Modal analysis of multi-degree-of-freedom dynamic system based on non-stationary response data

In connection with the nonstationarity of the huge offshore structure monitoring data, a method of constructing structure free response based on the non-stationary response data is proposed. This method uses a unilateral moving average to stabilize loads and the response data in the dynamic model of the multi-degree-of-freedom (mdof) structure, analyzes spectral characteristics of moving averages in some orders, researches filtering effects when the order q=1 (difference) and q>1 and constructs the free vibration equation of the structure by the random decrement technique (RDT). Through the identification of the second-order linear system simulation model, a comparison of modal parameters with the theoretical values is given, which are identified by different methods, and it shows good effects on the analysis of non-stationary response data using this method. Finally, the method is applied to the mode identification of the Floating Production Storage and Offloading (FPSO) single-point mooring structure, the distribution of the modal parameters of single-point mooring structure is analyzed and modal parameters identified by different values of q are compared.