[Nek5000-users] Solving for fluid flows on a sphere

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

Hi Paul,

Thanks for the diagnosing this problem. Indeed it is bad initial data. At
the moment I do not have specific initial data or forcing to work with and
so I'm just trying out the feasibility of using NEK to solve on the shell. I
should have some concrete initial data in the next couple of days.

When I try to repeat the run with

ux = 0.0
uy = 0.0
uz = 0.0

and

ffx = 0.0
ffy = 0.0
ffz = 1.0

NEK shows a lot of convergence errors. Could you check this out?

I've attached the .rea file.

Thanks,
Mani

On Sun, Aug 14, 2011 at 5:31 PM, <nek5000-users at lists.mcs.anl.gov> wrote:

>
> Hi Mani,
>
> I ran this with
>
> G="-g -Ktrap=fp"
>
> and the "nekd" script in serial (just gdb nek5000 after
> setting up requisite files).
>
> Here is the output:
>
> Program received signal SIGFPE, Arithmetic exception.
> 0x000000000040376c in useric_ (ix=1, iy=1, iz=1, ieg=3)
>    at /homes/fischer/nek_debug/mani/**z.f:83
> 83            utheta = 1.0/(x**2 + y**2)**0.5
> (gdb)
>
>
> This makes sense -- you have a pole singularity in
> this formulation.  I'm certain it's a removable singularity if you just
> rework your ux/uy velocity
> definition.
>
> Please let me know if this resolves the issue.
>
> Paul
>
>
>
>
>
> On Sun, 14 Aug 2011, nek5000-users at lists.mcs.anl.**gov<nek5000-users at lists.mcs.anl.gov>wrote:
>
>  Hi Paul,
>>
>> I setup a simulation but I keep getting NaN's when I give nontrivial
>> initial data. I'm attaching the relevant files. Could you please try it out?
>>
>> I checked that the initial data is divergence free and satisfies the
>> boundary conditions (u_r = 0, du_theta/dr = 0, du_phi/dr = 0).
>>
>> Regards,
>> Mani
>>
>> On 08/11/2011 05:46 PM, nek5000-users at lists.mcs.anl.**gov<nek5000-users at lists.mcs.anl.gov>wrote:
>>
>>>
>>> Hi Mani,
>>>
>>> Probably your best bet is to use a very thin layer of elements
>>> in a 3D spherical shell with SYM bcs on faces 5 & 6, plus the
>>> stress formulation.  I would imagine that a shell of thickness
>>> .001 with R=1.0 might be feasible.
>>>
>>> Instructions for constructing a 3D shell can be found in
>>> www.mcs.anl.gov/~fischer/**primer.pdf<http://www.mcs.anl.gov/~fischer/primer.pdf>
>>>
>>> (Some of this info may already have been transferred into
>>> current manual.)   We can help with this if you need any
>>> assistance.
>>>
>>> Regards,
>>>
>>> Paul
>>>
>>>
>>> On Thu, 11 Aug 2011, nek5000-users at lists.mcs.anl.**gov<nek5000-users at lists.mcs.anl.gov>wrote:
>>>
>>>  Hi Nek devs,
>>>>
>>>> Is it possible to use NEK to solve for Navier Stokes equations on the
>>>> surface of a sphere, where r is fixed and the velocity varies in theta
>>>> and
>>>> phi?
>>>>
>>>> Thanks,
>>>> Mani Chandra
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