ELASTIC-PLASTIC FINITE ELEMENT ANALYSIS OF SUBMARINE PIPELINE IMPACTED BY DROPPED OBJECTS

The process of a submarine pipeline impacted by dropped objects is simulated by using a nonlinear dynamic finite element method. The Ramberg-Osgood model is adopted to model the seabed and the different tensile and compressive nonlinear characteristics of concrete coating are considered at the same time. The interactions between the dropped object and seabed and pipeline are solved with the penalty function method. The influence of various factors on the plastic impact deformations of the pipeline are analyzed, including the object shape, impact angle, friction, internal pressure, concrete thickness, burial depth and free spanning of the pipeline. The results show that: the dropped object impacting the pipeline with a tip makes a larger dent depth, but a relatively small deformation range; the maximum dent depth of the pipeline occurs at an impact angle of 90° and friction makes little influence on the impact; the internal pressure increases the stress of the pipeline, but decreases the dent depth; concrete coating has a weak protective effect when the weights of dropped objects are larger; the pipeline can be effectively protected, when the buried depth was more than one meter; the free spanning decreases the dent depth of the pipeline but makes the integral damage of the pipeline more easily. The method in the paper is more suitable to the actual situation, comparing with the results obtained by the current codes.