[Nek5000-users] Restarting simulation in same run

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

Hi Praveen,

I would guess you need to develop your own timestepper because
Nek uses BDFk & EXTk  to time march, where typically k=3.  At
start-up, it uses k=1 and k=2 to bootstrap.   If you start timestepping
in the middle of the simulation then you need to overwrite the
existing coefficients so that you can restart the timestepper,
plus you need to store your initial condition (which presumably
amounts to overwriting vx,vy,vz, and pr).

There are others in the community who have done these kinds of
things (I have not), who might have some further comments.

Best,

Paul

PS ----- Are you trying to find eigenvalues associated with
the spatial operators ?   i.e., does the accuracy of the
timestepper matter?  If not, you can likely get away with
k=1, in which case you don't need much history in the backward
difference formula or extrapolation.  Pressure, however, is
a bit of a tricky business because we use splitting and there
is a residual O(dt^k) impact...



On Tue, 21 Oct 2014, nek5000-users at lists.mcs.anl.gov wrote:

> Dear neks
>
> I want to perform several simulations each with different initial condition
> in the same run of nek5000. This is for eigenvalue/vector computation with
> ARPACK and using time-stepping approach.
>
> I plan to do all of this in userchk. The call to ARPACK will be in userchk.
> Whenever ARPACK gives me a vector, I want to start a simulation with this
> vector as initial condition. I have to perform certain number of time-steps
> and return the result to ARPACK.
>
> What all do I need to do to initialize a simulation given the initial
> condition vector ?
>
> Thanks
> praveen
>