Hi @Anonymous
- If the threads are important (because you expect a high stress in the thread area), then you need to include them in the analysis and define separation contact between the parts at the threads. The only simplification that you can do in this case is remove the unused threads above the nut.
- if the threads are not important (because you expect the stress in that region to be acceptable), then you can remove all of the threads and use the nominal diameter for both parts. Then bond the nut to the cylinder; this will simulate as if the threads are tight and the two parts displace as one.
You mentioned that you put a constraint on the outer wall and ring. This implies that those surfaces are somehow welded or glued to a rigid part that is not included in the analysis. Is that what you want to simulate? (It does not sound correct to me.) The constraints should only be applied to locations where the model is rigidly connected to the earth.
If cases where the model has no constraints in real life (such as a machine sitting on the ground, "held" in place by its own weight), then you should apply the minimum constraints necessary to prevent the model from moving in X, Y, and Z, and apply those constraints as far from the regions of high displacement and stress and possible. In other words, you want the constraint to prevent the model from displacing an infinite amount, but you do not want the constraint to prevent the model from deforming in its natural shape.
John Holtz, P.E. Global Product Support
Autodesk, Inc. If not provided, indicate the version of Inventor Nastran you are using.If the issue is related to a model, attach the model! See What files to provide when the model is needed.
