Re: [Yade-dev] : GenericSpheresContact
Everyone on holidays already? Well I am still wondering why for the calculation of the stiffness of a sphere and a facet the radius of the facet is assumed to be twice the radius of the sphere. This is basically the value comming from GenericSpheresContact. In my opinion it doesn't make sense. The facet can be seen as a sphere with radius infinity. So if we take the harmonic average (as it is done in Ip2_FrictMat_FrictMat_FrictPhys ) considering e.g. rb-infinity the stiffnesses become kn = 2*Ea*ra and ks = 2*Ea*ra*Va. You agree? If so I could commit the changed code. Please let me know. On Sun, 11 Dec 2011 06:38:35 PM Klaus Thoeni wrote: Hi Guys, what value for refR does the GenericSpheresContact return for a facet? By introducing TRVAR2( Ra, Rb ) e.g. in Ip2_FrictMat_FrictMat_FrictPhys::go it seems if a sphere is intersecting with a facet the refR value for the facet is just 2*refR of the sphere. Is this true? And when yes, what's the reason? It's fundamental for kn and ks, isn't it? Thanks, Klaus ___ Mailing list: https://launchpad.net/~yade-dev Post to : yade-dev@lists.launchpad.net Unsubscribe : https://launchpad.net/~yade-dev More help : https://help.launchpad.net/ListHelp ___ Mailing list: https://launchpad.net/~yade-dev Post to : yade-dev@lists.launchpad.net Unsubscribe : https://launchpad.net/~yade-dev More help : https://help.launchpad.net/ListHelp
Re: [Yade-dev] : GenericSpheresContact
On 13 December 2011 10:35, Klaus Thoeni klaus.tho...@gmail.com wrote: Everyone on holidays already? Well I am still wondering why for the calculation of the stiffness of a sphere and a facet the radius of the facet is assumed to be twice the radius of the sphere. I can say that this is what is generally assumed in the current literature but I cannot say more as I wonder is only an assumption. Chiara This is basically the value comming from GenericSpheresContact. In my opinion it doesn't make sense. The facet can be seen as a sphere with radius infinity. So if we take the harmonic average (as it is done in Ip2_FrictMat_FrictMat_FrictPhys ) considering e.g. rb-infinity the stiffnesses become kn = 2*Ea*ra and ks = 2*Ea*ra*Va. You agree? If so I could commit the changed code. Please let me know. On Sun, 11 Dec 2011 06:38:35 PM Klaus Thoeni wrote: Hi Guys, what value for refR does the GenericSpheresContact return for a facet? By introducing TRVAR2( Ra, Rb ) e.g. in Ip2_FrictMat_FrictMat_FrictPhys::go it seems if a sphere is intersecting with a facet the refR value for the facet is just 2*refR of the sphere. Is this true? And when yes, what's the reason? It's fundamental for kn and ks, isn't it? Thanks, Klaus ___ Mailing list: https://launchpad.net/~yade-dev Post to : yade-dev@lists.launchpad.net Unsubscribe : https://launchpad.net/~yade-dev More help : https://help.launchpad.net/ListHelp ___ Mailing list: https://launchpad.net/~yade-dev Post to : yade-dev@lists.launchpad.net Unsubscribe : https://launchpad.net/~yade-dev More help : https://help.launchpad.net/ListHelp ___ Mailing list: https://launchpad.net/~yade-dev Post to : yade-dev@lists.launchpad.net Unsubscribe : https://launchpad.net/~yade-dev More help : https://help.launchpad.net/ListHelp
Re: [Yade-dev] : GenericSpheresContact
The question was already asked before, for boxes : http://www.mail-archive.com/yade-users@lists.launchpad.net/msg00269.html But the answer will not learn you so much... ___ Mailing list: https://launchpad.net/~yade-dev Post to : yade-dev@lists.launchpad.net Unsubscribe : https://launchpad.net/~yade-dev More help : https://help.launchpad.net/ListHelp
Re: [Yade-dev] : GenericSpheresContact
