VIV Suppression Research Articles

Investigation of the combined effect of control rods and forced rotation on a cylinder

A novel structure combining the application of control rods and forced rotation on a cylinder is proposed based on the cylindrical vibration suppression, and the combined structure is numerically simulated at a low Reynolds number of 200, an attack angle of 0°–105°, and a rotation rate of 0−1. The vortex-induced vibration responses, fluid forces, and cylindrical wake evolution are analyzed, and the VIV suppression is compared and discussed. The results show that the merging of the vortex layers on the cylinder and control rods promotes cylindrical vortex shedding, causing a high amplitude cylinder response. The cylinder vibrates at a low amplitude for no vortex layer merging. Rotation causes increased directional sensitivity of the control rod to cylindrical amplitude suppression. A 98%-cylinder amplitude suppression can be achieved by combining the control rod and rotation, while only 60% can be achieved by the control rods or rotation alone, indicating that the combined structure is highly effective for amplitude suppression.

Study on the parameters of detached dual splitter plates and comparison with single plate for VIV suppression

In the actual marine engineering environment, vortex-induced vibration will affect the safety of cylindrical structures. Rigid splitter plates have become one of the suitable VIV suppression solutions due to their simple structure and low maintenance costs. Therefore, on the basis of numerical simulation, this paper analyses the influence of the gap between parallel and non-parallel double splitter plates and the arrangement angle of non-parallel double splitter plates on the VIV suppression effect at a fixed flow rate. In addition, the VIV suppression effect of the single and dual splitter plates with the same parameter combination is evaluated under the condition of multi-flow velocity. It is found that the parallel dual splitter plate cannot provide good VIV suppression, especially when the gap exceeds the cylinder diameter, the suppression effect begins to deteriorate. However, on the basis of a certain gap between the plates, the dual splitter plate with arrangement angle is more effective than the single splitter plate in suppressing the transverse vibration of the cylinder. Therefore, when using dual splitter plates for VIV suppression, the parallel dual splitter plates should be avoided. When a better transverse vibration suppression effect is required, the arrangement angle can be appropriately changed.

Vortex-induced vibration of a slender flexible riser with grooved and spanwise strips subject to uniform currents

We report a numerical investigation of the suppression of “vortex-induced vibration” (VIV) of a cylindrical flexible riser to which are attached various grooved or strip configurations with the ensemble exposed to uniform flow. Based on the thick-strip model, the simulation is done using our in-house three-dimensional VIV solver based on the Open Field Operation and Manipulation toolbox and developed at Shanghai Jiao Tong University (referred to as “viv3D-FOAM-SJTU”). The solver is applied to calculate all the simulations; it uses the Navier–Stokes equations to calculate flow field and the Euler–Bernoulli bending-beam hypothesis to calculate the vibrational displacements of the riser. A slender flexible riser with two spanwise symmetrical strips is first used to determine the appropriate installation angle of the strips, and cylindrical or grooved risers with different strip configurations are used to improve VIV suppression. The numerical results show that the spanwise strip installation angles of 30° and 45° suppress VIV due to the secondary separation of the boundary layer, but suffer from higher crossflow vibration frequency, which brings the risk of inducing high-order mode vibration, the enhancement of the lift correlation along the spanwise direction, and the increment of total drag. The main function of spanwise strips installed at 135° and 150° is to divide the wake region, which also helps suppress VIV. The introduction of grooves in the riser combined with strips of suitable thickness reduces the correlation of lift along the span, which in turn reduces crossflow vibration frequency and the total drag, and enhances VIV suppression. Of all the configurations, the grooved riser with four staggered symmetrical strips most strongly suppresses VIV in the crossflow direction.

