A Case Study in the Visualization of Supernova Simulation Data

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A Case Study in the Visualization of Supernova
Simulation Data

• Ed Bachta
• Visualization and Interactive Spaces Lab

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Overview

• Introduction
• Lagrangian-Eulerian Advection
• Software Design
• Results
• Future Work

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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 1057 /s
• Strong force halts collapse
• Remaining material rebounds off the core
• Shock wave carries material away from the core

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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

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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 plot
LEA
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Lagrangian-Eulerian Advection for Unsteady Flow
Visualizaion
v
Noise at t-1
Lagrangian step
Eulerian step

• 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
  83)

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LEA Animated

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

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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

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Results

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

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LEA Scalars
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Velocity Entropy

• Shows the development of regions of high entropy
  in upper convective zones

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LEA Iso-Contours
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LEA Optical Depth

• The iso-contour where optical depth 1 describes
  the surface of last scattering

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8
2
3

• Generated for each energy group
• Our results show that these contours vary with
  energy group and evolve along with the shock

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LEA Dot Products
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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

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Comparison Over Energy
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Comparison of Gradients

• Lagrangian multipliers
• ?rf (r) ? ?rg(r)
• Describes a set of points where the iso-contours
  of f(r) and g(r) are tangential
• A positive ? indicates parallel gradients
• A negative ? indicates anti-parallel gradients
• Very similar to our dot product analysis
• The dot product reveals orthogonal conditions

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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

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Future Work

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