Dynamic Behavior of Tension Leg Platforms

Among compliant platforms the tension leg platform (TLP) is a hybrid structure which is generally used for deep water oil exploration. With respect to the horizontal degrees of freedom it is compliant and behaves like a floating structure moored by vertical tubular members or “tethers”. These tethers are pretensioned due to the excess buoyancy of the platform whereas with respect to the vertical degrees of freedom it is stiff and resembles a fixed structure and is not allowed to float freely. Dynamic analysis of squared and triangular TLP models under regular waves is presented considering the coupling between surge sway heave roll pitch and yaw degrees of freedom. The analysis considers various nonlinearities produced due to change in the tether tension and nonlinear hydrodynamic drag force. The wave forces on the elements of the structure are calculated using Airy’s wave theory with Chakrabarti (1971) approaches 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.