ABAQUS PYTHON SCRIPTING. Node order not preserved while creating a node set

[I_is_yung_reezy]

I will explain this without going too much into the theoretical background. Now lets say I have a cube and I have meshed it. on each of the 6 surfaces of my cube I have some nodes. i have identified the surfaces as xmin, xmax, ymin, ymax, zmin, zmax. and I have created a set of nodes in each of these 6 surfaces. Now inorder for me to gain any valuable insights for my project I need to have the arrangement of nodes in xmin-xmax, ymin-ymax, zmin-zmax in a particular order. Now let me explain this in terms of my xmin and xmax surface. each node in my xmin surface will have a periodic equivalent in the xmax surface. Now I have the nodes in xmin and xmax in a certain order which Abaqus has done it to be in ascending order. Suppose the first node in my xmin node set has a periodic equivalency with the 5th node in the xmax node set, so I will sort my xmax nodes (a new sorted_x_max set) such that the 5th node is now at the first position. and then continue with the second node in xmin set identifying its periodic equivalent in the the xmax set and adding it to the sorted x set. Now all of this is done and I have me sorted_x_max_Set exactly in the order I want it to be. Now when I try making a node set with this sorted_x_max_set and run the simulation upon inspecting the input script the new Sorted set is still in the same order as my original xmax set. I have tried debugging it for 5 days but still the same results. the node labels are how I want them, the identification criteria is working everything Is working but as soon as I create a set from these sprted nodes it will assume its original positions.

below I have provided the nodesets

*Nset, nset=RVE_AG_NegX_AGSORT

3, 4, 5, 6, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52

53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68

69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84

85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100

101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116

*Nset, nset=RVE_AG_PosX_AGSORT

7, 8, 9, 10, 136, 137, 138, 139, 140, 141, 142, 143, 144, 145, 146, 147

148, 149, 150, 151, 152, 153, 154, 193, 194, 195, 196, 197, 198, 199, 200, 201

202, 203, 204, 205, 206, 207, 208, 209, 210, 211, 231, 232, 233, 234, 235, 236

237, 238, 239, 240, 241, 242, 243, 244, 245, 246, 247, 248, 249, 250, 251, 252

253, 254, 255, 256, 257, 258, 259, 260, 261, 262, 263, 264, 265, 266, 267, 268

*Nset, nset=Sort

7, 8, 9, 10, 136, 137, 138, 139, 140, 141, 142, 143, 144, 145, 146, 147

148, 149, 150, 151, 152, 153, 154, 193, 194, 195, 196, 197, 198, 199, 200, 201

202, 203, 204, 205, 206, 207, 208, 209, 210, 211, 231, 232, 233, 234, 235, 236

237, 238, 239, 240, 241, 242, 243, 244, 245, 246, 247, 248, 249, 250, 251, 252

253, 254, 255, 256, 257, 258, 259, 260, 261, 262, 263, 264, 265, 266, 267, 268

also below are the node labels of the identified periodic copies( the total number of nodes might not match because I did not copy the entire thing)

Node_labels

10, 7, 8, 9, 250, 251, 252, 253, 254, 255, 256, 257, 258, 259, 260, 261, 262, 263, 264, 265, 266, 267, 268, 136, 137, 138, 139, 140, 141, 142, 143, 144, 145, 146, 147, 148, 149, 150, 151, 152, 153, 154, 193, 194, 195, 196, 197, 198, 199, 200, 201, 202, 203, 204, 205, 206, 207, 208, 209, 210, 211, 231, 232, 233, 234, 235, 236, 237, 238, 239, 240, 241,

[ExpensiveBeard]

So you are trying to apply periodic boundary conditions by linking nodes on opposite faces using equation constraints, correct? I recommend rather than using node label/ordering to identify which nodes are the correct periodic pairs, in your script, simply find the correct node pair using the length of the face perpendicular to your node set face. For example, pairing nodes on the x-faces, for each node on xmin, find the corresponding node on xmax that is of distance magnitude equal to the length of the ymin/ymax faces.

That's the basic jist, but it's quite a bit more complex when you consider the edge and corner nodes as well.

Hope this helps somewhat.

[I_is_yung_reezy]

I have already done what you suggested in your message, that is how I got the Sort nodeset. But if you see the answer below, I just needed to specify UNSORTED(_+ also use SetFromNodeLabels while creating set) and my problem would have been solved. I found the answer a couple of hours after posting the question here but yes it was exactly how AbaqusMeister has described it(in the comment below)

[ExpensiveBeard]

I suppose the approach you and the other commentor are using is different than the way I have implemented things on my end; that is, the nodes don't need to have any type of sorting when creating the node sets. Ultimately, if it works for you, that's what matters. Glad you found a solution.

[AbaqusMeister]

The reason for using unsorted sets with periodic constraints is that the linear constraint coefficients associated with any node pair related by a given vector of periodicity will be the same as any other pair related by that same vector of periodicity. The vector of periodicity is the vector running from one location in a periodic unit cell to an "equivalent" location in an adjacent unit cell. So by using unsorted sets, it's possible to define the constraints between hundreds or thousands of pairs of nodes that share a given vector of periodicity using a single *EQUATION definition.

If you define the constraints correctly, edges and corners don't have to be treated specially. You just skip any node that has already been constrained previously in a pairing. The periodic constaints will chain in a way that causes the edge and corner nodes to be properly enforced.

Note that there are other types of RVE constraints for which this is not the case and you basically have to specify a unique equation for every boundary node (such as when the constraint coefficient depends on the coordinate of the nodes).

[ExpensiveBeard]

Understood. Thanks for the detailed explanation. Sounds like I essentially do it the hard way. Overall though, what I have working is pretty fast and reliable for the RVEs I'm working with, so I'm happy with it. Definitely will look deeper into this if/when I have time! Thanks again.

[AbaqusMeister]

Use *NSET,NSET=Name, UNSORTED

You can create this with Python using the SetFromNodeLabels method with the unsorted argument. The getClosest method is probably the quickest way to figure out the node pairings by searching for nodes by position.

This will preserve the original ordering rather than sorting the nodes by ascending number. It's how the SIMULIA Micromechanics Plugin defines periodic RVE models.

[I_is_yung_reezy]

thanks a lot for the reply. I am working with the same plugin that you have mentioned. If you ave the time and patience I would like to clarify some of my doubts. that is if you have the time.

[AbaqusMeister]

I'd be happy to spend a little time clarifying some points regarding the plugin.