A Study on the Vortex Induced Vibration of a Cylindrical Structure with Surface Bulges

Inspired by the cactus in nature, a cactus-like cross-sectional structure was proposed to achieve the VIV suppression. The VIV of the elastically mounted cylinder was realized based on the ANSYS Fluent and User Defined Function (UDF). The dynamic motion of the cylinder was solved by the single-step time integration algorithms Newmark-β method. The in-house code was first validated by studying the 2DOF VIV of a circular cylinder with small mass ratio over the range U*=2~13, and the results agree well with the published literature. Then, the performance of surface bulge on VIV suppression was studied and four different coverage ratios (CR) were considered, i.e., 0%, 20%, 33%, and 40%. The VIV of a bulged cylinder can be effectively suppressed. CR20 performs the best in VIV suppression and the suppression efficiency in streamwise and transverse direction are 44.6% and 63.1%, respectively. The mechanism of surface bulge on the VIV suppression is the shift of separation point of the shear layer and vortices form between the surface bulges.

Numerical studies on passive suppression of one and two degrees-of-freedom vortex-induced vibrations using a rotative non-linear vibration absorber

This paper presents a numerical investigation on the use of a rotative non-linear vibration absorber (NVA) as a passive suppressor for the vortex-induced vibrations phenomenon (VIV). The structural model consists of rigid cylinders mounted on elastic supports and the hydrodynamic loads are calculated using phenomenological models. The NVA is defined as a rigid bar, fitted with a tip-mass and hinged to the cylinder. Energy is dissipated by means of a linear dashpot linked to the bar.Two major groups are studied, the first one being that in which the cylinder is constrained to oscillate in the cross-wise direction (1-dof VIV). The second group, herein named 2-dof VIV, refers to the condition in which simultaneous oscillations in the cross-wise and in-line directions are allowed.Characteristic oscillation amplitude curves are obtained as functions of reduced velocities covering the lock-in for different values of the control parameters that define the NVA (namely, its mass, radius and dashpot constant). In addition, quantitative and qualitative aspects of cylinder and suppressor responses are explored in the form of colormaps defined in the space of control parameters for three specific reduced velocities.The systematic study shows that the mass parameter of the NVA has more influence on the VIV suppression for both 1-dof VIV and 2-dof VIV. In general, the suppression has proved to be greater in the 1-dof VIV case.

Passive VIV Reduction of An Inclined Flexible Cylinder by Means of Helical Strakes with Round-Section

A series of experimental tests of passive VIV suppression of an inclined flexible cylinder with round-sectioned helical strakes were carried out in a towing tank. During the tests, the cylinder models fitted with and without helical strakes were towed along the tank. The towing velocity ranged from 0.05 to 1.0 m/s with an interval of 0.05 m/s. Four different yaw angles (a=0°, 15°, 30° and 45°), defined as the angle between the axis of the cylinder and the plane orthogonal of the oncoming flow, were selected in the experiment. The main purpose of present experimental work is to further investigate the VIV suppression effectiveness of round-sectioned helical strakes on the inclined flexible cylinder. The VIV responses of the smooth cylinder and the cylinder with square-sectioned strakes under the same experimental condition were also presented for comparison. The experimental results indicated that the round-Sectioned strake basically had a similar effect on VIV suppression compared with the square-sectioned one, and both can significantly reduce the VIV of the vertical cylinder which corresponded to the case of a=0°. But with the increase of yaw angle, the VIV suppression effectiveness of both round- and square-section strakes deteriorated dramatically, the staked cylinder even had a much stronger vibration than the smooth one did in the in-line (IL) direction.

