boundary integral

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1

Hello everyone,

I have done some NS analysis and now want to do some post-processing using my results, I want to calculate my lift and drag over a certain part of the boundary (i.e its a surface integral). I have my functional defined and I use following line to calculate the drag

     c_d = Integrate(cf=Drag(u_h,p0), mesh=mesh, VOL_or_BND=BND, definedon=mesh.Boundaries("cyl"), order=1)

but i get the error

Anyone knows what this is?

Thanks in advance.

2

My guess is, that you need to use the trace operator for the HDiv function if you want to evaluate on the boundary, so do u_h.Trace(), but if you provide an example it would be easier.
Best Christopher