Session: 04-01-03 Flexible Pipes III

Submission Number: 181026

Multi-Mode Vortex-Induced Vibration and its Spatiotemporal Evolutions of Double-Stepped Flexible Riser in Deep Water 

With the increase of water depth in offshore oil and gas production, the aspect ratio of flexible risers can reach the order of 10³, which greatly enhances the flexibility of the structure. Flexible risers suitable for deep water, such as the double-stepped flexible riser, have low natural frequencies and dense modes. In addition, the presence of non-uniformly distributed buoyancy modules makes the configuration very complex. In that case, the vortex-induced vibration (VIV) of double-stepped riser is more challenging due to the multi-mode participation and complex distribution of lock-in regions. In this study, a novel structural configuration, i.e. the double-stepped flexible riser, is considered for its VIV analysis. The distribution characteristics of the lock-in regions in the excitation domain of flexible risers are carefully examined. Then, the dominant modes of the VIV responses along the overall structural span are identified through the response spectrum. At last, the spatiotemporal evolution is conducted on the displacement response. The results indicated that several modes are involved in different lock-in regions. More importantly, lock-in regions of different modes are staggered along double-stepped riser span due to the low and dense modal frequencies, unlike traditional catenary riser where the modes in lock-in regions decrease sequentially from top to bottom. It is found that the dominant mode of the responses is consistent with the mode of lock-in region at both ends of the excited region. However, the dominant mode of the responses is different from the mode of lock-in region in some parts of the excited region. Based on the spatiotemporal evolution of the displacement response, the overall response of the riser exhibits obvious standing-wave characteristics, and traveling-wave effects are observed in transition areas between different lock-in regions with different modes.

Presenting Author: Xiangxu Liu Institute of Mechanics, Chinese Academy of Sciences

Presenting Author Biography: Xiangxu Liu, a graduate student of the Institute of Mechanics of the Chinese Academy of Sciences who majors in engineering mechanics. His research interests mainly focus on fluid structure interaction problems in aerospace and ocean engineering.

Authors:

Shuangxi Guo Institute of Mechanics, Chinese Academy of Sciences
Xiangxu Liu Institute of Mechanics, Chinese Academy of Sciences
Yucheng Guo International Innovation Institute, Beihang University
Yue Kong School of Naval Architecture & Ocean Engineering, Jiangsu University of Science and Technology
Weimin Chen Institute of Mechanics, Chinese Academy of Sciences
Min Li International Innovation Institute, Beihang University