Electrostatic results not clear

About the development of the FEM module/workbench.

Moderator: bernd

Post Reply
AlbertoR
Posts: 8
Joined: Mon May 29, 2023 7:50 am

Electrostatic results not clear

Post by AlbertoR »

Dear all,
I'm trying to use the FEM workbench in FC with very basic examples to make practice but I can not understand how to manage the constraints.

For instance I'm exploiting the two balls capacitance example.
https://wiki.freecad.org/FEM_Example_Ca ... _Two_Balls
If I set one of the two balls to 1 V and the other to -1 V I expect that the potential value at the surface is going to be +1 V and -1 V respectively. But I will found always positive values and in particular the second ball will be close to the background potential as if that ball has the Far Field constraint (Which should be 0V, although in the example is 1V too).

I hope to be clear enough.

Is this happening just to me? I'm reading the results in a wrong way?

Thanks in advance.

p.s.
My system

Code: Select all

OS: Windows 10 Version 2009
Word size of FreeCAD: 64-bit
Version: 0.20.2.29603 (Git)
Build type: Release
Branch: releases/FreeCAD-0-20
Hash: 930dd9a76203a3260b1e6256c70c1c3cad8c5cb8
Python 3.8.10, Qt 5.15.2, Coin 4.0.1, Vtk 8.2.0, OCC 7.6.3
Locale: Italian/Italy (it_IT)
AlbertoR
Posts: 8
Joined: Mon May 29, 2023 7:50 am

Re: Electrostatic results not clear

Post by AlbertoR »

I try to show a screenshot with the unclear results.
Image

As you can see in the left there is the contraint for one of two balls, it is set to -1V but in the plot there is no negative potential.

This result is straightforward from the two balls capacitance example for the Elmer solver. I just changed the constraints.

Alberto
RichB2k
Posts: 9
Joined: Thu Sep 08, 2022 8:50 pm

Re: Electrostatic results not clear

Post by RichB2k »

Hello,

The example of calculating the capacitance of two balls uses a feature of Elmer that sets the potential of one body at a time to 1.0 volts, while holding all other bodies at a potential of 0.0 volts. This allows calculation of a capacitance matrix. To disable this mode of operation, change the setting of 'Calculate Capacitance Matrix' to false. Then setting the potential to -1.0 volts will work.

Let us know how this works for you.

Rich.
AlbertoR
Posts: 8
Joined: Mon May 29, 2023 7:50 am

Re: Electrostatic results not clear

Post by AlbertoR »

Thank you,
Very easy explanation! And finally it works exactly as you described.

My apologies for such a basic question...
Post Reply