MIKE 21 BW, User Manual, Page: 76 / 196

Examples
76 MIKE 21 BW - © DHI
Figure 4.46 Visualisation (3D) of instantaneous surface elevation and the surface
rollers. The image (and animation) is created in MIKE Animator Plus
Due to the increased depth and due to depth refraction by the rip channel,
incipient wave breaking is seen to occur comparatively close to the shore
along the centre line. Here, the wave setup is quite small and the larger setup
appearing away from the rip channel gives an alongshore gradient in the
mean water surface forcing a current towards the centre line. The flow from
the two sides join to form a rip current and two symmetrical circulation cells
appear.
A combined vector and contour plot of the nearly steady state wave-induced
velocity field is shown Figure 4.47. The velocity is computed as the time-aver-
age of the depth-averaged velocity below the surface roller. A pronounced rip
current is seen along the centre line of the bathymetry (y= 300 grid points).
Figure 4.48 shows the cross-shore variation of the rip current. A maximum of
approximately 1 m/s for the mean depth-averaged return current is seen,
which is in good agreement with the experiments reported by Hamm (1992b),
see Sørensen et al (1998).