Dear Jaekwang 

Have you solved this problem? If yes, Could pls share your solution with us?
I am simulating a steady state flow over a cylinder, and the drag/lift 
coefficient shows an unexpected trend of change as i increase the 
discretization order and refine the mesh.


As is shown in the figure, the Cd increased as the cells increased for all 
the discretization orders, however, for a fixed cells, the Cd decreased as 
the discretization order increased.

In my opinion, to increase the order and refine the mesh should both make 
the approximation more close to the exact solution, thus should have the 
same trend of change.

在 2016年9月18日星期日 UTC+8下午11:57:16,Jaekwang Kim写道:
> 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  

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