L11. Diffraction behind a gap in a breakwater
The purpose of this test is to validate the diffraction approximation in Swan.
The approximation is described by Holthuijsen, Herman and Booij (2003).
The results are compared with observations reported by Yu et al.(2000).
Two tests have been used, both with a gap width equal to 4 times the wave length (2 m);
one test was carried out with regular incoming waves,
the other with unidirectional irregular waves.
A domain with horizontal bottom is considered.
In order to simulate the unidirectional incoming waves
at the Southern boundary an incident wave field is assumed with narrow directional distribution ([ms]=500)
and a Jonswap spectrum over frequencies with peak period of 1.2 s.
The wave field propagates in N direction.
7 cases are considered:
- Swan without diffraction
- Swan with standard diffration
- diffraction with enhanced smoothing
- diffraction with strong smoothing
- standard diffraction on a grid, rotated over i90 degrees, in order to
test the correct implementation
- standard diffraction on a grid, with singularity approximation
- as L11f, but with simplified representation of the breakwater
Graphs are shown for cases a, b and c, along lines parallel to the breakwater at various distances
behind the breakwater: 0 m (i.e. in the gap), 3 m, 6 m and 9 m.
- L.H. Holthuijsen, A. Herman, N. Booij (2003)
- Phase-decoupled refraction-diffraction in a spectral wave model,
Coastal Engineering, vol.49, PP.291-305
- Yu, Y.-X., S.-X., Li, Y.S., Onyx, Wai, W.H. (2000)
- Refraction and diffraction of random waves through breakwater,
Ocean Engng, vol. 27, pp.489-509