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Numerical simulations of astrophysical plasmas : a software point of view E. Audit, D. Pomar è de, R. Teyssier, B. Thooris CEA/DAPNIA – Saclay France. Outline. CEA/DAPNIA Saclay presentation The SNOOPY project : physics and algorithms Cosmological structures formation : code RAMSES

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  1. Numerical simulations of astrophysical plasmas :a software point of viewE. Audit, D. Pomarède, R. Teyssier, B. ThoorisCEA/DAPNIA – SaclayFrance

  2. Outline • CEA/DAPNIA Saclay presentation • The SNOOPY project : physics and algorithms • Cosmological structures formation : code RAMSES • Dynamics of the interstellar medium : code HERACLES • The SNOOPY project : software • Data handling • Visualization • Perspectives

  3. CEA • CEA stands for Commissariat à l’Energie Atomique French government-funded reseach institute • Working in 4 domains : • Energy • Health and information technologies • Defense • Fundamental Reseach • Teams mixing engineers and researchers 14000 employees, 1400 PhD students

  4. A presentation of DAPNIA • DAPNIA : Laboratory of research into the fundamental laws of the Universe, based at Saclay (near Paris) • Part of CEA Fundamental Research Division (DSM) • a CEA institute devoted to High Energy Physics, Nuclear Physics and Astrophysics. (800 physicists and engineers) • Strongly involved • in HEP International Experiments (CERN, Fermilab, SLAC,…) • in Astrophysics International Experiments • Ground-based telescopes (Spain,Hawaii,Chile) • Satellite telescopes (ISO,XMM,HUBBLE,JWST)

  5. The simulation project : astrophysics domains • Extensive program of simulations of astrophysical plasmas • Studies at various scales • Each domain treated by an independent numerical code COSMOLOGICAL STRUCTURES FORMATION RAMSES STELLAR EVOLUTION ASH DYNAMICS OF THE ISM HERACLES FORMATION OF PROTO-PLANETARY DISKS FARGO

  6. Cosmological structures : the RAMSES code (1) • Studies the interplay of dark matter component and baryon gas in cosmological structures • A hybrid simulation code • N-body treatment to solve the Dark Matter (DM) dynamics • Hydrodynamical treatment for the baryonic component • DM and Baryon Gas are playing different roles depending on scales studied • DM is believed to be the dominant component in mass of the cosmological density field, with only a small fraction in baryons • At intermediate scales such as galaxy clusters DM stills dominates but a gaseous component is introduced • At galaxy-size scales, gas-cooling and fluid dynamics play a dominant role in the structure

  7. The RAMSES code (2) • A 3-D AMR (adaptive mesh refinement) code in finite volumes (a necessity for solving the problem at different scales) • Algorithms • For DM particles the collisionless N-body system is described by the Vlasov-Poisson equations • Hydrodynamical solver based on a 2nd-order Godunov method • Simulations typically reach 14 levels of AMR refinement (with 4.1107 cells a formal resolution of 81923 )

  8. The RAMSES AMR level 2 level 3 level 5 level 9 level 11 level 14 AMR structure : In dense areas, cells are split in 2 at each level

  9. Visualization of RAMSES AMR data

  10. Interstellar Medium : the HERACLES code (1) • Studies the turbulences of interstellar molecular clouds A 3-D code in cartesian, cylindrical or spherical coordinates in finite volumes on a regular grid • Solves the equations of radiative transfer coupled to hydrodynamics : • fluid evolution is determined by the classical conservation equations (mass, momentum, energy) • + source terms characterizing the momentum and energy exchanges between the fluid and the radiation • The transfer equations are solved by a second order Godunov type method and integrated implicitly using iterative solvers

  11. The HERACLES code (2) • Current studies focus on the thermal fragmentation of turbulent flows of interstellar hydrogen • molecular clouds form through the condensation of a warm neutral phase (WNM) into a cold medium (CNM) • We are studying 4 different spatial scales • cooling length of the WNM typically ~ 10-20 pc • typical size of CNM fragments ~ 0.1 pc • conduction length in the 10-1-10-3 pc range • size of the shocked layer ~ 10-3 pc  this dynamic requires implementation of multiple grid algorithm

  12. Heracles simulation of turbulences (1) Turbulences in the interstellar medium on a 1200X1200X1200 grid with dimension 15 pc. Plasma density on a slice. Cold dense phase and diluted hot phase tightly interlinked

  13. Heracles simulation of turbulences (2) Turbulences in the interstellar medium Volume projection of the density The brightest spots are dense protostellar cores formed by the thermal instabilities

  14. Numerical simulations software project (1) • A core of software modules useable for all simulations. • Includes data handling, post-treatment, visualization, parallelization optimization,… RAMSES CORE SOFTWARE MODULES I/O, Graphics, Algorithms ASH HERACLES FARGO

