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.

Effect of Different Input Loading Form on Structure-Born Sound Radiation

2012 ◽  
Vol 518-523 ◽  
pp. 3768-3771
Author(s):  
Zhi Yong Xie ◽  
Qi Dou Zhou ◽  
Gang Ji
Keyword(s):  
Experimental Data ◽  
Forced Vibration ◽  
Sound Radiation ◽  
Added Mass ◽  
Elastic Vibration ◽  
Simulation And Experiment ◽  
Radiation Induced ◽  
Vibration And Sound Radiation ◽  
Loading Form ◽  
Good Agreement

The exciting force’s accurate measurement of is crucial to the structure-born sound radiation. Forced vibration and sound radiation of the ribbed cylinder is examined in the anechoic room. An approach called added mass and damping method is proposed to calculate the elastic vibration and acoustic field of the cylinder. Results obtained from simulation are show to be in good agreement with the experimental data. Sound radiation induced by different input loading form is examined via simulation and experiment. And the equipollence of force and pressure acting on the base is validated.

The Study on the Influence of Pipe-Soil Interaction on VIV for Different Free Span Types

2017 ◽  
Author(s):  
Chongyao Zhou ◽  
Gang Xu ◽  
Zhiming Huang ◽  
Dagang Zhang ◽  
Naiquan Ye ◽  
...  
Keyword(s):  
Time Domain ◽  
Cross Flow ◽  
Sensitivity Study ◽  
Structural Damping ◽  
Flexible Pipe ◽  
Wake Oscillator Model ◽  
Wake Oscillator ◽  
Different Types ◽  
Main Factors ◽  
Parameter Influence

Subsea pipeline laid on the seabed will experience free span when the lay path is long and seabed is rugged. Hydrodynamic loads caused by the currents around the pipeline can induce oscillations in both cross-flow and in-line directions. This phenomenon is called vortex-induced vibration (VIV) which is the most common case that could induce serious fatigue problems. The pipe-soil interaction is one of the main factors that influence the vibration. In this paper, a study focusing on the effect of pipe-soil interaction on VIV for different types of free span is presented. The Milan wake oscillator is applied to calculate the dynamic response induced by VIV in Orcaflex, and the results are compared with experimental data to identify its validity. A sensitivity study is also performed to study the parameter influence of the Milan wake oscillator model. Four types of free span (including the multiple free spans) are modeled in Orcaflex and time domain VIV analysis is carried out to study the influence of pipe-soil interaction. Comparison among different types of free span is discussed. The influence of structural damping is studied for flexible pipe only because its influence on steel pipe is negligible. The influence of structural damping on flexible pipe is studied by means of a predefined moment-curvature curve. In addition, several cases are studied to investigate the influence of tension on VIV by Milan wake oscillator.

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