Doc:2.6/Manual/Physics/Fluid/Obstacle

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Fluid Obstacle

This object will be used as an obstacle in the simulation. As with a fluid object, obstacle objects currently should not intersect. As for fluid objects, the actual mesh geometry is used for obstacles. For objects with a volume, make sure that the normals of the obstacle are calculated correctly, and radiating properly (use the Flip Normal button, in Edit mode, Mesh Tools panel, Editing context [F9]), particularly when using a spinned container. Applying the Modifier SubSurf before baking the simulation could also be a good idea if the mesh is not animated.

Boundary type

Determines the stickiness of the obstacle surface, called “Surface Adhesion”. Surface Adhesion depends in real-world on the fluid and the graininess or friction/adhesion/absorption qualities of the surface.

• Noslip causes the fluid to stick to the obstacle (zero velocity).
• Free(-slip) allows movement along the obstacle (only zero normal velocity).
• Part(-slip) mixes both types, with 0 being mostly noslip, and 1 being identical to freeslip.

Note that if the mesh is moving, it will be treated as noslip automatically.

Example of the different boundary types for a drop falling onto the slanted wall. From left to right: no-slip, part-slip 0.3, part-slip 0.7 and free-slip.

PartSlip Amount

Amount of mixing between no- and free-slip, described above.

Moving obstacles support Blender supports now moving obstacles. In the past, a moving obstacle was automatically treated as no slip (sticky), so if you wanted to splash off of a moving object, you had to put a transparent plane in the spot where the fluid will hit the moving object, exactly aligned and shaped as the object, to fake the splash. This is not needed anymore.

Impact Factor

Amount of fluid volume correction for gain/loss from impacting with moving objects. If this object is not moving, this setting has no effect. However, it if is and the fluid collides with it, a negative value takes volume away from the Domain, and a positive number adds to it. Ranges from -2.0 to 10.0.