Fatigue damage induced by vortex-induced vibrations in oscillatory flow |
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| Affiliation: | 1. State Key Laboratory of Ocean Engineering, Shanghai Jiao Tong University, Shanghai, China;2. Statoil, Trondheim, Norway;3. Marintek, Trondheim, Norway;4. Dept. of Marine Technology, Centre for Ships and Ocean Structures, NTNU, Trondheim, Norway;1. State Key Laboratory of Ocean Engineering, Shanghai Jiao Tong University, Shanghai 200240, China;2. Collaborative Innovation Center for Advanced Ship and Deep-Sea Exploration, Shanghai 200240, China;1. Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA;2. Department of Mechanical and Industrial Engineering, University of Massachusetts, Amherst, MA 01003, USA;1. State Key Laboratory of Oil and Gas Reservoir Geology and Exploration, Southwest Petroleum University, Chengdu 610500, China;2. State Key Laboratory of Ocean Engineering, Shanghai Jiao Tong University, Shanghai 200240, China;1. State Key Laboratory of Oil and Gas Reservoir Geology and Exploration, Southwest Petroleum University, Chengdu 610500, PR China;2. Department of Mechanical Engineering, The University of Tokyo, Tokyo 113-8656, Japan |
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| Abstract: | Vortex-induced vibration (VIV) of a flexible cylinder in oscillatory flow was experimentally investigated in an ocean basin. An intermittent VIV was confirmed to have occurred during the tests. The fatigue damage caused by VIV was calculated based on rainflow counting and a standard S–N curve. There are 3 main observations for fatigue damage from VIV in oscillatory flow: 1) the damage varied significantly with the KC number, which is a unique feature for VIV in oscillatory flow. 2) Fatigue damage at small KC number cases was found to be larger compared to those at large KC numbers owing to the fact that number of vortex shedding cycles per half of the motion cycle is low, and damping within half of the motion cycle will hence become low. The fact that vortices from the previous cycle still are active during the next may also contribute to the large response at small KC numbers. 3) ‘Amplitude modulation’ and ‘mode transition’, two specific features for VIV in oscillatory flow, were found to have a strong influence on fatigue. Fatigue damage has also been calculated by an empirical VIV prediction model assuming that all cases have steady flow at an equivalent velocity. Finally, a simplified method for calculating fatigue damage from VIV in oscillatory flow based on steady flow conditions is proposed. A modification factor diagram is presented, but the scope of the present study is too limited to provide a good basis for a general model for this factor. A general model for how to apply results from constant current analysis to predict fatigue in oscillatory flow will therefore need further research. |
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| Keywords: | Fatigue damage Vortex-induced vibration Oscillatory flow Modification factor |
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