A36. Diffraction test with semi-infInite breakwater

In this test results for Swan with diffraction are compared with the analytic solution by Sommerfeld for monochromatic and uni-directional incident waves. The results are compared for three semi-circles all having the breakwater tip as their centre. The radii of the semi-circles are 2L, 3L and 5L, where L is the wave length (39 m in this case).
Tests are carried out for various orientations of the computational grid, in order to verify whether the results are insensitive to grid rotations etc.
In order to keep as close to the assumptions of the analytical solution as possible, the obstacle is made reflecting.
In all computations with diffraction the number of iterations is enlarged to 100 in view of the slow convergence.

4 cases are considered:

no diffraction; standard orientation of the grid
standard diffraction; grid as A36a; this run is unstable!
diffraction with smoothing applied
as A36c; grid rotated over 90 degr

Run A36b is not Included in the graphs because the diffraction approximation is unstable without smoothing (this is standard in the present distributed version of Swan).

© 2012: Nico Booij