
L12. Diffraction around a shoal
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 Vincent and Briggs (1989)
and with computational results obtained by Ozkan and Kirby (1993) using their
parabolic refractiondiffraction model.
Results of computations by Panchang et al (1990) are also shown in the graphs.
These results and the observation by Vincent and Briggs (1989) are for regular waves
whereas the Swan results and the computations by Ozkan and Kirby (1993) are for
irregular waves. As expected the deviation between the latter two is smaller
than the deviation between Swan and the first two.
The upper panel of plot L12.plt shows the values of H_{s}/H_{s,inc}
along the line normal to the main wave direction, tangent to the shoal (line AA),
and the lower panel show the same quantity along the centre line over the top of the shoal.
Boundary conditions are applied at 3 sides of the computational grid.
2 cases are considered:
 L12a
 Swan without diffraction
 L12b
 Swan with standard diffraction
Graphs are shown for cases a, b and c, along the centre line across the shoal
and along the line tangent to the circumference of the shoal at its most downwave point.
 L.H. Holthuijsen, A. Herman, N. Booij (2003)
 Phasedecoupled refractiondiffraction in a spectral wave model,
Coastal Engineering, vol.49, PP.291305
 H.T. Ozkan and J.T. Kirby (1993)

 Evolution of breaking directional spectral waves in the nearshore zone,
Proc. 2nd Int. Conf. Ocean Wave Measurement and Analysis, WAVES '93,
ASCE, New York, pp. 849863
 V.G. Panchang, B.R. Pearce and M.J. Briggs (1990)

 Numerical simulation of irregular waves propagating over shoal,
J. Waterw., Port, Coastal and Ocean Engng., vol. 116, nr. 3, pp. 324340
 C.L. Vincent and M.J. Briggs (1989)

 ,
J. Waterway, Port, Coastal and Ocean Engng, vol. 115, no. 2, pp. 269284

