> > > > //Real Sinit = Mathr::PI * std::pow( std::min(Da,Db) , 2); > > > > I am wondering at which point it was commented -- it must have lead to > > packing stiffness change by that factor 1.57. > > > > > My bad habit of taking one file, changing what I like, and keeping some > old commented parts in case I want to know what was there before (I > obviously coded the "basic" version starting from the law inherited from > SDEC, and actually I think it was my first coding in Yade!). > For sure I'll remove that next time I commit a change in this file. > That would be a problem, but I see no solution. The factor is 1 > currently, couldn't be simpler, and _should not_ be modified. Everybody > should know (i.e. I'll have to document that) that in this law kn > between spheres will be E.d. The solution is to define things even if the definition is arbitrary.
To me it seems as if you were saying: Oh yes, at one point I just removed Sinit from Ip2_FM_FM_FP, because it is arbitrary anyway. But in any case I don't want people to do the same. > > 4. let us take (2r) as lengthOfContact (same radii, for simplicity) (the > > most obvious choice) > Ok, we converge here. The thing is, in theorems of dimensional analysis > (Buckingam), you really put the basic physical quantities, and size of > particles is really the fundamental size in the system, not just an > approximation of contact "length". My point was stronger. If you have particles of different radius, you will probably define contact-level "reference distance" by summing their radii. That can be different for each contact and is not just property of the system. I am reasoning for 2 particles in contact here. > > 5. there is a thing Material::young [Pa] (note E below), defined in > > Material class; we take is as the value of Young's modulus [Pa] (the > > most obvious choice again) > No. E is not "Young" modulus, it is the stiffness of contacts. It is > called young because again, I adapted existing code the lazy way, and > also because we have same data class for different laws, where the > meaning of the data is not the same in each law. > For a similar reason, I renamed Poisson -> KsDivKs some time ago in > preprocessors. I can't (or can I?) change the name in the data class though. Whatever you call it, it has dimension of stiffness (even you don't imagine stiffness of balls, which I tend to do somehow). > > > 6. let's call this b[m²] "contact area", since it is area related to the > > contact (pure terminology thing) > > > > 7. the current equation in yade is: kn=Er=E(2r²)/(2r), so "contact area" > > b[m²]=2r². Contrary to other obvious choices (4,5), it is very much > > non-obvious what is the geometrical meaning of 2r². > Irrelevant for me : no area and no length. As soon as you define length of a particular contact (not some average length dimension characterizing the packing -- see above), you might define the area as well...? > However, adopting your philosophy (which is as correct as mine I think), > I could say that contact area is obviously more than the projection of > the grain, since there is void around grains which should be associated > to each interaction (the sum of interaction "volumes" should be the > total volume of the packing right?). I wanted to avoid this volume discussion, because this pulls in packing configuration and leads to nowhere. For that reason I would not want having sum of interaction volumes equal to packing volume, since that is in general impossible. Reasoning about 2 spheres is simpler. Length and area. I see it is useless to continue. Howgh. _______________________________________________ Mailing list: https://launchpad.net/~yade-dev Post to : [email protected] Unsubscribe : https://launchpad.net/~yade-dev More help : https://help.launchpad.net/ListHelp
