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>Hi Bruno, > > >thanks for your suggestions, I will try to put them in place. > > > >Some further considerations/corrections: > > >For small range of final porosity I >was meaning having a fixed PSD and a constant friction angle. I was wrong in my >previous message, the porosity changes if I change the friction angle. > >Question: which value of friction angle do you use during the compaction phase? >Should be the final one or should be lower than that? Would it be possible to >run the analysis with a value equal to zero? > > >One important point regarding >the unbalanced force. I agree with you that the value of unbalanced force >should come down just cycling (the time step is not zero) but that doesn't >happen in the way I should expect. For instance in your code, once you choose >the expansion method, after each expansion you are actually cycling without >expanding for a certain number of iterations (look at the bool >isARadiusControlIteration), so I would expect that the unbalanced force comes >down during this process (of course before I have to get some stresses at the >walls) but it remains always around 1 until the stresses on the walls become >higher. I would expect that also at a small level of stress on the walls, this >value of unbalanced force remains quite low. I suppose that the reason you (if >it were you) put the bool isARadiusControlIteration relays in the concept of >maintaining a quasi-static equilibrium as much as possible during the analysis. >To make a summary I see that the unbalanced force reaches low values (say 0.07 >or whatever) only after having compressed the packing. Am I escaping something? > > > >Thanks, Chiara > > > > >>---- Messaggio originale---- >>Da: bruno.chareyre@xxxxxxxx. >fr >>Data: 19/01/2010 14.57 >>A: <yade-users@xxxxxxxxxxxxxxxxxxx> >>Ogg: Re: [Yade- >users] Porosity >> >>Hi, >>> I would need your help concerning the Triaxial. Since >I need a >>> specific value of final porosity, I am trying to do something in >your code but >>> without success (BTW, I DON'T want to modify your code, if it >will work I will >>> manage to add a flag or something like that). >>> >>No >problem. Just keep me updated so I know what happens in files. >>> so basically >in the line >>> (1) it is like saying "cycle" without expanding if the value of >Unb force is >>> too high. Unfortunately "cycling" doesn't help (why? Should >it?), the computed >>> unbalanced force is always very high and around 1. >>> > >>There is nothing "bad" in keeping a constant radius until unbF is small. >> If >the unbalanced force does not approach 0 with cycles "_supposed to >>be_" doing >nothing else than dynamic integration, there is clearly >>something wrong. The >timestep is not 0? >> >>The only problem I see in your approach is you force the >porosity you >>want, which will result in very big overlaps and high stress >most >>likely. The porosity should be the result of a "realistic" packing > >>evolution. >> >>> Could you give me any >>> suggestions or directions how to do >that? I mean, how to fix the value of final >>> porosity.. >>> >>Keep a >constant stress and decrease friction a little bit at each step. >>The packing >will self-reorganize, and porosity will decrease. Save the >>packing state when >porosity value cross the value you want. >>You can use this function to modify >friction : >> >>void TriaxialCompressionEngine::setContactProperties(Scene * ncb, >Real >>frictionDegree)//I really mean "use", not copy ;) >> >>All you have to do >is a loop that will keep assigning frictionDegree >>each n=~10 steps, with a >decreased frictionDegree each time. >>Note that big porosity variations usually >occur with small values of >>friction, in the range 0° < f < 5°. >> >>> I have >got that having a specific PSD and a >>> friction angle we can get only one >possible value of final porosity (or a very >>> small range of it) and that's >true with the DEM (cause we are dealing with >>> spheres and not irregular >shapes) but to me it is always possible to say that >>> for the same PSD I >would like to run the Triaxial with an higher porosity >>> (higher than that >maximum dense packing I get with this method either with >>> compaction or >expansion). >>> >>> >>What is small range? I tried that after your message and >I got different >>poro from different friction. >> >>> Merci beaucoup. >>> >>> > >>Prego. >> >>Bruno >> >>_______________________________________________ >>Mailing >list: https: //launchpad.net/~yade-users >>Post to : yade-users@lists. >launchpad.net >>Unsubscribe : https://launchpad.net/~yade-users >>More help : >https: //help.launchpad.net/ListHelp >> > >
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