Wake oscillator equations in modelling vortex-induced vibrations at low mass ratios

The current research explores the capabilities of Rayleigh and Van der Pol equations from the standpoint of accuracy of vortex-induced vibrations (VIV) modelling for low mass ratio cases. The two degree-of-freedom rigid structure model suggested by Postnikov et al. [1] is used as the base case, and the fluid equations are modified to create 7 options as alternatives to this model. The considered options constitute variation in damping terms, including introduction of additional damping coefficients (as different Van der Pol or Rayleigh parameters). Then the calibration is performed to identify the best set of coefficients to provide accurate match with the experimental data. The main aim is to predict correctly the development of the super-upper branch [2]. Experimental results by Stappenbelt and Lalji [3] for mass ratio 2.36 are utilised for the model calibration. Then the obtained models are validated using data from the series of experiments by Stappenbelt and Lalji [3] and published experimental data from other sources [2, 4]. The obtained results demonstrate the advantages of changes in damping terms. Overall, it is concluded that Rayleigh oscillator can be recommended to approximate the lift coefficient for low mass ratios.