Stress Error Plot - What are the units?
Stress Error Plot - What are the units?
(OP)
Can anyone explain to me the basis of the stress error when plotted using the ERR option.
Specifically, is this reporting the error in the energy norm or a more tangible error such as actual "stress" or a percentage error?
I can't find anything in the user manual that explains this.






RE: Stress Error Plot - What are the units?
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RE: Stress Error Plot - What are the units?
RE: Stress Error Plot - What are the units?
Nagi Elabbasi
www.veryst.com
RE: Stress Error Plot - What are the units?
RE: Stress Error Plot - What are the units?
It is important to remember also that even a mesh convergence study only shows that you are converging to the exact solution of your FE model. If the boundary conditions, loads, material model or properties do not match the physical model then it creates a false sense of confidence in the results!
Nagi Elabbasi
www.veryst.com
RE: Stress Error Plot - What are the units?
RE: Stress Error Plot - What are the units?
Here is for example a warning from the Abaqus manual against just that:
"Warning: Error indicator output variables are approximate and do not represent an accurate or conservative estimate of your solution error. The quality of an error indicator can be particularly poor if your mesh is coarse. The error indicator quality improves as you refine the mesh; however, you should never interpret these variables as indicating what the value of a solution variable would be upon further refinement of the mesh"
Here is also a link to a good but older paper about error estimation using ANSYS: http://w
There is no black art/touchy feely whatever involved in good error estimation (it is a little subjective though). It's a complex topic that is still the subject of research in academia and commercial simulation software.
Nagi Elabbasi
www.veryst.com
RE: Stress Error Plot - What are the units?
RE: Stress Error Plot - What are the units?
If the solution, to the problem on which you are working, is to be compared to a limiting stress then would it not be a reasonable approach to use the error estimation to estimate an upper bound stress value to ensure that the acceptance criteria is still satisfied. In suggesting this I am making the assumption that convergence has been demonstrated, mesh refinement is adequate and that the 'error' is 'low'. The solution will never be 100% accurate. If you have a number of stress categories to which stress limits apply then it seems logical, as a final operation, to quantify the maximum predicted stress. This would be particularly relevant where the predicted stresses are close to the stress limits.
I am also considering other software, such as Ansys, that can report upper bound values.
RE: Stress Error Plot - What are the units?
Nagi Elabbasi
www.veryst.com