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RE: fuzzy wave height output for example case of '1953_stormsurge'

JH
James Harper, modified 3 Years ago.

fuzzy wave height output for example case of '1953_stormsurge'

Capillary Posts: 1 Join Date: 2/11/16 Recent Posts
Hi,

I am running the '1953_stormsurge' case which I downloaded from:
http://oss.deltares.nl/web/xbeach/documentation

I did not change any of the inputs. However, when I look at the input vs. output wave height at the boundary (x=0), the time series of the input wave heights (Hmo from jonswap_*.txt files) and direct wave height outputs (parameter 'H') at x=0 are quite different (I attached the plot), the output wave heights at the boundary (x=0, and actually everywhere else) are quite 'fuzzy' (so is other parameter, such as ue, ve, urms, etc.), although the input wave height time series are smooth. (I used SWAN before, and I don't see such features.)

Does this have any physical meaning? (I assume the wave heights between jonswap_1.txt and jonswap_2.txt at each time step (~0.1sec) are linearly interpolated). The plot tells me between Time=0 and Time=200, there was a time that wave height is below 1 meter, however the input wave height was above 4 meter, what caused the oscillations? (I am running hydrostatic XBeach (did not change any inputs)).

Thank you very much for your help!!!


Jim
Arnold van Rooijen, modified 3 Years ago.

RE: fuzzy wave height output for example case of '1953_stormsurge'

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

These oscillations are generated by XBeach because it is an instationairy wave model. The variations you see represent the (sea-swell) wave groups. This is a crucial difference with SWAN (=stationary), and allows for simulation of infragravity waves. The variations you see in ue, zs etc. are variations due to IG waves (in SWAN they would be constant).

The wave height (Hm0) you give as input is translated into a wave energy time series by XBeach using the other paramters you specify (e.g. Tp, duration, wave direction). If you average the wave height output over the wave condition duration you should end up with the initial wave height again. Please note that while the input of XBeach is Hm0 (Hsig), the output is Hrms (computed from the wave energy). So to compare fairly you should multiply with sqrt(2).

Hope this helps.

Cheers
Arnold