Dear Yves, Thank you very much for your reply. There’s still something I don’t understand from your explanation.
The equation q” = D*(Tair-T) = k*grad(T).n is the specific heat flow through a unitary surface [ex. W/m2]. If I multiply epsilon only to the rhs term, then I change the conduction heat flow since the surface is epsilon wide in one direction, but for the heat flow equilibrium I should multiply also the lhs term by epsilon, since also the convection heat flow pass throw the same epsilon wide surface, and so the two epsilon disappear for simplification. Also, I cannot see k in both your source_term and Fourier_Robin bricks input data, but k is part of the surface heat flow equations. These are the reasons why I’d replace D/epsilon with D/k in your implementation. Thank you in advance for your kind feedback. Regards, Lorenzo > Il giorno 29 apr 2021, alle ore 19:44, Yves Renard <yves.ren...@insa-lyon.fr> > ha scritto: > > > 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 http://getfem.org/python/cmdref_Model.html 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, > > Yves > > > > 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 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.ren...@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.ren...@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 >>> >>> --------- >>> > > -- > > Yves Renard (yves.ren...@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 > > --------- >
