[Nek5000-users] Tripping mechanism

nek5000-users at lists.mcs.anl.gov nek5000-users at lists.mcs.anl.gov
Fri Feb 23 15:49:37 CST 2018

Hi Juan Diego,

Indeed, we describe in our paper the trip forcing. The tripping has a 
temporal part (third-order Lagrange interpolants with specific time 
scale) and a spatial part (the h^i(z)). We typically use white noise for 
these h(z), low-pass filtered with a spectral cutoff filter at a 
wavenumber 2pi/z_s. So what one gets in h(z) is just random sines and 
cosines up to a spanwise scale z_s.

The implementation of course needs to make sure i) that you have the 
same random numbers for the whole spanwise extent, and ii) that when 
restarting a simulation you continue the previous tripping in a smooth 
way as to not generate any peaks (discontinuities) at the restart.

Please let me know if you have further questions, and I am happy to help 

Best regards,
Philipp Schlatter

On 2018-02-23 18:29, nek5000-users at lists.mcs.anl.gov wrote:
> Dear all,
> I've seen several papers using Nek5000 with a tripping mechanism based 
> on a forcing term, explained in a paper by Schlatter & Örlü (2012). 
> However, they talk about using random harmonic signals h^{i}(z). My 
> question is: What is the shape of such signals and how do you make them 
> random?
> Thanks,
> Juan Diego
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