Dynamic behaviour of square and triangular offshore tension leg platforms under regular wave loads

Among compliant platforms, the tension leg platform (TLP) is a hybrid struc ture. With respect to the horizontal degrees of freedom, it is compliant an d behaves like to a floating structure, whereas with respect to the vertica l degrees of freedom, it is stiff and resembles a fixed structure and is no t allowed to float freely. The greatest potential for reducing costs of a T LP in the short term is to go through previously applied design approaches, to simplify the design and reduce the conservatism that so far has been in corporated in the TLP design to accommodate for the unproven nature of this type of platform. Dynamic analysis of a triangular model TLP to regular wa ves is presented, considering the coupling between surge, sway, heave, roll , pitch and yaw degrees of freedom. The analysis considers various nonlinea rities produced due to change in the tether tension and nonlinear hydrodyna mic drag force. The wave forces on the elements of the pontoon structure ar e calculated using Airy's wave theory and Morison's equation, ignoring the diffraction effects. The nonlinear equation of motion is solved in the time domain using Newmark's beta integration scheme. Numerical studies are cond ucted to compare the coupled response of a triangular TLP with that of a sq uare TLP and the effects of different parameters that influence the respons e are then investigated. (C) 2001 Elsevier Science Ltd. All rights reserved .