<HTML><BODY>Hi Philipp!<br><br>Thank you for your answer!<br><br>In fact I have almost the DNS resolution (<span id="result_box" class="short_text" lang="en"><span>the grid spacing is comparable with the Kolmogorov scale from the literature data) and rather small error in the dissipation field. But I want to see a smooth dissipation, so I really want to try to filter it.<br><br>As I understood filtering procedure is in <em>dssum</em> subroutine. But looking at it didn't help to me to realize the process of the filtering.<br>So could you explain, please, how can I choose the filter to be used? Cause now I think that my filter doesn't go beyond one element and it is the reason why it <span id="result_box" class="short_text" lang="en"><span>makes my dissipation field worse</span></span>.<br><br>Best regards,<br>Vlad<br><br></span></span><br><br><br><blockquote style="border-left:1px solid #0857A6; margin:10px; padding:0 0 0 10px;">
Понедельник, 25 июня 2018, 23:05 +07:00 от nek5000-users@lists.mcs.anl.gov:<br>
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<div id="style_15299427150000000671_BODY">Hi,<br>
I guess your only chance is to increase the resolution, which will make <br>
the discontinuities of the derivatives decrease. This is one of the <br>
characteristics of spectral methods; you will see a lack of resolution <br>
directly in the fields. Similar resolution with other methods will not <br>
give you more accurate results, but they appear nicer (smoother).<br>
<br>
Indeed, filtering does not help much. But if you want to try, make sure <br>
you use a filter that actually goes beyond one element (e.g. using a <br>
Laplace operator).<br>
Philipp<br>
<br>
On 2018-06-25 17:54, <a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.gov</a> wrote:<br>
> Because I need to analyze the dissipation field<br>
> <br>
> понедельник, 25 июня 2018г., 20:58 +07:00 от <br>
> <a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.gov</a> <mailto:nek5000-users@lists.mcs.anl.gov>:<br>
> <br>
> This is correct, derivatives in SEM are not C0. Your code forces the<br>
> field to be C0 but it does not make it smooth across elements.<br>
> Typically filtering doesn’t help. Why do you want a smooth<br>
> derivative field?<br>
> <br>
> <br>
> > On 25 Jun 2018, at 12:55, "<a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.gov</a><br>
> <mailto:nek5000-users@lists.mcs.anl.gov>"<br>
> <<a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.gov</a><br>
> <mailto:nek5000-users@lists.mcs.anl.gov>> wrote:<br>
> ><br>
> > Hi, Neks!<br>
> ><br>
> > 1) I am doing a DNS study of turbulent pipe jets and looking at<br>
> turbulent kinetic energy budgets.<br>
> ><br>
> > I take derivatives via gradm1 subroutine, for example:<br>
> ><br>
> > call gradm1(uxdx,uxdy,uxdz,ux)<br>
> ><br>
> > After all, if I look at my dissipation field (via outpost), I see<br>
> some wrong values on the surface between spectral elements.<br>
> > I want to filter them using:<br>
> ><br>
> > call col2(uxdx,bm1,ntot)<br>
> > call dssum(uxdx,lx1,ly1,lz1)<br>
> > call col2(uxdx,binvm1,ntot)<br>
> ><br>
> > call dsavg(dxux)<br>
> ><br>
> > for every array. But conversely it leads to an increase in gaps.<br>
> What am I doing wrong?<br>
> ><br>
> > 2) How does a filter-function in dssum look and how much points<br>
> does it use for filtering? <br>
> ><br>
> > Best regards,<br>
> > Vlad.<br>
> > _______________________________________________<br>
> ><br>
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<br>-- <br>С уважением,<br><br>Иващенко Владислав, ИТ СО РАН<br></BODY></HTML>