## 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

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: 2961
Joined: Wed Oct 05, 2011 7:36 am

### Re: Understanding the Calculix .inp

moved to FEM forum
bernd
Posts: 9862
Joined: Sun Sep 08, 2013 8:07 pm
Location: Zürich, Switzerland

### Re: Understanding the Calculix .inp

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
bernd
Posts: 9862
Joined: Sun Sep 08, 2013 8:07 pm
Location: Zürich, Switzerland

### Re: Understanding the Calculix .inp

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
bernd
Posts: 9862
Joined: Sun Sep 08, 2013 8:07 pm
Location: Zürich, Switzerland

### Re: Understanding the Calculix .inp

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``````
Kunda1
Posts: 7370
Joined: Thu Jan 05, 2017 9:03 pm

### Re: Understanding the Calculix .inp

Also OP should probably use 0.18_pre when for FEM related tasks
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