Coupled dynamics of deep water tension leg platforms under steep regular waves

The paper investigates the coupled dynamics of the hull–tether system of deep water TLPs under steep regular waves. The nonlinear finite element analysis program (NAOS) in time domain is used to include the wave frequency and high-frequency components. The first-order forces are calculated using relative velocity model of Morison. The second- and third-order force components are calculated using the FNV (Faltinsen, Newman and Vinjie, J Fluid Mech 289:179–198, 1995) [3] model. A hybrid model is developed combining all the force components. An incremental-iterative solution based on Newmark’s integration scheme is adopted. The TLPs are analyzed for regular waves of steepness values 0.025, 0.05, 0.075, and 0.1, at water depths 900, 1800 and 3000 m. Results are reported in the form of power spectral density functions as well as mean and dynamic responses. Maximum surge is found at 1800 m. To examine the participation of natural modes of vibration, the natural periods of vibration are also captured. The heave and tether tension are minimum at 1800 m water depth and increases with wave steepness. The study emphasizes the need for including the effect of higher order exciting forces for understanding the response behavior of deep and ultra-deep water TLPs.