[Nek5000-users] mesh precision

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

Hi Paul,

I doubt that the input precision of the mesh could be causing this
problem.  The instability is not at all a weak one.  

As an unrelated aside, the Intel and Sun compilers can generate quad
precision code.  I use this quite often when computing derivatives of
objective functions wrt a discrete velocity.

Cheers,
Frank


On Thu, 2010-04-29 at 15:54 -0500, nek5000-users at lists.mcs.anl.gov
wrote:
> Hi Frank,
> 
> For most engineering calculations, single precision is
> sufficient and the code was written w/ this in mind.
> 
> That being said, for convergence studies and for stability
> simulations like yours, it can be of use to have higher
> precision.
> 
> In fact, I'm wondering if that's the source of difficulty
> in your current high Reynolds number runs - but haven't
> had time yet to test this hypothesis.   My std. approach
> is to project the input coordinates, xc(), yc(), and zc(),
> onto the cylinder in usrdat(), at which point they are
> then used to generate the geometry arrays, xm1, ym1, zm1.
> 
> usrdat() was originally designed for precisely this type
> of application.
> 
> hth,
> 
> Paul
> 
> 
> On Thu, 29 Apr 2010, nek5000-users at lists.mcs.anl.gov wrote:
> 
> > Hello all,
> 
> >From the *.rea files I have seen (including in the examples), all
> numbers describing the mesh are single precision.  I am wondering why
> that is the case; would not double precision values be better?
> 
> Cheers,
> Frank
> 
> -- 
> Frank Herbert Muldoon, Ph.D. Mechanical Engineering
> Technische Universität Wien (Technical University of Vienna)
> Inst. f. Strömungsmechanik und Wärmeübertragung (Institute of Fluid
> Mechanics and Heat Transfer)
> Resselgasse 3
> 1040 Wien
> Tel: +4315880132232
> Fax: +4315880132299 
> Cell:+436765203470
> fmuldoo (skype)
> http://tetra.fluid.tuwien.ac.at/fmuldoo/public_html/webpage/frank-muldoon.html
> 
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-- 
Frank Herbert Muldoon, Ph.D. Mechanical Engineering
Technische Universität Wien (Technical University of Vienna)
Inst. f. Strömungsmechanik und Wärmeübertragung (Institute of Fluid
Mechanics and Heat Transfer)
Resselgasse 3
1040 Wien
Tel: +4315880132232
Fax: +4315880132299 
Cell:+436765203470
fmuldoo (skype)
http://tetra.fluid.tuwien.ac.at/fmuldoo/public_html/webpage/frank-muldoon.html