PC-based computation for second-order wave loads on large-volume multi-column structures
Additional Document Info
An efficient and reliable PC-based computer program for the computation of second-order sum- and difference-frequency wave excitations and wave drift damping on large-volume multi-column structures, such as tension leg platforms (TLPs), has been developed, and its theoretical background and some numerical results are presented here. The first-order diffraction and radiation potentials for deep-draft multiple circular cylinders are first obtained in analytic forms. The second-order potential force is then calculated by the indirect method using an assisting radiation potential. The second-order force component from the quadratic products of first-order quantities is obtained in closed forms. A rational approximation method for the cylinder bottom and pontoon contributions is developed based on the asymptotic expression of the second-order potential at large depths. The method is validated through comparison with existing data. The present method is especially powerful when the number of cylinders is large, for which the use of existing panel programs seems not feasible. The developed first- and second-order programs are an order of magnitude faster and require much less memory space than existing panel programs, and can thus be routinely run on personal computers. In addition, it is free of grid generation and requires minimum human effort for input preparation and convergence test; hence it is particularly suitable for the parametric study in the preliminary design stage.