Display results as vectors

[arun-maniam]

Hello,

in APDL there is a command called plvect to display vectors with element centroids as the origin for the vectors. How can I do this in pymapdl if the x,y, and z values for the vectors are saved as numpy array? I was thinking that maybe i can get the locations of the element centroid but not sure how. Once i have that maybe i could use the command plotter.add_arrows() to display the vectors. Do anyone have a better suggestion? Thanks in advance!

Arun

[germa89]

Hello @arun-maniam !

You could accomplish that using pyvista:

import pyvista as pv

grid = mapdl.mesh._grid

mapdl.post1()
mapdl.set("last")  # Important! Otherwise the element values are zero.

centers = np.array(grid.cell_centers().points)
scalars = mapdl.post_processing.element_displacement("NORM")  # Just for plotting
direction = np.array(mapdl.post_processing.element_displacement("ALL"))

size_arrow_respect_full_model = 10 # th times smaller
arrow_size = np.mean(centers.max(axis=0) - centers.min(axis=0))/size_arrow_respect_full_model
magnitude = arrow_size/direction.max()

pl = pv.Plotter()
# pl.add_mesh(grid, opacity=0.5, color='grey')  # In case you want to plot the cylinder too
pl.add_points(centers,scalars=scalars, cmap="bwr")
pl.add_arrows(centers, direction, magnitude, cmap="bwr", show_scalar_bar=False)
pl.show()

Model

Details

from ansys.mapdl.core import launch_mapdl
import numpy as np

mapdl = launch_mapdl(start_instance=False)
mapdl.clear()
mapdl.prep7()
mapdl.clear()

define cylinder and mesh parameters

torque = 100
radius = 2
h_tip = 2
height = 20
elemsize = 0.5
pi = np.arccos(-1)
force = 100 / radius
pressure = force / (h_tip * 2 * np.pi * radius)

Define higher-order SOLID186

Define surface effect elements SURF154 to apply torque

as a tangential pressure

mapdl.prep7()
mapdl.et(1, 186)
mapdl.et(2, 154)
mapdl.r(1)
mapdl.r(2)

Aluminum properties (or something)

mapdl.mp("ex", 1, 10e6)
mapdl.mp("nuxy", 1, 0.3)
mapdl.mp("dens", 1, 0.1 / 386.1)
mapdl.mp("dens", 2, 0)

Simple cylinder

for i in range(4):
mapdl.cylind(radius, "", "", height, 90 * (i - 1), 90 * i)

mapdl.nummrg("kp")

mesh cylinder

mapdl.lsel("s", "loc", "x", 0)
mapdl.lsel("r", "loc", "y", 0)
mapdl.lsel("r", "loc", "z", 0, height - h_tip)
mapdl.lesize("all", elemsize * 2)
mapdl.mshape(0)
mapdl.mshkey(1)
mapdl.esize(elemsize)
mapdl.allsel("all")
mapdl.vsweep("ALL")
mapdl.csys(1)
mapdl.asel("s", "loc", "z", "", height - h_tip + 0.0001)
mapdl.asel("r", "loc", "x", radius)
mapdl.local(11, 1)
mapdl.csys(0)
mapdl.aatt(2, 2, 2, 11)
mapdl.amesh("all")
mapdl.finish()

mapdl.slashsolu() # Using Slash instead of / due to duplicate SOLU command
mapdl.antype("static", "new")
mapdl.eqslv("pcg", 1e-8)

Apply tangential pressure

mapdl.esel("s", "type", "", 2)
mapdl.sfe("all", 2, "pres", "", pressure)

Constrain bottom of cylinder/rod

mapdl.asel("s", "loc", "z", 0)
mapdl.nsla("s", 1)

mapdl.d("all", "all")
mapdl.allsel()
mapdl.psf("pres", "", 2)
mapdl.pbc("u", 1)
mapdl.solve()

[arun-maniam]

@germa89 Thanks for the input. It worked. I have another question. I have made changes such that all the arrows have the same size. However I would like to show the actual 'magnitude' of the arrows with the colours of the arrows. Is this possible? Thanks in advance!

[germa89]

It is possible, but it becomes more a pyvista question than anything else. Check the following examples,

• https://tutorial.pyvista.org/tutorial/04_filters/exercises/e_glyphs.html
• https://tutorial.pyvista.org/tutorial/04_filters/solutions/e_glyphs.html

I did also implemented something similar for plotting boundary conditions, which uses glyphs and it scales it according to their magnitude. The implementation is here:

pymapdl/src/ansys/mapdl/core/plotting.py

Lines 1032 to 1056 in 03c9db3

	pcloud = pv.PolyData(bc_nodes)
	pcloud["scale"] = bc_scale * bc_glyph_size
	# Specify tolerance in terms of fraction of bounding box length.
	# Float value is between 0 and 1. Default is None.
	# If absolute is True then the tolerance can be an absolute distance.
	# If None, points merging as a preprocessing step is disabled.
	glyphs = pcloud.glyph(
	orient=False,
	scale="scale",
	# tolerance=0.05,
	geom=BC_plot_settings[each_label]["glyph"],
	)
	name_ = f"{each_label}"
	pl.add_mesh(
	glyphs,
	color=BC_plot_settings[each_label]["color"],
	style="surface",
	# style='wireframe',
	# edge_color=BC_plot_settings[each_label]['color'],
	# line_width=3,
	name=name_,
	label=name_,
	)

[arun-maniam]

Thanks @germa89! I will look into the examples and give it a try.