[Nek5000-users] Boundary nodes cordinates and random generator

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

But I guess you want some temporal correlation as well, i.e. your modes 
will evolve as a harmonic signal also in time? Typically, we chose a few 
modes (say 150) with random wavenumbers and phases, but then we just 
evolve them in space and time. So the problem is then rather to evaluate 
the complex exponential (i.e. cosine and sine signals) than random numbers.

So in that case, one needs to have a RNG that works well in parallel and 
you can restart a simulation without "kinks".

But if you do not need these properties, I would say that computing 150 
random numbers is not very expensive. I typically use a quite "simple" 
generator from Numerical recipes, just because it is portable and gives 
the same numbers on all machines.

Philipp

On 2018-10-16 16:49, nek5000-users at lists.mcs.anl.gov wrote:
> Hello Philip,
> 
> The turbulent velocity field is generated by random Fourier modes. So, yes I have to generate 150 random numbers for 4 different variables(Angles) at each time step. Or do you have any other simple way to suggest to make it computationally cheaper?
> 
> Thanks
> 
> Sijo
> 
> ----- Mail original -----
> De: "nek5000-users" <nek5000-users at lists.mcs.anl.gov>
> À: "nek5000-users" <nek5000-users at lists.mcs.anl.gov>
> Envoyé: Mardi 16 Octobre 2018 16:38:12
> Objet: Re: [Nek5000-users] Boundary nodes cordinates and random generator
> 
> Hi, how would your inflow turbulence model work? Do you need to create
> 150 random numbers every time step?
> 
> Philipp
> 
> On 2018-10-16 16:01, nek5000-users at lists.mcs.anl.gov wrote:
>> Hello Neks,
>>
>> Its been a long time that I posted something in NEK5000. Here I came up
>> with something which is simple.
>> First thing is, I was trying to access the co ordinates of the inlet
>> boundary elements for my free stream turbulence model(Von karman).
>>
>> I have an idea to get the using cbc(f,e,1) but I just would like to know
>> is there any quick way to get the inlet bounday nodes coordinate.
>>
>> Second thing is about the making of random numbers.
>> I know that in fortran there is an inbuilt function to generate random
>> numbers (call random_generator(iseed)) but it seems it is an expensive
>> process since my number of modes of turbulence model is 150.
>>
>> So just I have a question that how you usually generate random numbers
>> when you model free stream turbulence?
>>
>> By the way I have completed the FSI calculation of NACA0012 at Re 64000
>> in NEK5000. Thanks for your help.
>>
>> Regards
>>
>> Sijo GEORGE
>>
>>
>>
>>
>>
>>
>>
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