Nonlinear Motions and Forces on Tension Leg Platforms

摘要

New computational methods have been applied in an investigation of the nonlinear surge motions and springing loads in the tendons of tension leg platforms (TLPs). The second-order wave drift forces as well as the linear hydrodynamic coefficients and the wave-induced exciting forces are computed by a three-dimensional hybrid-finite-element method (HFEM). Both a new formula for predicting the viscous drag forces and the conventional Morison drag formula have been used in a time-domain computational procedure to predict the nonlinear surge motions for two TLP configurations due to wind, current and wave excitations. The wave-induces first-and second-order pitch springing exciting moments and the resulting springing tension loads in the tendons are computed for regular waves, two waves (wave groups) and irregular waves using a short-wave approximation method. Upper bound estimates of the surge motions and the tendon springing loads are computed for some selected extreme environmental conditions. 'Average' surge displacements and 'average' springing loads are also selected typical operational conditions. Finally, the surge motions and the springing loads of a TLP with one tendon removed have been predicted and compared to the results for the same TLP with all of the tendons intact.