Sensitive Analysis of the Static Response of Compliant Vertical Access Risers

Abstract

Compliant vertical access risers (CVARs) are considered as efficient and robust alternative options to achieve cost efficiency and safety. Design uncertainties emerge owing to the limited understanding of the effects of various parameters related to the structural properties and marine loads. In this paper, a reasonable three-dimensional (3D) numerical model of CVAR with internal flow is presented based on the slender rod theory. Accordingly, the finite element method combined with a Newton-Raphson scheme is employed to discretize and solve the equations. A sensitivity analysis is performed to investigate the influence of the structural and external load parameters on the static behavior of the CVAR. The effects of the weight and length of the respective functional segments with unchanged wet weight are analyzed and compared. The results indicate that the lengths of the buoyancy and weight segments affect not only the bending moment extremums and effective tension of the CVAR but also the extremum locations of the bending moment. Moreover, an increase in the weight per unit length of these segments leads to an increase in the bending moment extremums of the CVAR. The overall deformation of the CVAR is sensitive to current velocity along the y-direction. However, large tension and bending moment responses are easily provoked by the current velocity along the x-direction. This is also true for the tension and bending moment in the riser induced by the vessel motion along the x-direction.