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Spatial instability with XBeachX nonh at high resolution

JB
James Bramante, modified 1 Month ago.

Spatial instability with XBeachX nonh at high resolution

Capillary Posts: 5 Join Date: 4/8/15 Recent Posts

I'm running a simple, 1D simulation of a plane beach (roughly 1.5 degree slope) from -10 to 2 m depth at 0.5 m cross-shore resolution. The non-hydrostatic model is forced at the offshore boundary by a JONSWAP spectrum. When I average velocity over an hour of model time, the output has high frequency oscillations in the spatial domain (wavelength 2.5-5 m). I have fiddled with basically every conceivably relevant knob in XBeach, but can't get rid of the oscillations.

 

The oscillations have their highest magnitude in the vicinity of breaking waves, but are also found seaward of the breaking waves.

 

Is this an unavoidable aspect of how the non-hydrostatic model handles breaking waves?

 

 

Things that have worked a little bit:

-Coarsening the grid resolution

-Increasing the flow friction coefficient

 

Things I have tried that haven't worked:
-Very high and very low CFL

-Using nonhq3D and not using it

-Altering model bathymetry, including maximum depth

-Changing land boundary types

-Altering alongshore grid resolution

-Changing flow boundary condition numerics

 

non-hydrostatic boundary conditions instability 1d xbeachx resolution