Research of complex modal parameters extraction of a multi-degree-of-freedom structure based on similarity search

We present a method for the extraction of modal parameters that could be useful for the parameter identification of complex structural dynamic modes of multi degree of freedom systems that may be subject to environmental load excitations. The approach is linear and in this sense it operates on the basis of the principles suggested by the so-called Rayleigh superposition method. This atoms which have the form of free vibration are constructed. The method combined with MP (Matching Putsuit) and GA (Genetic Algorithm). MP is borrowed to extract every most similar atom to the random decrement of the structure response to identify modal parameters. GA is used to speed up this process. The method is applied on the analysis of model experiments for an FPSO single point mooring system and results are compared against real monitoring data. It is shown that the method is capable of extracting successfully modal characteristics such as complex modal frequency, damping ratio and mode shapes.