Getting Heat Flux at nodes/elements

[VHB4910]

I am running a steady state heat equation problem in PyMAPDL. The calculation runs fine and I can plot the

1. solution nodal Temperatures

result = mapdl.result

result.plot_nodal_temperature(0)

2. solutions heat flux vectors:

mapdl.allsel()
mapdl.plesol("TF","X")
mapdl.plesol("TF","Y")

However, when I try to extract the heat flux solutions using

mapdl.allsel("ALL")
mapdl.etable("HFX","TF","Y") 
mapdl.get_array("ETAB", "HFX")

, I get an array of 0's as the solution.

What am I doing wrong? What can I do to get the element heat flux vectors/magnitudes?

P.S.: Also, I don't think the postprocessing class has any attribute for thermal flux? [https://mapdl.docs.pyansys.com/version/0.68/api/_autosummary/ansys.mapdl.core.post.PostProcessing.html]

[mikerife]

Hi @VHB4910
The get_array should be getting the element result of the element table. So this instead:

mapdl.get_array('elem', '', 'etab', 'hfx')

Try that and let us know what happens.
Mike

[VHB4910]

Thanks, I think this works. But a quick follow-up:

mapdl.etable("HFX", "TF", "X")  # Heat flux in X direction
mapdl.etable("HFY", "TF", "Y")  # Heat flux in Y direction

# Get heat flux data
hfx = mapdl.get_array('elem', '', 'etab', 'hfx')
hfy = mapdl.get_array('elem', '', 'etab', 'hfy')

What is the convention followed?: Is hfx[i] the X-direction thermal flux component of element i+1 evaluated at the element centroid (per Table 55.1 https://www.mm.bme.hu/~gyebro/files/ans_help_v182/ans_elem/Hlp_E_PLANE55.html).

Now if I print the length of hfx and hfy, I find that this is equal to the number of elements in the mesh. .
Is it because the output is at the element centroid (and not integration points?). I am using PLANE 55 elements.

[mikerife]

@VHB4910 yes that is correct; ETABLES hold one value per element. So it's an interpolated value from the integration points to the centroid.

The matching of "i" and "i+1" of hfx and element number is not necessarily correct; for example if there are gaps in the element numbering. Or if the element numbering simply does not start at element 1. But you can match with the mesh.enum list of element numbers if needed.

MIke

[VHB4910]

Thanks, @mikerife it makes sense.

One final question: How can I use mapdl.get_array to get the interpolated valued of hfx and hfy at the nodes instead of at the element centroids.

[mikerife]

Hi @VHB4910
Check the PyMAPDL documentation on get_array - it is using MAPDL *VGET behind the scenes. So then check on the MAPDL Help on *VGET. It gives all the results you can get for nodes/elements. Here we just get that result directly for nodes like:

mapdl.get_array('node', '', 'tf', 'x')

Mike

[VHB4910]

Thanks, will take a look.