【作者】 周援衡；

【导师】 王永和；

【作者基本信息】 中南大学 ， 岩土工程， 2011， 博士

【摘要】 波浪作用下海床地基的动力稳定性是近海岸及离岸工程建筑物在设计和建造过程中必须充分考虑的重要问题之一。海洋上传播的波浪在海水与海床的交界面处施加了循环波压力荷载。在这种循环的波压力作用之下,会引起海床内孔隙水压力与有效应力变化,致使海床出现土体位移和变形,在一定条件下可能发生土体剪切破坏和砂土液化现象；而波浪与防波堤相互作用及其海床和抛石介质的动力响应问题求解也是海洋工程中普遍存在的另一技术难题,对基岩特性的忽视和不适当的工程处置可能导致海床失稳,乃至海床上建筑物的破坏。因此研究波浪与防波堤相互作用及其海床动力响应和基岩特性影响问题具有重要理论及工程意义。文中针对波浪与带有抛石介质防波堤的相互作用及其相应的砂质海床和没有建筑物的纯砂质海床的动弹性响应问题,通过国内外广泛调研、理论分析、模型试验和数值模拟计算对其进行了深入研究,获取的研究成果主要有以下几方面：(1)通过室内物理模型试验,研究了线性波或浅水椭圆余弦波作用下不同海床介质、波浪类型、波高、周期和水深等因素影响下抛石潜堤、海床和带抛石基床防波堤海床的动力响应问题,获得了孔隙水压力等物理量分布及其响应变化规律；(2)基于对波浪域和孔隙流体域的理论分析,建立波浪域的紊流Navier-Stokes方程和抛石多孔介质孔隙流体域的Forchheimer方程,采用VOF方法对自由表面进行跟踪,引入k-e模型来封闭雷诺方程,籍之构建了整个波浪场的控制方程,来描述非线性较强的波浪行为及大颗粒多孔介质内部的孔隙流；(3)基于描述波浪-抛石介质相互耦合作用的VOFFDM计算模型程序,计算得到了不同入射波要素、水深、抛石介质孔隙率和堤断面尺寸等因素影响下海床的动力响应规律,揭示了堤前堤后波高、堤内孔隙水压力和孔隙流场随波浪性质、波要素、水深以及抛石介质孔隙率和堤断面尺寸等因素影响下的变化特征,为进一步分析防波堤下卧海床内沿程动力响应以及抛石单体和防波堤整体的稳定性提供了重要依据。物模试验结果验证了VOFFDM程序的有效性与可靠性。(4)针对天然饱和海床固有的各向异性特征,将天然海床假定为横观各向同性的饱和多孔介质,基于横观各向同性饱和多孔介质Biot动力渗透-固结理论,文中首次建立了横观各向同性饱和海床的动力方程,编制了动力固结有限元程序BCFEM,模型试验结果验证了程序的有效性与可靠性。(5)应用动力固结有限元程序BCFEM,对线性波和浅水椭圆余弦波作用下的均质各向同性饱和海床、非均质各向异性饱和海床的动力响应问题进行了深入研究,获取了不同波浪要素组合下及其有无防波堤海床内孔隙水压力等参数的变化规律,揭示了海床对波浪的动力响应是由波浪要素和海床介质特性共同决定的,其中波高和波周期是其主要的控制参数,海床固有的非均质性和各向异性特征对其孔隙水压力和有效应力等分布具有较显著影响。更多还原

【Abstract】 It is of importance to analyze the dynamic stability of seabed or structure foundation under wave action in the design and construction of offshore and coastal structures. When wave propagates over ocean surface, a sequence of wave pressure is induced on the seafloor, which causes the fluctuations of pore water pressure or effective stress, displacement of soil particles, and deformation of soil skeleton within seabed simultaneously. Because of unsuitable treatment in engineering, part of seabed may even lead to soil shear fracture or sandy liquefaction under certain conditions, which is responsible to the damage or destruction of offshore structures. In spite of the technologic difficulties widely existing in offshore engineering, it has important significance in theory and application to study the interaction between wave and breakwater, the corresponding dynamic pore water pressure etc. responses within sandy seabed and riprap porous media of breakwater.This paper researches those questions, the interaction between wave and breakwater with riprap porous media, the corresponding elastic dynamic response within its sandy seabed or riprap porous media and the natural sandy seabed without breakwater as well as following.(1) A series of lab tests in wave tank were performed for the models of breakwater with riprap media, sandy seabed with or without breakwater, to study the interaction between wave and breakwater and the dynamic responses within seabed or riprap media. By means of different lab group situation, such as different seabed media,water depth, approaching wave height or wave period, under the action of linear wave or shallow water cnoidal wave,the laws of the pore water pressure within sandy seabed or riprap media and the wave height before or after breakwater were obtained and analyzed as well.(2) Based on the theoretical analysis of wave field and porous fluid field within riprap media, the optimum numerical model was built, which applied turbulent Navier—Stokes Equation and introduced k-εmodel to close Renault Equation, can describe more objectively the nonlinear effect caused by fluid—solid boundary action and the turbulent fluctuation effect by viscous fluid action in wave field domain. As for porous fluid field, turbulent Forchheimer Equation was used to reveal the relationship between Non—ancy porous flow velocity and pressure gradient. On the basis of the analysis model above, this paper developed a large-scale practical finite difference method program so called VOFFDM, in which, VOF method was employed to trace water free surface and the problem of the fluid-solid coupling on the interface between wave field and porous media was solved by making sure that the velocities or pressures of the two field flows on the interface keep to be equal all the time, so that the program VOFFDM can calculate the wave field and porous media simultaneously with any type of breakwater and complicated boundary.(3) The comparison between VOFFDM numerical results and test results showed good agreement and demonstrated that the numerical model can successfully simulated the interaction between wave and breakwater with riprap porous media. With different wave parameter, water depth, riprap porosity, the dimension of breakwater section, and under the action of linear wave or shallow water cnoidal wave, the details of wave height before or after breakwater and pore water pressure or flow velocity within riprap media were discussed. The analysis results above were the important basis on further studying not only the responses of the seabed below breakwater but also the stability of riprap single or the structure itself.(4) Based on the inherent anisotropy characteristics of natural saturation seabed, the natural seabed was assumed to be transversely isotropic saturated porous media. According to Biot dynamic penetration- consolidation theory of transversely isotropic saturated porous media, this paper built the dynamic equation of transversely isotropic saturated seabed for the first time and developed the dynamic consolidation finite element program so called BCFEM. Furthermore, its correctness was verified by model tests.(5) By applying the dynamic consolidation finite element program BCFEM, an amount of system parameter analysis on the dynamic responses of homogeneous and isotropic saturated seabed and the responses of heterogeneous anisotropic saturated seabed was carried out,and the laws of pore water pressure etc. within seabed under the action of linear wave or shallow water cnoidal wave were obtained with different conditions such as the sandy seabed with or without breakwater, different wave parameter group, water depth etc.. From the results above, it was concluded that the wave dynamic responses are decided by both wave parameters and the characteristics of seabed media, wave parameters such as wave height or wave period are mainly controlling elements, seabed inherent heterogeneity and anisotropy have significant effect on the distribution of pore water pressure or effective stress within it.更多还原