But the answer will not learn you so much... Except that it suggests that definition of a radius should be useless for facets ?.. (I never used facets personly) ___ Mailing list: https://launchpad.net/~yade-dev Post to : yade-dev@lists.launchpad.net Unsubscribe : https://launchpad.net/~yade-dev More help : https://help.launchpad.net/ListHelp
Re: [Yade-dev] : GenericSpheresContact
I have no explanation for the 2*refR other than that: - there was 2*refR in box-sphere interactions a while ago (I don't know why), - facet-sphere interactions inherited this 2* from box-sphere interactions (my assumption). The thing is I changed that in box-sphere, and now refR of a box is the radius of the sphere. I can at least invoke symmetry to justify this. Infinite radius could be justified too, the problem is it would give contacts twice stiffer than the contacts between spheres, hence smaller timestep, without clear advantage. Bruno On 13/12/11 11:35, Klaus Thoeni wrote: Everyone on holidays already? Well I am still wondering why for the calculation of the stiffness of a sphere and a facet the radius of the facet is assumed to be twice the radius of the sphere. This is basically the value comming from GenericSpheresContact. In my opinion it doesn't make sense. The facet can be seen as a sphere with radius infinity. So if we take the harmonic average (as it is done in Ip2_FrictMat_FrictMat_FrictPhys ) considering e.g. rb-infinity the stiffnesses become kn = 2*Ea*ra and ks = 2*Ea*ra*Va. You agree? If so I could commit the changed code. Please let me know. On Sun, 11 Dec 2011 06:38:35 PM Klaus Thoeni wrote: Hi Guys, what value for refR does the GenericSpheresContact return for a facet? By introducing TRVAR2( Ra, Rb ) e.g. in Ip2_FrictMat_FrictMat_FrictPhys::go it seems if a sphere is intersecting with a facet the refR value for the facet is just 2*refR of the sphere. Is this true? And when yes, what's the reason? It's fundamental for kn and ks, isn't it? Thanks, Klaus ___ Mailing list: https://launchpad.net/~yade-dev Post to : yade-dev@lists.launchpad.net Unsubscribe : https://launchpad.net/~yade-dev More help : https://help.launchpad.net/ListHelp ___ Mailing list: https://launchpad.net/~yade-dev Post to : yade-dev@lists.launchpad.net Unsubscribe : https://launchpad.net/~yade-dev More help : https://help.launchpad.net/ListHelp -- ___ Bruno Chareyre Associate Professor ENSE³ - Grenoble INP 11, rue des Mathématiques BP 46 38402 St Martin d'Hères, France Tél : +33 4 56 52 86 21 Fax : +33 4 76 82 70 43 ___ Mailing list: https://launchpad.net/~yade-dev Post to : yade-dev@lists.launchpad.net Unsubscribe : https://launchpad.net/~yade-dev More help : https://help.launchpad.net/ListHelp
Re: [Yade-dev] : GenericSpheresContact
Hi all, thanks for the active discussion. So I guess we just leave it as it is and use 2 for boxes and facets if this is the usual assumption. No problem. And introducing r-infinity ignores the material properties of the facet, so I guess my suggestion was not the best one however mathematically correct ;-) Thanks again! Klaus On Tue, 13 Dec 2011 10:10:08 PM Bruno Chareyre wrote: I have no explanation for the 2*refR other than that: - there was 2*refR in box-sphere interactions a while ago (I don't know why), - facet-sphere interactions inherited this 2* from box-sphere interactions (my assumption). The thing is I changed that in box-sphere, and now refR of a box is the radius of the sphere. I can at least invoke symmetry to justify this. Infinite radius could be justified too, the problem is it would give contacts twice stiffer than the contacts between spheres, hence smaller timestep, without clear advantage. Bruno On 13/12/11 11:35, Klaus Thoeni wrote: Everyone on holidays already? Well I am still wondering