Transcript Kein Folientitel

Automotive Soiling Simulation
Based On Massive Particle Tracing
Stefan Röttger
Martin Schulz
Wolf Bartelheimer
Thomas Ertl
Visualization and Interactive Systems Group
University of Stuttgart
Introduction
• Where did we start?
• Lattice-Boltzmann
CFD solver
(PowerFlow) used
at BMW
• Hierarchical
cartesian grids
• Fast tri-linear
interpolation
Visualization and Interactive Systems Group, University of Stuttgart
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Standard Flow Visualization Tools
• Interactive and
immersive navigation
in virtual windtunnel
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Stream lines
Stream ribbons
Glyphs
Cutting planes
Visualization and Interactive Systems Group, University of Stuttgart
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Goals
• What did we want?
• Massive particles for simulation of dust particles
• Interactively animated particles for more
intuitive flow visualization
• Automotive soiling simulation
Visualization and Interactive Systems Group, University of Stuttgart
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Massive Particles
• Each particle is treated as ideal sphere with specific
mass, diameter and initial position and velocity
• Particle drag, gravity and electrostatic forces affect
acceleration of particles
• Stokes approximation of the drag is not good enough
• Particle drag in the flow is approximated by the formula
of O´Seen for low Reynolds numbers
Visualization and Interactive Systems Group, University of Stuttgart
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Massive Particle Tracing
• Second order differential equations: a(t)=>v(t)=>x(t)
• Adaptive, embedded Runge-Kutta tracer of order 4(3)
• Below 3 µm the differential equations are becoming
stiff, but then massive and massless particle tracing is
almost equivalent => no soiling
• Average dust particle diameter in real world evalutions
is 5 to 500 µm
Visualization and Interactive Systems Group, University of Stuttgart
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Animated Massive Particles
• Define emitters that generate particles at a certain
frequency
• Emitters can be sized and positioned interactively
• Initial parameters of particles are assigned
stochastically
• Particle stream is traced and displayed step by step
• The stream is displayed in slow motion at a given target
frame rate
• Camera exposure model => particles leave short traces
Visualization and Interactive Systems Group, University of Stuttgart
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Animated Massive Particles
• Intuitive visualization
analogue to smoke
probes
• Simultaneous display of
multiple particles
• Particle velocity is
visible implicitly
• Better three-dimensional
impression due to
animation
• Life time is color coded
Visualization and Interactive Systems Group, University of Stuttgart
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Automotive Soiling Simulation
• Stochastically generate and
trace massive particles
• Check for collision with the
70,000 surface triangles by
utilizing an octree
• Color the hit points on the
car body (nearest mesh
vertex)
• Color code the number of
hits on the surface (blue =
no hits)
Visualization and Interactive Systems Group, University of Stuttgart
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Simulation Performance
• Hit probability is low
• Large number of particles
• Simulation can be
parallelized efficiently
(e.g. 64 CPU SGI Onyx)
• On an SGI Octane with
2x250MHz MIPS R10K
approximately 1000
particles can be traced
simultaneously at 7 Hz
• Scales well with #CPUs
1 hour
3 hours
Visualization and Interactive Systems Group, University of Stuttgart
Page 10
Simulation Quality
• Now using stationary flow
fields (120M per time step)
• Turbulences are smoothed
away in time averaged
flow fields and hit
probability is reduced even
further
• => Instationary flow fields
• Electrostatic forces
influence dust aggregation
as well
Stokes
O´Seen
Visualization and Interactive Systems Group, University of Stuttgart
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Conclusion
• Animated massive particle streams for intuitive data set
exploration
• Massive particle tracing used to compute automotive
soiling simulation by employing collision detection
• Good coincidence with real world soiling situation
• More accurate simulations require instationary flow
fields and research about near surface effects
• Massive particle tracing can be applied to other regions
of interest like smog or droplet distribution simulations
Visualization and Interactive Systems Group, University of Stuttgart
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Discussion
Questions?
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