Visualization of ASH Simulationsof Stellar MHD with SDvisioni r f uD. Pomarède, A.S. Brun
Institut de Recherche sur les Lois Fondamentales de l’Univers
CEA/Irfu, Saclay, 91191 Gif-sur-Yvette, Francepomarede@cea.frs a c la yWith the growing power of high performance computing centers, simulation is playing a leading role in the study of astrophysical objects. The ASH Anelastic Spherical
Harmonics program is used to perform high-resolution three-dimensional simulations on massively parallel mainframes with up to several thousands processors, with aspecial emphasis on the MHD processes occurring in the convection zone of the Sun and other stars. The size and complexity of the data produced in these simulations
require to use special software tools at the post-treatment, visualization and analysis stages. The need for interactive and immersive visualization of such data has
motivated the development of the SDvision graphical interface. This tool is deployed in the framework of IDL Object Graphics and offers several ways to visualize thescalar and vector fields produced in the simulations. Scalar fields are visualized through either a ray-casting volume rendering, an isosurface reconstruction, a texture
mapping algorithm, or through volume slicing. In the volume rendering implementation, the RGB colors and transparencies lookup tables can be tuned interactively toenhance the visualization of the turbulent structures that characterize these data. Vector fields are visualized by hedgehog displays or by streamlines that can beseeded interactively. The SDvision tool provides a visualization of the scene though either an OpenGL, hardware-based rendering or through a pure software
computation.

The SDvision graphical interface used here to visualize the azimutal component of the magnetic field in the solar convection zone. The rendering is obtained with the ray
casting technique with alpha-blending compositing. The color and opacity lookup tables are fine-tuned and displayed against the data distribution on the right-hand side
widget.

Rendering of isosurfaces(marching-cube algorithm)

Rendering of volume
with a stack of 2D textures

Visualization of the velocity field withcolor-coded streamlines seeded on a grid

Volume clipping in the ray-casting rendering

Wide-angle, immersive view, of a 500x500x500 simulationof the magnetic field in the solar convection zone

Visualization of a streamtube seeded interactively in the scene.
The image is a slice of the magnetic energy field

Development of a magnetic field loop
visualized by the ray-casting technique

References
ASH simulations : Global-Scale Turbulent Convection and Magnetic Dynamo Action in the Solar Envelope, A.S. Brun, M.S. Miesch, J. Toomre, Ap.J. 614 (2004) 1073
Three-Dimensional Nonlinear Evolution of a Magnetic Flux Tube in a Spherical Shell: Influence of Turbulent Convection and Associated Mean Flows, L. Jouve, A.S. Brun, Ap.J. 701 (2009) 1300

SDvision : Interactive Visualization of Astrophysical Plasma Simulations with SDvision, D. Pomarède, et al., ASP Conf Series, 385 (2008) 327

Acknowledgements
The developments of ASH and SDvision are part of the COAST Project, a CEA/Irfu program of high performances computing in astrophysics, see http://irfu.cea.fr/Projets/COAST
Simulations used in this work are part of the STARS2 « Simulations of Turbulent, Active and Rotating Suns and Stars » Project, see http://www.stars2.eu
The STARS2 Project is founded by the European Research Council : http://erc.europa.eu