Investigation Of Vortex-induced Vibration Research Articles

Experimental Investigation of Vortex-Induced Vibrations on Yawed and Inclined Flexible Cylinders

Abstract An experimental setup was built to investigate the vortex-induced vibration (VIV) phenomenon on yawed and inclined flexible cylinders, in which five yaw angles θ = 0 deg, 10 deg, 20 deg, 30 deg, and 45 deg and five azimuth angles β = 0 deg, 45 deg, 90 deg, 135 deg, and 180 deg were combined. The experiments were carried out in a towing tank facility at Reynolds numbers from 1800 to 18,000, comprising vibrations up to the eighth natural mode. Time histories of displacements were recorded using a submerged optical system that tracks 17 reflective targets. A modal decomposition scheme based on Galerkin’s method was applied, aiming multimodal behavior investigations. Such an approach allowed the analysis of the modal amplitude throughout time, revealing interesting results for such a class of VIV tests. The flexible cylinder total response is generally a combination of two or more modes. Only for azimuths 0 deg, 90 deg, and 180 deg, a unimodal response was observed for the two first lock-in regimes. The frequency response showed that when the response was multimodal, non-dominant modes can follow the vibration frequency of the dominant one. Assuming a priori the independence principle (IP) valid to define the reduced velocities (Vr), it was observed that the resonance region was restricted to 3 ≤ Vr ≤ ~8 for the tested cases, indicating that the IP can be at least partially applied for flexible structures. As the literature scarcely explores the simultaneous yawed and inclined configurations, the present work may contribute to further code validation and improvements regarding the design of slender offshore structures.

Investigation of Vortex-Induced Vibration with Different Width of Two Bluff Bodies in Tandem Arrangement for Energy Harvesting System

Due to imperative of enhancement on Vortex-induced vibration (VIV) energy harvesting as renewable energy sources, dual bluff bodies which are triangle and cylinder in tandem arrangement with different width from each other are studied in terms of total deformation, directional deformation and voltage generated in order to determine the better bluff bodies for the piezoelectric film. This is due to the unsymmetrical wakes pattern, low frequency vortices, and low energy output produced by the system. The length and height of the bluff bodies were fixed to 0.1m and airflow used for simulations was 1.46m/s. The spacing ratio was calculated from 1 to 6 to examine various width between two bluff bodies that will affect the formation of the vortex at the downstream area. From the results, it can be concluded that triangle bluff bodies in tandem arrangement 0.6m from each other have resulted in the highest total deformation and effective voltage generated of 0.47mm, and 3.05mV, respectively. These data indicated the highest ability of energy harnessing. Furthermore, this model results in a consistent flagging direction of the piezoelectric that implying a good energy harvesting system.

Numerical investigation of vortex-induced vibration for two tandem circular cylinders with different diameters

Vortex-induced vibration of two tandem circular cylinders with different diameters under low Reynolds number (Re = 200) is investigated numerically by solving the uncompressible two-dimensional Navier–Stokes equations. The arbitrary Lagrange–Euler method is used to simulate the movement of mesh. Effects of diameters and gap ratios are considered. Numerical results show that diameter ratios and gap ratios have little effect on maximum vibration amplitude. Four different vortex shedding modes are detected in this study.

Numerical Investigation of Vortex Induced Vibration for Submerged Floating Tunnel under Different Reynolds Numbers

A 2D numerical model was established to investigate vortex induced vibration (VIV) for submerged floating tunnel (SFT) by solving incompressible viscous Reynolds average Navier-Stokes equations in the frame of Abitrary Lagrangian Eulerian (ALE). The numerical model was closed by solving SST k-ω turbulence model. The present numerical model was firstly validated by comparing with published experimental data, and the comparison shows that good achievement is obtained. Then, the numerical model is used to investigate VIV for SFT under current. In the simulation, the SFT was allowed to oscillate in cross flow direction only under the constraint of spring and damping. The force coefficients and motion of SFT were obtained under different reduced velocity. Further research showed that Reynolds number has not only a great influence on the vibration amplitude and ‘lock-in’ region, but also on the force coefficients on of the SFT. A large Reynolds number results in a relatively small ‘lock-in’ region and force coefficient.

