advantage in the design of a VO infrastructure.

  17. Adaptive-Grid Methods for Phase Field Models of Microstructure Development

    NASA Technical Reports Server (NTRS)

    Provatas, Nikolas; Goldenfeld, Nigel; Dantzig, Jonathan A.

    1999-01-01

    In this work the authors show how the phase field model can be solved in a computationally efficient manner that opens a new large-scale simulational window on solidification physics. Our method uses a finite element, adaptive-grid formulation, and exploits the fact that the phase and temperature fields vary significantly only near the interface. We illustrate how our method allows efficient simulation of phase-field models in very large systems, and verify the predictions of solvability theory at intermediate undercooling. We then present new results at low undercoolings that suggest that solvability theory may not give the correct tip speed in that regime. We model solidification using the phase-field model used by Karma and Rappel.

  18. Adaptive face space coding in congenital prosopagnosia: typical figural aftereffects but abnormal identity aftereffects.

    PubMed

    Palermo, Romina; Rivolta, Davide; Wilson, C Ellie; Jeffery, Linda

    2011-12-01

    People with congenital prosopagnosia (CP) report difficulty recognising faces in everyday life and perform poorly on face recognition tests. Here, we investigate whether impaired adaptive face space coding might contribute to poor face recognition in CP. To pinpoint how adaptation may affect face processing, a group of CPs and matched controls completed two complementary face adaptation tasks: the figural aftereffect, which reflects adaptation to general distortions of shape, and the identity aftereffect, which directly taps the mechanisms involved in the discrimination of different face identities. CPs displayed a typical figural aftereffect, consistent with evidence that they are able to process some shape-based information from faces, e.g., cues to discriminate sex. CPs also demonstrated a significant identity aftereffect. However, unlike controls, CPs impression of the identity of the neutral average face was not significantly shifted by adaptation, suggesting that adaptive coding of identity is abnormal in CP. In sum, CPs show reduced aftereffects but only when the task directly taps the use of face norms used to code individual identity. This finding of a reduced face identity aftereffect in individuals with severe face recognition problems is consistent with suggestions that adaptive coding may have a functional role in face recognition.

  19. Bayesian strong gravitational-lens modelling on adaptive grids: objective detection of mass substructure in Galaxies

    NASA Astrophysics Data System (ADS)

    Vegetti, S.; Koopmans, L. V. E.

    2009-01-01

    We introduce a new adaptive and fully Bayesian grid-based method to model strong gravitational lenses with extended images. The primary goal of this method is to quantify the level of luminous and dark mass substructure in massive galaxies, through their effect on highly magnified arcs and Einstein rings. The method is adaptive on the source plane, where a Delaunay tessellation is defined according to the lens mapping of a regular grid on to the source plane. The Bayesian penalty function allows us to recover the best non-linear potential-model parameters and/or a grid-based potential correction and to objectively quantify the level of regularization for both the source and potential. In addition, we implement a Nested-Sampling technique to quantify the errors on all non-linear mass model parameters - marginalized over all source and regularization parameters - and allow an objective ranking of different potential models in terms of the marginalized evidence. In particular, we are interested in comparing very smooth lens mass models with ones that contain mass substructures. The algorithm has been tested on a range of simulated data sets, created from a model of a realistic lens system. One of the lens systems is characterized by a smooth potential with a power-law density profile, 12 include a Navarro, Frenk and White (NFW) dark matter substructure of different masses and at different positions and one contains two NFW dark substructures with the same mass but with different positions. Reconstruction of the source and lens potential for all of these systems shows the method is able, in a realistic scenario, to identify perturbations with masses >~107Msolar when located on the Einstein ring. For positions both inside and outside of the ring, masses of at least 109Msolar are required (i.e. roughly the Einstein ring of the perturber needs to overlap with that of the main lens). Our method provides a fully novel and objective test of mass substructure in massive

  20. Deficits in context-dependent adaptive coding of reward in schizophrenia

    PubMed Central

    Kirschner, Matthias; Hager, Oliver M; Bischof, Martin; Hartmann-Riemer, Matthias N; Kluge, Agne; Seifritz, Erich; Tobler, Philippe N; Kaiser, Stefan

    2016-01-01

    Theoretical principles of information processing and empirical findings suggest that to efficiently represent all possible rewards in the natural environment, reward-sensitive neurons have to adapt their coding range dynamically to the current reward context. Adaptation ensures that the reward system is most sensitive for the most likely rewards, enabling the system to efficiently represent a potentially infinite range of reward information. A deficit in neural adaptation would prevent precise representation of rewards and could have detrimental effects for an organism’s ability to optimally engage with its environment. In schizophrenia, reward processing is known to be impaired and has been linked to different symptom dimensions. However, despite the fundamental significance of coding reward adaptively, no study has elucidated whether adaptive reward processing is impaired in schizophrenia. We therefore studied patients with schizophrenia (n=27) and healthy controls (n=25), using functional magnetic resonance imaging in combination with a variant of the monetary incentive delay task. Compared with healthy controls, patients with schizophrenia showed less efficient neural adaptation to the current reward context, which leads to imprecise neural representation of reward. Importantly, the deficit correlated with total symptom severity. Our results suggest that some of the deficits in reward processing in schizophrenia might be due to inefficient neural adaptation to the current reward context. Furthermore, because adaptive coding is a ubiquitous feature of the brain, we believe that our findings provide an avenue in defining a general impairment in neural information processing underlying this debilitating disorder. PMID:27430009

  1. Moving Overlapping Grids with Adaptive Mesh Refinement for High-Speed Reactive and Non-reactive Flow

    SciTech Connect

    Henshaw, W D; Schwendeman, D W

    2005-08-30

    We consider the solution of the reactive and non-reactive Euler equations on two-dimensional domains that evolve in time. The domains are discretized using moving overlapping grids. In a typical grid construction, boundary-fitted grids are used to represent moving boundaries, and these grids overlap with stationary background Cartesian grids. Block-structured adaptive mesh refinement (AMR) is used to resolve fine-scale features in the flow such as shocks and detonations. Refinement grids are added to base-level grids according to an estimate of the error, and these refinement grids move with their corresponding base-level grids. The numerical approximation of the governing equations takes place in the parameter space of each component grid which is defined by a mapping from (fixed) parameter space to (moving) physical space. The mapped equations are solved numerically using a second-order extension of Godunov's method. The stiff source term in the reactive case is handled using a Runge-Kutta error-control scheme. We consider cases when the boundaries move according to a prescribed function of time and when the boundaries of embedded bodies move according to the surface stress exerted by the fluid. In the latter case, the Newton-Euler equations describe the motion of the center of mass of the each body and the rotation about it, and these equations are integrated numerically using a second-order predictor-corrector scheme. Numerical boundary conditions at slip walls are described, and numerical results are presented for both reactive and non-reactive flows in order to demonstrate the use and accuracy of the numerical approach.

  2. PHURBAS: AN ADAPTIVE, LAGRANGIAN, MESHLESS, MAGNETOHYDRODYNAMICS CODE. I. ALGORITHM

    SciTech Connect

    Maron, Jason L.; McNally, Colin P.; Mac Low, Mordecai-Mark E-mail: cmcnally@amnh.org

    2012-05-01

    We present an algorithm for simulating the equations of ideal magnetohydrodynamics and other systems of differential equations on an unstructured set of points represented by sample particles. Local, third-order, least-squares, polynomial interpolations (Moving Least Squares interpolations) are calculated from the field values of neighboring particles to obtain field values and spatial derivatives at the particle position. Field values and particle positions are advanced in time with a second-order predictor-corrector scheme. The particles move with the fluid, so the time step is not limited by the Eulerian Courant-Friedrichs-Lewy condition. Full spatial adaptivity is implemented to ensure the particles fill the computational volume, which gives the algorithm substantial flexibility and power. A target resolution is specified for each point in space, with particles being added and deleted as needed to meet this target. Particle addition and deletion is based on a local void and clump detection algorithm. Dynamic artificial viscosity fields provide stability to the integration. The resulting algorithm provides a robust solution for modeling flows that require Lagrangian or adaptive discretizations to resolve. This paper derives and documents the Phurbas algorithm as implemented in Phurbas version 1.1. A following paper presents the implementation and test problem results.

  3. QoS Differential Scheduling in Cognitive-Radio-Based Smart Grid Networks: An Adaptive Dynamic Programming Approach.

    PubMed

    Yu, Rong; Zhong, Weifeng; Xie, Shengli; Zhang, Yan; Zhang, Yun

    2016-02-01

    As the next-generation power grid, smart grid will be integrated with a variety of novel communication technologies to support the explosive data traffic and the diverse requirements of quality of service (QoS). Cognitive radio (CR), which has the favorable ability to improve the spectrum utilization, provides an efficient and reliable solution for smart grid communications networks. In this paper, we study the QoS differential scheduling problem in the CR-based smart grid communications networks. The scheduler is responsible for managing the spectrum resources and arranging the data transmissions of smart grid users (SGUs). To guarantee the differential QoS, the SGUs are assigned to have different priorities according to their roles and their current situations in the smart grid. Based on the QoS-aware priority policy, the scheduler adjusts the channels allocation to minimize the transmission delay of SGUs. The entire transmission scheduling problem is formulated as a semi-Markov decision process and solved by the methodology of adaptive dynamic programming. A heuristic dynamic programming (HDP) architecture is established for the scheduling problem. By the online network training, the HDP can learn from the activities of primary users and SGUs, and adjust the scheduling decision to achieve the purpose of transmission delay minimization. Simulation results illustrate that the proposed priority policy ensures the low transmission delay of high priority SGUs. In addition, the emergency data transmission delay is also reduced to a significantly low level, guaranteeing the differential QoS in smart grid.

  4. A two-stage adaptive stochastic collocation method on nested sparse grids for multiphase flow in randomly heterogeneous porous media

    NASA Astrophysics Data System (ADS)

    Liao, Qinzhuo; Zhang, Dongxiao; Tchelepi, Hamdi

    2017-02-01

    A new computational method is proposed for efficient uncertainty quantification of multiphase flow in porous media with stochastic permeability. For pressure estimation, it combines the dimension-adaptive stochastic collocation method on Smolyak sparse grids and the Kronrod-Patterson-Hermite nested quadrature formulas. For saturation estimation, an additional stage is developed, in which the pressure and velocity samples are first generated by the sparse grid interpolation and then substituted into the transport equation to solve for the saturation samples, to address the low regularity problem of the saturation. Numerical examples are presented for multiphase flow with stochastic permeability fields to demonstrate accuracy and efficiency of the proposed two-stage adaptive stochastic collocation method on nested sparse grids.

  5. Adaptive λ estimation in Lagrangian rate-distortion optimization for video coding

    NASA Astrophysics Data System (ADS)

    Chen, Lulin; Garbacea, Ilie

    2006-01-01

    In this paper, adaptive Lagrangian multiplier λ estimation in Larangian R-D optimization for video coding is presented that is based on the ρ-domain linear rate model and distortion model. It yields that λ is a function of rate, distortion and coding input statistics and can be written as λ(R, D, σ2) = β(ln(σ2/D) + δ)D/R + k 0, with β, δ and k 0 as coding constants, σ2 is variance of prediction error input. λ(R, D, σ2) describes its ubiquitous relationship with coding statistics and coding input in hybrid video coding such as H.263, MPEG-2/4 and H.264/AVC. The lambda evaluation is de-coupled with quantization parameters. The proposed lambda estimation enables a fine encoder design and encoder control.

  6. A Domain-Decomposed Multilevel Method for Adaptively Refined Cartesian Grids with Embedded Boundaries

    NASA Technical Reports Server (NTRS)

    Aftosmis, M. J.; Berger, M. J.; Adomavicius, G.

    2000-01-01

    Preliminary verification and validation of an efficient Euler solver for adaptively refined Cartesian meshes with embedded boundaries is presented. The parallel, multilevel method makes use of a new on-the-fly parallel domain decomposition strategy based upon the use of space-filling curves, and automatically generates a sequence of coarse meshes for processing by the multigrid smoother. The coarse mesh generation algorithm produces grids which completely cover the computational domain at every level in the mesh hierarchy. A series of examples on realistically complex three-dimensional configurations demonstrate that this new coarsening algorithm reliably achieves mesh coarsening ratios in excess of 7 on adaptively refined meshes. Numerical investigations of the scheme's local truncation error demonstrate an achieved order of accuracy between 1.82 and 1.88. Convergence results for the multigrid scheme are presented for both subsonic and transonic test cases and demonstrate W-cycle multigrid convergence rates between 0.84 and 0.94. Preliminary parallel scalability tests on both simple wing and complex complete aircraft geometries shows a computational speedup of 52 on 64 processors using the run-time mesh partitioner.

  7. Axisymmetric modeling of cometary mass loading on an adaptively refined grid: MHD results

    NASA Technical Reports Server (NTRS)

    Gombosi, Tamas I.; Powell, Kenneth G.; De Zeeuw, Darren L.

    1994-01-01

    The first results of an axisymmetric magnetohydrodynamic (MHD) model of the interaction of an expanding cometary atmosphere with the solar wind are presented. The model assumes that far upstream the plasma flow lines are parallel to the magnetic field vector. The effects of mass loading and ion-neutral friction are taken into account by the governing equations, whcih are solved on an adaptively refined unstructured grid using a Monotone Upstream Centered Schemes for Conservative Laws (MUSCL)-type numerical technique. The combination of the adaptive refinement with the MUSCL-scheme allows the entire cometary atmosphere to be modeled, while still resolving both the shock and the near nucleus of the comet. The main findingsare the following: (1) A shock is formed approximately = 0.45 Mkm upstream of the comet (its location is controlled by the sonic and Alfvenic Mach numbers of the ambient solar wind flow and by the cometary mass addition rate). (2) A contact surface is formed approximately = 5,600 km upstream of the nucleus separating an outward expanding cometary ionosphere from the nearly stagnating solar wind flow. The location of the contact surface is controlled by the upstream flow conditions, the mass loading rate and the ion-neutral drag. The contact surface is also the boundary of the diamagnetic cavity. (3) A closed inner shock terminates the supersonic expansion of the cometary ionosphere. This inner shock is closer to the nucleus on dayside than on the nightside.

  8. Adaptive uniform grayscale coded aperture design for high dynamic range compressive spectral imaging

    NASA Astrophysics Data System (ADS)

    Diaz, Nelson; Rueda, Hoover; Arguello, Henry

    2016-05-01

    Imaging spectroscopy is an important area with many applications in surveillance, agriculture and medicine. The disadvantage of conventional spectroscopy techniques is that they collect the whole datacube. In contrast, compressive spectral imaging systems capture snapshot compressive projections, which are the input of reconstruction algorithms to yield the underlying datacube. Common compressive spectral imagers use coded apertures to perform the coded projections. The coded apertures are the key elements in these imagers since they define the sensing matrix of the system. The proper design of the coded aperture entries leads to a good quality in the reconstruction. In addition, the compressive measurements are prone to saturation due to the limited dynamic range of the sensor, hence the design of coded apertures must consider saturation. The saturation errors in compressive measurements are unbounded and compressive sensing recovery algorithms only provide solutions for bounded noise or bounded with high probability. In this paper it is proposed the design of uniform adaptive grayscale coded apertures (UAGCA) to improve the dynamic range of the estimated spectral images by reducing the saturation levels. The saturation is attenuated between snapshots using an adaptive filter which updates the entries of the grayscale coded aperture based on the previous snapshots. The coded apertures are optimized in terms of transmittance and number of grayscale levels. The advantage of the proposed method is the efficient use of the dynamic range of the image sensor. Extensive simulations show improvements in the image reconstruction of the proposed method compared with grayscale coded apertures (UGCA) and adaptive block-unblock coded apertures (ABCA) in up to 10 dB.

  9. Grid Work

    NASA Technical Reports Server (NTRS)

    1998-01-01

    Pointwise Inc.'s, Gridgen Software is a system for the generation of 3D (three dimensional) multiple block, structured grids. Gridgen is a visually-oriented, graphics-based interactive code used to decompose a 3D domain into blocks, distribute grid points on curves, initialize and refine grid points on surfaces and initialize volume grid points. Gridgen is available to U.S. citizens and American-owned companies by license.

  10. The role of overset grids in the development of the general purpose CFD code

    NASA Technical Reports Server (NTRS)

    Belk, Davy M.

    1995-01-01

    A discussion of the strengths and weaknesses of overset composite grid and solution technology is given, along with a sampling of current work in the area. Major trends are identified, and the observation is made that generalized and hybridized overset methods provide a natural framework for combining disparate mesh types and physics models. Because of this, the author concludes that overset methods will be the foundation for the general purpose computational fluid dynamics programs of the future.

  11. Shape-adaptive discrete wavelet transform for coding arbitrarily shaped texture

    NASA Astrophysics Data System (ADS)

    Li, Shipeng; Li, Weiping

    1997-01-01

    This paper presents a shape adaptive discrete wavelet transform (SA-DWT) scheme for coding arbitrarily shaped texture. The proposed SA-DWT can be used for object-oriented image coding. The number of coefficients after SA-DWT is identical to the number of pels contained in the arbitrarily shaped image objects. The locality property of wavelet transform and self-similarity among subbands are well preserved throughout this process.For a rectangular region, the SA-DWT is identical to a standard wavelet transform. With SA-DWT, conventional wavelet based coding schemes can be readily extended to the coding of arbitrarily shaped objects. The proposed shape adaptive wavelet transform is not unitary but the small energy increase is restricted at the boundary of objects in subbands. Two approaches of using the SA-DWT algorithm for object-oriented image and video coding are presented. One is to combine scalar SA-DWT with embedded zerotree wavelet (EZW) coding technique, the other is an extension of the normal vector wavelet coding (VWC) technique to arbitrarily shaped objects. Results of applying SA-VWC to real arbitrarily shaped texture coding are also given at the end of this paper.

  12. On the Numerical Dispersion of Electromagnetic Particle-In-Cell Code : Finite Grid Instability

    SciTech Connect

    Meyers, Michael David; Huang, Chengkun; Zeng, Yong; Yi, Sunghwan; Albright, Brian James

    2014-07-15

    The Particle-In-Cell (PIC) method is widely used in relativistic particle beam and laser plasma modeling. However, the PIC method exhibits numerical instabilities that can render unphysical simulation results or even destroy the simulation. For electromagnetic relativistic beam and plasma modeling, the most relevant numerical instabilities are the finite grid instability and the numerical Cherenkov instability. We review the numerical dispersion relation of the electromagnetic PIC algorithm to analyze the origin of these instabilities. We rigorously derive the faithful 3D numerical dispersion of the PIC algorithm, and then specialize to the Yee FDTD scheme. In particular, we account for the manner in which the PIC algorithm updates and samples the fields and distribution function. Temporal and spatial phase factors from solving Maxwell's equations on the Yee grid with the leapfrog scheme are also explicitly accounted for. Numerical solutions to the electrostatic-like modes in the 1D dispersion relation for a cold drifting plasma are obtained for parameters of interest. In the succeeding analysis, we investigate how the finite grid instability arises from the interaction of the numerical 1D modes admitted in the system and their aliases. The most significant interaction is due critically to the correct representation of the operators in the dispersion relation. We obtain a simple analytic expression for the peak growth rate due to this interaction.

  13. Unsupervised learning approach to adaptive differential pulse code modulation.

    PubMed

    Griswold, N C; Sayood, K

    1982-04-01

    This research is concerned with investigating the problem of data compression utilizing an unsupervised estimation algorithm. This extends previous work utilizing a hybrid source coder which combines an orthogonal transformation with differential pulse code modulation (DPCM). The data compression is achieved in the DPCM loop, and it is the quantizer of this scheme which is approached from an unsupervised learning procedure. The distribution defining the quantizer is represented as a set of separable Laplacian mixture densities for two-dimensional images. The condition of identifiability is shown for the Laplacian case and a decision directed estimate of both the active distribution parameters and the mixing parameters are discussed in view of a Bayesian structure. The decision directed estimators, although not optimum, provide a realizable structure for estimating the parameters which define a distribution which has become active. These parameters are then used to scale the optimum (in the mean square error sense) Laplacian quantizer. The decision criteria is modified to prevent convergence to a single distribution which in effect is the default condition for a variance estimator. This investigation was applied to a test image and the resulting data demonstrate improvement over other techniques using fixed bit assignments and ideal channel conditions.

  14. Edge equilibrium code for tokamaks

    SciTech Connect

    Li, Xujing; Drozdov, Vladimir V.

    2014-01-15

    The edge equilibrium code (EEC) described in this paper is developed for simulations of the near edge plasma using the finite element method. It solves the Grad-Shafranov equation in toroidal coordinate and uses adaptive grids aligned with magnetic field lines. Hermite finite elements are chosen for the numerical scheme. A fast Newton scheme which is the same as implemented in the equilibrium and stability code (ESC) is applied here to adjust the grids.

  15. Simulation of 2D Kinetic Effects in Plasmas using the Grid Based Continuum Code LOKI

    NASA Astrophysics Data System (ADS)

    Banks, Jeffrey; Berger, Richard; Chapman, Tom; Brunner, Stephan

    2016-10-01

    Kinetic simulation of multi-dimensional plasma waves through direct discretization of the Vlasov equation is a useful tool to study many physical interactions and is particularly attractive for situations where minimal fluctuation levels are desired, for instance, when measuring growth rates of plasma wave instabilities. However, direct discretization of phase space can be computationally expensive, and as a result there are few examples of published results using Vlasov codes in more than a single configuration space dimension. In an effort to fill this gap we have developed the Eulerian-based kinetic code LOKI that evolves the Vlasov-Poisson system in 2+2-dimensional phase space. The code is designed to reduce the cost of phase-space computation by using fully 4th order accurate conservative finite differencing, while retaining excellent parallel scalability that efficiently uses large scale computing resources. In this poster I will discuss the algorithms used in the code as well as some aspects of their parallel implementation using MPI. I will also overview simulation results of basic plasma wave instabilities relevant to laser plasma interaction, which have been obtained using the code.

  16. Context-adaptive binary arithmetic coding with precise probability estimation and complexity scalability for high-efficiency video coding

    NASA Astrophysics Data System (ADS)

    Karwowski, Damian; Domański, Marek

    2016-01-01

    An improved context-based adaptive binary arithmetic coding (CABAC) is presented. The idea for the improvement is to use a more accurate mechanism for estimation of symbol probabilities in the standard CABAC algorithm. The authors' proposal of such a mechanism is based on the context-tree weighting technique. In the framework of a high-efficiency video coding (HEVC) video encoder, the improved CABAC allows 0.7% to 4.5% bitrate saving compared to the original CABAC algorithm. The application of the proposed algorithm marginally affects the complexity of HEVC video encoder, but the complexity of video decoder increases by 32% to 38%. In order to decrease the complexity of video decoding, a new tool has been proposed for the improved CABAC that enables scaling of the decoder complexity. Experiments show that this tool gives 5% to 7.5% reduction of the decoding time while still maintaining high efficiency in the data compression.

  17. On the numerical dispersion of electromagnetic particle-in-cell code: Finite grid instability

    SciTech Connect

    Meyers, M.D.; Huang, C.-K.; Zeng, Y.; Yi, S.A.; Albright, B.J.

    2015-09-15

    The Particle-In-Cell (PIC) method is widely used in relativistic particle beam and laser plasma modeling. However, the PIC method exhibits numerical instabilities that can render unphysical simulation results or even destroy the simulation. For electromagnetic relativistic beam and plasma modeling, the most relevant numerical instabilities are the finite grid instability and the numerical Cherenkov instability. We review the numerical dispersion relation of the Electromagnetic PIC model. We rigorously derive the faithful 3-D numerical dispersion relation of the PIC model, for a simple, direct current deposition scheme, which does not conserve electric charge exactly. We then specialize to the Yee FDTD scheme. In particular, we clarify the presence of alias modes in an eigenmode analysis of the PIC model, which combines both discrete and continuous variables. The manner in which the PIC model updates and samples the fields and distribution function, together with the temporal and spatial phase factors from solving Maxwell's equations on the Yee grid with the leapfrog scheme, is explicitly accounted for. Numerical solutions to the electrostatic-like modes in the 1-D dispersion relation for a cold drifting plasma are obtained for parameters of interest. In the succeeding analysis, we investigate how the finite grid instability arises from the interaction of the numerical modes admitted in the system and their aliases. The most significant interaction is due critically to the correct representation of the operators in the dispersion relation. We obtain a simple analytic expression for the peak growth rate due to this interaction, which is then verified by simulation. We demonstrate that our analysis is readily extendable to charge conserving models.

  18. On the numerical dispersion of electromagnetic particle-in-cell code: Finite grid instability

    NASA Astrophysics Data System (ADS)

    Meyers, M. D.; Huang, C.-K.; Zeng, Y.; Yi, S. A.; Albright, B. J.

    2015-09-01

    The Particle-In-Cell (PIC) method is widely used in relativistic particle beam and laser plasma modeling. However, the PIC method exhibits numerical instabilities that can render unphysical simulation results or even destroy the simulation. For electromagnetic relativistic beam and plasma modeling, the most relevant numerical instabilities are the finite grid instability and the numerical Cherenkov instability. We review the numerical dispersion relation of the Electromagnetic PIC model. We rigorously derive the faithful 3-D numerical dispersion relation of the PIC model, for a simple, direct current deposition scheme, which does not conserve electric charge exactly. We then specialize to the Yee FDTD scheme. In particular, we clarify the presence of alias modes in an eigenmode analysis of the PIC model, which combines both discrete and continuous variables. The manner in which the PIC model updates and samples the fields and distribution function, together with the temporal and spatial phase factors from solving Maxwell's equations on the Yee grid with the leapfrog scheme, is explicitly accounted for. Numerical solutions to the electrostatic-like modes in the 1-D dispersion relation for a cold drifting plasma are obtained for parameters of interest. In the succeeding analysis, we investigate how the finite grid instability arises from the interaction of the numerical modes admitted in the system and their aliases. The most significant interaction is due critically to the correct representation of the operators in the dispersion relation. We obtain a simple analytic expression for the peak growth rate due to this interaction, which is then verified by simulation. We demonstrate that our analysis is readily extendable to charge conserving models.

  19. Convergence rate enhancement of navier-stokes codes on clustered grids

    NASA Technical Reports Server (NTRS)

    Choi, Kwang-Yoon; Dulikravich, George S.

    1994-01-01

    Our Sensitivity-Based Minimal Residual (SBMR) method which is based on our earlier Distributed Minimal Residual (DMR) method allows each component of the solution vector in a system of equations to have its own convergence speed. Our global SBMR method was found to consistently outperform the DMR method while requiring considerably less computer memory. Recently, we have developed and tested a new Line SBMR or LSBMR method and a Time-Step-Scaling (TSS) method that are even more robust and computationally efficient than our global SBMR method, especially on highly clustered computational grids in laminar and turbulent flow computations.

  20. REMAP: A computer code that transfers node information between dissimilar grids

    SciTech Connect

    Shapiro, A.B.

    1990-04-01

    REMAP is a computer code that transfers the axisymmetric, two dimensional planar, or three dimensional temperature field from one finite element mesh to another. The meshes may be arbitrary as far as the number of elements and their geometry. REMAP interpolates or extrapolates the node temperatures from the old mesh to the new mesh using linear, bilinear, or trilinear isoparametric finite element shape functions. REMAP is used to transfer the temperature field from a thermal analysis mesh to a more finely discretized structural analysis mesh when performing a thermal stress analysis. REMAP was designed to be used with the finite element heat transfer codes TOPAZ2D and TOPAZ3D, and the solid mechanics codes NIKE2D and NIKE3D. The I/O formats in REMAP can be easily modified to accept input from other codes (e.g., finite difference) and generate output files for other structural codes. REMAP can be used to transfer any scalar field variable between dissimilar finite element meshes. The idea of a coarse filter by a fine filter to determine which element from the old mesh contains a node point from the new mesh was used. The coarse filter determines a subset of elements from the old mesh that may contain the new node point. The fine filter determines the element that contains the new node point. REMAP uses the ray-surface intersection algorithm developed for the FACET code for the fine filter. This algorithm has the added capability to determine which element the node is closest to if the node point lies outside the perimeter of the old mesh. Once an element from the old mesh has been identified as containing or closest to the new node point, the natural coordinates for the node point are calculated. The isoparametric finite element shape functions are calculated next. These shape functions are then used to interpolate or extrapolate the temperatures from the nodes comprising the old element to the new node point.

  1. Conversion of a phase- to a rate-coded position signal by a three-stage model of theta cells, grid cells, and place cells.

    PubMed

    Blair, Hugh T; Gupta, Kishan; Zhang, Kechen

    2008-01-01

    As a rat navigates through a familiar environment, its position in space is encoded by firing rates of place cells and grid cells. Oscillatory interference models propose that this positional firing rate code is derived from a phase code, which stores the rat's position as a pattern of phase angles between velocity-modulated theta oscillations. Here we describe a three-stage network model, which formalizes the computational steps that are necessary for converting phase-coded position signals (represented by theta oscillations) into rate-coded position signals (represented by grid cells and place cells). The first stage of the model proposes that the phase-coded position signal is stored and updated by a bank of ring attractors, like those that have previously been hypothesized to perform angular path integration in the head-direction cell system. We show analytically how ring attractors can serve as central pattern generators for producing velocity-modulated theta oscillations, and we propose that such ring attractors may reside in subcortical areas where hippocampal theta rhythm is known to originate. In the second stage of the model, grid fields are formed by oscillatory interference between theta cells residing in different (but not the same) ring attractors. The model's third stage assumes that hippocampal neurons generate Gaussian place fields by computing weighted sums of inputs from a basis set of many grid fields. Here we show that under this assumption, the spatial frequency spectrum of the Gaussian place field defines the vertex spacings of grid cells that must provide input to the place cell. This analysis generates a testable prediction that grid cells with large vertex spacings should send projections to the entire hippocampus, whereas grid cells with smaller vertex spacings may project more selectively to the dorsal hippocampus, where place fields are smallest.

  2. A general multiblock Euler code for propulsion integration. Volume 2: User guide for BCON, pre-processor for grid generation and GMBE

    NASA Technical Reports Server (NTRS)

    Su, T. Y.; Appleby, R. A.; Chen, H. C.

    1991-01-01

    The BCON is a menu-driven graphics interface program whose input consists of strings or arrays of points generated from a computer aided design (CAD) tool or any other surface geometry source. The user needs to design the block topology and prepare the surface geometry definition and surface grids separately. The BCON generates input files that contain the block definitions and the block relationships required for generating a multiblock volume grid with the EAGLE grid generation package. The BCON also generates the block boundary conditions file which is used along with the block relationship file as input for the general multiblock Euler (GMBE) code (GMBE, volumes 1 and 3).

  3. Validation of elastic registration algorithms based on adaptive irregular grids for medical applications

    NASA Astrophysics Data System (ADS)

    Franz, Astrid; Carlsen, Ingwer C.; Renisch, Steffen; Wischmann, Hans-Aloys

    2006-03-01

    Elastic registration of medical images is an active field of current research. Registration algorithms have to be validated in order to show that they fulfill the requirements of a particular clinical application. Furthermore, validation strategies compare the performance of different registration algorithms and can hence judge which algorithm is best suited for a target application. In the literature, validation strategies for rigid registration algorithms have been analyzed. For a known ground truth they assess the displacement error at a few landmarks, which is not sufficient for elastic transformations described by a huge number of parameters. Hence we consider the displacement error averaged over all pixels in the whole image or in a region-of-interest of clinical relevance. Using artificially, but realistically deformed images of the application domain, we use this quality measure to analyze an elastic registration based on transformations defined on adaptive irregular grids for the following clinical applications: Magnetic Resonance (MR) images of freely moving joints for orthopedic investigations, thoracic Computed Tomography (CT) images for the detection of pulmonary embolisms, and transmission images as used for the attenuation correction and registration of independently acquired Positron Emission Tomography (PET) and CT images. The definition of a region-of-interest allows to restrict the analysis of the registration accuracy to clinically relevant image areas. The behaviour of the displacement error as a function of the number of transformation control points and their placement can be used for identifying the best strategy for the initial placement of the control points.

  4. A Domain-Decomposed Multi-Level Method for Adaptively Refined Cartesian Grids with Embedded Boundaries

    NASA Technical Reports Server (NTRS)

    Aftosmis, M. J.; Berger, M. J.; Adomavicius, G.; Nixon, David (Technical Monitor)

    1998-01-01

    The work presents a new method for on-the-fly domain decomposition technique for mapping grids and solution algorithms to parallel machines, and is applicable to both shared-memory and message-passing architectures. It will be demonstrated on the Cray T3E, HP Exemplar, and SGI Origin 2000. Computing time has been secured on all these platforms. The decomposition technique is an outgrowth of techniques used in computational physics for simulations of N-body problems and the event horizons of black holes, and has not been previously used by the CFD community. Since the technique offers on-the-fly partitioning, it offers a substantial increase in flexibility for computing in heterogeneous environments, where the number of available processors may not be known at the time of job submission. In addition, since it is dynamic it permits the job to be repartitioned without global communication in cases where additional processors become available after the simulation has begun, or in cases where dynamic mesh adaptation changes the mesh size during the course of a simulation. The platform for this partitioning strategy is a completely new Cartesian Euler solver tarcreted at parallel machines which may be used in conjunction with Ames' "Cart3D" arbitrary geometry simulation package.

  5. Estimation of Model's Marginal likelihood Using Adaptive Sparse Grid Surrogates in Bayesian Model Averaging

    NASA Astrophysics Data System (ADS)

    Zeng, X.

    2015-12-01

    A large number of model executions are required to obtain alternative conceptual models' predictions and their posterior probabilities in Bayesian model averaging (BMA). The posterior model probability is estimated through models' marginal likelihood and prior probability. The heavy computation burden hinders the implementation of BMA prediction, especially for the elaborated marginal likelihood estimator. For overcoming the computation burden of BMA, an adaptive sparse grid (SG) stochastic collocation method is used to build surrogates for alternative conceptual models through the numerical experiment of a synthetical groundwater model. BMA predictions depend on model posterior weights (or marginal likelihoods), and this study also evaluated four marginal likelihood estimators, including arithmetic mean estimator (AME), harmonic mean estimator (HME), stabilized harmonic mean estimator (SHME), and thermodynamic integration estimator (TIE). The results demonstrate that TIE is accurate in estimating conceptual models' marginal likelihoods. The BMA-TIE has better predictive performance than other BMA predictions. TIE has high stability for estimating conceptual model's marginal likelihood. The repeated estimated conceptual model's marginal likelihoods by TIE have significant less variability than that estimated by other estimators. In addition, the SG surrogates are efficient to facilitate BMA predictions, especially for BMA-TIE. The number of model executions needed for building surrogates is 4.13%, 6.89%, 3.44%, and 0.43% of the required model executions of BMA-AME, BMA-HME, BMA-SHME, and BMA-TIE, respectively.

  6. Features of CPB: a Poisson-Boltzmann solver that uses an adaptive Cartesian grid.

    PubMed

    Fenley, Marcia O; Harris, Robert C; Mackoy, Travis; Boschitsch, Alexander H

    2015-02-05

    The capabilities of an adaptive Cartesian grid (ACG)-based Poisson-Boltzmann (PB) solver (CPB) are demonstrated. CPB solves various PB equations with an ACG, built from a hierarchical octree decomposition of the computational domain. This procedure decreases the number of points required, thereby reducing computational demands. Inside the molecule, CPB solves for the reaction-field component (ϕrf ) of the electrostatic potential (ϕ), eliminating the charge-induced singularities in ϕ. CPB can also use a least-squares reconstruction method to improve estimates of ϕ at the molecular surface. All surfaces, which include solvent excluded, Gaussians, and others, are created analytically, eliminating errors associated with triangulated surfaces. These features allow CPB to produce detailed surface maps of ϕ and compute polar solvation and binding free energies for large biomolecular assemblies, such as ribosomes and viruses, with reduced computational demands compared to other Poisson-Boltzmann equation solvers. The reader is referred to http://www.continuum-dynamics.com/solution-mm.html for how to obtain the CPB software.

