The work described in this paper is part of a research project conducted at the University of Texas at Austin in conjunction with the Offshore Technology Research Center. The research studies the contribution of different nonliearities to the global response of tension leg platforms. A rigid body with three degrees of freedom is selected to represent a TLP hull which consists of four columns and four pontoons. The tendons are modelled as elastic springs allowing for the variation of the axial forces and the effect of setdown. The lateral forces are computed using Morison's equation in the hull's instantaneous position and up to the wave free surace. The longitudinal forces on the bottom of the columns are computed using diffraction and radiation results for truncated cylinders. The analyses are performed in the time domain and the time histories of the motions and the tendon forces are obtained. The variations of the steady state surge amplitude and mean offset and the maximum and minimum tendon forces are obtained for different wave frequencies and heights, different water depths, different spacing between the TLP columns and different tendon properties.
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