Non-Harmonic Decomposition of Sea Measured Data of Offshore Platforms

The measured data are often required and taken as the input of different kinds of algorithms for modal parameter identification, model updating and/or damage detection of offshore platforms. This paper investigates the application performance of the approach to offshore platforms, by using real measured data. Considering the fact of a recorded loading is always finite in duration, most likely aperiodic, and even damped because of the existence of damping of the structures, a recent developed complex exponential decomposition method [1] was employed to deal with real measured data. Therefore, in this article, three kinds of measured data will be used. The first one is a measured wave force that was collected through an experiment conducted in the lab of Ocean University of China, to investigate the feasibility of original external loading decomposition. To study the performance of the proposed method when applied to offshore structures, two sets of typical signals are used: one set was collected from the JZ20-2MUQ offshore platform when it was excited by ice, and the other was collected from the WZ11-4D platform when it was excited by waves. The results show that the approach can decompose the real measured data into a series of non-harmonic components, and a large model order is often suggested.