  7. Adaptive control paradigm for photovoltaic and solid oxide fuel cell in a grid-integrated hybrid renewable energy system

    PubMed Central

    Khan, Laiq

    2017-01-01

    The hybrid power system (HPS) is an emerging power generation scheme due to the plentiful availability of renewable energy sources. Renewable energy sources are characterized as highly intermittent in nature due to meteorological conditions, while the domestic load also behaves in a quite uncertain manner. In this scenario, to maintain the balance between generation and load, the development of an intelligent and adaptive control algorithm has preoccupied power engineers and researchers. This paper proposes a Hermite wavelet embedded NeuroFuzzy indirect adaptive MPPT (maximum power point tracking) control of photovoltaic (PV) systems to extract maximum power and a Hermite wavelet incorporated NeuroFuzzy indirect adaptive control of Solid Oxide Fuel Cells (SOFC) to obtain a swift response in a grid-connected hybrid power system. A comprehensive simulation testbed for a grid-connected hybrid power system (wind turbine, PV cells, SOFC, electrolyzer, battery storage system, supercapacitor (SC), micro-turbine (MT) and domestic load) is developed in Matlab/Simulink. The robustness and superiority of the proposed indirect adaptive control paradigm are evaluated through simulation results in a grid-connected hybrid power system testbed by comparison with a conventional PI (proportional and integral) control system. The simulation results verify the effectiveness of the proposed control paradigm. PMID:28329015

  8. Adaptive control paradigm for photovoltaic and solid oxide fuel cell in a grid-integrated hybrid renewable energy system.

    PubMed

    Mumtaz, Sidra; Khan, Laiq

    2017-01-01

    The hybrid power system (HPS) is an emerging power generation scheme due to the plentiful availability of renewable energy sources. Renewable energy sources are characterized as highly intermittent in nature due to meteorological conditions, while the domestic load also behaves in a quite uncertain manner. In this scenario, to maintain the balance between generation and load, the development of an intelligent and adaptive control algorithm has preoccupied power engineers and researchers. This paper proposes a Hermite wavelet embedded NeuroFuzzy indirect adaptive MPPT (maximum power point tracking) control of photovoltaic (PV) systems to extract maximum power and a Hermite wavelet incorporated NeuroFuzzy indirect adaptive control of Solid Oxide Fuel Cells (SOFC) to obtain a swift response in a grid-connected hybrid power system. A comprehensive simulation testbed for a grid-connected hybrid power system (wind turbine, PV cells, SOFC, electrolyzer, battery storage system, supercapacitor (SC), micro-turbine (MT) and domestic load) is developed in Matlab/Simulink. The robustness and superiority of the proposed indirect adaptive control paradigm are evaluated through simulation results in a grid-connected hybrid power system testbed by comparison with a conventional PI (proportional and integral) control system. The simulation results verify the effectiveness of the proposed control paradigm.

  9. Individual differences in adaptive coding of face identity are linked to individual differences in face recognition ability.

    PubMed

    Rhodes, Gillian; Jeffery, Linda; Taylor, Libby; Hayward, William G; Ewing, Louise

    2014-06-01

    Despite their similarity as visual patterns, we can discriminate and recognize many thousands of faces. This expertise has been linked to 2 coding mechanisms: holistic integration of information across the face and adaptive coding of face identity using norms tuned by experience. Recently, individual differences in face recognition ability have been discovered and linked to differences in holistic coding. Here we show that they are also linked to individual differences in adaptive coding of face identity, measured using face identity aftereffects. Identity aftereffects correlated significantly with several measures of face-selective recognition ability. They also correlated marginally with own-race face recognition ability, suggesting a role for adaptive coding in the well-known other-race effect. More generally, these results highlight the important functional role of adaptive face-coding mechanisms in face expertise, taking us beyond the traditional focus on holistic coding mechanisms.

  10. Dopamine Modulates Adaptive Prediction Error Coding in the Human Midbrain and Striatum

    PubMed Central

    Ziauddeen, Hisham; Vestergaard, Martin D.; Spencer, Tom

    2017-01-01

    Learning to optimally predict rewards requires agents to account for fluctuations in reward value. Recent work suggests that individuals can efficiently learn about variable rewards through adaptation of the learning rate, and coding of prediction errors relative to reward variability. Such adaptive coding has been linked to midbrain dopamine neurons in nonhuman primates, and evidence in support for a similar role of the dopaminergic system in humans is emerging from fMRI data. Here, we sought to investigate the effect of dopaminergic perturbations on adaptive prediction error coding in humans, using a between-subject, placebo-controlled pharmacological fMRI study with a dopaminergic agonist (bromocriptine) and antagonist (sulpiride). Participants performed a previously validated task in which they predicted the magnitude of upcoming rewards drawn from distributions with varying SDs. After each prediction, participants received a reward, yielding trial-by-trial prediction errors. Under placebo, we replicated previous observations of adaptive coding in the midbrain and ventral striatum. Treatment with sulpiride attenuated adaptive coding in both midbrain and ventral striatum, and was associated with a decrease in performance, whereas bromocriptine did not have a significant impact. Although we observed no differential effect of SD on performance between the groups, computational modeling suggested decreased behavioral adaptation in the sulpiride group. These results suggest that normal dopaminergic function is critical for adaptive prediction error coding, a key property of the brain thought to facilitate efficient learning in variable environments. Crucially, these results also offer potential insights for understanding the impact of disrupted dopamine function in mental illness. SIGNIFICANCE STATEMENT To choose optimally, we have to learn what to expect. Humans dampen learning when there is a great deal of variability in reward outcome, and two brain regions that

  11. Dopamine Modulates Adaptive Prediction Error Coding in the Human Midbrain and Striatum.

    PubMed

    Diederen, Kelly M J; Ziauddeen, Hisham; Vestergaard, Martin D; Spencer, Tom; Schultz, Wolfram; Fletcher, Paul C

    2017-02-15

    Learning to optimally predict rewards requires agents to account for fluctuations in reward value. Recent work suggests that individuals can efficiently learn about variable rewards through adaptation of the learning rate, and coding of prediction errors relative to reward variability. Such adaptive coding has been linked to midbrain dopamine neurons in nonhuman primates, and evidence in support for a similar role of the dopaminergic system in humans is emerging from fMRI data. Here, we sought to investigate the effect of dopaminergic perturbations on adaptive prediction error coding in humans, using a between-subject, placebo-controlled pharmacological fMRI study with a dopaminergic agonist (bromocriptine) and antagonist (sulpiride). Participants performed a previously validated task in which they predicted the magnitude of upcoming rewards drawn from distributions with varying SDs. After each prediction, participants received a reward, yielding trial-by-trial prediction errors. Under placebo, we replicated previous observations of adaptive coding in the midbrain and ventral striatum. Treatment with sulpiride attenuated adaptive coding in both midbrain and ventral striatum, and was associated with a decrease in performance, whereas bromocriptine did not have a significant impact. Although we observed no differential effect of SD on performance between the groups, computational modeling suggested decreased behavioral adaptation in the sulpiride group. These results suggest that normal dopaminergic function is critical for adaptive prediction error coding, a key property of the brain thought to facilitate efficient learning in variable environments. Crucially, these results also offer potential insights for understanding the impact of disrupted dopamine function in mental illness.SIGNIFICANCE STATEMENT To choose optimally, we have to learn what to expect. Humans dampen learning when there is a great deal of variability in reward outcome, and two brain regions that

  12. QoS-Aware Error Recovery in Wireless Body Sensor Networks Using Adaptive Network Coding

    PubMed Central

    Razzaque, Mohammad Abdur; Javadi, Saeideh S.; Coulibaly, Yahaya; Hira, Muta Tah

    2015-01-01

    Wireless body sensor networks (WBSNs) for healthcare and medical applications are real-time and life-critical infrastructures, which require a strict guarantee of quality of service (QoS), in terms of latency, error rate and reliability. Considering the criticality of healthcare and medical applications, WBSNs need to fulfill users/applications and the corresponding network's QoS requirements. For instance, for a real-time application to support on-time data delivery, a WBSN needs to guarantee a constrained delay at the network level. A network coding-based error recovery mechanism is an emerging mechanism that can be used in these systems to support QoS at very low energy, memory and hardware cost. However, in dynamic network environments and user requirements, the original non-adaptive version of network coding fails to support some of the network and user QoS requirements. This work explores the QoS requirements of WBSNs in both perspectives of QoS. Based on these requirements, this paper proposes an adaptive network coding-based, QoS-aware error recovery mechanism for WBSNs. It utilizes network-level and user-/application-level information to make it adaptive in both contexts. Thus, it provides improved QoS support adaptively in terms of reliability, energy efficiency and delay. Simulation results show the potential of the proposed mechanism in terms of adaptability, reliability, real-time data delivery and network lifetime compared to its counterparts. PMID:25551485

  13. QOS-aware error recovery in wireless body sensor networks using adaptive network coding.

    PubMed

    Razzaque, Mohammad Abdur; Javadi, Saeideh S; Coulibaly, Yahaya; Hira, Muta Tah

    2014-12-29

    Wireless body sensor networks (WBSNs) for healthcare and medical applications are real-time and life-critical infrastructures, which require a strict guarantee of quality of service (QoS), in terms of latency, error rate and reliability. Considering the criticality of healthcare and medical applications, WBSNs need to fulfill users/applications and the corresponding network's QoS requirements. For instance, for a real-time application to support on-time data delivery, a WBSN needs to guarantee a constrained delay at the network level. A network coding-based error recovery mechanism is an emerging mechanism that can be used in these systems to support QoS at very low energy, memory and hardware cost. However, in dynamic network environments and user requirements, the original non-adaptive version of network coding fails to support some of the network and user QoS requirements. This work explores the QoS requirements of WBSNs in both perspectives of QoS. Based on these requirements, this paper proposes an adaptive network coding-based, QoS-aware error recovery mechanism for WBSNs. It utilizes network-level and user-/application-level information to make it adaptive in both contexts. Thus, it provides improved QoS support adaptively in terms of reliability, energy efficiency and delay. Simulation results show the potential of the proposed mechanism in terms of adaptability, reliability, real-time data delivery and network lifetime compared to its counterparts.

  14. Grid flexibility and patching techniques

    NASA Technical Reports Server (NTRS)

    Keith, T. G.; Smith, L. W.; Yung, C. N.; Barthelson, S. H.; Dewitt, K. J.

    1984-01-01

    The numerical determination of combustor flowfields is of great value to the combustor designer. An a priori knowledge of the flow behavior can speed the combustor design process and reduce the number of experimental test rigs required to arrive at an optimal design. Even 2-D steady incompressible isothermal flow predictions are of use; many codes of this kind are available, each employing different techniques to surmount the difficulties arising from the nonlinearity of the governing equations and from typically irregular combustor geometries. Mapping techniques (algebraic and elliptic PDE), and adaptive grid methods (both multi-grid and grid embedding) as applied to axisymmetric combustors are discussed.

  15. Object-adaptive depth compensated inter prediction for depth video coding in 3D video system

    NASA Astrophysics Data System (ADS)

    Kang, Min-Koo; Lee, Jaejoon; Lim, Ilsoon; Ho, Yo-Sung

    2011-01-01

    Nowadays, the 3D video system using the MVD (multi-view video plus depth) data format is being actively studied. The system has many advantages with respect to virtual view synthesis such as an auto-stereoscopic functionality, but compression of huge input data remains a problem. Therefore, efficient 3D data compression is extremely important in the system, and problems of low temporal consistency and viewpoint correlation should be resolved for efficient depth video coding. In this paper, we propose an object-adaptive depth compensated inter prediction method to resolve the problems where object-adaptive mean-depth difference between a current block, to be coded, and a reference block are compensated during inter prediction. In addition, unique properties of depth video are exploited to reduce side information required for signaling decoder to conduct the same process. To evaluate the coding performance, we have implemented the proposed method into MVC (multiview video coding) reference software, JMVC 8.2. Experimental results have demonstrated that our proposed method is especially efficient for depth videos estimated by DERS (depth estimation reference software) discussed in the MPEG 3DV coding group. The coding gain was up to 11.69% bit-saving, and it was even increased when we evaluated it on synthesized views of virtual viewpoints.

  16. Lossless image compression based on optimal prediction, adaptive lifting, and conditional arithmetic coding.

    PubMed

    Boulgouris, N V; Tzovaras, D; Strintzis, M G

    2001-01-01

    The optimal predictors of a lifting scheme in the general n-dimensional case are obtained and applied for the lossless compression of still images using first quincunx sampling and then simple row-column sampling. In each case, the efficiency of the linear predictors is enhanced nonlinearly. Directional postprocessing is used in the quincunx case, and adaptive-length postprocessing in the row-column case. Both methods are seen to perform well. The resulting nonlinear interpolation schemes achieve extremely efficient image decorrelation. We further investigate context modeling and adaptive arithmetic coding of wavelet coefficients in a lossless compression framework. Special attention is given to the modeling contexts and the adaptation of the arithmetic coder to the actual data. Experimental evaluation shows that the best of the resulting coders produces better results than other known algorithms for multiresolution-based lossless image coding.

  17. Sample-adaptive-prediction for HEVC SCC intra coding with ridge estimation from spatially neighboring samples

    NASA Astrophysics Data System (ADS)

    Kang, Je-Won; Ryu, Soo-Kyung

    2017-02-01

    In this paper a sample-adaptive prediction technique is proposed to yield efficient coding performance in an intracoding for screen content video coding. The sample-based prediction is to reduce spatial redundancies in neighboring samples. To this aim, the proposed technique uses a weighted linear combination of neighboring samples and applies the robust optimization technique, namely, ridge estimation to derive the weights in a decoder side. The ridge estimation uses L2 norm based regularization term, and, thus the solution is more robust to high variance samples such as in sharp edges and high color contrasts exhibited in screen content videos. It is demonstrated with the experimental results that the proposed technique provides an improved coding gain as compared to the HEVC screen content video coding reference software.

  18. A Neural Mechanism for Time-Window Separation Resolves Ambiguity of Adaptive Coding

    PubMed Central

    Hildebrandt, K. Jannis; Ronacher, Bernhard; Hennig, R. Matthias; Benda, Jan

    2015-01-01

    The senses of animals are confronted with changing environments and different contexts. Neural adaptation is one important tool to adjust sensitivity to varying intensity ranges. For instance, in a quiet night outdoors, our hearing is more sensitive than when we are confronted with the plurality of sounds in a large city during the day. However, adaptation also removes available information on absolute sound levels and may thus cause ambiguity. Experimental data on the trade-off between benefits and loss through adaptation is scarce and very few mechanisms have been proposed to resolve it. We present an example where adaptation is beneficial for one task—namely, the reliable encoding of the pattern of an acoustic signal—but detrimental for another—the localization of the same acoustic stimulus. With a combination of neurophysiological data, modeling, and behavioral tests, we show that adaptation in the periphery of the auditory pathway of grasshoppers enables intensity-invariant coding of amplitude modulations, but at the same time, degrades information available for sound localization. We demonstrate how focusing the response of localization neurons to the onset of relevant signals separates processing of localization and pattern information temporally. In this way, the ambiguity of adaptive coding can be circumvented and both absolute and relative levels can be processed using the same set of peripheral neurons. PMID:25761097

  19. Code Development of Three-Dimensional General Relativistic Hydrodynamics with AMR (Adaptive-Mesh Refinement) and Results from Special and General Relativistic Hydrodynamics

    NASA Astrophysics Data System (ADS)

    Dönmez, Orhan

    2004-09-01

    In this paper, the general procedure to solve the general relativistic hydrodynamical (GRH) equations with adaptive-mesh refinement (AMR) is presented. In order to achieve, the GRH equations are written in the conservation form to exploit their hyperbolic character. The numerical solutions of GRH equations are obtained by high resolution shock Capturing schemes (HRSC), specifically designed to solve nonlinear hyperbolic systems of conservation laws. These schemes depend on the characteristic information of the system. The Marquina fluxes with MUSCL left and right states are used to solve GRH equations. First, different test problems with uniform and AMR grids on the special relativistic hydrodynamics equations are carried out to verify the second-order convergence of the code in one, two and three dimensions. Results from uniform and AMR grid are compared. It is found that adaptive grid does a better job when the number of resolution is increased. Second, the GRH equations are tested using two different test problems which are Geodesic flow and Circular motion of particle In order to do this, the flux part of GRH equations is coupled with source part using Strang splitting. The coupling of the GRH equations is carried out in a treatment which gives second order accurate solutions in space and time.

  20. Grid generation and adaptation for the Direct Simulation Monte Carlo Method. [for complex flows past wedges and cones

    NASA Technical Reports Server (NTRS)

    Olynick, David P.; Hassan, H. A.; Moss, James N.

    1988-01-01

    A grid generation and adaptation procedure based on the method of transfinite interpolation is incorporated into the Direct Simulation Monte Carlo Method of Bird. In addition, time is advanced based on a local criterion. The resulting procedure is used to calculate steady flows past wedges and cones. Five chemical species are considered. In general, the modifications result in a reduced computational effort. Moreover, preliminary results suggest that the simulation method is time step dependent if requirements on cell sizes are not met.

  1. MAGNETIC GRID

    DOEpatents

    Post, R.F.

    1960-08-01

    An electronic grid is designed employing magnetic forces for controlling the passage of charged particles. The grid is particularly applicable to use in gas-filled tubes such as ignitrons. thyratrons, etc., since the magnetic grid action is impartial to the polarity of the charged particles and, accordingly. the sheath effects encountered with electrostatic grids are not present. The grid comprises a conductor having sections spaced apart and extending in substantially opposite directions in the same plane, the ends of the conductor being adapted for connection to a current source.

  2. Adapting a commercial power system simulator for smart grid based system study and vulnerability assessment

    NASA Astrophysics Data System (ADS)

    Navaratne, Uditha Sudheera

    The smart grid is the future of the power grid. Smart meters and the associated network play a major role in the distributed system of the smart grid. Advance Metering Infrastructure (AMI) can enhance the reliability of the grid, generate efficient energy management opportunities and many innovations around the future smart grid. These innovations involve intense research not only on the AMI network itself but as also on the influence an AMI network can have upon the rest of the power grid. This research describes a smart meter testbed with hardware in loop that can facilitate future research in an AMI network. The smart meters in the testbed were developed such that their functionality can be customized to simulate any given scenario such as integrating new hardware components into a smart meter or developing new encryption algorithms in firmware. These smart meters were integrated into the power system simulator to simulate the power flow variation in the power grid on different AMI activities. Each smart meter in the network also provides a communication interface to the home area network. This research delivers a testbed for emulating the AMI activities and monitoring their effect on the smart grid.

  3. An adaptive discretization of compressible flow using a multitude of moving Cartesian grids

    NASA Astrophysics Data System (ADS)

    Qiu, Linhai; Lu, Wenlong; Fedkiw, Ronald

    2016-01-01

    We present a novel method for simulating compressible flow on a multitude of Cartesian grids that can rotate and translate. Following previous work, we split the time integration into an explicit step for advection followed by an implicit solve for the pressure. A second order accurate flux based scheme is devised to handle advection on each moving Cartesian grid using an effective characteristic velocity that accounts for the grid motion. In order to avoid the stringent time step restriction imposed by very fine grids, we propose strategies that allow for a fluid velocity CFL number larger than 1. The stringent time step restriction related to the sound speed is alleviated by formulating an implicit linear system in order to find a pressure consistent with the equation of state. This implicit linear system crosses overlapping Cartesian grid boundaries by utilizing local Voronoi meshes to connect the various degrees of freedom obtaining a symmetric positive-definite system. Since a straightforward application of this technique contains an inherent central differencing which can result in spurious oscillations, we introduce a new high order diffusion term similar in spirit to ENO-LLF but solved for implicitly in order to avoid any associated time step restrictions. The method is conservative on each grid, as well as globally conservative on the background grid that contains all other grids. Moreover, a conservative interpolation operator is devised for conservatively remapping values in order to keep them consistent across different overlapping grids. Additionally, the method is extended to handle two-way solid fluid coupling in a monolithic fashion including cases (in the appendix) where solids in close proximity do not properly allow for grid based degrees of freedom in between them.

  4. Adaptive software-defined coded modulation for ultra-high-speed optical transport

    NASA Astrophysics Data System (ADS)

    Djordjevic, Ivan B.; Zhang, Yequn

    2013-10-01

    In optically-routed networks, different wavelength channels carrying the traffic to different destinations can have quite different optical signal-to-noise ratios (OSNRs) and signal is differently impacted by various channel impairments. Regardless of the data destination, an optical transport system (OTS) must provide the target bit-error rate (BER) performance. To provide target BER regardless of the data destination we adjust the forward error correction (FEC) strength. Depending on the information obtained from the monitoring channels, we select the appropriate code rate matching to the OSNR range that current channel OSNR falls into. To avoid frame synchronization issues, we keep the codeword length fixed independent of the FEC code being employed. The common denominator is the employment of quasi-cyclic (QC-) LDPC codes in FEC. For high-speed implementation, low-complexity LDPC decoding algorithms are needed, and some of them will be described in this invited paper. Instead of conventional QAM based modulation schemes, we employ the signal constellations obtained by optimum signal constellation design (OSCD) algorithm. To improve the spectral efficiency, we perform the simultaneous rate adaptation and signal constellation size selection so that the product of number of bits per symbol × code rate is closest to the channel capacity. Further, we describe the advantages of using 4D signaling instead of polarization-division multiplexed (PDM) QAM, by using the 4D MAP detection, combined with LDPC coding, in a turbo equalization fashion. Finally, to solve the problems related to the limited bandwidth of information infrastructure, high energy consumption, and heterogeneity of optical networks, we describe an adaptive energy-efficient hybrid coded-modulation scheme, which in addition to amplitude, phase, and polarization state employs the spatial modes as additional basis functions for multidimensional coded-modulation.

  5. An edge-based solution-adaptive method applied to the AIRPLANE code

    NASA Technical Reports Server (NTRS)

    Biswas, Rupak; Thomas, Scott D.; Cliff, Susan E.

    1995-01-01

    Computational methods to solve large-scale realistic problems in fluid flow can be made more efficient and cost effective by using them in conjunction with dynamic mesh adaption procedures that perform simultaneous coarsening and refinement to capture flow features of interest. This work couples the tetrahedral mesh adaption scheme, 3D_TAG, with the AIRPLANE code to solve complete aircraft configuration problems in transonic and supersonic flow regimes. Results indicate that the near-field sonic boom pressure signature of a cone-cylinder is improved, the oblique and normal shocks are better resolved on a transonic wing, and the bow shock ahead of an unstarted inlet is better defined.

  6. An edge-based solution-adaptive method applied to the AIRPLANE code

    NASA Astrophysics Data System (ADS)

    Biswas, Rupak; Thomas, Scott D.; Cliff, Susan E.

    1995-11-01

    Computational methods to solve large-scale realistic problems in fluid flow can be made more efficient and cost effective by using them in conjunction with dynamic mesh adaption procedures that perform simultaneous coarsening and refinement to capture flow features of interest. This work couples the tetrahedral mesh adaption scheme, 3D_TAG, with the AIRPLANE code to solve complete aircraft configuration problems in transonic and supersonic flow regimes. Results indicate that the near-field sonic boom pressure signature of a cone-cylinder is improved, the oblique and normal shocks are better resolved on a transonic wing, and the bow shock ahead of an unstarted inlet is better defined.

  7. Three-dimensional computational fluid dynamics modeling of particle uptake by an occupational air sampler using manually-scaled and adaptive grids.

    PubMed

    Landázuri, Andrea C; Sáez, A Eduardo; Anthony, T Renée

    2016-05-01

    This work presents fluid flow and particle trajectory simulation studies to determine the aspiration efficiency of a horizontally oriented occupational air sampler using computational fluid dynamics (CFD). Grid adaption and manual scaling of the grids were applied to two sampler prototypes based on a 37-mm cassette. The standard k-ε model was used to simulate the turbulent air flow and a second order streamline-upwind discretization scheme was used to stabilize convective terms of the Navier-Stokes equations. Successively scaled grids for each configuration were created manually and by means of grid adaption using the velocity gradient in the main flow direction. Solutions were verified to assess iterative convergence, grid independence and monotonic convergence. Particle aspiration efficiencies determined for both prototype samplers were undistinguishable, indicating that the porous filter does not play a noticeable role in particle aspiration. Results conclude that grid adaption is a powerful tool that allows to refine specific regions that require lots of detail and therefore better resolve flow detail. It was verified that adaptive grids provided a higher number of locations with monotonic convergence than the manual grids and required the least computational effort.

  8. Grid generation strategies for turbomachinery configurations

    NASA Technical Reports Server (NTRS)

    Lee, K. D.; Henderson, T. L.

    1991-01-01

    Turbomachinery flow fields involve unique grid generation issues due to their geometrical and physical characteristics. Several strategic approaches are discussed to generate quality grids. The grid quality is further enhanced through blending and adapting. Grid blending smooths the grids locally through averaging and diffusion operators. Grid adaptation redistributes the grid points based on a grid quality assessment. These methods are demonstrated with several examples.

  9. Adapting a Navier-Stokes code to the ICL-DAP

    NASA Technical Reports Server (NTRS)

    Grosch, C. E.

    1985-01-01

    The results of an experiment are reported, i.c., to adapt a Navier-Stokes code, originally developed on a serial computer, to concurrent processing on the CL Distributed Array Processor (DAP). The algorithm used in solving the Navier-Stokes equations is briefly described. The architecture of the DAP and DAP FORTRAN are also described. The modifications of the algorithm so as to fit the DAP are given and discussed. Finally, performance results are given and conclusions are drawn.

  10. Effective wavelet-based compression method with adaptive quantization threshold and zerotree coding

    NASA Astrophysics Data System (ADS)

    Przelaskowski, Artur; Kazubek, Marian; Jamrogiewicz, Tomasz

    1997-10-01

    Efficient image compression technique especially for medical applications is presented. Dyadic wavelet decomposition by use of Antonini and Villasenor bank filters is followed by adaptive space-frequency quantization and zerotree-based entropy coding of wavelet coefficients. Threshold selection and uniform quantization is made on a base of spatial variance estimate built on the lowest frequency subband data set. Threshold value for each coefficient is evaluated as linear function of 9-order binary context. After quantization zerotree construction, pruning and arithmetic coding is applied for efficient lossless data coding. Presented compression method is less complex than the most effective EZW-based techniques but allows to achieve comparable compression efficiency. Specifically our method has similar to SPIHT efficiency in MR image compression, slightly better for CT image and significantly better in US image compression. Thus the compression efficiency of presented method is competitive with the best published algorithms in the literature across diverse classes of medical images.

  11. Data compression using adaptive transform coding. Appendix 1: Item 1. Ph.D. Thesis

    NASA Technical Reports Server (NTRS)

    Rost, Martin Christopher

    1988-01-01

    Adaptive low-rate source coders are described in this dissertation. These coders adapt by adjusting the complexity of the coder to match the local coding difficulty of the image. This is accomplished by using a threshold driven maximum distortion criterion to select the specific coder used. The different coders are built using variable blocksized transform techniques, and the threshold criterion selects small transform blocks to code the more difficult regions and larger blocks to code the less complex regions. A theoretical framework is constructed from which the study of these coders can be explored. An algorithm for selecting the optimal bit allocation for the quantization of transform coefficients is developed. The bit allocation algorithm is more fully developed, and can be used to achieve more accurate bit assignments than the algorithms currently used in the literature. Some upper and lower bounds for the bit-allocation distortion-rate function are developed. An obtainable distortion-rate function is developed for a particular scalar quantizer mixing method that can be used to code transform coefficients at any rate.

  12. An Adaptive Source-Channel Coding with Feedback for Progressive Transmission of Medical Images

    PubMed Central

    Lo, Jen-Lung; Sanei, Saeid; Nazarpour, Kianoush

    2009-01-01

    A novel adaptive source-channel coding with feedback for progressive transmission of medical images is proposed here. In the source coding part, the transmission starts from the region of interest (RoI). The parity length in the channel code varies with respect to both the proximity of the image subblock to the RoI and the channel noise, which is iteratively estimated in the receiver. The overall transmitted data can be controlled by the user (clinician). In the case of medical data transmission, it is vital to keep the distortion level under control as in most of the cases certain clinically important regions have to be transmitted without any visible error. The proposed system significantly reduces the transmission time and error. Moreover, the system is very user friendly since the selection of the RoI, its size, overall code rate, and a number of test features such as noise level can be set by the users in both ends. A MATLAB-based TCP/IP connection has been established to demonstrate the proposed interactive and adaptive progressive transmission system. The proposed system is simulated for both binary symmetric channel (BSC) and Rayleigh channel. The experimental results verify the effectiveness of the design. PMID:19190770

  13. CRASH: A BLOCK-ADAPTIVE-MESH CODE FOR RADIATIVE SHOCK HYDRODYNAMICS-IMPLEMENTATION AND VERIFICATION

    SciTech Connect

    Van der Holst, B.; Toth, G.; Sokolov, I. V.; Myra, E. S.; Fryxell, B.; Drake, R. P.; Powell, K. G.; Holloway, J. P.; Stout, Q.; Adams, M. L.; Morel, J. E.; Karni, S.

    2011-06-01

    We describe the Center for Radiative Shock Hydrodynamics (CRASH) code, a block-adaptive-mesh code for multi-material radiation hydrodynamics. The implementation solves the radiation diffusion model with a gray or multi-group method and uses a flux-limited diffusion approximation to recover the free-streaming limit. Electrons and ions are allowed to have different temperatures and we include flux-limited electron heat conduction. The radiation hydrodynamic equations are solved in the Eulerian frame by means of a conservative finite-volume discretization in either one-, two-, or three-dimensional slab geometry or in two-dimensional cylindrical symmetry. An operator-split method is used to solve these equations in three substeps: (1) an explicit step of a shock-capturing hydrodynamic solver; (2) a linear advection of the radiation in frequency-logarithm space; and (3) an implicit solution of the stiff radiation diffusion, heat conduction, and energy exchange. We present a suite of verification test problems to demonstrate the accuracy and performance of the algorithms. The applications are for astrophysics and laboratory astrophysics. The CRASH code is an extension of the Block-Adaptive Tree Solarwind Roe Upwind Scheme (BATS-R-US) code with a new radiation transfer and heat conduction library and equation-of-state and multi-group opacity solvers. Both CRASH and BATS-R-US are part of the publicly available Space Weather Modeling Framework.

  14. A optimized context-based adaptive binary arithmetic coding algorithm in progressive H.264 encoder

    NASA Astrophysics Data System (ADS)

    Xiao, Guang; Shi, Xu-li; An, Ping; Zhang, Zhao-yang; Gao, Ge; Teng, Guo-wei

    2006-05-01

    Context-based Adaptive Binary Arithmetic Coding (CABAC) is a new entropy coding method presented in H.264/AVC that is highly efficient in video coding. In the method, the probability of current symbol is estimated by using the wisely designed context model, which is adaptive and can approach to the statistic characteristic. Then an arithmetic coding mechanism largely reduces the redundancy in inter-symbol. Compared with UVLC method in the prior standard, CABAC is complicated but efficiently reduce the bit rate. Based on thorough analysis of coding and decoding methods of CABAC, This paper proposed two methods, sub-table method and stream-reuse methods, to improve the encoding efficiency implemented in H.264 JM code. In JM, the CABAC function produces bits one by one of every syntactic element. Multiplication operating times after times in the CABAC function lead to it inefficient.The proposed algorithm creates tables beforehand and then produce every bits of syntactic element. In JM, intra-prediction and inter-prediction mode selection algorithm with different criterion is based on RDO(rate distortion optimization) model. One of the parameter of the RDO model is bit rate that is produced by CABAC operator. After intra-prediction or inter-prediction mode selection, the CABAC stream is discard and is recalculated to output stream. The proposed Stream-reuse algorithm puts the stream in memory that is created in mode selection algorithm and reuses it in encoding function. Experiment results show that our proposed algorithm can averagely speed up 17 to 78 MSEL higher speed for QCIF and CIF sequences individually compared with the original algorithm of JM at the cost of only a little memory space. The CABAC was realized in our progressive h.264 encoder.

  15. GridMan: A grid manipulation system

    NASA Technical Reports Server (NTRS)

    Eiseman, Peter R.; Wang, Zhu

    1992-01-01

    GridMan is an interactive grid manipulation system. It operates on grids to produce new grids which conform to user demands. The input grids are not constrained to come from any particular source. They may be generated by algebraic methods, elliptic methods, hyperbolic methods, parabolic methods, or some combination of methods. The methods are included in the various available structured grid generation codes. These codes perform the basic assembly function for the various elements of the initial grid. For block structured grids, the assembly can be quite complex due to a large number of clock corners, edges, and faces for which various connections and orientations must be properly identified. The grid generation codes are distinguished among themselves by their balance between interactive and automatic actions and by their modest variations in control. The basic form of GridMan provides a much more substantial level of grid control and will take its input from any of the structured grid generation codes. The communication link to the outside codes is a data file which contains the grid or section of grid.

  16. Computations of Unsteady Viscous Compressible Flows Using Adaptive Mesh Refinement in Curvilinear Body-fitted Grid Systems

    NASA Technical Reports Server (NTRS)

    Steinthorsson, E.; Modiano, David; Colella, Phillip

    1994-01-01

    A methodology for accurate and efficient simulation of unsteady, compressible flows is presented. The cornerstones of the methodology are a special discretization of the Navier-Stokes equations on structured body-fitted grid systems and an efficient solution-adaptive mesh refinement technique for structured grids. The discretization employs an explicit multidimensional upwind scheme for the inviscid fluxes and an implicit treatment of the viscous terms. The mesh refinement technique is based on the AMR algorithm of Berger and Colella. In this approach, cells on each level of refinement are organized into a small number of topologically rectangular blocks, each containing several thousand cells. The small number of blocks leads to small overhead in managing data, while their size and regular topology means that a high degree of optimization can be achieved on computers with vector processors.

  17. Dynamic response of shock waves in transonic diffuser and supersonic inlet - An analysis with the Navier-Stokes equations and adaptive grid

    NASA Technical Reports Server (NTRS)

    Liu, N.-S.; Shamroth, S. J.; Mcdonald, H.

    1984-01-01

    An existing method which solves the multi-dimensional ensemble-averaged compressible time-dependent Navier-Stokes equations in conjunction with mixing length turbulence model and shock capturing technique has been extended to include the shock-tracking adaptive grid systems. The numerical scheme for solving the governing equations is based on a linearized block implicit approach. The effects of grid-motion and grid-distribution on the calculated flow solutions have been studied in relative detail and this is carried out in the context of physically steady, shocked flows computed with non-stationary grids. Subsequently, the unsteady dynamics of the flows occurring in a supercritically operated transonic diffuser and a mixed compression supersonic inlet have been investigated with the adaptive grid systems by solving the Navier-Stokes equations.

  18. Adaptive three-dimensional motion-compensated wavelet transform for image sequence coding

    NASA Astrophysics Data System (ADS)

    Leduc, Jean-Pierre

    1994-09-01

    This paper describes a 3D spatio-temporal coding algorithm for the bit-rate compression of digital-image sequences. The coding scheme is based on different specificities namely, a motion representation with a four-parameter affine model, a motion-adapted temporal wavelet decomposition along the motion trajectories and a signal-adapted spatial wavelet transform. The motion estimation is performed on the basis of four-parameter affine transformation models also called similitude. This transformation takes into account translations, rotations and scalings. The temporal wavelet filter bank exploits bi-orthogonal linear-phase dyadic decompositions. The 2D spatial decomposition is based on dyadic signal-adaptive filter banks with either para-unitary or bi-orthogonal bases. The adaptive filtering is carried out according to a performance criterion to be optimized under constraints in order to eventually maximize the compression ratio at the expense of graceful degradations of the subjective image quality. The major principles of the present technique is, in the analysis process, to extract and to separate the motion contained in the sequences from the spatio-temporal redundancy and, in the compression process, to take into account of the rate-distortion function on the basis of the spatio-temporal psycho-visual properties to achieve the most graceful degradations. To complete this description of the coding scheme, the compression procedure is therefore composed of scalar quantizers which exploit the spatio-temporal 3D psycho-visual properties of the Human Visual System and of entropy coders which finalize the bit rate compression.

