Midside nodes in pyMAPDL?

a-s-yehia

I'm currently use pyMAPDL to extract strains for an optimization problem. On the software side, ANSYS calculates midside nodes but on the pyMAPDL side, retrieving strains return N/A for midside nodes. With elements such as SOLID186, this means manually calculating 12 nodes for each element, which can be time consuming in an iterative process.
1. I have tried the solutions listed here: https://github.com/ansys/pymapdl/discussions/4533

Is there a function in pyMAPDL that will allow me to extract these strains automatically (to put into a data frame for other functions) or is manually averaging them the only way currently?

Shashidhar Reddy

MAPDL only stores results at corner nodes in the RST file. Midside node values are computed on-the-fly during post-processing (plotting) in Mechanical/MAPDL — they are never persisted. So result.nodal_elastic_strain() correctly returns NaN for midside nodes since the data simply doesn't exist in the result file.

You can either manually average them or you can use DPF operator dpf.operators.averaging.extend_to_mid_nodes()

Here is the exmple.

source_path = r'….\dp0\SYS\MECH\file.rst'
datasource = dpf.DataSources(source_path)
strain_op = dpf.operators.result.elastic_strain(data_sources=datasource)

strain_fc = strain_op.outputs.fields_container.GetData()[0]
mid_op = dpf.operators.averaging.extend_to_mid_nodes()

mid_op.inputs.field.Connect(strain_fc)

mid_op.outputs.field.GetData()

You can also go through this discussion.

Midside node stress - Community Forum

Another way is to extract them using PRNSOL command.

Here is the sample APDL script. You can explore corresponding inputs in PyMAPDL. PRNSOL will print the results into a file. Then parse the text output into a DataFrame.

/post1

set,last          ! Last load step and substep

esel,all

cmsel,s,CZ_1,node   ! selecting the nodal named selection 

nsle,r,mid                ! selecting the mid side nodes from the current selection

/graphics,power

/efacet,2

/page,,,1e6

/header,off,off,off,off,off,off

/out,R_S,txt           ! redirect the output file R_S.txt 

prns,s,comp          ! Print the nodal stress 

/outp                   ! ! turn off redirection