Synthesis of first order TLP wave load from semi-analytical solutions for pontoons and columns

A solution scheme for the synthesis of first order wave loads on a tension-leg platform (TLP) that includes a semi-analytical approach for the hydrodynamics of the TLP superstructure is outlined. The large volume vertical cylinders and rectangular pontoons of the platform are treated independently and these individual solutions are combined in a consistent manner such that the total wave forces on the TLP may be evaluated. Although phase differences between the various pontoons and columns are accounted for, interference effects are not included. Numerical results are presented for sub-assemblies of a TLP such a group of four columns on a square grid, and configuration of four pontoons linking the TLP columns. These are compared with results from the literature which were developed using the Green's function approach whereby the total TLP surface area is discretized into small panels. Satisfactory accuracy for engineering design purposes is achieved with the semi-analytical method. The advantage of the present approach for non-specialists in hydrodynamics is ease of application and interfacing with solutions for riser and tether forces and motions.