  19. Edge Equilibrium Code (EEC) For Tokamaks

    SciTech Connect

    Li, Xujling

    2014-02-24

    The edge equilibrium code (EEC) described in this paper is developed for simulations of the near edge plasma using the finite element method. It solves the Grad-Shafranov equation in toroidal coordinate and uses adaptive grids aligned with magnetic field lines. Hermite finite elements are chosen for the numerical scheme. A fast Newton scheme which is the same as implemented in the equilibrium and stability code (ESC) is applied here to adjust the grids

  20. Effects of selective adaptation on coding sugar and salt tastes in mixtures.

    PubMed

    Frank, Marion E; Goyert, Holly F; Formaker, Bradley K; Hettinger, Thomas P

    2012-10-01

    Little is known about coding of taste mixtures in complex dynamic stimulus environments. A protocol developed for odor stimuli was used to test whether rapid selective adaptation extracted sugar and salt component tastes from mixtures as it did component odors. Seventeen human subjects identified taste components of "salt + sugar" mixtures. In 4 sessions, 16 adapt-test stimulus pairs were presented as atomized, 150-μL "taste puffs" to the tongue tip to simulate odor sniffs. Stimuli were NaCl, sucrose, "NaCl + sucrose," and water. The sugar was 98% identified but the suppressed salt 65% identified in unadapted mixtures of 2 concentrations of NaCl, 0.1 or 0.05 M, and sucrose at 3 times those concentrations, 0.3 or 0.15 M. Rapid selective adaptation decreased identification of sugar and salt preadapted ambient components to 35%, well below the 74% self-adapted level, despite variation in stimulus concentration and adapting time (<5 or >10 s). The 96% identification of sugar and salt extra mixture components was as certain as identification of single compounds. The results revealed that salt-sugar mixture suppression, dependent on relative mixture-component concentration, was mutual. Furthermore, like odors, stronger and recent tastes are emphasized in dynamic experimental conditions replicating natural situations.

  1. Adaptive analog-SSOR iterative method for solving grid equations with nonselfadjoint operators

    NASA Astrophysics Data System (ADS)

    Alekseenko, Elena; Sukhinov, Alexander; Chistyakov, Alexander; Shishenya, Alexander; Roux, Bernard

    2013-04-01

    Motion models of wave processes in the coastal zone are highly demanded in the projection and construction of coastal surface structures and breakwaters, and also as a component of other models. The most common of the grid approaches is currently vof-method. A significant drawback of this method is in the necessity to solve the convection equation to find fullness of cells. The numerical solution of this equation leads to a strong grid viscosity and "smearing" of the interface. In this paper, we propose a method, which is based on the idea of using a fill, as in vof method, but its conversion is not required to solve the equation of convection. Thus in this work, a mathematical model for the wave hydrodynamics problem, describing wash ashore and taking into account such physical parameters as turbulent exchange, complexity of domain and coastal line geometry, and bottom friction is developed. For the given mathematical model a discrete model is constructed, taking into account dynamical changing of the calculation domain. Discretization of the model is performed on the structured rectangular grid with a new developed finite-volume technique that takes into account fullness of the grid cells that allows describing geometry more accurate. Proposed technique allows improving the real accuracy of a solution in case of complex domain geometry, by improving approximation of the boundary. A software implementation and numerical experiments of the posed problem of the wave hydrodynamics is performed. The results of numerical experiments show the feasibility of using discrete mathematical models of processes that take into account fullness of grid cells, for the simulation of systems with complex geometry of the border. Numerical experiments show that the use of this technique sufficiently smooth solutions are obtained even on coarse grids.

  2. Design of signal-adapted multidimensional lifting scheme for lossy coding.

    PubMed

    Gouze, Annabelle; Antonini, Marc; Barlaud, Michel; Macq, Benoît

    2004-12-01

    This paper proposes a new method for the design of lifting filters to compute a multidimensional nonseparable wavelet transform. Our approach is stated in the general case, and is illustrated for the 2-D separable and for the quincunx images. Results are shown for the JPEG2000 database and for satellite images acquired on a quincunx sampling grid. The design of efficient quincunx filters is a difficult challenge which has already been addressed for specific cases. Our approach enables the design of less expensive filters adapted to the signal statistics to enhance the compression efficiency in a more general case. It is based on a two-step lifting scheme and joins the lifting theory with Wiener's optimization. The prediction step is designed in order to minimize the variance of the signal, and the update step is designed in order to minimize a reconstruction error. Application for lossy compression shows the performances of the method.

  3. Pilot-Assisted Adaptive Channel Estimation for Coded MC-CDMA with ICI Cancellation

    NASA Astrophysics Data System (ADS)

    Yui, Tatsunori; Tomeba, Hiromichi; Adachi, Fumiyuki

    One of the promising wireless access techniques for the next generation mobile communications systems is multi-carrier code division multiple access (MC-CDMA). MC-CDMA can provide good transmission performance owing to the frequency diversity effect in a severe frequency-selective fading channel. However, the bit error rate (BER) performance of coded MC-CDMA is inferior to that of orthogonal frequency division multiplexing (OFDM) due to the residual inter-code interference (ICI) after frequency-domain equalization (FDE). Recently, we proposed a frequency-domain soft interference cancellation (FDSIC) to reduce the residual ICI and confirmed by computer simulation that the MC-CDMA with FDSIC provides better BER performance than OFDM. However, ideal channel estimation was assumed. In this paper, we propose adaptive decision-feedback channel estimation (ADFCE) and evaluate by computer simulation the average BER and throughput performances of turbo-coded MC-CDMA with FDSIC. We show that even if a practical channel estimation is used, MC-CDMA with FDSIC can still provide better performance than OFDM.

  4. Control Dynamics of Adaptive and Scalable Power and Energy Systems for Military Micro Grids

    DTIC Science & Technology

    2006-12-01

    quality at the levels required for Army installations ( Fairley 2004; Apt et al. 2004; Sheblé 2006; Weaver 2004; EPRI 2003; Silberman 2001; Blum 2004; Behr...Challenges of the 21st Century: 2003 Summary and Synthesis. Report # 1010929. Fairley , P. 2004. The unruly power grid. IEEE Spectrum 41(8): 16-21

  5. Contour coding based rotating adaptive model for human detection and tracking in thermal catadioptric omnidirectional vision.

    PubMed

    Tang, Yazhe; Li, Youfu

    2012-09-20

    In this paper, we introduce a novel surveillance system based on thermal catadioptric omnidirectional (TCO) vision. The conventional contour-based methods are difficult to be applied to the TCO sensor for detection or tracking purposes due to the distortion of TCO vision. To solve this problem, we propose a contour coding based rotating adaptive model (RAM) that can extract the contour feature from the TCO vision directly as it takes advantage of the relative angle based on the characteristics of TCO vision to change the sequence of sampling automatically. A series of experiments and quantitative analyses verify that the performance of the proposed RAM-based contour coding feature for human detection and tracking are satisfactory in TCO vision.

  6. Long-range accelerated BOTDA sensor using adaptive linear prediction and cyclic coding.

    PubMed

    Muanenda, Yonas; Taki, Mohammad; Pasquale, Fabrizio Di

    2014-09-15

    We propose and experimentally demonstrate a long-range accelerated Brillouin optical time domain analysis (BOTDA) sensor that exploits the complementary noise reduction benefits of adaptive linear prediction and optical pulse coding. The combined technique allows using orders of magnitude less the number of averages of the backscattered BOTDA traces compared to a standard single pulse BOTDA, enabling distributed strain measurement over 10 km of a standard single mode fiber with meter-scale spatial resolution and 1.8 MHz Brillouin frequency shift resolution. By optimizing the system parameters, the measurement is achieved with only 20 averages for each Brillouin gain spectrum scanned frequency, allowing for an eight times faster strain measurement compared to the use of cyclic pulse coding alone.

  7. PHURBAS: AN ADAPTIVE, LAGRANGIAN, MESHLESS, MAGNETOHYDRODYNAMICS CODE. II. IMPLEMENTATION AND TESTS

    SciTech Connect

    McNally, Colin P.; Mac Low, Mordecai-Mark; Maron, Jason L. E-mail: jmaron@amnh.org

    2012-05-01

    We present an algorithm for simulating the equations of ideal magnetohydrodynamics and other systems of differential equations on an unstructured set of points represented by sample particles. The particles move with the fluid, so the time step is not limited by the Eulerian Courant-Friedrichs-Lewy condition. Full spatial adaptivity is required to ensure the particles fill the computational volume and gives the algorithm substantial flexibility and power. A target resolution is specified for each point in space, with particles being added and deleted as needed to meet this target. We have parallelized the code by adapting the framework provided by GADGET-2. A set of standard test problems, including 10{sup -6} amplitude linear magnetohydrodynamics waves, magnetized shock tubes, and Kelvin-Helmholtz instabilities is presented. Finally, we demonstrate good agreement with analytic predictions of linear growth rates for magnetorotational instability in a cylindrical geometry. This paper documents the Phurbas algorithm as implemented in Phurbas version 1.1.

  8. Introducing Enabling Computational Tools to the Climate Sciences: Multi-Resolution Climate Modeling with Adaptive Cubed-Sphere Grids

    SciTech Connect

    Jablonowski, Christiane

    2015-07-14

    The research investigates and advances strategies how to bridge the scale discrepancies between local, regional and global phenomena in climate models without the prohibitive computational costs of global cloud-resolving simulations. In particular, the research explores new frontiers in computational geoscience by introducing high-order Adaptive Mesh Refinement (AMR) techniques into climate research. AMR and statically-adapted variable-resolution approaches represent an emerging trend for atmospheric models and are likely to become the new norm in future-generation weather and climate models. The research advances the understanding of multi-scale interactions in the climate system and showcases a pathway how to model these interactions effectively with advanced computational tools, like the Chombo AMR library developed at the Lawrence Berkeley National Laboratory. The research is interdisciplinary and combines applied mathematics, scientific computing and the atmospheric sciences. In this research project, a hierarchy of high-order atmospheric models on cubed-sphere computational grids have been developed that serve as an algorithmic prototype for the finite-volume solution-adaptive Chombo-AMR approach. The foci of the investigations have lied on the characteristics of both static mesh adaptations and dynamically-adaptive grids that can capture flow fields of interest like tropical cyclones. Six research themes have been chosen. These are (1) the introduction of adaptive mesh refinement techniques into the climate sciences, (2) advanced algorithms for nonhydrostatic atmospheric dynamical cores, (3) an assessment of the interplay between resolved-scale dynamical motions and subgrid-scale physical parameterizations, (4) evaluation techniques for atmospheric model hierarchies, (5) the comparison of AMR refinement strategies and (6) tropical cyclone studies with a focus on multi-scale interactions and variable-resolution modeling. The results of this research project

  9. COLLABORATIVE RESEARCH: CONTINUOUS DYNAMIC GRID ADAPTATION IN A GLOBAL ATMOSPHERIC MODEL: APPLICATION AND REFINEMENT

    SciTech Connect

    Prusa, Joseph

    2012-05-08

    This project had goals of advancing the performance capabilities of the numerical general circulation model EULAG and using it to produce a fully operational atmospheric global climate model (AGCM) that can employ either static or dynamic grid stretching for targeted phenomena. The resulting AGCM combined EULAG's advanced dynamics core with the physics of the NCAR Community Atmospheric Model (CAM). Effort discussed below shows how we improved model performance and tested both EULAG and the coupled CAM-EULAG in several ways to demonstrate the grid stretching and ability to simulate very well a wide range of scales, that is, multi-scale capability. We leveraged our effort through interaction with an international EULAG community that has collectively developed new features and applications of EULAG, which we exploited for our own work summarized here. Overall, the work contributed to over 40 peer- reviewed publications and over 70 conference/workshop/seminar presentations, many of them invited.

  10. Parallel Unsteady Overset Mesh Methodology for Adaptive and Moving Grids with Multiple Solvers

    DTIC Science & Technology

    2010-01-01

    Runge - Kutta time-stepping framework and is capable of up to fifth-order accurate spatial discretizations. Further, the Cartesian grids in the off-body are...no user intervention or explicit hole-map specification is necessary. The capabilities and performance of the package are presented for several test...connectivity approaches have been investigated in the past by various research groups . The prominent among them are PEGASUS5 [5], OVERFLOW-DCF [6, 7], SUGGAR

  11. Parallel Unsteady Overset Mesh Methodology for a Multi-Solver Paradigm with Adaptive Cartesian Grids

    DTIC Science & Technology

    2008-08-21

    a multi-stage Runge - Kutta time-stepping framework and is capable of up to fifth-order accurate spatial discretizations. Further, the Cartesian grids...cutting methodology such that no user inter- vention or explicit hole-map specification is necessary. The capabilities and performance of the package are...application to rotorcraft aerodynamics. Several Domain-Connectivity approaches have been investigated in the past by various research groups . The

  12. 3D Composite Grids Using Bezier Curves and Surfaces in Component Adaptive Methods

    DTIC Science & Technology

    1993-08-01

    bounding curves, an algebraic grid generation method, such as transfinite interpolation of these curves, results in a definition of the interior of...dependent variables is assembled and solved iteratively. The interior generated by the transfinite interpolation technique is used as the initial guess...The boundaries of the face are first parameterized in this fashion Transfinite interpolation is then employed first to obtain a parameterization of

  13. Dynamic optical aberration correction with adaptive coded apertures techniques in conformal imaging

    NASA Astrophysics Data System (ADS)

    Li, Yan; Hu, Bin; Zhang, Pengbin; Zhang, Binglong

    2015-02-01

    Conformal imaging systems are confronted with dynamic aberration in optical design processing. In classical optical designs, for combination high requirements of field of view, optical speed, environmental adaption and imaging quality, further enhancements can be achieved only by the introduction of increased complexity of aberration corrector. In recent years of computational imaging, the adaptive coded apertures techniques which has several potential advantages over more traditional optical systems is particularly suitable for military infrared imaging systems. The merits of this new concept include low mass, volume and moments of inertia, potentially lower costs, graceful failure modes, steerable fields of regard with no macroscopic moving parts. Example application for conformal imaging system design where the elements of a set of binary coded aperture masks are applied are optimization designed is presented in this paper, simulation results show that the optical performance is closely related to the mask design and the reconstruction algorithm optimization. As a dynamic aberration corrector, a binary-amplitude mask located at the aperture stop is optimized to mitigate dynamic optical aberrations when the field of regard changes and allow sufficient information to be recorded by the detector for the recovery of a sharp image using digital image restoration in conformal optical system.

  14. Flexible Coding of Task Rules in Frontoparietal Cortex: An Adaptive System for Flexible Cognitive Control.

    PubMed

    Woolgar, Alexandra; Afshar, Soheil; Williams, Mark A; Rich, Anina N

    2015-10-01

    How do our brains achieve the cognitive control that is required for flexible behavior? Several models of cognitive control propose a role for frontoparietal cortex in the structure and representation of task sets or rules. For behavior to be flexible, however, the system must also rapidly reorganize as mental focus changes. Here we used multivoxel pattern analysis of fMRI data to demonstrate adaptive reorganization of frontoparietal activity patterns following a change in the complexity of the task rules. When task rules were relatively simple, frontoparietal cortex did not hold detectable information about these rules. In contrast, when the rules were more complex, frontoparietal cortex showed clear and decodable rule discrimination. Our data demonstrate that frontoparietal activity adjusts to task complexity, with better discrimination of rules that are behaviorally more confusable. The change in coding was specific to the rule element of the task and was not mirrored in more specialized cortex (early visual cortex) where coding was independent of difficulty. In line with an adaptive view of frontoparietal function, the data suggest a system that rapidly reconfigures in accordance with the difficulty of a behavioral task. This system may provide a neural basis for the flexible control of human behavior.

  15. Complexity modeling for context-based adaptive binary arithmetic coding (CABAC) in H.264/AVC decoder

    NASA Astrophysics Data System (ADS)

    Lee, Szu-Wei; Kuo, C.-C. Jay

    2007-09-01

    One way to save the power consumption in the H.264 decoder is for the H.264 encoder to generate decoderfriendly bit streams. By following this idea, a decoding complexity model of context-based adaptive binary arithmetic coding (CABAC) for H.264/AVC is investigated in this research. Since different coding modes will have an impact on the number of quantized transformed coeffcients (QTCs) and motion vectors (MVs) and, consequently, the complexity of entropy decoding, the encoder with a complexity model can estimate the complexity of entropy decoding and choose the best coding mode to yield the best tradeoff between the rate, distortion and decoding complexity performance. The complexity model consists of two parts: one for source data (i.e. QTCs) and the other for header data (i.e. the macro-block (MB) type and MVs). Thus, the proposed CABAC decoding complexity model of a MB is a function of QTCs and associated MVs, which is verified experimentally. The proposed CABAC decoding complexity model can provide good estimation results for variant bit streams. Practical applications of this complexity model will also be discussed.

  16. Dynamic Power Grid Simulation

    SciTech Connect

    Top, Philip; Woodward, Carol; Smith, Steve; Banks, Lawrence; Kelley, Brian

    2015-09-14

    GridDyn is a part of power grid simulation toolkit. The code is designed using modern object oriented C++ methods utilizing C++11 and recent Boost libraries to ensure compatibility with multiple operating systems and environments.

  17. Evaluation of in-network adaptation of scalable high efficiency video coding (SHVC) in mobile environments

    NASA Astrophysics Data System (ADS)

    Nightingale, James; Wang, Qi; Grecos, Christos; Goma, Sergio

    2014-02-01

    High Efficiency Video Coding (HEVC), the latest video compression standard (also known as H.265), can deliver video streams of comparable quality to the current H.264 Advanced Video Coding (H.264/AVC) standard with a 50% reduction in bandwidth. Research into SHVC, the scalable extension to the HEVC standard, is still in its infancy. One important area for investigation is whether, given the greater compression ratio of HEVC (and SHVC), the loss of packets containing video content will have a greater impact on the quality of delivered video than is the case with H.264/AVC or its scalable extension H.264/SVC. In this work we empirically evaluate the layer-based, in-network adaptation of video streams encoded using SHVC in situations where dynamically changing bandwidths and datagram loss ratios require the real-time adaptation of video streams. Through the use of extensive experimentation, we establish a comprehensive set of benchmarks for SHVC-based highdefinition video streaming in loss prone network environments such as those commonly found in mobile networks. Among other results, we highlight that packet losses of only 1% can lead to a substantial reduction in PSNR of over 3dB and error propagation in over 130 pictures following the one in which the loss occurred. This work would be one of the earliest studies in this cutting-edge area that reports benchmark evaluation results for the effects of datagram loss on SHVC picture quality and offers empirical and analytical insights into SHVC adaptation to lossy, mobile networking conditions.

  18. FPGA-based rate-adaptive LDPC-coded modulation for the next generation of optical communication systems.

    PubMed

    Zou, Ding; Djordjevic, Ivan B

    2016-09-05

    In this paper, we propose a rate-adaptive FEC scheme based on LDPC codes together with its software reconfigurable unified FPGA architecture. By FPGA emulation, we demonstrate that the proposed class of rate-adaptive LDPC codes based on shortening with an overhead from 25% to 42.9% provides a coding gain ranging from 13.08 dB to 14.28 dB at a post-FEC BER of 10-15 for BPSK transmission. In addition, the proposed rate-adaptive LDPC coding combined with higher-order modulations have been demonstrated including QPSK, 8-QAM, 16-QAM, 32-QAM, and 64-QAM, which covers a wide range of signal-to-noise ratios. Furthermore, we apply the unequal error protection by employing different LDPC codes on different bits in 16-QAM and 64-QAM, which results in additional 0.5dB gain compared to conventional LDPC coded modulation with the same code rate of corresponding LDPC code.

  19. Spatially adaptive bases in wavelet-based coding of semi-regular meshes

    NASA Astrophysics Data System (ADS)

    Denis, Leon; Florea, Ruxandra; Munteanu, Adrian; Schelkens, Peter

    2010-05-01

    In this paper we present a wavelet-based coding approach for semi-regular meshes, which spatially adapts the employed wavelet basis in the wavelet transformation of the mesh. The spatially-adaptive nature of the transform requires additional information to be stored in the bit-stream in order to allow the reconstruction of the transformed mesh at the decoder side. In order to limit this overhead, the mesh is first segmented into regions of approximately equal size. For each spatial region, a predictor is selected in a rate-distortion optimal manner by using a Lagrangian rate-distortion optimization technique. When compared against the classical wavelet transform employing the butterfly subdivision filter, experiments reveal that the proposed spatially-adaptive wavelet transform significantly decreases the energy of the wavelet coefficients for all subbands. Preliminary results show also that employing the proposed transform for the lowest-resolution subband systematically yields improved compression performance at low-to-medium bit-rates. For the Venus and Rabbit test models the compression improvements add up to 1.47 dB and 0.95 dB, respectively.

  20. Hyperspectral image compression: adapting SPIHT and EZW to anisotropic 3-D wavelet coding.

    PubMed

    Christophe, Emmanuel; Mailhes, Corinne; Duhamel, Pierre

    2008-12-01

    Hyperspectral images present some specific characteristics that should be used by an efficient compression system. In compression, wavelets have shown a good adaptability to a wide range of data, while being of reasonable complexity. Some wavelet-based compression algorithms have been successfully used for some hyperspectral space missions. This paper focuses on the optimization of a full wavelet compression system for hyperspectral images. Each step of the compression algorithm is studied and optimized. First, an algorithm to find the optimal 3-D wavelet decomposition in a rate-distortion sense is defined. Then, it is shown that a specific fixed decomposition has almost the same performance, while being more useful in terms of complexity issues. It is shown that this decomposition significantly improves the classical isotropic decomposition. One of the most useful properties of this fixed decomposition is that it allows the use of zero tree algorithms. Various tree structures, creating a relationship between coefficients, are compared. Two efficient compression methods based on zerotree coding (EZW and SPIHT) are adapted on this near-optimal decomposition with the best tree structure found. Performances are compared with the adaptation of JPEG 2000 for hyperspectral images on six different areas presenting different statistical properties.

  1. Improving Inpatient Surveys: Web-Based Computer Adaptive Testing Accessed via Mobile Phone QR Codes

    PubMed Central

    2016-01-01

    Background The National Health Service (NHS) 70-item inpatient questionnaire surveys inpatients on their perceptions of their hospitalization experience. However, it imposes more burden on the patient than other similar surveys. The literature shows that computerized adaptive testing (CAT) based on item response theory can help shorten the item length of a questionnaire without compromising its precision. Objective Our aim was to investigate whether CAT can be (1) efficient with item reduction and (2) used with quick response (QR) codes scanned by mobile phones. Methods After downloading the 2008 inpatient survey data from the Picker Institute Europe website and analyzing the difficulties of this 70-item questionnaire, we used an author-made Excel program using the Rasch partial credit model to simulate 1000 patients’ true scores followed by a standard normal distribution. The CAT was compared to two other scenarios of answering all items (AAI) and the randomized selection method (RSM), as we investigated item length (efficiency) and measurement accuracy. The author-made Web-based CAT program for gathering patient feedback was effectively accessed from mobile phones by scanning the QR code. Results We found that the CAT can be more efficient for patients answering questions (ie, fewer items to respond to) than either AAI or RSM without compromising its measurement accuracy. A Web-based CAT inpatient survey accessed by scanning a QR code on a mobile phone was viable for gathering inpatient satisfaction responses. Conclusions With advances in technology, patients can now be offered alternatives for providing feedback about hospitalization satisfaction. This Web-based CAT is a possible option in health care settings for reducing the number of survey items, as well as offering an innovative QR code access. PMID:26935793

  2. Adaptive Transmission Planning: Implementing a New Paradigm for Managing Economic Risks in Grid Expansion

    SciTech Connect

    Hobbs, Benjamin F.; Xu, Qingyu; Ho, Jonathan; Donohoo, Pearl; Kasina, Saamrat; Ouyang, Jasmine; Park, Sang Woo; Eto, Joseph; Satyal, Vijay

    2016-07-01

    The problem of whether, where, when, and what types of transmission facilities to build in terms of minimizing costs and maximizing net economic benefits has been a challenge for the power industry from the beginning-ever since Thomas Edison debated whether to create longer dc distribution lines (with their high losses) or build new power stations in expanding his urban markets. Today's planning decisions are far more complex, as grids cover the continent and new transmission, generation, and demand-side technologies emerge.

  3. Coding and decoding with adapting neurons: a population approach to the peri-stimulus time histogram.

    PubMed

    Naud, Richard; Gerstner, Wulfram

    2012-01-01

    The response of a neuron to a time-dependent stimulus, as measured in a Peri-Stimulus-Time-Histogram (PSTH), exhibits an intricate temporal structure that reflects potential temporal coding principles. Here we analyze the encoding and decoding of PSTHs for spiking neurons with arbitrary refractoriness and adaptation. As a modeling framework, we use the spike response model, also known as the generalized linear neuron model. Because of refractoriness, the effect of the most recent spike on the spiking probability a few milliseconds later is very strong. The influence of the last spike needs therefore to be described with high precision, while the rest of the neuronal spiking history merely introduces an average self-inhibition or adaptation that depends on the expected number of past spikes but not on the exact spike timings. Based on these insights, we derive a 'quasi-renewal equation' which is shown to yield an excellent description of the firing rate of adapting neurons. We explore the domain of validity of the quasi-renewal equation and compare it with other rate equations for populations of spiking neurons. The problem of decoding the stimulus from the population response (or PSTH) is addressed analogously. We find that for small levels of activity and weak adaptation, a simple accumulator of the past activity is sufficient to decode the original input, but when refractory effects become large decoding becomes a non-linear function of the past activity. The results presented here can be applied to the mean-field analysis of coupled neuron networks, but also to arbitrary point processes with negative self-interaction.

  4. Advanced Unstructured Grid Generation for Complex Aerodynamic Applications

    NASA Technical Reports Server (NTRS)

    Pirzadeh, Shahyar Z.

    2008-01-01

    A new approach for distribution of grid points on the surface and in the volume has been developed and implemented in the NASA unstructured grid generation code VGRID. In addition to the point and line sources of prior work, the new approach utilizes surface and volume sources for automatic curvature-based grid sizing and convenient point distribution in the volume. A new exponential growth function produces smoother and more efficient grids and provides superior control over distribution of grid points in the field. All types of sources support anisotropic grid stretching which not only improves the grid economy but also provides more accurate solutions for certain aerodynamic applications. The new approach does not require a three-dimensional background grid as in the previous methods. Instead, it makes use of an efficient bounding-box auxiliary medium for storing grid parameters defined by surface sources. The new approach is less memory-intensive and more efficient computationally. The grids generated with the new method either eliminate the need for adaptive grid refinement for certain class of problems or provide high quality initial grids that would enhance the performance of many adaptation methods.

  5. Computational Aerothermodynamic Simulation Issues on Unstructured Grids

    NASA Technical Reports Server (NTRS)

    Gnoffo, Peter A.; White, Jeffery A.

    2004-01-01

    The synthesis of physical models for gas chemistry and turbulence from the structured grid codes LAURA and VULCAN into the unstructured grid code FUN3D is described. A directionally Symmetric, Total Variation Diminishing (STVD) algorithm and an entropy fix (eigenvalue limiter) keyed to local cell Reynolds number are introduced to improve solution quality for hypersonic aeroheating applications. A simple grid-adaptation procedure is incorporated within the flow solver. Simulations of flow over an ellipsoid (perfect gas, inviscid), Shuttle Orbiter (viscous, chemical nonequilibrium) and comparisons to the structured grid solvers LAURA (cylinder, Shuttle Orbiter) and VULCAN (flat plate) are presented to show current capabilities. The quality of heating in 3D stagnation regions is very sensitive to algorithm options in general, high aspect ratio tetrahedral elements complicate the simulation of high Reynolds number, viscous flow as compared to locally structured meshes aligned with the flow.

  6. Fast 3-D large-scale gravity and magnetic modeling using unstructured grids and an adaptive multilevel fast multipole method

    NASA Astrophysics Data System (ADS)

    Ren, Zhengyong; Tang, Jingtian; Kalscheuer, Thomas; Maurer, Hansruedi

    2017-01-01

    A novel fast and accurate algorithm is developed for large-scale 3-D gravity and magnetic modeling problems. An unstructured grid discretization is used to approximate sources with arbitrary mass and magnetization distributions. A novel adaptive multilevel fast multipole (AMFM) method is developed to reduce the modeling time. An observation octree is constructed on a set of arbitrarily distributed observation sites, while a source octree is constructed on a source tetrahedral grid. A novel characteristic is the independence between the observation octree and the source octree, which simplifies the implementation of different survey configurations such as airborne and ground surveys. Two synthetic models, a cubic model and a half-space model with mountain-valley topography, are tested. As compared to analytical solutions of gravity and magnetic signals, excellent agreements of the solutions verify the accuracy of our AMFM algorithm. Finally, our AMFM method is used to calculate the terrain effect on an airborne gravity data set for a realistic topography model represented by a triangular surface retrieved from a digital elevation model. Using 16 threads, more than 5800 billion interactions between 1,002,001 observation points and 5,839,830 tetrahedral elements are computed in 453.6 s. A traditional first-order Gaussian quadrature approach requires 3.77 days. Hence, our new AMFM algorithm not only can quickly compute the gravity and magnetic signals for complicated problems but also can substantially accelerate the solution of 3-D inversion problems.

  7. Impact of Load Balancing on Unstructured Adaptive Grid Computations for Distributed-Memory Multiprocessors

    NASA Technical Reports Server (NTRS)

    Sohn, Andrew; Biswas, Rupak; Simon, Horst D.

    1996-01-01

    The computational requirements for an adaptive solution of unsteady problems change as the simulation progresses. This causes workload imbalance among processors on a parallel machine which, in turn, requires significant data movement at runtime. We present a new dynamic load-balancing framework, called JOVE, that balances the workload across all processors with a global view. Whenever the computational mesh is adapted, JOVE is activated to eliminate the load imbalance. JOVE has been implemented on an IBM SP2 distributed-memory machine in MPI for portability. Experimental results for two model meshes demonstrate that mesh adaption with load balancing gives more than a sixfold improvement over one without load balancing. We also show that JOVE gives a 24-fold speedup on 64 processors compared to sequential execution.

  8. An adaptive sparse-grid high-order stochastic collocation method for Bayesian inference in groundwater reactive transport modeling

    SciTech Connect

    Zhang, Guannan; Webster, Clayton G; Gunzburger, Max D

    2012-09-01

    Although Bayesian analysis has become vital to the quantification of prediction uncertainty in groundwater modeling, its application has been hindered due to the computational cost associated with numerous model executions needed for exploring the posterior probability density function (PPDF) of model parameters. This is particularly the case when the PPDF is estimated using Markov Chain Monte Carlo (MCMC) sampling. In this study, we develop a new approach that improves computational efficiency of Bayesian inference by constructing a surrogate system based on an adaptive sparse-grid high-order stochastic collocation (aSG-hSC) method. Unlike previous works using first-order hierarchical basis, we utilize a compactly supported higher-order hierar- chical basis to construct the surrogate system, resulting in a significant reduction in the number of computational simulations required. In addition, we use hierarchical surplus as an error indi- cator to determine adaptive sparse grids. This allows local refinement in the uncertain domain and/or anisotropic detection with respect to the random model parameters, which further improves computational efficiency. Finally, we incorporate a global optimization technique and propose an iterative algorithm for building the surrogate system for the PPDF with multiple significant modes. Once the surrogate system is determined, the PPDF can be evaluated by sampling the surrogate system directly with very little computational cost. The developed method is evaluated first using a simple analytical density function with multiple modes and then using two synthetic groundwater reactive transport models. The groundwater models represent different levels of complexity; the first example involves coupled linear reactions and the second example simulates nonlinear ura- nium surface complexation. The results show that the aSG-hSC is an effective and efficient tool for Bayesian inference in groundwater modeling in comparison with conventional

  9. Adaptive coded spreading OFDM signal for dynamic-λ optical access network

    NASA Astrophysics Data System (ADS)

    Liu, Bo; Zhang, Lijia; Xin, Xiangjun

    2015-12-01

    This paper proposes and experimentally demonstrates a novel adaptive coded spreading (ACS) orthogonal frequency division multiplexing (OFDM) signal for dynamic distributed optical ring-based access network. The wavelength can be assigned to different remote nodes (RNs) according to the traffic demand of optical network unit (ONU). The ACS can provide dynamic spreading gain to different signals according to the split ratio or transmission length, which offers flexible power budget for the network. A 10×13.12 Gb/s OFDM access with ACS is successfully demonstrated over two RNs and 120 km transmission in the experiment. The demonstrated method may be viewed as one promising for future optical metro access network.

  10. Image sensor system with bio-inspired efficient coding and adaptation.

    PubMed

    Okuno, Hirotsugu; Yagi, Tetsuya

    2012-08-01

    We designed and implemented an image sensor system equipped with three bio-inspired coding and adaptation strategies: logarithmic transform, local average subtraction, and feedback gain control. The system comprises a field-programmable gate array (FPGA), a resistive network, and active pixel sensors (APS), whose light intensity-voltage characteristics are controllable. The system employs multiple time-varying reset voltage signals for APS in order to realize multiple logarithmic intensity-voltage characteristics, which are controlled so that the entropy of the output image is maximized. The system also employs local average subtraction and gain control in order to obtain images with an appropriate contrast. The local average is calculated by the resistive network instantaneously. The designed system was successfully used to obtain appropriate images of objects that were subjected to large changes in illumination.

  11. MPI parallelization of full PIC simulation code with Adaptive Mesh Refinement

    NASA Astrophysics Data System (ADS)

    Matsui, Tatsuki; Nunami, Masanori; Usui, Hideyuki; Moritaka, Toseo

    2010-11-01

    A new parallelization technique developed for PIC method with adaptive mesh refinement (AMR) is introduced. In AMR technique, the complicated cell arrangements are organized and managed as interconnected pointers with multiple resolution levels, forming a fully threaded tree structure as a whole. In order to retain this tree structure distributed over multiple processes, remote memory access, an extended feature of MPI2 standards, is employed. Another important feature of the present simulation technique is the domain decomposition according to the modified Morton ordering. This algorithm can group up the equal number of particle calculation loops, which allows for the better load balance. Using this advanced simulation code, preliminary results for basic physical problems are exhibited for the validity check, together with the benchmarks to test the performance and the scalability.

  12. Development of a framework and coding system for modifications and adaptations of evidence-based interventions

    PubMed Central

    2013-01-01

    Background Evidence-based interventions are frequently modified or adapted during the implementation process. Changes may be made to protocols to meet the needs of the target population or address differences between the context in which the intervention was originally designed and the one into which it is implemented [Addict Behav 2011, 36(6):630–635]. However, whether modification compromises or enhances the desired benefits of the intervention is not well understood. A challenge to understanding the impact of specific types of modifications is a lack of attention to characterizing the different types of changes that may occur. A system for classifying the types of modifications that are made when interventions and programs are implemented can facilitate efforts to understand the nature of modifications that are made in particular contexts as well as the impact of these modifications on outcomes of interest. Methods We developed a system for classifying modifications made to interventions and programs across a variety of fields and settings. We then coded 258 modifications identified in 32 published articles that described interventions implemented in routine care or community settings. Results We identified modifications made to the content of interventions, as well as to the context in which interventions are delivered. We identified 12 different types of content modifications, and our coding scheme also included ratings for the level at which these modifications were made (ranging from the individual patient level up to a hospital network or community). We identified five types of contextual modifications (changes to the format, setting, or patient population that do not in and of themselves alter the actual content of the intervention). We also developed codes to indicate who made the modifications and identified a smaller subset of modifications made to the ways that training or evaluations occur when evidence-based interventions are implemented. Rater

  13. ADAPTIVE-GRID SIMULATION OF GROUNDWATER FLOW IN HETEROGENEOUS AQUIFERS. (R825689C068)

    EPA Science Inventory

    Abstract

    The prediction of contaminant transport in porous media requires the computation of the flow velocity. This work presents a methodology for high-accuracy computation of flow in a heterogeneous isotropic formation, employing a dual-flow formulation and adaptive...

  14. WHITE DWARF MERGERS ON ADAPTIVE MESHES. I. METHODOLOGY AND CODE VERIFICATION

    SciTech Connect

    Katz, Max P.; Zingale, Michael; Calder, Alan C.; Swesty, F. Douglas; Almgren, Ann S.; Zhang, Weiqun

    2016-03-10

    The Type Ia supernova (SN Ia) progenitor problem is one of the most perplexing and exciting problems in astrophysics, requiring detailed numerical modeling to complement observations of these explosions. One possible progenitor that has merited recent theoretical attention is the white dwarf (WD) merger scenario, which has the potential to naturally explain many of the observed characteristics of SNe Ia. To date there have been relatively few self-consistent simulations of merging WD systems using mesh-based hydrodynamics. This is the first paper in a series describing simulations of these systems using a hydrodynamics code with adaptive mesh refinement. In this paper we describe our numerical methodology and discuss our implementation in the compressible hydrodynamics code CASTRO, which solves the Euler equations, and the Poisson equation for self-gravity, and couples the gravitational and rotation forces to the hydrodynamics. Standard techniques for coupling gravitation and rotation forces to the hydrodynamics do not adequately conserve the total energy of the system for our problem, but recent advances in the literature allow progress and we discuss our implementation here. We present a set of test problems demonstrating the extent to which our software sufficiently models a system where large amounts of mass are advected on the computational domain over long timescales. Future papers in this series will describe our treatment of the initial conditions of these systems and will examine the early phases of the merger to determine its viability for triggering a thermonuclear detonation.

