I see two different datums when I run a simulation. It appears to be random as some of my sims have it, some don't. I'm not sure which one is used to choose the axes for simulation plots. Any help is appreciated.
Those are not 'datums' (which has a very specific meaning in GD&T) but are really 'triads' which define the orthogonal directions. Looks like you are working with two different origins, one is for the body of the part but I can't really tell where the other one comes from with only your picture.
The Triad on the Left is the global model triad or co-ordinate system that you have used to create the part/assembly.
The Triad in the bottom right shows simulation specific orientation when you plot a result in a particular direction (Cartesian co-ordinate system) with respect to a reference plane or surface. You can do this by editing a result plot and choosing a reference under the 'Advanced Options'. (see image below for example where shear stress in XY has been plotted for a simple example).
The triad in the bottom left can also change for cylindrical components or disks when you plot radial results using an axis reference point. The triad then changes to a polar co-ordinate system as indicated by the graphic in the bottom right in the image below.
I hope that helps.
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