Variability of TLP motion analysis against various design methodologies/parameters

Nonlinear hull/tendon/riser coupled dynamic analyses of a TLP (tension-leg platform) designed for 3000-ft water depth are conducted in the time domain. The first-order and second-order sum- and difference-frequency wave loads and other hydrodynamic coefficients for the hull are calculated from a second-order diffraction/radiation program, while the forces on slender members, 8 vertical tethers and 8 vertical tensioned risers, are calculated from Morison formula. The numerical simulations were conducted for 100-yr Hurricane condition with non-parallel wind, wave, and current. The results are compared with those of uncoupled quasi-static analysis and semi-coupled dynamic analysis, in which the tethers and risers are replaced by a set of massless nonlinear springs. A comprehensive sensitivity study of the simulation results against various analysis/environment parameters was carried out to better understand the underlying physics and the role of each parameter. In all cases considered, the wave frequency co mponents remain almost the same, while the slowly-varying motions change case by case. It is particularly underscored that the viscous damping from tethers and risers may be significant and the equivalent static wind modeling may lead to underestimation of slowly varying surge/sway responses.

Variability of TLP motion analysis against various design methodologies/parameters Conference Paper