On the Design of a Suspension System for Oil and Gas Transporting Pipelines Below Ocean Surface

Abstract

Expanding demand on oil transportation through submarine pipeline brings an immediate need for a proper design of underwater transporting pipeline system. A substantial amount of work has been conducted in the modeling of submarine pipelines laid on the seabed with the awareness of the downsides of such design approach. The high cost and labor intensiveness, due to installation and maintenance, are some of the disadvantages of such design. This paper discusses a new design of suspended pipelines which can be considered a favorable option as opposed to laying oil pipelines on the sea floor. An optimum design of a suspended oil transporting pipeline is considered in this study and a simple nonlinear mathematical model is developed to predict the dynamic behavior of the pipeline. The system consists of buoys as a suspension mechanism, transporting pipeline and vibration absorbers against ocean waves and vortex-shedding excitations. Nonlinearities in the model are due to vortex-shedding effects and fluid damping of the pipeline. The system design parameters considered for optimization are the absorber natural frequency, damping ratio and the buoy diameter. Other system parameters are assumed to be given to avoid design complexity. The design criterion is to minimize vibration amplitude of the pipeline and consequently the internal normal stresses with given constraints of maximum absorber displacement and buoy maximum diameter.