  15. White Dwarf Mergers on Adaptive Meshes. I. Methodology and Code Verification

    NASA Astrophysics Data System (ADS)

    Katz, Max P.; Zingale, Michael; Calder, Alan C.; Swesty, F. Douglas; Almgren, Ann S.; Zhang, Weiqun

    2016-03-01

    The Type Ia supernova (SN Ia) progenitor problem is one of the most perplexing and exciting problems in astrophysics, requiring detailed numerical modeling to complement observations of these explosions. One possible progenitor that has merited recent theoretical attention is the white dwarf (WD) merger scenario, which has the potential to naturally explain many of the observed characteristics of SNe Ia. To date there have been relatively few self-consistent simulations of merging WD systems using mesh-based hydrodynamics. This is the first paper in a series describing simulations of these systems using a hydrodynamics code with adaptive mesh refinement. In this paper we describe our numerical methodology and discuss our implementation in the compressible hydrodynamics code CASTRO, which solves the Euler equations, and the Poisson equation for self-gravity, and couples the gravitational and rotation forces to the hydrodynamics. Standard techniques for coupling gravitation and rotation forces to the hydrodynamics do not adequately conserve the total energy of the system for our problem, but recent advances in the literature allow progress and we discuss our implementation here. We present a set of test problems demonstrating the extent to which our software sufficiently models a system where large amounts of mass are advected on the computational domain over long timescales. Future papers in this series will describe our treatment of the initial conditions of these systems and will examine the early phases of the merger to determine its viability for triggering a thermonuclear detonation.

  16. Adaptive Coding and Modulation Experiment With NASA's Space Communication and Navigation Testbed

    NASA Technical Reports Server (NTRS)

    Downey, Joseph A.; Mortensen, Dale J.; Evans, Michael A.; Briones, Janette C.; Tollis, Nicholas

    2016-01-01

    National Aeronautics and Space Administration (NASA)'s Space Communication and Navigation Testbed is an advanced integrated communication payload on the International Space Station. This paper presents results from an adaptive coding and modulation (ACM) experiment over S-band using a direct-to-earth link between the SCaN Testbed and the Glenn Research Center. The testing leverages the established Digital Video Broadcasting Second Generation (DVB-S2) standard to provide various modulation and coding options, and uses the Space Data Link Protocol (Consultative Committee for Space Data Systems (CCSDS) standard) for the uplink and downlink data framing. The experiment was con- ducted in a challenging environment due to the multipath and shadowing caused by the International Space Station structure. Several approaches for improving the ACM system are presented, including predictive and learning techniques to accommodate signal fades. Performance of the system is evaluated as a function of end-to-end system latency (round- trip delay), and compared to the capacity of the link. Finally, improvements over standard NASA waveforms are presented.

  17. Hybrid threshold adaptable quantum secret sharing scheme with reverse Huffman-Fibonacci-tree coding

    PubMed Central

    Lai, Hong; Zhang, Jun; Luo, Ming-Xing; Pan, Lei; Pieprzyk, Josef; Xiao, Fuyuan; Orgun, Mehmet A.

    2016-01-01

    With prevalent attacks in communication, sharing a secret between communicating parties is an ongoing challenge. Moreover, it is important to integrate quantum solutions with classical secret sharing schemes with low computational cost for the real world use. This paper proposes a novel hybrid threshold adaptable quantum secret sharing scheme, using an m-bonacci orbital angular momentum (OAM) pump, Lagrange interpolation polynomials, and reverse Huffman-Fibonacci-tree coding. To be exact, we employ entangled states prepared by m-bonacci sequences to detect eavesdropping. Meanwhile, we encode m-bonacci sequences in Lagrange interpolation polynomials to generate the shares of a secret with reverse Huffman-Fibonacci-tree coding. The advantages of the proposed scheme is that it can detect eavesdropping without joint quantum operations, and permits secret sharing for an arbitrary but no less than threshold-value number of classical participants with much lower bandwidth. Also, in comparison with existing quantum secret sharing schemes, it still works when there are dynamic changes, such as the unavailability of some quantum channel, the arrival of new participants and the departure of participants. Finally, we provide security analysis of the new hybrid quantum secret sharing scheme and discuss its useful features for modern applications. PMID:27515908

  18. Hybrid threshold adaptable quantum secret sharing scheme with reverse Huffman-Fibonacci-tree coding.

    PubMed

    Lai, Hong; Zhang, Jun; Luo, Ming-Xing; Pan, Lei; Pieprzyk, Josef; Xiao, Fuyuan; Orgun, Mehmet A

    2016-08-12

    With prevalent attacks in communication, sharing a secret between communicating parties is an ongoing challenge. Moreover, it is important to integrate quantum solutions with classical secret sharing schemes with low computational cost for the real world use. This paper proposes a novel hybrid threshold adaptable quantum secret sharing scheme, using an m-bonacci orbital angular momentum (OAM) pump, Lagrange interpolation polynomials, and reverse Huffman-Fibonacci-tree coding. To be exact, we employ entangled states prepared by m-bonacci sequences to detect eavesdropping. Meanwhile, we encode m-bonacci sequences in Lagrange interpolation polynomials to generate the shares of a secret with reverse Huffman-Fibonacci-tree coding. The advantages of the proposed scheme is that it can detect eavesdropping without joint quantum operations, and permits secret sharing for an arbitrary but no less than threshold-value number of classical participants with much lower bandwidth. Also, in comparison with existing quantum secret sharing schemes, it still works when there are dynamic changes, such as the unavailability of some quantum channel, the arrival of new participants and the departure of participants. Finally, we provide security analysis of the new hybrid quantum secret sharing scheme and discuss its useful features for modern applications.

  19. Hybrid threshold adaptable quantum secret sharing scheme with reverse Huffman-Fibonacci-tree coding

    NASA Astrophysics Data System (ADS)

    Lai, Hong; Zhang, Jun; Luo, Ming-Xing; Pan, Lei; Pieprzyk, Josef; Xiao, Fuyuan; Orgun, Mehmet A.

    2016-08-01

    With prevalent attacks in communication, sharing a secret between communicating parties is an ongoing challenge. Moreover, it is important to integrate quantum solutions with classical secret sharing schemes with low computational cost for the real world use. This paper proposes a novel hybrid threshold adaptable quantum secret sharing scheme, using an m-bonacci orbital angular momentum (OAM) pump, Lagrange interpolation polynomials, and reverse Huffman-Fibonacci-tree coding. To be exact, we employ entangled states prepared by m-bonacci sequences to detect eavesdropping. Meanwhile, we encode m-bonacci sequences in Lagrange interpolation polynomials to generate the shares of a secret with reverse Huffman-Fibonacci-tree coding. The advantages of the proposed scheme is that it can detect eavesdropping without joint quantum operations, and permits secret sharing for an arbitrary but no less than threshold-value number of classical participants with much lower bandwidth. Also, in comparison with existing quantum secret sharing schemes, it still works when there are dynamic changes, such as the unavailability of some quantum channel, the arrival of new participants and the departure of participants. Finally, we provide security analysis of the new hybrid quantum secret sharing scheme and discuss its useful features for modern applications.

  20. Vertical Scan (V-SCAN) for 3-D Grid Adaptive Mesh Refinement for an atmospheric Model Dynamical Core

    NASA Astrophysics Data System (ADS)

    Andronova, N. G.; Vandenberg, D.; Oehmke, R.; Stout, Q. F.; Penner, J. E.

    2009-12-01

    One of the major building blocks of a rigorous representation of cloud evolution in global atmospheric models is a parallel adaptive grid MPI-based communication library (an Adaptive Blocks for Locally Cartesian Topologies library -- ABLCarT), which manages the block-structured data layout, handles ghost cell updates among neighboring blocks and splits a block as refinements occur. The library has several modules that provide a layer of abstraction for adaptive refinement: blocks, which contain individual cells of user data; shells - the global geometry for the problem, including a sphere, reduced sphere, and now a 3D sphere; a load balancer for placement of blocks onto processors; and a communication support layer which encapsulates all data movement. A major performance concern with adaptive mesh refinement is how to represent calculations that have need to be sequenced in a particular order in a direction, such as calculating integrals along a specific path (e.g. atmospheric pressure or geopotential in the vertical dimension). This concern is compounded if the blocks have varying levels of refinement, or are scattered across different processors, as can be the case in parallel computing. In this paper we describe an implementation in ABLCarT of a vertical scan operation, which allows computing along vertical paths in the correct order across blocks transparent to their resolution and processor location. We test this functionality on a 2D and a 3D advection problem, which tests the performance of the model’s dynamics (transport) and physics (sources and sinks) for different model resolutions needed for inclusion of cloud formation.

  1. Context adaptive binary arithmetic coding-based data hiding in partially encrypted H.264/AVC videos

    NASA Astrophysics Data System (ADS)

    Xu, Dawen; Wang, Rangding

    2015-05-01

    A scheme of data hiding directly in a partially encrypted version of H.264/AVC videos is proposed which includes three parts, i.e., selective encryption, data embedding and data extraction. Selective encryption is performed on context adaptive binary arithmetic coding (CABAC) bin-strings via stream ciphers. By careful selection of CABAC entropy coder syntax elements for selective encryption, the encrypted bitstream is format-compliant and has exactly the same bit rate. Then a data-hider embeds the additional data into partially encrypted H.264/AVC videos using a CABAC bin-string substitution technique without accessing the plaintext of the video content. Since bin-string substitution is carried out on those residual coefficients with approximately the same magnitude, the quality of the decrypted video is satisfactory. Video file size is strictly preserved even after data embedding. In order to adapt to different application scenarios, data extraction can be done either in the encrypted domain or in the decrypted domain. Experimental results have demonstrated the feasibility and efficiency of the proposed scheme.

  2. Coding and adaptation during mechanical stimulation in the leech nervous system.

    PubMed

    Pinato, G; Torre, V

    2000-12-15

    The experiments described here were designed to characterise sensory coding and adaptation during mechanical stimulation in the leech (Hirudo medicinalis). A chain of three ganglia and a segment of the body wall connected to the central ganglion were used. Eight extracellular suction pipettes and one or two intracellular electrodes were used to record action potentials from all mechanosensory neurones of the three ganglia. When the skin of the body wall was briefly touched with a filament exerting a force of about 2 mN, touch (T) cells in the central ganglion, but also those in adjacent ganglia (i.e. anterior and posterior), fired one or two action potentials. However, the threshold for action potential initiation was lower for T cells in the central ganglion than for those in adjacent ganglia. The timing of the first evoked action potential in a T cell was very reproducible with a jitter often lower than 100 us. Action potentials in T cells were not significantly correlated. When the force exerted by the filament was increased above 20 mN, pressure (P) cells in the central and neighbouring ganglia fired action potentials. Action potentials in P cells usually followed those evoked in T cells with a delay of about 20 ms and had a larger jitter of 0.5-10 ms. With stronger stimulations exceeding 50 mN, noxious (N) cells also fired action potentials. With such stimulations the majority of mechanosensory neurones in the three ganglia fired action potentials. The spatial properties of the whole receptive field of the mechanosensory neurones were explored by touching different parts of the skin. When the mechanical stimulation was applied for a longer time, i.e. 1 s, only P cells in the central ganglion continued to fire action potentials. P cells in neighbouring ganglia fully adapted after firing two or three action potentials.P cells in adjacent ganglia, having fully adapted to a steady mechanical stimulation of one part of the skin, fired action potentials following

  3. Adjoint-Based Algorithms for Adaptation and Design Optimizations on Unstructured Grids

    NASA Technical Reports Server (NTRS)

    Nielsen, Eric J.

    2006-01-01

    Schemes based on discrete adjoint algorithms present several exciting opportunities for significantly advancing the current state of the art in computational fluid dynamics. Such methods provide an extremely efficient means for obtaining discretely consistent sensitivity information for hundreds of design variables, opening the door to rigorous, automated design optimization of complex aerospace configuration using the Navier-Stokes equation. Moreover, the discrete adjoint formulation provides a mathematically rigorous foundation for mesh adaptation and systematic reduction of spatial discretization error. Error estimates are also an inherent by-product of an adjoint-based approach, valuable information that is virtually non-existent in today's large-scale CFD simulations. An overview of the adjoint-based algorithm work at NASA Langley Research Center is presented, with examples demonstrating the potential impact on complex computational problems related to design optimization as well as mesh adaptation.

  4. Parallel Adaptive Mesh Refinement Library

    NASA Technical Reports Server (NTRS)

    Mac-Neice, Peter; Olson, Kevin

    2005-01-01

    Parallel Adaptive Mesh Refinement Library (PARAMESH) is a package of Fortran 90 subroutines designed to provide a computer programmer with an easy route to extension of (1) a previously written serial code that uses a logically Cartesian structured mesh into (2) a parallel code with adaptive mesh refinement (AMR). Alternatively, in its simplest use, and with minimal effort, PARAMESH can operate as a domain-decomposition tool for users who want to parallelize their serial codes but who do not wish to utilize adaptivity. The package builds a hierarchy of sub-grids to cover the computational domain of a given application program, with spatial resolution varying to satisfy the demands of the application. The sub-grid blocks form the nodes of a tree data structure (a quad-tree in two or an oct-tree in three dimensions). Each grid block has a logically Cartesian mesh. The package supports one-, two- and three-dimensional models.

  5. The fluid dynamic approach to equidistribution methods for grid generation and adaptation

    SciTech Connect

    Delzanno, Gian Luca; Finn, John M

    2009-01-01

    The equidistribution methods based on L{sub p} Monge-Kantorovich optimization [Finn and Delzanno, submitted to SISC, 2009] and on the deformation [Moser, 1965; Dacorogna and Moser, 1990, Liao and Anderson, 1992] method are analyzed primarily in the context of grid generation. It is shown that the first class of methods can be obtained from a fluid dynamic formulation based on time-dependent equations for the mass density and the momentum density, arising from a variational principle. In this context, deformation methods arise from a fluid formulation by making a specific assumption on the time evolution of the density (but with some degree of freedom for the momentum density). In general, deformation methods do not arise from a variational principle. However, it is possible to prescribe an optimal deformation method, related to L{sub 1} Monge-Kantorovich optimization, by making a further assumption on the momentum density. Some applications of the L{sub p} fluid dynamic formulation to imaging are also explored.

  6. Adaptive Generation of Multimaterial Grids from imaging data for Biomedical Lagrangian Fluid-Structure Simulations

    SciTech Connect

    Carson, James P.; Kuprat, Andrew P.; Jiao, Xiangmin; Dyedov, Volodymyr; del Pin, Facundo; Guccione, Julius M.; Ratcliffe, Mark B.; Einstein, Daniel R.

    2010-04-01

    Spatial discretization of complex imaging-derived fluid-solid geometries, such as the cardiac environment, is a critical but often overlooked challenge in biomechanical computations. This is particularly true in problems with Lagrangian interfaces, where, the fluid and solid phases must match geometrically. For simplicity and better accuracy, it is also highly desirable for the two phases to share the same surface mesh at the interface between them. We outline a method for solving this problem, and illustrate the approach with a 3D fluid-solid mesh of the mouse heart. An MRI perfusion-fixed dataset of a mouse heart with 50μm isotropic resolution was semi-automatically segmented using a customized multimaterial connected-threshold approach that divided the volume into non-overlapping regions of blood, tissue and background. Subsequently, a multimaterial marching cubes algorithm was applied to the segmented data to produce two detailed, compatible isosurfaces, one for blood and one for tissue. Both isosurfaces were simultaneously smoothed with a multimaterial smoothing algorithm that exactly conserves the volume for each phase. Using these two isosurfaces, we developed and applied novel automated meshing algorithms to generate anisotropic hybrid meshes on arbitrary biological geometries with the number of layers and the desired element anisotropy for each phase as the only input parameters. Since our meshes adapt to the local feature sizes and include boundary layer prisms, they are more efficient and accurate than non-adaptive, isotropic meshes, and the fluid-structure interaction computations will tend to have relative error equilibrated over the whole mesh.

  7. Computationally Efficient Blind Code Synchronization for Asynchronous DS-CDMA Systems with Adaptive Antenna Arrays

    NASA Astrophysics Data System (ADS)

    Hu, Chia-Chang

    2005-12-01

    A novel space-time adaptive near-far robust code-synchronization array detector for asynchronous DS-CDMA systems is developed in this paper. There are the same basic requirements that are needed by the conventional matched filter of an asynchronous DS-CDMA system. For the real-time applicability, a computationally efficient architecture of the proposed detector is developed that is based on the concept of the multistage Wiener filter (MWF) of Goldstein and Reed. This multistage technique results in a self-synchronizing detection criterion that requires no inversion or eigendecomposition of a covariance matrix. As a consequence, this detector achieves a complexity that is only a linear function of the size of antenna array ([InlineEquation not available: see fulltext.]), the rank of the MWF ([InlineEquation not available: see fulltext.]), the system processing gain ([InlineEquation not available: see fulltext.]), and the number of samples in a chip interval ([InlineEquation not available: see fulltext.]), that is,[InlineEquation not available: see fulltext.]. The complexity of the equivalent detector based on the minimum mean-squared error (MMSE) or the subspace-based eigenstructure analysis is a function of[InlineEquation not available: see fulltext.]. Moreover, this multistage scheme provides a rapid adaptive convergence under limited observation-data support. Simulations are conducted to evaluate the performance and convergence behavior of the proposed detector with the size of the[InlineEquation not available: see fulltext.]-element antenna array, the amount of the[InlineEquation not available: see fulltext.]-sample support, and the rank of the[InlineEquation not available: see fulltext.]-stage MWF. The performance advantage of the proposed detector over other DS-CDMA detectors is investigated as well.

  8. Robust image transmission using a new joint source channel coding algorithm and dual adaptive OFDM

    NASA Astrophysics Data System (ADS)

    Farshchian, Masoud; Cho, Sungdae; Pearlman, William A.

    2004-01-01

    In this paper we consider the problem of robust image coding and packetization for the purpose of communications over slow fading frequency selective channels and channels with a shaped spectrum like those of digital subscribe lines (DSL). Towards this end, a novel and analytically based joint source channel coding (JSCC) algorithm to assign unequal error protection is presented. Under a block budget constraint, the image bitstream is de-multiplexed into two classes with different error responses. The algorithm assigns unequal error protection (UEP) in a way to minimize the expected mean square error (MSE) at the receiver while minimizing the probability of catastrophic failure. In order to minimize the expected mean square error at the receiver, the algorithm assigns unequal protection to the value bit class (VBC) stream. In order to minimizes the probability of catastrophic error which is a characteristic of progressive image coders, the algorithm assigns more protection to the location bit class (LBC) stream than the VBC stream. Besides having the advantage of being analytical and also numerically solvable, the algorithm is based on a new formula developed to estimate the distortion rate (D-R) curve for the VBC portion of SPIHT. The major advantage of our technique is that the worst case instantaneous minimum peak signal to noise ratio (PSNR) does not differ greatly from the averge MSE while this is not the case for the optimal single stream (UEP) system. Although both average PSNR of our method and the optimal single stream UEP are about the same, our scheme does not suffer erratic behavior because we have made the probability of catastrophic error arbitarily small. The coded image is sent via orthogonal frequency division multiplexing (OFDM) which is a known and increasing popular modulation scheme to combat ISI (Inter Symbol Interference) and impulsive noise. Using dual adaptive energy OFDM, we use the minimum energy necessary to send each bit stream at a

  9. Performance of an adaptive coding scheme in a fixed wireless cellular system working in millimeter-wave bands

    NASA Astrophysics Data System (ADS)

    Farahvash, Shayan; Akhavan, Koorosh; Kavehrad, Mohsen

    1999-12-01

    This paper presents a solution to problem of providing bit- error rate performance guarantees in a fixed millimeter-wave wireless system, such as local multi-point distribution system in line-of-sight or nearly line-of-sight applications. The basic concept is to take advantage of slow-fading behavior of fixed wireless channel by changing the transmission code rate. Rate compatible punctured convolutional codes are used to implement adaptive coding. Cochannel interference analysis is carried out for downlink direction; from base station to subscriber premises. Cochannel interference is treated as a noise-like random process with a power equal to the sum of the power from finite number of interfering base stations. Two different cellular architectures based on using single or dual polarizations are investigated. Average spectral efficiency of the proposed adaptive rate system is found to be at least 3 times larger than a fixed rate system with similar outage requirements.

  10. GENIE - Generation of computational geometry-grids for internal-external flow configurations

    NASA Technical Reports Server (NTRS)

    Soni, B. K.

    1988-01-01

    Progress realized in the development of a master geometry-grid generation code GENIE is presented. The grid refinement process is enhanced by developing strategies to utilize bezier curves/surfaces and splines along with weighted transfinite interpolation technique and by formulating new forcing function for the elliptic solver based on the minimization of a non-orthogonality functional. A two step grid adaptation procedure is developed by optimally blending adaptive weightings with weighted transfinite interpolation technique. Examples of 2D-3D grids are provided to illustrate the success of these methods.

  11. Development of an Atmospheric Climate Model with Self-Adapting Grid and Physics

    SciTech Connect

    Penner, Joyce E.

    2013-08-10

    This project was targeting the development of a computational approach that would allow resolving cloud processes on small-scales within the framework of the most recent version of the NASA/NCAR Finite-Volume Community Atmospheric Model (FVCAM). The FVCAM is based on the multidimensional Flux-Form Semi-Lagrangian (FFSL) dynamical core and uses a ?vertically Lagrangian? finite-volume (FV) representation of the model equations with a mass-conserving re-mapping algorithm. The Lagrangian coordinate requires a remapping of the Lagrangian volume back to Eulerian coordinates to restore the original resolution and keep the mesh from developing distortions such as layers with overlapping interfaces. The main objectives of the project were, first, to develop the 3D library which allows refinement and coarsening of the model domain in spherical coordinates, and second, to develop a non-hydrostatic code for calculation of the model variables within the refined areas that could be seamlessly incorporated with the hydrostatic finite volume dynamical core when higher resolution is wanted. We also updated the aerosol simulation model in CAM in order to ready the model for the treatment of aerosol/cloud interactions.

  12. Memristor fabrication and characterization: an adaptive coded aperture imaging and sensing opportunity

    NASA Astrophysics Data System (ADS)

    Yakopcic, Chris; Taha, Tarek M.; Shin, Eunsung; Subramanyam, Guru; Murray, P. Terrence; Rogers, Stanley

    2010-08-01

    The memristor, experimentally verified for the first time in 2008, is one of four fundamental passive circuit elements (the others being resistors, capacitors, and inductors). Development and characterization of memristor devices and the design of novel computing architectures based on these devices can potentially provide significant advances in intelligence processing systems for a variety of applications including image processing, robotics, and machine learning. In particular, adaptive coded aperture (diffraction) sensing, an emerging technology enabling real-time, wide-area IR/visible sensing and imaging, could benefit from new high performance biologically inspired image processing architectures based on memristors. In this paper, we present results from the fabrication and characterization of memristor devices utilizing titanium oxide dielectric layers in a parallel plate conuration. Two versions of memristor devices have been fabricated at the University of Dayton and the Air Force Research Laboratory utilizing varying thicknesses of the TiO2 dielectric layers. Our results show that the devices do exhibit the characteristic hysteresis loop in their I-V plots.

  13. A preprocessor for numerical grid generation of boundary-fitted grids - An application to a solid propellant ablating boundary problem

    NASA Astrophysics Data System (ADS)

    Garriz, J. A.

    1985-01-01

    A code is described which demonstrates the versatility of the differential equations method of grid generation for generating boundary-fitted grids. Two problems from the field of solid mechanics are used to show the code's utility. The problem of successively generating grids for a geometry which changes with time is illustrated with the case of an ablating solid rocket propellant grain. On a more quantitative basis, the problem of successively generating grids whose grid points automatically position or 'adapt' themselves in order to resolve gradients of interest in an evolving solution is illustrated with the classic case of analyzing the state of stress in an axially loaded, rectangular plate with a centered circular hole.

  14. Two general methods for population pharmacokinetic modeling: non-parametric adaptive grid and non-parametric Bayesian.

    PubMed

    Tatarinova, Tatiana; Neely, Michael; Bartroff, Jay; van Guilder, Michael; Yamada, Walter; Bayard, David; Jelliffe, Roger; Leary, Robert; Chubatiuk, Alyona; Schumitzky, Alan

    2013-04-01

    Population pharmacokinetic (PK) modeling methods can be statistically classified as either parametric or nonparametric (NP). Each classification can be divided into maximum likelihood (ML) or Bayesian (B) approaches. In this paper we discuss the nonparametric case using both maximum likelihood and Bayesian approaches. We present two nonparametric methods for estimating the unknown joint population distribution of model parameter values in a pharmacokinetic/pharmacodynamic (PK/PD) dataset. The first method is the NP Adaptive Grid (NPAG). The second is the NP Bayesian (NPB) algorithm with a stick-breaking process to construct a Dirichlet prior. Our objective is to compare the performance of these two methods using a simulated PK/PD dataset. Our results showed excellent performance of NPAG and NPB in a realistically simulated PK study. This simulation allowed us to have benchmarks in the form of the true population parameters to compare with the estimates produced by the two methods, while incorporating challenges like unbalanced sample times and sample numbers as well as the ability to include the covariate of patient weight. We conclude that both NPML and NPB can be used in realistic PK/PD population analysis problems. The advantages of one versus the other are discussed in the paper. NPAG and NPB are implemented in R and freely available for download within the Pmetrics package from www.lapk.org.

  15. Two general methods for population pharmacokinetic modeling: non-parametric adaptive grid and non-parametric Bayesian

    PubMed Central

    Neely, Michael; Bartroff, Jay; van Guilder, Michael; Yamada, Walter; Bayard, David; Jelliffe, Roger; Leary, Robert; Chubatiuk, Alyona; Schumitzky, Alan

    2013-01-01

    Population pharmacokinetic (PK) modeling methods can be statistically classified as either parametric or nonparametric (NP). Each classification can be divided into maximum likelihood (ML) or Bayesian (B) approazches. In this paper we discuss the nonparametric case using both maximum likelihood and Bayesian approaches. We present two nonparametric methods for estimating the unknown joint population distribution of model parameter values in a pharmacokinetic/pharmacodynamic (PK/PD) dataset. The first method is the NP Adaptive Grid (NPAG). The second is the NP Bayesian (NPB) algorithm with a stick-breaking process to construct a Dirichlet prior. Our objective is to compare the performance of these two methods using a simulated PK/PD dataset. Our results showed excellent performance of NPAG and NPB in a realistically simulated PK study. This simulation allowed us to have benchmarks in the form of the true population parameters to compare with the estimates produced by the two methods, while incorporating challenges like unbalanced sample times and sample numbers as well as the ability to include the covariate of patient weight. We conclude that both NPML and NPB can be used in realistic PK/PD population analysis problems. The advantages of one versus the other are discussed in the paper. NPAG and NPB are implemented in R and freely available for download within the Pmetrics package from www.lapk.org. PMID:23404393

  16. MRAG-I2D: Multi-resolution adapted grids for remeshed vortex methods on multicore architectures

    NASA Astrophysics Data System (ADS)

    Rossinelli, Diego; Hejazialhosseini, Babak; van Rees, Wim; Gazzola, Mattia; Bergdorf, Michael; Koumoutsakos, Petros

    2015-05-01

    We present MRAG-I2D, an open source software framework, for multiresolution simulations of two-dimensional, incompressible, viscous flows on multicore architectures. The spatiotemporal scales of the flow field are captured by remeshed vortex methods enhanced by high order average-interpolating wavelets and local time-stepping. The multiresolution solver of the Poisson equation relies on the development of a novel, tree-based multipole method. MRAG-I2D implements a number of HPC strategies to map efficiently the irregular computational workload of wavelet-adapted grids on multicore nodes. The capabilities of the present software are compared to the current state-of-the-art in terms of accuracy, compression rates and time-to-solution. Benchmarks include the inviscid evolution of an elliptical vortex, flow past an impulsively started cylinder at Re = 40- 40 000 and simulations of self-propelled anguilliform swimmers. The results indicate that the present software has the same or better accuracy than state-of-the-art solvers while it exhibits unprecedented performance in terms of time-to-solution.

  17. Reduced adaptability, but no fundamental disruption, of norm-based face-coding mechanisms in cognitively able children and adolescents with autism.

    PubMed

    Rhodes, Gillian; Ewing, Louise; Jeffery, Linda; Avard, Eleni; Taylor, Libby

    2014-09-01

    Faces are adaptively coded relative to visual norms that are updated by experience. This coding is compromised in autism and the broader autism phenotype, suggesting that atypical adaptive coding of faces may be an endophenotype for autism. Here we investigate the nature of this atypicality, asking whether adaptive face-coding mechanisms are fundamentally altered, or simply less responsive to experience, in autism. We measured adaptive coding, using face identity aftereffects, in cognitively able children and adolescents with autism and neurotypical age- and ability-matched participants. We asked whether these aftereffects increase with adaptor identity strength as in neurotypical populations, or whether they show a different pattern indicating a more fundamental alteration in face-coding mechanisms. As expected, face identity aftereffects were reduced in the autism group, but they nevertheless increased with adaptor strength, like those of our neurotypical participants, consistent with norm-based coding of face identity. Moreover, their aftereffects correlated positively with face recognition ability, consistent with an intact functional role for adaptive coding in face recognition ability. We conclude that adaptive norm-based face-coding mechanisms are basically intact in autism, but are less readily calibrated by experience.

  18. A multiblock/multizone code (PAB 3D-v2) for the three-dimensional Navier-Stokes equations: Preliminary applications

    NASA Technical Reports Server (NTRS)

    Abdol-Hamid, Khaled S.

    1990-01-01

    The development and applications of multiblock/multizone and adaptive grid methodologies for solving the three-dimensional simplified Navier-Stokes equations are described. Adaptive grid and multiblock/multizone approaches are introduced and applied to external and internal flow problems. These new implementations increase the capabilities and flexibility of the PAB3D code in solving flow problems associated with complex geometry.

  19. Time-splitting finite difference method with the wavelet-adaptive grids for semiclassical Gross-Pitaevskii equation in supercritical case

    NASA Astrophysics Data System (ADS)

    Li, Xueyang; Xiao, Aiguo

    2014-06-01

    The Gross-Pitaevskii equation is the model equation of the single-particle wave function in a Bose-Einstein condensation. A computation difficulty of the Gross-Pitaevskii equation comes from the semiclassical problem in supercritical case. In this paper, we apply a diffeomorphism to transform the original one-dimensional Gross-Pitaevskii equation into a modified equation. The adaptive grids are constructed through the interpolating wavelet method. Then, we use the time-splitting finite difference method with the wavelet-adaptive grids to solve the modified Gross-Pitaevskii equation, where the approximation to the second-order derivative is given by the Lagrange interpolation method. At last, the numerical results are given. It is shown that the obtained time-splitting finite difference method with the wavelet-adaptive grids is very efficient for solving the one-dimensional semiclassical Gross-Pitaevskii equation in supercritical case and it is suitable to deal with the local high oscillation of the solution.

  20. A new algorithm for high-dimensional uncertainty quantification based on dimension-adaptive sparse grid approximation and reduced basis methods

    NASA Astrophysics Data System (ADS)

    Chen, Peng; Quarteroni, Alfio

    2015-10-01

    In this work we develop an adaptive and reduced computational algorithm based on dimension-adaptive sparse grid approximation and reduced basis methods for solving high-dimensional uncertainty quantification (UQ) problems. In order to tackle the computational challenge of "curse of dimensionality" commonly faced by these problems, we employ a dimension-adaptive tensor-product algorithm [16] and propose a verified version to enable effective removal of the stagnation phenomenon besides automatically detecting the importance and interaction of different dimensions. To reduce the heavy computational cost of UQ problems modelled by partial differential equations (PDE), we adopt a weighted reduced basis method [7] and develop an adaptive greedy algorithm in combination with the previous verified algorithm for efficient construction of an accurate reduced basis approximation. The efficiency and accuracy of the proposed algorithm are demonstrated by several numerical experiments.

  1. Phase-shifting profilometry combined with Gray-code patterns projection: unwrapping error removal by an adaptive median filter.

    PubMed

    Zheng, Dongliang; Da, Feipeng; Kemao, Qian; Seah, Hock Soon

    2017-03-06

    Phase-shifting profilometry combined with Gray-code patterns projection has been widely used for 3D measurement. In this technique, a phase-shifting algorithm is used to calculate the wrapped phase, and a set of Gray-code binary patterns is used to determine the unwrapped phase. In the real measurement, the captured Gray-code patterns are no longer binary, resulting in phase unwrapping errors at a large number of erroneous pixels. Although this problem has been attended and well resolved by a few methods, it remains challenging when a measured object has step-heights and the captured patterns contain invalid pixels. To effectively remove unwrapping errors and simultaneously preserve step-heights, in this paper, an effective method using an adaptive median filter is proposed. Both simulations and experiments can demonstrate its effectiveness.

  2. Poisson-Boltzmann model for protein-surface electrostatic interactions and grid-convergence study using the PyGBe code

    NASA Astrophysics Data System (ADS)

    Cooper, Christopher D.; Barba, Lorena A.

    2016-05-01

    Interactions between surfaces and proteins occur in many vital processes and are crucial in biotechnology: the ability to control specific interactions is essential in fields like biomaterials, biomedical implants and biosensors. In the latter case, biosensor sensitivity hinges on ligand proteins adsorbing on bioactive surfaces with a favorable orientation, exposing reaction sites to target molecules. Protein adsorption, being a free-energy-driven process, is difficult to study experimentally. This paper develops and evaluates a computational model to study electrostatic interactions of proteins and charged nanosurfaces, via the Poisson-Boltzmann equation. We extended the implicit-solvent model used in the open-source code PyGBe to include surfaces of imposed charge or potential. This code solves the boundary integral formulation of the Poisson-Boltzmann equation, discretized with surface elements. PyGBe has at its core a treecode-accelerated Krylov iterative solver, resulting in O(N log N) scaling, with further acceleration on hardware via multi-threaded execution on GPUs. It computes solvation and surface free energies, providing a framework for studying the effect of electrostatics on adsorption. We derived an analytical solution for a spherical charged surface interacting with a spherical dielectric cavity, and used it in a grid-convergence study to build evidence on the correctness of our approach. The study showed the error decaying with the average area of the boundary elements, i.e., the method is O(1 / N) , which is consistent with our previous verification studies using PyGBe. We also studied grid-convergence using a real molecular geometry (protein G B1 D4‧), in this case using Richardson extrapolation (in the absence of an analytical solution) and confirmed the O(1 / N) scaling. With this work, we can now access a completely new family of problems, which no other major bioelectrostatics solver, e.g. APBS, is capable of dealing with. PyGBe is open

  3. Parallelization of TWOPORFLOW, a Cartesian Grid based Two-phase Porous Media Code for Transient Thermo-hydraulic Simulations

    NASA Astrophysics Data System (ADS)

    Trost, Nico; Jiménez, Javier; Imke, Uwe; Sanchez, Victor

    2014-06-01

    TWOPORFLOW is a thermo-hydraulic code based on a porous media approach to simulate single- and two-phase flow including boiling. It is under development at the Institute for Neutron Physics and Reactor Technology (INR) at KIT. The code features a 3D transient solution of the mass, momentum and energy conservation equations for two inter-penetrating fluids with a semi-implicit continuous Eulerian type solver. The application domain of TWOPORFLOW includes the flow in standard porous media and in structured porous media such as micro-channels and cores of nuclear power plants. In the latter case, the fluid domain is coupled to a fuel rod model, describing the heat flow inside the solid structure. In this work, detailed profiling tools have been utilized to determine the optimization potential of TWOPORFLOW. As a result, bottle-necks were identified and reduced in the most feasible way, leading for instance to an optimization of the water-steam property computation. Furthermore, an OpenMP implementation addressing the routines in charge of inter-phase momentum-, energy- and mass-coupling delivered good performance together with a high scalability on shared memory architectures. In contrast to that, the approach for distributed memory systems was to solve sub-problems resulting by the decomposition of the initial Cartesian geometry. Thread communication for the sub-problem boundary updates was accomplished by the Message Passing Interface (MPI) standard.

