基于Level-Set法的有限元非饱和渗流方法在黄壁庄水库中的应用

Application of Level-Set method-based finite element unsaturated seepage method to Huangbizhuang Reservoir

针对传统非饱和渗流分析方法中忽略气相作用而导致无法处理气相参与的含自由面渗流这一问题,建立了一种耦合Level-Set法的有限元非饱和渗流分析方法。该方法基于有限元非饱和渗流分析理论,利用Level-Set方法隐式地捕捉自由界面,考虑了入渗过程中的气相可压缩性,能够反映多孔介质中水气两相界面的运动与融合,可以用来求解常规方法无法处理的气相参与的含自由面渗流问题,同时具有自由面构造简单、计算稳定性好、收敛速度快等优点。本文将该方法应用于黄壁庄水库在库水位骤升后出现坝前水面冒泡现象的原因分析中,模拟了该水库坝前水-气两相运移过程,揭示了冒泡现象发生的原因。计算结果表明,此方法可简单、直观地描述水气界面在多孔介质中的运动过程,模拟结果与实际情况较为符合。研究表明,黄壁庄水库坝前水面出现冒泡现象是由水位骤升将铺盖内的空气封住,并随水体入渗压缩空气,出现憋气现象,最后气体释放所致。

Aiming at the problem of that the air phase-involved seepage with free surface is unable to be dealt with in the conventional analysis method for the unsaturated seepage caused by ignoring the air phase effect,a coupled level-set method-based finite element unsaturated seepage analysis method is established herein.Based on the finite element unsaturated seepage analysis theory,this method can reflect the movement and fusion of the two-phase interface between water and air in the porous media through the implicit capture of the free face with Level-Set method under the consideration of the compressibility of air phase during the infiltration process,thus can be used to solve the problem of that the air phase-involved seepage with free surface cannot be dealt with by the relevant conventional method;which has the merits of simple free face structure,better calculation stability and rapid convergence rate.The method is applied to the analysis of the causation of the water surface bubbling phenomenon occurred in front of the dam after the sharp rise of the water level of Huangbizhuang Reservoir,and then the water-air two phase migration process in front of the dam of the reservoir is simulated,thus the causation of the bubbling phenomenon is revealed.The calculation result shows that the method can simply and intuitively describe the movement process of the water-air interface in the porous media,from which the simulated result is more coincided with that of the reality.The causation of the bubbling phenomenon of the water surface in front of the dam of Huangbizhuang Reservoir is that the air inside the blanket is sealed by the sharp rise of the water level and then is compressed along with water infiltration,thus the air is closed and released at last.