Understanding the Calculix .inp

About the development of the FEM module/workbench.

Moderator: bernd

mainengineer
Posts: 1
Joined: Mon Feb 25, 2019 7:10 pm

Understanding the Calculix .inp

Postby mainengineer » Mon Feb 25, 2019 7:26 pm

Hi,

I'm using FreeCad 0.17 on Ubuntu 18.04 LTS.
I am doing an analysis with pressure on faces of an airfoil. I applied the pressure on the faces and wrote the analysis to the .inp
On a particular face, I applied a pressure of 0.258 kPa.
When looking at the .inp file, I see below:

***********************************************************
** Element + CalculiX face + load in [MPa]
** written by write_constraints_pressure function
** FemConstraintPressure_root_LE
*DLOAD
** FemConstraintPressure: face load
86423,P4,0.000258
86928,P2,0.000258
86946,P1,0.000258
86991,P2,0.000258
87013,P4,0.000258
87039,P4,0.000258
87044,P4,0.000258
(and so on).


When I sum up all the pressures/loads (in the last column: 0.000258), I get 0.648, which I understand is 0.648 MPa (or 648 kPa).
I don't understand how this could be.
If these were just nodal loads, it wouldn't be right because that should sum up to 2.26 N.

Can someone clear this up for me?
ickby
Posts: 2912
Joined: Wed Oct 05, 2011 7:36 am

Re: Understanding the Calculix .inp

Postby ickby » Wed Feb 27, 2019 7:01 am

moved to FEM forum
User avatar
bernd
Posts: 8205
Joined: Sun Sep 08, 2013 8:07 pm
Location: Zürich, Switzerland

Re: Understanding the Calculix .inp

Postby bernd » Wed Feb 27, 2019 7:56 am

for pressure it is easy. You applied 0.258 kPa, your inp file is in MPa. As you will know 0.258 kPa = 0.000258 MPa. Thus in the inp file there is 0.000258 MPa on all elementfaces.

hope that helps bernd

BTW: welcome to the world of FreeCAD FEM :)
User avatar
bernd
Posts: 8205
Joined: Sun Sep 08, 2013 8:07 pm
Location: Zürich, Switzerland

Re: Understanding the Calculix .inp

Postby bernd » Wed Feb 27, 2019 7:58 am

ConstraintPressure = DLOAD in ccx inpfile, which is applied on mesh element faces in MPa

ConstraintForce = CLOD in ccx inpfile, which is applied on mesh element nodes in N
User avatar
bernd
Posts: 8205
Joined: Sun Sep 08, 2013 8:07 pm
Location: Zürich, Switzerland

Re: Understanding the Calculix .inp

Postby bernd » Wed Feb 27, 2019 10:53 am

mainengineer wrote:
Mon Feb 25, 2019 7:26 pm
** Element + CalculiX face + load in [MPa]
...
86423,P4,0.000258
oder noch deutlicher ...

Code: Select all

Element, CalculiX face, load in [MPa]
86423,P4,0.000258
User avatar
Kunda1
Posts: 5134
Joined: Thu Jan 05, 2017 9:03 pm

Re: Understanding the Calculix .inp

Postby Kunda1 » Thu Feb 28, 2019 9:56 pm

Also OP should probably use 0.18_pre when for FEM related tasks
Want to contribute back to FC? Checkout:
#lowhangingfruit | Use the Source, Luke. | How to Help FreeCAD | How to report FC bugs and features