  4. Adaptation of the Advanced Spray Combustion Code to Cavitating Flow Problems

    NASA Technical Reports Server (NTRS)

    Liang, Pak-Yan

    1993-01-01

    A very important consideration in turbopump design is the prediction and prevention of cavitation. Thus far conventional CFD codes have not been generally applicable to the treatment of cavitating flows. Taking advantage of its two-phase capability, the Advanced Spray Combustion Code is being modified to handle flows with transient as well as steady-state cavitation bubbles. The volume-of-fluid approach incorporated into the code is extended and augmented with a liquid phase energy equation and a simple evaporation model. The strategy adopted also successfully deals with the cavity closure issue. Simple test cases will be presented and remaining technical challenges will be discussed.

  5. Reading the second code: mapping epigenomes to understand plant growth, development, and adaptation to the environment.

    PubMed

    2012-06-01

    We have entered a new era in agricultural and biomedical science made possible by remarkable advances in DNA sequencing technologies. The complete sequence of an individual's set of chromosomes (collectively, its genome) provides a primary genetic code for what makes that individual unique, just as the contents of every personal computer reflect the unique attributes of its owner. But a second code, composed of "epigenetic" layers of information, affects the accessibility of the stored information and the execution of specific tasks. Nature's second code is enigmatic and must be deciphered if we are to fully understand and optimize the genetic potential of crop plants. The goal of the Epigenomics of Plants International Consortium is to crack this second code, and ultimately master its control, to help catalyze a new green revolution.

  6. Development of an Adaptive Boundary-Fitted Coordinate Code for Use in Coastal and Estuarine Areas.

    DTIC Science & Technology

    1985-09-01

    34 Miscellaneous Paper HL-80-3, US Army Engineer Waterways Experiment Station, Vicksburg, Miss. Johnson, B. H., Thompson , J . F ., and Baker, A. J. 1984. "A...34 prepared for CERC, US Army Engineer Water- ways Experiment Station, Vicksburg, Miss. Thompson , J . F . 1983. "A Boundary-Fitted Coordinate Code for...Vol 1. Thompson , J . F ., Thames, F. C., and Mastin, C. W. 1977. "TOMCAT - A Code for Numerical Generation Systems on Fields Containing Any Number of

  7. Autistic traits are linked to reduced adaptive coding of face identity and selectively poorer face recognition in men but not women.

    PubMed

    Rhodes, Gillian; Jeffery, Linda; Taylor, Libby; Ewing, Louise

    2013-11-01

    Our ability to discriminate and recognize thousands of faces despite their similarity as visual patterns relies on adaptive, norm-based, coding mechanisms that are continuously updated by experience. Reduced adaptive coding of face identity has been proposed as a neurocognitive endophenotype for autism, because it is found in autism and in relatives of individuals with autism. Autistic traits can also extend continuously into the general population, raising the possibility that reduced adaptive coding of face identity may be more generally associated with autistic traits. In the present study, we investigated whether adaptive coding of face identity decreases as autistic traits increase in an undergraduate population. Adaptive coding was measured using face identity aftereffects, and autistic traits were measured using the Autism-Spectrum Quotient (AQ) and its subscales. We also measured face and car recognition ability to determine whether autistic traits are selectively related to face recognition difficulties. We found that men who scored higher on levels of autistic traits related to social interaction had reduced adaptive coding of face identity. This result is consistent with the idea that atypical adaptive face-coding mechanisms are an endophenotype for autism. Autistic traits were also linked with face-selective recognition difficulties in men. However, there were some unexpected sex differences. In women, autistic traits were linked positively, rather than negatively, with adaptive coding of identity, and were unrelated to face-selective recognition difficulties. These sex differences indicate that autistic traits can have different neurocognitive correlates in men and women and raise the intriguing possibility that endophenotypes of autism can differ in males and females.

  8. Using specific and adaptive arrangement of grid-type pilot in channel estimation for white-lightLED-based OFDM visible light communication system

    NASA Astrophysics Data System (ADS)

    Lin, Wan-Feng; Chow, Chi-Wai; Yeh, Chien-Hung

    2015-03-01

    Orthogonal frequency division multiplexing (OFDM) is a promising candidate for light emitting diode (LED)-based optical wireless communication (OWC); however, precise channel estimation is required for synchronization and equalization. In this work, we study and discover that the channel response of the white-lightLED-based OWC was smooth and stable. Hence we propose and demonstrate using a specific and adaptive arrangement of grid-type pilot scheme to estimate the LED OWC channel response. Experimental results show that our scheme can achieve better transmission performance and with some transmission capacity enhancement when compared with the method using training-symbol scheme (also called block-type pilot scheme).

  9. Simulation of Supersonic Jet Noise with the Adaptation of Overflow CFD Code and Kirchhoff Surface Integral

    NASA Technical Reports Server (NTRS)

    Kandula, Max; Caimi, Raoul; Steinrock, T. (Technical Monitor)

    2001-01-01

    An acoustic prediction capability for supersonic axisymmetric jets was developed on the basis of OVERFLOW Navier-Stokes CFD (Computational Fluid Dynamics) code of NASA Langley Research Center. Reynolds-averaged turbulent stresses in the flow field are modeled with the aid of Spalart-Allmaras one-equation turbulence model. Appropriate acoustic and outflow boundary conditions were implemented to compute time-dependent acoustic pressure in the nonlinear source-field. Based on the specification of acoustic pressure, its temporal and normal derivatives on the Kirchhoff surface, the near-field and the far-field sound pressure levels are computed via Kirchhoff surface integral, with the Kirchhoff surface chosen to enclose the nonlinear sound source region described by the CFD code. The methods are validated by a comparison of the predictions of sound pressure levels with the available data for an axisymmetric turbulent supersonic (Mach 2) perfectly expanded jet.

  10. Multiple grid problems on concurrent-processing computers

    NASA Technical Reports Server (NTRS)

    Eberhardt, D. S.; Baganoff, D.

    1986-01-01

    Three computer codes were studied which make use of concurrent processing computer architectures in computational fluid dynamics (CFD). The three parallel codes were tested on a two processor multiple-instruction/multiple-data (MIMD) facility at NASA Ames Research Center, and are suggested for efficient parallel computations. The first code is a well-known program which makes use of the Beam and Warming, implicit, approximate factored algorithm. This study demonstrates the parallelism found in a well-known scheme and it achieved speedups exceeding 1.9 on the two processor MIMD test facility. The second code studied made use of an embedded grid scheme which is used to solve problems having complex geometries. The particular application for this study considered an airfoil/flap geometry in an incompressible flow. The scheme eliminates some of the inherent difficulties found in adapting approximate factorization techniques onto MIMD machines and allows the use of chaotic relaxation and asynchronous iteration techniques. The third code studied is an application of overset grids to a supersonic blunt body problem. The code addresses the difficulties encountered when using embedded grids on a compressible, and therefore nonlinear, problem. The complex numerical boundary system associated with overset grids is discussed and several boundary schemes are suggested. A boundary scheme based on the method of characteristics achieved the best results.

  11. SLGRID: spectral synthesis software in the grid

    NASA Astrophysics Data System (ADS)

    Sabater, J.; Sánchez, S.; Verdes-Montenegro, L.

    2011-11-01

    SLGRID (http://www.e-ciencia.es/wiki/index.php/Slgrid) is a pilot project proposed by the e-Science Initiative of Andalusia (eCA) and supported by the Spanish e-Science Network in the frame of the European Grid Initiative (EGI). The aim of the project was to adapt the spectral synthesis software Starlight (Cid-Fernandes et al. 2005) to the Grid infrastructure. Starlight is used to estimate the underlying stellar populations (their ages and metallicities) using an optical spectrum, hence, it is possible to obtain a clean nebular spectrum that can be used for the diagnostic of the presence of an Active Galactic Nucleus (Sabater et al. 2008, 2009). The typical serial execution of the code for big samples of galaxies made it ideal to be integrated into the Grid. We obtain an improvement on the computational time of order N, being N the number of nodes available in the Grid. In a real case we obtained our results in 3 hours with SLGRID instead of the 60 days spent using Starlight in a PC. The code has already been ported to the Grid. The first tests were made within the e-CA infrastrusture and, later, itwas tested and improved with the colaboration of the CETA-CIEMAT. The SLGRID project has been recently renewed. In a future it is planned to adapt the code for the reduction of data from Integral Field Units where each dataset is composed of hundreds of spectra. Electronic version of the poster at http://www.iaa.es/~jsm/SEA2010

  12. Integer-Linear-Programing Optimization in Scalable Video Multicast with Adaptive Modulation and Coding in Wireless Networks

    PubMed Central

    Lee, Chaewoo

    2014-01-01

    The advancement in wideband wireless network supports real time services such as IPTV and live video streaming. However, because of the sharing nature of the wireless medium, efficient resource allocation has been studied to achieve a high level of acceptability and proliferation of wireless multimedia. Scalable video coding (SVC) with adaptive modulation and coding (AMC) provides an excellent solution for wireless video streaming. By assigning different modulation and coding schemes (MCSs) to video layers, SVC can provide good video quality to users in good channel conditions and also basic video quality to users in bad channel conditions. For optimal resource allocation, a key issue in applying SVC in the wireless multicast service is how to assign MCSs and the time resources to each SVC layer in the heterogeneous channel condition. We formulate this problem with integer linear programming (ILP) and provide numerical results to show the performance under 802.16 m environment. The result shows that our methodology enhances the overall system throughput compared to an existing algorithm. PMID:25276862

  13. Integer-linear-programing optimization in scalable video multicast with adaptive modulation and coding in wireless networks.

    PubMed

    Lee, Dongyul; Lee, Chaewoo

    2014-01-01

    The advancement in wideband wireless network supports real time services such as IPTV and live video streaming. However, because of the sharing nature of the wireless medium, efficient resource allocation has been studied to achieve a high level of acceptability and proliferation of wireless multimedia. Scalable video coding (SVC) with adaptive modulation and coding (AMC) provides an excellent solution for wireless video streaming. By assigning different modulation and coding schemes (MCSs) to video layers, SVC can provide good video quality to users in good channel conditions and also basic video quality to users in bad channel conditions. For optimal resource allocation, a key issue in applying SVC in the wireless multicast service is how to assign MCSs and the time resources to each SVC layer in the heterogeneous channel condition. We formulate this problem with integer linear programming (ILP) and provide numerical results to show the performance under 802.16 m environment. The result shows that our methodology enhances the overall system throughput compared to an existing algorithm.

  14. Euler and N-S grid generation for Halis configuration with body flap

    SciTech Connect

    Haeuser, J.; Xia, Y.; Muylaert, J.

    1996-12-31

    The purpose of this paper is two fold. First, a high quality grid for the Halis geometry has been generated. The grid is optimized with regard to smoothness, orthogonality, and skewness. In particular, the grid is almost orthogonal on fixed boundaries to simplify the usage of turbulence models. Second, a topology has been designed that aligns the grid with the expected streamline distribution as much as possible to improve the accuracy of the numerical solution, and, at the same time, allows the reduction of the number of grid points needed. This is an important aspect in driving down computing time. For a flow adapted grid topology the number of blocks is higher than for a simple topology. Consequently, the number of points per block is smaller. In addition, the number of grid points may differ substantially from block to block. This feature has two consequences. First, an advanced topology cannot be used by codes that rely on large blocks, for instance, codes that ran on vector computers demanding long vector lengths. This type of topology will also be difficult for codes using the mult-grid technique because grid coarsening win be less effective for smaller blocks.

  15. Scientific Final Report: COLLABORATIVE RESEARCH: CONTINUOUS DYNAMIC GRID ADAPTATION IN A GLOBAL ATMOSPHERIC MODEL: APPLICATION AND REFINEMENT

    SciTech Connect

    William J. Gutowski; Joseph M. Prusa, Piotr K. Smolarkiewicz

    2012-04-09

    This project had goals of advancing the performance capabilities of the numerical general circulation model EULAG and using it to produce a fully operational atmospheric global climate model (AGCM) that can employ either static or dynamic grid stretching for targeted phenomena. The resulting AGCM combined EULAG's advanced dynamics core with the 'physics' of the NCAR Community Atmospheric Model (CAM). Effort discussed below shows how we improved model performance and tested both EULAG and the coupled CAM-EULAG in several ways to demonstrate the grid stretching and ability to simulate very well a wide range of scales, that is, multi-scale capability. We leveraged our effort through interaction with an international EULAG community that has collectively developed new features and applications of EULAG, which we exploited for our own work summarized here. Overall, the work contributed to over 40 peer-reviewed publications and over 70 conference/workshop/seminar presentations, many of them invited.

  16. An adaptive scan of high frequency subbands for dyadic intra frame in MPEG4-AVC/H.264 scalable video coding

    NASA Astrophysics Data System (ADS)

    Shahid, Z.; Chaumont, M.; Puech, W.

    2009-01-01

    This paper develops a new adaptive scanning methodology for intra frame scalable coding framework based on a subband/wavelet(DWTSB) coding approach for MPEG-4 AVC/H.264 scalable video coding (SVC). It attempts to take advantage of the prior knowledge of the frequencies which are present in different higher frequency subbands. We propose dyadic intra frame coding method with adaptive scan (DWTSB-AS) for each subband as traditional zigzag scan is not suitable for high frequency subbands. Thus, by just modification of the scan order of the intra frame scalable coding framework of H.264, we can get better compression. The proposed algorithm has been theoretically justified and is thoroughly evaluated against the current SVC test model JSVM and DWTSB through extensive coding experiments for scalable coding of intra frame. The simulation results show the proposed scanning algorithm consistently outperforms JSVM and DWTSB in PSNR performance. This results in extra compression for intra frames, along with spatial scalability. Thus Image and video coding applications, traditionally serviced by separate coders, can be efficiently provided by an integrated coding system.

  17. CAGI: Computer Aided Grid Interface. A work in progress

    NASA Technical Reports Server (NTRS)

    Soni, Bharat K.; Yu, Tzu-Yi; Vaughn, David

    1992-01-01

    Progress realized in the development of a Computer Aided Grid Interface (CAGI) software system in integrating CAD/CAM geometric system output and/or Interactive Graphics Exchange Standard (IGES) files, geometry manipulations associated with grid generation, and robust grid generation methodologies is presented. CAGI is being developed in a modular fashion and will offer fast, efficient and economical response to geometry/grid preparation, allowing the ability to upgrade basic geometry in a step-by-step fashion interactively and under permanent visual control along with minimizing the differences between the actual hardware surface descriptions and corresponding numerical analog. The computer code GENIE is used as a basis. The Non-Uniform Rational B-Splines (NURBS) representation of sculptured surfaces is utilized for surface grid redistribution. The computer aided analysis system, PATRAN, is adapted as a CAD/CAM system. The progress realized in NURBS surface grid generation, the development of IGES transformer, and geometry adaption using PATRAN will be presented along with their applicability to grid generation associated with rocket propulsion applications.

  18. Application of Parallel Adjoint-Based Error Estimation and Anisotropic Grid Adaptation for Three-Dimensional Aerospace Configurations

    NASA Technical Reports Server (NTRS)

    Lee-Rausch, E. M.; Park, M. A.; Jones, W. T.; Hammond, D. P.; Nielsen, E. J.

    2005-01-01

    This paper demonstrates the extension of error estimation and adaptation methods to parallel computations enabling larger, more realistic aerospace applications and the quantification of discretization errors for complex 3-D solutions. Results were shown for an inviscid sonic-boom prediction about a double-cone configuration and a wing/body segmented leading edge (SLE) configuration where the output function of the adjoint was pressure integrated over a part of the cylinder in the near field. After multiple cycles of error estimation and surface/field adaptation, a significant improvement in the inviscid solution for the sonic boom signature of the double cone was observed. Although the double-cone adaptation was initiated from a very coarse mesh, the near-field pressure signature from the final adapted mesh compared very well with the wind-tunnel data which illustrates that the adjoint-based error estimation and adaptation process requires no a priori refinement of the mesh. Similarly, the near-field pressure signature for the SLE wing/body sonic boom configuration showed a significant improvement from the initial coarse mesh to the final adapted mesh in comparison with the wind tunnel results. Error estimation and field adaptation results were also presented for the viscous transonic drag prediction of the DLR-F6 wing/body configuration, and results were compared to a series of globally refined meshes. Two of these globally refined meshes were used as a starting point for the error estimation and field-adaptation process where the output function for the adjoint was the total drag. The field-adapted results showed an improvement in the prediction of the drag in comparison with the finest globally refined mesh and a reduction in the estimate of the remaining drag error. The adjoint-based adaptation parameter showed a need for increased resolution in the surface of the wing/body as well as a need for wake resolution downstream of the fuselage and wing trailing edge

  19. N-body simulations for f(R) gravity using a self-adaptive particle-mesh code

    SciTech Connect

    Zhao Gongbo; Koyama, Kazuya; Li Baojiu

    2011-02-15

    We perform high-resolution N-body simulations for f(R) gravity based on a self-adaptive particle-mesh code MLAPM. The chameleon mechanism that recovers general relativity on small scales is fully taken into account by self-consistently solving the nonlinear equation for the scalar field. We independently confirm the previous simulation results, including the matter power spectrum, halo mass function, and density profiles, obtained by Oyaizu et al.[Phys. Rev. D 78, 123524 (2008)] and Schmidt et al.[Phys. Rev. D 79, 083518 (2009)], and extend the resolution up to k{approx}20 h/Mpc for the measurement of the matter power spectrum. Based on our simulation results, we discuss how the chameleon mechanism affects the clustering of dark matter and halos on full nonlinear scales.

  20. A study on H and O-H grid generation and associated flow codes for gas turbine 3D Navier Stokes analyses

    NASA Astrophysics Data System (ADS)

    Choi, D.; Knight, C. J.

    1991-06-01

    A method to generate H and O-H grid systems for 3D gas turbine geometries has been developed. It is a simple procedure which solves a set of elliptic equations starting from an initial grid system generated algebraically. This grid generation procedure is for 3D Navier-Stokes analysis based on the scalar or diagonalized form of approximate factorization. The grids generated by this procedure have been applied to 3D heat transfer calculations and compared with experimental results. Detailed comparisons are given for both H and O-H grid topologies, considering the Low Aspect Ratio Turbine (LART) and using a two-equation turbulence model with viscous sublayer resolution.

  1. A new type of color-coded light structures for an adapted and rapid determination of point correspondences for 3D reconstruction

    NASA Astrophysics Data System (ADS)

    Caulier, Yannick; Bernhard, Luc; Spinnler, Klaus

    2011-05-01

    This paper proposes a new type of color coded light structures for the inspection of complex moving objects. The novelty of the methods relies on the generation of free-form color patterns permitting the projection of color structures adapted to the geometry of the surfaces to be characterized. The point correspondence determination algorithm consists of a stepwise procedure involving simple and computationally fast methods. The algorithm is therefore robust against varying recording conditions typically arising in real-time quality control environments and can be further integrated for industrial inspection purposes. The proposed approach is validated and compared on the basis of different experimentations concerning the 3D surface reconstruction by projecting adapted spatial color coded patterns. It is demonstrated that in case of certain inspection requirements, the method permits to code more reference points that similar color coded matrix methods.

  2. An Adaptive Data Gathering Scheme for Multi-Hop Wireless Sensor Networks Based on Compressed Sensing and Network Coding

    PubMed Central

    Yin, Jun; Yang, Yuwang; Wang, Lei

    2016-01-01

    Joint design of compressed sensing (CS) and network coding (NC) has been demonstrated to provide a new data gathering paradigm for multi-hop wireless sensor networks (WSNs). By exploiting the correlation of the network sensed data, a variety of data gathering schemes based on NC and CS (Compressed Data Gathering—CDG) have been proposed. However, these schemes assume that the sparsity of the network sensed data is constant and the value of the sparsity is known before starting each data gathering epoch, thus they ignore the variation of the data observed by the WSNs which are deployed in practical circumstances. In this paper, we present a complete design of the feedback CDG scheme where the sink node adaptively queries those interested nodes to acquire an appropriate number of measurements. The adaptive measurement-formation procedure and its termination rules are proposed and analyzed in detail. Moreover, in order to minimize the number of overall transmissions in the formation procedure of each measurement, we have developed a NP-complete model (Maximum Leaf Nodes Minimum Steiner Nodes—MLMS) and realized a scalable greedy algorithm to solve the problem. Experimental results show that the proposed measurement-formation method outperforms previous schemes, and experiments on both datasets from ocean temperature and practical network deployment also prove the effectiveness of our proposed feedback CDG scheme. PMID:27043574

  3. An Adaptive Data Gathering Scheme for Multi-Hop Wireless Sensor Networks Based on Compressed Sensing and Network Coding.

    PubMed

    Yin, Jun; Yang, Yuwang; Wang, Lei

    2016-04-01

    Joint design of compressed sensing (CS) and network coding (NC) has been demonstrated to provide a new data gathering paradigm for multi-hop wireless sensor networks (WSNs). By exploiting the correlation of the network sensed data, a variety of data gathering schemes based on NC and CS (Compressed Data Gathering--CDG) have been proposed. However, these schemes assume that the sparsity of the network sensed data is constant and the value of the sparsity is known before starting each data gathering epoch, thus they ignore the variation of the data observed by the WSNs which are deployed in practical circumstances. In this paper, we present a complete design of the feedback CDG scheme where the sink node adaptively queries those interested nodes to acquire an appropriate number of measurements. The adaptive measurement-formation procedure and its termination rules are proposed and analyzed in detail. Moreover, in order to minimize the number of overall transmissions in the formation procedure of each measurement, we have developed a NP-complete model (Maximum Leaf Nodes Minimum Steiner Nodes--MLMS) and realized a scalable greedy algorithm to solve the problem. Experimental results show that the proposed measurement-formation method outperforms previous schemes, and experiments on both datasets from ocean temperature and practical network deployment also prove the effectiveness of our proposed feedback CDG scheme.

  4. Complex Volume Grid Generation Through the Use of Grid Reusability

    NASA Technical Reports Server (NTRS)

    Alter, Stephen J.

    1997-01-01

    This paper presents a set of surface and volume grid generation techniques which reuse existing surface and volume grids. These methods use combinations of data manipulations to reduce grid generation time, improve grid characteristics, and increase the capabilities of existing domain discretization software. The manipulation techniques utilize physical and computational domains to produce basis function on which to operate and modify grid character and smooth grids using Trans-Finite Interpolation, a vector interpolation method and parametric re-mapping technique. With these new techniques, inviscid grids can be converted to viscous grids, multiple zone grid adaption can be performed to improve CFD solver efficiency, and topological changes to improve modeling of flow fields can be done simply and quickly. Examples of these capabilities are illustrated as applied to various configurations.

  5. A Load Frequency Control in an Off-Grid Sustainable Power System Based on a Parameter Adaptive PID-Type Fuzzy Controller

    NASA Astrophysics Data System (ADS)

    Ronilaya, Ferdian; Miyauchi, Hajime

    2014-10-01

    This paper presents a new implementation of a parameter adaptive PID-type fuzzy controller (PAPIDfc) for a grid-supporting inverter of battery to alleviate frequency fluctuations in a wind-diesel power system. A variable speed wind turbine that drives a permanent magnet synchronous generator is assumed for demonstrations. The PAPIDfc controller is built from a set of control rules that adopts the droop method and uses only locally measurable frequency signal. The output control signal is determined from the knowledge base and the fuzzy inference. The input-derivative gain and the output-integral gain of the PAPIDfc are tuned online. To ensure safe battery operating limits, we also propose a protection scheme called intelligent battery protection (IBP). Several simulation experiments are performed by using MATLAB®/SimPowersystems™. Next, to verify the scheme's effectiveness, the simulation results are compared with the results of conventional controllers. The results demonstrate the effectiveness of the PAPIDfc scheme to control a grid-supporting inverter of the battery in the reduction of frequency fluctuations.

  6. Reconfigurable mask for adaptive coded aperture imaging (ACAI) based on an addressable MOEMS microshutter array

    NASA Astrophysics Data System (ADS)

    McNie, Mark E.; Combes, David J.; Smith, Gilbert W.; Price, Nicola; Ridley, Kevin D.; Brunson, Kevin M.; Lewis, Keith L.; Slinger, Chris W.; Rogers, Stanley

    2007-09-01

    Coded aperture imaging has been used for astronomical applications for several years. Typical implementations use a fixed mask pattern and are designed to operate in the X-Ray or gamma ray bands. More recent applications have emerged in the visible and infra red bands for low cost lens-less imaging systems. System studies have shown that considerable advantages in image resolution may accrue from the use of multiple different images of the same scene - requiring a reconfigurable mask. We report on work to develop a novel, reconfigurable mask based on micro-opto-electro-mechanical systems (MOEMS) technology employing interference effects to modulate incident light in the mid-IR band (3-5μm). This is achieved by tuning a large array of asymmetric Fabry-Perot cavities by applying an electrostatic force to adjust the gap between a moveable upper polysilicon mirror plate supported on suspensions and underlying fixed (electrode) layers on a silicon substrate. A key advantage of the modulator technology developed is that it is transmissive and high speed (e.g. 100kHz) - allowing simpler imaging system configurations. It is also realised using a modified standard polysilicon surface micromachining process (i.e. MUMPS-like) that is widely available and hence should have a low production cost in volume. We have developed designs capable of operating across the entire mid-IR band with peak transmissions approaching 100% and high contrast. By using a pixelated array of small mirrors, a large area device comprising individually addressable elements may be realised that allows reconfiguring of the whole mask at speeds in excess of video frame rates.

  7. Safe Grid

    NASA Technical Reports Server (NTRS)

    Chow, Edward T.; Stewart, Helen; Korsmeyer, David (Technical Monitor)

    2003-01-01

    The biggest users of GRID technologies came from the science and technology communities. These consist of government, industry and academia (national and international). The NASA GRID is moving into a higher technology readiness level (TRL) today; and as a joint effort among these leaders within government, academia, and industry, the NASA GRID plans to extend availability to enable scientists and engineers across these geographical boundaries collaborate to solve important problems facing the world in the 21 st century. In order to enable NASA programs and missions to use IPG resources for program and mission design, the IPG capabilities needs to be accessible from inside the NASA center networks. However, because different NASA centers maintain different security domains, the GRID penetration across different firewalls is a concern for center security people. This is the reason why some IPG resources are been separated from the NASA center network. Also, because of the center network security and ITAR concerns, the NASA IPG resource owner may not have full control over who can access remotely from outside the NASA center. In order to obtain organizational approval for secured remote access, the IPG infrastructure needs to be adapted to work with the NASA business process. Improvements need to be made before the IPG can be used for NASA program and mission development. The Secured Advanced Federated Environment (SAFE) technology is designed to provide federated security across NASA center and NASA partner's security domains. Instead of one giant center firewall which can be difficult to modify for different GRID applications, the SAFE "micro security domain" provide large number of professionally managed "micro firewalls" that can allow NASA centers to accept remote IPG access without the worry of damaging other center resources. The SAFE policy-driven capability-based federated security mechanism can enable joint organizational and resource owner approved remote

  8. Adaptive Code Division Multiple Access Protocol for Wireless Network-on-Chip Architectures

    NASA Astrophysics Data System (ADS)

    Vijayakumaran, Vineeth

    Massive levels of integration following Moore's Law ushered in a paradigm shift in the way on-chip interconnections were designed. With higher and higher number of cores on the same die traditional bus based interconnections are no longer a scalable communication infrastructure. On-chip networks were proposed enabled a scalable plug-and-play mechanism for interconnecting hundreds of cores on the same chip. Wired interconnects between the cores in a traditional Network-on-Chip (NoC) system, becomes a bottleneck with increase in the number of cores thereby increasing the latency and energy to transmit signals over them. Hence, there has been many alternative emerging interconnect technologies proposed, namely, 3D, photonic and multi-band RF interconnects. Although they provide better connectivity, higher speed and higher bandwidth compared to wired interconnects; they also face challenges with heat dissipation and manufacturing difficulties. On-chip wireless interconnects is one other alternative proposed which doesn't need physical interconnection layout as data travels over the wireless medium. They are integrated into a hybrid NOC architecture consisting of both wired and wireless links, which provides higher bandwidth, lower latency, lesser area overhead and reduced energy dissipation in communication. However, as the bandwidth of the wireless channels is limited, an efficient media access control (MAC) scheme is required to enhance the utilization of the available bandwidth. This thesis proposes using a multiple access mechanism such as Code Division Multiple Access (CDMA) to enable multiple transmitter-receiver pairs to send data over the wireless channel simultaneously. It will be shown that such a hybrid wireless NoC with an efficient CDMA based MAC protocol can significantly increase the performance of the system while lowering the energy dissipation in data transfer. In this work it is shown that the wireless NoC with the proposed CDMA based MAC protocol

  9. Prediction and Control of Network Cascade: Example of Power Grid or Networking Adaptability from WMD Disruption and Cascading Failures

    SciTech Connect

    Chertkov, Michael

    2012-07-24

    The goal of the DTRA project is to develop a mathematical framework that will provide the fundamental understanding of network survivability, algorithms for detecting/inferring pre-cursors of abnormal network behaviors, and methods for network adaptability and self-healing from cascading failures.

  10. Evaluation of the Operational Multi-scale Environment model with Grid Adaptivity (OMEGA) for use in Wind Energy Applications in the Great Basin of Nevada

    NASA Astrophysics Data System (ADS)

    King, Kristien C.

    In order to further assess the wind energy potential for Nevada, the accuracy of a computational meteorological model, the Operational Multi-scale Environment model with Grid Adaptivity (OMEGA), was evaluated by comparing simulation results with data collected from a wind monitoring tower near Tonopah, NV. The state of Nevada is characterized by high mountains and low-lying valleys, therefore, in order to determine the wind potential for the state, meteorological models that predict the wind must be able to accurately represent and account for terrain features and simulate topographic forcing with accuracy. Topographic forcing has a dominant role in the development and modification of mesoscale flows in regions of complex terrain, like Tonopah, especially at the level of wind turbine blade heights (~80 m). Additionally, model factors such as horizontal resolution, terrain database resolution, model physics, time of model initialization, stability regime, and source of initial conditions may each affect the ability of a mesoscale model to forecast winds correctly. The observational tower used for comparison was located at Stone Cabin, Nevada. The tower had both sonic anemometers and cup anemometers installed at heights of 40 m, 60 m, and 80 m above the surface. During a previous experiment, tower data were collected for the period February 9 through March 10, 2007 and compared to model simulations using the MM5 and WRF models at a number of varying horizontal resolutions. In this previous research, neither the MM5 nor the WRF showed a significant improvement in ability to forecast wind speed with increasing horizontal grid resolution. The present research evaluated the ability of OMEGA to reproduce point winds as compared to the observational data from the Stone Cabin Tower at heights of 40 m, 60 m, and 80 m. Unlike other mesoscale atmospheric models, OMEGA incorporates an unstructured triangular adaptive grid which allows for increased flexibility and accuracy in

  11. Image set based face recognition using self-regularized non-negative coding and adaptive distance metric learning.

    PubMed

    Mian, Ajmal; Hu, Yiqun; Hartley, Richard; Owens, Robyn

    2013-12-01

    Simple nearest neighbor classification fails to exploit the additional information in image sets. We propose self-regularized nonnegative coding to define between set distance for robust face recognition. Set distance is measured between the nearest set points (samples) that can be approximated from their orthogonal basis vectors as well as from the set samples under the respective constraints of self-regularization and nonnegativity. Self-regularization constrains the orthogonal basis vectors to be similar to the approximated nearest point. The nonnegativity constraint ensures that each nearest point is approximated from a positive linear combination of the set samples. Both constraints are formulated as a single convex optimization problem and the accelerated proximal gradient method with linear-time Euclidean projection is adapted to efficiently find the optimal nearest points between two image sets. Using the nearest points between a query set and all the gallery sets as well as the active samples used to approximate them, we learn a more discriminative Mahalanobis distance for robust face recognition. The proposed algorithm works independently of the chosen features and has been tested on gray pixel values and local binary patterns. Experiments on three standard data sets show that the proposed method consistently outperforms existing state-of-the-art methods.

  12. The neural code for taste in the nucleus of the solitary tract of the rat: effects of adaptation.

    PubMed

    Di Lorenzo, P M; Lemon, C H

    2000-01-10

    Adaptation of the tongue to NaCl, HCl, quinine or sucrose was used as a tool to study the stability and organization of response profiles in the nucleus of the solitary tract (NTS). Taste responses in the NTS were recorded in anesthetized rats before and after adaptation of the tongue to NaCl, HCl, sucrose or quinine. Results showed that the magnitude of response to test stimuli following adaptation was a function of the context, i.e., adaptation condition, in which the stimuli were presented. Over half of all taste responses were either attenuated or enhanced following the adaptation procedure: NaCl adaptation produced the most widespread, non-stimulus-selective cross-adaptation and sucrose adaptation produced the least frequent cross-adaptation and the most frequent enhancement of taste responses. Adaptation to quinine cross-adapted to sucrose and adaptation to HCl cross-adapted to quinine in over half of the units tested. The adaptation procedure sometimes unmasked taste responses where none were present beforehand and sometimes altered taste responses to test stimuli even though the adapting stimulus did not itself produce a response. These effects demonstrated a form of context-dependency of taste responsiveness in the NTS and further suggest a broad potentiality in the sensitivity of NTS units across taste stimuli. Across unit patterns of response remained distinct from each other under all adaptation conditions. Discriminability of these patterns may provide a neurophysiological basis for residual psychophysical abilities following adaptation.

  13. Adaptation.

    PubMed

    Broom, Donald M

    2006-01-01

    The term adaptation is used in biology in three different ways. It may refer to changes which occur at the cell and organ level, or at the individual level, or at the level of gene action and evolutionary processes. Adaptation by cells, especially nerve cells helps in: communication within the body, the distinguishing of stimuli, the avoidance of overload and the conservation of energy. The time course and complexity of these mechanisms varies. Adaptive characters of organisms, including adaptive behaviours, increase fitness so this adaptation is evolutionary. The major part of this paper concerns adaptation by individuals and its relationships to welfare. In complex animals, feed forward control is widely used. Individuals predict problems and adapt by acting before the environmental effect is substantial. Much of adaptation involves brain control and animals have a set of needs, located in the brain and acting largely via motivational mechanisms, to regulate life. Needs may be for resources but are also for actions and stimuli which are part of the mechanism which has evolved to obtain the resources. Hence pigs do not just need food but need to be able to carry out actions like rooting in earth or manipulating materials which are part of foraging behaviour. The welfare of an individual is its state as regards its attempts to cope with its environment. This state includes various adaptive mechanisms including feelings and those which cope with disease. The part of welfare which is concerned with coping with pathology is health. Disease, which implies some significant effect of pathology, always results in poor welfare. Welfare varies over a range from very good, when adaptation is effective and there are feelings of pleasure or contentment, to very poor. A key point concerning the concept of individual adaptation in relation to welfare is that welfare may be good or poor while adaptation is occurring. Some adaptation is very easy and energetically cheap and

  14. An overview of the activities of the OECD/NEA Task Force on adapting computer codes in nuclear applications to parallel architectures

    SciTech Connect

    Kirk, B.L.; Sartori, E.

    1997-06-01

    Subsequent to the introduction of High Performance Computing in the developed countries, the Organization for Economic Cooperation and Development/Nuclear Energy Agency (OECD/NEA) created the Task Force on Adapting Computer Codes in Nuclear Applications to Parallel Architectures (under the guidance of the Nuclear Science Committee`s Working Party on Advanced Computing) to study the growth area in supercomputing and its applicability to the nuclear community`s computer codes. The result has been four years of investigation for the Task Force in different subject fields - deterministic and Monte Carlo radiation transport, computational mechanics and fluid dynamics, nuclear safety, atmospheric models and waste management.

  15. Parallel Power Grid Simulation Toolkit

    SciTech Connect

    Smith, Steve; Kelley, Brian; Banks, Lawrence; Top, Philip; Woodward, Carol

    2015-09-14

    ParGrid is a 'wrapper' that integrates a coupled Power Grid Simulation toolkit consisting of a library to manage the synchronization and communication of independent simulations. The included library code in ParGid, named FSKIT, is intended to support the coupling multiple continuous and discrete even parallel simulations. The code is designed using modern object oriented C++ methods utilizing C++11 and current Boost libraries to ensure compatibility with multiple operating systems and environments.

