An efficient hybrid Laplace-time domain method for dynamic analysis of nonlinear floating systems

The dynamic analysis for nonlinear floating systems has been traditionally conducted in the time domain. Although the time-domain method can obtain a sufficiently accurate result, it is usually time-consuming in computation. This paper proposes a novel hybrid Laplace-time domain method for computing the response of nonlinear floating systems. In the proposed method, the nonlinearities of the system are treated as an additional external load. The external excitation is then divided into a number of segments, of which the response of the floating structure under each segment is computed by the pole-residue method operated in the Laplace domain. Along with the pole-residue method in each segment computation, the iterative technique is employed for dealing with system nonlinearities in the time domain. As the pole-residue method computes the response through simple algebraic operations in the complex plane and obtains analytical solutions, the proposed hybrid Laplace-time domain method is more efficient and accurate. Two numerical examples are carried out in this paper, in which one is an analytical single-degree-of-freedom (SDOF) nonlinear floating system and the other is a semi-submersible floating offshore wind turbine (FOWT) foundation with nonlinear damping. Both computational accuracy and efficiency of the proposed method are demonstrated through these numerical examples, by comparing the responses with those obtained by traditional time-domain methods.