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Convert nodal coordinates field to local coordinate system#
Currently, there is no native operator to get nodal coordinates in an Local
Coordinate System (LCS). The operator rotate
rotates the input field in Global Coordinate System (GCS) as per the input rotation matrix.
So, if the LCS is at the same origin as the GCS, only one operation using the
rotate
operator give the desired output.
However, if the aim is to obtain the LCS in a case where the LCS origin does not coincide with
the GCS, a transformation is required after the rotation to get the correct coordinates in LCS.
The script below demonstrates the methodology using PyDPF.
# Import necessary modules
from ansys.dpf import core as dpf
from ansys.dpf.core import examples
from ansys.dpf.gate.errors import DPFServerException
Create a model object to establish a connection with an example result file:
model = dpf.Model(examples.download_hemisphere())
Get the property coordinates_field
from nodes
:
ncoord_f = model.metadata.meshed_region.nodes.coordinates_field
Get the rotation matrix of the LCS ID 12.
The first 9 values in the cs
output is the rotation matrix.
try:
# Starting with DPF 2025.1.pre1
cs = dpf.operators.result.coordinate_system()
cs.inputs.data_sources.connect(model)
except (KeyError, DPFServerException) as e:
# For previous DPF versions
cs = model.operator(r"mapdl::rst::CS")
cs.inputs.cs_id.connect(12)
cs_rot_mat = cs.outputs.field.get_data().data.T[0:9]
Create a 3x3 rotation matrix field rot_mat_f
:
rot_mat_f = dpf.fields_factory.create_scalar_field(1)
rot_mat_f.data = cs_rot_mat
Create a 3D vector field for the position vector of the LCS’s origin and
rotate the origin as per the rotation matrix of the LCS.
The last 3 entries of cs
output is the LCS’s origin in GCS.
pos_vec = dpf.fields_factory.create_3d_vector_field(1)
pos_vec.data = cs.outputs.field.get_data().data.T[-3:]
pos_vec_rot = dpf.operators.geo.rotate(field=pos_vec, field_rotation_matrix=rot_mat_f)
Get rotated nodal coordinates field:
ncoord_rot_f = dpf.operators.geo.rotate(field=ncoord_f, field_rotation_matrix=rot_mat_f)
Transform rotated nodal coordinates field along rotated position vector
pos_vec_rot
:
pos_vec_rot_neg_f = dpf.operators.math.scale(field=pos_vec_rot, ponderation=-1.0)
pos_vec_rot_neg = pos_vec_rot_neg_f.outputs.field.get_data().data_as_list
ncoord_translate = dpf.operators.math.add_constant(field=ncoord_rot_f, ponderation=pos_vec_rot_neg)
Get the nodal coordinates field ncoord_lcs_f
in LCS:
ncoord_lcs_f = ncoord_translate.outputs.field.get_data()
Coordinates of NID 1 in GCS
print(ncoord_f.get_entity_data_by_id(1))
[[-2.74445261 13.2627943 4.68419313]]
Coordinates of NID 1 in LCS
print(ncoord_lcs_f.get_entity_data_by_id(1))
[[11.71685114 -4.83846377 -2.35002614]]
Total running time of the script: (0 minutes 6.097 seconds)