[Nek5000-users] Rayleigh Benard with symmetry BCs

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

Hi Jared,

If you send me your .box file, I will check that just in case.

Also, I see you are using variable time steps, so try reducing the target
Courant number to 1/2.

Another thing to be aware of with variable time stepping: if the Rayleigh
number is large and the simulation starts from a static state, the
exponentially growing velocities might still cause the CFL condition to be
violated. The solution to this is to decrease the maximum allowed time
step, DT. This is unlikely to be your problem at the current Rayleigh
number, however.

-David

On Mon, Feb 18, 2013 at 11:53 AM, <nek5000-users at lists.mcs.anl.gov> wrote:

>  My apologies upfront for any simple misconceptions as I'm new to nek.
>
> I have successfully run the included 2d RB example and thought things
> looked reasonable.  I then changed the mesh to an aspect ratio 2, 4x8
> element mesh and modified the boundary conditions to be 'SYM' sidewalls and
> 'SYM' (free-slip) for the top and bottom velocity (see attached rea and map
> file).
>
> Without changing anything else from the example (I did not modify SIZE)
> the velocities appear to blow up, and I get a series of errors like the
> following in the logfile:
>
>      1   100 **ERROR**: Failed in HMHOLTZ: TEMP   1.4999E-02
> 3.7064E+01   2.4836E-03
>           1   2.0000E-02  6.0370E-03 Heat done
>
>      1   100 **ERROR**: Failed in HMHOLTZ: VELX   2.8743E-21
> 1.7086E-16   2.3416E-23
>   0.000000000000000E+000  p22            1           1
>  New CG1-tolerance (RINIT*epsm) =   1.010379228335448E-010
>   2.341589846098494E-023
>
>
>      1   100 **ERROR**: Failed in HMHOLTZ: VELY   1.0837E-01
> 1.0104E+03   1.0104E-10
>  New CG2-tolerance (RINIT*10-5/10-10) =   2.795810823528297E-003
>   3.472834773690102E-025
>
>
>
> Do I need to adjust the tolerances because the mesh/BCs are different?
>
>
> I don't think it matters, but I ran this on 16 procs (there are 16 per
> node on the machine I'm using).
>
>                                                -Jared
>
> CCS2/CNLS Postdoctoral Research Associate
> Los Alamos National Laboratory
>
> _______________________________________________
> Nek5000-users mailing list
> Nek5000-users at lists.mcs.anl.gov
> https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users
>
>


On Mon, Feb 18, 2013 at 11:53 AM, <nek5000-users at lists.mcs.anl.gov> wrote:

>  My apologies upfront for any simple misconceptions as I'm new to nek.
>
> I have successfully run the included 2d RB example and thought things
> looked reasonable.  I then changed the mesh to an aspect ratio 2, 4x8
> element mesh and modified the boundary conditions to be 'SYM' sidewalls and
> 'SYM' (free-slip) for the top and bottom velocity (see attached rea and map
> file).
>
> Without changing anything else from the example (I did not modify SIZE)
> the velocities appear to blow up, and I get a series of errors like the
> following in the logfile:
>
>      1   100 **ERROR**: Failed in HMHOLTZ: TEMP   1.4999E-02
> 3.7064E+01   2.4836E-03
>           1   2.0000E-02  6.0370E-03 Heat done
>
>      1   100 **ERROR**: Failed in HMHOLTZ: VELX   2.8743E-21
> 1.7086E-16   2.3416E-23
>   0.000000000000000E+000  p22            1           1
>  New CG1-tolerance (RINIT*epsm) =   1.010379228335448E-010
>   2.341589846098494E-023
>
>
>      1   100 **ERROR**: Failed in HMHOLTZ: VELY   1.0837E-01
> 1.0104E+03   1.0104E-10
>  New CG2-tolerance (RINIT*10-5/10-10) =   2.795810823528297E-003
>   3.472834773690102E-025
>
>
>
> Do I need to adjust the tolerances because the mesh/BCs are different?
>
>
> I don't think it matters, but I ran this on 16 procs (there are 16 per
> node on the machine I'm using).
>
>                                                -Jared
>
> CCS2/CNLS Postdoctoral Research Associate
> Los Alamos National Laboratory
>
> _______________________________________________
> Nek5000-users mailing list
> Nek5000-users at lists.mcs.anl.gov
> https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users
>
>
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