Applying a torque using FORCE and TRANSFORM constraints

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KgoaOT
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Applying a torque using FORCE and TRANSFORM constraints

Post by KgoaOT »

The transform constraint has been extended to allow for applied forces to be transformed into in a new coordinate system.

- start FreeCAD --> StartWB --> load "TorqueExample" file
TorqueExample.fcstd
(738.21 KiB) Downloaded 255 times
Essentially in this a example, a force is applied to the external surface of a pipe and then the coordinate system of the external surface is transformed into a cylindrical coordinate system. The direction of the applied force is in the global Y direction (this corresponds to the Tangential direction after the coordinate transformation).

Depicted below is pipe showing no displacement:
WithoutDisplacement.PNG
WithoutDisplacement.PNG (44.07 KiB) Viewed 4009 times
Depicted below is pipe showing the displacement:
WithDisplacement.PNG
WithDisplacement.PNG (48.9 KiB) Viewed 4009 times
The new branch can be found here:
https://github.com/makkemal/FreeCAD/tre ... traint/src
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bernd
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Re: Applying a torque using FORCE and TRANSFORM constraints

Post by bernd »

works great ! Added to my development branch for next FEM pull request.

https://github.com/berndhahnebach/FreeC ... meshregion
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Re: Applying a torque using FORCE and TRANSFORM constraints

Post by bernd »

I wanted to calculate the results myself. For this I used a simpler example.

full cylinder
lenght = 1000 m
diameter = 60 mm
G = 81000 MPa --> E = 210600 MPa
Twist (delta) = 0.4 degree

twisting moment (torsional moment):
Mt = (delta_in_rad x Pi X r^4 x G) / (2 x l) = (delta x Pi^2 X r^4 x G) / (180 x 2 x l)
Mt = (0.4 x 3.14^2 x 30^4 x 81000) / (180 x 2 x 1000)
Mt = 71.80e4 Nmm

max twisted stress:
max tau = 2 x Mt / (Pi x r^3)
max tau = (2 x 78.80e4) / (3,14 x 30^3)
max tau = 17.0 N/mm2

Force = 71.8 N/mm / 30 mm = 29933.33 N on top edge.

max deformation x = max deformation y = max deformation = 30 mm sin 0.4 degree = 0.209 mm

attached is the file ...


torque_simple_1.FCStd
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screen.png
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Re: Applying a torque using FORCE and TRANSFORM constraints

Post by bernd »

max Tresca stress is red in the bar and constant around 18.08 N/mm2 similar to max tau = 17.0 N/mm2 from the math

screen1.png
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Re: Applying a torque using FORCE and TRANSFORM constraints

Post by bernd »

My mechanical knowledge about twisted steel structures is limited. :oops: Is someone able to do the math for the example of the first post?
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Re: Applying a torque using FORCE and TRANSFORM constraints

Post by bernd »

bernd wrote: Wed Jul 22, 2020 10:53 am My mechanical knowledge about twisted steel structures is limited. :oops: Is someone able to do the math for the example of the first post?
thschrader wrote: :bell:
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Re: Applying a torque using FORCE and TRANSFORM constraints

Post by bernd »

up
user1234
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Re: Applying a torque using FORCE and TRANSFORM constraints

Post by user1234 »

I wanted to make a test case, but gmsh 4.7.1 and 4.8.4 does not seem to work anymore. Could it be that the FEM workbench does not work with VTK9? I got a ton of errors.


gmsh info:

Code: Select all

file found: /usr/bin/gmsh
Gmsh: StdOut:
Version       : 4.7.1
License       : GNU General Public License
Build OS      : Linux64-sdk
Build date    : 20210302
Build host    : debian-build-farm
Build options : 64Bit ALGLIB Bamg Blossom DIntegration Dlopen DomHex Eigen[system] Fltk GMP Gmm[system] Hxt Jpeg Kbipack LinuxJoystick MathEx Mesh Metis[system] Mpeg Netgen ONELAB ONELABMetamodel OpenCASCADE OpenCASCADE-CAF OpenGL OpenMP OptHom Parser Plugins Png Post QuadTri Solver TetGen/BR Voro++[system] Zlib
FLTK version  : 1.3.5
OCC version   : 7.5.1
Packaged by   : nobody
Web site      : https://gmsh.info
Issue tracker : https://gitlab.onelab.info/gmsh/gmsh/issues

FreeCAD info:

Code: Select all

OS: Debian GNU/Linux 11 (bullseye) (X-Cinnamon/lightdm-xsession)
Word size of FreeCAD: 64-bit
Version: 0.20.25192 (Git)
Build type: Release
Branch: master
Hash: f1db4bc83e8946991008dfccaae6af92d51a4347
Python version: 3.9.2
Qt version: 5.15.2
Coin version: 4.0.0
OCC version: 7.5.1
Locale: English/United States (en_US)
VTK version: 9.0.1+dfsg1-8

error massages:

Code: Select all

  ElementDimension: 3
  No Group meshing for analysis.
  /tmp/fcfem_94otf124/Body_Geometry.brep
  /tmp/fcfem_94otf124/Body_Mesh.unv
  /tmp/fcfem_94otf124/shape2mesh.geo
  /usr/bin/gmsh
2021-07-06 18:18:14.986 (  28.967s) [         B01F640]       vtkCellArray.cxx:551    ERR| vtkCellArray (0x562a87f80390): Invalid location.
.....
arround 160000 times
.....
2021-07-06 18:20:16.778 ( 150.758s) [         B01F640]       vtkCellArray.cxx:551    ERR| vtkCellArray (0x562a85db2fe0): Invalid location.
  New mesh was added to the mesh object.
Clean run of Gmsh


Greetings
user1234
Attachments
test32_FEM_torque.FCStd
(35.03 KiB) Downloaded 26 times
0.png
0.png (330.31 KiB) Viewed 2136 times
user1234
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Re: Applying a torque using FORCE and TRANSFORM constraints

Post by user1234 »

I recompile FreeCAD with VTK7. Yes, VTK9 seems to be the issue. Works flawless with:

Code: Select all

OS: Debian GNU/Linux 11 (bullseye) (X-Cinnamon/lightdm-xsession)
Word size of FreeCAD: 64-bit
Version: 0.20.25192 (Git)
Build type: Release
Branch: master
Hash: f1db4bc83e8946991008dfccaae6af92d51a4347
Python version: 3.9.2
Qt version: 5.15.2
Coin version: 4.0.0
OCC version: 7.5.1
Locale: English/United States (en_US)
VTK version: 7.1.1+dfsg2-8
Attachments
0.png
0.png (344.09 KiB) Viewed 2120 times
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bernd
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Re: Applying a torque using FORCE and TRANSFORM constraints

Post by bernd »

but gmsh meshing does not depend on vtk ?!
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