Hi David, Thank you so much for talking to Sylvain! It's really nice that I can hear from the thoughts of the original implementer. That makes sense to me.
For future reference for anyone who might be interested, the original author in the book recommended a value of 1e-4 to 1e-7 (maybe for more general cases). For this specific problem, I tried to compare the results of alpha = 1 and alpha = 1e-6, the results are *marginally* improved. With alpha = 1: z-displacement of the point C: 156.824 Analytic solution: 164.24 y-displacement of the point D: 4.05575 Analytic solution: 4.114 With alpha = 1e-6: z-displacement of the point C: 157.149 Analytic solution: 164.24 y-displacement of the point D: 4.06329 Analytic solution: 4.114 I suggest add a comment of author-recommended alpha values in the example. I could do a pull-request if anyone thinks that it is worth it? Best, Shawn On Mon, Oct 22, 2018 at 5:23 AM David Knezevic <[email protected]> wrote: > On Sun, Oct 21, 2018 at 3:48 AM Yuxiang Wang <[email protected]> wrote: > >> Dear all, >> >> I seem to find a mistake in the implementation of the MITC4 shell >> element, in the miscellaneous example 12. >> >> In the reference used, "Modelisation des structures par elements finis, >> Vol. 3: Coques.", on page 372 equation 6.3.90 it only added a small >> drilling stiffness. This was done by a coefficient alpha that is >> sufficiently small (1e-4 to 1e-7). However, in line 779 >> < >> https://github.com/libMesh/libmesh/blob/master/examples/miscellaneous/miscellaneous_ex12/miscellaneous_ex12.C#L779 >> >of >> the code (corresponding to this equation), this coefficient is dropped. >> >> Could anyone please help discuss this issue? >> > > Hello, > > My colleague Sylvain implemented that example, and I passed your question > onto him. His reply was "The drilling dof coefficient value is very > empirical, and I think in that specific example I just got good results > with a value of 1." So there is no bug here, it's just that he had to set > the value in a way that worked well for this example. > > Best, > David > -- Yuxiang "Shawn" Wang, PhD [email protected] +1 (434) 284-0836 _______________________________________________ Libmesh-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/libmesh-users