why for the calculation of the stiffness of a sphere and a facet the radius of the facet is assumed to be twice the radius of the sphere. This is basically the value comming from GenericSpheresContact. In my opinion it doesn't make sense. The facet can be seen as a sphere with radius infinity. So if we take the harmonic average (as it is done in Ip2_FrictMat_FrictMat_FrictPhys ) considering e.g. rb-infinity the stiffnesses become kn = 2*Ea*ra and ks = 2*Ea*ra*Va. You agree? If so I could commit the changed code. Please let me know. On Sun, 11 Dec 2011 06:38:35 PM Klaus Thoeni wrote: Hi Guys, what value for refR does the GenericSpheresContact return for a facet? By introducing TRVAR2( Ra, Rb ) e.g. in Ip2_FrictMat_FrictMat_FrictPhys::go it seems if a sphere is intersecting with a facet the refR value for the facet is just 2*refR of the sphere. Is this true? And when yes, what's the reason? It's fundamental for kn and ks, isn't it? Thanks, Klaus ___ Mailing list: https://launchpad.net/~yade-dev Post to : yade-dev@lists.launchpad.net Unsubscribe : https://launchpad.net/~yade-dev More help : https://help.launchpad.net/ListHelp ___ Mailing list: https://launchpad.net/~yade-dev Post to : yade-dev@lists.launchpad.net Unsubscribe : https://launchpad.net/~yade-dev More help : https://help.launchpad.net/ListHelp ___ Mailing list: https://launchpad.net/~yade-dev Post to : yade-dev@lists.launchpad.net Unsubscribe : https://launchpad.net/~yade-dev More help : https://help.launchpad.net/ListHelp
Re: [Yade-dev] : GenericSpheresContact
thanks for the active discussion. So I guess we just leave it as it is and use 2 for boxes and facets if this is the usual assumption. It is 1 for boxes now (and good like this). I didn't know 2 was usual. I would make it 1 for facet as well, but since I'm not using facets a lot, I can't decide for others. Bruno ___ Mailing list: https://launchpad.net/~yade-dev Post to : yade-dev@lists.launchpad.net Unsubscribe : https://launchpad.net/~yade-dev More help : https://help.launchpad.net/ListHelp
Re: [Yade-dev] : GenericSpheresContact
Well if it is 1 for boxes now I don't see any reason why it should be 2 for facets. Or is there a reason? Any other opinions? On Tue, 13 Dec 2011 10:46:31 PM Bruno Chareyre wrote: thanks for the active discussion. So I guess we just leave it as it is and use 2 for boxes and facets if this is the usual assumption. It is 1 for boxes now (and good like this). I didn't know 2 was usual. I would make it 1 for facet as well, but since I'm not using facets a lot, I can't decide for others. Bruno ___ Mailing list: https://launchpad.net/~yade-dev Post to : yade-dev@lists.launchpad.net Unsubscribe : https://launchpad.net/~yade-dev More help : https://help.launchpad.net/ListHelp ___ Mailing list: https://launchpad.net/~yade-dev Post to : yade-dev@lists.launchpad.net Unsubscribe : https://launchpad.net/~yade-dev More help : https://help.launchpad.net/ListHelp
Re: [Yade-dev] : GenericSpheresContact
Frederic introduced this double radius. And it has a reasoning and derivation from formulas. Problem is that I can't remember now this derivation. But When I reproduced his derivation it actually made sense to use double radius for flat surfaces. Maybe Frederic remembers and we can ask him. I can only recall that it has something to do with - penetration depth - point of contact - stiffness and from this derivation a sphere in contact with mirror double radius sphere behaved exactly the same as if it was in contact with flat surface. Maybe that also had something to do with shearing, but I'm not sure now). A critical point in this derivation was that the double radius spheres was moving following (==mirror) the real sphere that