  15. Numerical simulations software project (2) • Numerical codes written in FORTRAN 90/95 • Running under Unix or Linux • Parallelized with MPI library • Using supercomputers up to 2048 processors in parallel (CEA CC, Mare Nostrum Barcelona) • HDF5 as unique data files format • Visualization tools written in IDL framework using object-oriented programming

  16. Data Handling • A unique format : HDF5, the Hierarchical Data Format developed by the NCSA (National Center for Supercomputing Applications) • HDF5 is a general purpose library and file format for storing scientific data on parallel computing systems • Two primary objects are handled : • Datasets = multidimensional array of data elements • Groups = structures • Free, open source software, including utilities (browser)

  17. Browser of HDF5 files

  18. Visualization • Visualization plays important role in validation, analysis and interpretation of results • A graphical Widget performed in the framework of IDL • Using the object-oriented programming offered by IDL’s Object Graphics • Input data : scalar and vector fields on regular grids and on AMR tree structures, and particles clouds

  19. The graphical widget • Select : • density • pressure • velocity • radiative energy • radiative flux • particles • custom variable navigation surface object menus sliders buttons droplist dialog fields axis object profile plot object image object

  20. Visualization of regular grids and AMR data Max grid : regular 3D 1200x1200x1200 = 1.728 109 cells regular 2D 10000x10000 AMR up to level 10 projected in grid 1024x1024x1024 image of 2D 10000x10000 HERACLES simulation surface of a density slice on a restricted region of the RAMSES AMR (level 7 to level 11)

  21. Visualization of iso-surfaces Simulation of ISM hydrogen turbulences density field - volume of size 15 pc grid 12003 Interactive setting of the contour value on the density histogram

  22. Visualization of 3D vector fields Hedgehog display of hydrodynamical velocity field Blue semi-transparent volume = iso-surface of the density RAMSES cosmological simulation box of size 100 h-1 Mpc HERACLES simulation of ISM turbulences

  23. Visualization of particles particle cloud display of a dark matter sample yellow semi-transparent volume = iso-surface of the hydrodynami-cal density field DM haloes

  24. Visualization of AMR data : composite scenes

  25. Immersive capabilities of the SDvision widget (1) The viewing point is located within the simulation volume and the scene is observed with a wide-angle focal. This simulation of cosmological structures formation for a volume of size 100 Mpc is obtained with RAMSES with a resolution up to the level 8 of the AMR, equivalent to a 256256256 regular Cartesian grid. From this internal viewpoint, the scene is augmented with various graphical objects allowing to better interpret, analyze and validate the simulation.

  26. Immersive capabilities of the SDvision widget (2) In a) are displayed the high-density Dark Matter cores embedded in an a gray isosurface of the baryon density. A red and a yellow lower-density isosurfaces are also added.

  27. Immersive capabilities of the SDvision widget (3) In b) the image is kept and the view is augmented with a display of a maximum-intensity projection of the baryon density. Filamentary structures are observed, well-correlated to the grey isosurface topology in a). The effect of the AMR algorithm can be inferred from the varying granularity of the graphical objects.

  28. Immersive capabilities of the SDvision widget (4) The red Dark Matter high-density cores displayed in c) are correlated with the most dense baryonic regions, where galaxy clusters are in development.

  29. Immersive capabilities of the SDvision widget (5) In d) the baryonic hydrodynamical velocity field is added; the streamlines are seen plunging toward the DM cores..

  30. Immersive capabilities of the SDvision widget (6) In e) the transparent image gives another profile of the baryonic density which exhibits filaments and halos. This immersive investigation of the structures gives strong indication of the validity of the simulation.

  31. Conclusion and outlooks • An extensive program of simulations of astrophysical plasmas is pursued • Developments in codes and tools , for example : • HERACLES : implementation of multiple grid • RAMSES : algorithm optimization to improve load balancing • MHD treatment in both codes • Visualization : parallelization to improve speed (use fastDL/mpiDL) • Open to use our Visualization Tools to other domains : • Meteorology: Climate Modeling • Interface with hydrodynamics finite volumes codes • Open for collaboration in other subjects

  32. Some references • [1] The SNOOPY Project Web Site : http://www-dapnia.cea.fr/Projets/SNOOPY/ • [2] “Cosmological Hydrodynamics with Adaptive Mesh Refinement – A New High Resolution Code Called RAMSES”, R. Teyssier, Astronomy and Astrophysics, 385, 2002, 337-364 • [3] “HERACLES : a new, parallelized, multi geometry and tridimensional RHD code”, M. González, E. Audit, P. Huynh, to be submitted to Astronomy and Astrophysics (2006).

  33. Special thanks to : • Mma Ramotswe for making me discover Botswana

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