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

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

Sorry, I should have attached the .usr file instead of the .rea file.

On Sun, Aug 14, 2011 at 6:26 PM, Mani Chandra <mc0710 at gmail.com> wrote:

> 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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>>>>>
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