Re: [Nektar-users] [EXTERNAL] Re: Noise Force Specification

8 Oct 2021


      Thanks Stan!  I will try to add NSTEPS.


On Fri, Oct 8, 2021 at 2:17 PM Stanislaw Gepner <sgepner@meil.pw.edu.pl>
wrote:
...
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Hi Marc,
I have the following set up for a transitional flow and it works for me:
<FUNCTION NAME="BodyForce">
      <E VAR="u" VALUE="0" />
      <E VAR="v" VALUE="0" />
      <E VAR="w" VALUE="0.5*Kinvis" />
    </FUNCTION>
</CONDITIONS>
<FORCING>
        <FORCE TYPE="Body">
            <BODYFORCE> BodyForce </BODYFORCE>
        </FORCE>
        <FORCE TYPE="Noise">
          <WHITENOISE> 0.005 </WHITENOISE>
          <UPDATEFREQ> 100 </UPDATEFREQ>
          <NSTEPS> 1000 </NSTEPS>
        </FORCE>
    </FORCING>
Compared to what you have, I have the NSTEPS to set the number of time
steps over which forcing is applied (not sure what is the default). The
value you put as White noise is (I think) variance. So putting to much does
not necessarily yield the result I want.
Cheers!
Stan
On 10/8/21 3:26 PM, Marc Goldbach wrote:
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Hi All,
What is the proper way to specify a noise force and a body force at the
same time?
I am new to Nektar++, and am attempting to run a simulation of turbulent
channel flow using a body force to drive the bulk flow, and a noise force
to generate some initial "turbulent-like" fluctuations of the velocity
field.  However, when I setup the case based on the details found in the
user guide (Forcing (nektar.info)
<https://doc.nektar.info/userguide/latest/user-guidese10.html#x16-810003.5> ),
the resulting flow field doesn't show any "noise component".  Is there some
error in my settings for this case?:
<NEKTAR>
   <CONDITIONS>
      ...
     <FUNCTION NAME="BodyForce">
             <E VAR="u" VALUE="-(Re*Kinvis/H)^2/H" />
             <E VAR="v" VALUE="0" />
             <E VAR="w" VALUE="0" />
         </FUNCTION>
</CONDITIONS>
     <FORCING>
         <FORCE TYPE="Body">
             <BODYFORCE> BodyForce </BODYFORCE>
         </FORCE>
         <FORCE TYPE="Noise">
             <WHITENOISE> 0.5 </WHITENOISE>
             <UPDATEFREQ> 10 </UPDATEFREQ>
         </FORCE>
     </FORCING>
 </NEKTAR>
Regards,
*Marc Goldbach*
PhD Student, Department of Mechanical Engineering
University of North Carolina at Charlotte
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Pozdrawiam,
dr inż. Stanisław Gepner,
*Wydział Mechaniczny Energetyki i Lotnictwa*
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Str.
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tel. +48 (22) 234 51 70
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*Marc Goldbach*
PhD Student, Department of Mechanical Engineering