Controlling Fluid Simulations with Custom Fields in Houdini Master ...

Figure 15: Two spheres emitting density and color with a vortex force applied.5. Diuse the color eld using a Gas Diuse microsolver, the diusion rateshould match the density diusion rate. For fast mixing of the color, thisvalue can be increased.In Figure (15) two spheres can be seen emitting density and color informationinto a simulation. This simulation has the color elds dened as copies of thedensity values for either the red or the blue component of the Cd vector eldand does not actually require the transfer tool in SOPS. In Figure (16) you cansee a helix curve emitting density, colour and the temperature eld is driven bythe red values of the colour which causes the red smoke to rise quicker. The hueof the colour is mapped to the parametric u value of the curve.5.3.2 Advect by curveIn this example the tangent vectors of a curve are used as an extra force thatis continuously added to the velocity eld. A relatively large amount of force isapplied. Also the density eld is temporarely blurred, the gradient is taken fromthis blurred density, then normalized and applied as an additional force. Thecombined force points towards the density of the curve and along the tangentof the curve. A sphere is placed at the bottom of the helix and is emittingdensity into the simulation. The density and tangent velocity elds can be seenin Figure (17).The node tree can be seen in Figure (18) and consists of the main followingareas:26