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Re: Using Getfem for a flash-butt welding simulation

From: Yves Renard
Subject: Re: Using Getfem for a flash-butt welding simulation
Date: Thu, 29 Apr 2021 19:44:24 +0200
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Dear Lorenzo,

You are right. The boundary conditions of the thermal problem do not follow what is announced and  the equation on the top and bottom edges are the one you indicate but with a small correction (D*(Tair-T) = epsilon*k*grad(T).n). The term epsilon comes from the fact that the temperature is assumed constant in the thickness. And yes, the Fourier_Robin_brick works only on the stiffness matrix (see for a short description). Of course, it is possible to use directly GWFL to describe the terms instead of using the Fourier_Robin_bricks, these is equivalent.

And so concerning the question 1, it seems to me that the terms are corrects (integration of the equation in the thickness).

Best regards,


Le 26/04/2021 à 16:56, Lorenzo Ferro a écrit :
Dear Yves,

Thank you for your reply, thanks to which  I’ve started studying the tutorials, 
and I’ve a question related to the Thermo-elastic and electrical coupling 

Looking at the python file I can read that the convection coefficient D is 
applied to all the surfaces  except the holes and the left surface (in my 
opinion it is not applied to the right surface too, can you confirm?).

Then I see that Fourier_Robin_brick and source_term_brick are used to impose 
the convection condition the Top and Bottom edges.
I suppose that the equation to be included is something like q” = D*(Tair-T) = 
k*grad(T).n => grad(T).n + D/k*T = D/k*Tair

The left side term is supposed to be assembled via the Fourier_Robin_brick 
whereas the right side term via the source_term_brick.


1) Looking at the python file I see that you calculate D/epsilon and 
D*Tamb/epsilon where epsilon is the plate thickness. Is this an error and we 
should replace epsilon with k?

2) Does the Fourier_Robin_brick work only on the stiffness matrix?

I’m asking because the usage of these bricks, their convection equations and 
relevant assembly, are not mentioned/explained in the tutorial.

Thank you very much.

Il giorno 20 apr 2021, alle ore 11:02, Yves Renard <> 
ha scritto:

Dear Lorenzo,

Through its Python interface, GetFEM offers generic tools for complex modeling 
and evolutionary equations, even non-linear ones, can be taken into account 
using the weak form language (GWFL). Practical tools for managing meshes, 
regions in these meshes, meshes cut by level-sets complete the system, as well 
as post-processing functions. These tools allow to build complex static or 
transient codes, but of course, GetFEM is above all a toolbox, not a ready-made 
code allowing to do simulations quickly.

Examples are given in the interface/src/python directory on basic modeling. In 
particular, it may be interesting to follow the tutorial example on the thermo-elastic problem.

Best regards,


On 19/04/2021 18:48, Lorenzo Ferro wrote:
Dear All,

I need to simulate a flash-butt welding process, where two steel bars are 
welded together, head to head, applying electrical current (flash welding) 
until the bar heads reach the melting temperature, eventually pushing them 
together to make the joint.
During this process, some metal reaches the melting point (almost evaporation) 
and bursts away, so some metal is lost during the heating phase and the two 
bars must be brought closer together to keep the current flowing and the 
process going on.

So the model would include (at least):
A) a transient thermal simulation with external convection and radiation
B) internal heat generated by joule effect
C) non-linear material properties
D) elements removal from the simulation once the melting temperature has been 
reached, with consequent change of boundary elements on the heads of the bars
E) moving the bars closer, step-by-step, to restore the surface contact and 
current flow (no need of a real contact function, contact can be estimated 
based on the boundary elements distance, since some current can flow also when 
the faces are enough close).

To do so I've two options:
1) making a simulation model with a programming language like Python, etc...
2) exploring the usage of the GetFEM library. At the end of the work, a new 
scientific article will follow. The simulation is only the first part, the 
article will also include a part related to the automation control of the 
welding process.

i) can GetFEM be convenient for the implementation of the above mentioned 
ii) does GetFEM allows to implement all of the above features?
iii) principally, can you give me guidance about the needed GetFEM native 

I've never used GetFEM before but I'd like to learn how to use it, also in view 
of other future projects and publications.

Thank you in advance.


  Yves Renard (       tel : (33)
  20, rue Albert Einstein
  69621 Villeurbanne Cedex, FRANCE



  Yves Renard (       tel : (33)
  20, rue Albert Einstein
  69621 Villeurbanne Cedex, FRANCE


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