[Nek5000-users] Stochastic inflow boundary condition using previous time step velocities?

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

Hi Harish,

You might try in userbc:

       subroutine userbc(ix,iy,iz,iside,eg)
       include 'SIZE'
       include 'TOTAL'
       integer e,eg

       e = gllel(eg)

       uold = vxlag(ix,iy,iz,e,1)


.... Be sure to verify that this gives what you expect.

Also, be careful on timestep number 1.

Also, it's possible that uold is already stored in ux,uy,uz
that are passed in through the NEKUSE common blocks, and are
simply awaiting to be updated to the user prescribed values.

Looking at subroutine nekasgn in bdry.f this is the case --
what is _actually_ there is the value of vx which is the
velocity at the "old" step (n-1, say) and vxlag would 
therefore be velocity at n-2.

Paul



Paul



>> Are they stored in VXLAG(LX1,LY1,LZ1,LELV,1)? How can I call those


On Fri, 30 Jul 2010, nek5000-users at lists.mcs.anl.gov wrote:

> Hi,
>
> I had asked this question yesterday.
>
> How do I call the velocities from the previous time step (time-dt) in
> subroutine userbc()?
>
> Thanks,
>
> Harish.
>
>
> On Thu, July 29, 2010 3:27 pm, nek5000-users at lists.mcs.anl.gov wrote:
>> Hello,
>>
>> I am trying to code a stochastic inlet boundary condition for a backward
>> facing step case. I am using the PN/PN-2 formualtion at Re=28,000.
>>
>> In this b.c., we use previous time step values to initialize the
>> fluctuations and final fluctuations are done using the stochastic model.
>>
>>   ufluct = u(t-dt) - umean
>>   ...........
>>   ...........
>>   ...........
>>   ux = uprime + umean
>>
>> To implement this in subroutine USERBC, I am facing trouble to use the
>> previous time step values.
>>
>> Are they stored in VXLAG(LX1,LY1,LZ1,LELV,1)? How can I call those
>> velocities in USERBC? And can I do this?
>>
>>   ufluct = vxlag(1,1,1,1,1) - umean
>>
>> Thanks,
>>
>> Harish.
>>
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