Third Order Model For the Polyester Mooring Cables Dynamics

The use of polyester cables has become the preferred alternative for the installation of some deepwater platforms. In Campos Basin, offshore Brazil, the use of such cables on deepwater (more than 700 m and with 1360 m cases) goes from Semi-Submersible Platforms as the PETROBRAS 19 to FPSOs (Floating Production Storage and Offloading) as the PETROBRAS 34. While this is happening, more fundamental research is also being performed and new physical modeling is being considered in order to clarify the observed behavior, with a particular focus on the dynamic properties. In this respect, the present work proposes and justifies a Third Order Model which considers the following aspects: I) besides a static stiffness, the polyester cable may become stiffer or softer depending respectively on the average load and the load amplitude; ii) the damping although negligible, must be present to explain resonant behavior. The Third Order Model is still simple enough, since linear, allowing a frequency domain analysis as shown in the work.