均质各向异性含水层稳定态地下水盐度分布及海底地下水排泄的数值模拟

发布时间：2018-03-02 06:43

本文关键词： 海底地下水排泄(SGD) 盐度分布密度差异坡度稳定态数值模拟　出处：《中国地质大学(北京)》2015年硕士论文　论文类型：学位论文

【摘要】：海底地下水排泄和海水入侵是两个相互作用、相互影响的处于动态平衡的过程,为了进一步了解稳定状态下均质各向异性潜水含水层中海水与地下水之间的相互作用,本文利用数值模拟法重点研究了渗透系数、各向异性比、纵横向弥散度之比和海底坡度对含水层中盐度分布和海底地下水排泄量的影响。其中,渗透系数的变化范围为10-9m/s~1m/s(弱透层到含水层、粘土层到砾石层),各向异性比的取值范围为1~100,纵横向弥散度之比的取值范围为1~500,海底坡度的变化范围为0.01~?2(弧度)。模型区域内陆边界为给定水头边界、盐度为零,区域底部为隔水边界,上边界(地表)为不考虑降雨和入渗的隔水边界,海向边界的压力水头为作用于其上的海水水柱的压强,当海水流入含水层时为给定浓度35g/L,当水流流出含水层时为零弥散边界条件。采用二维数值代码MARUN来求数值解,空间离散采用三角形有限单元法,依据海底坡度的不同,所考察区域的海向延伸长度不等,结点数在16605到41123间变化,三角形单元数在32320到80160之间变化,网格的Peclet数均小于2,Courant数小于0.95,计算过程采用Picard迭代法,压力水头迭代收敛标准为10-5m。研究结果表明:当zx L?KK?10-6m2/s时(其中zK是垂直渗透系数、L?是纵向弥散度),盐度的空间分布几乎独立于水平渗透系数xK,且此时地下淡水排泄量fQ和海水再循环量sQ均与水平渗透系数xK呈线性关系,同时用一个半解析方法验证了这一系统性结论;各向异性比增大时,咸淡水界面向海向移动、并使海水再循环量sQ减小,消除了相关文献对此的争议;给定纵向弥散度后、增大纵横向弥散度之比会使混合带变倾斜并降低海水再循环量sQ;当海底坡度?从0.01增大到?2时,咸淡水混合带会向内陆方向移动,当??4时,海底坡度?的增大会使海水再循环量sQ有轻微的增加,当??4时,海底坡度?的增大会降低海水再循环量sQ。这些研究结果填补了前人在研究稳定态海水-地下水相互作用时时尚存的空白,进一步对影响SGD的因素进行了挖掘与分析,具有重要的意义。
[Abstract]:Undersea groundwater discharge and seawater intrusion are two interactive, interactive processes in dynamic equilibrium, in order to further understand the interaction between seawater and groundwater in homogeneous anisotropic aquifers in a stable state. In this paper, the effects of permeability coefficient, anisotropy ratio, longitudinal and transverse dispersion ratio and submarine slope on salinity distribution and groundwater discharge in aquifers are studied by numerical simulation. The variation range of permeability coefficient is 10-9 m / s / s (weak permeability layer to aquifer, clay layer to gravel layer), anisotropy ratio is in the range of 1 ~ 100, longitudinal and horizontal dispersion ratio is in the range of 1 ~ 500, and the variation range of submarine slope is 0.01? 2 (Radian). The inland boundary of the model area is a given head boundary, the salinity is zero, the bottom of the region is a water-barrier boundary, and the upper boundary (surface) is a water-barrier boundary that does not take into account rainfall and infiltration. The pressure head of the sea boundary is the pressure of the water column acting on it. When the seawater flows into the aquifer, it is 35 g / L of given concentration, and when the water flows out of the aquifer, it is a zero dispersion boundary condition. The numerical solution is obtained by using the two-dimensional numerical code MARUN. The spatial discretization adopts the triangular finite element method. According to the difference of submarine slope, the length of sea direction extension varies from 16605 to 41123, the number of triangular elements varies from 32320 to 80160, the number of nodes varies from 16605 to 41123, and the number of triangular elements varies from 32320 to 80160. The Peclet number of the grid is less than 2? Courant number less than 0. 95. The Picard iteration method is used in the calculation process, and the convergence criterion of pressure head iteration is 10 ~ (-5) m. The results show that: when ZX L? KK? 10-6 m2 / s (where ZK is a vertical permeability coefficient L? The spatial distribution of salinity is almost independent of the horizontal permeability coefficient (XK), and there is a linear relationship between the underground fresh water discharge (f Q) and the seawater recirculation volume (sQ) with the horizontal permeability coefficient (XK), and the spatial distribution of salinity is almost independent of the horizontal permeability coefficient (XK). At the same time, a semi-analytical method is used to verify this systematic conclusion. When the anisotropy ratio increases, the salt-water interface moves toward the sea and decreases the seawater recirculation volume (sQ), which eliminates the controversy in the relevant literature. Increasing the ratio of longitudinal and transverse dispersion causes the mixing zone to be tilted and reduces the seawater recirculation sQ. when the seabed slope is? From 0.01 to? 2:00, the salt and fresh water mixing zone will move inland, when? ? 4:00, bottom slope? The increase of seawater recycling volume (sq) will cause a slight increase in seawater recirculation volume (sq). ? 4:00, bottom slope? These results fill the gaps in the previous researches on the interaction between seawater and groundwater in a stable state, and further excavate and analyze the factors affecting SGD, which is of great significance.
【学位授予单位】：中国地质大学(北京)
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P641;P731.2

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