I've noticed that rigid body constraint is not yet implemented in FreeCAD. It's a very common and useful CalculiX feature that has 3 main applications:
- defining rigid bodies - if part of the model is very stiff when compared with the rest of the structure, usually we model it as rigid to speed up the analysis significantly
- applying torque or boundary conditions on rotational DOFs - currently the only way to simulate torsion in FreeCAD is to use the transform constraint but it's limited to cylindrical faces so you can't analyze torsion of rectangular or elliptical bar for instance
- defining remote loads - for example you could define a force acting at a distance from the surface to which it's applied (eccentric load, quite common)
The keyword syntax for this feature is:
Code: Select all
*RIGID BODY, NSET=..., REF NODE=... ROT NODE=...
The problem is that new a object will have to be introduced - a reference point. It's an arbitrary point selected by the user. Loads (force/torque) and boundary conditions (displacement/rotation) can be applied to it, so their codes may require some changes too. Reference point can be defined using *NODE keyword and given coordinates. Apart from REF NODE there's also ROT NODE that has to be specified but they can share the same coordinates.
What do you think about the potential implementation of this feature ? Are you interested in participating in its development ? I won't be able to do it alone but with your help it should be possible.