Hull/Mooring/Riser Coupled Dynamic Analysis of a Tanker-Based Turret-moored FPSO in Deep Water
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A taker-based FPSO using 12 chain-polyester-chain taut mooring lines with 13 steel catenary risers designed for 6000-ft water depth is numerically simulated to investigate the characteristics of nonlinear behaviors and hull/mooring/riser dynamic coupling. The coupled dynamic analysis is conducted in time domain by using the newly developed program, WINPOST-FPSO. The first-order wave-frequency and second-order difference-frequency wave loads, fluid added mass and radiation damping for the hull are calculated in the frequency domain from the second-order diffraction/radiation program WAMIT. The computed hydrodynamic coefficients and wave forces for vessels are then converted to proper forms in the time-domain equation of motion. The wave-current induced forces on slender members are calculated from Morison formula. An 100-yr Hurricane with non-parallel wind, wave, and current is used as environmental condition. The wind and current forces are calculated from the empirical data provided by OCIMF (Oil Company International Marine Forum, 1994). Three different cases; (1) fully coupled system with Newman's approximation, (2) system (1) with mass-less riser modeling, (3) fully coupled system with full QTF, are studied to assess the effects of risers and Newman's approximation in the global motion/tension analysis of turret-moored FPSOs.
