Based on engineering practice of the picking-up and laying-down processes of offshore pipelines, a finite element model was established. On the basis of the model, methods and steps of the picking-up and laying-down operations were determined, and the impacts of currents and seedbed friction on the two operations were studied. The shape and stress distribution of the pipeline under the influences of longitudinal current, lateral current and seabed friction when picked up and laid down were analyzed using finite element analysis software. The results show that the longitudinal current has almost no effect on the pipeline shape and stress distribution in the picking-up and laying-down processes, while the lateral current results in significant deformation of the pipeline in the horizontal plane and raises the overall stress level of the pipeline. The friction between the seabed and the pipeline impedes the lateral displacement of the pipeline when it is laid down. The rougher the seabed, the smaller the overall lateral displacement of the pipeline is. When the pipeline reaches the equilibrium state after it is laid down, the friction between the pipeline and the seabed becomes larger with the increase of the friction coefficient.%基于海洋管道海上提吊、沉放的工程实际,建立了管道提吊沉放的有限元模型,以建立的模型为基础确定了管道提吊沉放的方法和步骤,并对纵向水流、侧向水流及海床摩擦对管道提吊沉放的影响进行了研究.利用有限元分析软件研究了纵向水流、侧向水流及海床摩擦作用下管道提吊及沉放过程中的管道形态及应力分布.研究结果表明:纵向水流对管道提吊及沉放过程中的空间形态及应力分布几乎没有影响;侧向水流会使管道在水平面内产生明显变形,并提高管道的整体应力水平;海床与管道间的摩擦对管道沉放过程中的侧移有一定的阻碍作用,海床越粗糙,管道最终的整体侧移变形越小,沉放完成后管道达到平衡状态时,管道与海床之间的摩擦力随摩擦系数增大而增大.
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