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Problem : facSk and facAs haven't any influence on final bed level

AM
Arthur Mouragues, modified 3 Years ago.

Problem : facSk and facAs haven't any influence on final bed level

Capillary Posts: 4 Join Date: 2/10/16 Recent Posts
Dear all,

I'm running a 1D non hydrostatic case of a sandy barrier in overwash condition. I'm trying to calibrate and see the influence of some factors on the morphology and more particulary the Skewness and Asymmetry factors (facSk and facAs).
However, when varying it from 0 to 1 (0:0.1:1), there is no change in the final bed level. I may have forgotten to activate other parameters.

I've attached the file required : params.txt (for facSk=0.1) , bound_U.bcf, x.grd and depth.dep

Thank you very much for your help.

Arthur
Arnold van Rooijen, modified 3 Years ago.

RE: Problem : facSk and facAs haven't any influence on final bed level

Swell Posts: 239 Join Date: 11/7/11 Recent Posts
Hi Arthur,

Unfortunately the non-hydrostatic mode of XBeach does not have a proper sediment transport formulation yet. This is one of the ongoing developments at the moment.

For testing you can activate sediment transport from the XBeach surfbeat mode also in non-hydrostatic mode, but you should be very careful in interpreting the results, since the sediment transport formulation is essentially designed for wave averaged parameters and not instantaneous output. But facAs and facSk won't do anything, since they are a function of the wave height (H) which is not used in nonh mode.

One of the advantages of having a sediment transport formulation for the nonh mode is that we would not need the parameterization for wave skewness and asymmetry (i.e. facAs and facSk) anymore, since the nonh mode solves the entire wave shape and therefore should take this account directly.

In your case it is probably best to continue with the surfbeat mode to study barrier overwash.

Hope this helps.

Cheers,

Arnold
AM
Arthur Mouragues, modified 3 Years ago.

RE: Problem : facSk and facAs haven't any influence on final bed level

Capillary Posts: 4 Join Date: 2/10/16 Recent Posts
Hi Arnold,

Thanks for your help.

- So, should i write "nonh=1" and "wavemodel=surfbeat" to check the influence ?
- What's the difference between "nonh=1" and "wavemodel=1" ?

Thanks again.

Arthur
Arnold van Rooijen, modified 3 Years ago.

RE: Problem : facSk and facAs haven't any influence on final bed level

Swell Posts: 239 Join Date: 11/7/11 Recent Posts
Hi Arthur,

As far as I know 'wavemodel' is not a keyword you can specify in XBeach, nonh=1 means that you are taking into account the non-hydrostatic pressure term in the nonlinear shallow water equations. This will allow you to not only solve the infragravity (long) waves but also the short waves.

Please have a look in the new manual for an overview of all the keywords that XBeach accepts:
https://oss.deltares.nl/documents/48999/49476/XBeach_manual_Kingsday.pdf?version=1.1

For the different modes, in short, these are the main keywords:

surfbeat mode (default XBeach mode)
swave = 1 (turn on short wave energy balance)
instat = all options except 'stat', 'bichrom', 'stat_table' and 'ts_nonh', most common is 'jons' or 'jons_table', see table 4.4 of manual
nonh = 0 (turn off nonh pres term)

stationary mode (wave boundary conditions constant in time, similar to SWAN):
swave = 1
instat = stat or stat_table
nonh = 0

non-hydrostatic mode (resolve full short wave motions)
swave = 0 (turn off wave energy balance)
nonh = 1
instat = several options available including 'stat', 'jons', 'ts_nonh'

This is just a brief overview, but you can find a more detailed description on these different modes in the manual.

Cheers,
Arnold
AM
Arthur Mouragues, modified 3 Years ago.

RE: Problem : facSk and facAs haven't any influence on final bed level

Capillary Posts: 4 Join Date: 2/10/16 Recent Posts
Hi Arnold,

Thank you for your help.

So if I'm using the nonh mode, there is no sediment transport formulation used by XBeach ? What does it do ?

thank you again

Arthur
Arnold van Rooijen, modified 3 Years ago.

RE: Problem : facSk and facAs haven't any influence on final bed level

Swell Posts: 239 Join Date: 11/7/11 Recent Posts
Hi Arthur,

If you are running in nonhydrostatic mode (nonh = 1) and turn sediment transport on (sedtrans = 1) XBeach will simply use the default sediment transport model that is developed for the surfbeat mode.

Arnold