  16. Constructing the ASCI computational grid

    SciTech Connect

    BEIRIGER,JUDY I.; BIVENS,HUGH P.; HUMPHREYS,STEVEN L.; JOHNSON,WILBUR R.; RHEA,RONALD E.

    2000-06-01

    The Accelerated Strategic Computing Initiative (ASCI) computational grid is being constructed to interconnect the high performance computing resources of the nuclear weapons complex. The grid will simplify access to the diverse computing, storage, network, and visualization resources, and will enable the coordinated use of shared resources regardless of location. To match existing hardware platforms, required security services, and current simulation practices, the Globus MetaComputing Toolkit was selected to provide core grid services. The ASCI grid extends Globus functionality by operating as an independent grid, incorporating Kerberos-based security, interfacing to Sandia's Cplant{trademark},and extending job monitoring services. To fully meet ASCI's needs, the architecture layers distributed work management and criteria-driven resource selection services on top of Globus. These services simplify the grid interface by allowing users to simply request ''run code X anywhere''. This paper describes the initial design and prototype of the ASCI grid.

  17. Spectral-element adaptive refinement magnetohydrodynamic simulations of the island coalescence instability

    NASA Astrophysics Data System (ADS)

    Rosenberg, D.; Pouquet, A.; Germaschewski, K.; Ng, C. S.; Bhattacharjee, A.

    2006-10-01

    A recently developed spectral-element adaptive refinement incompressible magnetohydrodynamic (MHD) code is applied to simulate the problem of island coalescence instability (ICI) in 2D. The MHD solver is explicit, and uses the Elsasser formulation on high-order elements. It automatically takes advantage of the adaptive grid mechanics that have been described in [Rosenberg, Fournier, Fischer, Pouquet, J. Comp. Phys., 215, 59-80 (2006)], allowing both statically refined and dynamically refined grids. ICI is a MHD process that can produce strong current sheets and subsequent reconnection and heating in a high-Lundquist number plasma such as the solar corona [cf., Ng and Bhattacharjee, Phys. Plasmas, 5, 4028 (1998)]. Thus, it is desirable to use adaptive refinement grids to increase resolution, and to maintain accuracy at the same time. Results are compared with simulations using finite difference method with the same refinement grid, as well as pesudo-spectral simulations using uniform grid.

  18. Comparison of DAC and MONACO DSMC Codes with Flat Plate Simulation

    NASA Technical Reports Server (NTRS)

    Padilla, Jose F.

    2010-01-01

    Various implementations of the direct simulation Monte Carlo (DSMC) method exist in academia, government and industry. By comparing implementations, deficiencies and merits of each can be discovered. This document reports comparisons between DSMC Analysis Code (DAC) and MONACO. DAC is NASA's standard DSMC production code and MONACO is a research DSMC code developed in academia. These codes have various differences; in particular, they employ distinct computational grid definitions. In this study, DAC and MONACO are compared by having each simulate a blunted flat plate wind tunnel test, using an identical volume mesh. Simulation expense and DSMC metrics are compared. In addition, flow results are compared with available laboratory data. Overall, this study revealed that both codes, excluding grid adaptation, performed similarly. For parallel processing, DAC was generally more efficient. As expected, code accuracy was mainly dependent on physical models employed.

  19. Verification of the Calore thermal analysis code.

    SciTech Connect

    Dowding, Kevin J.; Blackwell, Bennie Francis

    2004-07-01

    Calore is the ASC code developed to model steady and transient thermal diffusion with chemistry and dynamic enclosure radiation. An integral part of the software development process is code verification, which addresses the question 'Are we correctly solving the model equations'? This process aids the developers in that it identifies potential software bugs and gives the thermal analyst confidence that a properly prepared input will produce satisfactory output. Grid refinement studies have been performed on problems for which we have analytical solutions. In this talk, the code verification process is overviewed and recent results are presented. Recent verification studies have focused on transient nonlinear heat conduction and verifying algorithms associated with (tied) contact and adaptive mesh refinement. In addition, an approach to measure the coverage of the verification test suite relative to intended code applications is discussed.

  20. Evaluation of damage-induced permeability using a three-dimensional Adaptive Continuum/Discontinuum Code (AC/DC)

    NASA Astrophysics Data System (ADS)

    Fabian, Dedecker; Peter, Cundall; Daniel, Billaux; Torsten, Groeger

    Digging a shaft or drift inside a rock mass is a common practice in civil engineering when a transportation way, such as a motorway, railway tunnel or storage shaft is to be built. In most cases, the consequences of the disturbance on the medium must be known in order to estimate the behaviour of the disturbed rock mass. Indeed, excavating part of the rock causes a new distribution of the stress field around the excavation that can lead to micro-cracking and even to the failure of some rock volume in the vicinity of the shaft. Consequently, the formed micro-cracks modify the mechanical and hydraulic properties of the rock. In this paper, we present an original method for the evaluation of damage-induced permeability. ITASCA has developed and used discontinuum models to study rock damage by building particle assemblies and checking the breakage of bonds under stress. However, such models are limited in size by the very large number of particles needed to model even a comparatively small volume of rock. In fact, a large part of most models never experiences large strains and does not require the accurate description of large-strain/damage/post-peak behaviour afforded by a discontinuum model. Thus, a large model frequently can be separated into a strongly strained “core” area to be represented by a Discontinuum and a peripheral area for which continuum zones would be adequate. Based on this observation, Itasca has developed a coupled, three-dimensional, continuum/discontinuum modelling approach. The new approach, termed Adaptive Continuum/Discontinuum Code (AC/DC), is based on the use of a periodic discontinuum “base brick” for which more or less simplified continuum equivalents are derived. Depending on the level of deformation in each part of the model, the AC/DC code can dynamically select the appropriate brick type to be used. In this paper, we apply the new approach to an excavation performed in the Bure site, at which the French nuclear waste agency

  1. National electrical code changes for 1996 and USA participation in International Energy Agency activities related to photovoltaics safety and grid interconnection

    SciTech Connect

    Bower, W.

    1995-01-01

    As photovoltaic (PV) systems gain more acceptance in utility-interactive applications throughout the world, many organizations are placing increasingly higher priorities on writing guidelines, codes and standards. These guidelines and codes are being written to improve safety, installation, acceptance, listing or certification of the PV components or systems. Sandia National Laboratories` PV System Applications Department is working closely with the PV industry to address issues that are associated with fire and personnel safety and with National Electrical Code (NEC) requirements. Additionally, the United States has agreed to participate in two of the International Energy Agency (IEA) Annexes (topical tasks) of the Implementing Agreement for a Cooperative Programme on Photovoltaic Power Systems. This paper describes events and activities associated with the NEC and the IEA that are being led by Sandia National Laboratories with broad participation by the US PV industry.

  2. Adapt

    NASA Astrophysics Data System (ADS)

    Bargatze, L. F.

    2015-12-01

    Active Data Archive Product Tracking (ADAPT) is a collection of software routines that permits one to generate XML metadata files to describe and register data products in support of the NASA Heliophysics Virtual Observatory VxO effort. ADAPT is also a philosophy. The ADAPT concept is to use any and all available metadata associated with scientific data to produce XML metadata descriptions in a consistent, uniform, and organized fashion to provide blanket access to the full complement of data stored on a targeted data server. In this poster, we present an application of ADAPT to describe all of the data products that are stored by using the Common Data File (CDF) format served out by the CDAWEB and SPDF data servers hosted at the NASA Goddard Space Flight Center. These data servers are the primary repositories for NASA Heliophysics data. For this purpose, the ADAPT routines have been used to generate data resource descriptions by using an XML schema named Space Physics Archive, Search, and Extract (SPASE). SPASE is the designated standard for documenting Heliophysics data products, as adopted by the Heliophysics Data and Model Consortium. The set of SPASE XML resource descriptions produced by ADAPT includes high-level descriptions of numerical data products, display data products, or catalogs and also includes low-level "Granule" descriptions. A SPASE Granule is effectively a universal access metadata resource; a Granule associates an individual data file (e.g. a CDF file) with a "parent" high-level data resource description, assigns a resource identifier to the file, and lists the corresponding assess URL(s). The CDAWEB and SPDF file systems were queried to provide the input required by the ADAPT software to create an initial set of SPASE metadata resource descriptions. Then, the CDAWEB and SPDF data repositories were queried subsequently on a nightly basis and the CDF file lists were checked for any changes such as the occurrence of new, modified, or deleted

  3. Multiple block grid generation in the interactive environment

    NASA Astrophysics Data System (ADS)

    Steinbrenner, John P.; Chawner, John R.; Fouts, Chris L.

    1990-06-01

    Concepts employed in grid generation codes to speed up the process of obtaining a CFD solution are reviewed, including the use of multiple blocks and interactive graphics. The GRIDGEN interactive, multiple block grid generation codes, are presented as an example of grid generation software that employs these techniques. The features of a hypothetical ideal interactive multiple block grid generation code are identified through a brief discussion of existing technology.

  4. Current Grid operation and future role of the Grid

    NASA Astrophysics Data System (ADS)

    Smirnova, O.

    2012-12-01

    Grid-like technologies and approaches became an integral part of HEP experiments. Some other scientific communities also use similar technologies for data-intensive computations. The distinct feature of Grid computing is the ability to federate heterogeneous resources of different ownership into a seamless infrastructure, accessible via a single log-on. Like other infrastructures of similar nature, Grid functioning requires not only technologically sound basis, but also reliable operation procedures, monitoring and accounting. The two aspects, technological and operational, are closely related: weaker is the technology, more burden is on operations, and other way around. As of today, Grid technologies are still evolving: at CERN alone, every LHC experiment uses an own Grid-like system. This inevitably creates a heavy load on operations. Infrastructure maintenance, monitoring and incident response are done on several levels, from local system administrators to large international organisations, involving massive human effort worldwide. The necessity to commit substantial resources is one of the obstacles faced by smaller research communities when moving computing to the Grid. Moreover, most current Grid solutions were developed under significant influence of HEP use cases, and thus need additional effort to adapt them to other applications. Reluctance of many non-HEP researchers to use Grid negatively affects the outlook for national Grid organisations, which strive to provide multi-science services. We started from the situation where Grid organisations were fused with HEP laboratories and national HEP research programmes; we hope to move towards the world where Grid will ultimately reach the status of generic public computing and storage service provider and permanent national and international Grid infrastructures will be established. How far will we be able to advance along this path, depends on us. If no standardisation and convergence efforts will take place

  5. Interactive Hyperbolic Grid Generation for Projectile CFD

    DTIC Science & Technology

    1992-05-01

    J . F . "A Composite Grid Generation Code for General 3D Regions - The EAGLE Code." AIAA Journal, vol. 26, no. 3, p. 271, March 1988. Thompson , J . F ., and...Grid Generation." AGARD FDP Specialists Meeting on "Mesh Generation for Complex Three-Dimensional Configurations." Leon, Norway, May 1989. Thompson

  6. AZEuS: AN ADAPTIVE ZONE EULERIAN SCHEME FOR COMPUTATIONAL MAGNETOHYDRODYNAMICS

    SciTech Connect

    Ramsey, Jon P.; Clarke, David A.; Men'shchikov, Alexander B.

    2012-03-01

    A new adaptive mesh refinement (AMR) version of the ZEUS-3D astrophysical magnetohydrodynamical fluid code, AZEuS, is described. The AMR module in AZEuS has been completely adapted to the staggered mesh that characterizes the ZEUS family of codes on which scalar quantities are zone-centered and vector components are face-centered. In addition, for applications using static grids, it is necessary to use higher-order interpolations for prolongation to minimize the errors caused by waves crossing from a grid of one resolution to another. Finally, solutions to test problems in one, two, and three dimensions in both Cartesian and spherical coordinates are presented.

  7. Memory-efficient table look-up optimized algorithm for context-based adaptive variable length decoding in H.264/advanced video coding

    NASA Astrophysics Data System (ADS)

    Wang, Jianhua; Cheng, Lianglun; Wang, Tao; Peng, Xiaodong

    2016-03-01

    Table look-up operation plays a very important role during the decoding processing of context-based adaptive variable length decoding (CAVLD) in H.264/advanced video coding (AVC). However, frequent table look-up operation can result in big table memory access, and then lead to high table power consumption. Aiming to solve the problem of big table memory access of current methods, and then reduce high power consumption, a memory-efficient table look-up optimized algorithm is presented for CAVLD. The contribution of this paper lies that index search technology is introduced to reduce big memory access for table look-up, and then reduce high table power consumption. Specifically, in our schemes, we use index search technology to reduce memory access by reducing the searching and matching operations for code_word on the basis of taking advantage of the internal relationship among length of zero in code_prefix, value of code_suffix and code_lengh, thus saving the power consumption of table look-up. The experimental results show that our proposed table look-up algorithm based on index search can lower about 60% memory access consumption compared with table look-up by sequential search scheme, and then save much power consumption for CAVLD in H.264/AVC.

  8. Application of multi-objective controller to optimal tuning of PID gains for a hydraulic turbine regulating system using adaptive grid particle swam optimization.

    PubMed

    Chen, Zhihuan; Yuan, Yanbin; Yuan, Xiaohui; Huang, Yuehua; Li, Xianshan; Li, Wenwu

    2015-05-01

    A hydraulic turbine regulating system (HTRS) is one of the most important components of hydropower plant, which plays a key role in maintaining safety, stability and economical operation of hydro-electrical installations. At present, the conventional PID controller is widely applied in the HTRS system for its practicability and robustness, and the primary problem with respect to this control law is how to optimally tune the parameters, i.e. the determination of PID controller gains for satisfactory performance. In this paper, a kind of multi-objective evolutionary algorithms, named adaptive grid particle swarm optimization (AGPSO) is applied to solve the PID gains tuning problem of the HTRS system. This newly AGPSO optimized method, which differs from a traditional one-single objective optimization method, is designed to take care of settling time and overshoot level simultaneously, in which a set of non-inferior alternatives solutions (i.e. Pareto solution) is generated. Furthermore, a fuzzy-based membership value assignment method is employed to choose the best compromise solution from the obtained Pareto set. An illustrative example associated with the best compromise solution for parameter tuning of the nonlinear HTRS system is introduced to verify the feasibility and the effectiveness of the proposed AGPSO-based optimization approach, as compared with two another prominent multi-objective algorithms, i.e. Non-dominated Sorting Genetic Algorithm II (NSGAII) and Strength Pareto Evolutionary Algorithm II (SPEAII), for the quality and diversity of obtained Pareto solutions set. Consequently, simulation results show that this AGPSO optimized approach outperforms than compared methods with higher efficiency and better quality no matter whether the HTRS system works under unload or load conditions.

  9. Staggered-grid split-node method for spontaneous rupture simulation

    NASA Astrophysics Data System (ADS)

    Dalguer, Luis A.; Day, Steven M.

    2007-02-01

    We adapt the traction-at-split-node method for spontaneous rupture simulations to the velocity-stress staggered-grid finite difference scheme. The staggered-grid implementation introduces both velocity and stress discontinuities via split nodes. The staggered traction components on the fault plane are interpolated to form the traction vector at split nodes, facilitating alignment of the vectors of sliding friction and slip velocity. To simplify the split-node partitioning of the equations of motion, spatial differencing is reduced from fourth to second order along the fault plane, but in the remainder of the grid the spatial differencing scheme remains identical to conventional spatially fourth-order three-dimensional staggered-grid schemes. The resulting staggered-grid split node (SGSN) method has convergence rates relative to rupture-time, final-slip, and peak-slip-velocity metrics that are very similar to the corresponding rates for both a partly staggered split-node code (DFM) and the boundary integral method. The SGSN method gives very accurate solutions (in the sense that errors are comparable to the uncertainties in the reference solution) when the median resolution of the cohesive zone is 4.4 grid points. Combined with previous results for other grid types and other fault-discontinuity approximations, the SGSN results demonstrate that accuracy in finite difference solutions to the spontaneous rupture problem is controlled principally by the scheme used to represent the fault discontinuity, and is relatively insensitive to the grid geometry used to represent the continuum. The method provides an efficient and accurate means of adding spontaneous rupture capability to velocity-stress staggered-grid finite difference codes, while retaining the computational advantages of those codes for problems of wave propagation in complex media.

  10. Reading the Second Code: Mapping Epigenomes to Understand Plant Growth, Development, and Adaptation to the Environment[OA

    PubMed Central

    2012-01-01

    We have entered a new era in agricultural and biomedical science made possible by remarkable advances in DNA sequencing technologies. The complete sequence of an individual’s set of chromosomes (collectively, its genome) provides a primary genetic code for what makes that individual unique, just as the contents of every personal computer reflect the unique attributes of its owner. But a second code, composed of “epigenetic” layers of information, affects the accessibility of the stored information and the execution of specific tasks. Nature’s second code is enigmatic and must be deciphered if we are to fully understand and optimize the genetic potential of crop plants. The goal of the Epigenomics of Plants International Consortium is to crack this second code, and ultimately master its control, to help catalyze a new green revolution. PMID:22751210

  11. Performance Analysis of MIMO-STBC Systems with Higher Coding Rate Using Adaptive Semiblind Channel Estimation Scheme

    PubMed Central

    Kumar, Ravi

    2014-01-01

    Semiblind channel estimation method provides the best trade-off in terms of bandwidth overhead, computational complexity and latency. The result after using multiple input multiple output (MIMO) systems shows higher data rate and longer transmit range without any requirement for additional bandwidth or transmit power. This paper presents the detailed analysis of diversity coding techniques using MIMO antenna systems. Different space time block codes (STBCs) schemes have been explored and analyzed with the proposed higher code rate. STBCs with higher code rates have been simulated for different modulation schemes using MATLAB environment and the simulated results have been compared in the semiblind environment which shows the improvement even in highly correlated antenna arrays and is found very close to the condition when channel state information (CSI) is known to the channel. PMID:24688379

  12. Performance analysis of MIMO-STBC systems with higher coding rate using adaptive semiblind channel estimation scheme.

    PubMed

    Kumar, Ravi; Saxena, Rajiv

    2014-01-01

    Semiblind channel estimation method provides the best trade-off in terms of bandwidth overhead, computational complexity and latency. The result after using multiple input multiple output (MIMO) systems shows higher data rate and longer transmit range without any requirement for additional bandwidth or transmit power. This paper presents the detailed analysis of diversity coding techniques using MIMO antenna systems. Different space time block codes (STBCs) schemes have been explored and analyzed with the proposed higher code rate. STBCs with higher code rates have been simulated for different modulation schemes using MATLAB environment and the simulated results have been compared in the semiblind environment which shows the improvement even in highly correlated antenna arrays and is found very close to the condition when channel state information (CSI) is known to the channel.

  13. Progress in Grid Generation: From Chimera to DRAGON Grids

    NASA Technical Reports Server (NTRS)

    Liou, Meng-Sing; Kao, Kai-Hsiung

    1994-01-01

    Hybrid grids, composed of structured and unstructured grids, combines the best features of both. The chimera method is a major stepstone toward a hybrid grid from which the present approach is evolved. The chimera grid composes a set of overlapped structured grids which are independently generated and body-fitted, yielding a high quality grid readily accessible for efficient solution schemes. The chimera method has been shown to be efficient to generate a grid about complex geometries and has been demonstrated to deliver accurate aerodynamic prediction of complex flows. While its geometrical flexibility is attractive, interpolation of data in the overlapped regions - which in today's practice in 3D is done in a nonconservative fashion, is not. In the present paper we propose a hybrid grid scheme that maximizes the advantages of the chimera scheme and adapts the strengths of the unstructured grid while at the same time keeps its weaknesses minimal. Like the chimera method, we first divide up the physical domain by a set of structured body-fitted grids which are separately generated and overlaid throughout a complex configuration. To eliminate any pure data manipulation which does not necessarily follow governing equations, we use non-structured grids only to directly replace the region of the arbitrarily overlapped grids. This new adaptation to the chimera thinking is coined the DRAGON grid. The nonstructured grid region sandwiched between the structured grids is limited in size, resulting in only a small increase in memory and computational effort. The DRAGON method has three important advantages: (1) preserving strengths of the chimera grid; (2) eliminating difficulties sometimes encountered in the chimera scheme, such as the orphan points and bad quality of interpolation stencils; and (3) making grid communication in a fully conservative and consistent manner insofar as the governing equations are concerned. To demonstrate its use, the governing equations are

  14. AN ADAPTIVE PARTICLE-MESH GRAVITY SOLVER FOR ENZO

    SciTech Connect

    Passy, Jean-Claude; Bryan, Greg L.

    2014-11-01

    We describe and implement an adaptive particle-mesh algorithm to solve the Poisson equation for grid-based hydrodynamics codes with nested grids. The algorithm is implemented and extensively tested within the astrophysical code Enzo against the multigrid solver available by default. We find that while both algorithms show similar accuracy for smooth mass distributions, the adaptive particle-mesh algorithm is more accurate for the case of point masses, and is generally less noisy. We also demonstrate that the two-body problem can be solved accurately in a configuration with nested grids. In addition, we discuss the effect of subcycling, and demonstrate that evolving all the levels with the same timestep yields even greater precision.

  15. Overture: The grid classes

    SciTech Connect

    Brislawn, K.; Brown, D.; Chesshire, G.; Henshaw, W.

    1997-01-01

    Overture is a library containing classes for grids, overlapping grid generation and the discretization and solution of PDEs on overlapping grids. This document describes the Overture grid classes, including classes for single grids and classes for collections of grids.

  16. Grid cell distortion and MODFLOW's integrated finite-difference numerical solution.

    PubMed

    Romero, Dave M; Silver, Steven E

    2006-01-01

    The ground water flow model MODFLOW inherently implements a nongeneralized integrated finite-difference (IFD) numerical scheme. The IFD numerical scheme allows for construction of finite-difference model grids with curvilinear (piecewise linear) rows. The resulting grid comprises model cells in the shape of trapezoids and is distorted in comparison to a traditional MODFLOW finite-difference grid. A version of MODFLOW-88 (herein referred to as MODFLOW IFD) with the code adapted to make the one-dimensional DELR and DELC arrays two dimensional, so that equivalent conductance between distorted grid cells can be calculated, is described. MODFLOW IFD is used to inspect the sensitivity of the numerical head and velocity solutions to the level of distortion in trapezoidal grid cells within a converging radial flow domain. A test problem designed for the analysis implements a grid oriented such that flow is parallel to columns with converging widths. The sensitivity analysis demonstrates MODFLOW IFD's capacity to numerically derive a head solution and resulting intercell volumetric flow when the internal calculation of equivalent conductance accounts for the distortion of the grid cells. The sensitivity of the velocity solution to grid cell distortion indicates criteria for distorted grid design. In the radial flow test problem described, the numerical head solution is not sensitive to grid cell distortion. The accuracy of the velocity solution is sensitive to cell distortion with error <1% if the angle between the nonparallel sides of trapezoidal cells is <12.5 degrees. The error of the velocity solution is related to the degree to which the spatial discretization of a curve is approximated with piecewise linear segments. Curvilinear finite-difference grid construction adds versatility to spatial discretization of the flow domain. MODFLOW-88's inherent IFD numerical scheme and the test problem results imply that more recent versions of MODFLOW 2000, with minor

  17. Fibonacci Grids

    NASA Technical Reports Server (NTRS)

    Swinbank, Richard; Purser, James

    2006-01-01

    Recent years have seen a resurgence of interest in a variety of non-standard computational grids for global numerical prediction. The motivation has been to reduce problems associated with the converging meridians and the polar singularities of conventional regular latitude-longitude grids. A further impetus has come from the adoption of massively parallel computers, for which it is necessary to distribute work equitably across the processors; this is more practicable for some non-standard grids. Desirable attributes of a grid for high-order spatial finite differencing are: (i) geometrical regularity; (ii) a homogeneous and approximately isotropic spatial resolution; (iii) a low proportion of the grid points where the numerical procedures require special customization (such as near coordinate singularities or grid edges). One family of grid arrangements which, to our knowledge, has never before been applied to numerical weather prediction, but which appears to offer several technical advantages, are what we shall refer to as "Fibonacci grids". They can be thought of as mathematically ideal generalizations of the patterns occurring naturally in the spiral arrangements of seeds and fruit found in sunflower heads and pineapples (to give two of the many botanical examples). These grids possess virtually uniform and highly isotropic resolution, with an equal area for each grid point. There are only two compact singular regions on a sphere that require customized numerics. We demonstrate the practicality of these grids in shallow water simulations, and discuss the prospects for efficiently using these frameworks in three-dimensional semi-implicit and semi-Lagrangian weather prediction or climate models.

  18. Grids = Structure.

    ERIC Educational Resources Information Center

    Barrington, Linda; Carter, Jacky

    2003-01-01

    Proposes that narrow columns provide a flexible system of organization for designers. Notes that grids serve the content on the pages, help to develop a layout that will clearly direct the reader to information; and prevent visual monotony. Concludes when grid layouts are used, school publications look as good as professional ones. (PM)

  19. GridTool: A surface modeling and grid generation tool

    NASA Technical Reports Server (NTRS)

    Samareh-Abolhassani, Jamshid

    1995-01-01

    GridTool is designed around the concept that the surface grids are generated on a set of bi-linear patches. This type of grid generation is quite easy to implement, and it avoids the problems associated with complex CAD surface representations and associated surface parameterizations. However, the resulting surface grids are close to but not on the original CAD surfaces. This problem can be alleviated by projecting the resulting surface grids onto the original CAD surfaces. GridTool is designed primary for unstructured grid generation systems. Currently, GridTool supports VGRID and FELISA systems, and it can be easily extended to support other unstructured grid generation systems. The data in GridTool is stored parametrically so that once the problem is set up, one can modify the surfaces and the entire set of points, curves and patches will be updated automatically. This is very useful in a multidisciplinary design and optimization process. GridTool is written entirely in ANSI 'C', the interface is based on the FORMS library, and the graphics is based on the GL library. The code has been tested successfully on IRIS workstations running IRIX4.0 and above. The memory is allocated dynamically, therefore, memory size will depend on the complexity of geometry/grid. GridTool data structure is based on a link-list structure which allows the required memory to expand and contract dynamically according to the user's data size and action. Data structure contains several types of objects such as points, curves, patches, sources and surfaces. At any given time, there is always an active object which is drawn in magenta, or in their highlighted colors as defined by the resource file which will be discussed later.

  20. Non-tables look-up search algorithm for efficient H.264/AVC context-based adaptive variable length coding decoding

    NASA Astrophysics Data System (ADS)

    Han, Yishi; Luo, Zhixiao; Wang, Jianhua; Min, Zhixuan; Qin, Xinyu; Sun, Yunlong

    2014-09-01

    In general, context-based adaptive variable length coding (CAVLC) decoding in H.264/AVC standard requires frequent access to the unstructured variable length coding tables (VLCTs) and significant memory accesses are consumed. Heavy memory accesses will cause high power consumption and time delays, which are serious problems for applications in portable multimedia devices. We propose a method for high-efficiency CAVLC decoding by using a program instead of all the VLCTs. The decoded codeword from VLCTs can be obtained without any table look-up and memory access. The experimental results show that the proposed algorithm achieves 100% memory access saving and 40% decoding time saving without degrading video quality. Additionally, the proposed algorithm shows a better performance compared with conventional CAVLC decoding, such as table look-up by sequential search, table look-up by binary search, Moon's method, and Kim's method.

  1. caTIES: a grid based system for coding and retrieval of surgical pathology reports and tissue specimens in support of translational research.

    PubMed

    Crowley, Rebecca S; Castine, Melissa; Mitchell, Kevin; Chavan, Girish; McSherry, Tara; Feldman, Michael

    2010-01-01

    The authors report on the development of the Cancer Tissue Information Extraction System (caTIES)--an application that supports collaborative tissue banking and text mining by leveraging existing natural language processing methods and algorithms, grid communication and security frameworks, and query visualization methods. The system fills an important need for text-derived clinical data in translational research such as tissue-banking and clinical trials. The design of caTIES addresses three critical issues for informatics support of translational research: (1) federation of research data sources derived from clinical systems; (2) expressive graphical interfaces for concept-based text mining; and (3) regulatory and security model for supporting multi-center collaborative research. Implementation of the system at several Cancer Centers across the country is creating a potential network of caTIES repositories that could provide millions of de-identified clinical reports to users. The system provides an end-to-end application of medical natural language processing to support multi-institutional translational research programs.

  2. HASEonGPU-An adaptive, load-balanced MPI/GPU-code for calculating the amplified spontaneous emission in high power laser media

    NASA Astrophysics Data System (ADS)

    Eckert, C. H. J.; Zenker, E.; Bussmann, M.; Albach, D.

    2016-10-01

    We present an adaptive Monte Carlo algorithm for computing the amplified spontaneous emission (ASE) flux in laser gain media pumped by pulsed lasers. With the design of high power lasers in mind, which require large size gain media, we have developed the open source code HASEonGPU that is capable of utilizing multiple graphic processing units (GPUs). With HASEonGPU, time to solution is reduced to minutes on a medium size GPU cluster of 64 NVIDIA Tesla K20m GPUs and excellent speedup is achieved when scaling to multiple GPUs. Comparison of simulation results to measurements of ASE in Y b 3 + : Y AG ceramics show perfect agreement.

  3. CFD code evaluation for internal flow modeling

    NASA Technical Reports Server (NTRS)

    Chung, T. J.

    1990-01-01

    Research on the computational fluid dynamics (CFD) code evaluation with emphasis on supercomputing in reacting flows is discussed. Advantages of unstructured grids, multigrids, adaptive methods, improved flow solvers, vector processing, parallel processing, and reduction of memory requirements are discussed. As examples, researchers include applications of supercomputing to reacting flow Navier-Stokes equations including shock waves and turbulence and combustion instability problems associated with solid and liquid propellants. Evaluation of codes developed by other organizations are not included. Instead, the basic criteria for accuracy and efficiency have been established, and some applications on rocket combustion have been made. Research toward an ultimate goal, the most accurate and efficient CFD code, is in progress and will continue for years to come.

  4. NAS Grid Benchmarks: A Tool for Grid Space Exploration

    NASA Technical Reports Server (NTRS)

    Frumkin, Michael; VanderWijngaart, Rob F.; Biegel, Bryan (Technical Monitor)

    2001-01-01

    We present an approach for benchmarking services provided by computational Grids. It is based on the NAS Parallel Benchmarks (NPB) and is called NAS Grid Benchmark (NGB) in this paper. We present NGB as a data flow graph encapsulating an instance of an NPB code in each graph node, which communicates with other nodes by sending/receiving initialization data. These nodes may be mapped to the same or different Grid machines. Like NPB, NGB will specify several different classes (problem sizes). NGB also specifies the generic Grid services sufficient for running the bench-mark. The implementor has the freedom to choose any specific Grid environment. However, we describe a reference implementation in Java, and present some scenarios for using NGB.

  5. Adaptation of multidimensional group particle tracking and particle wall-boundary condition model to the FDNS code

    NASA Technical Reports Server (NTRS)

    Chen, Y. S.; Farmer, R. C.

    1992-01-01

    A particulate two-phase flow CFD model was developed based on the FDNS code which is a pressure based predictor plus multi-corrector Navier-Stokes flow solver. Turbulence models with compressibility correction and the wall function models were employed as submodels. A finite-rate chemistry model was used for reacting flow simulation. For particulate two-phase flow simulations, a Eulerian-Lagrangian solution method using an efficient implicit particle trajectory integration scheme was developed in this study. Effects of particle-gas reaction and particle size change to agglomeration or fragmentation were not considered in this investigation. At the onset of the present study, a two-dimensional version of FDNS which had been modified to treat Lagrangian tracking of particles (FDNS-2DEL) had already been written and was operational. The FDNS-2DEL code was too slow for practical use, mainly because it had not been written in a form amenable to vectorization on the Cray, nor was the full three-dimensional form of FDNS utilized. The specific objective of this study was to reorder to calculations into long single arrays for automatic vectorization on the Cray and to implement the full three-dimensional version of FDNS to produce the FDNS-3DEL code. Since the FDNS-2DEL code was slow, a very limited number of test cases had been run with it. This study was also intended to increase the number of cases simulated to verify and improve, as necessary, the particle tracking methodology coded in FDNS.

  6. Grid oscillators

    NASA Technical Reports Server (NTRS)

    Popovic, Zorana B.; Kim, Moonil; Rutledge, David B.

    1988-01-01

    Loading a two-dimensional grid with active devices offers a means of combining the power of solid-state oscillators in the microwave and millimeter-wave range. The grid structure allows a large number of negative resistance devices to be combined. This approach is attractive because the active devices do not require an external locking signal, and the combining is done in free space. In addition, the loaded grid is a planar structure amenable to monolithic integration. Measurements on a 25-MESFET grid at 9.7 GHz show power-combining and frequency-locking without an external locking signal, with an ERP of 37 W. Experimental far-field patterns agree with theoretical results obtained using reciprocity.

  7. Verification of the CENTRM Module for Adaptation of the SCALE Code to NGNP Prismatic and PBR Core Designs

    SciTech Connect

    Ganapol, Barry; Maldonado, Ivan

    2014-01-23

    The generation of multigroup cross sections lies at the heart of the very high temperature reactor (VHTR) core design, whether the prismatic (block) or pebble-bed type. The design process, generally performed in three steps, is quite involved and its execution is crucial to proper reactor physics analyses. The primary purpose of this project is to develop the CENTRM cross-section processing module of the SCALE code package for application to prismatic or pebble-bed core designs. The team will include a detailed outline of the entire processing procedure for application of CENTRM in a final report complete with demonstration. In addition, they will conduct a thorough verification of the CENTRM code, which has yet to be performed. The tasks for this project are to: Thoroughly test the panel algorithm for neutron slowing down; Develop the panel algorithm for multi-materials; Establish a multigroup convergence 1D transport acceleration algorithm in the panel formalism; Verify CENTRM in 1D plane geometry; Create and test the corresponding transport/panel algorithm in spherical and cylindrical geometries; and, Apply the verified CENTRM code to current VHTR core design configurations for an infinite lattice, including assessing effectiveness of Dancoff corrections to simulate TRISO particle heterogeneity.

  8. P1 adaptation of TRIPOLI-4® code for the use of 3D realistic core multigroup cross section generation

    NASA Astrophysics Data System (ADS)

    Cai, Li; Pénéliau, Yannick; Diop, Cheikh M.; Malvagi, Fausto

    2014-06-01

    In this paper, we discuss some improvements we recently implemented in the Monte-Carlo code TRIPOLI-4® associated with the homogenization and collapsing of subassemblies cross sections. The improvement offered us another approach to get critical multigroup cross sections with Monte-Carlo method. The new calculation method in TRIPOLI-4® tries to ensure the neutronic balances, the multiplicative factors and the critical flux spectra for some realistic geometries. We make it by at first improving the treatment of the energy transfer probability, the neutron excess weight and the neutron fission spectrum. This step is necessary for infinite geometries. The second step which will be enlarged in this paper is aimed at better dealing with the multigroup anisotropy distribution law for finite geometries. Usually, Monte-Carlo homogenized multi-group cross sections are validated within a core calculation by a deterministic code. Here, the validation of multigroup constants will also be carried out by Monte-Carlo core calculation code. Different subassemblies are tested with the new collapsing method, especially for the fast neutron reactors subassemblies.

  9. Grid Computing

    NASA Astrophysics Data System (ADS)

    Foster, Ian

    2001-08-01

    The term "Grid Computing" refers to the use, for computational purposes, of emerging distributed Grid infrastructures: that is, network and middleware services designed to provide on-demand and high-performance access to all important computational resources within an organization or community. Grid computing promises to enable both evolutionary and revolutionary changes in the practice of computational science and engineering based on new application modalities such as high-speed distributed analysis of large datasets, collaborative engineering and visualization, desktop access to computation via "science portals," rapid parameter studies and Monte Carlo simulations that use all available resources within an organization, and online analysis of data from scientific instruments. In this article, I examine the status of Grid computing circa 2000, briefly reviewing some relevant history, outlining major current Grid research and development activities, and pointing out likely directions for future work. I also present a number of case studies, selected to illustrate the potential of Grid computing in various areas of science.

  10. Dengue virus genomic variation associated with mosquito adaptation defines the pattern of viral non-coding RNAs and fitness in human cells.

