## Fluids

#### CFX Rigid body solution

• vinnakbm
Subscriber
Hello, In CFX rigid body solution, is it possible to couple motion of 2 rigid bodies so that they don't intersect (unrealistic as one body cannot penetrate the other during the motion)? Thank you!
• rfblumen
Ansys Employee
Assuming you're modeling rigid bodies in CFX using a collection of 2D regions, the resulting motion of the two rigid bodies cannot intersect or touch as this would result in an invalid mesh.
The motion of the two bodies may be coupled such that the bodies don't collide by using the position of the two bodies relative to each other. The position of the two bodies is determined using the rbstate function along with the Position state variable (i.e. rbstate(Position X)@RigidBody1 gives the x position of RigidBody1 relative to the coordinate frame associated with RigidBody1, rbstate(Position X)@RigidBody2 gives the x position of RigidBody2 relative to the coordinate frame associated with RigidBody2) and calculation the distance. An external force could be applied to each body where the magnitude of the force is inversely proportional to the distance between the two bodies.
• vinnakbm
Subscriber
Thank you for the suggestions. I'm using immersed solids for the rigid bodies. They have rotary motion about z axis and I constrained the translations. At t=0 sec, there is no overlap between the rotors. However, as fluid starts turning the rotors, I want to define the angular relationship between the 2 rotors so that they don't overlap or intersect. In the initial run I did, I noticed in post processing that the rotors are overlapping in some timesteps. Could this be only a visualization issue? There are no other external forces acting on the rotors. The coupling you mentioned using rbstate, will I be able to do it in the set up so that the angular rotation of one rotor is a function of angular rotation of the other? This would allow me to define a drive and driven kind of relationship between the rotors.