Mechanistic research on the complex motion response of a TLP in a tender-assisted drilling state

In this study, nonlinear motion characteristics have been studied in the coupled behavior of a Tension Leg Platform (TLP) combined with a Tender-assisted Drilling Unit (TADU). A time-domain numerical model has been established that accounts for the nonlinear behavior of mooring systems and hydrodynamic interference. Experiments are performed to verify the numerical model. Nonlinear motion characteristics of the steady-state response of the time-domain results are analyzed using Poincaré mapping and fast Fourier transform. The focus of this study is on investigating the motion response of the TLP platform in three degrees of freedom under coupled states. The surge motion is found to mainly consist of the wave frequency component and the half-wave frequency subharmonic component, while the wave-frequency, subharmonic, and super harmonic vibration components are observed in both heave and pitch motions. Three types of nonlinear regimes, namely chaos, transition, and multiple periodic, are identified in the heave and pitch motions under different wave conditions.