Request for help meshing and and analysing a part {Solved}

About the development of the FEM module/workbench.

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thschrader
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Re: Request for help meshing and and analysing a part

Post by thschrader »

Laurie Hartley wrote: Sun Sep 12, 2021 11:48 am ... Am I being too simplistic? :?
You get more vertical loading at the inner fixings.
The numbers differ because you do not have a perfect symmetrical structure (the diagonals, bottom chords).
However, the loading 24x5,1 kN=122,4 kN is exactly the summation of the vertical reaction forces.
You can check that with FC. You must define a separate case for each fixing in the analysis.
fixings.JPG
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cad1234
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Re: Request for help meshing and and analysing a part

Post by cad1234 »

thschrader wrote: Sun Sep 12, 2021 1:24 pm
Thanks Thomas for clarification!!! Very helpfull!
thschrader
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Re: Request for help meshing and and analysing a part

Post by thschrader »

@Laurie:
Here is the system with separate fixings.
Run FEM, see ccx-dat and add all z-parameters.
sum z = 122 kN = 122 kN total vertical loading.
File with cleared mesh:
spaceframe_statics.FCStd
(453.88 KiB) Downloaded 558 times

We need a better approach for drafting the structure.
Changing the geometry is impossible, we need a parametric design. Sketcher only?
How to add hinges (= subdivide beams)? curves-wb, "discretize edge" tool?

fixings2.JPG
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thschrader
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Re: Request for help meshing and and analysing a part

Post by thschrader »

Hinges in beams:
Here is a video about FC-FEM using the "constraint-tie" tool.
Is it possible to reverse this for defining hinges?
==> constraint-untie
https://www.youtube.com/watch?v=wzo_YxOBshw
balrobs
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Re: Request for help meshing and and analysing a part

Post by balrobs »

thschrader wrote: Sun Sep 12, 2021 11:26 am Is there a tool/command in aster to add hinges at the nodes?
AFAIK there are three methods in CodeAster to add hinges at the end of a beam (if someone knows it better please correct me):

- simulate hinges on both ends by using BAR elements. They can only support axial forces (no subdivisions, no trasversal loadings, no buckling analysis)
- create short elements (called DIS_TR) with specified stiffness at the end of beams
- duplicate nodes and bind their dof together with the command LIASION_UNIF

At first sight all these methods seem rather cumbersome to me ... I will give them a depper look and report back.
Cheers
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bernd
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Re: Request for help meshing and and analysing a part

Post by bernd »

moved code aster posts, sorry guys for the interruption ... https://forum.freecadweb.org/viewtopic.php?f=18&t=62165
Laurie Hartley
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Re: Request for help meshing and and analysing a part

Post by Laurie Hartley »

thschrader wrote: Sun Sep 12, 2021 2:50 pm @Laurie:
We need a better approach for drafting the structure.
Changing the geometry is impossible, we need a parametric design. Sketcher only?
How to add hinges (= subdivide beams)? curves-wb, "discretize edge" tool?
Thanks for the explanation on the reactions Thomas. Its starting to fall in to place for me now.

On the need for a parametric design and Sketcher. I think I can make a start on that. This would be my approach:-

Sketcher with Spreadsheet Workbenches
Square on square grid size = 1500 (or whatever)
Therefore chord length = xxxx
Therefore strut length = xxxx
Therefore plan brace length = xxxx

SHS section size of chord = xxxx (eg 65)
SHS section thickness of chord = xxxx (eg 4)

SHS section size of strut = xxxx (eg 50)
SHS section thickness of strut = xxxx (eg 4)

SHS section size of plan brace = xxxx (eg 50)
SHS section thickness of chord = xxxx (eg 4)

Dimensions of “node cube” = H x W x D (I can get the volume of my node from the model

Switch to Part Design Work Bench

Create circular bar chord based on sketcher dimensions
Create circular bar strut based on sketcher dimension
Create circular bar plan brace based on sketcher dimension
Create solid cube based on sketcher dimensions

Switch to Assembly 2 workbench

Assemble base model from parts created using Array tool
Maybe a macro to define “bays (“wedges”?) long x bays (wedges) wide.

Then I do what I always used to do - hand it over to the engineers to do the serious stuff in the FEM workbench. ;)

Before I start ——- Am I on the right track??

EDIT: - apologies - I overlooked your reference to the curves workbench (I did not know about it) - it looks interesting. I have made a start on the sketcher/spreadsheet geometry but I will investigate the curve workbench in more detail before proceeding.
Last edited by Laurie Hartley on Mon Sep 13, 2021 12:09 pm, edited 1 time in total.
cad1234
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Re: Request for help meshing and and analysing a part

Post by cad1234 »

Is it possible to simulate thermal expansion in our model with FC-FEM, including the associated structure internal stresses and the influence to the reaction forces, if we fix all supports x,y z for example (just as test and to see the differences between different kind of support fixings and the influence to max normal stress/force and to the reaction forces, depending on the thermal expansion related to the temperature)?

Lets say rising the temperature from a reference temperature of 20 degree up to 60 degree or down to -20 degree?

Here is a screenshot from Mastan with all supports fixed x,y,z. (which of course is not a good idea for the real construction ;) ..only for testing the function) and delta temperature +40 degree.
With the same external load as before, the max element force is now in the lower chord and rises up to -103 KN, reaction forces are corresponding high..
displacement upward 2.3 mm, buckle 0.76

However, see this more as a system check with the target, to minimize thermal effects, find own failures, room for improvements
and how this function works..

Hope, made all right with Mastan using "temperature effects"..??
Attachments
fix deflection shape.jpg
fix deflection shape.jpg (370.83 KiB) Viewed 27710 times
Mastan Fixing.jpg
Mastan Fixing.jpg (333.93 KiB) Viewed 27727 times
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bernd
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Re: Request for help meshing and and analysing a part

Post by bernd »

offtopic:

updated BOLTS no new profiles an no changes in gui, but lots of stuff under the hut. Thus would you guys update BOLTSFC and give some feedback if something does not work as expected.

@Laurie:
I do not have forgotten the profiles you sent to me. I will integrate them hopefully not far from today ...
cad1234
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Re: Request for help meshing and and analysing a part

Post by cad1234 »

bernd wrote: Mon Sep 13, 2021 8:41 pm
Update successfull and works!

OS: Windows 10 Version 2004
Word size of FreeCAD: 64-bit
Version: 0.20.25645 (Git)
Build type: Release
Branch: master
Hash: 37d9757399b4c2ec30318eb88d7cd7c508246345
Python version: 3.8.6+
Qt version: 5.15.2
Coin version: 4.0.1
OCC version: 7.5.0
Locale: German/Germany (de_DE)
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