[Nek5000-users] The first time step in a Nek file must contain a mesh

[nek5000-users at lists.mcs.anl.gov]

Hi,

Generally speaking, nek should automatically dump the geometry on step 1.
I'm not 100% certain why that did not happen in your case.  It could be
because your call to outpost executes on step 0 (i.e., after init. cond.
is defined, but prior to the first step).

Regarding vorticity, are you looking at a 2D case, or 3D?

If 2D, for which vorticity is a scalar, I would recommend putting
the vorticity in a temperature field and letting nek dump it.

       parameter(lt=lx1*ly1*lz1*lelv)
       common /scrns/ vort(lt*lelv,3),w1(lt),w2(lt)

       call comp_vort3(vort,w1,w2,vx,vy,vz)

       n=nx1*ny1*nz1*nelv
       k=1
       call copy(t(1,1,1,1,k),vort,n)  ! Put vorticity in temperature fld
       ifto=.true.                     ! Tell nek to dump temperature


....That's all you need, because now nek will dump the other
variables as well as vorticity, which it will put into the 
temperature array.  If you are also doing heat transfer, you
will need to increase k and then set ipsco(k-1) to be .true.

For 3D, a separate outpost call is a good idea.  Here is a std. approach:

       parameter(lt=lx1*ly1*lz1*lelv)
       common /scrns/ vort(lt*lelv,3),w1(lt),w2(lt)


       if (istep.gt.0.and.mod(istep,iostep.eq.0)) then
          ifxyo=.false.
          if (istep.eq.1) ifxyo=.true.
          call comp_vort3(vort,w1,w2,vx,vy,vz)
          call outpost (vort(1,1),vort(1,2),vort(1,3),pr,t,'vrt')
       endif

which puts the 3 vorticity components in the file where velocity would
normally be.

Also, it seems likely that you have param(66) and (67) set to 4 in
your .usr file.  This is fine, but if you are using VisIt, there
are some potential advantages to not setting these values and letting
nek set the default (which happens automatically if you set p66 and p67
to 0 in your .rea file and do not over-ride in the .usr file).

Hope this helps,

Paul




On Fri, 2 Mar 2012, nek5000-users at lists.mcs.anl.gov wrote:

> Hi neks,
>
> I try to visualize the V.karman' vortexes by computing the vorticity field 
> with this subroutine :
>
>       if(mod(istep,iostep).eq.0) then
>       call comp_vort3(vort,work1,work2,vx,vy,vz) 
> call outpost(vort(1,3),vort(1,2),vort(1,1),pr,t,'vrt')
>       endif
> Which works but, when i try to post-processes the data with Vizit i got the 
> fallowing error message :
>
> "The first time step in a Nek file must contain a mesh"
>
>
> i try to open my vrt[mycase].fld* files with vis.nek3D which contains
>
> NEK5000
> version 1.0
> filetemplate: vrtvkarman2.fld%02d
> firsttimestep: 1
> numtimesteps: 2
>
> Is there a way to fix this ?
> Sorry for my poor english ..
> B.regards
> Can
>
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