Session: 08-03-01 Fundamental Vortex Induced Vibrations & Cylinder Hydrodynamics

Submission Number: 180127

A Comparative Study on the Hydrodynamic Forces of Bare and Buoyancy-Covered Cylinders Under Forced Oscillation 

Flexible pipes with buoyancy elements, such as lazy-wave risers and cables, are widely used in offshore energy systems to effectively accommodate platform motions and reduce top tension. However, compared to bare pipes, these buoyancy-covered pipes exhibit distinct vortex-induced vibration (VIV) characteristics in currents due to the spatial variation in their hydrodynamic outer diameters. Therefore, investigation into their hydrodynamic characteristics under oscillation is required. In this study, harmonic forced-oscillation tests in the cross-flow (CF) direction were conducted on a circular cylinder equipped with staggered buoyancy elements of a 50% coverage. The Reynolds numbers (Re) based on the buoyancy elements and the bare cylinder were approximately 1×10⁵ and 3×10⁴, respectively. The non-dimensional frequency f^* and amplitude A^* were varied from 0.1 to 0.3 and 0.1 to 1.0, respectively. Stationary towing tests revealed that the mean drag coefficient of the buoyancy-covered cylinder decreased to about 0.9. The hydrodynamic coefficient databases of buoyancy-covered cylinder were further established and analyzed based on the forced-oscillation tests. The results show that the hydrodynamic characteristics of the buoyancy-covered cylinder differs significantly from those of a bare cylinder. Its excitation region occurs at lower non-dimensional frequencies, below f^* = 0.16. The maximum drag force does not appear within the excitation region, instead, it increases monotonically with both f^* and A^*. In contrast, the added mass coefficient first increases and then decreases with f^*, reaching its maximum around f^* = 0.16.

Presenting Author: Ruoning Du tate Key Laboratory of Ocean Engineering, Shanghai Jiao Tong University

Presenting Author Biography: I am Du Ruoning, a doctoral student from Shanghai Jiao Tong University. My research field is oceanic pipe cable vortex-induced vibration.

Authors:

Ruoning Du State Key Laboratory of Ocean Engineering, Shanghai Jiao Tong University
Huailiang Li Offshore Oil Engineering Co., Ltd., Tianjin, China
Chunhong Hu Offshore Oil Engineering Co., Ltd., Tianjin, China
Shixiao Fu State Key Laboratory of Ocean Engineering, Shanghai Jiao Tong University
Jiawei Shen State Key Laboratory of Ocean Engineering, Shanghai Jiao Tong University
Mengmeng Zhang State Key Laboratory of Ocean Engineering, Shanghai Jiao Tong University
Bin Song State Key Laboratory of Ocean Engineering, Shanghai Jiao Tong University