Detuning and wave breaking during nonlinear surface wave focusing

Using an energy focusing technique, several transient wave trains were generated in a two-dimensional wave flume to investigate their nonlinear evolution. By increasing the initial wave steepness (S0), while all other parameters remained the same, non-breaking through breaking conditions were achieved. The experimental results demonstrated that the waves' initial steepness affected the focusing process significantly. As expected, the nonlinear effects on wave packets with a low initial steepness were very small. However, for cases with large initial steepness, nonlinearity increased causing the wave packet to focus and break prematurely, a “detuning” process. As a result of the detuning process more than one breaker may occur, and more importantly when this ensues, energy loss was altered. It is found that for S0<0.274, only one breaker occurred, and the energy loss increased with increased initial steepness. For larger steepness, two breakers occurred and the total energy loss remained nearly constant (~17%) as the initial steepness was increased. As the initial steepness was increased still further, a large plunging breaking was obtained with additional energy loss (4%). These results suggest that the “detuning” has a pronounced influence not only on the resulting wave field, but on the resulting energy loss.