Freak Wave Simulation And The Basic Characteristics Of Study

Freak wave is a single "mammoth" short crested wave with, apparently, little relation to its neighboring waves. It has a high crest but not necessarily a corresponding pronounced trough. It does not stay long but break down in small waves. The appearance probability of the freak wave is so small and unanticipated that we could not get many actual sea waves data of freak wave. This study aims to look for a numerical method to simulate freak waves in laboratory. The main content:Based on many references on the definition of freak wave, the definition of freak degree is suggested, which can describe freak waves more accurate.By the Longuet-Hinggins Model, freak waves in a random sea state were simulated. Based on the results of simulation, the character and the appearance probability of freak wave were studied. When the initial phases distribute symmetrically, we can hardly get the freak waves which agree well with actual freak waves by observations.· When the simulation method was developed, that is when the initial phases distribute asymmetrically, the freak waves which agree well with actual ones have been generated. When 1/10, 1/4 and 1/3 of total initial phases are identical, the appearance probability of freak waves is respectively 1/1000-2/10000, 1/220-1/250 and 1/130-1/70. When 1/3 of total initial phases are identical, the freak waves are strongly nonlinear. And freak waves under deep and shallow water conditions have been simulated. If do not consider the terrain of ocean, the appearance probability of freak wave is more and the waves are freaker under deep water condition than those under shallow water condition.· Based on numerical simulation, the superposition method of composing waves and 2-order Stokes wave theory have been used to compute the Eular velocity of wave particle of freak waves, and comparison has been made between the results of calculation. When the depth of a water particle, Z/d, is more than 0.75, particular around the water surface, result of the superposition method of composing waves is larger than that of 2-order Stokes wave theory, even 32.8% .Velocity field of negative Z direction computed by the superposition method of composing waves is greatly different to the result calculated by 2-order Stokes wave theory, even 200%.