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Drag is a force opposite to the relative velocity of a moving object inside a fluid.
The drag force, D, is applied to the middle of the exposed surface on all types of surfaces for all collision geometries, according to the following formula:
In Vortex®, drag is set up for a collision geometry by modifying the drag coefficients along the respective translation and rotation axes of the volume. The drag force is applied considering the linear and the angular velocities of the geometry and the linear fluid flow velocity. The latter can be specified in the fluid state. If a mesh is used to represent the body's shape in the interaction with the fluid, the body's surface is discretized into small surface patches and the contributions to the total drag force of every patch are computed and integrated.
It is recommended to use a fine triangular mesh (ideally with equilateral triangles) to represent rigid bodies. If you need to change the value of the drag coefficient, you can set it in the Editor or Vx::VxCollisionGeometry::FluidInteractionData::setDragCoefficient.
For information about how to set the drag force in the Editor, see Enabling the Drag Force.