Print Email Facebook Twitter On the dependency of the development of frequency lock-in on the mode shape amplitude for higher structural modes Title On the dependency of the development of frequency lock-in on the mode shape amplitude for higher structural modes Author Hammer, T.C. (TU Delft Offshore Engineering) Hendrikse, H. (TU Delft Offshore Engineering) Date 2023 Abstract Drifting sea ice failing in crushing against vertically-sided offshore structures can cause ice-induced vibrations. Offshore structures are typically founded on slender structures to minimize the load effect of waves and currents. In combination with large top masses, those offshore structures often provide sufficient compliance for ice-induced vibrations to develop. Although modern offshore structures can be expected to experience ice-induced vibrations in higher structural modes, this phenomenon is rarely considered during experiments and numerical analysis of dynamic ice-structure interaction. Inspired by this challenge, we investigated experimentally how the sole change of mode shape amplitude relation between higher structural modes at the water level of a multi-degree-of-freedom structure influences the development of frequency lock-in. Experiments of four different multi-degree-of-freedom structures in cold model ice have been performed in Aalto Ice and Wave Tank. To allow full control over the eigensystem during testing, modal representations of structures wereimplemented in the numerical domain of a hybrid test setup. When changing the mode shape amplitude, the total structural stiffness at the ice action point and modal damping as a fraction of critical were kept constant between the four structures. We found that the structureexperienced sustained frequency lock-in vibrations in a frequency corresponding to the mode shape amplitude of artificially high magnitude. When mode shape amplitudes of two eigenmodes were equalized, the structure experienced oscillations in the frequency of the mode with lower frequency or lower damping mainly. It was found that ice-induced vibrations of multi-degree-of-freedom structures are highly dependent on the relative velocity between the ice and structure and thus on the superposition of higher mode oscillations with lower mode oscillations. Subject Model testingMulti-modal vibrationsFrequency lock-inHybrid test setup To reference this document use: http://resolver.tudelft.nl/uuid:888ace77-5823-4bfa-b3de-002e56c2673d Publisher POAC Source Proceedings of the 27th International Conference on Port and Ocean Engineering under Arctic Conditions Event POAC 2023, 2023-06-12 → 2023-06-14, University of Strathclyde, Technology & Inovation Centre, Glasgow, United Kingdom Series Proceedings - International Conference on Port and Ocean Engineering under Arctic Conditions, 0376-6756 Part of collection Institutional Repository Document type conference paper Rights © 2023 T.C. Hammer, H. Hendrikse Files PDF Paper23_Hammer.pdf 3.01 MB Close viewer /islandora/object/uuid:888ace77-5823-4bfa-b3de-002e56c2673d/datastream/OBJ/view