A modified wake oscillator model for vortex-induced vibration of circular cylinders for a wide range of mass-damping ratio

Vortex-induced vibrations (VIV) need to be accounted for in the design of marine structures such as risers and umbilicals. If a resonance state of the slender structure develops due to its interaction with the surrounding fluid flow, the consequences can be severe resulting in the accelerated fatigue and structural damage. Wake oscillator models allow to estimate the fluid force acting on the structure without complex and time consuming CFD analysis of the fluid domain. However, contemporary models contain a number of empirical coeffcients which are required to be tuned using experimental data. This is often left for the future work with the opened question on how to calibrate a model for a wide range of cases and find out what is working and is not. The current research is focused on the problem of the best choice of the fluid nonlinearities for the base wake oscillator model [1] in order to improve the accuracy of prediction for the cases with mass ratios around 6.0. The paper investigates six nonlinear damping types for two fluid equations of the base model. The calibration is conducted using the data by Stappenbelt and Lalji [2] for 2 degrees-of-freedom rigid structure for mass ratio 6.54. The conducted analysis shows that predicted in-line and cross-flow displacements are more accurate if modelled separately using different damping types than using only one version of the model. The borders of application for each found option in terms of mass ratio are discussed in this work, and appropriate recommendations are provided.

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Wake oscillator model for assessment of vortex-induced vibration of flexible structures under wind action

Journal of Wind Engineering and Industrial Aerodynamics ◽

10.1016/j.jweia.2014.11.002 ◽

2015 ◽

Vol 136 ◽

pp. 192-200 ◽

Cited By ~ 14

Author(s):

Kun Xu ◽

Yaojun Ge ◽

Dongchang Zhang

Keyword(s):

Flexible Structures ◽

Oscillator Model ◽

Vortex Induced Vibration ◽

Wind Action ◽

Wake Oscillator Model ◽

Wake Oscillator

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Prediction of Vortex-Induced Vibration of Flexible Riser Using an Improved Wake-Oscillator Model

Volume 5: Polar and Arctic Sciences and Technology; CFD and VIV ◽

10.1115/omae2009-79336 ◽

2009 ◽

Cited By ~ 4

Author(s):

Wein-min Chen ◽

Liwu Zhang ◽

Min Li

Keyword(s):

Analytical Model ◽

Flow Distribution ◽

Experimental Result ◽

Oscillator Model ◽

Flexible Riser ◽

Vortex Induced Vibration ◽

Wake Oscillator Model ◽

Wake Oscillator ◽

Uniform Current ◽

Lock In

Based on improving the wake-oscillator model, an analytical model for vortex-induced vibration (VIV) of flexible riser under non-uniform current is presented, in which the variation of added mass at lock-in and the nonlinear relationship between amplitude of response and reduced velocity are considered. By means of empirical formula combining iteration computation, the improved analytical model can be conveniently programmed into computer code with simpler and faster computation process than CFD so as to be suitable to application of practical engineering. This model is validated by comparing with experimental result and numerical simulation. Our results show that the improved model can predict VIV response and lock-in region more accurately. At last, illustrative examples are given in which the amplitude of response of flexible riser experiencing VIV under action of non-uniform current is calculated and effects of riser tension and flow distribution along span of riser are explored. It is demonstrated that with the variation of tension and flow distribution, lock-in region of mode behaves in different way, and thus the final response is a synthesis of response of locked modes.

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