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<p style="margin-top:0;margin-bottom:0">Dear Emily,</p>
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<p style="margin-top:0;margin-bottom:0">At that amplitude, you are seeing the nonlinear</p>
<p style="margin-top:0;margin-bottom:0">effects - this is at it should be. </p>
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<p style="margin-top:0;margin-bottom:0">If you wish to compare against linear theory, then</p>
<p style="margin-top:0;margin-bottom:0">the amplitude needs to be small enough such that the</p>
<p style="margin-top:0;margin-bottom:0">u.grad u term is quite small.</p>
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<p style="margin-top:0;margin-bottom:0">I'm not certain of your ultimate objective -- if you're</p>
<p style="margin-top:0;margin-bottom:0">trying to measure convergence, then a small amplitude</p>
<p style="margin-top:0;margin-bottom:0">is important. If you are interested in large amplitude</p>
<p style="margin-top:0;margin-bottom:0">effects, then you won't be able to compare with linear</p>
<p style="margin-top:0;margin-bottom:0">theory results.</p>
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<p style="margin-top:0;margin-bottom:0">hth,</p>
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<p style="margin-top:0;margin-bottom:0">Paul</p>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>From:</b> Nek5000-users <nek5000-users-bounces@lists.mcs.anl.gov> on behalf of nek5000-users@lists.mcs.anl.gov <nek5000-users@lists.mcs.anl.gov><br>
<b>Sent:</b> Friday, April 27, 2018 10:34:51 AM<br>
<b>To:</b> nek5000-users@lists.mcs.anl.gov<br>
<b>Subject:</b> Re: [Nek5000-users] Finite-amplitude disturbance based on os7000</font>
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<p class="x_MsoNormal">Dear all,</p>
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<p class="x_MsoNormal">First of all, thank you a lot for your help and feedback. The amplitude of ux’ in my case is 1.82E-1 which is superimposed on the base flow u = 1 – y**2 along with uy’ (this setting is identical to the literature paper). An order of
BDF 3 is employed. Polynomial order is 8 with 4 elements in streamwise direction and 12 elements in the wall-normal direction. 1 wave length is simulated in the channel.</p>
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<p class="x_MsoNormal">The default setting of os7000 was what I started. I have also tried to increase the spatial resolution, and reduce the time steps (dt = 0.05, 0.01, 0.005). However, it did not really change anything. The distortion is less obvious if
the magnitude of perturbation is decreased and totally disappears if it is as small as 1.82E-3.</p>
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<p class="x_MsoNormal">Again, thank you a lot for the help and I will further explore the parameters and see what I can find.</p>
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<p class="x_MsoNormal">Regards,</p>
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<p class="x_MsoNormal">Emily</p>
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