I’m currently running a 3D spherical model (aspect-2.6.0-pre) and want to output stress by adding “stress” to the Postprocess/Visualization/List of output variables. I checked the manual that the format of output is in the order of t_{xx}, t_{xy}, t_{xz}, t_{yx}, t_{yy}, t_{yz}, t_{zx}, t_{zy}, t_{zz}. After loading the stress tensor [S]_{xyz}, I transform this into r, \theta, \phi coordinate system (theta begins from the polar) by the following method:

Also, in my model, I apply a free-slip boundary (Tangential velocity boundary indicators = top, bottom) and want to check whether or not t_{r\theta}, t_{r\phi} are nearly zero around the surface. But unfortunately, they are not and some of them can even become larger than 100 MPa. I don’t know whether or not it is caused by my misunderstanding of the data output format or cartesian coordinate system in ASPECT. Are there any ideas for this?

@xiang Can you post a picture that shows how the stress looks like? Oftentimes, one can tell from a picture what might be wrong. It could be, for example, that the picture you see shows an angular patterns that might suggest that the matrix A you implement is wrong. Or perhaps it shows that the deviations you observe are nonzero but really quite small compared to the overall stresses/pressures and so “effectively zero”. In any case, what I want to say is that pictures often help in debugging
Best
W.

Thank you so much! It’s my mistake. In my data, there are some points with quite large shear stress values near the surface, but the overall values are quite small compared to normal stress (effectively small). Before plotting, I only checked those super maximum values of shear stress and ignore the whole image, which leaded me to a wrong conclusion. And by the way, I also incorrectly applied that matrix A. Below is the modified formula: (Keep the same elements of matrix A shown above)