Hydrodynamics of A Flexible Riser Undergoing the Vortex-Induced Vibration at High Reynolds Number

• Published in: China ocean engineering Vol. 32; no. 5; pp. 570 - 581
• Main Authors: Ren, Tie, Zhang, Meng-meng, Fu, Shi-xiao, Song, Lei-jian
• Format: Journal Article
• Language: English
• Published: Nanjing Chinese Ocean Engineering Society 01.10.2018; Springer Nature B.V; Collaborative Innovation Centre for Advanced Ship and Deep-Sea Exploration, Shanghai 200240, China; Marine Design & Research Institute of China, Shanghai 200011, China%State Key Laboratory of Ocean Engineering, Shanghai Jiao Tong University, Shanghai 200240, China; Collaborative Innovation Centre for Advanced Ship and Deep-Sea Exploration, Shanghai 200240, China%Shanghai Electric Wind Power Group, Shanghai 200030, China; State Key Laboratory of Ocean Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
• Subjects: Coastal Sciences; Computational fluid dynamics; Cross flow; Damping; Direction; Drag coefficient; Drag coefficients; Engineering; Excitation; Fluid flow; Fluid- and Aerodynamics; Forces (mechanics); Fourier series; High frequencies; High frequency; High Reynolds number; Hydrodynamics; Inverse method; Marine & Freshwater Sciences; Mathematical models; Model testing; Numerical and Computational Physics; Oceanography; Offshore Engineering; Reynolds number; Simulation; Uniform flow; Vibration; Vibration measurement; Vortex-induced vibrations; Vortices; excitation coefficient; drag coefficient; added-mass coefficient; flexible riser; vortex-induced force; vortex-induced vibration
• ISSN: 0890-5487; 2191-8945
• DOI: 10.1007/s13344-018-0059-0

This study proposed a method to obtain hydrodynamic forces and coefficients for a flexible riser undergoing the vortex-induced vibration (VIV), based on the measured strains collected from the scale-model testing with the Reynolds numbers ranging from 1.34E5 to 2.35E5. The riser is approximated as a tensioned spatial beam, and an inverse method based on the FEM of spatial beam is adopted for the calculation of hydrodynamic forces in the cross flow (CF) and inline (IL) directions. The drag coefficients and vortex-induced force coefficients are obtained through the Fourier Series Theory. Finally, the hydrodynamic characteristics of a flexible riser model undergoing the VIV in a uniform flow are carefully investigated. The results indicate that the VIV amplifies the drag coefficient, and the drag coefficient does not change with time when the CF VIV is stable. Only when the VIVs in the CF and IL directions are all steady vibrations, the vortex-induced force coefficients keep as a constant with time, and under “lock-in” condition, whether the added-mass coefficient changes with time or not, the oscillation frequency of the VIV keeps unchanged. It further shows that the CF excitation coefficients at high frequency are much smaller than those at the dominant frequency, while, the IL excitation coefficients are in the same range. The axial distributions of the excitation and damping region at the dominant frequency and high frequency are approximately consistent in the CF direction, while, in the IL direction, there exists a great difference.