Numerical Study On Dynamic Response And Liquefaction Of Sandy Bed Foundation Near Semi-circular Breakwater Due To The Wave Load

In recent years,marine resources have been continuously developed.In order to prevent waves from causing damage to coastal zone,new breakwaters have been designed and developed.As a new type of marine protection structure,semi-circular breakwaters have emerged.The semi-circular breakwater will face complex marine environment during.The wave load not only has an impact on the breakwater,causing damage to the structure itself,but also interacts with the seabed foundation,resulting in liquefaction of the seabed soil and affecting the stability of the structure and reducing the service time.The stability of seabed foundation is one of the important prerequisites to ensure the safe operation of marine structures.The dynamic response and liquefaction analysis near structures under wave loads have attracted the attention of many scholars.Therefore,this paper will study the dynamic response and liquefaction of seabed soil around semi-circular breakwater under wave load by numerical simulation.The details are as follows:Based on Open FOAM,a coupled numerical model of wave-structure-seabed is established to study the dynamic response of seabed near the structure.The flow field model is based on the existing Ola Flow solver to simulate the generation and propagation of waves and the interaction with breakwater structures.The seabed model is developed based on the Biot consolidation model and the semi-dynamic model respectively to realize the consolidation of the seabed under the self-weight of the structure and the dynamic response due to the wave load.Based on the above simulation results and liquefaction criteria,the seabed liquefaction analysis is carried out.The wave model and the seabed model are coupled by the pressure continuity boundary condition which the control equation of the seabed model is solved by solving the wave pressure at the bottom of the wave tank as the load boundary condition of the seabed surface.Firstly,the grid convergence analysis of the wave-structure-seabed coupling model is carried out to ensure that the model has high calculation accuracy and fast calculation efficiency.Then,the reliability of the numerical model established will be verified by comparing the existing flume test results with the digital simulation results.The flume test with the nonstructure and the structure are verified respectively,and the liquid level time history curves and the pore water pressure change of the seabed soil at different positions are analyzed.The numerical simulation results are in good agreement with the experimental results,indicating that the numerical coupling model established can accurately simulate the hydrodynamic characteristics and seabed response characteristics around the west breakwater under wave action.The effects of different wave parameters,seabed characteristics and geometric parameters of semi-circular breakwater on the dynamic response of seabed soil around semi-circular breakwater are studied and analyzed.The results show that maximum pore water pressure in the seabed decreases with the increase of seabed depth under wave load.The maximum effective stress increases first and then decreases with the increase of seabed depth.The peak value appears at the shallow seabed,and dynamic response at the junction of breakwater and riprap foundation bed is the strongest.The increase of wave height and period will aggravate the dynamic response of seabed soil,and the increase of water depth will weaken the dynamic response of seabed.The permeability coefficient and the diameter of the semi-circular breakwater are negatively correlated with the dynamic response of the seabed,and Poisson ’s ratio has less effect on the the seabed’s dynamic response.Based on the above simulation results,combined with the liquefaction criteria,the maximum liquefaction depth of the seabed under different parameter changes is further studied.The dynamic response of the seabed around the semi-circular breakwater is studied.The results show that the interaction between the wave and the breakwater changes the waveform around the structure,the peak becomes sharp and trough becomes slow.The pore water pressure decreases sharply in the shallow seabed and remains basically unchanged in the deeper seabed soil.The seabed foundation under the structure undergoes seepage consolidation under the gravity of the breakwater,the effective stress increases,and liquefaction is not easy to occur under dynamic wave load.The middle area of the separated breakwater forms a transient liquefaction zone at a certain time,and the breakwater has the risk of tilting,which threatens the overall stability of the structure.