    PubMed

    Filomatori, Claudia V; Carballeda, Juan M; Villordo, Sergio M; Aguirre, Sebastian; Pallarés, Horacio M; Maestre, Ana M; Sánchez-Vargas, Irma; Blair, Carol D; Fabri, Cintia; Morales, Maria A; Fernandez-Sesma, Ana; Gamarnik, Andrea V

    2017-03-01

    The Flavivirus genus includes a large number of medically relevant pathogens that cycle between humans and arthropods. This host alternation imposes a selective pressure on the viral population. Here, we found that dengue virus, the most important viral human pathogen transmitted by insects, evolved a mechanism to differentially regulate the production of viral non-coding RNAs in mosquitos and humans, with a significant impact on viral fitness in each host. Flavivirus infections accumulate non-coding RNAs derived from the viral 3'UTRs (known as sfRNAs), relevant in viral pathogenesis and immune evasion. We found that dengue virus host adaptation leads to the accumulation of different species of sfRNAs in vertebrate and invertebrate cells. This process does not depend on differences in the host machinery; but it was found to be dependent on the selection of specific mutations in the viral 3'UTR. Dissecting the viral population and studying phenotypes of cloned variants, the molecular determinants for the switch in the sfRNA pattern during host change were mapped to a single RNA structure. Point mutations selected in mosquito cells were sufficient to change the pattern of sfRNAs, induce higher type I interferon responses and reduce viral fitness in human cells, explaining the rapid clearance of certain viral variants after host change. In addition, using epidemic and pre-epidemic Zika viruses, similar patterns of sfRNAs were observed in mosquito and human infected cells, but they were different from those observed during dengue virus infections, indicating that distinct selective pressures act on the 3'UTR of these closely related viruses. In summary, we present a novel mechanism by which dengue virus evolved an RNA structure that is under strong selective pressure in the two hosts, as regulator of non-coding RNA accumulation and viral fitness. This work provides new ideas about the impact of host adaptation on the variability and evolution of flavivirus 3'UTRs with

  11. CFD Process Automation Using Overset Grids

    NASA Technical Reports Server (NTRS)

    Buning, Pieter G.; George, Michael W. (Technical Monitor)

    1995-01-01

    This talk summarizes three applications of the overset grid method for CFD using some level of automated grid generation, flow solution and post-processing. These applications are 2D high-lift airfoil analysis (INS2D code), turbomachinery applications (ROTOR2/3 codes), and subsonic transport wing/body configurations (OVERFLOW code). These examples provide a forum for discussing the advantages and disadvantages of overset gridding for use in an automated CFD process. The goals and benefits of the automation incorporated in each application will be described, as well as the shortcomings of the approaches.

  12. Cross-code comparisons of mixing during the implosion of dense cylindrical and spherical shells

    NASA Astrophysics Data System (ADS)

    Joggerst, C. C.; Nelson, Anthony; Woodward, Paul; Lovekin, Catherine; Masser, Thomas; Fryer, Chris L.; Ramaprabhu, P.; Francois, Marianne; Rockefeller, Gabriel

    2014-10-01

    We present simulations of the implosion of a dense shell in two-dimensional (2D) spherical and cylindrical geometry performed with four different compressible, Eulerian codes: RAGE, FLASH, CASTRO, and PPM. We follow the growth of instabilities on the inner face of the dense shell. Three codes employed Cartesian grid geometry, and one (FLASH) employed polar grid geometry. While the codes are similar, they employ different advection algorithms, limiters, adaptive mesh refinement (AMR) schemes, and interface-preservation techniques. We find that the growth rate of the instability is largely insensitive to the choice of grid geometry or other implementation details specific to an individual code, provided the grid resolution is sufficiently fine. Overall, all simulations from different codes compare very well on the fine grids for which we tested them, though they show slight differences in small-scale mixing. Simulations produced by codes that explicitly limit numerical diffusion show a smaller amount of small-scale mixing than codes that do not. This difference is most prominent for low-mode perturbations where little instability finger interaction takes place, and less prominent for high- or multi-mode simulations where a great deal of interaction takes place, though it is still present. We present RAGE and FLASH simulations to quantify the initial perturbation amplitude to wavelength ratio at which metrics of mixing agree across codes, and find that bubble/spike amplitudes are converged for low-mode and high-mode simulations in which the perturbation amplitude is more than 1% and 5% of the wavelength of the perturbation, respectively. Other metrics of small-scale mixing depend on details of multi-fluid advection and do not converge between codes for the resolutions that were accessible.

  13. TranAir: A full-potential, solution-adaptive, rectangular grid code for predicting subsonic, transonic, and supersonic flows about arbitrary configurations. User's manual

    NASA Technical Reports Server (NTRS)

    Johnson, F. T.; Samant, S. S.; Bieterman, M. B.; Melvin, R. G.; Young, D. P.; Bussoletti, J. E.; Hilmes, C. L.

    1992-01-01

    The TranAir computer program calculates transonic flow about arbitrary configurations at subsonic, transonic, and supersonic freestream Mach numbers. TranAir solves the nonlinear full potential equations subject to a variety of boundary conditions modeling wakes, inlets, exhausts, porous walls, and impermeable surfaces. Regions with different total temperature and pressure can be represented. The user's manual describes how to run the TranAir program and its graphical support programs.

  14. GridMol: a grid application for molecular modeling and visualization

    NASA Astrophysics Data System (ADS)

    Sun, Yanhua; Shen, Bin; Lu, Zhonghua; Jin, Zhong; Chi, Xuebin

    2008-02-01

    In this paper we present GridMol, an extensible tool for building a high performance computational chemistry platform in the grid environment. GridMol provides computational chemists one-stop service for molecular modeling, scientific computing and molecular information visualization. GridMol is not only a visualization and modeling tool but also simplifies control of remote Grid software that can access high performance computing resources. GridMol has been successfully integrated into China National Grid, the most powerful Chinese Grid Computing platform. In Section "Grid computing" of this paper, a computing example is given to show the availability and efficiency of GridMol. GridMol is coded using Java and Java3D for portability and cross-platform compatibility (Windows, Linux, MacOS X and UNIX). GridMol can run not only as a stand-alone application, but also as an applet through web browsers. In this paper, we will present the techniques for molecular visualization, molecular modeling and grid computing. GridMol is available free of charge under the GNU Public License (GPL) from our website: http://www.sccas.cn/ syh/GridMol/index.html.

  15. Surface Modeling and Grid Generation of Orbital Sciences X34 Vehicle. Phase 1

    NASA Technical Reports Server (NTRS)

    Alter, Stephen J.

    1997-01-01

    The surface modeling and grid generation requirements, motivations, and methods used to develop Computational Fluid Dynamic volume grids for the X34-Phase 1 are presented. The requirements set forth by the Aerothermodynamics Branch at the NASA Langley Research Center serve as the basis for the final techniques used in the construction of all volume grids, including grids for parametric studies of the X34. The Integrated Computer Engineering and Manufacturing code for Computational Fluid Dynamics (ICEM/CFD), the Grid Generation code (GRIDGEN), the Three-Dimensional Multi-block Advanced Grid Generation System (3DMAGGS) code, and Volume Grid Manipulator (VGM) code are used to enable the necessary surface modeling, surface grid generation, volume grid generation, and grid alterations, respectively. All volume grids generated for the X34, as outlined in this paper, were used for CFD simulations within the Aerothermodynamics Branch.

  16. User Manual for Beta Version of TURBO-GRD: A Software System for Interactive Two-Dimensional Boundary/ Field Grid Generation, Modification, and Refinement

    NASA Technical Reports Server (NTRS)

    Choo, Yung K.; Slater, John W.; Henderson, Todd L.; Bidwell, Colin S.; Braun, Donald C.; Chung, Joongkee

    1998-01-01

    TURBO-GRD is a software system for interactive two-dimensional boundary/field grid generation. modification, and refinement. Its features allow users to explicitly control grid quality locally and globally. The grid control can be achieved interactively by using control points that the user picks and moves on the workstation monitor or by direct stretching and refining. The techniques used in the code are the control point form of algebraic grid generation, a damped cubic spline for edge meshing and parametric mapping between physical and computational domains. It also performs elliptic grid smoothing and free-form boundary control for boundary geometry manipulation. Internal block boundaries are constructed and shaped by using Bezier curve. Because TURBO-GRD is a highly interactive code, users can read in an initial solution, display its solution contour in the background of the grid and control net, and exercise grid modification using the solution contour as a guide. This process can be called an interactive solution-adaptive grid generation.

  17. Fast coeff_token decoding method and new memory architecture design for an efficient H.264/AVC context-based adaptive variable length coding decoder

    NASA Astrophysics Data System (ADS)

    Moon, Yong Ho; Yoon, Kun Su; Ha, Seok Wun

    2009-12-01

    A fast coeff_token decoding method based on new memory architecture is proposed to implement an efficient context-based adaptive variable length-coding (CAVLC) decoder. The heavy memory access needed in CAVLC decoding is a significant issue in designing a real system, such as digital multimedia broadcasting players, portable media players, and mobile phones with video, because it results in high power consumption and delay in operations. Recently, a new coeff_token variable-length decoding method has been suggested to achieve memory access reduction. However, it still requires a large portion of the total memory access in CAVLC decoding. In this work, an effective memory architecture is designed through careful examination of codewords in variable-length code tables. In addition, a novel fast decoding method is proposed to further reduce the memory accesses required for reconstructing the coeff_token element. Only one memory access is used for reconstructing each coeff_token element in the proposed method.

  18. CDF software distribution on the grid using Parrot

    SciTech Connect

    Compostella, G.; Pagan Griso, S.; Lucchesi, D.; Sfiligoi, I.; Thain, D.; /Notre Dame U.

    2010-01-01

    Large international collaborations that use decentralized computing models are becoming a custom rather than an exception in High Energy Physics. A good computing model for such big collaborations has to deal with the distribution of the experiment-specific software around the world. When the CDF experiment developed its software infrastructure, most computing was done on dedicated clusters. As a result, libraries, configuration files and large executables were deployed over a shared file system. In order to adapt its computing model to the Grid, CDF decided to distribute its software to all European Grid sites using Parrot, a user-level application capable of attaching existing programs to remote I/O systems through the filesystem interface. This choice allows CDF to use just one centralized source of code and a scalable set of caches all around Europe to efficiently distribute its code and requires almost no interaction with the existing Grid middleware or with local system administrators. This system has been in production at CDF in Europe since almost two years. Here, we present CDF implementation of Parrot and some comments on its performances.

  19. CDF software distribution on the Grid using Parrot

    NASA Astrophysics Data System (ADS)

    Compostella, G.; Pagan Griso, S.; Lucchesi, D.; Sfiligoi, I.; Thain, D.

    2010-04-01

    Large international collaborations that use decentralized computing models are becoming a custom rather than an exception in High Energy Physics. A good computing model for such big collaborations has to deal with the distribution of the experiment-specific software around the world. When the CDF experiment developed its software infrastructure, most computing was done on dedicated clusters. As a result, libraries, configuration files and large executables were deployed over a shared file system. In order to adapt its computing model to the Grid, CDF decided to distribute its software to all European Grid sites using Parrot, a user-level application capable of attaching existing programs to remote I/O systems through the filesystem interface. This choice allows CDF to use just one centralized source of code and a scalable set of caches all around Europe to efficiently distribute its code and requires almost no interaction with the existing Grid middleware or with local system administrators. This system has been in production at CDF in Europe since almost two years. Here, we present CDF implementation of Parrot and some comments on its performances.

  20. Automation and adaptation: Nurses' problem-solving behavior following the implementation of bar coded medication administration technology.

    PubMed

    Holden, Richard J; Rivera-Rodriguez, A Joy; Faye, Héléne; Scanlon, Matthew C; Karsh, Ben-Tzion

    2013-08-01

    The most common change facing nurses today is new technology, particularly bar coded medication administration technology (BCMA). However, there is a dearth of knowledge on how BCMA alters nursing work. This study investigated how BCMA technology affected nursing work, particularly nurses' operational problem-solving behavior. Cognitive systems engineering observations and interviews were conducted after the implementation of BCMA in three nursing units of a freestanding pediatric hospital. Problem-solving behavior, associated problems, and goals, were specifically defined and extracted from observed episodes of care. Three broad themes regarding BCMA's impact on problem solving were identified. First, BCMA allowed nurses to invent new problem-solving behavior to deal with pre-existing problems. Second, BCMA made it difficult or impossible to apply some problem-solving behaviors that were commonly used pre-BCMA, often requiring nurses to use potentially risky workarounds to achieve their goals. Third, BCMA created new problems that nurses were either able to solve using familiar or novel problem-solving behaviors, or unable to solve effectively. Results from this study shed light on hidden hazards and suggest three critical design needs: (1) ecologically valid design; (2) anticipatory control; and (3) basic usability. Principled studies of the actual nature of clinicians' work, including problem solving, are necessary to uncover hidden hazards and to inform health information technology design and redesign.

  1. Automation and adaptation: Nurses’ problem-solving behavior following the implementation of bar coded medication administration technology

    PubMed Central

    Holden, Richard J.; Rivera-Rodriguez, A. Joy; Faye, Héléne; Scanlon, Matthew C.; Karsh, Ben-Tzion

    2012-01-01

    The most common change facing nurses today is new technology, particularly bar coded medication administration technology (BCMA). However, there is a dearth of knowledge on how BCMA alters nursing work. This study investigated how BCMA technology affected nursing work, particularly nurses’ operational problem-solving behavior. Cognitive systems engineering observations and interviews were conducted after the implementation of BCMA in three nursing units of a freestanding pediatric hospital. Problem-solving behavior, associated problems, and goals, were specifically defined and extracted from observed episodes of care. Three broad themes regarding BCMA’s impact on problem solving were identified. First, BCMA allowed nurses to invent new problem-solving behavior to deal with pre-existing problems. Second, BCMA made it difficult or impossible to apply some problem-solving behaviors that were commonly used pre-BCMA, often requiring nurses to use potentially risky workarounds to achieve their goals. Third, BCMA created new problems that nurses were either able to solve using familiar or novel problem-solving behaviors, or unable to solve effectively. Results from this study shed light on hidden hazards and suggest three critical design needs: (1) ecologically valid design; (2) anticipatory control; and (3) basic usability. Principled studies of the actual nature of clinicians’ work, including problem solving, are necessary to uncover hidden hazards and to inform health information technology design and redesign. PMID:24443642

  2. Dengue virus genomic variation associated with mosquito adaptation defines the pattern of viral non-coding RNAs and fitness in human cells

    PubMed Central

    Aguirre, Sebastian; Pallarés, Horacio M.; Blair, Carol D.; Fabri, Cintia; Morales, Maria A.; Fernandez-Sesma, Ana; Gamarnik, Andrea V.

    2017-01-01

    The Flavivirus genus includes a large number of medically relevant pathogens that cycle between humans and arthropods. This host alternation imposes a selective pressure on the viral population. Here, we found that dengue virus, the most important viral human pathogen transmitted by insects, evolved a mechanism to differentially regulate the production of viral non-coding RNAs in mosquitos and humans, with a significant impact on viral fitness in each host. Flavivirus infections accumulate non-coding RNAs derived from the viral 3’UTRs (known as sfRNAs), relevant in viral pathogenesis and immune evasion. We found that dengue virus host adaptation leads to the accumulation of different species of sfRNAs in vertebrate and invertebrate cells. This process does not depend on differences in the host machinery; but it was found to be dependent on the selection of specific mutations in the viral 3’UTR. Dissecting the viral population and studying phenotypes of cloned variants, the molecular determinants for the switch in the sfRNA pattern during host change were mapped to a single RNA structure. Point mutations selected in mosquito cells were sufficient to change the pattern of sfRNAs, induce higher type I interferon responses and reduce viral fitness in human cells, explaining the rapid clearance of certain viral variants after host change. In addition, using epidemic and pre-epidemic Zika viruses, similar patterns of sfRNAs were observed in mosquito and human infected cells, but they were different from those observed during dengue virus infections, indicating that distinct selective pressures act on the 3’UTR of these closely related viruses. In summary, we present a novel mechanism by which dengue virus evolved an RNA structure that is under strong selective pressure in the two hosts, as regulator of non-coding RNA accumulation and viral fitness. This work provides new ideas about the impact of host adaptation on the variability and evolution of flavivirus 3

  3. Adaptive coding of the value of social cues with oxytocin, an fMRI study in autism spectrum disorder.

    PubMed

    Andari, Elissar; Richard, Nathalie; Leboyer, Marion; Sirigu, Angela

    2016-03-01

    The neuropeptide oxytocin (OT) is one of the major targets of research in neuroscience, with respect to social functioning. Oxytocin promotes social skills and improves the quality of face processing in individuals with social dysfunctions such as autism spectrum disorder (ASD). Although one of OT's key functions is to promote social behavior during dynamic social interactions, the neural correlates of this function remain unknown. Here, we combined acute intranasal OT (IN-OT) administration (24 IU) and fMRI with an interactive ball game and a face-matching task in individuals with ASD (N = 20). We found that IN-OT selectively enhanced the brain activity of early visual areas in response to faces as compared to non-social stimuli. OT inhalation modulated the BOLD activity of amygdala and hippocampus in a context-dependent manner. Interestingly, IN-OT intake enhanced the activity of mid-orbitofrontal cortex in response to a fair partner, and insula region in response to an unfair partner. These OT-induced neural responses were accompanied by behavioral improvements in terms of allocating appropriate feelings of trust toward different partners' profiles. Our findings suggest that OT impacts the brain activity of key areas implicated in attention and emotion regulation in an adaptive manner, based on the value of social cues.

  4. Grid generation on surfaces in 3 dimensions

    NASA Technical Reports Server (NTRS)

    Eiseman, Peter R.

    1986-01-01

    The development of a surface grid generation algorithm was initiated. The basic adaptive movement technique of mean-value-relaxation was extended from the viewpoint of a single coordinate grid over a surface described by a single scalar function to that of a surface more generally defined by vector functions and covered by a collection of smoothly connected grids. Within the multiconnected assemblage, the application of control was examined in several instances.

  5. The surveillance error grid.

    PubMed

    Klonoff, David C; Lias, Courtney; Vigersky, Robert; Clarke, William; Parkes, Joan Lee; Sacks, David B; Kirkman, M Sue; Kovatchev, Boris

    2014-07-01

    Currently used error grids for assessing clinical accuracy of blood glucose monitors are based on out-of-date medical practices. Error grids have not been widely embraced by regulatory agencies for clearance of monitors, but this type of tool could be useful for surveillance of the performance of cleared products. Diabetes Technology Society together with representatives from the Food and Drug Administration, the American Diabetes Association, the Endocrine Society, and the Association for the Advancement of Medical Instrumentation, and representatives of academia, industry, and government, have developed a new error grid, called the surveillance error grid (SEG) as a tool to assess the degree of clinical risk from inaccurate blood glucose (BG) monitors. A total of 206 diabetes clinicians were surveyed about the clinical risk of errors of measured BG levels by a monitor. The impact of such errors on 4 patient scenarios was surveyed. Each monitor/reference data pair was scored and color-coded on a graph per its average risk rating. Using modeled data representative of the accuracy of contemporary meters, the relationships between clinical risk and monitor error were calculated for the Clarke error grid (CEG), Parkes error grid (PEG), and SEG. SEG action boundaries were consistent across scenarios, regardless of whether the patient was type 1 or type 2 or using insulin or not. No significant differences were noted between responses of adult/pediatric or 4 types of clinicians. Although small specific differences in risk boundaries between US and non-US clinicians were noted, the panel felt they did not justify separate grids for these 2 types of clinicians. The data points of the SEG were classified in 15 zones according to their assigned level of risk, which allowed for comparisons with the classic CEG and PEG. Modeled glucose monitor data with realistic self-monitoring of blood glucose errors derived from meter testing experiments plotted on the SEG when compared to

  6. Solving Partial Differential Equations on Overlapping Grids

    SciTech Connect

    Henshaw, W D

    2008-09-22

    We discuss the solution of partial differential equations (PDEs) on overlapping grids. This is a powerful technique for efficiently solving problems in complex, possibly moving, geometry. An overlapping grid consists of a set of structured grids that overlap and cover the computational domain. By allowing the grids to overlap, grids for complex geometries can be more easily constructed. The overlapping grid approach can also be used to remove coordinate singularities by, for example, covering a sphere with two or more patches. We describe the application of the overlapping grid approach to a variety of different problems. These include the solution of incompressible fluid flows with moving and deforming geometry, the solution of high-speed compressible reactive flow with rigid bodies using adaptive mesh refinement (AMR), and the solution of the time-domain Maxwell's equations of electromagnetism.

  7. Generating Composite Overlapping Grids on CAD Geometries

    SciTech Connect

    Henshaw, W.D.

    2002-02-07

    We describe some algorithms and tools that have been developed to generate composite overlapping grids on geometries that have been defined with computer aided design (CAD) programs. This process consists of five main steps. Starting from a description of the surfaces defining the computational domain we (1) correct errors in the CAD representation, (2) determine topology of the patched-surface, (3) build a global triangulation of the surface, (4) construct structured surface and volume grids using hyperbolic grid generation, and (5) generate the overlapping grid by determining the holes and the interpolation points. The overlapping grid generator which is used for the final step also supports the rapid generation of grids for block-structured adaptive mesh refinement and for moving grids. These algorithms have been implemented as part of the Overture object-oriented framework.

  8. Multiblock grid generation with automatic zoning

    NASA Technical Reports Server (NTRS)

    Eiseman, Peter R.

    1995-01-01

    An overview will be given for multiblock grid generation with automatic zoning. We shall explore the many advantages and benefits of this exciting technology and will also see how to apply it to a number of interesting cases. The technology is available in the form of a commercial code, GridPro(registered trademark)/az3000. This code takes surface geometry definitions and patterns of points as its primary input and produces high quality grids as its output. Before we embark upon our exploration, we shall first give a brief background of the environment in which this technology fits.

  9. Criteria for evaluation of grid generation systems

    NASA Technical Reports Server (NTRS)

    Ascoli, Edward P.; Barson, Steven L.; Decroix, Michele E.; Hsu, Wayne W.

    1993-01-01

    Many CFD grid generation systems are in use nationally, but few comparative studies have been performed to quantify their relative merits. A study was undertaken to systematically evaluate and select the best CFD grid generation codes available. Detailed evaluation criteria were established as the basis for the evaluation conducted. Descriptions of thirty-four separate criteria, grouped into eight general categories are provided. Benchmark test cases, developed to test basic features of selected codes, are described in detail. Scoring guidelines were generated to establish standards for measuring code capabilities, ensuring uniformity of ratings, and minimizing personal bias among the three code evaluators. Ten candidate codes were identified from government, industry, universities, and commercial software companies. A three phase evaluation was conducted. In Phase 1, ten codes identified were screened through conversations with code authors and other industry experts. Seven codes were carried forward into a Phase 2 evaluation in which all codes were scored according to the predefined criteria. Two codes emerged as being significantly better than the others: RAGGS and GRIDGEN. Finally, these two codes were carried forward into a Phase 3 evaluation in which complex 3-D multizone grids were generated to verify capability.

  10. Regulatory versus coding signatures of natural selection in a candidate gene involved in the adaptive divergence of whitefish species pairs (Coregonus spp.).

    PubMed

    Jeukens, Julie; Bernatchez, Louis

    2012-01-01

    While gene expression divergence is known to be involved in adaptive phenotypic divergence and speciation, the relative importance of regulatory and structural evolution of genes is poorly understood. A recent next-generation sequencing experiment allowed identifying candidate genes potentially involved in the ongoing speciation of sympatric dwarf and normal lake whitefish (Coregonus clupeaformis), such as cytosolic malate dehydrogenase (MDH1), which showed both significant expression and sequence divergence. The main goal of this study was to investigate into more details the signatures of natural selection in the regulatory and coding sequences of MDH1 in lake whitefish and test for parallelism of these signatures with other coregonine species. Sequencing of the two regions in 118 fish from four sympatric pairs of whitefish and two cisco species revealed a total of 35 single nucleotide polymorphisms (SNPs), with more genetic diversity in European compared to North American coregonine species. While the coding region was found to be under purifying selection, an SNP in the proximal promoter exhibited significant allele frequency divergence in a parallel manner among independent sympatric pairs of North American lake whitefish and European whitefish (C. lavaretus). According to transcription factor binding simulation for 22 regulatory haplotypes of MDH1, putative binding profiles were fairly conserved among species, except for the region around this SNP. Moreover, we found evidence for the role of this SNP in the regulation of MDH1 expression level. Overall, these results provide further evidence for the role of natural selection in gene regulation evolution among whitefish species pairs and suggest its possible link with patterns of phenotypic diversity observed in coregonine species.

  11. Datums, Ellipsoids, Grids, and Grid Reference Systems

    DTIC Science & Technology

    1992-01-01

    Tunisie Grid, Sud Algerie Grid, Sud Maroc Grid, and Sud Tunisie Grid. 4-1.1.8 The...REFERENCES ON THE SUD ALGERIE AND SUD TUNISIE GRIDS 6-8.5.2 When oil reference boxes cannot be accommodated in the margin, the excess is shown in expanses...GIVING REFERENCES ON THE SUD ALGERIE AND SUD TUNISIE GRIDS 6-21 DMA TM 8358.1 I CHAPTER 7 GRIDS ON MAPS AT 1:250,000 AND 1:500,000 SCALE 7.1 GENERAL.

  12. Scientific Computing on the Grid

    SciTech Connect

    Allen, Gabrielle; Seidel, Edward; Shalf, John

    2001-12-12

    Computer simulations are becoming increasingly important as the only means for studying and interpreting the complex processes of nature. Yet the scope and accuracy of these simulations are severely limited by available computational power, even using today's most powerful supercomputers. As we endeavor to simulate the true complexity of nature, we will require much larger scale calculations than are possible at present. Such dynamic and large scale applications will require computational grids and grids require development of new latency tolerant algorithms, and sophisticated code frameworks like Cactus to carry out more complex and high fidelity simulations with a massive degree of parallelism.

  13. Visual Adaptation

    PubMed Central

    Webster, Michael A.

    2015-01-01

    Sensory systems continuously mold themselves to the widely varying contexts in which they must operate. Studies of these adaptations have played a long and central role in vision science. In part this is because the specific adaptations remain a powerful tool for dissecting vision, by exposing the mechanisms that are adapting. That is, “if it adapts, it's there.” Many insights about vision have come from using adaptation in this way, as a method. A second important trend has been the realization that the processes of adaptation are themselves essential to how vision works, and thus are likely to operate at all levels. That is, “if it's there, it adapts.” This has focused interest on the mechanisms of adaptation as the target rather than the probe. Together both approaches have led to an emerging insight of adaptation as a fundamental and ubiquitous coding strategy impacting all aspects of how we see. PMID:26858985

  14. Parallel grid library for rapid and flexible simulation development

    NASA Astrophysics Data System (ADS)

    Honkonen, I.; von Alfthan, S.; Sandroos, A.; Janhunen, P.; Palmroth, M.

    2013-04-01

    We present an easy to use and flexible grid library for developing highly scalable parallel simulations. The distributed cartesian cell-refinable grid (dccrg) supports adaptive mesh refinement and allows an arbitrary C++ class to be used as cell data. The amount of data in grid cells can vary both in space and time allowing dccrg to be used in very different types of simulations, for example in fluid and particle codes. Dccrg transfers the data between neighboring cells on different processes transparently and asynchronously allowing one to overlap computation and communication. This enables excellent scalability at least up to 32 k cores in magnetohydrodynamic tests depending on the problem and hardware. In the version of dccrg presented here part of the mesh metadata is replicated between MPI processes reducing the scalability of adaptive mesh refinement (AMR) to between 200 and 600 processes. Dccrg is free software that anyone can use, study and modify and is available at https://gitorious.org/dccrg. Users are also kindly requested to cite this work when publishing results obtained with dccrg. Catalogue identifier: AEOM_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEOM_v1_0.html Program obtainable from: CPC Program Library, Queen’s University, Belfast, N. Ireland Licensing provisions: GNU Lesser General Public License version 3 No. of lines in distributed program, including test data, etc.: 54975 No. of bytes in distributed program, including test data, etc.: 974015 Distribution format: tar.gz Programming language: C++. Computer: PC, cluster, supercomputer. Operating system: POSIX. The code has been parallelized using MPI and tested with 1-32768 processes RAM: 10 MB-10 GB per process Classification: 4.12, 4.14, 6.5, 19.3, 19.10, 20. External routines: MPI-2 [1], boost [2], Zoltan [3], sfc++ [4] Nature of problem: Grid library supporting arbitrary data in grid cells, parallel adaptive mesh refinement, transparent remote neighbor data updates and

  15. Integron-associated mobile gene cassettes code for folded proteins: the structure of Bal32a, a new member of the adaptable alpha+beta barrel family.

    PubMed

    Robinson, Andrew; Wu, Peter S-C; Harrop, Stephen J; Schaeffer, Patrick M; Dosztányi, Zsuzsanna; Gillings, Michael R; Holmes, Andrew J; Nevalainen, K M Helena; Stokes, H W; Otting, Gottfried; Dixon, Nicholas E; Curmi, Paul M G; Mabbutt, Bridget C

    2005-03-11

    The wide-ranging physiology and large genetic variability observed for prokaryotes is largely attributed, not to the prokaryotic genome itself, but rather to mechanisms of lateral gene transfer. Cassette PCR has been used to sample the integron/gene cassette metagenome from different natural environments without laboratory cultivation of the host organism, and without prior knowledge of any target protein sequence. Since over 90% of cassette genes are unrelated to any sequence in the current databases, it is not clear whether these genes code for folded functional proteins. We have selected a sample of eight cassette-encoded genes with no known homologs; five have been isolated as soluble protein products and shown by biophysical techniques to be folded. In solution, at least three of these proteins organise as stable oligomeric assemblies. The tertiary structure of one of these, Bal32a derived from a contaminated soil site, has been solved by X-ray crystallography to 1.8 A resolution. From the three-dimensional structure, Bal32a is found to be a member of the highly adaptable alpha+beta barrel family of transport proteins and enzymes. In Bal32a, the barrel cavity is unusually deep and inaccessible to solvent. Polar side-chains in its interior are reminiscent of catalytic sites of limonene-1,2-epoxide hydrolase and nogalonic acid methyl ester cyclase. These studies demonstrate the viability of direct sampling of mobile DNA as a route for the discovery of novel proteins.

  16. Generation of unstructured grids and Euler solutions for complex geometries

    NASA Technical Reports Server (NTRS)

    Loehner, Rainald; Parikh, Paresh; Salas, Manuel D.

    1989-01-01

    Algorithms are described for the generation and adaptation of unstructured grids in two and three dimensions, as well as Euler solvers for unstructured grids. The main purpose is to demonstrate how unstructured grids may be employed advantageously for the economic simulation of both geometrically as well as physically complex flow fields.

  17. Software systems used for unstructured grid generation at NASA Langley

    NASA Technical Reports Server (NTRS)

    Bockelie, Michael J.

    1993-01-01

    These viewgraphs provide an overview of grid generation system for 3D configurations (Euler Grids) and grid generators of viscous and inviscid flow, solution adaptive for steady and unsteady flow. The five systems presented are VGRID, FELISA, TETRA, NGP, and TGRID.

  18. High order finite volume methods on wavelet-adapted grids with local time-stepping on multicore architectures for the simulation of shock-bubble interactions

    NASA Astrophysics Data System (ADS)

    Hejazialhosseini, Babak; Rossinelli, Diego; Bergdorf, Michael; Koumoutsakos, Petros

    2010-11-01

    We present a space-time adaptive solver for single- and multi-phase compressible flows that couples average interpolating wavelets with high-order finite volume schemes. The solver introduces the concept of wavelet blocks, handles large jumps in resolution and employs local time-stepping for efficient time integration. We demonstrate that the inherently sequential wavelet-based adaptivity can be implemented efficiently in multicore computer architectures using task-based parallelism and introducing the concept of wavelet blocks. We validate our computational method on a number of benchmark problems and we present simulations of shock-bubble interaction at different Mach numbers, demonstrating the accuracy and computational performance of the method.

  19. A point implicit unstructured grid solver for the Euler and Navier-Stokes equations

    NASA Technical Reports Server (NTRS)

    Thareja, Rajiv R.; Stewart, James R.; Hassan, Obey; Morgan, Ken; Peraire, Jaime

    1988-01-01

    An upwind finite element technique that uses cell centered quantities and implicit and/or explicit time marching has been developed for computing hypersonic laminar viscous flows using adaptive unstructured triangular grids. A structured grid of quadrilaterals is laid out near the body surface. For inviscid flows the method is stable at Courant numbers of over 100,000. A first order basic scheme and a higher order flux corrected transport (FCT) scheme have been implemented. This technique has been applied to the problem of predicting type III and IV shock wave interactions on a cylinder, with a view of simulating the pressure and heating rate augmentation caused by an impinging shock on the leading edge of a cowl lip of an engine inlet. The predictions of wall pressure and heating rates compare very well with experimental data. The flow features are very distinctly captured with a sequence of adaptively generated grids. The adaptive mesh generator and the upwind Navier-Stokes solver are combined in a set of programs called LARCNESS, an acronym for Langley Adaptive Remeshing Code and Navier-Stokes Solver.

  20. Compressible Astrophysics Simulation Code

    SciTech Connect

    Howell, L.; Singer, M.

    2007-07-18

    This is an astrophysics simulation code involving a radiation diffusion module developed at LLNL coupled to compressible hydrodynamics and adaptive mesh infrastructure developed at LBNL. One intended application is to neutrino diffusion in core collapse supernovae.

  1. ARPA-E: Advancing the Electric Grid

    SciTech Connect

    Lemmon, John; Ruiz, Pablo; Sommerer, Tim; Aziz, Michael

    2014-02-24

    The electric grid was designed with the assumption that all energy generation sources would be relatively controllable, and grid operators would always be able to predict when and where those sources would be located. With the addition of renewable energy sources like wind and solar, which can be installed faster than traditional generation technologies, this is no longer the case. Furthermore, the fact that renewable energy sources are imperfectly predictable means that the grid has to adapt in real-time to changing patterns of power flow. We need a dynamic grid that is far more flexible. This video highlights three ARPA-E-funded approaches to improving the grid's flexibility: topology control software from Boston University that optimizes power flow, gas tube switches from General Electric that provide efficient power conversion, and flow batteries from Harvard University that offer grid-scale energy storage.

  2. ARPA-E: Advancing the Electric Grid

    ScienceCinema

    Lemmon, John; Ruiz, Pablo; Sommerer, Tim; Aziz, Michael

    2016-07-12

    The electric grid was designed with the assumption that all energy generation sources would be relatively controllable, and grid operators would always be able to predict when and where those sources would be located. With the addition of renewable energy sources like wind and solar, which can be installed faster than traditional generation technologies, this is no longer the case. Furthermore, the fact that renewable energy sources are imperfectly predictable means that the grid has to adapt in real-time to changing patterns of power flow. We need a dynamic grid that is far more flexible. This video highlights three ARPA-E-funded approaches to improving the grid's flexibility: topology control software from Boston University that optimizes power flow, gas tube switches from General Electric that provide efficient power conversion, and flow batteries from Harvard University that offer grid-scale energy storage.

  3. Wavelet-Based Grid Generation

    NASA Technical Reports Server (NTRS)

    Jameson, Leland

    1996-01-01

    Wavelets can provide a basis set in which the basis functions are constructed by dilating and translating a fixed function known as the mother wavelet. The mother wavelet can be seen as a high pass filter in the frequency domain. The process of dilating and expanding this high-pass filter can be seen as altering the frequency range that is 'passed' or detected. The process of translation moves this high-pass filter throughout the domain, thereby providing a mechanism to detect the frequencies or scales of information at every location. This is exactly the type of information that is needed for effective grid generation. This paper provides motivation to use wavelets for grid generation in addition to providing the final product: source code for wavelet-based grid generation.

  4. Development of Three-Dimensional DRAGON Grid Technology

    NASA Technical Reports Server (NTRS)

    Zheng, Yao; Kiou, Meng-Sing; Civinskas, Kestutis C.

