波浪作用下管道冲刷暴发计算的边界元方法

Boundary Element Method for Calculating the Onset of Scour Beneath Marine Pipelines Under the Wave Action

管道冲刷暴发临界条件是海底管道设计和运营的重要参数。Sumer等给出了3个Keulegan-Carpenter(KC)数的波浪作用下冲刷暴发的试验曲线。但对于任意KC数,Sumer等的方法并不准确。因此,建立波浪作用下冲刷暴发条件计算方法,具有重要意义。因管道与床面相交形成了复杂的几何形状,管道与床面的交叉点是数值奇点,因而管道冲刷暴发临界条件计算较为复杂。本研究采用边界元方法计算波浪运动及渗流压力。边界元可准确地拟合海底与管壁边界,方便地处理管道与海床交叉点的数值奇点问题,并可直接计算出奇点处的垂向压力梯度,准确地计算冲刷暴发的临界条件。本研究计算结果与实测值符合良好。

The critical condition of the onset of scour beneath marine pipelines is one of the important fundamental parameters for the design and operation of submarine pipelines.Sumer et al gave the test curves of pipeline scour onset under the wave action,which included only three curves of Keulegan-Carpenter(KC)number.For an arbitrary KC number,however,the Sumer et al's method is not convenient for use and also not accurate.It is,therefore,necessary to establish a numerical model for calculating the critical condition of the onset of pipeline scour under the wave action.Because the intersection of the pipelines with the seabed can form a complex geometrical shape and the cross points are numerical singularity,the calculation of the critical condition of the onset of pipeline scour becomes very difficult.For this reason,the Boundary Element Method(BEM)is applied to calculate the wave motion and the seepage pressure.The boundary elements can precisely fit the boundary between the seabed and the pipeline wall,easily solve the problem about the numerical singularity at the cross points of the pipeline and the seabed and directly calculate the vertical pressure gradient at the cross points.Thus,the critical condition of the onset of pipeline scour can be accurately calculated.The calculated results agree well with the experiments available in literatures.