scholarly journals A wake oscillator model with nonlinear coupling for the vortex-induced vibration of a rigid cylinder constrained to vibrate in the cross-flow direction

2020 ◽  
Vol 469 ◽  
pp. 115161 ◽  
Author(s):  
Yang Qu ◽  
Andrei V. Metrikine
Keyword(s):  
Flow Direction ◽  
Cross Flow ◽  
Oscillator Model ◽  
Nonlinear Coupling ◽  
Vortex Induced Vibration ◽  
Rigid Cylinder ◽  
Wake Oscillator Model ◽  
Wake Oscillator ◽  
The Cross

A Wake Oscillator Model With Nonlinear Coupling for the VIV of Rigid Cylinder Constrained to Vibrate in the Cross-Flow Direction

2016 ◽  
Author(s):  
Y. Qu ◽  
A. V. Metrikine
Keyword(s):  
Forced Vibration ◽  
Flow Direction ◽  
Cross Flow ◽  
Added Mass ◽  
Oscillator Model ◽  
Nonlinear Coupling ◽  
Rigid Cylinder ◽  
Wake Oscillator Model ◽  
Wake Oscillator ◽  
Good Agreement

In this paper a new wake oscillator model with nonlinear coupling term is proposed to model the vortex-induced vibration of an elastically supported rigid cylinder constrained to vibrate in the cross-flow direction. The superiority of this new model lies in its ability to satisfy at the same time both free and forced vibration experiments. The new wake oscillator model is based on an existing van der Pol wake oscillator model and nonlinear coupling terms are added to improve its performance in the modelling of forced vibration. The tuning of this new model to the forced vibration shows good agreement with experiments in terms of the added damping but failed to capture the negative added mass at high reduced velocities. To eliminate this discrepancy the model is further enhanced by relaxing the assumption of constant potential added mass. Using the parameters obtained from the forced vibration experiments, the free vibration simulation is conducted and results are compared with the experiments. Comparison indicates good agreement between simulation and experiments, and the main features of VIV are captured.

scholarly journals Fluid nonlinearities effect on wake oscillator model performance

2018 ◽  
Vol 148 ◽  
pp. 04002 ◽  
Author(s):  
Victoria Kurushina ◽  
Ekaterina Pavlovskaia
Keyword(s):  
Structural Damage ◽  
Degrees Of Freedom ◽  
Model Performance ◽  
Cross Flow ◽  
Resonance State ◽  
Oscillator Model ◽  
Mass Ratio ◽  
Wake Oscillator Model ◽  
Wake Oscillator ◽  
Wide Range

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.

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

2009 ◽  
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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