In the paper, the method for the generation of multidirectional focusing wave was described. A numerical model based on the High Order Spectral (HOS) method was developed, in which, the wave maker boundary condition was introduced to simulate the wave generation. The effect of the wave parameters such as the wave spectral type, center frequency, frequency width and the directional spreading on the focusing wave surface elevation, the generated maximum wave crest, the shifting of the focusing point and the wave spectrum are numerically investigated in the paper. The obtained results can be a good reference for the physical simulation of focusing extreme and breaking waves.
In general, wave focusing is one of the most important mechanisms that contributed to the large waves or wave breaking in ocean, which impose large or extreme forces on ship and offshore structures. Recently, the concept of a focused wave group has been used to represent the profile of the extreme wave. Many researchers had paid a considerable attention to the studies of wave focusing, with the aim of understanding physical mechanisms of creating large waves. Rapp and Melville (1990) studied breaking criterion associated with a focused wave group, and it showed that the deviation in the breaking location from that predicted by linear theory may be attributed to nonlinear effects, which become important as the amplitude is increased. Taylor and Haagsma (1994) showed that as a group focuses it becomes narrower and much higher than that linear theory would predict. Baldock et al. (1996) investigated nonlinear surface water waves undertaken in 2-dimenional wave flume by a large number of water waves were focused at one point in space and time to produce a large transient wave group. The results showed that the focused amplitude, shift of focusing point increased with the wave amplitude increasing.
