[Nek5000-users] Impose localized noise

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

Dear JC,

Do you want "random_noise" to be a function of
space and time? or of time only ?

Paul


On Mon, 6 Dec 2010, nek5000-users at lists.mcs.anl.gov wrote:

> Hi Nek's,
>
> I would like to impose noise localized in time and space in my stenotic
> pipe, pretty much like an impulse.
> I would be tempted to use the userf subroutine like this:
>
> subroutine userf (ix,iy,iz,eg)
> include 'SIZE'
> include 'TOTAL'
> include 'NEKUSE'
>
> integer e,f,eg
> real z_0, sigma_z, istep_0, istep_min, istep_max, Amplitude, Theta
>
> z_0 = 0.
> sigma_z = 1.
>
> istept_0 = 100.
> istep_min = 90.
> istep_max = 110.
> sigma_t = 1.
>
> if(istep.GE.istep_min.AND.istep.LE.istep_max)
>
> Theta = atan2(y,x)
>                           ! I would like my forcing to be on u_theta only
> Amplitude = exp(-((z-z_0)/sigma_z)**2 - ((istep-istep_0)/sigma_t)**2)
>
> ffx = - sin(Theta) * Amplitude * Random Noise
> ffy = cos(Theta) * Amplitude * Random Noise
> ffz = 0.0
>
> return
> end
>
> The thing is I don't know how I could impose some random noise on the whole
> domain. Using " call random_number(Random_Noise) " would only give me one
> single random number. I assume the solution is not to hard but I am however
> missing the point. Any idea?
>
> Kind regards,
> JC
>