Graphics Reference
In-Depth Information
Time, Size, and Resolution
In running the previous examples, you probably noticed that this default simulation setup is moving in slow
motion. This is because the fluid simulator's default time span does not coincide with the 10-second default an-
imationlengthinBlender.Thefluidsimulatorcalculatestimeandspaceindependentlyfromwhatisgoingonin
other parts of Blender, enabling you to set the parameters for the fluid simulation directly in real-world terms.
Starting and Ending
The time span for the fluid simulation is set in the Fluid panel of the Domain object. It is set in seconds. By
default, the Start time of the fluid simulation is set to 0 and the End time is set to 4, meaning that the simulation
covers a time span of 4 seconds. As I mentioned, this is totally independent of the actual animation length. The
animation's length of time is the number of frames divided by the frame rate. By default, the number of frames
is set to 250 and the frame rate is set to 25 frames per second, so the default length of a Blender animation is
10 seconds. If the fluid time span is shorter than the animation time span, the fluid simulation will “stretch”
to fit the animation time, and so the fluid movement will be in slow motion when the animation is viewed at
regularspeed.IfthetimespansetintheFluidSimulationpanelislongerinsecondsthantheactuallengthofthe
rendered animation, the motion will be sped up to fit into the time span of the animation. For realistic speeds,
the time span of the animation in seconds should be equal to the number of frames divided by the frame rate of
the animation.
Real-World Size
Thereal-worldsizeofthesimulationdomainissetindependentlywithinthesimulationitselfandrelatestohow
fast the fluid appears to move. The size is set in the Real World Size field on the Domain panel in the Fluid
Simulation panel of the Domain object. The size is measured in meters, so the default size of 0.500 means that
the fluid simulation is calculated within a half-meter cube. If the shape of the Domain object is oblong, the size
value represents the longest edge of the Domain object's bounding box.
How you set the size value depends on the size of the area within your scene that needs to have fluid sim-
ulation enabled. Take into consideration the relative size of the props you are using and also the area in which
splashes and spills need to happen. The maximum real-world size for a fluid simulation is 10 meters.
Obviously, with a real-world size limit of 10 meters, the fluid simulator is not designed to directly simulate
large bodies of water. This is not a limitation of Blender's fluid simulation so much as a reflection of the as-
tronomical computing resources required to do such a simulation at meaningful resolutions. In fact, the city-
destroying tidal waves, raging oceans, and sinking ships you see in CG movies are usually not created direc-
tly with one-button, full-sized fluid simulations, which would be prohibitively resource intensive and not of-
fer sufficient control. Rather, these effects are accomplished by ingenious combinations of a variety of tech-
nical solutions. As you'll see in this chapter, there are ways to use particles to fake higher-resolution fluid
simulations, but also remember that you have numerous tools at your disposal besides fluids: modifiers, an-
imated textures, lattices, shapes, hooks, parenting, particles, compositing tools, and more. If you want to
sink the
Titanic
or deluge New York, you will want to think in terms of solutions that bring these tools to
bear.
