Spectral analysis of simulated acceleration records of deepwater SCR for identification of modal parameters

In riser projects it is important to determine modal parameters, such as periods and mode shapes, to evaluate their dynamic behavior. To obtain these parameters of risers, various methods have been developed based on free vibrations theory. These methods do not take into account the variations of the dynamic behavior of the riser in different sea state conditions and also cannot be applied in monitoring activities of risers. In these situations, an alternative method should be investigated because of the need to monitor the structural behavior of future deepwater risers. This work presents a Fourier analysis methodology for the identification of modal parameters; namely natural periods and mode shapes, for a deepwater steel catenary riser (SCR), solely based on acceleration records. A structural model of a riser in 1800 m water depth was considered for the theoretical determination of modal parameters. This theoretical data was compared with the modal parameters identified in different sea states through spectral analyses of simulated acceleration records, assuming the presence of accelerometers at 15 discrete locations along the riser. The main advantage of the proposed methodology is that the estimated modal parameters are solely based on the motion (acceleration) records of the riser, which proves to be an efficient way to identify modal parameters that are being exited. This could be considered for structural health monitoring purposes, especially for damage detection and fatigue analysis.

► A Fourier spectral analysis to compute periods and mode shapes of a SCR was used.
► The modal parameters of riser was obtained based solely on acceleration records.
► The proposed method can identify the damped frequencies of the riser.
► Results show that is possible the identification of the modes that are being excited.