gather scatter for surface integral

[Chunheng Zhao]

Hi all,

I am confused about the surface integral area in Nek5000.

When I evaluate the flux at each node, for which I have to multiply the area for the node. I would like to know after the evaluation, do I have to do the gather scatter and multiply the inverse mass matrix, and are they the same as doing nothing?

for example 

flux=area*a

call fgslib_gs_op(gsh_fld(1),flux,1,1,0)

call col2(flux,binvm1, npts)

after the gather scatter and inverse, can I expect it is equal to the previous value?

Thanks,

Chunheng.

[Fischer, Paul]

Dear Chunheng,

The code below (also included as attachment) shows how to compute

 a surface integral over a desired patch.

 surface_flux() is a similar routine, also found in navier5.f

Hth. 

Best,

Paul

c-----------------------------------------------------------------------

      subroutine test

      include 'SIZE'

      include 'TOTAL'

      integer e,f

      nface = 2*ndim

      pr_int = 0.   ! Integrate pressure over given section

      ar_int = 0.   ! Compute area over given section

      do e=1,nelv

         xbar = xm1(2,2,1,e)

         if (-1.lt.xbar.and.xbar.lt.1) then ! Near the origin

           do f=1,nface

              if (cbc(f,e,1).eq.'v  ') then ! on the "moving" wall

                 call surface_int(pr_loc,ar_loc,pr,e,f)

                 pr_int = pr_int + pr_loc ! Integrated pressure

                 ar_int = ar_int + ar_loc ! Integrated area

              endif

           enddo

         endif

      enddo

      pr_int = glsum(pr_int,1)   ! Sum across all processors

      ar_int = glsum(ar_int,1)   ! Sum across all processors

      pr_avg = pr_int / ar_int   ! Average pressure

      return

      end

c-----------------------------------------------------------------------

---

From: 'Chunheng Zhao' via Nek5000 <nek...@googlegroups.com>
Sent: Tuesday, December 9, 2025 7:14 PM
To: Nek5000 <nek...@googlegroups.com>
Subject: [nek5000] gather scatter for surface integral

 

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