How do I get element beneath the selected Hex element in a mesh using PyDPF?

Ayush Kumar

How do I get element beneath the selected Hex element in a mesh using PyDPF?

Ayush Kumar

The methodology used is:

1. Get the normal and centroid of the selected element.
2. Generate a 3D line passing through the centroid and along the normal.
3. Get centroids of all the neighboring elements.
4. Filter out the centroid with the smallest distance to the 3D line.
5. Fetch the corresponding element ID to the centroid in step 4.

Below is the Python code using PyDPF for the above steps:

 import numpy as np
from ansys.dpf import core as dpf

rst_path = r"\Path\to\file.rst"
ds = dpf.DataSources(rst_path)

model = dpf.Model(rst_path)
mesh = model.metadata.meshed_region

# Replace EID of the selected element
eid = 1959

ms_eid = dpf.Scoping()
ms_eid.ids = [eid]

# Get Nodal scoping
ns = dpf.Scoping()
ns.ids = mesh.elements.element_by_id(eid).node_ids

# Get neighbouring elements
es = dpf.operators.scoping.transpose(
    mesh_scoping=ns,
    meshed_region=mesh,
    inclusive=1,
    requested_location=dpf.locations.elemental
)
es_scoping = es.outputs.mesh_scoping_as_scoping.get_data()

# Get normal on the element of interest
normals_op = dpf.operators.geo.normals(mesh=mesh, mesh_scoping=ms_eid)
normals = normals_op.outputs.field.get_data().data
print(normals)

# Get element centroids
ec = model.operator("centroids")
ec_f = ec.outputs.fields_container.get_data()[0]
point_start = ec_f.get_entity_data_by_id(eid)
ec_res_field = dpf.operators.scoping.rescope(
    fields=ec_f, mesh_scoping=es_scoping).outputs.fields_as_field.get_data()
ec_res = ec_res_field.data


def distance_to_line(A, B, C):
    # Calculate the distance of point C from the line AB
    n = B - A
    v = C - A
    distance = np.linalg.norm(np.cross(n, v)) / np.linalg.norm(n)
    return distance


def find_nearest_points_along_line(points, start, direction):
    # Convert the line to a vector
    line_vec = direction / np.linalg.norm(direction)

    # Calculate distances for each point
    distances = []
    for point in points:
        d = distance_to_line(start, start + line_vec, point)
        distances.append(d)

    # Sort points by distance
    sorted_indices = np.argsort(distances)
    nearest_indices = sorted_indices[:3]

    return nearest_indices


# Get indices of points nearest to the normal
nearest_indices = find_nearest_points_along_line(ec_res, point_start, normals)

# Element beneath
second_closest_index = nearest_indices[1]

eid_res = ec_res_field.scoping.ids[second_closest_index]
print(f"Element closest to centroid of Element {eid} is {eid_res}")