Fully coupled large amplitude simulations of theme offshore structures in water depths of up to 10,000 feet are studied. The linear and slow-drift responses and the mooring-line/tendon dynamic tension of a Spar and a TLP in wind, waves and currents are presented. Hydrodynamic computations for the linear and second-order surface wave problems are carried out in the frequency domain by accurate and efficient solution techniques. Motion simulations are carried out in the time domain using efficient FFT summation of linear and quadratic time series coupled with a nonlinear solution algorithm for the treatment of the dynamic response of mooring lines, risers and tethers.
The design of offshore platforms operating in hostile weather environments and in waters of depths approaching 10,000 feet, increasingly requires the development and use of integrated solution methods, which are accurate, robust and efficient for the routine evaluation of the attributes of candidate designs and actual platform concepts. The methods described in the present article are the outgrowth of a 10 year research and development effort funded by the oil industry. Continuous input and guidance by the project sponsors has contributed appreciably to the validation and refinement of the solution algorithms, which have been independently applied to realistic offshore platform concepts. The current status of this development and its application to the theme structures in water depths of 3,000 ft to 10,00Oft is the subject of the present article. The solution of the linear and second-order radiation and diffraction problems around offshore platforms is treated in the frequency domain. Efficient and accurate analytic techniques for the solution of the linear, slow-drift excitation and drift-damping second-order problems have been developed by Emmerhoffand Sclavounos (1995) and Kim and Sclavounos (1997).
