Reversed tension characteristics in subsea mooring connectors for an FPSO SPM in shallow water

Abstract

The reversed tension on subsea mooring connectors is studied to prove its appearance. The mooring line is chosen from the real single point mooring system of Floating Production Storage and Offloading Unit (FPSO) wording in the South China Sea. The forced motion excitations are applied on the top end of the mooring line with the data monitored by the GPS device on the FPSO. The simulations are carried out with the lumped mass model and the nonlinear finite element model to verify the accuracy of the whole process. In the results of the forced excitation case, the reversed tensions are found three times. The occurrence of the revered tensions is consistent with the minus peak of the vertical displacement in time history, and the vertical displacement is recognized as the key factor for the reason of reversed tension. The reversed tension will apply a compression force on the rigid subsea mooring connect after a generous vertical displacement change. It may lead to the failure of the connector, and then the mooring line. Therefore, the minimum tension design is suggested to be added to the rules of classification society to avoid the reversed tension and slack condition of the mooring line.