[Nek5000-users] element order range
nek5000-users at lists.mcs.anl.gov
nek5000-users at lists.mcs.anl.gov
Mon Sep 20 09:53:43 CDT 2010
Stefan,
I'm about to start some comparison simulations on this problem. Are you still interested in looking over the input files for potential improvements?
Thanks.
--Mike
On Sep 14, 2010, at 12:43 PM, <nek5000-users at lists.mcs.anl.gov> <nek5000-users at lists.mcs.anl.gov> wrote:
> Stefan,
>
> Thanks for the offer. If you'd like to look, I put the relevant files in a .tar.gz file at
>
> http://michaelasprague.com/couette_scale.tar.gz
>
> It's fairly simple. The dimensions are (Lx,Ly,Lz) = (6,5,1) with periodic BCs in x and y. At z = 0, (ux,uy,uz) = (0,0,0) and at z = 1, (ux,uy,uz)=(1,0,0).
>
> The domain is discretized as (Nx,Ny,Nz)=(24,16,16), and N = 13.
>
> Please let me know if you have any suggestions for parameter improvements and/or need more information.
>
> --Mike
>
> On Sep 14, 2010, at 11:37 AM, <nek5000-users at lists.mcs.anl.gov> wrote:
>
>> Mike:
>>
>> If you're ready with the NEK case we're more than happy to have a look at it.
>> Sometimes it can get a little bit tricky to find the right solver parameters to get the most out of it.
>>
>> We're very interested into comparisons like this!
>>
>> -Stefan
>>
>>
>> ----- Original Message -----
>> From: nek5000-users at lists.mcs.anl.gov
>> To: nek5000-users at lists.mcs.anl.gov
>> Sent: Tuesday, September 14, 2010 12:31:40 PM GMT -06:00 US/Canada Central
>> Subject: Re: [Nek5000-users] element order range
>>
>> Paul,
>>
>> Thanks for that info and for the document. Both are very helpful.
>>
>> There's interest here in using OpenFOAM (second-order finite-volume), and I'm interested to see how Nek does in a head to head comparison. We're using turbulent planar Couette flow as our comparison test case with Re = 8000 (See, e.g. Sullivan et al. (JFM 404, 2000). We're looking at accuracy for a given number of grid points and scalability over 16-1024 cores.
>>
>> I'll let you know how things turn out with the comparison.
>>
>> --Mike
>>
>>
>> On Sep 14, 2010, at 10:33 AM, <nek5000-users at lists.mcs.anl.gov> wrote:
>>
>>>
>>> Hi Mike,
>>>
>>> I've run with N=120 in the past and just this past
>>> week was running w/ N=64. (I had to bump up a couple
>>> of parameters past the 40 or 50 mark to do so.)
>>>
>>> Stefan has run the Pn-Pn variant with N=1 (lx1=2).
>>>
>>> lx1=6-12 is the general sweet spot for the code because
>>> of the way the operators are evaluated...
>>>
>>> When comparing to a low-order code it's generally best
>>> to compare for an equal number of gridpoints - i.e.,
>>> roughly the same resolution. The main reason for this is that
>>> higher order does not buy you increased resolution. (The
>>> Nyquist sampling theorem dictates at least 2*k points are
>>> required to resolve a signal of wavenumber k.) What the
>>> high-order method gains is improved accuracy for the modes
>>> that _are_ resolved. My goal is to try to ensure that
>>> the performance is comparable to a low-order code - i.e.,
>>> that costs are not inordinate w/ N.
>>>
>>> What type of comparison did you have in mind ? You might
>>> be interested in: www.mcs.anl.gov/~fischer/users.pdf
>>> which is a work-in-progress.
>>>
>>> Paul
>>>
>>>
>>>
>>> On Tue, 14 Sep 2010, nek5000-users at lists.mcs.anl.gov wrote:
>>>
>>>> Hello All.
>>>>
>>>> I am doing some tests of Nek5000 against a low-order code. Under "Performance tips", it is recommended to "design your resolution (mesh) for N=7 or N=9"
>>>>
>>>> Are there any limitations on the range of values for N? For example, what is the smallest N and largest N that the code can/has been run with? What are the limitations with running at, say, N = 16?
>>>>
>>>> Thanks.
>>>> --Mike
>>>>
>>>>
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