Buoyancy Force

Buoyancy is an upward force opposed to the weight of a object immersed in fluid. The buoyancy force, B, acts on the center of the submerged volume according to the following formula:

where:

  • ρ is the fluid density
  • b is the buoyancy scale computed from the displaced volume
  • V is the volume of the immersed part of the object collision geometry
  • g is the gravity force
Note
The buoyancy scale is a factor used in Vortex® to fine-tune the buoyancy force. It can be used to compensate for volumetric information which is not captured by the collision geometry (e.g., holes in the structure).

Consequently, if the rigid body is above the fluid surface, no forces are generated; if it is below, the buoyancy force is determined using the entire volume of the object (VCG) computed using the volume of its associated collision geometry. Otherwise, the exact submerged volume of the rigid body is computed to achieve an accurate simulation.

You can set Vx::VxCollisionGeometry::FluidInteractionData::setBuoyancyCenter if the buoyancy force is intended to act on a position other than the default position. This position can also be set in the Editor.

In the Vortex Studio Editor, you must set the displaced volume. The relationship between the displaced volume VDISP, the buoyancy scale b and the collision geometry volume VCG is given by the following equation:

For information about setting the buoyancy in the Editor, see Enabling Buoyancy.