Towards a model of hydrodynamic damping for a circular cylinder with helical strakes at low KC |
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| Institution: | 1. State Key Laboratory of Ocean Engineering, Shanghai Jiao Tong University, Shanghai, 200240, China;2. Collaborative Innovation Centre for Advanced Ship and Deep-Sea Exploration, Shanghai, 200240, China;3. Department of Mechanical Engineering, University of California at Berkeley, Berkeley, CA, 94720, USA;1. Department of Mechanical and Structural Engineering and Material Sciences, University of Stavanger, Stavanger, Norway;2. Oceans Graduate School, The University of Western Australia, 35 Stirling Highway, Crawley, WA, 6009, Australia;1. State Key Laboratory of Ocean Engineering, Shanghai Jiao Tong University, Shanghai, China;2. Collaborative Innovation Center for Advanced Ship and Deep-Sea Exploration, Shanghai 200240, China;3. Marintek, Trondheim, Norway;4. Mechanical Engineering School of Engineering, University of Kansas, 1450 Jayhawk Blvd, Lawrence, KS 66045, USA;1. National University of Singapore, Department of Civil and Environmental Engineering, 1 Engineering Drive 2, Singapore 117576, Singapore;2. School of Marine Science and Technology, Newcastle University, Armstrong Building, Newcastle upon Tyne NE1 7RU, UK |
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| Abstract: | This paper investigates the hydrodynamic damping of a circular cylinder with helical strakes at Keulegan-Carpenter (KC) number from 0.07 to 3 in the presence of steady currents. Experiments were performed with a straked cylinder oscillating in either in-line or cross currents over Reynolds number (based on the oscillating velocity amplitude) varying from 1260 to 54,000. With in-line current being present, the measured drag coefficients of the straked cylinder are found to depend on the ratio between the oscillating velocity amplitude and the steady current velocity. This phenomenon is further confirmed by computational fluid dynamics using large-eddy simulations. The drag coefficients obtained from the numerical simulations agree well with the experimentally determined values. Similar phenomenon is observed for the cases with cross background current. Based on the experimental data, empirical formulae are proposed to evaluate drag coefficients. These results are of importance in estimating the resonant motion and the fatigue life of risers, e.g. water intake risers, in the flow regime of low KC. Finally, recommendations are provided for fatigue analysis of risers with helical strakes from the perspective of engineering practice. |
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| Keywords: | Hydrodynamic damping Water intake risers Morison equation Fatigue analysis Oscillatory flow |
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