Numerical Study Of Coastal Disaster Wave Evolution

Wave is one of the main hydraulics factors in the ocean.Water movement of wave is one of the influence factors to human activities in(near)the sea,so that wave researching is significative in science and engineering.In most cases,wave brings disasters to mankind in(near)the sea.Investigation of wave transformation and flow field,especially of disasters wave,is the precondition for marine resources exploitation and the theoretical basis for marine disaster forecasting.In this paper,disaster wave was selected as research object.According to the spatial scale,disaster wave can be divided into two types:1)Large-scale wave,such as tsunami;2)Small-scale wave,such as freak wave.Numerical simulations and physical experiments were carried out to study the process of tsunami transformation in the near shore area and freak wave transformation on a submerged breakwater.Most attentions were paid on the characteristic of wave breaking and flow field.In this paper,numerical simulations and physical experiments were both performed.Phys-ical experiments were completed in Ocean College,Zhejiang University.Numerical simulations were performed with a CIP(Constrained interpolation profile)-based model.The model based on incompressible Navier-Stokes equations,the high-order constrained interpolation profile(CiP)method was employed as the base flow solver.The free surface was captured by a modified VOF-type scheme,the tangent of hyperbola for interface capturing with slope weighting scheme(THINC/SW),the internal solid boundary was treated by an immersed boundary method(IBM).Firstly,the processes of tsunami wave evolved on the coast was investigated numerically.The topography included submarine gentle slope and coastal cliff.Numerical results were compared with available data and good agreement was obtained.Time evolution data of tsunami wave were obtained,which were scarce in field measurement.The results of tsunami amplification factor,time series of relative wave elevation,wave height in front of the cliff and wave run-up on the cliff were analyzed.Besides,most attentions were paid on the pressure.The time histories of impact pressure,appearance of maximum pressures and pressure field were studied deeply.It was found that there were two opportunities for the appearance of extreme pressure:impact and back flow.Then,numerical simulations and physical experiments were performed to reappear the process of freak wave passed on a submerged breakwater.Numerical results and experiment data were compared and good agreement was obtained.The influence of nonlinearity was studied.Time series of relative wave elevation were discussed.Special attentions were paid to the variation of free-surface and flow field,the relationships of flow field and free-surface were discussed.It was found that when wave breaking happened,wave energy dissipated quickly,and the stronger the nonlinear,the smaller the transmittance was.Finally,two-liquid phase VOF method has been applied in the numerical model to simulate the variation of internal interface.The processes of regular wave and freak wave pass through the submerged breakwater were reappeared.The mixing of water-water has been discussed.It was found that when wave breaking happened,the mixing water was mainly distributed in the bubble regions,and as the process of wave breaking ended,water from different sources mixed together soon.The highlights of this work includes:1.The flow fields,which were scarce in the previous studies,were analysed.There were two occasions for the appearance of extreme pressure:impact and backflow.The extreme pressure of impact was large and focus.The extreme pressure of backflow was widely distributed which could not be ignored.2.The relationships of flow field and free-surface in freak wave were discussed,the freak wave breaking was described detailedly and the characteristics hydrodynamics were revealed for the first time.The wave energy focused in the wave crest due to the submerged breakwater,which inducing wave breaking.In broken zone,the velocities of water particles are high.3.Two-liquid phase VOF method has been applied to study the mixing of water-water in wave-structure interaction for the first time.Breaking of internal interface was independent of wave breaking.Under the continuous action of non-breaking wave,the internal interfaces were found broken.As for breaking wave,the water from leaping head distributed around the bubbles.