Supposing to have square with hole,
I would like to fixe to the ground constraint at the middle of your length
and at the center of the internal circumference (as show in image below)
I thought to create an external point ,
then create a rigid link between internal surface and the point
When I try to insert a displacement on the point, I obtain this error message
What is the error?
A small but significant point: this is a warning, not an error. You may still run your analysis with warnings.
Can you share a screenshot of your complete model? It sounds like there is another constraint (e.g. mirror), perhaps on a surface which shares an edge with the rigid link.
Bear in mind that the rigid link will make the bore of the hole infinitely stiff. Another way to do this is to use a weighted link, but you then need to use two points in the centre, with a spring element connecting the weighted link to the displacement constraint. This approach allows the bore to deform, but also allows the part to move by an amount that depends on the stiffness of the spring.
Ah - I think I remember now that it does this when you constrain a rigid link directly. Basically, it's saying that you've connected some geometry with a rigid link - but you've also constrained a point on the rigid link, which can be the same as constraining the geometry.
As I said, it's a warning not an error; my recommendation with warnings is usually to continue the run, but check the behaviour of the model carefully to make sure that it is as you intended.