Response analyses of offshore triceratops to seismic activities

Offshore triceratops is one of the alternate structural forms that is desirable for the deep-sea oil exploration. It consists of a deck and buoyant leg structures (BLS) that are positively buoyant and the platform is position-restrained by tethers. Ball joints, which connect the deck and the BLS units, restrain the transfer of rotations between them. These platforms experience a significant tether tension variation under the vertical seismic excitations that are caused at the seabed. In the present study, response analyses of triceratops to seismic activity in the presence of waves are examined. Records of the El Centro earthquake and the artificially generated earthquake using Kanai-Tajimi (K-T) power spectrum are considered for the study. Earthquake excitations are imposed on the tethers to determine the dynamic tether tension variations caused by the seismic excitations. Triceratops is then analysed numerically for these tether tension variations in the presence of regular waves. Based on the numerical studies conducted, it is seen that the heave and pitch responses of the BLS units and the deck are significantly high under these tether tension variations. It is also seen that the response amplitude operator of the deck in the pitch degree of freedom is lesser than that of the BLS units. This study quantifies the response variations of the triceratops under seismic activities, which is useful for the design and development of new generation offshore platforms for deep waters.