Active closed-loop vortex-induced vibration control of an elastically mounted circular cylinder at low Reynolds number using feedback rotary oscillations

An active rotary oscillation feedback control methodology is adopted to suppress the flow-induced transverse vibration (VIV) of an elastically supported impenetrable circular cylinder in a uniform low Reynolds number flow (\(\textit{Re} = 100\)). The coupled fluid–structure interaction is replicated by applying the moving mesh technique via a user-defined function (UDF) in the main code of a commercial CFD solver. The closed-loop VIV control action is realized by active forced rotational oscillations of the circular cylinder about its axis based on the feedback signal of the lift coefficient. This prevents the occurrence of resonance by shifting the vortex shedding frequency away from the natural oscillator frequency. Three different active closed-loop proportional controllers are implemented, and their superior performance in cylinder VIV suppression is demonstrated against that of a representative open-loop control system with pre-specified rotational oscillations. It is shown that, in comparison with the open-loop system, the selected closed-loop controller achieves a better cylinder VIV response suppression with a much lower control effort along with considerable reductions in the associated lift/drag coefficients. Furthermore, the closed-loop controller is very effective in a wide range of reduced velocities and does not need to find the “lock-on” forcing frequency for proper de-synchronization. Moreover, the imposed feedback cylinder rotary oscillation is found to considerably affect the spatial characteristics of the wake flow structure by changing the 2S-Coalescent wake pattern (C-2S-mode) of an uncontrolled cylinder into the classical von Karman vortex street (2S-mode), very similar to that of a stationary obstacle. Lastly, when the system is in the fully developed condition, the proportional controller can be complemented by a fuzzy logic inference system for intelligent tuning of gain parameter in order to suppress the impulsive upsurge observed in the cylinder force coefficients of the proportional controller at the start of the control action.

Numerical investigation on the suppression of VIV for a circular cylinder by three small control rods

Laminar flow past a circular cylinder with 3 small control rods is investigated by numerical simulation. This study is concerned with the suppression efficacy of vortex induced vibration by small control rods located around a main cylinder. The effects of the attack angle and rod-to-cylinder gap ratio on the hydrodynamics and vibration responses of the main cylinder are investigated. The attack angle of α=45° is performed as the critical angle for VIV suppression of 3 control rods. The 3 control rods have no effect on VIV suppression when the attack angle is less than the critical angle. The 3 control rods have an excellent VIV suppression efficacy when the attack angle is larger than the critical angle. The transverse vibration frequency of the cylinder with 3 control rods is less than that for an isolated cylinder for all the configurations. The numerical results for the configurations of α=45° & 60°, G/D=0.6–1.2 show excellent suppression efficient among the cases investigated in this study. The best suppression efficient is found at α=45°, G/D=0.9 for 3 control rods. 2 rods in behind of the main cylinder perform more efficient than that of 1 rod in front for VIV suppression as the gap ratio of G/D less than 1.0.

Experimental Research and Analysis of Vortex Excited Vibration Suppression of Spiral Stripe Strake

This paper carries out the experimental research and analysis on the vortex-excited vibration suppression effect of the spiral stripe strake via the laser particle velocimeter (PIV) under vortex speed U=0.6 m/s and attack angle α=300, and discusses the VIV suppression mechanism of the spiral stripe strake by using the numerical simulation of the computational fluid dynamics (CFD) in order to objectively further know inherent mechanism of VIV, further optimize parameters of the spiral stripe strake, and provide references for theoretical research in future.

VIV response of a flexible cylinder with varied coverage by buoyancy elements and helical strakes

Many significant engineering challenges have emerged as the petroleum industry has moved their field development and production activities into increasingly deeper water depths. The design of deepwater marine risers presents the combined challenges to minimize top tensioning requirements, mitigate any flow-induced vibrations, and if possible to increase the expected fatigue life of these slender structural members. As part of the design process to achieve these goals external buoyancy modules and strakes have been employed. To gain insight into the complex multi-mode response behavior a recent experimental study was performed and the analysis of selected data sets is presented. In the experiments a horizontal cylinder with a length to diameter ratio of 263 was fitted with a variety of strake and buoyancy element configurations. The models were towed at uniform speeds ranging from 0.4 to 2.0 m/s and fiber optic strain gages were used to measure both in-line and cross-flow strain response. The resulting time series information was processed utilizing the method of time domain decomposition formulated for strain data input and the introduction of modal assurance criterion to resolve the modal strain information that included frequency, mode shape, and critical damping ratio information. The pre-tensioned cylinder without appendages was used as a base case and the results were basically consistent with expectations. In the case of 0.8 m/s low-tension test, multiple closely spaced non-overlapping peaks were observed in both in-line and cross-flow directions and were identified as being of the same mode with mode shapes distorted away from purely sinusoidal behavior. The test data for the 100% coverage by helical stakes demonstrated the effectiveness of that suppression device over the range of current velocities investigated. The most interesting case was that of a staggered combination of helical strakes and buoyancy element whose total for each type of coverage was equal. This effective asymmetric VIV suppression approach is presented and discussed in detail.

