Operational modal analysis on a lighthouse structure subjected to ice actions

• Published in: Procedia Engineering
• Main Authors: Nord, Torodd S. (author), Kvåle, Knut Andreas (author), Petersen, Oyvind W. (author), Bjerkås, Morten (author), Lourens, E. (author)
• Other Authors: Vestroni, Fabrizio (editor), Gattulli, Vincenzo (editor), Romeo, Francesco (editor)
• Format: Conference Object
• Language: English
• Published: 2017
• Subjects: Ice-structure interaction; Operational modal analysis; System identification; Sea ice
• Online Access: http://resolver.tudelft.nl/uuid:acd9aab4-25e3-44ef-afd8-a2b2eb9ac862; https://doi.org/10.1016/j.proeng.2017.09.268

The sea ice interaction with a structure may cause system changes and affect the feasibility of common approaches to track modal parameters. In this paper, a covariance-driven stochastic subspace identification method is used to identify the natural frequencies from 190 time series of ice actions against a lighthouse structure. The results are sorted into groups defined by the observed ice conditions and governing ice failure mechanisms during the ice-structure interaction. The identified natural frequencies vary substantially within each individual group and between the groups. Recordings with flexural failures and a north-south ice-drift direction consistently rendered the same identified frequencies, whereas crushing seemed to create large amounts of variability in the identified frequencies. The results show the need for more high-fidelity data to assess whether modern system identification methods can be used to monitor system changes and support decision-making for operations of structures in ice-infested waters, such as offshore wind structures. Offshore Engineering