Physically based animation

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Physically based animation. General idea take physical models, make assumptions, solve render solution Influential areas we’ve seen particles, collision+ballistic Others fluids (includes gasses). Example: Suspended particle explosion. - PowerPoint PPT Presentation

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  • Physically based animationGeneral ideatake physical models, make assumptions, solverender solutionInfluential areasweve seen particles, collision+ballisticOthersfluids (includes gasses)

  • Example: Suspended particle explosionThere is hot gas, moving under forces generated byburningmomentumchanges in pressureviscosityetc.In the gas, there are particles that moveheat and coolRender by rendering the particlesFeldman, OBrien, Arikan, 03

  • Incompressible, inviscid moving fluidsImportantcompressible, viscous fluids are hard to modelcompressible flow doesnt happen at low mach numberscompression is important in explosions, but very hard to modeland most undesirable in hollywood style explosionsdry water

  • Dry waterEuler equations

    Mass is conservedChange of momentum is due tochange of pressureexternal forces

  • Solving dry waterSet up a gridvalues of u, P at grid vertices

    Get intermediate velocity fieldby taking a small time step, ignoring pressure effectswe will choose a pressure field to correct this to be an incompressible flow

    Correct the intermediate velocity field

  • Modified dry waterFor an explosion, we must have some fluid expansionat points of detonationwe do not want to allow the fluid to expand everywhere, or couple this to the fluids dynamicspressure waves

    So the pressure update step changes

  • Particles in the fluidMove


  • Particle fluid interactionsDrag on particleforce in opposite direction applied to fluidlow mass - no drag

    Thermal exchangeheat transfer to a particle from fluidtransfer goes both waysT - fluid temperature field

  • Particle behaviourParticles burnSimplified combustioncombustion is independent of oxygenindependent of temperatureproducts do not depend on temperatureModelParticle ignites when its temperature exceeds a fixed thresholdfixed amount of fueldies when its mass is zeroProductsHeatGas

  • Products of combustionHeat


    Sootthis builds up to a threshold - then a soot particle is released.

  • Advection

  • Further phenomenaSmokesimulate the fluid flowsmoke is distributed (rather than particles)Temperature and density are constant at an elementi.e. are advectedBuoyancyheavy smoke sinks, hot gas risesFedkiw, Stam, Jensen 01

  • Vortices and vorticity confinementSmoke tends to produce vorticeshard to get fine vortices with a coarse gridvortices tend to die out too fast with simple integratorsthis is called dampingstrategyestimate where vortices are being suppressedinsert a paddle wheel force

  • Rendering SmokePhenomenain/out scatteringextinctionStrategyphoton mapmarch along rays

  • Examinable materialRenderingray tracing in all its formssampling and aliasingshading modelsincluding general radiometrydiffuse interreflections and finite element methodsrandom integrationfor area light sourcesfor final gatheringfor path tracingphoton mapstexture synthesisprocedural shadingprocedural texturing

  • Examinable material

    Curves and surfacesBezier, de CasteljauB-splines, de Boortensor productssubdivisionAnimationparticle systems and Forward Eulerballistic motion and collisionsideas, rather than exact formulation of dynamicscollisionHuman motionmotion graphsincompressible fluids (without viscosity)


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