Steady current induced vibration of near-bed piggyback pipelines: Configuration effects on VIV suppression

A series of experiments on steady current induced vibration of piggyback pipelines close to a plane seabed were conducted with a hydro-elastic facility in a conventional water flume. The effects of the mass-damping parameter, the diameter ratio, the gap-to-diameter ratio, the spacing-to-diameter ratio and the position angle on the VIV response were studied. The VIV suppression for the piggyback pipeline system by the small pipe was investigated based on the analysis of the vibration amplitude and the critical reduced velocity for the onset of VIV. Comparison with the prediction with the modified Griffin plot by Govardhan and Williamson (2006) [10] shows that the peak vibration amplitude of near-wall piggyback pipelines is smaller than that for a wall-free single pipe. The configuration parameters of piggyback pipelines have significant effects on the VIV suppression. For the configuration of the small pipe above the main pipe (θ=90°), the minimum peak amplitude and the maximum critical reduced velocity occur at the spacing-to-diameter ratio of G/D≈0.25, indicating that VIV is suppressed most effectively by the small pipe at this value of G/D. For a constant value of G/D=0.25, both the minimum peak amplitude and the maximum critical reduced velocity occur at the position angle of θ≈120°.

VIV suppression of a two-degree-of-freedom circular cylinder and drag reduction of a fixed circular cylinder by the use of helical grooves

Experimental investigations have been carried out to examine the effects of triple-starting helical grooves on the drag of fixed circular cylinders and the vortex-induced vibration of elastically supported cylinders. For the elastically supported cylinder, the Reynolds number varied from 1.3×10 4 to 4.6×10 4, whilst for the fixed cylinder from 3.1×10 4 to 3.75×10 5. A comparative approach which allows direct comparisons of the results was adopted where two cylinders of identical dimensions and physical properties with or without helical surface grooves were tested in exactly same experimental set-ups. In the elastically supported cylinder tests, the cylinders were attached to a vertically cantilevered supporting rod and towed in a towing tank. Both the in-line and cross-flow vibrations were permitted. In the fixed cylinder tests, the cylinders were supported on rigid vertical struts and towed horizontally in the same towing tank. It is found that for the case investigated the helical grooves were effective in suppressing the vortex-induced cross-flow vibration amplitudes with the peak amplitude reduced by 64%. Drag reductions of up to 25% were also achieved in the sub-critical Reynolds number range tested in the study for the fixed cylinders.

Low drag solutions for suppressing vortex-induced vibration of circular cylinders

Abstract Measurements are presented of response and drag for a flexibly mounted circular cylinder with low mass and damping. In one set of experiments it is free to respond in only the cross-flow direction and in a second it is free to respond in two degrees of freedom. It is shown how vortex-induced vibration can be practically eliminated by using free-to-rotate, two-dimensional control plates. Further it is shown that these devices achieve VIV suppression with drag reduction. The device producing the largest drag reduction was found to have a drag coefficient equal to about 60 % of that for a plain, fixed cylinder over the Reynolds number range of the experiments, up to 30 000. The importance of torsional resistance of the devices is discussed and it is shown that if it is too low large oscillations of the device and cylinder will develop and if it is too high galloping is initiated.