Accessing Mesh properties in a fast and efficient way

[germa89]

From internal user:

Hi everyone,

I'm currently supporting a group of customers who are developing a new PyAnsys library. Their goal is to implement custom mesh morphing techniques, and for that they need low‑level programmatic access to mesh node coordinates so they can apply displacements, translations, and rotations to large sets of nodes.

In Ansys Mechanical they previously relied on:
Helpers.MoveNodesByBody(mesh, body_id, n[body_id], r[body_id])
We are trying to determine whether an equivalent capability exists in PyAnsys, ideally something that allows updating node positions directly at scale.

I’m aware that PyMAPDL exposes commands such as:
mapdl.n(node_number, x, y, z, thxy, thyz, thzx)
which let you manually update the coordinates (and rotations) of a single node. However, this approach becomes limiting and inefficient when working with large sets of nodes, as these customers want to apply transformations in bulk and as efficiently as possible.

Does PyMAPDL (or another PyAnsys component) provide a more direct or lower‑level way to modify node coordinates for many nodes at once?

Any insights or examples would be greatly appreciated. Thanks

[germa89]

PyMAPDL executes MAPDL commands on the backend. Based on the #757 the best is to use non_interactive.

# Slow
for i in range(1000):
    mapdl.n(i, x, y, z)

# Very fast 
with mapdl.non_interactive:
    for i in range(1000):
         mapdl.n(i, x, y, z)

# The fastest
with mapdl.non_interactive:
    mapdl.run("*do,i,0,1000)
    mapdl.n(i, x, y, z)
    mapdl.run("*enddo")

Alternatively, you can use other MAPDL commands that perform actions in batch, for instance NBLOCK.

If you provide an example I can give you better advice.

[dpat-ansys]

Hi @germa89,

thanks a lot for the detailed answer. You mentioned NBLOCK as a batch‑oriented option. Do you have any pointers to docs or examples on how to use it for node updates? That would be very helpful.

If we end up with a concrete PyRBF (Radial Basis Functions mesh morphing) use case example that could benefit from further optimization, I’ll definitely follow up here with more details.

Thanks again for the guidance!

[germa89]

There is a full guide about this. Check the MAPDL "Programmer reference" guide.

Also you can get example codes that uses NBLOCK if you go to Mechanical and export the model to ds.dat file. That will export the mesh using EBLOCK and NBLOCK.

[mikerife]

Hi @germa89 @dpat-ansys Would the direct MAPDL database access be faster than N or NBLOCK? I think we tested it but quite a while ago...
Mike

[germa89]

I dont think so... most performant is normally running APDL commands in non_interactive mode. #757