A Case Study in the Visualization of Supernova Simulation Data Ed Bachta Visualization and Interactive Spaces Lab

Overview Introduction Lagrangian-Eulerian Advection Software Design Results Future Work

A Core-collapse Supernova Begins with a star of 8+ solar masses Eventually, fusion produces Fe in the core Pressure from fusion loses to gravitation Material falls inward, increasing density Neutrinos radiated at a rate of /s Strong force halts collapse Remaining material rebounds off the core Shock wave carries material away from the core

Simulation Doug Swesty & Eric Myra, SUNY Stony Brook Exploring the role of convection Radiation hydro code scales to 1000s of procs 2 spatial dimensions (soon to be extended to 3) 20 groups of neutrinos at different energies

Lagrangian-Eulerian Advection A process for visualizing vector fields, valid for unsteady flows Noise is advected along the flow, generating an image as output Results  Single frames portray instantaneous flow  Animations simulate motion of material in flow Vector plotLEA

“Lagrangian-Eulerian Advection for Unsteady Flow Visualizaion” Particles seeded randomly each iteration Backward integration finds upstream cell Color of upstream cell advected forward Results blended temporally with bias toward most recent Jobard, Erlebacher, Hussaini (IEEE Vis & CG 2002 [8:3]) Noise at t-1 v Lagrangian step Eulerian step

LEA Animated Applied to velocity Propagation of light and dark areas indicates direction of flow Areas where noise remains have near-zero velocities

Software Vis modules provided by the Visualization Tool Kit (VTK) LEA filter for VTK developed at the Swiss National Supercomputing Centre Scripts programmed in Python

Results Combination of LEA with:  Scalar data representations Via colormaps Via iso-contours  Vector data comparisons Via visualization of dot products

LEA & Scalars

Velocity & Entropy Shows the development of regions of high entropy in upper convective zones

LEA & Iso-Contours

LEA & Optical Depth The iso-contour where optical depth = 1 describes the surface of last scattering Generated for each energy group Our results show that these contours vary with energy group and evolve along with the shock

LEA & Dot Products

Advective vs. Radiative NeutrinoFlux Radiative neutrino flux  Tendency to propagate outward Advective neutrino flux  Effect of convection Dot product indicates:  “Constructive” flux  “Destructive” flux  Orthogonal flux

Comparison Over Energy

Comparison of Gradients Lagrangian multipliers:  ∂ r f (r) = λ ∂ r g(r)  Describes a set of points where the iso-contours of f(r) and g(r) are tangential  A positive λ indicates parallel gradients  A negative λ indicates anti-parallel gradients  Very similar to our dot product analysis The dot product reveals orthogonal conditions

Entropy & Temp. Using our visualization scheme, we can see:  Where the gradients are ||  Where they are anti-||  Where they are orthogonal  How this relates to the flow of a vector field

Future Work Extending the framework to support iteration Developing new visualization techniques Enabling remote visualization  Intended for batch processing  Investigating Web Services