[MITgcm-support] Open Boundary Conditions in MITgcm

Sun Mar 6 02:11:45 EST 2011

Jody.

You understood properly.
Thank You very much for help.

Sincerely, Serge Semin.

On Sun, Mar 6, 2011 at 2:24 AM, Klymak Jody <jklymak at uvic.ca> wrote:

> Hi Serge,
>
> On 2011-03-04, at 12:23 PM, fancer fancer wrote:
>
> Jody, or somebody who know.
>
> Could You please tell me some approach (may be different from Orlanski),
> what can decide our problem without manipulating with sponge layer? May be
> some algorithm. Send me link with approach description, or try to explain
> here.
> I can try to implement it (at this summer).
>
>
> I'm not sure I understand the question.... If you are asking for methods to
> make the boundaries transparent to waves, I think you might look at Carter
> and Merrifield, 2007, Ocean Modelling who consider different BCs for tidal
> simulations.  I think they decided a sponge was best for internal tide
> problems.
>
> Cheers,   Jody
>
>
>
>
> Serge
>
> On Tue, Mar 1, 2011 at 7:43 PM, Klymak Jody <jklymak at uvic.ca> wrote:
>
>> >  I suggest that you hope that someone else will provide and answer, or
>> you'll have to go and read the original papers. In orlanski_east.F there is
>> some text about the parameters and suggestions about setting them.
>> >
>> > Your configuration looks OK to me, but what happens when you do not use
>> the balancing code (useOBCSbalance = .false.)? Maybe this velocity
>> correction causes some of the reflection?
>>
>> I think that the problem with Orlanski or its elaborations is that the
>> assume one wave speed (Orlanski is worse in that it assumes one wave
>> propagation direction).  So, for a stratified internal wave problem it might
>> do fine at getting rid of mode 1, but can't help you for higher modes.  So,
>> I bet if you do a Hovmoller diagram you see that it is mode 2 that reflects.
>>   Dale Durran has some papers on the subject - a google of "Durran Orlanski"
>> turns them up.
>>
>> I looked into all this for a few days a couple of years ago and decided
>> the sponge was a fine way to do things for my applications.  It comes at the
>> expense of some computational domain, but again I take care of this by
>> telescoping the sponges so that the forcing reservoir is very large and far
>> from the regions of interest.  You can usually get pretty clean waves this
>> way.
>>
>> Hopefully someone who is an expert in this can say something more
>> definitive.
>>
>> Cheers,   Jody
>>
>> PS, Serge, you are correct, that the forcing is done in obcs_calc.F.  My
>> mistake.
>>
>>
>> > Martin
>> >
>> > On Feb 28, 2011, at 9:59 PM, fancer fancer wrote:
>> >
>> >> Hi Martin. Sorry for belated answer and thanks for replies.
>> >>
>> >> There are small changes then I use Orlanski conditions, reflected waves
>> have smaller amplitudes, but they are still reflected.
>> >> I use default values CMAX and cVelTimeScale. I have not found some
>> information about Orlanski radiation boundary condition in free access.
>> Could You please tell me some formula or rule for these parameters selection
>> (for waves reflection minimizing)? Not trivial task to get it from code.
>> >>
>> >> P.S. My project in attachment, if it needed.
>> >>
>> >> -Serge
>> >>
>> >> On Thu, Feb 24, 2011 at 10:31 AM, Martin Losch <Martin.Losch at awi.de>
>> wrote:
>> >> Serge,
>> >> claim
>> >> you might have noticed that the documentation of the obcs-pkg is
>> incomplete:
>> >> <
>> http://mitgcm.org/public/r2_manual/latest/online_documents/node236.html>
>> >> but can find all the information about the OB_Ieast etc. indices and
>> other run-time parameters. For more you'll have to consult the code in
>> pkg/obcs and the corresponding experiments in verification I am afraid.
>> >>
>> >> There is a orlanski-radiation conditions. To turn it on you need to
>> re-compile with
>> >> #define ALLOW_ORLANSKI
>> >> in OBCS_OPTIONS.h and useOrlanskiNorth/South/East/West=.true. for the
>> boundary of intererst. There are some experiments that use this option (e.g.
>> tutorial_plume_on_slope, dome). If you are not happy with that, you'll need
>> to implement something on your own.
>> >>
>> >> I hope this helps,
>> >> Martin
>> >>
>> >> On Feb 20, 2011, at 5:12 PM, fancer fancer wrote:
>> >>
>> >>> Hello, MIT gcm support.
>> >>> I am novic at modeling with MIT gcm, thus I have several questions
>> about this model and about obcs package, especially.
>> >>>      • My first application describe itnternal waves propagation,
>> generated by temperature and salinity stratification, in 2D area. This is
>> the trivial task, because MIT gcm has internal waves verification example.
>> It is necessary, what waves go through boundaries, but not reflect of that
>> boundaries. How made it with obcs package or with other way? I made many
>> experiments, but whitout positive results.
>> >>>      • Is there more detailed information about open boundies setting
>> in MIT gcm, it is desirable with picture, where OB_Ieast, OB_Iwest,
>> OB_Jsouth, OB_Jnorth represented in a modeling area?
>> >>> In advance, thanks for help.
>> >>> Yours sincerely, Serge Semin.
>> >>> P.S, Sorry for my emglish, I'm still learning.
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