was in contact with flat surface. I can't recall this now. best regards Janek Kozicki Klaus Thoeni said: (by the date of Tue, 13 Dec 2011 23:00:24 +1100) Well if it is 1 for boxes now I don't see any reason why it should be 2 for facets. Or is there a reason? Any other opinions? On Tue, 13 Dec 2011 10:46:31 PM Bruno Chareyre wrote: thanks for the active discussion. So I guess we just leave it as it is and use 2 for boxes and facets if this is the usual assumption. It is 1 for boxes now (and good like this). I didn't know 2 was usual. I would make it 1 for facet as well, but since I'm not using facets a lot, I can't decide for others. Bruno ___ Mailing list: https://launchpad.net/~yade-dev Post to : yade-dev@lists.launchpad.net Unsubscribe : https://launchpad.net/~yade-dev More help : https://help.launchpad.net/ListHelp ___ Mailing list: https://launchpad.net/~yade-dev Post to : yade-dev@lists.launchpad.net Unsubscribe : https://launchpad.net/~yade-dev More help : https://help.launchpad.net/ListHelp -- Janek Kozicki http://janek.kozicki.pl/ | ___ Mailing list: https://launchpad.net/~yade-dev Post to : yade-dev@lists.launchpad.net Unsubscribe : https://launchpad.net/~yade-dev More help : https://help.launchpad.net/ListHelp
Re: [Yade-dev] : GenericSpheresContact
If I recall this derivation I will let you know ASAP. I only remember that it was quite convincing... But maybe Bruno you can ask Frederic (is he in France now?) Janek Kozicki said: (by the date of Tue, 13 Dec 2011 14:19:04 +0100) Frederic introduced this double radius. And it has a reasoning and derivation from formulas. Problem is that I can't remember now this derivation. But When I reproduced his derivation it actually made sense to use double radius for flat surfaces. Maybe Frederic remembers and we can ask him. I can only recall that it has something to do with - penetration depth - point of contact - stiffness and from this derivation a sphere in contact with mirror double radius sphere behaved exactly the same as if it was in contact with flat surface. Maybe that also had something to do with shearing, but I'm not sure now). A critical point in this derivation was that the double radius spheres was moving following (==mirror) the real sphere that was in contact with flat surface. I can't recall this now. best regards Janek Kozicki Klaus Thoeni said: (by the date of Tue, 13 Dec 2011 23:00:24 +1100) Well if it is 1 for boxes now I don't see any reason why it should be 2 for facets. Or is there a reason? Any other opinions? On Tue, 13 Dec 2011 10:46:31 PM Bruno Chareyre wrote: thanks for the active discussion. So I guess we just leave it as it is and use 2 for boxes and facets if this is the usual assumption. It is 1 for boxes now (and good like this). I didn't know 2 was usual. I would make it 1 for facet as well, but since I'm not using facets a lot, I can't decide for others. Bruno ___ Mailing list: https://launchpad.net/~yade-dev Post to : yade-dev@lists.launchpad.net Unsubscribe : https://launchpad.net/~yade-dev More help : https://help.launchpad.net/ListHelp ___ Mailing list: https://launchpad.net/~yade-dev Post to : yade-dev@lists.launchpad.net Unsubscribe : https://launchpad.net/~yade-dev More help : https://help.launchpad.net/ListHelp -- Janek Kozicki http://janek.kozicki.pl/ | ___ Mailing list: https://launchpad.net/~yade-dev Post to : yade-dev@lists.launchpad.net Unsubscribe : https://launchpad.net/~yade-dev More help : https://help.launchpad.net/ListHelp -- Janek Kozicki http://janek.kozicki.pl/ | ___ Mailing list: https://launchpad.net/~yade-dev Post to : yade-dev@lists.launchpad.net Unsubscribe : https://launchpad.net/~yade-dev More help : https://help.launchpad.net/ListHelp
