Re: Using Getfem for a flash-butt welding simulation

[Lorenzo Ferro]

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 
example.

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.

Questions:

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.
Lorenzo 



> Il giorno 20 apr 2021, alle ore 11:02, Yves Renard <Yves.Renard@insa-lyon.fr> 
> 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 
> http://getfem.org/tutorial/index.html on the thermo-elastic problem.
> 
> Best regards,
> 
> Yves
> 
> 
> 
> 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.
>> 
>> Questions:
>> i) can GetFEM be convenient for the implementation of the above mentioned 
>> problem?
>> ii) does GetFEM allows to implement all of the above features?
>> iii) principally, can you give me guidance about the needed GetFEM native 
>> functions?
>> 
>> 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.
>> Lorenzo
> 
> 
> -- 
> 
>  Yves Renard (Yves.Renard@insa-lyon.fr)       tel : (33) 04.72.43.87.08
>  INSA-Lyon
>  20, rue Albert Einstein
>  69621 Villeurbanne Cedex, FRANCE
>  http://math.univ-lyon1.fr/~renard
> 
> ---------
>