A nonmode-shape-based model updating method for offshore structures using extracted components from measured accelerations. (April 2022)

• Record Type: Journal Article
• Authors: Li, Xingguo; Liu, Fushun
• Is Part Of: Applied ocean research. Volume 121(2022)
• Publication Date: 2022-04
• Subjects: Model updating -- Acceleration components -- Damping -- Robustness -- Spatial incompleteness; Ocean engineering -- Periodicals; 620.416205
• DOI: 10.1016/j.apor.2022.103087
• Languages: English
• ISSNs: 0141-1187

Abstract

Abstract: As the precision of model updating based on modal parameters usually depends on the accuracy of mode shapes, which are frequently affected by measurement noise and spatial incompleteness, there has been paid much attention to the research on this topic arising from the practical marine engineering. To overcome this challenging issue, a novel nonmode-shape-based model updating method has been proposed in this paper for reliable and effective identification of complex engineering structures. Based on the measured signals from accelerometers, the acceleration components corresponding to the first several natural frequencies of the structure have been extracted. Following that, a series of linear equations containing the updating coefficients have been established with the fuse of modal information from the baseline model to determinate the change in structural parameters. The major contributions of this research include: (1) The underlying principle of the proposed method is based on the time-dependent acceleration components instead of mode shapes in traditional methods to construct more equations, which represents more structural parameters such as the mass, stiffness and damping properties under considerations and (2) The isolation of noise and acceleration components has been achieved by the developed complex exponential decomposition technique, leading to the proposed method with the capability of denoising suitable for marine engineering applications. Moreover, the analytical signal can also be obtained to construct equations for the calculation of structural damping property using Hilbert transform. To verify the effectiveness of the proposed method, a numerical example of the cantilever beam has been examined under the consideration of spatial completeness, spatial incompleteness and measurement noise. Results have shown that the updating coefficients of the model can be accurately calculated using more equations constructed purely by the first-order acceleration components in the proposed method. Meanwhile, the absolute maximum error of the natural frequency has been reduced from 4.711% to 0.785% for the acceleration containing 5% measurement noise. Next, a jacket platform model has been established to verify the performance of the proposed method applicable to complex engineering structures. It has been noted that the maximum error (0.957%) of the first three natural frequencies of the updated model has been evaluated. Finally, a set of experiments of cantilever beams have been carried out. These tests have been designed according to the number and location of the cracks. The maximum error (1.559%) of the natural frequencies has been observed as compared with the real results, which have further demonstrated the effectiveness of the proposed method. Highlights: A novel nonmode-shape-based model updating method using acceleration components has been proposed. Time-dependent acceleration components instead of mode shapes enable to efficiently construct more equations. The proposed method with the denoising capability suitable for various marine engineering applications. The damping property of the model can be calculated using analytical signals generated by the Hilbert transform.