[Nek5000-users] "convert" a given u_x(i, j, k) in an uniform grid to a vx(i, j, k, e) in a GLL grid ??

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

nek5000-users at lists.mcs.anl.gov a écrit :
> Hi Can,
>
> Sorry if I am missing something but what do you mean by projection of random field on uniform mesh to GLL grid?  Interpolation won't work since it relies on at least some smoothness of the field.
>
> Do you want to do it in wavenumber space instead?  
>
> Thanks.
> Aleks
>
> ----- Original Message -----
> From: nek5000-users at lists.mcs.anl.gov
> To: nek5000-users at lists.mcs.anl.gov
> Sent: Thursday, March 29, 2012 7:25:04 AM
> Subject: [Nek5000-users] "convert" a given u_x(i, j, k) in an uniform grid  to a  vx(i, j, k, e) in a GLL grid ??
>
> Hi neks,
>
> I am trying to set a random turbulent velocity field as an initial 
> condition for my simulation. The domaine is a cube 2pi * 2pi * 2pi and  
> nelx = nely=nelz=32 (lx1=12)
>
> And i was wondering if they are some routines for "project" a given 
> value of  u_x(i,j,k) (x component of the velocity field in a regular 
> grid) to vx(i,j,k,e) (x component of the velocity field on GLL grid) ??
> In one of the emails you said "given i,j,k,e,p, one can find the 
> associated (x,y,z) point. The inverse problem of finding i,j,k,e,p for a 
> given (x,y,z) value is much more difficult (and expensive), but we have 
> routines to handle this.)"
> Can you tell me more about this ??
> B.regards
> Can
>
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>   
I generated an isotropic velocity field on the Fourier space that i 
transformed to the physical spatial space (x,y,z) with some IFFT routine.
I did this with an external fortran program in an uniform grid (number 
of cell per direction n=32)  with the velocity field being expressed as 
u(i,j,k). The velocity field is then known on every nodes of my 
equi-spaced grid.
Having an identical domain (a cube of 2pi*2pi*2pi and 
nelx=nely=nelz=32), i want to project this velocity field in my nek GLL 
grid to use it as an initial condition.
i wonder if there is an interpolating routine for doing this.
Thanks for helping me
B.regards
Can