Parametric Investigation and Mechanism of Low-Drag Fairing Devices for Suppressing Vortex-Induced Vibration

2016 ◽  
Author(s):  
Yun Zhi Law ◽  
Tan Jui Hang Benjamin ◽  
Rajeev K. Jaiman
Keyword(s):  
Reynolds Number ◽  
Drag Reduction ◽  
Drag Force ◽  
Numerical Study ◽  
Flow Direction ◽  
Wake Flow ◽  
Hydrodynamic Performance ◽  
Vortex Induced Vibration ◽  
New Device ◽  
Viv Suppression

It is well known that fairing devices are better alternatives than helical strakes due to their low-drag performance while suppressing vortex-induced vibration (VIV). Our objective is to present a systematic numerical study to understand the hydrodynamic performance and physical mechanism of fairing configurations and then propose a new device for suppressing VIV and reducing drag force. In this work, we simplify our investigation by allowing the cylinder-fairing system to oscillate in cross-flow direction without rotation. Firstly, we present a set of simulations of vortex-induced vibration for Short Crab Claw (SCC) fairings [1] with different nondimensional length (Lf/D), where Lf is the length of fairing and D denotes the diameter of cylinder. To establish the relation between the length of fairing and the performance with respect to VIV suppression and drag reduction, we consider the length ratio Lf/D = 1.25, 1.50, 2.00. The underlying VIV suppression mechanism is investigated with the aid of force and amplitude variations, wake flow structures and frequency ratios. Our results show that the SCC fairing with longer length performs better by suppressing the amplitude up to 84% and reduces the drag coefficient by 40%. This finding implies that by offsetting the vortices shed away from the main cylinder, it lowers the influence of vortex interactions, which leads to the suppression of VIV and net reduction in the drag force generation. Based on this mechanism, we propose a new design of fairing, namely the “Hinged C-shaped”, which consists of a thin splitter plate (connected at the base of main cylinder) bifurcating into a C-shaped geometry after a certain distance. Through our numerical study on its hydrodynamic performance, it is shown to be efficient with respect to VIV suppression and drag reduction. To understand the VIV suppression physics, the numerical study is conducted in two-dimension for the cylinder-fairing mounted elastically with mass ratio m* = 2.6 and the damping ξ = 0.001 at low Reynolds number. We further demonstrate the performance of the new fairing device in three-dimension at sub-critical Reynolds number.

VIV Suppression and Drag Reduction With Pivoted Control Plates on a Circular Cylinder

2008 ◽  
Author(s):  
Gustavo R. S. Assi ◽  
Peter W. Bearman
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Drag Reduction ◽  
Flow Direction ◽  
Cross Flow ◽  
Two Dimensional ◽  
Dimensional Control ◽  
Helical Strakes ◽  
Low Mass ◽  
Viv Suppression

Experiments have been carried out on two-dimensional devices fitted to a rigid length of circular cylinder to investigate the efficiency of pivoting control plates as VIV suppressors. Measurements are presented for a circular cylinder with low mass and damping which is free to respond in the cross-flow direction. It is shown how vortex-induced vibration can be practically eliminated by using free to rotate, two-dimensional control plates. Unlike helical strakes, the devices achieve VIV suppression with drag reduction. The device producing the largest drag reduction was found to have a drag coefficient equal to about 70% of that for a plain cylinder at the same Reynolds number.

Practical Design Considerations for Managing Marine Growth on VIV Suppression Devices

2015 ◽  
Author(s):  
Don W. Allen ◽  
Li Lee ◽  
Dean Henning ◽  
Stergios Liapis
Keyword(s):  
Reynolds Number ◽  
Fatigue Life ◽  
Strong Influence ◽  
Low Reynolds Number ◽  
Vortex Induced Vibration ◽  
Design Considerations ◽  
Drag Forces ◽  
Practical Design ◽  
Helical Strakes ◽  
Viv Suppression

Most deepwater tubulars experiencing high currents frequently require vortex-induced vibration (VIV) suppression to maintain an acceptable fatigue life. Helical strakes and fairings are the most popular VIV suppression devices in use today. Marine growth can significantly affect the VIV of a bare riser, often within just a few weeks or months after riser installation. Marine growth can have a strong influence on the performance of helical strakes and fairings on deepwater tubulars. This influence affects both suppression effectiveness as well as the drag forces on the helical strakes and fairings. Unfortunately, many VIV analyses and suppression designs fail to account for the effects of marine growth at all, even on a bare riser. This paper utilizes results from both high and low Reynolds number VIV test programs to provide some design considerations for managing marine growth for VIV suppression devices.

