Modal and Wave Load Identification by ARMA Calibration

In this note, modal parameter and wave load identification by calibration of ARMA models are considered for a simple offshore structure. The theory of identification by ARMA calibration is introduced as an identification technique in the time domain, which can be applied for white noise–excited systems. The technique also is generalized to include the case of ambient excitation processes, such as wave excitation, which are a nonwhite process. Due to those results, a simple but effective approach for identification of the load process is proposed. Finally, the technique is illustrated by an experimental example of a monopile model excited by random waves. The identification results show that the approach is able to give very reliable estimates of the modal parameters. Furthermore, a comparison of the identified wave load process and the calculated load process based on the Morison equation shows that important information can be obtained about the wave loading by this approach.