Potential Issue with Node Ordering of Abaqus Output

[JustinPorter88]

In a trial run following a similar procedure as the tutorial, my Abaqus run output the mtx file with the nodes from the bottom surface first and then the top surface. This renders line 53 of main.m (here) wrong in that the signs need to be flipped. This is more of a discussion point for the text since I do not know how the output order of surfaces is decided or if it is consistent.

My input deck used parts, rather than following the tutorial advice of "It is also helpful to use global node and element indexing henceforth. This can be specified in Model->Edit Attributes->Model-1 as follows" (see here). If that is the issue with node numbering, then this sentence should be more strongly phrased as a requirement.

More generally, I am not sure if it is safe to assume node ordering for M and K matrices within the Top/Bottom surfaces is preserved in the substructuring step. The output mtx file does list the node numbers for the order of the M and K matrices, but additional edits may be needed so that Elements.dat and Nodes.dat are compatible with this information.

[Nidish96]

This is indeed puzzling, thanks for pointing it out. The lines of code in the python script that request the retained DOFs are:

# The name dictates ordering. A comes before B.
mdl.RetainedNodalDofsBC(name="A", createStepName="HCBCMS", 
                        region=ras.sets['TOPS_NDS'], 
                        u1=ON, u2=ON, u3=ON)
mdl.RetainedNodalDofsBC(name="B", createStepName="HCBCMS", 
                        region=ras.sets['BOTS_NDS'], 
                        u1=ON, u2=ON, u3=ON)

When I first wrote it, the "name" was used to sort the occurrence of the DOFs in the retained set, but now it seems it follows a "first in last out" stack sequence. Maybe it's a behavior that changed across
Right now, if these lines are swapped, it does what we expect. I'm going to look into Abaqus documentation a little bit before I make a commit on this.

Thanks for pointing this out, I had completely missed it!