Influence of Sea Current on Stabilization of Moments and Forces in Risers

Abstract

One of the important aspects in the design of floating, production, storage, and offloading (FPSO) systems is to ensure a fairly constant load on risers despite the base motion caused by sea waves. The paper presents the authors’ own formulation of the finite segment method for dynamic analysis of risers and its application to the solution of a dynamic optimization problem. This task consists in defining vertical displacements of the top of the riser which compensate horizontal movements of the vessel or platform caused by sea waves. Compensation involves stabilizing the bending moment in the risers or the force in the connection of the riser and the wellhead. The model takes into account the influence of the sea by means of Morison equations. Different sea current profiles are considered. Calculation of vertical displacements of the top of the riser is carried out in order to stabilize the force or the bending moment for a defined function of horizontal displacements of the riser.