[MITgcm-support] Surface waves relaxation without viscosity terms

[Jean-Michel Campin]

Hi Sergey,

Just a comment regarding this:
> it says, that this is not yet possible with non-hydrostatic code, so you'd have to try to implement that.
I think the documentation is not up to date. Crank-Nicholson type time 
stepping has also been implemented for the non-hydrostatic pressure gradient 
(parameter: implicitNHPress, which default to implicSurfPress) 
and is tested in the verification experiment "short_surf_wave".

Cheers,
Jean-Michel

On Wed, Jan 23, 2013 at 11:19:00AM +0100, Martin Losch wrote:
> Sergey,
> 
> for your first question, you might want to consider turning off the implicit free surface, which will have a damping effect, and use an explicit Crank-Nicholson scheme instead. Unfortunately, here: <http://mitgcm.org/public/r2_manual/latest/online_documents/node41.html>
> it says, that this is not yet possible with non-hydrostatic code, so you'd have to try to implement that.
> Without any dissipation, the code will blow up sooner or later
> 
> question 2: I cannot look at all the details, but from comparing obcs_calc.F in both setups I see that your "wn" is twice as large as (and has a differen sign) in your second case.
> 
> Martin
> 
> 
> On Jan 22, 2013, at 6:07 PM, fancer lancer <fancer.lancer at gmail.com> wrote:
> 
> > Hello dear MITgcm developers and users.
> > 
> > I am trying to create the MITgcm setup, which could describe the
> > following two laboratory experiment cases:
> > 1) There is 2D tank with depth 0.196 m and length 12.4 m, bottom is
> > plain. Left boundary is solid, but the right boundary is opened. The
> > open boundary represents a wave-producer, which generates a sinusoidal
> > surface wave with frequency 1.5 Gz.
> > 2) The same experiment as above, but the left boundary is also opened
> > and the background flow runs from left to right with velocity 0.232
> > m/s.
> > 
> > Both setups are attached to the e-mail. The modeling works pretty well
> > except the following issues:
> > 1. I turned off all the dissipation (horizontal - viscAh=0, vertical -
> > viscAr=0, biharmonic - viscA4=0, even the viscosity term in the
> > momentum equation - momViscosity=.true.), but the surface waves keep
> > dissipating (picture 02_U.jpg, blue line under the 0 vertical level is
> > the surface elevation). Of course, the reason can be in the numerical
> > viscosity (diffusion), but the dissipation is too intensive. It can be
> > possible, that I miss something and there is another term of
> > dissipation, which I haven't tuned off. Can anybody check whether I
> > miss something or not?
> > If the reason still is the numerical viscosity what can I do to
> > decrease such the annoying effect?
> > 
> > 2. The second issue is a bit more complex. We use the formulas of the
> > vertical and horizontal waves velocities in the basin with the finite
> > depth (see the obcs_calc.F file) to create the harmonic on the right
> > boundary (some kind of wave-maker). That formulas work pretty well in
> > case of the zero background flow (see 01_U.jpg, 01_W.jpg). But if the
> > background flow exists then the high-frequency patterns appear on the
> > picture of the vertical velocity (see 02_W.jpg, 02_U.jpg).
> > 
> > The attached files:
> > 01_U.jpg - horizontal velocity and surface displacement (t ~ 17 s), no
> > background flow
> > 01_W.jpg - vertical velocity and surface displacement (t ~ 17 s), no
> > background flow
> > 02_U.jpg - horizontal velocity and surface displacement (t ~ 25 s),
> > with background flow
> > 02_W.jpg - vertical velocity and surface displacement (t ~ 25 s), with
> > background flow
> > 
> > Does anybody have any suggestion what can be the reason of the
> > patterns? I am quite sure, that the formulas of the wave-maker are
> > correct.
> > 
> > In addition here are my projects:
> > 1.zip - experiment without the background flow,
> > 2.zip - experiment with the background flow.
> > 
> > Any help would be highly appreciated.
> > 
> > Best regards,
> > Sergey V. Semin
> > Post graduate course student
> > Department of Mathematics,
> > Nizhny Novgorod State Technical University n.a. R.E.Alekseeva
> > http://www.nntu.ru/
> > 117-24 ulitsa Minina, Nizhny Novgorod, 603950, Russia
> > e-mail: fancer.lancer at gmail.com
> > <1.zip><01_U.jpg><01_W.jpg><2.zip><02_U.jpg><02_W.jpg>_______________________________________________
> > MITgcm-support mailing list
> > MITgcm-support at mitgcm.org
> > http://mitgcm.org/mailman/listinfo/mitgcm-support
> 
> 
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