Duplicated Points in ParaView When Extracting Stress Data from ASPECT

ASPECT
1

Hello everyone,

I encountered an issue while using ParaView to process ASPECT output. When I tried to extract stress data, I noticed that some points appear duplicated. I’m not sure how to extract the stress field directly from ASPECT’s output files.

For example:

"velocity:0","velocity:1","velocity:2","stress:0","stress:1","stress:2","stress:3","stress:4","stress:5","stress:6","stress:7","stress:8","maximum_horizontal_compressive_stress:0","maximum_horizontal_compressive_stress:1","maximum_horizontal_compressive_stress:2","p","T","upper_crust","lower_crust","strain_rate","dynamic_topography","density","thermal_expansivity","specific_heat","viscosity","Points:0","Points:1","Points:2"
-1.6415e-05,-2.7732e-05,2.9225e-05,2.0194e+10,-2.007e+05,3.2308e+05,-2.007e+05,2.0198e+10,1.0753e+05,3.2308e+05,1.0753e+05,2.0181e+10,1.2491e+05,-2.9659e+06,0,2.0034e+10,1717.6,0,0,7.9101e-17,0,3157,3e-05,1300,4.8804e+22,13875,13875,10000
-1.6415e-05,-2.7732e-05,2.9225e-05,1.9879e+10,-1.1179e+05,6.9821e+05,-1.1179e+05,1.9882e+10,3.0298e+05,6.9821e+05,3.0298e+05,1.9871e+10,1.2468e+05,-2.9603e+06,0,2.0034e+10,1717.6,0,0,8.0727e-17,0,3157,3e-05,1300,4.8712e+22,13875,13875,10000

Note that the spatial coordinates (Points:0, Points:1, Points:2) are identical in both rows, but the stress components differ — suggesting that the same point is being output multiple times.

This duplication might be caused by my setting set Interpolate output = true. Would turning off interpolated output solve this issue, or is there a recommended way to output or extract non-duplicated stress data from ASPECT?

Thank you for your time and attention.

Best regards,
Haolin

2

This is expected, Haolin:

The finite element method computes a velocity solution that is made out of polynomials on each cell (typically we use quadratic elements in ASPECT). The velocity is continuous going from one cell to the next but not differentiable. As such, the stress (which contains velocity derivatives) has two different values on a cell boundary depending on what cell you are coming from. We output all values.

This has nothing to do with interpolated output.

3

@XHL-CUG What Timo already explained is also a frequently asked question for deal.II :slight_smile: Take a look here: Frequently Asked Questions · dealii/dealii Wiki · GitHub

Best

W.

4

Thank you very much for the clear and insightful explanations, @tjhei @bangerth

Best,

Haolin