As a typical complaint offshore structure, the tension leg platform (TLP)has been observed that it is very sensitive to the state of its foundationswhere the seabed is seismically active. In this paper, a programconsidering several nonlinearities induced by finite displacements areused for computing TLP responses and tether tensions under randomwaves. The seismic loads are simulated using IBC spectrum and addedexplicitly to the position of tether anchorages. Parametric analyses,including wave heading angles, PGAs, ground motion directions, andseismic components in different directions, are carried out in detail tofind the major factors. Results indicated earthquakes mainly affect thetranslational motions of the platform and will lead to sharp change in theheave motion due to resonance in the vertical direction. Earthquakesresults a sharp change in tether tensions and play a major role in thecoupling effects of earthquakes and waves. The vertical ground motionis the major component of seismic ground motions and determines thechanges in tether tensions as it is parallel to the direction of heave motion.The upward ground motion results a sharp decrease in tether tensions,which may lead to an overall buckling of tethers. The downward groundmotion results a sharp increase in tether tensions
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