A general procedure for time domain two-dimensional nonlinear dynamic analysis of Tension Leg Platform (TLP) models including a variety of nonlinear effects has been developed. Morison’s equation with several modifications allowing to include or neglect various sources of nonlinearities are implemented and used in the time domain dynamic analysis. A single cylinder, several cylinders and TLP hulls with and without pontoons are subjected to regular and irregular waves. The models are floating or connected to the sea floor by tendons. The tendons are assumed to be massless elastic springs, allowing for time varying tension forces. The nonlinearities investigated are those associated with the wave kinematics, hydrodynamic forces and structural geometry.
The time histories and the corresponding spectral densities, obtained using Fast Fourier Transform, for the motions of the three degrees of freedom (surge, heave and pitch) as well as for the tendon forces are presented and discussed. The contributions of the low and high frequency response components of the TLPs to the surge amplitude and mean drift and to the limits (maximum and minimum) of the tendon forces are evaluated. The relations between some of the structural and wave parameters are also examined.