海流作用下海底管道局部冲刷数值分析

在任意拉格朗日-欧拉参考坐标系下,采用基于雷诺平均的Navier-Stokes方程组(RANS)、流线迎风有限元方法、泥沙输运模型以及底床变形方程,对海流引起的海底管道局部冲刷进行了数值模拟。着重讨论了均匀来流流速和海底管道直径对局部冲刷发展过程及平衡冲刷深度的影响作用。数值结果表明,在冲刷的初始阶段,冲刷深度随时间迅速增加,之后缓慢逼近极限平衡深度;在管径一定的情况下,管道附近的局部平衡冲刷深度与流速大致呈线性关系;当流速超过某一临界区域后,最大平衡冲刷深度出现的位置并不在管道正下方,而是随流速的增加向管道下游方向移动;另外,管道直径也会对平衡冲刷深度产生比较明显的影响,在相同流速下,平衡冲刷深度大致随管径呈线性增大。在本文的计算范围内,海底管道的相对局部平衡冲刷深度基本随雷诺数线性增加,但流速对冲刷深度的影响作用要比管径的影响作用更为明显。

Numerical examination of steady current-induced local scour around submarine pipeline

Local scour around submarine pipeline under steady current is investigated numerically in this work.The numerical model is based on the finite element solution of the Reynolds-averaged Navier-Stokes equations(RANS)and sediment transportation model within the frame of Arbitrary Lagrangian-Eulerian reference system.The influences of current speed and pipeline diameter on the local scour evolution and the equilibrium depth are investigated.The numerical results show that a power law is applied to the evolution of scour depth during the early stage,whereas it can be approximated by an exponential relationship as the local scour approaches to the equilibrium state.Several linear relationships are found in this work,including the equilibrium depth of local scour versus the current speed and pipeline diameter,the position of maximal scour depth against current speed,and the non-dimensional equilibrium scour depth with Reynolds number.It is also demonstrated that the steady current has more significant influence on the dimensionless equilibrium scour depth than the diameter of submarine pipeline.