Dear Jaekwank, In addition to what Daniel and Wolfgang said: One does definitely benefit from going to higher degrees and deal.II is able to handle this (the accurate boundary representation by a mapping is one thing that is easily forgotten). In a recent preprint, we considered the flow around a cylinder, a standard benchmark test for the incompressible Navier-Stokes equations: http://arxiv.org/pdf/1607.01323v1.pdf Go to page 23, Table 1, to see how the solution quality increases as the polynomial degree is increased from 4 to 7.

Best, Martin On Sunday, September 18, 2016 at 5:57:16 PM UTC+2, JAEKWANG KIM wrote: > > > Hello, I am a starter of dealii and am learning a lot these days with the > help of video lectures and tutorial examples. > > I modified step-22 code (stokes flow code) into my own problem, the flow > around sphere. > > and I intend to evaluate the drag force (which is analytically given by > stokes equation) > > My code reached quite close to the value since the absolute error : > abs(drag_calculated-drag_exact)/drag_exact is around 10^(-3) > > However, I expected that if I input higher 'degree' I will receive more > accurate result, but it didn't > > Obviously Q2 is better than Q1. and Q3 is better than Q2. But Q4 or Q4 is > not better than Q2 or Q3? > > Is there any reason on this? > > (To be specific, if i say degree 2 , that mean I use (2+1) for velocity, > (2) for pressure, and (2+2) for Gauss integral.... > > > Thank you > > Jaekwang Kim > -- The deal.II project is located at http://www.dealii.org/ For mailing list/forum options, see https://groups.google.com/d/forum/dealii?hl=en --- You received this message because you are subscribed to the Google Groups "deal.II User Group" group. To unsubscribe from this group and stop receiving emails from it, send an email to dealii+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.