Ambient vibration responses denoising for operational modal analysis of a jacket-type offshore platform. (15th January 2019) - Bao, Xingxian
Abstract: Operational modal analysis based on the ambient vibration data has drawn great attention. However, measured responses are inevitably contaminated with noise and may not be clean enough for estimating the modal parameters with proper accuracy. This study develops an operational modal analysis procedure named NExT-SLRA-CE, based on noise removal from measured ambient vibration responses, including three steps: (1) Using natural excitation technique (NExT) to get free decay responses (auto- and cross-correlation functions) from measured (noisy) ambient vibration data, (2) Implementing iterative Cadzow's algorithm for the structured low rank approximation (SLRA) to remove noise from the noisy correlation functions, and (3) Applying the complex exponential (CE) method to extract modal parameters from the filtered correlation functions. The validity of the proposed operational modal analysis procedure is verified by using a numerical simulation of a four-story shear building subjected to white noise excitation, with considering the effects of noise, record length and different reference channel. Furthermore, the proposed procedure is applied to a field test of a jacket-type offshore platform. Results indicate that the NExT-SLRA-CE method can remove noise from measured signals and improve the efficiency and accuracy of the modal frequencies and damping ratios estimation. Highlights: Propose an operational modal analysis procedure combined NExT, SLRA, and CE methods. Record length and reference channel is considered when NExT is performed. Implement the SLRA to remove noise from the noisy correlation functions. Validate the modal analysis procedure by the numerical simulation and field test of a jacket-type offshore platform.