Experimental study of the vortex-induced vibration of marine risers under middle flow

A considerable number of studies for vortex induced vibration (VIV) under uniform flow have been performed. However, investigation of VIV under middle flow is scarce. An experiment for VIV under middle flow was conducted in a deep-water offshore basin. Various measurements were obtained by the fiber Bragg grating strain sensors placed on the riser, and VIV under the effect of middle flow with was investigated. Results show that the riser vibrates at different order natural frequencies along the water depth in the CF and IL directions appearing as the multi-frequencies under middle flow. The variation vortex shedding frequencies along the riser under middle flow may generate different wake modes and vibration modals as the corresponding vortex shedding frequencies approach the riser natural frequencies. The dominant vibration frequency of the entire riser is consistent, and determined by high order natural frequency and the corresponding closing vortex shedding frequencies under the middle flow. Meanwhile, the vibration modal under middle flow appears multi-modals and other lower modal have effect on riser vibration. The VIV mechanism under middle flow possesses some aspects similar to those of uniform flow and several unique features.

Investigation of Vortex Induced Vibration of Offshore Pipelines near Seabed

Recently, dynamic interaction between pipelines, seabed and the ocean currents has received wide concern from marine pipeline designers and researchers. The analysis of dynamic responses of subsea pipeline, in vicinity of the seabed in severe ocean environments, is very important. In this regard, this study reviews and sums up recent researches and investigations performed on vortex induced vibration of pipelines near seabed for analysis and design. In addition, the preliminary results of a developed model around a pipe subjected to steady current have been presented. Future trends and challenges in this research are also identified.

Two-degree-of-freedom vortex-induced vibration of circular cylinders with very low aspect ratio and small mass ratio

The investigation of vortex-induced vibration on very short cylinders with two degrees of freedom has drawn the attention of a large number of researchers. Some investigations on such a problem are carried out in order to have a better understanding of the physics involved in vortex-induced motions of floating bodies such as offshore platforms. In this paper, experiments were carried out in a recirculating water channel over the range of Reynolds number 6000<Re<70000. Measured response amplitudes and frequencies of cylinders with two degrees of freedom, three different small mass ratios (m⁎=1.00; 2.62 and 4.36) and very low aspect ratios (0.3≤L/D≤2.0) were shown and the results were discussed in depth. Conversely to what would be expected for cylinders with very low aspect ratio, the results showed large motions in the transverse direction with maximum amplitudes around 1.5 diameters for cylinders with L/D=2.0, despite being smaller when the aspect ratio is reduced. Moreover, the response amplitudes presented high values around 0.4 diameters in the in-line direction. In fact, the large transverse motions were related to a strong coupling with the in-line responses, visibly identified in the plots of nondimensional frequency, as well as by the trajectories in the XY-plane, Lissajous figures, particularly in the case of m⁎=1.00 and L/D=2.0, when 8-shape trajectories were clearly observed. The case of m⁎=1.00 deserves more attention because of its smaller amplitude compared to the cases with the same aspect ratio and a larger mass ratio. This counter-intuitive behavior seems to be related to the energy transferring process from the steady stream to the oscillatory hydroelastic system. Finally, it is noteworthy that the characteristic of the “Strouhal-like” number decreases when the aspect ratio decreases, as also observed in previous works available in the literature, most of them for stationary cylinders.

Numerical investigation of vortex-induced vibrations for flow past a circular cylinder

The objective of the present investigation is to study the vortex-induced vibrations (VIV) for flow past a circular cylinder. The turbulent flow is simulated by using a 2-D standardk-ɛ model incorporating the finite volume method (FVM) and the Semi-Implicit Method for the Pressure Linked Equations (SIMPLE) algorithm on non-orthogonal boundary-fitted collocated grids. The wall boundaries are approximated with wall functions. In the numerical cases, the turbulent wake patterns are studied by plotting the streamlines and the turbulent kinetic energy contours. The pressure distributions are investigated. Analyses of the vortex-induced force coefficients and the structural vibrations are carried out. The variations of the Strouhal number with the Reynolds number and of the vortex-induced force coefficients with the reduced velocity are obtained. The results show that this numerical approach is feasible and efficient in investigating the VIV problem for a circular cylinder.

Numerical Investigation of Vortex Induced Vibration on an Elastically Mounted Cylinder

The Vortex-Induced Vibration on a circular cylinder is investigated by the numerical solution of the two-dimensional Reynolds Averaged Navier-Stokes equations. Results are compared with experimental measurements obtained by different author to verify the quality of the numerical solution. The Beam and Warming implicit factorization scheme is used to solve the governing equations and the Baldwin - Lomax model is used to simulate the turbulent flow in the wake of the cylinder. The cylinder is laterally supported by a spring and a damper and free to oscillate in the transversal direction. The numerical results showed that the curve of transversal oscillation amplitude presents a quite different behaviour as the data is obtained with increasing or decreasing velocity, characterizing a hysteresis effect. The best agreement with experiment is obtained as the numerical results are obtained with decreasing velocity.