[Nek5000-users] problem with applying boundary conditions

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

Could it be that he uses V instead of v in the rea file?

++
JC

Le 14 sept. 2017 18:41, <nek5000-users at lists.mcs.anl.gov> a écrit :

> Hi,
> Not sure if I understand your question well, but I guess what happens
> during the first time step is that through the continuity equation and the
> incompressibility constraint you will have velocity about one everywhere.
> This is just to maintain mass conservation.
>
> Philipp
>
> On 2017-09-14 18:29, nek5000-users at lists.mcs.anl.gov wrote:
>
>> Dear Neks,
>>
>> I am trying to run a simulation, replicating the Nek5000 run from this
>> youtube video:
>> https://www.youtube.com/watch?v=RmmN-KFSvAY
>>
>> The inlet BC is constant velocity (which is set to 1.0), and as can be
>> seen from the video, the velocity magnitude reasonably away from the inlet
>> is zero at starting times. However, in all of my simulations, I see the
>> velocity magnitude as one at all the interior points away from the inlet
>> from the beginning (the inlet BC ux=1.0 I am applying is somehow propagated
>> to all interior elements). Am I doing something wrong somewhere, or is this
>> the expected behavior? Please see my userbc() and useric() from my .usr
>> file below:
>>
>>        subroutine userbc (ix,iy,iz,iside,eg)
>>        include 'SIZE'
>>        include 'TOTAL'
>>        include 'NEKUSE'
>>        integer ix,iy,iz,eg,e,i,n
>>
>> CC "My inlet is at x=0"
>>
>>        if (x.le.1e-4) then
>>          ux=1.0
>>        endif
>>
>>        return
>>        end
>>
>>        subroutine useric (ix,iy,iz,eg)
>>        include 'SIZE'
>>        include 'TOTAL'
>>        include 'NEKUSE'
>>
>>        ux=0
>>        uy=0
>>
>>        return
>>        end
>>
>> I believe userbc() is executed for only 'v' in my case. For the other
>> constraints on the elements (like 'W', 'O', 'E'),  I think userbc() would
>> not run (please correct me if I am wrong, I am learning here). Since the
>> above functions wouldn't work as expected, I changed userchk() and removed
>> the above if statements in userbc(). My userchk() is as follows:
>>
>>        subroutine userchk
>>        include 'SIZE'
>>        include 'TOTAL'
>>        integer i,n
>>
>>        n = nx1*ny1*nz1*nelv
>>
>>        if (istep.eq.0) then
>>          do i=1,n
>>            if (xm1(i,1,1,1).le.1e-4) then
>>              vx(i,1,1,1)=1
>>            endif
>>          enddo
>>        endif
>>
>>        return
>>        end
>>
>> This didn't work either. Can somebody point me in the right direction?
>>
>> Thanks,
>> Ajay
>>
>>
>>
>>
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