Vibration analysis for the determination of modal parameters of steel catenary risers based on response-only data

Modal analysis is one of the most preferred method in the structural engineering community to investigate vibration characteristics. When dealing with response-only data of specific operating conditions, this method could be useful to characterize its dynamic behavior. It could also be used for damage detection, and damping estimation, among others. However, existing methods are not yet robust enough to be used in a daily basis for any kind of structures; thus, numerical simulations must be carried out to investigate the performance of existing and newly developed methods. In the case of deepwater risers, they present highly nonlinear dynamic behavior due to large displacements of the floating structure. Under these circumstances it is convenient to identify the dynamic behavior of operational risers due to the variability of environmental conditions. This paper presents a comparative study to determine modal parameters (periods and mode shapes) of a Steel Catenary Riser (SCR) taking into account only output data of acceleration records. Two methods are used to identify the operational frequencies of a riser, the Frequency Domain Decomposition Method (FDDM) and the Conventional Spectral Analysis Method (CSAM). This work takes into account the output response obtained through numerical simulations at various points along the riser. The identified and the theoretical parameters show good agreement.