Abstract
This paper investigated the platform motion and tether tension of tension leg platform subjected to eight sea states ranging from extreme to moderate states. The mass, stiffness and damping force matrices were formulated for the platform and the tethers were considered as non-linear springs. The surface elevation and wave kinematics were calculated by small wave amplitude theory. On the other hand, the force vector was calculated by integrating over the entire length of the hull members using Morison equation. The various degree of non-linearity considered include the drag force, the variable added mass, large displacement as well as variations in tether tension. A finite element numerical research program was developed for solution of the nonlinear problem. The statistical response parameters for the degrees of freedom show that as we move towards the less severe sea states, all the responses were decreasing. Response comparison of one tether missing and an intact tendon of tension leg platform show an increase in surge and tether tension but heave response decreased due to reduction in stiffness against vertical movement. Dynamic analysis of the platform under the combined action of wave, current and wind is recommended so as to know true platform behaviours.