Predictions for combined In-Line and Cross-Flow VIV responses with a novel model for estimation of tension

Abstract

The dynamic responses of slender cylinders with high aspect ratios undergoing vortex-induced vibrations (VIV) are studied.In detail, a three-dimensional model predicting the VIV responses in both the In-Line and Cross-Flow directions of slender cylinders is proposed based on the nonlinear equation governing the dynamic deformation and a wake oscillator. The tension in the cylinder is estimated according to the incoming stream velocities. To predict the VIV responses, the cylinder is discretized into finite segments, and the vibrations of each segment are estimated from solving the governing equation when the excitation forces are modelled using the Van Der Pol's wake oscillator. Considering that the wake oscillator model estimates the excitation forces according to the dynamics of the cylinder, it reveals the interactions between the flow and the dynamics of the cylinder. In order to verify the model calculating the mean tension, the VIV responses, which has been experimentally tested, is numerically studied. The comparison between the numerically predicted and experimentally measured responses shows that, the approach, especially the novel tension model, proposed herein is reliable as the frequency

Vortex-induced vibrations of flexible cylinders predicted by wake oscillator model with random components of mean drag coefficient and lift coefficient

“…It is noted that the meanings of the symbols used here and in the following text are consistent with the derivation presented by Feng et al (2019), which are also listed in APPENDIX: LIST of SYMBOLS. For more details about the model derivations and limitations, readers are suggested to refer to the work of Feng et al (2019). In equations (1-2), the displacement vector of r and the excitation force vector of F are represented by complexes and i is the imaginary unit.…”

“…It should be noted that, the tension is included in the model via the term ( ∂ ∂z (𝑇 ∂y ∂z )), which theoretically alters the stiffness of the riser significantly and therefore modifies the motion of the riser. In equation ( 1), the tension is actually considered as a function of the vertical coordinate of 𝑧, which unavoidably induces extra computational burden in numerically seeking its solution as discussed in Feng et al (2019). Therefore, the tension is assumed constant along the length of the cylinder as in the previous studies (Gu et al, 2012;Gu et al, 2013).…”

“…The beam deformation, axial tension (Gu et al, 2013) and the vibration frequency (Lee and Allen, 2010) of a riser are found, however, increase with the free stream velocity. Therefore, it is suggested, following Feng et al (2019), that the tension should be modelled as a constant along the axis of the riser but varies with the external free stream velocity as,…”

“…With the help of the wake oscillator with random drag and lift coefficients, the experiment conducted by Trim et al (2005) is numerically reproduced to exhibit the influences of random hydrodynamics on the prediction of the VIV. In addition to directly comparing to the experimental data, the model predictions are also compared to the corresponding results produced by a model without random effects (Feng et al, 2019). The properties of the idealized cylinder and the values of model parameters are listed in Table 3 and 4, respectively, as reported by Feng et al (2019).…”

Effect of Top Tension on Vortex-Induced Vibration of Deep-Sea Risers

“…However, the lock-in frequency range of the riser was wider in the sheared current, and the maximum stress was smaller than in the uniform current. The contribution from in-line vibration has been noticed by many researchers [7][8][9][10][11]. The coupled model of In-Line (IL) and Cross-Flow (CF) VIV was established, and the results showed that IL VIV would affect the mode of the vortex and the amplitude of the CF VIV.…”