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Why are oceanic models written in primitive variables?

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Old   September 16, 2010, 12:17
Default Why are oceanic models written in primitive variables?
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Hi. I always wandered why all the oceanic models solving the 3D hydrostatic shallow water equations(ROMS,DELF3D,FVCOM)are written in primitive variables. I think the reason is that they do not usually have to deal with shocks, as instead is true for river models in which you can have discontinuos phenomena like dam break or hydraulic jump. Is this the main reason? and if this is the reason, what is the advantage of using primitive variables?
And finally,if this is the reason, these models are not able to compute, for example, a tzunami wave approaching the coast, since the discontinuos wave that forms has the wrong speed (Toro,2001) , hasn't it?
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Old   September 20, 2010, 07:39
Jed Brown
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Shocks are generally thought to be unimportant over long time periods. The methods used are only valid for smooth solutions anyway (this is enforced through artificial dissipation), and are thus not appropriate for purposes like modeling tsunami run-up. I'm not aware of any true advantage of velocity-thickness form, I suspect that choice is mostly historical.
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