A study on the dynamic responses of a steel catenary riser transporting varying-density flow and subjected to regular waves

Abstract

In order to transport crude oil and natural gas from seabed wells to surface floating platforms, the steel catenary risers have been widely used, which are long, flexible and inclined with geometric and structural nonlinearities. These risers are inevitably subjected to waves and vibrate with time. Meanwhile, they may transport oil and natural gas at the same time, in which the total fluid density may change with time and space. In this paper, a nonlinear dynamic model of a steel catenary riser excited by the internal varying-density flow and the external regular waves is theoretically modelled. The present model is numerically solved and validated with the comparisons to experiments and simulation results. The dynamic responses of the riser are analysed and the results demonstrate that when the fluid density inside the riser is fluctuating with a small circular frequency, the vibrations of the riser will be dominated by the internal varying-density flow, however for a large circular frequency, the vibrations of the riser will be dominated by the external regular waves. The dynamic responses of the riser in the region dominated by the external regular waves will be seldom affected by the internal varying-density flow and vice versa.