Print Email Facebook Twitter Ice-induced vibrations of the Norströmsgrund lighthouse Title Ice-induced vibrations of the Norströmsgrund lighthouse Author Nord, Torodd S. (Norwegian University of Science and Technology (NTNU); The University Centre in Svalbard) Samardžija, Ilija (Norwegian University of Science and Technology (NTNU)) Hendrikse, H. (TU Delft Offshore Engineering) Bjerkås, Morten (Norwegian University of Science and Technology (NTNU)) Høyland, Knut V. (Norwegian University of Science and Technology (NTNU)) Li, Hongtao (Norwegian University of Science and Technology (NTNU)) Date 2018-11-01 Abstract The signature and occurrence of frequency lock-in (FLI) vibrations of full-scale offshore structures are not well understood. Although several structures have experienced FLI, limited amounts of time histories of the responses alongside measured met-ocean data are available in the literature. This paper presents an analysis of 61 measured events of resonant vibrations of the Norströmsgrund lighthouse from 2001 until 2003. The vibrations of most of these events did not reach a steady state; thus, they violate an often-quoted criterion for frequency lock-in vibrations and remain outside any modes of ice-induced vibrations suggested in standards. Met-ocean data from both in situ measurements and from the Copernicus marine service information database are further used to better understand the occurrence of resonant ice-induced vibrations. All events between 2001 and 2003 occurred during days with ice concentrations of 8–10/10, closely packed consolidated drift ice. The locally measured ice velocity and thickness ranged from 0.023 to 0.075 m s−1 and from 0.26 to 1.9 m, respectively. These measurements included level ice, rafted ice and ridged ice. The events of resonant vibrations are further compared with measurements from the same structure between 1979 and 1988. Most events of resonant vibrations were recorded in the winter of 1988, followed by the winters of 2003 and 1980. The winter of 1988 had fewer freezing degree days (FDD) than the 65-year average, whereas the winters of 2003 and 1980 had more FDD than the 65-year average. Subject Frequency lock-inIce-induced vibrationsNorströmsgrund lighthouse To reference this document use: http://resolver.tudelft.nl/uuid:992a3d89-e2f6-407c-947e-44672229558e DOI https://doi.org/10.1016/j.coldregions.2018.08.005 Embargo date 2022-08-09 ISSN 0165-232X Source Cold Regions Science and Technology, 155, 237-251 Bibliographical note Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public. Part of collection Institutional Repository Document type journal article Rights © 2018 Torodd S. Nord, Ilija Samardžija, H. Hendrikse, Morten Bjerkås, Knut V. Høyland, Hongtao Li Files PDF 1_s2.0_S0165232X18301149_main.pdf 6.85 MB Close viewer /islandora/object/uuid:992a3d89-e2f6-407c-947e-44672229558e/datastream/OBJ/view