浅水区海底管道周围海床渗透压力计算研究

Research on the calculation of seepage force on buried pipelines in shallow water

我国海上油田开采起步较晚,大部分油田处于浅水区,因此,在设计管道时,应充分考虑由浅水区波浪引起的管道周围海床渗流力。根据浅水波相关假设,考虑自由水面非线性影响,推导出椭圆余弦波的波面方程,在此基础上进一步得到一个关于速度势的表达式,并根据该表达式得出作用于海床表面的波压公式。考虑海床土的压缩性,推导出一阶近似椭圆余弦波作用下浅水区埋置管道周围海床的渗流压力解析解,最后将计算结果与大型水槽试验及以往研究成果作对比。结果表明,在椭圆余弦波的作用下,由一阶椭圆余弦波理论得到的计算结果与试验结果规律基本一致,与相似工况下的现有理论成果数值基本相同,具有一定的可行性和工程价值。

China developed of offshore oil fields later than other countries,and most oil fields in China are located shallow waters. Due to the effect caused by the nonlinear shallow wave,the nonlinear wave load has a great influence on the pipelines buried in shallow regions. The study of the stability of submarine pipelines needs to fully consider the characteristics of the shallow water waves. Because the total vertical wave force acting on the pipeline is one of the main environmental load,we should take full account of the wave force which causes by the shallow water waves at the beginning of the pipeline design in China. According to the assumptions of shallow water wave,and considering the nonlinear effects of the free surface,the wave equation of cnoidal wave is derived. Based on the equation,the solutions of the wave pressure on the surface of seabed caused by waves are obtained. Considering pore water and compressibility of the seabed soil and based on Biot consolidation theory and the first-order approximate elliptical cosine wave theory,seepage force caused by nonlinear wave around buried pipelines in shallow water is derived by the method of seperation of variables,and the analytic solution of wave force around buried pipelines is proposed,and the solution is compared with test result. The numerical results show that the seepage force around buried pipelines makes a Sine distribution under the effect of cnoidal wave,and the conclusion agrees well with the experiment results. The theoretical model has certain feasibility and engineering value.