[Nek5000-users] problem with applying boundary conditions

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

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Il giorno 14 set 2017, 18:41, alle ore 18:41, nek5000-users at lists.mcs.anl.gov ha scritto:
>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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