Dynamic performance and heave suppression of FDPSO vessel based on model tests

This paper studies the dynamic performance of a new deep-water octagonal floating drilling production storage and offloading (FDPSO) unit under different heave plate arrangements to provide guidance for the design of an FDPSO in the South China Sea.

Models are made with a scale ratio of 1∶60. Single-layer and double-layer heave plates with different spacings are set up. Free decay tests, white noise tests, and combined wind-wave-current tests for one-year and one-hundred-year return periods are carried out. The six-degree-of-freedom motion at the center of gravity of the FDPSO, mooring system loads, acceleration at typical positions, etc. are measured.

The results show that the single-layer heave plate has the smallest natural period of floating body motion and the largest dimensionless damping ratio for heave. Considering the drag-increasing effect and the problem of heave plate emergence, the optimal non-dimensional spacing for the double-layer heave plate is selected as λ = 0.5. The peak response amplitude operator (RAO) of the double-layer heave plate with λ = 0.5 is greater than that of the single-layer heave plate. Under the one-hundred-year return period sea state, the double-layer heave plate shows emergence and wave climbing phenomena, while the single-layer heave plate has a better motion suppression effect with smaller floating body motion, mooring force, and acceleration at typical positions than those of the double-layer heave plate. In the one-year return period sea state, the difference in anchor chain forces for different heave plate arrangements is not significant, and in the one-hundred-year return period sea state, the anchor chain force of the single-layer heave plate is significantly smaller than that of the double-layer heave plate.

Based on various tests, the single-layer heave plate has better motion suppression performance. In actual design, the single-layer heave plate arrangement can be considered, but a more detailed experimental analysis is required to determine the spacing of the double-layer heave plate.