PyDPF - Remove midside nodes

TommasoMarella

Hi guys,

Can I remove midside nodes from the extracted nodes, using Pydpf?

Pierre Thieffry

Hi @TommasoMarella what are you trying to achieve? Is this to scope a result to just corner nodes?

TommasoMarella

Hi @Pierre Thieffry ,

Yes, it is.

I need to analyse a rst file extracting (for a specific component) nodal stress. In the model are presents also midside nodes, so when I get the results I have all nodes (corner + midside).

I'm not interested in midside, so I would like to removed them during the extraction, or extract only corner nodes (it is the same). Is it possible?

Thanks for the help,

Tommaso

Pierre Thieffry

Two things: when you extract stresses at nodes (location='Nodal' or converting from 'ElementalNodal' to 'Nodal' with the elemental_nodal_to_nodal operator), they should only be scoped to corner nodes - to get the midside nodes, you will need to use the extend_to_mid_nodes operator.

Now, if one wants the list of corner nodes, I can propose this function. We have requested our developers to create specific operators for this, but in the meantime, this should work for 10 noded tets and 20 noded hex:

def get_corner_nodes(mesh,scoping=None):
  corner_nodes=[]
  type_info={1:[20,8],0:[10,4]} # Element type with number of nodes and number of corner nodes
   
  # scope to few elements if scoping is defined
  if scoping!=None:
    mscope = dpf.operators.mesh.from_scoping(scoping=scoping,mesh=mesh)
    scopedmesh=mscope.outputs.mesh.get_data()
  else:
    scopedmesh=mesh
     
  # Loop over element type to extract corner nodes
  eltypes=scopedmesh.property_field('eltype').data   
  elements=scopedmesh.elements
  nodes=scopedmesh.nodes
  # Look over element type
  for iprop in range(len(eltypes)):
    if not(eltypes[iprop] in type_info.keys()):
      # we assume linear element, send back all nodes
      el_nodes=elements.element_by_index(iprop).connectivity
      for idx in el_nodes:
        corner_nodes.append(nodes.node_by_index(idx).id)
    else:
      # quadratic element, send back corner nodes (first in the connectivity)
      num_corner_nodes=type_info[eltypes[iprop]][1]
      el_nodes=elements.element_by_index(iprop).connectivity
      for i in range(0,num_corner_nodes):
        corner_nodes.append(nodes.node_by_index(el_nodes[i]).id)
  corner_nodes=list(dict.fromkeys(corner_nodes))
   
  return corner_nodes   

mesh=model.metadata.meshed_region
# get corner nodes for element 1
scoping=dpf.Scoping(location='Elemental')
scoping.ids=[1]
cn_scoped=get_corner_nodes(mesh,scoping)     
# get corner nodes for all elements
cn_all=get_corner_nodes(mesh)     

Pierre Thieffry

Here's another option with the take_mid_nodes option on scoping.connectivity_ids operator

from ansys.dpf import core as dpf 
from ansys.dpf.core import examples 
model = dpf.Model(examples.download_all_kinds_of_complexity()) 

all_node_ids = model.metadata.meshed_region.nodes.scoping.ids 
print("Nb of nodes:", len(all_node_ids)) 

# Instantiate operator and connect inputs in one line 
op = dpf.operators.scoping.connectivity_ids(mesh_scoping=model.metadata.meshed_region.elements.scoping,
mesh=model.metadata.meshed_region, take_mid_nodes=False, ) 

# Get output data 
corner_node_ids = list(set(op.outputs.mesh_scoping().ids))

print("Nb of corner nodes:", len(corner_node_ids)) 

mid_node_ids = list(set(all_node_ids).symmetric_difference(set(corner_node_ids))) 

print("Nb of middle nodes:", len(mid_node_ids)) 
print(f"Check total: {len(corner_node_ids) + len(mid_node_ids)}")

dafedin

Hi @Pierre Thieffry!

I have the reversed task. I'd like to have the capability to get stresses from any nodes in model, not only corner nodes. It's well known, that result file doesn't store stresses for mid-side nodes. Mechanical does averaging on-fly when user ask for them. So, I wonder if we have another way to get stresses in mid-side nodes using DPF instead of using node connectivity operator and manual averaging stress values in neighbor corner nides?