Numerical Study On Machenisim Of Occurrence And Evolution Of Rogue Wave In Deep Water Considering Wave-current Interaction

Rogue wave is a crucial phenomenon in ocean, which is notorious forappearing without omen and destructive high wave height and energy.Moreover, because of lack in real sea measurements, the mechanism ofrogue wave is still confusing even though some theoretical and numericalmethods have been proposed so far by researchers. Besides that, the effectof wave-current cannot be overlooked as the existence of current wouldinfluence wave parameter, wave propagation and evolution considerably.And wave countering current is thought to be one of the main reasons forthe occurrence of rogue wave. In this thesis, a viscous model is introducedto include viscosity effect on rogue wave. Wave focusing due to dispersionis considered to explore mechanism of occurrence and evolution process ofrogue wave. Generation of rogue wave by viscous model and investigationinto the effect of wave-current interaction on rogue wave are essential partsof this study.The main contents of thesis are:1) Regular waves on preexistinglarge-scale uniform current are generated by using RANS equation withRNG-based k-ε turbulence model. VOF method is adopted for dealing withfree surface.2) Based on the experiments on regular waves propagatingwithout and along current conducted, a reliable numerical tank for wavegeneration is established through validation.3) The influence of current onregular waves is discussed. Variation of wave parameters is analyzedquantitatively. Furthermore, the effect of counter-current is investigated in detail in terms of wave steepness, wave asymmetry, wave breaking andwave blocking.4) Based on the proposed wave tank, rogue wave isreproduced by adopting wave focusing techniques. The current effect onrogue wave is also studied. The influence of viscosity is investigated anddiscussed by comparing with nonlinear potential flow theory (NonlinearSchr dinger Equation).The main conclusions of this thesis are:1) Consistent with the resultsof previous studies, wave height and steepness decrease as the velocity ofuniform current increases when wave propagates along preexistinglarge-scale current whereas counter-current has the opposite influence.2)Viscous model performs better in predicting wave height enhancementwhen regular waves propagate along current.3) The existence of countercurrent steepens wave and aggravates the asymmetry of wave shapedramatically, and wave breaking occurs occasionally as a result.4) It hasbeen confirmed that wave “blocking” associated with significant energytransfer occurs when current speed is comparable with group velocity ofwaves based on viscous model.5) The concentration times of waveestimated by viscous model are compared with modified nonlinearSchr dinger Equation and linear theory, respectively. The prediction ofconcentration time by viscous model is remarkably different. And this factshould be taken into account carefully while generating or predicting roguewaves.6) The current effect on asymmetry of rogue wave is notable. It isshown that the variation laws of crest wave height, and the maximum waveheight, as well as the ratio of the wave crest to wave height are slightlydifferent among viscous model, linear and nonlinear wave theory.7)Concentration time at given position decreases when propagating alongcurrent while it increases against current.8)The existence ofcounter-current exacerbates wave breaking of rogue wave.