An efficient frequency-domain method for computing transient responses of floating structures to irregular waves

Traditionally, computing dynamic responses of floating structures to waves can be conducted efficiently in the frequency domain, but only steady-state responses are computed. For computing transient responses of floating structures to irregular waves, this paper, assuming that the frequency response functions (FRFs) have been obtained from running a hydrodynamic software, develops an efficient frequency-domain method using pole-residue operations. In contrast to the pole-residue method using “true” poles in the Laplace domain, the proposed frequency-domain approach assigns “artificial” poles associated with the wave-structure system directly from the given FRFs. The proposed method is easy to implement and efficient in computational time, especially when the FFT algorithm is utilized; its accuracy is verified by using a time-domain method through numerical examples of an FPSO system to regular and irregular wave elevations.