[Nek5000-users] Linearized Nek: Compute only the right-hand side

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

Jean-Christophe,

Have you already looked at the perturbation code in nek?
It already does these things.

Also, it's not clear that you want everything in strong
form, particularly the 2nd-order spatial terms, since
the solution is only C0?

Paul


On Fri, 21 Oct 2011, nek5000-users at lists.mcs.anl.gov wrote:


> Hi Nek's,
>
> Given a random initial vector u and the Jacobian matrix of the linearized
> Navier-Stokes, I would like to calculate the matrix-vector product J * u. In
> Nek, that would consists in calculating only the right hand side of the
> equations, that is:
>
> RHS = ( -U.grad(u) - u.grad(U) - grad(p) + 1/Re Lap(u)    ;    div(u) )
>
> I have a few questions on how to compute those different terms in userchk
> (Nek is used in post-process mode):
>
>   - I would tend to use convop() for the convection terms, however I'm not
>   sure whereas it would output the strong or weak form (and I need the strong
>   one obviously)?
>   - Same question regarding grad(p) and div(u) if I use opgradt() and
>   opdiv() to calculate them?
>
> Last but not least, for the Laplacian I've read a previous mail where it is
> said that it can be computed using a sequence of wgradm1() and vec_dssum()
> so I guess I kown how to compute at the strong form for it.
>
> Sincerely,
> -- 
> Jean-Christophe
>