Calculating Euler angles of principal stresses in Mechanical ACT or DPF?

J Wong

With Mechanical APDL, I can get the Euler angles of principal stresses using *VFUN Euler. How can I do this with ACT or DPF?

Ayush Kumar

@J Wong

There is not direct operator with DPF to do this but you can use a combination of eigen-vectors and functions to convert Eigenvectors to Euler Angles.

PyDPF:

import numpy as np
from ansys.dpf import core as dpf
from scipy.spatial.transform import Rotation as R

def normalize(v):
    return v / np.linalg.norm(v)

def build_right_handed_rotation_matrix(v1, v2, v3):
    # Normalize vectors
    v1 = normalize(v1)
    v2 = normalize(v2)
    v3 = normalize(v3)

    # Form matrix
    R_matrix = np.column_stack((v1, v2, v3))

    # Check determinant
    det = np.linalg.det(R_matrix)
    if det < 0:
        v3 = -v3
        R_matrix = np.column_stack((v1, v2, v3))

    return R_matrix

def get_euler_angles(v1, v2, v3, convention='xyz', degrees=True):
    R_matrix = build_right_handed_rotation_matrix(v1, v2, v3)
    rot = R.from_matrix(R_matrix)
    return rot.as_euler(convention, degrees=degrees)


rst = r"D:\…\file.rst"

ds = dpf.DataSources(rst)

stress = dpf.operators.result.stress(data_sources=ds, requested_location="Nodal")
ev = dpf.operators.invariant.eigen_vectors_fc(fields_container=stress)
ev_f = ev.outputs.fields_container.get_data()[0]

euler_angles = []
for nid in ev_f.scoping.ids:
    v1 = ev_f.get_entity_data_by_id(nid)[0][0: 3]
    v2 = ev_f.get_entity_data_by_id(nid)[0][3: 6]
    v3 = ev_f.get_entity_data_by_id(nid)[0][6: 9]
    
    roll, pitch, yaw = get_euler_angles(v1, v2, v3, convention='xyz')
    euler_angles.append((yaw, roll, pitch))

# Euler angles field
ea_f = dpf.fields_factory.create_3d_vector_field(num_entities=len(ev_f.scoping.ids))
ea_f.unit = "deg"
ea_f.data = np.array(euler_angles).flatten()
ea_f.scoping.ids = ev_f.scoping.ids

# PrintEuler angle of principal stresses for NID 2436
print(ea_f.get_entity_data_by_id(2436))