Numerical assessment of the global performance of spar and FPSO connected by horizontal pipeline bundle

Abstract

The global performance of a Spar and FPSO (floating production storage and offloading) connected by horizontal fluid transfer lines (FTLs) bundled with a large carrier pipe, called GAP (gravity actuated pipeline), is evaluated by using a fully coupled multi-body-mooring-riser time-domain analysis program. The horizontal pipeline bundle is attached to a carrier pipe to give sufficient bending stiffness and make the system neutrally buoyant. The pipeline bundle is supported by chains attached to Spar at one end and to FPSO at the other end allowing the movement mainly in the axial direction. The FPSO is to weathervane with respect to a bow external turret. The hydrodynamic coefficients are obtained from multi-body diffraction/radiation 3D panel program in the frequency domain and they are subsequently used in the time-domain simulation program to carry out the fully coupled time-domain global motion analysis. The moorings and risers attached to the FPSO and Spar are modeled with high-order finite elements (FEs). The pipeline bundle is also modeled with finite elements as one line member with the equivalent diameter and structural properties. The axial friction forces as well as the transverse drags on the pipeline bundle are considered because their accumulated effects along the very long FTL can be significant. The coupled relative motions of the Spar and FPSO can significantly affect the dynamics and tensions of the FTL. The dynamics of the FTL can also affect the relative motions of the two platforms too. The complex coupled system is also significantly affected by the headings of environmental loadings.