Hydrodynamic response of tension-leg platforms—A model

The tension-leg platform (TLP) is a hybrid type of offshore platform, fixed for the vertical degrees of freedom and compliant for the horizontal degrees of freedom. The platform structure is connected to the sea-bed foundation by vertical moorings (tension legs) which are kept in tension under all conditions by the excess buoyancy over weight of the platform. Hydrodynamic analysis is an important stage of the design of these structures; model tests are usually done for this purpose. This paper gives the details of an experimental study to analyze the behavior of a 1:50 TLP model subjected to the action of regular and irregular waves. Platform motions in surge, sway and heave directions were measured using accelerometers. Tether tensions were measured using specially developed load cells. Details of instrumentation, testing and analysis to obtain response amplitude operators (RAOs) are explained. The connection of tether to the column, arrangement for adjusting pretension from top, connection of load cell to the tether and provision for changing the angle of incidence of waves are some special features of this experimental study. The work reported will serve as a useful practical guide for similar types of experimental study. In addition, the conclusions on the comparison of RAOs of the model for regular and irregular waves will be useful in planning hydrodynamic model tests.