【作者】 邓斌；

【导师】 张金凤； 严冰；

【作者基本信息】 天津大学 ， 水利工程， 2018， 硕士

【摘要】 波浪荷载对近岸及海上结构物的稳定性有着重大的影响,海床在循环波浪作用下会出现变形、软化、液化等现象,丧失自身承载力导致危及其上部结构物的安全。本文基于开源离散元法软件Yade,通过耦合离散元方法(DEM)和孔隙尺度有限体积法(PFV)来建立DEM-PFV耦合模型,并改进模型中的对波浪作用部分的模拟。通过在海床表面加载波压数据,模拟规则波作用和不规则波作用下的不同土体性质海床的液化。本文的主要结论及成果如下:(1)基于开源离散元(DEM)软件Yade,在固相部分采用离散元方法(DEM)和在液相采用孔隙尺度有限体积法(PFV)相耦合建立DEM-PFV模型,分析波浪作用下多孔介质海床的动力响应。(2)对建立的数值模型进行验证,通过与实验解、解析解和数值解结果进行对比验证模型合理性。对模型中选取代表颗粒粒径进行敏感性分析,得知适当增大颗粒粒径(小于提取最小尺度的1/6),不仅不影响模拟结果,而且可以减小算例中的颗粒数,进而有效地提高计算效率。(3)分析了规则波作用下,考虑海床土体的孔隙率和弹性模量两个变量对海床孔隙水压力变化和液化情况的影响,并且分析海床土体性质的动态变化,如孔隙率、颗粒总动能等。结果显示:在砂质海床中,通过减小孔隙率和增强弹性模量会降低海床孔隙率变化和颗粒运动,能够有效地增强海床土体在规则波作用下的抗液化能力;而且观察到海床在波浪作用下发生密实过程和液化现象。(4)分析了不规则波作用下,不同孔隙率和不同弹性模量海床土体的孔隙水压力变化和液化情况以及海床土体性质的动态变化。与规则波作用下结论一致,通过减小孔隙率和增加弹性模量能有效地增强砂质海床的抗液化能力。和规则波相比,不规则波由于有波压特大值的出现,对海床土体的稳定性影响更大。更多还原

【Abstract】 The stability of nearshore/offshore structures will be affected by wave loads.The deformation,softening and liquefaction of the seabed under the action of cyclic wave will result in loss of the self-bearing capacity,which endangers the safety of the structure.Based on the open-sourced discretization method software Yade,DEM-PFV coupled model is established by coupling discrete element method(DEM)and porescale finite volume method(PFV),and the simulation of wave action in the model is improved.By loading the wave pressure on the surface of the seabed,the liquefaction of the seabed with different soil properties under the action of regular wave and irregular wave is simulated.The main conclusions and achievements of the study are as follows:(1)A DEM-PFV model was established by using the discrete element method(DEM)in the solid phase and coupled with PFV in the liquid phase based on the opensource DEM software Yade.The dynamic response of porous seabed under wave is analyzed.(2)The established numerical model is verified by comparison with the experimental data,analytical data and numerical results.Sensitivity analysis of selected representative particle size in the model shows that properly increasing the particle size(less than 1/6 of the minimum dimension of the model)will take no effect on the simulation results.Furthermore,the decrease of the number of particles will effectively improve the computational efficiency.(3)Under the action of regular wave,the influences of the porosity and elastic modulus of seabed on pore-pressure and liquefaction of seabed are considered,and the dynamic changes of seabed soils are analyzed,such as porosity and total kinetic energy of particles and so on.The results show that the liquefaction resistance of sandy seabed soils under regular wave can be effectively enhanced by decreasing the porosity and increasing the elastic modulus.The processes of consolidation,compaction and liquefaction on the seabed under wave actions are explored.(4)The pore-water pressure changes and liquefaction of seabed with different porosities and elastic modulus are analyzed under the action of irregular waves,and the dynamic responses of seabed soils are analyzed.It is consistent with the results of regular wave that the liquefaction resistance of sandy seabed can be effectively enhanced by decreasing the porosity and increasing the elastic modulus.And compared with the regular wave,the irregular wave has a greater influence on the stability of the seabed soils due to the appearance of wave pressure large value.更多还原