    1999-01-01

    For a typical three dimensional flow in a practical engineering device, the time spent in grid generation can take 70 percent of the total analysis effort, resulting in a serious bottleneck in the design/analysis cycle. The present research attempts to develop a procedure that can considerably reduce the grid generation effort. The DRAGON grid, as a hybrid grid, is created by means of a Direct Replacement of Arbitrary Grid Overlapping by Nonstructured grid. The DRAGON grid scheme is an adaptation to the Chimera thinking. The Chimera grid is a composite structured grid, composing a set of overlapped structured grids, which are independently generated and body-fitted. The grid is of high quality and amenable for efficient solution schemes. However, the interpolation used in the overlapped region between grids introduces error, especially when a sharp-gradient region is encountered. The DRAGON grid scheme is capable of completely eliminating the interpolation and preserving the conservation property. It maximizes the advantages of the Chimera scheme and adapts the strengths of the unstructured and while at the same time keeping its weaknesses minimal. In the present paper, we describe the progress towards extending the DRAGON grid technology into three dimensions. Essential and programming aspects of the extension, and new challenges for the three-dimensional cases, are addressed.

  5. Automatic structured grid generation using Gridgen (some restrictions apply)

    NASA Technical Reports Server (NTRS)

    Chawner, John R.; Steinbrenner, John P.

    1995-01-01

    The authors have noticed in the recent grid generation literature an emphasis on the automation of structured grid generation. The motivation behind such work is clear; grid generation is easily the most despised task in the grid-analyze-visualize triad of computational analysis (CA). However, because grid generation is closely coupled to both the design and analysis software and because quantitative measures of grid quality are lacking, 'push button' grid generation usually results in a compromise between speed, control, and quality. Overt emphasis on automation obscures the substantive issues of providing users with flexible tools for generating and modifying high quality grids in a design environment. In support of this paper's tongue-in-cheek title, many features of the Gridgen software are described. Gridgen is by no stretch of the imagination an automatic grid generator. Despite this fact, the code does utilize many automation techniques that permit interesting regenerative features.

  6. GRChombo: Numerical relativity with adaptive mesh refinement

    NASA Astrophysics Data System (ADS)

    Clough, Katy; Figueras, Pau; Finkel, Hal; Kunesch, Markus; Lim, Eugene A.; Tunyasuvunakool, Saran

    2015-12-01

    In this work, we introduce {\\mathtt{GRChombo}}: a new numerical relativity code which incorporates full adaptive mesh refinement (AMR) using block structured Berger-Rigoutsos grid generation. The code supports non-trivial ‘many-boxes-in-many-boxes’ mesh hierarchies and massive parallelism through the message passing interface. {\\mathtt{GRChombo}} evolves the Einstein equation using the standard BSSN formalism, with an option to turn on CCZ4 constraint damping if required. The AMR capability permits the study of a range of new physics which has previously been computationally infeasible in a full 3 + 1 setting, while also significantly simplifying the process of setting up the mesh for these problems. We show that {\\mathtt{GRChombo}} can stably and accurately evolve standard spacetimes such as binary black hole mergers and scalar collapses into black holes, demonstrate the performance characteristics of our code, and discuss various physics problems which stand to benefit from the AMR technique.

  7. Adaptive Correlation Space Adjusted Open-Loop Tracking Approach for Vehicle Positioning with Global Navigation Satellite System in Urban Areas.

    PubMed

    Ruan, Hang; Li, Jian; Zhang, Lei; Long, Teng

    2015-08-28

    For vehicle positioning with Global Navigation Satellite System (GNSS) in urban areas, open-loop tracking shows better performance because of its high sensitivity and superior robustness against multipath. However, no previous study has focused on the effects of the code search grid size on the code phase measurement accuracy of open-loop tracking. Traditional open-loop tracking methods are performed by the batch correlators with fixed correlation space. The code search grid size, which is the correlation space, is a constant empirical value and the code phase measuring accuracy will be largely degraded due to the improper grid size, especially when the signal carrier-to-noise density ratio (C/N₀) varies. In this study, the Adaptive Correlation Space Adjusted Open-Loop Tracking Approach (ACSA-OLTA) is proposed to improve the code phase measurement dependent pseudo range accuracy. In ACSA-OLTA, the correlation space is adjusted according to the signal C/N₀. The novel Equivalent Weighted Pseudo Range Error (EWPRE) is raised to obtain the optimal code search grid sizes for different C/N₀. The code phase measuring errors of different measurement calculation methods are analyzed for the first time. The measurement calculation strategy of ACSA-OLTA is derived from the analysis to further improve the accuracy but reduce the correlator consumption. Performance simulation and real tests confirm that the pseudo range and positioning accuracy of ASCA-OLTA are better than the traditional open-loop tracking methods in the usual scenarios of urban area.

  8. Grid Convergence for Turbulent Flows(Invited)

    NASA Technical Reports Server (NTRS)

    Diskin, Boris; Thomas, James L.; Rumsey, Christopher L.; Schwoppe, Axel

    2015-01-01

    A detailed grid convergence study has been conducted to establish accurate reference solutions corresponding to the one-equation linear eddy-viscosity Spalart-Allmaras turbulence model for two dimensional turbulent flows around the NACA 0012 airfoil and a flat plate. The study involved three widely used codes, CFL3D (NASA), FUN3D (NASA), and TAU (DLR), and families of uniformly refined structured grids that differ in the grid density patterns. Solutions computed by different codes on different grid families appear to converge to the same continuous limit, but exhibit different convergence characteristics. The grid resolution in the vicinity of geometric singularities, such as a sharp trailing edge, is found to be the major factor affecting accuracy and convergence of discrete solutions, more prominent than differences in discretization schemes and/or grid elements. The results reported for these relatively simple turbulent flows demonstrate that CFL3D, FUN3D, and TAU solutions are very accurate on the finest grids used in the study, but even those grids are not sufficient to conclusively establish an asymptotic convergence order.

  9. The Construction of an Ontology-Based Ubiquitous Learning Grid

    ERIC Educational Resources Information Center

    Liao, Ching-Jung; Chou, Chien-Chih; Yang, Jin-Tan David

    2009-01-01

    The purpose of this study is to incorporate adaptive ontology into ubiquitous learning grid to achieve seamless learning environment. Ubiquitous learning grid uses ubiquitous computing environment to infer and determine the most adaptive learning contents and procedures in anytime, any place and with any device. To achieve the goal, an…

  10. Nyx: A MASSIVELY PARALLEL AMR CODE FOR COMPUTATIONAL COSMOLOGY

    SciTech Connect

    Almgren, Ann S.; Bell, John B.; Lijewski, Mike J.; Lukic, Zarija; Van Andel, Ethan

    2013-03-01

    We present a new N-body and gas dynamics code, called Nyx, for large-scale cosmological simulations. Nyx follows the temporal evolution of a system of discrete dark matter particles gravitationally coupled to an inviscid ideal fluid in an expanding universe. The gas is advanced in an Eulerian framework with block-structured adaptive mesh refinement; a particle-mesh scheme using the same grid hierarchy is used to solve for self-gravity and advance the particles. Computational results demonstrating the validation of Nyx on standard cosmological test problems, and the scaling behavior of Nyx to 50,000 cores, are presented.

  11. Grid Generation Issues and CFD Simulation Accuracy for the X33 Aerothermal Simulations

    NASA Technical Reports Server (NTRS)

    Polsky, Susan; Papadopoulos, Periklis; Davies, Carol; Loomis, Mark; Prabhu, Dinesh; Langhoff, Stephen R. (Technical Monitor)

    1997-01-01

    Grid generation issues relating to the simulation of the X33 aerothermal environment using the GASP code are explored. Required grid densities and normal grid stretching are discussed with regards to predicting the fluid dynamic and heating environments with the desired accuracy. The generation of volume grids is explored and includes discussions of structured grid generation packages such as GRIDGEN, GRIDPRO and HYPGEN. Volume grid manipulation techniques for obtaining desired outer boundary and grid clustering using the OUTBOUND code are examined. The generation of the surface grid with the required surface grid with the required surface grid topology is also discussed. Utilizing grids without singular axes is explored as a method of avoiding numerical difficulties at the singular line.

  12. Evaluation of total effective dose due to certain environmentally placed naturally occurring radioactive materials using a procedural adaptation of RESRAD code.

    PubMed

    Beauvais, Z S; Thompson, K H; Kearfott, K J

    2009-07-01

    Due to a recent upward trend in the price of uranium and subsequent increased interest in uranium mining, accurate modeling of baseline dose from environmental sources of radioactivity is of increasing interest. Residual radioactivity model and code (RESRAD) is a program used to model environmental movement and calculate the dose due to the inhalation, ingestion, and exposure to radioactive materials following a placement. This paper presents a novel use of RESRAD for the calculation of dose from non-enhanced, or ancient, naturally occurring radioactive material (NORM). In order to use RESRAD to calculate the total effective dose (TED) due to ancient NORM, a procedural adaptation was developed to negate the effects of time progressive distribution of radioactive materials. A dose due to United States' average concentrations of uranium, actinium, and thorium series radionuclides was then calculated. For adults exposed in a residential setting and assumed to eat significant amounts of food grown in NORM concentrated areas, the annual dose due to national average NORM concentrations was 0.935 mSv y(-1). A set of environmental dose factors were calculated for simple estimation of dose from uranium, thorium, and actinium series radionuclides for various age groups and exposure scenarios as a function of elemental uranium and thorium activity concentrations in groundwater and soil. The values of these factors for uranium were lowest for an adult exposed in an industrial setting: 0.00476 microSv kg Bq(-1) y(-1) for soil and 0.00596 microSv m(3) Bq(-1) y(-1) for water (assuming a 1:1 234U:238U activity ratio in water). The uranium factors were highest for infants exposed in a residential setting and assumed to ingest food grown onsite: 34.8 microSv kg Bq(-1) y(-1) in soil and 13.0 microSv m(3) Bq(-1) y(-1) in water.

  13. An adaptive-in-temperature method for on-the-fly sampling of thermal neutron scattering data in continuous-energy Monte Carlo codes

    NASA Astrophysics Data System (ADS)

    Pavlou, Andrew Theodore

    The Monte Carlo simulation of full-core neutron transport requires high fidelity data to represent not only the various types of possible interactions that can occur, but also the temperature and energy regimes for which these data are relevant. For isothermal conditions, nuclear cross section data are processed in advance of running a simulation. In reality, the temperatures in a neutronics simulation are not fixed, but change with respect to the temperatures computed from an associated heat transfer or thermal hydraulic (TH) code. To account for the temperature change, a code user must either 1) compute new data at the problem temperature inline during the Monte Carlo simulation or 2) pre-compute data at a variety of temperatures over the range of possible values. Inline data processing is computationally inefficient while pre-computing data at many temperatures can be memory expensive. An alternative on-the-fly approach to handle the temperature component of nuclear data is desired. By on-the-fly we mean a procedure that adjusts cross section data to the correct temperature adaptively during the Monte Carlo random walk instead of before the running of a simulation. The on-the-fly procedure should also preserve simulation runtime efficiency. While on-the-fly methods have recently been developed for higher energy regimes, the double differential scattering of thermal neutrons has not been examined in detail until now. In this dissertation, an on-the-fly sampling method is developed by investigating the temperature dependence of the thermal double differential scattering distributions. The temperature dependence is analyzed with a linear least squares regression test to develop fit coefficients that are used to sample thermal scattering data at any temperature. The amount of pre-stored thermal scattering data has been drastically reduced from around 25 megabytes per temperature per nuclide to only a few megabytes per nuclide by eliminating the need to compute data

  14. caGrid 1.0 : an enterprise Grid infrastructure for biomedical research.

    SciTech Connect

    Oster, S.; Langella, S.; Hastings, S.; Ervin, D.; Madduri, R.; Phillips, J.; Kurc, T.; Siebenlist, F.; Covitz, P.; Shanbhag, K.; Foster, I.; Saltz, J.; Mathematics and Computer Science; The Ohio State Univ.; National Cancer Inst. Centerfor Bioinformatics; SemanticBits

    2008-03-01

    To develop software infrastructure that will provide support for discovery, characterization, integrated access, and management of diverse and disparate collections of information sources, analysis methods, and applications in biomedical research. Design: An enterprise Grid software infrastructure, called caGrid version 1.0 (caGrid 1.0), has been developed as the core Grid architecture of the NCI-sponsored cancer Biomedical Informatics Grid (caBIG{trademark}) program. It is designed to support a wide range of use cases in basic, translational, and clinical research, including (1) discovery, (2) integrated and large-scale data analysis, and (3) coordinated study. Measurements: The caGrid is built as a Grid software infrastructure and leverages Grid computing technologies and the Web Services Resource Framework standards. It provides a set of core services, toolkits for the development and deployment of new community provided services, and application programming interfaces for building client applications. Results: The caGrid 1.0 was released to the caBIG community in December 2006. It is built on open source components and caGrid source code is publicly and freely available under a liberal open source license. The core software, associated tools, and documentation can be downloaded from the following URL: Grid>.

  15. Data Grid Management Systems

    NASA Technical Reports Server (NTRS)

    Moore, Reagan W.; Jagatheesan, Arun; Rajasekar, Arcot; Wan, Michael; Schroeder, Wayne

    2004-01-01

    The "Grid" is an emerging infrastructure for coordinating access across autonomous organizations to distributed, heterogeneous computation and data resources. Data grids are being built around the world as the next generation data handling systems for sharing, publishing, and preserving data residing on storage systems located in multiple administrative domains. A data grid provides logical namespaces for users, digital entities and storage resources to create persistent identifiers for controlling access, enabling discovery, and managing wide area latencies. This paper introduces data grids and describes data grid use cases. The relevance of data grids to digital libraries and persistent archives is demonstrated, and research issues in data grids and grid dataflow management systems are discussed.

  16. AstroGrid-D: Grid technology for astronomical science

    NASA Astrophysics Data System (ADS)

    Enke, Harry; Steinmetz, Matthias; Adorf, Hans-Martin; Beck-Ratzka, Alexander; Breitling, Frank; Brüsemeister, Thomas; Carlson, Arthur; Ensslin, Torsten; Högqvist, Mikael; Nickelt, Iliya; Radke, Thomas; Reinefeld, Alexander; Reiser, Angelika; Scholl, Tobias; Spurzem, Rainer; Steinacker, Jürgen; Voges, Wolfgang; Wambsganß, Joachim; White, Steve

    2011-02-01

    We present status and results of AstroGrid-D, a joint effort of astrophysicists and computer scientists to employ grid technology for scientific applications. AstroGrid-D provides access to a network of distributed machines with a set of commands as well as software interfaces. It allows simple use of computer and storage facilities and to schedule or monitor compute tasks and data management. It is based on the Globus Toolkit middleware (GT4). Chapter 1 describes the context which led to the demand for advanced software solutions in Astrophysics, and we state the goals of the project. We then present characteristic astrophysical applications that have been implemented on AstroGrid-D in chapter 2. We describe simulations of different complexity, compute-intensive calculations running on multiple sites (Section 2.1), and advanced applications for specific scientific purposes (Section 2.2), such as a connection to robotic telescopes (Section 2.2.3). We can show from these examples how grid execution improves e.g. the scientific workflow. Chapter 3 explains the software tools and services that we adapted or newly developed. Section 3.1 is focused on the administrative aspects of the infrastructure, to manage users and monitor activity. Section 3.2 characterises the central components of our architecture: The AstroGrid-D information service to collect and store metadata, a file management system, the data management system, and a job manager for automatic submission of compute tasks. We summarise the successfully established infrastructure in chapter 4, concluding with our future plans to establish AstroGrid-D as a platform of modern e-Astronomy.

  17. Revised Extended Grid Library

    SciTech Connect

    Martz, Roger L.

    2016-07-15

    The Revised Eolus Grid Library (REGL) is a mesh-tracking library that was developed for use with the MCNP6TM computer code so that (radiation) particles can track on an unstructured mesh. The unstructured mesh is a finite element representation of any geometric solid model created with a state-of-the-art CAE/CAD tool. The mesh-tracking library is written using modern Fortran and programming standards; the library is Fortran 2003 compliant. The library was created with a defined application programmer interface (API) so that it could easily integrate with other particle tracking/transport codes. The library does not handle parallel processing via the message passing interface (mpi), but has been used successfully where the host code handles the mpi calls. The library is thread-safe and supports the OpenMP paradigm. As a library, all features are available through the API and overall a tight coupling between it and the host code is required. Features of the library are summarized with the following list: • can accommodate first and second order 4, 5, and 6-sided polyhedra • any combination of element types may appear in a single geometry model • parts may not contain tetrahedra mixed with other element types • pentahedra and hexahedra can be together in the same part • robust handling of overlaps and gaps • tracks element-to-element to produce path length results at the element level • finds element numbers for a given mesh location • finds intersection points on element faces for the particle tracks • produce a data file for post processing results analysis • reads Abaqus .inp input (ASCII) files to obtain information for the global mesh-model • supports parallel input processing via mpi • support parallel particle transport by both mpi and OpenMP

  18. RAMSES: A new N-body and hydrodynamical code

    NASA Astrophysics Data System (ADS)

    Teyssier, Romain

    2010-11-01

    A new N-body and hydrodynamical code, called RAMSES, is presented. It has been designed to study structure formation in the universe with high spatial resolution. The code is based on Adaptive Mesh Refinement (AMR) technique, with a tree based data structure allowing recursive grid refinements on a cell-by-cell basis. The N-body solver is very similar to the one developed for the ART code (Kravtsov et al. 97), with minor differences in the exact implementation. The hydrodynamical solver is based on a second-order Godunov method, a modern shock-capturing scheme known to compute accurately the thermal history of the fluid component. The accuracy of the code is carefully estimated using various test cases, from pure gas dynamical tests to cosmological ones. The specific refinement strategy used in cosmological simulations is described, and potential spurious effects associated to shock waves propagation in the resulting AMR grid are discussed and found to be negligible. Results obtained in a large N-body and hydrodynamical simulation of structure formation in a low density LCDM universe are finally reported, with 256^3 particles and 4.1 10^7 cells in the AMR grid, reaching a formal resolution of 8192^3. A convergence analysis of different quantities, such as dark matter density power spectrum, gas pressure power spectrum and individual haloes temperature profiles, shows that numerical results are converging down to the actual resolution limit of the code, and are well reproduced by recent analytical predictions in the framework of the halo model.

  19. Polar Codes

    DTIC Science & Technology

    2014-12-01

    density parity check (LDPC) code, a Reed–Solomon code, and three convolutional codes. iii CONTENTS EXECUTIVE SUMMARY...the most common. Many civilian systems use low density parity check (LDPC) FEC codes, and the Navy is planning to use LDPC for some future systems...other forward error correction methods: a turbo code, a low density parity check (LDPC) code, a Reed–Solomon code, and three convolutional codes

  20. A GPU-enabled Finite Volume solver for global magnetospheric simulations on unstructured grids

    NASA Astrophysics Data System (ADS)

    Lani, Andrea; Yalim, Mehmet Sarp; Poedts, Stefaan

    2014-10-01

    This paper describes an ideal Magnetohydrodynamics (MHD) solver for global magnetospheric simulations based on a B1 +B0 splitting approach, which has been implemented within the COOLFluiD platform and adapted to run on modern heterogeneous architectures featuring General Purpose Graphical Processing Units (GPGPUs). The code is based on a state-of-the-art Finite Volume discretization for unstructured grids and either explicit or implicit time integration, suitable for both steady and time accurate problems. Innovative object-oriented design and coding techniques mixing C++ and CUDA are discussed. Performance results of the modified code on single and multiple processors are presented and compared with those provided by the original solver.

  1. Efficient entropy coding for scalable video coding

    NASA Astrophysics Data System (ADS)

    Choi, Woong Il; Yang, Jungyoup; Jeon, Byeungwoo

    2005-10-01

    The standardization for the scalable extension of H.264 has called for additional functionality based on H.264 standard to support the combined spatio-temporal and SNR scalability. For the entropy coding of H.264 scalable extension, Context-based Adaptive Binary Arithmetic Coding (CABAC) scheme is considered so far. In this paper, we present a new context modeling scheme by using inter layer correlation between the syntax elements. As a result, it improves coding efficiency of entropy coding in H.264 scalable extension. In simulation results of applying the proposed scheme to encoding the syntax element mb_type, it is shown that improvement in coding efficiency of the proposed method is up to 16% in terms of bit saving due to estimation of more adequate probability model.

  2. Cloud feedback studies with a physics grid

    SciTech Connect

    Dipankar, Anurag; Stevens, Bjorn

    2013-02-07

    During this project the investigators implemented a fully parallel version of dual-grid approach in main frame code ICON, implemented a fully conservative first-order interpolation scheme for horizontal remapping, integrated UCLA-LES micro-scale model into ICON to run parallely in selected columns, and did cloud feedback studies on aqua-planet setup to evaluate the classical parameterization on a small domain. The micro-scale model may be run in parallel with the classical parameterization, or it may be run on a "physics grid" independent of the dynamics grid.

  3. Three-dimensional elliptic grid generation for an F-16

    NASA Technical Reports Server (NTRS)

    Sorenson, Reese L.

    1988-01-01

    A case history depicting the effort to generate a computational grid for the simulation of transonic flow about an F-16 aircraft at realistic flight conditions is presented. The flow solver for which this grid is designed is a zonal one, using the Reynolds averaged Navier-Stokes equations near the surface of the aircraft, and the Euler equations in regions removed from the aircraft. A body conforming global grid, suitable for the Euler equation, is first generated using 3-D Poisson equations having inhomogeneous terms modeled after the 2-D GRAPE code. Regions of the global grid are then designated for zonal refinement as appropriate to accurately model the flow physics. Grid spacing suitable for solution of the Navier-Stokes equations is generated in the refinement zones by simple subdivision of the given coarse grid intervals. That grid generation project is described, with particular emphasis on the global coarse grid.

  4. Interactive grid generation for turbomachinery flow field simulations

    NASA Technical Reports Server (NTRS)

    Choo, Yung K.; Reno, Charles; Eiseman, Peter R.

    1988-01-01

    The control point form of algebraic grid generation presented provides the means that are needed to generate well structured grids of turbomachinery flow simulations. It uses a sparse collection of control points distributed over the flow domain. The shape and position of coordinate curves can be adjusted from these control points while the grid conforms precisely to all boundaries. An interactive program called TURBO, which uses the control point form, is being developed. Basic features of the code are discussed and sample grids are presented. A finite volume LU implicit scheme is used to simulate flow in a turbine cascade on the grid generated by the program.

  5. A perspective on unstructured grid flow solvers

    NASA Technical Reports Server (NTRS)

    Venkatakrishnan, V.

    1995-01-01

    This survey paper assesses the status of compressible Euler and Navier-Stokes solvers on unstructured grids. Different spatial and temporal discretization options for steady and unsteady flows are discussed. The integration of these components into an overall framework to solve practical problems is addressed. Issues such as grid adaptation, higher order methods, hybrid discretizations and parallel computing are briefly discussed. Finally, some outstanding issues and future research directions are presented.

  6. Clinical coding. Code breakers.

    PubMed

    Mathieson, Steve

    2005-02-24

    --The advent of payment by results has seen the role of the clinical coder pushed to the fore in England. --Examinations for a clinical coding qualification began in 1999. In 2004, approximately 200 people took the qualification. --Trusts are attracting people to the role by offering training from scratch or through modern apprenticeships.

  7. caGrid 1.0: An Enterprise Grid Infrastructure for Biomedical Research

    PubMed Central

    Oster, Scott; Langella, Stephen; Hastings, Shannon; Ervin, David; Madduri, Ravi; Phillips, Joshua; Kurc, Tahsin; Siebenlist, Frank; Covitz, Peter; Shanbhag, Krishnakant; Foster, Ian; Saltz, Joel

    2008-01-01

    Objective To develop software infrastructure that will provide support for discovery, characterization, integrated access, and management of diverse and disparate collections of information sources, analysis methods, and applications in biomedical research. Design An enterprise Grid software infrastructure, called caGrid version 1.0 (caGrid 1.0), has been developed as the core Grid architecture of the NCI-sponsored cancer Biomedical Informatics Grid (caBIG™) program. It is designed to support a wide range of use cases in basic, translational, and clinical research, including 1) discovery, 2) integrated and large-scale data analysis, and 3) coordinated study. Measurements The caGrid is built as a Grid software infrastructure and leverages Grid computing technologies and the Web Services Resource Framework standards. It provides a set of core services, toolkits for the development and deployment of new community provided services, and application programming interfaces for building client applications. Results The caGrid 1.0 was released to the caBIG community in December 2006. It is built on open source components and caGrid source code is publicly and freely available under a liberal open source license. The core software, associated tools, and documentation can be downloaded from the following URL: https://cabig.nci.nih.gov/workspaces/Architecture/caGrid. Conclusions While caGrid 1.0 is designed to address use cases in cancer research, the requirements associated with discovery, analysis and integration of large scale data, and coordinated studies are common in other biomedical fields. In this respect, caGrid 1.0 is the realization of a framework that can benefit the entire biomedical community. PMID:18096909

  8. Parallel grid population

    DOEpatents

    Wald, Ingo; Ize, Santiago

    2015-07-28

    Parallel population of a grid with a plurality of objects using a plurality of processors. One example embodiment is a method for parallel population of a grid with a plurality of objects using a plurality of processors. The method includes a first act of dividing a grid into n distinct grid portions, where n is the number of processors available for populating the grid. The method also includes acts of dividing a plurality of objects into n distinct sets of objects, assigning a distinct set of objects to each processor such that each processor determines by which distinct grid portion(s) each object in its distinct set of objects is at least partially bounded, and assigning a distinct grid portion to each processor such that each processor populates its distinct grid portion with any objects that were previously determined to be at least partially bounded by its distinct grid portion.

  9. Optimal moving grids for time-dependent partial differential equations

    NASA Technical Reports Server (NTRS)

    Wathen, A. J.

    1992-01-01

    Various adaptive moving grid techniques for the numerical solution of time-dependent partial differential equations were proposed. The precise criterion for grid motion varies, but most techniques will attempt to give grids on which the solution of the partial differential equation can be well represented. Moving grids are investigated on which the solutions of the linear heat conduction and viscous Burgers' equation in one space dimension are optimally approximated. Precisely, the results of numerical calculations of optimal moving grids for piecewise linear finite element approximation of PDE solutions in the least-squares norm are reported.

  10. Optimal moving grids for time-dependent partial differential equations

    NASA Technical Reports Server (NTRS)

    Wathen, A. J.

    1989-01-01

    Various adaptive moving grid techniques for the numerical solution of time-dependent partial differential equations were proposed. The precise criterion for grid motion varies, but most techniques will attempt to give grids on which the solution of the partial differential equation can be well represented. Moving grids are investigated on which the solutions of the linear heat conduction and viscous Burgers' equation in one space dimension are optimally approximated. Precisely, the results of numerical calculations of optimal moving grids for piecewise linear finite element approximation of partial differential equation solutions in the least squares norm.

  11. TRIM: A finite-volume MHD algorithm for an unstructured adaptive mesh

    SciTech Connect

    Schnack, D.D.; Lottati, I.; Mikic, Z.

    1995-07-01

    The authors describe TRIM, a MHD code which uses finite volume discretization of the MHD equations on an unstructured adaptive grid of triangles in the poloidal plane. They apply it to problems related to modeling tokamak toroidal plasmas. The toroidal direction is treated by a pseudospectral method. Care was taken to center variables appropriately on the mesh and to construct a self adjoint diffusion operator for cell centered variables.

  12. Parallel Adaptive Mesh Refinement for High-Order Finite-Volume Schemes in Computational Fluid Dynamics

    NASA Astrophysics Data System (ADS)

    Schwing, Alan Michael

    For computational fluid dynamics, the governing equations are solved on a discretized domain of nodes, faces, and cells. The quality of the grid or mesh can be a driving source for error in the results. While refinement studies can help guide the creation of a mesh, grid quality is largely determined by user expertise and understanding of the flow physics. Adaptive mesh refinement is a technique for enriching the mesh during a simulation based on metrics for error, impact on important parameters, or location of important flow features. This can offload from the user some of the difficult and ambiguous decisions necessary when discretizing the domain. This work explores the implementation of adaptive mesh refinement in an implicit, unstructured, finite-volume solver. Consideration is made for applying modern computational techniques in the presence of hanging nodes and refined cells. The approach is developed to be independent of the flow solver in order to provide a path for augmenting existing codes. It is designed to be applicable for unsteady simulations and refinement and coarsening of the grid does not impact the conservatism of the underlying numerics. The effect on high-order numerical fluxes of fourth- and sixth-order are explored. Provided the criteria for refinement is appropriately selected, solutions obtained using adapted meshes have no additional error when compared to results obtained on traditional, unadapted meshes. In order to leverage large-scale computational resources common today, the methods are parallelized using MPI. Parallel performance is considered for several test problems in order to assess scalability of both adapted and unadapted grids. Dynamic repartitioning of the mesh during refinement is crucial for load balancing an evolving grid. Development of the methods outlined here depend on a dual-memory approach that is described in detail. Validation of the solver developed here against a number of motivating problems shows favorable

  13. Scientific Grid computing.

    PubMed

    Coveney, Peter V

    2005-08-15

    We introduce a definition of Grid computing which is adhered to throughout this Theme Issue. We compare the evolution of the World Wide Web with current aspirations for Grid computing and indicate areas that need further research and development before a generally usable Grid infrastructure becomes available. We discuss work that has been done in order to make scientific Grid computing a viable proposition, including the building of Grids, middleware developments, computational steering and visualization. We review science that has been enabled by contemporary computational Grids, and associated progress made through the widening availability of high performance computing.

  14. UUGM Code Development

    DTIC Science & Technology

    1993-07-26

    flow (very low speed and subsonic flows, transonic flow, supersonic and hypersonic flows), 2) advances in unstructured adaptive gridding techniques ...realistically simulated by CFD techniques . SAIC has been involved in all aspects of these developments and is on the forefront of CFD technology...differential equations of gasdynamnics. Presently, as a result of steady improvement ii the various integration techniques , the advantages which could be gained

  15. A Flow Solver for Three-Dimensional DRAGON Grids

    NASA Technical Reports Server (NTRS)

    Liou, Meng-Sing; Zheng, Yao

    2002-01-01

    DRAGONFLOW code has been developed to solve three-dimensional Navier-Stokes equations over a complex geometry whose flow domain is discretized with the DRAGON grid-a combination of Chimera grid and a collection of unstructured grids. In the DRAGONFLOW suite, both OVERFLOW and USM3D are presented in form of module libraries, and a master module controls the invoking of these individual modules. This report includes essential aspects, programming structures, benchmark tests and numerical simulations.

  16. Unstructured grids on SIMD torus machines

    NASA Technical Reports Server (NTRS)

    Bjorstad, Petter E.; Schreiber, Robert

    1994-01-01

    Unstructured grids lead to unstructured communication on distributed memory parallel computers, a problem that has been considered difficult. Here, we consider adaptive, offline communication routing for a SIMD processor grid. Our approach is empirical. We use large data sets drawn from supercomputing applications instead of an analytic model of communication load. The chief contribution of this paper is an experimental demonstration of the effectiveness of certain routing heuristics. Our routing algorithm is adaptive, nonminimal, and is generally designed to exploit locality. We have a parallel implementation of the router, and we report on its performance.

  17. Adaptive mesh refinement in titanium

    SciTech Connect

    Colella, Phillip; Wen, Tong

    2005-01-21

    In this paper, we evaluate Titanium's usability as a high-level parallel programming language through a case study, where we implement a subset of Chombo's functionality in Titanium. Chombo is a software package applying the Adaptive Mesh Refinement methodology to numerical Partial Differential Equations at the production level. In Chombo, the library approach is used to parallel programming (C++ and Fortran, with MPI), whereas Titanium is a Java dialect designed for high-performance scientific computing. The performance of our implementation is studied and compared with that of Chombo in solving Poisson's equation based on two grid configurations from a real application. Also provided are the counts of lines of code from both sides.

  18. Adaptive Mesh Refinement for ICF Calculations

    NASA Astrophysics Data System (ADS)

    Fyfe, David

    2005-10-01

    This paper describes our use of the package PARAMESH to create an Adaptive Mesh Refinement (AMR) version of NRL's FASTRAD3D code. PARAMESH was designed to create an MPI-based AMR code from a block structured serial code such as FASTRAD3D. FASTRAD3D is a compressible hydrodynamics code containing the physical effects relevant for the simulation of high-temperature plasmas including inertial confinement fusion (ICF) Rayleigh-Taylor unstable direct drive laser targets. These effects include inverse bremmstrahlung laser energy absorption, classical flux-limited Spitzer thermal conduction, real (table look-up) equation-of-state with either separate or identical electron and ion temperatures, multi-group variable Eddington radiation transport, and multi-group alpha particle transport and thermonuclear burn. Numerically, this physics requires an elliptic solver and a ray tracing approach on the AMR grid, which is the main subject of this paper. A sample ICF calculation will be presented. MacNeice et al., ``PARAMESH: A parallel adaptive mesh refinement community tool,'' Computer Physics Communications, 126 (2000), pp. 330-354.

  19. Mapping PetaSHA Applications to TeraGrid Architectures

    NASA Astrophysics Data System (ADS)

    Cui, Y.; Moore, R.; Olsen, K.; Zhu, J.; Dalguer, L. A.; Day, S.; Cruz-Atienza, V.; Maechling, P.; Jordan, T.

    2007-12-01

    The Southern California Earthquake Center (SCEC) has a science program in developing an integrated cyberfacility - PetaSHA - for executing physics-based seismic hazard analysis (SHA) computations. The NSF has awarded PetaSHA 15 million allocation service units this year on the fastest supercomputers available within the NSF TeraGrid. However, one size does not fit all, a range of systems are needed to support this effort at different stages of the simulations. Enabling PetaSHA simulations on those TeraGrid architectures to solve both dynamic rupture and seismic wave propagation have been a challenge from both hardware and software levels. This is an adaptation procedure to meet specific requirements of each architecture. It is important to determine how fundamental system attributes affect application performance. We present an adaptive approach in our PetaSHA application that enables the simultaneous optimization of both computation and communication at run-time using flexible settings. These techniques optimize initialization, source/media partition and MPI-IO output in different ways to achieve optimal performance on the target machines. The resulting code is a factor of four faster than the orignial version. New MPI-I/O capabilities have been added for the accurate Staggered-Grid Split-Node (SGSN) method for dynamic rupture propagation in the velocity-stress staggered-grid finite difference scheme (Dalguer and Day, JGR, 2007), We use execution workflow across TeraGrid sites for managing the resulting data volumes. Our lessons learned indicate that minimizing time to solution is most critical, in particular when scheduling large scale simulations across supercomputer sites. The TeraShake platform has been ported to multiple architectures including TACC Dell lonestar and Abe, Cray XT3 Bigben and Blue Gene/L. Parallel efficiency of 96% with the PetaSHA application Olsen-AWM has been demonstrated on 40,960 Blue Gene/L processors at IBM TJ Watson Center. Notable

  20. High-order central ENO finite-volume scheme for hyperbolic conservation laws on three-dimensional cubed-sphere grids

    NASA Astrophysics Data System (ADS)

    Ivan, L.; De Sterck, H.; Susanto, A.; Groth, C. P. T.

    2015-02-01

    A fourth-order accurate finite-volume scheme for hyperbolic conservation laws on three-dimensional (3D) cubed-sphere grids is described. The approach is based on a central essentially non-oscillatory (CENO) finite-volume method that was recently introduced for two-dimensional compressible flows and is extended to 3D geometries with structured hexahedral grids. Cubed-sphere grids feature hexahedral cells with nonplanar cell surfaces, which are handled with high-order accuracy using trilinear geometry representations in the proposed approach. Varying stencil sizes and slope discontinuities in grid lines occur at the boundaries and corners of the six sectors of the cubed-sphere grid where the grid topology is unstructured, and these difficulties are handled naturally with high-order accuracy by the multidimensional least-squares based 3D CENO reconstruction with overdetermined stencils. A rotation-based mechanism is introduced to automatically select appropriate smaller stencils at degenerate block boundaries, where fewer ghost cells are available and the grid topology changes, requiring stencils to be modified. Combining these building blocks results in a finite-volume discretization for conservation laws on 3D cubed-sphere grids that is uniformly high-order accurate in all three grid directions. While solution-adaptivity is natural in the multi-block setting of our code, high-order accurate adaptive refinement on cubed-sphere grids is not pursued in this paper. The 3D CENO scheme is an accurate and robust solution method for hyperbolic conservation laws on general hexahedral grids that is attractive because it is inherently multidimensional by employing a K-exact overdetermined reconstruction scheme, and it avoids the complexity of considering multiple non-central stencil configurations that characterizes traditional ENO schemes. Extensive numerical tests demonstrate fourth-order convergence for stationary and time-dependent Euler and magnetohydrodynamic flows on