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Abstract In recent years, extreme waves, which appear from nowhere with extremely large wave height in the ocean, have attracted extensive attention and research in academic and engineering fields. A simple linear model proposed by Tromans et al.–NewWave theory2, has been widely used to explain the occurrence of extreme waves. The NewWave model requires that all frequency components in a random seastate focus at a specific time and location to generate a large wave group, which however is unlikely to happen naturally. In this work, we consider an otherwise more realistic condition where wave energies are only partially focused. Focused wave groups are generated by partial energy focusing using a JONSWAP wave spectrum and their characteristics are studied. The effects of different frequency components and bandwidths on the characteristics of wave groups are investigated. A high order spectral (HOS) model, which is validated by physical experiments, is utilized to simulate the propagation of partial focusing waves. Both second-order and fifth-order simulations are carried out to understand the influence of modulation instability. The nonlinear characteristics of partial focusing waves during its propagation are studied simultaneously. Overall, this work provides some new insights into the mechanism of formation of extreme waves.
Cui et al. (Sun,) studied this question.