Experimental investigation on vortex-induced force of a Steel Catenary Riser under in-plane vessel motion |
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| Institution: | 1. School of Naval Architecture and Marine Engineering, National Technical University of Athens, Greece;2. School of Mathematics, University of East Anglia, Norwich, UK;1. State Key Laboratory of Ocean Engineering, Shanghai Jiao Tong University, Shanghai, 200240, China;2. Institute of Polar and Ocean Technology, Institute of Marine Equipment, Shanghai Jiao Tong University, Shanghai, 200240, China;3. Sun Yat-Sen University, Zhuhai, 528478, China;4. China National Offshore Oil Corporation (CNOOC) Research Institute, Chaoyang District, Beijing, 10010, China;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 Jiao Tong University, Shanghai, China;3. Department of Mechanical and Structural Engineering and Materials Science, University of Stavanger, Stavanger, Norway;4. SINTEF Ocean, Trondheim, Norway;5. Department of Marine Technology, Centre for Ships and Ocean Structures, Norwegian University of Science and Technology, Trondheim, Norway;6. Statoil, Trondheim, Norway |
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| Abstract: | A method to identify vortex-induced forces and coefficients from measured strains of a Steel Catenary Riser (SCR) undergoing vessel motion-induced Vortex-induced Vibration (VIV) is proposed. Euler–Bernoulli beam vibration equations with time-varying tension is adopted to describe the out-of-plane VIV responses. Vortex-induced forces are reconstructed via inverse analysis method, and the Forgetting Factor Least Squares (FF-LS) method is employed to identify time-varying vortex-induced force coefficients, including excitation coefficients and added mass coefficients. The method is verified via a finite element analysis procedure in commercial software Orcaflex. The time-varying excitation coefficients and added mass coefficients of an SCR undergoing vessel motion-induced VIV are investigated. Results show that vessel motion-induced VIV is excited at the middle or lower part of the SCR and in the acceleration period of in-plane velocity, where most of the excitation coefficients are positive, while during the deceleration period, the excitation coefficients becomes too small to excite VIVs. Parameter γ 1] has strong correlation with excitation coefficients. In addition, time-varying tensions contribute significantly to the variations of added mass coefficients under the condition that the ratio of dynamic top tension to pretension exceeds the range of 0.7–1.3. Moreover, chaotic behaviors are observed in vortex-induced force coefficients and are more evident with the increase of vessel motion velocity. This behavior may attribute to the randomness existing in in-plane velocity and its coupling with out-of-plane vibrations. |
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| Keywords: | Vessel motion-induced vibration Steel catenary riser Vortex-induced forces Time-varying excitation coefficients Time varying added mass coefficients |
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