Re: [Yade-users] [Question #256283]: Problem with Damping, Facets and Contact Model
Question #256283 on Yade changed: https://answers.launchpad.net/yade/+question/256283 Bruno Chareyre posted a new comment: It is easily avoided in most cases by using a corner. A quick fix for now. Do you mean that you implemented this fix? I'm curious to know how you did that. -- You received this question notification because you are a member of yade-users, which is an answer contact for Yade. ___ 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
Re: [Yade-users] [Question #256283]: Problem with Damping, Facets and Contact Model
Question #256283 on Yade changed: https://answers.launchpad.net/yade/+question/256283 Chiara Modenese posted a new comment: Great, thanks! Yes, you are right about the computation of the mass, it shows how important it is to read understand the code! It should be a detail written in the documentation though - please feel free to add it (thanks in advance!). Glad to have confirmation that everything works fine, Chiara On 30 October 2014 15:06, Chareyre question256...@answers.launchpad.net wrote: Question #256283 on Yade changed: https://answers.launchpad.net/yade/+question/256283 Chareyre posted a new comment: Thank you for your feedback. PFC is excellent for benchmarks. -- You received this question notification because you are a member of yade-users, which is an answer contact for Yade. ___ 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 -- You received this question notification because you are a member of yade-users, which is an answer contact for Yade. ___ 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
Re: [Yade-users] [Question #256283]: Problem with Damping, Facets and Contact Model
Question #256283 on Yade changed: https://answers.launchpad.net/yade/+question/256283 Status: Answered = Solved Alexander Smith confirmed that the question is solved: Hi Bruno and Chiara, Thanks for the heads up about facets. It is easily avoided in most cases by using a corner. A quick fix for now. I have found why damping was not present. Non-linear damping uses instantaneous critical damping where the equivalent mass is calculated as: Real mbar = (!b1-isDynamic() b2-isDynamic()) ? de2-mass : ((!b2-isDynamic() b1-isDynamic()) ? de1-mass : (de1-mass*de2-mass / (de1-mass + de2-mass))); In the case of two spheres it works fine if either (or both) are fixed. However, if one body is a facet and the contacting sphere is Fixed as was the case in the script above, then the equivalent mass is zero. Hence the damping coefficients are zero. I also checked the Hertz Mindlin rolling friction model and I can confidently say that it behaves on a facet exactly as expected for suitable model parameters (it matches the results produced by Wensrich and Katterfeld in Rolling friction as a technique for modelling particle shape, 2011). Though I am not suggesting PFC3D is a good benchmark :-) Thank you both for your help. It is much appreciated. Alex -- You received this question notification because you are a member of yade-users, which is an answer contact for Yade. ___ 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
Re: [Yade-users] [Question #256283]: Problem with Damping, Facets and Contact Model
Question #256283 on Yade changed: https://answers.launchpad.net/yade/+question/256283 Chareyre posted a new comment: Thank you for your feedback. PFC is excellent for benchmarks. -- You received this question notification because you are a member of yade-users, which is an answer contact for Yade. ___ 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
Re: [Yade-users] [Question #256283]: Problem with Damping, Facets and Contact Model
Question #256283 on Yade changed: https://answers.launchpad.net/yade/+question/256283 Chiara Modenese proposed the following answer: Just to say that the HM contact model has been widely tested for sphere-sphere contacts but not with other elements. I am not familiar with the formulation of facets but maybe somebody who is might be able to help you? Cheers, Chiara On 28 October 2014 16:46, Chareyre question256...@answers.launchpad.net wrote: Question #256283 on Yade changed: https://answers.launchpad.net/yade/+question/256283 Status: Open = Answered Chareyre proposed the following answer: Hi, On 28/10/14 08:16, Alexander Smith wrote: I tested the Hertz Mindlin contact model and noticed that shear and normal viscous damping is not accounted for in a sphere-facet contact. It behaves correctly with a sphere-sphere contact. I have attached a simple script below to illustrate my point. I just wanted to check before I report a bug. To me it sounds like a bug, but maybe it is intentional. Devs of the viscous model will tell. Also, I noticed that a facet is made of two triangles and at the junction of the two it appears the sphere is in contact with both surfaces. This increases the normal force and effects shear force and contact moments (shown by setting a=0 in the script below). Is this correct? No, it is not correct. It is a known issue of facet-sphere contacts, and it is more or less solutionless in the context of facets as they are now. Thus, I would not recommend to try and fix this by yourself. Some solutions are being implemented and should be released soon. They replace facets by more advanced shapes. I am developing a contact model and I need some guidance on how to fix it to ensure that the contact model behaves correctly on flat surfaces. If the surface is flat, then it can be a single facet, or a a box. Problem solved (or?). Bruno -- You received this question notification because you are a member of yade-users, which is an answer contact for Yade. ___ 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 -- You received this question notification because you are a member of yade-users, which is an answer contact for Yade. ___ 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
Re: [Yade-users] [Question #256283]: Problem with Damping, Facets and Contact Model
Question #256283 on Yade changed: https://answers.launchpad.net/yade/+question/256283 Status: Open = Answered Chareyre proposed the following answer: Hi, On 28/10/14 08:16, Alexander Smith wrote: I tested the Hertz Mindlin contact model and noticed that shear and normal viscous damping is not accounted for in a sphere-facet contact. It behaves correctly with a sphere-sphere contact. I have attached a simple script below to illustrate my point. I just wanted to check before I report a bug. To me it sounds like a bug, but maybe it is intentional. Devs of the viscous model will tell. Also, I noticed that a facet is made of two triangles and at the junction of the two it appears the sphere is in contact with both surfaces. This increases the normal force and effects shear force and contact moments (shown by setting a=0 in the script below). Is this correct? No, it is not correct. It is a known issue of facet-sphere contacts, and it is more or less solutionless in the context of facets as they are now. Thus, I would not recommend to try and fix this by yourself. Some solutions are being implemented and should be released soon. They replace facets by more advanced shapes. I am developing a contact model and I need some guidance on how to fix it to ensure that the contact model behaves correctly on flat surfaces. If the surface is flat, then it can be a single facet, or a a box. Problem solved (or?). Bruno -- You received this question notification because you are a member of yade-users, which is an answer contact for Yade. ___ 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
