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02-12-2016 05:41 AM

Hello,

I just noticed that Transforming (Model-Output-Transform) vectors produces incorrect results if carried out on output sets that have been generated from linear combination (Model-Output-Process-Linear combination). When I try it the transformed vectors are actually not tranformed at all but remain in the local element coordinate system! They are however presented in the output as if they were transformed correctly.

-Kris

3 REPLIES

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02-15-2016 12:07 PM

I tried the following in v11.2.2:

- Open the platepost.modfem sample model
- Re-run the analysis to create a secondary output set (same thing could also be accomplished using Model->Output->Process, Linear Combination)
- Peform a linear combination of results set 1 and 2, using Model->Output->Process, Linear Combination
- If we look at a criteria plot of X and Y membrane forces (7206, 7207), we'll see the following for result sets 1, 2 and 3, respectively
- If you look at the element in the upper left hand corner, Nxx is 792 for cases 1 and 2 and 1584 for the combination case 3. Accordingly, Nyy is -48 for cases 1 and 2 and -96 for the combination case
- Using the Model->Output->Transform command, select plate transforms into the Y axis of CS0, then select output sets 1 and 2, the membrane force vectors 7206-7208. This command creates in-place user vectors within the selected output set, in this case 9000000-9000002 for the transformed membrane forces
- If we look at transformed Nxx for either case 1 or 2, it's -48, which is the same as the Nyy in the original orientation (X being oriented with the global X axis)
- Now, to redo the linear combination, essentially performing transform first, then combination, use Model->Output->Process, Linear combination. Select output sets 1 and 2, but only vectors 9000000-9000002.
- The previous operation creates a new output set (4), where plate X membrane force is now -96, or twice the transformed Nxx:
- Now, if we do the transformation command on the first combined set (3), this gives the combination first and transformation second:
- Like before, the transformation creates vectors in-place in the selected output set(s) and the combined then transformed Nxx shows up as -96, consistent with transformed then combined

I performed a similar operation in V11.0.1 (the dialogs are a little different, but essentially the process is the same) and got the same results.

If you could provide a little more information on the exact process you're using as well as specifically which version of FEMAP, I could certainly look more into it and help try to identify exactly what the issue may be.

Regards,

Patrick

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02-23-2016 06:29 AM

Hello Patrick,

I made a similar test on a simple model using FEMAP v11.2.0. I will attach the model.

The element in the upper right corner is oriented differently from the others.

1. Analyze two load cases: Longitudinal stress and vertical stress

2. Combine load cases 1*Longitudinal stres + 2*vertical stress

3. Run transformation on the resulting output set selecting 7020, 7021, 7023, 7420, 7421 and 7423 in global X-axis direction.

If alternatively I change the order so that I:

1. Analyze two load cases: Longitudinal stress and vertical stress

2. Run transformation on the resulting output set selecting 7020, 7021, 7023, 7420, 7421 and 7423 in global X-axis direction.

3. Combine load cases 1*Longitudinal stres + 2*vertical stress

I get the following result for 9000000..Plate Top X Normal Stress (X CSys 0)

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02-23-2016 11:30 AM

Thanks for the reply. There was a bug specific to v11.2.0 where vectors created via Model->Output->Process-> Linear combination / RSS Combination were not properly tracked and could not be transformed. This was fixed in the v11.2.1 release.

There's a workaround in v11.2.0 if you create a results processing data surface to do the linear combination instead and the Result Data Creation option is set to "As Needed / Temporary"

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