Analyses of Offshore Systems with Selective Activation of Finite Elements

Abstract

Several procedures that are executed in offshore environment involve the coupling and decoupling of cables, payment and collect of lines. Moreover, some offshore structures can suffer from fails in the systems that guarantee their average positioning as, for example, the rupture of floating platforms mooring lines. In general, these structures are dynamically simulated through numerical tools based at the Finite Elements method. Situations where meshes must be added or removed from dynamic simulations are commonly carried through the division of the numerical model in stages, losing, when it is relevant, information of the structure behavior during the transition from a situation to another. This work presents two studies of real offshore systems cases involving a numerical tool that has been developed with the capacity to add or to remove finite elements during the execution of a numerical simulation. The first case presents a typical model of a semi-submersible platform in which the rupture of a line from its mooring system occurs due to the action of environmental load effects. The second one analyzes a pipeline that is going to be laid on the seabed through the Floating Spiral method, at the stage in which its last wrap is ready to be unwound. At this stage, a cable system proposed in order to guarantee the control and the security of the operation is sequentially decoupled and the stresses acting on the pipeline are verified.