Hi @Anonymous
I think I understand what you are asking now, but correct me if I am wrong. In the model with multiple parts combined, the gravity arrow appears near the "center" of the model. In the original model with the separate parts, the gravity arrow is near the arm on the -Z side of the model, as shown in this image.
Figure 1: Gravity arrow in model with separate bodies.
If that is your question, then it is nothing to worry about. Gravity is applied to the entire model, so the arrow can be shown anywhere and the results will be the same. According to the help, the arrow is supposed to be shown at the global origin (which is not where it is shown in Figure 1, and it is not near the center of the model). I do not know how it gets located where it is shown in your example.
Like you said, you found a way to have it show differently.
The more important issue is whether the results are correct or not. In the above analysis, the displacement results are very close to being symmetric, so the gravity load is applied correctly. (The -Z arm is displacing slightly more because the mesh is too coarse to give a symmetric result.) The stress results are highly sensitive to the mesh size, especially when there is point contact between bodies. It is not unusual to have a point stress at a corner or contact that is much higher it should be. (This is known as a singularity or stress concentration; it is a limitation of the simulation theory.) The displacements are not nearly as sensitive to the mesh size, so they are a good indication of whether the results are symmetric or not.
By the way. The multi-body model did not have any constraint, load (other than gravity), or contact setup. I just made everything bonded in order to get quick results.
Also, the mesher either does not know that parts are identical or does not care. It creates a mesh on each part independently of the other parts, and there is some "randomness" to where it starts. This is why the mesh is not symmetric or even throughout the model.
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.