The Study Of Hydrodynamic Characteristics Of Waves On Permeable Submerged Breakwater

Permeable submerged breakwater is a structure arranged in water.Compared with impermeable submerged breakwater,permeable submerged breakwater has good permeability,which can not only make waves break in advance,but also reduce the energy of incident wave more effectively due to the damping effect of porous media itself,thus reducing the erosion of beach by waves.However,a large proportion of established submerged breakwaters on the world have failed to protect shoals effectively and cause unexpected erosion.At present,the research experience on submerged breakwater is limited,and the research on its permeability is even less.The content of this paper is mainly divided into two parts.In the first part,the comparison experiment between permeable and impermeable submerged breakwater is carried out.And in the second part,the open source program Open FOAM is used to study the wave motion on permeable submerged breakwater.In the model experiment,5cm glass balls were used to pile up the submerged breakwater,and smooth wood boards were used to build the impermeable submerged breakwater,to avoid wave attenuation caused by the surface friction of the submerged breakwater material.Choose non-broken regular wave and irregular wave as far as possible,in order to discuss the wave attenuation caused by the permeability of submerged breakwater.However,wave breaking inevitably occurred on impermeable submerged breakwater during the experiment.In the regular wave experiment,the waveform changes,wave height attenuation and harmonic attenuation of permeable submerged breakwater and impermeable submerged breakwater are compared.It is found that the submerged breakwater has outstanding advantages in reducing wave nonlinearity,damping wave height and suppressing high frequency harmonics.In the experiment of irregular wave,the difference of spectrum,skewness and kurtosis between permeable submerged breakwater and impermeable submerged breakwater is mainly compared.It is found that seepage submerged breakwater can effectively consume the second order harmonic wave energy,and its skewness and kurtosis are smaller than those of impermeable submerged breakwater.The wave surface elevation on permeable submerged breakwater is closer to normal distribution,and the nonlinear is weaker.The relationship between skewness and kurtosis of wave on both permeable submerged breakwater and impermeable submerged breakwater is basically consistent with the relationship proposed by Mori et al.By comparing the degree of asymmetry,it can be found that the wave shape changes from front dip to back dip on the submerged breakwater.Ola Foam,a two-phase flow solver that can simulate pore flow,was selected as the numerical simulation program.The physical model experiment focused on the influence of wave conditions on the wave-breaking ability of the submerged breakwater,while the numerical simulation focused on the characteristics of the submerged breakwater itself.Firstly,the appropriate laminar and turbulent drag coefficients are determined by referring to previous research results and repeated attempts of individuals.In this paper,the effects of porosity,median particle size and top width of submerged breakwater on wave evolution,flow velocity inside and outside the submerged breakwater and turbulent kinetic energy near the submerged breakwater are studied,and the relevant conclusions are given.