Time varying hydrodynamic characteristics identification of a flexible riser under multi-frequency VIVs
LIU Chang1,2 FU Shixiao1 TANG Xiaoying3 ZHANG Mengmeng1 REN Haojie1
1. State Key Laboratory of Ocean Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
2. Department of Mechanical Engineering, Johns Hopkins University, Baltimore, MD 21218, USA
3. School of Naval Architecture and Ocean Engineering, Jiangsu University of Science and Technology, Zhenjiang Jiangsu 212003, China
Abstract：Here, the forgetting factor least squares (FF-LS) method was proposed for identification of time-varying vortex-induced force coefficients of a flexible riser under multi-frequency vortex-induced vibrations (VIVs).This method introduced a forgetting factor to give a greater weight to the data closer to the present time instant.This modification improved the sensitivity of the algorithm to time varying parameters to make it be able to recognize a system’s time-varying parameters.Here, a mass-spring-damping model was used to verify the FF-LS algorithm’s ability to identify a system’s time-varying parameters accurately.Then, the FF-LS algorithm was used to identify time-varying vortex-induced force coefficients in cross-flow (CF) direction of a flexible riser under multi-frequency VIVs.The results showed that under multi-frequency VIVs, vortex-induced force coefficients of the flexible riser change periodically, their time mean values are different from the riser’s vortex-induced force coefficients under the fundamental frequency VIVs, this is due to coupling effect between fundamental frequency VIV and higher frequencies VIV; the vortex-induced force the reconstructed using identified time-varying vortex-induced force coefficients agrees well with the actual vortex-induced force to verify the time-varying vortex-induced force coefficients under multi-frequency coupling identified by the FF-LS algorithm being able to reconstruct vortex-induced force correctly.
刘畅1,2， 付世晓1，唐笑颖3，张萌萌1，任浩杰1. 多频涡激振动状态下柔性立管的时变水动力特性识别[J]. 振动与冲击, 2019, 38(1): 149-158.
LIU Chang1,2 FU Shixiao1 TANG Xiaoying3 ZHANG Mengmeng1 REN Haojie1. Time varying hydrodynamic characteristics identification of a flexible riser under multi-frequency VIVs. JOURNAL OF VIBRATION AND SHOCK, 2019, 38(1): 149-158.
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