水平面渗流有限元中利用接触单元模拟悬挂式阻水结构

Simulateing suspended cut-off structures by horizontal seepage FEM with contact elements

区域性渗流场由于范围大,通常忽略掉竖向的水头损失而用水平面二维有限元进行分析,但在城区区域渗流场中悬挂式阻水结构物量多,竖向绕流现象突出,用一般水平面二维有限元进行分析将产生较大的偏差。针对这一问题在悬挂式结构体周边引入一层无厚度界面接触单元。在水平面有限元中利用它考虑因竖向绕流产生的局部水头损失。利用阻力系数的方法和二维状态下截面突变流道流动的解析解,同时考虑防渗墙本身的弱透水性,推导了接触单元的导水矩阵。应用接触单元编制了相关程序,在水平面有限元中利用接触单元对悬挂式阻水结构进行分析,并将结果与三维有限元进行比较,两者的计算结果在流量上保持一致,在水头上前者是后者在同一位置处沿高程方向平均值。提出的该计算方法,对于用水平面二维有限元分析含有悬挂式阻水结构的大区域渗流问题,是一个有效的手段。

For the large scale of regional seepage fields the horizontal 2D FEM is usually chosen as the analysis tool which assumes that the hydraulic head loss caused by vertical flow can be ignored. However, the hydraulic head loss around suspended structures is apparent. If the horizontal 2D FEM is used to model the suspended structures a major error will occur. In order to simulate suspended structures using the horizontal 2D FEM, a contact element is introduced. The contact element is used to consider the hydraulic head loss caused by vertical flow near suspended structures. The matrix equation of contact elements is deduced. The deduction is based on the coefficient resistance method and the analytical solution of flow near suspended cut-off walls under plane condition. The corresponding procedure is programmed. Two examples are studied. The result accuracy is assessed by comparison with 3D FEM. It is shown that they coincide each other on discharge; and that the hydraulic head gained by proposed method is the mean value of that computed by 3D FEM at the same location. The method presented is an effective way to simulate suspended cut-off structures in regional seepage fields.