[Nek5000-users] Average in arbitrary direction

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

Hi Josh,

You can use the interp() routines --- let me check if we have
examples in the repo.

These are somewhat expensive, so if you're also integrating in
time (even over just 10 steps), it would pay to only interpolate
the time-averaged data, rather than interpolating every timestep
and then averaging the profiles.   However, I can understand that
there are times you'd want the full time signal.

The best integration formulae for periodic signals (e.g., in 
your theta direction and perhaps in z, if you have periodicity)
is to simply sum the values, sampled uniformly in space (z or
theta), and dived by n, the number of samples.   You do need
to sample with sufficient density to capture all the wiggles ---
another reason that time averaging has value.

Paul



On Wed, 18 May 2011, nek5000-users at lists.mcs.anl.gov wrote:

> Hello Neks,
>
> I have looked at the turbChannel example for an example on planar averaging.
>
> However, I was wondering if there was any advice  on how to do this if
> the elements aren't exactly "nice"... (i.e., the elements may have
> arbitrary rotations)
>
> Specifically, I have a pipe flow, and I am wanting to do an average in
> the z (axial) direction.  My initial thoughts were to interpolate my
> values to set R, theta components, and then average this along z.  I'm
> stuck on the best way to do either one of these operations, however
> (especially because I would like to use an integration rule to compute
> the average in the z direction).
>
> If anyone could point me in the right direction, that would be a big
> help.  Thanks!
>
> -- 
> Josh Camp
>
> "All that is necessary for the triumph of evil is that good men do
> nothing" -- Edmund Burke
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