FEM Pipeline units on last dev versions

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scuj
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FEM Pipeline units on last dev versions

Post by scuj »

Hello

When using FEM Pipeline with last development versions I am getting stresses in Pa by default when I was getting stresses in MPa with 0.19.3 or older 0.20 development versions (for example: FreeCAD_weekly-builds-25288):

Image

It doesn't affect FEM result ("CCX_Result") but only FEM Pipeline objects ("ResultPipeline"). Could you help me to know what am I missing, please ?

Let me know if you need more details.

Thanks
scuj

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OS: Ubuntu 20.04.1 LTS (LXDE/LXDE)
Word size of FreeCAD: 64-bit
Version: 0.20.28765 (Git) AppImage
Build type: Release
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Python 3.9.12, Qt 5.12.9, Coin 4.0.0, OCC 7.5.3
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NewJoker
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Re: FEM Pipeline units on last dev versions

Post by NewJoker »

Here's a quote from the release notes for 0.20:

Starting from this release, the scale of result pipelines and their filters will use SI units (m, kg, s, K, A, mol, cd). So the displacement is given in meter, the stress in Pascal. This applies for all SI-derived FreeCAD unit systems.
https://wiki.freecadweb.org/Release_not ... _Workbench
user1234
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Re: FEM Pipeline units on last dev versions

Post by user1234 »

See https://forum.freecadweb.org/viewtopic.php?f=18&t=68010

NewJoker wrote: Fri May 06, 2022 10:08 am Here's a quote from the release notes for 0.20:
I never saw that, and it makes no sense. I thougt this is a bug. The results in FreeCAD without pipeline differ from with pipeline is not only missleanding, also N/mm² (or MPa) is absolutly common. Never saw someone give results in Pa.

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user1234
NewJoker
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Re: FEM Pipeline units on last dev versions

Post by NewJoker »

user1234 wrote: Fri May 06, 2022 10:15 am I never saw that, and it makes no sense. I thougt this is a bug. The results in FreeCAD without pipeline differ from with pipeline is not only missleanding, also N/mm² (or MPa) is absolutly common. Never saw someone give results in Pa.
I also haven't noticed that before, and I'm skeptical about this change too. If SI(m) system stays as the default, it should be at least possible to choose units for the plot. Pascals and meters are very incovenient in most cases.
user1234
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Re: FEM Pipeline units on last dev versions

Post by user1234 »

NewJoker wrote: Fri May 06, 2022 10:21 am Pascals and meters are very incovenient in most cases.
Yes, if must respect bendings or shrinks, then meters makes also no sense.

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user1234
scuj
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Re: FEM Pipeline units on last dev versions

Post by scuj »

NewJoker wrote: Fri May 06, 2022 10:08 am Here's a quote from the release notes for 0.20:
...
Wow, I've missed that. By the way, thanks for your answer.

I agree with both of you, we need units consistency. That's a strange modification!
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Kunda1
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Re: FEM Pipeline units on last dev versions

Post by Kunda1 »

scuj wrote: Fri May 06, 2022 10:37 am
NewJoker wrote: Fri May 06, 2022 10:08 am Here's a quote from the release notes for 0.20:
...
Wow, I've missed that. By the way, thanks for your answer.

I agree with both of you, we need units consistency. That's a strange modification!
Aside, does anyone know if this is documented in the GH issue tracker?
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uwestoehr
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Re: FEM Pipeline units on last dev versions

Post by uwestoehr »

user1234 wrote: Fri May 06, 2022 10:15 am I never saw that, and it makes no sense. I thougt this is a bug. The results in FreeCAD without pipeline differ from with pipeline is not only missleanding, also N/mm² (or MPa) is absolutly common. Never saw someone give results in Pa.
1 MPa is the same as 1e6 Pa. so the unit is still correct only the display changed.
We had to change the display to fix a bunch of bugs when the simulation result if e.g. an electric voltage.
SI units are sensible for multiphysics simulations. Otherwise it is a nightmare as user to understand why e.g. a result of 1 V appears as "1^6".

Now we assure that
- the magnitude is correct
- the unit is correct

Also note that we fixed several bugs in the pipeline plots. You complain that one cannot change the display unit. That is right, but one never could.
Please open a feature request issue for this..
user1234
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Re: FEM Pipeline units on last dev versions

Post by user1234 »

uwestoehr wrote: Fri May 27, 2022 12:27 am Also note that we fixed several bugs in the pipeline plots.
I do not want to seem unthankful. I really appreciate your fixes.


uwestoehr wrote: Fri May 27, 2022 12:27 am 1 MPa is the same as 1e6 Pa. so the unit is still correct only the display changed.
Yes, but there are sometimes you have areas, where with this display an analysis is more or less impossible (or extremely error prone). This is the reason why the display for tensions/pressure is mainly fixed and quasi standardized in machine engineering in MPa (N/mm²) and mm, and not with an long written base and a sometimes different exponent (very hard to read, especially in the edge of the screen, when i have make the display for an other program smaller, i can not see the exponent).


uwestoehr wrote: Fri May 27, 2022 12:27 am You complain that one cannot change the display unit. That is right, but one never could.
Please open a feature request issue for this.
I never said, that it was possible before. Sadly i have not github account.


I think it should addressed before 0.20 (because of the standardization). Unit to show and fix the floating point or make it like before. I am sure at that state, many people will be with that unlucky.


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uwestoehr
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Re: FEM Pipeline units on last dev versions

Post by uwestoehr »

user1234 wrote: Fri May 27, 2022 12:55 am Yes, but there are sometimes you have areas, where with this display an analysis is more or less impossible (or extremely error prone).
FC does not yet have the possibility to print the unit. So seeing e.g. "964.83", what does this mean? Since you run the simulation you know the the result is e.g. a pressure. But is it kPa or MPa?
And pipelines are a multipurpose tool, for any kind of results, no only stresses.
The CCX tool in contrary is fixed to displacements and stresses.

Also note that we have very different user base. Architects deal with other dimensions than microfluidics guys.

user1234 wrote: Fri May 27, 2022 12:55 am I never said, that it was possible before. Sadly i have not github account.
Please create one. It is worth it.
user1234 wrote: Fri May 27, 2022 12:55 am I think it should addressed before 0.20 (because of the standardization).
SI is THE standard almost everyone uses/understands.
When users claim that they are e.g. machine engineers and therefore length unit mm is the standard, microtech guys say, no it is micron and structural engineers say it is meters.
But what do the electrical engineers say? If the length unit is mm, derived units like volt go crazy.
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