Drag Reduction for Blunt Body With Cross Flow by Extremum-Seeking Control

2008 ◽  
Author(s):  
Nobuhiko Kamagata ◽  
Susumu Horio ◽  
Koichi Hishida
Keyword(s):  
Control System ◽  
Drag Reduction ◽  
Shear Layer ◽  
Flow Velocity ◽  
Drag Force ◽  
Lift Force ◽  
Flow Direction ◽  
Extremum Seeking ◽  
Extremum Seeking Control ◽  
Separated Shear Layer

The active flow control, which can adapt to variation of flow velocity and/or direction, is an effective technique to achieve drag reduction. The present study has investigated a separated shear layer and established two control systems; the system reduces drag force and lift force by controlling the separated shear layer to reattachment for variation of flow velocity and /or direction. The adaptive control system to the variation of flow velocity was constructed by using a hot wire anemometer as a sensor to detect flow separation. The system to flow direction was constructed by using pressure transducers as a sensor to estimate drag force and lift force. The extremum-seeking control was introduced as a controller of the both systems. It is indicated from the experimental results that adaptive drag/lift control system to various flow velocity ranging from 3 to 7 m/s and various flow direction ranging from 0 to 30 deg. was established.

scholarly journals U-shaped fairings suppress vortex-induced vibrations for cylinders in cross-flow

2015 ◽  
Vol 782 ◽  
pp. 300-332 ◽  
Author(s):  
Fangfang Xie ◽  
Yue Yu ◽  
Yiannis Constantinides ◽  
Michael S. Triantafyllou ◽  
George Em Karniadakis
Keyword(s):  
Reynolds Number ◽  
Drag Force ◽  
Three Dimensional ◽  
Cross Flow ◽  
Wake Flow ◽  
Streamwise Vorticity ◽  
Combined System ◽  
Force Coefficient ◽  
Vortex Induced Vibrations ◽  
Adjacent Segments

We employ three-dimensional direct and large-eddy numerical simulations of the vibrations and flow past cylinders fitted with free-to-rotate U-shaped fairings placed in a cross-flow at Reynolds number $100\leqslant \mathit{Re}\leqslant 10\,000$. Such fairings are nearly neutrally buoyant devices fitted along the axis of long circular risers to suppress vortex-induced vibrations (VIVs). We consider three different geometric configurations: a homogeneous fairing, and two configurations (denoted A and AB) involving a gap between adjacent segments. For the latter two cases, we investigate the effect of the gap on the hydrodynamic force coefficients and the translational and rotational motions of the system. For all configurations, as the Reynolds number increases beyond 500, both the lift and drag coefficients decrease. Compared to a plain cylinder, a homogeneous fairing system (no gaps) can help reduce the drag force coefficient by 15 % for reduced velocity $U^{\ast }=4.65$, while a type A gap system can reduce the drag force coefficient by almost 50 % for reduced velocity $U^{\ast }=3.5,4.65,6$, and, correspondingly, the vibration response of the combined system, as well as the fairing rotation amplitude, are substantially reduced. For a homogeneous fairing, the cross-flow amplitude is reduced by about 80 %, whereas for fairings with a gap longer than half a cylinder diameter, VIVs are completely eliminated, resulting in additional reduction in the drag coefficient. We have related such VIV suppression or elimination to the features of the wake flow structure. We find that a gap causes the generation of strong streamwise vorticity in the gap region that interferes destructively with the vorticity generated by the fairings, hence disorganizing the formation of coherent spanwise cortical patterns. We provide visualization of the incoherent wake flow that leads to total elimination of the vibration and rotation of the fairing–cylinder system. Finally, we investigate the effect of the friction coefficient between cylinder and fairing. The effect overall is small, even when the friction coefficients of adjacent segments are different. In some cases the equilibrium positions of the fairings are rotated by a small angle on either side of the centreline, in a symmetry-breaking bifurcation, which depends strongly on Reynolds number.

scholarly journals Vortex-induced vibration of a transversely rotating sphere

2018 ◽  
Vol 847 ◽  
pp. 786-820 ◽  
Author(s):  
Methma M. Rajamuni ◽  
Mark C. Thompson ◽  
Kerry Hourigan
Keyword(s):  
Reynolds Number ◽  
Drag Force ◽  
Rotation Rate ◽  
Lift Force ◽  
Oscillation Amplitude ◽  
Fluid Viscosity ◽  
Sphere Diameter ◽  
Force Coefficient ◽  
Vortex Induced Vibration ◽  
Rotation Rates

The effects of transverse rotation on the vortex-induced vibration (VIV) of a sphere in a uniform flow are investigated numerically. The one degree-of-freedom sphere motion is constrained to the cross-stream direction, with the rotation axis orthogonal to flow and vibration directions. For the current simulations, the Reynolds number of the flow, $Re=UD/\unicode[STIX]{x1D708}$, and the mass ratio of the sphere, $m^{\ast }=\unicode[STIX]{x1D70C}_{s}/\unicode[STIX]{x1D70C}_{f}$, were fixed at 300 and 2.865, respectively, while the reduced velocity of the flow was varied over the range $3.5\leqslant U^{\ast }~(\equiv U/(f_{n}D))\leqslant 11$, where, $U$ is the upstream velocity of the flow, $D$ is the sphere diameter, $\unicode[STIX]{x1D708}$ is the fluid viscosity, $f_{n}$ is the system natural frequency and $\unicode[STIX]{x1D70C}_{s}$ and $\unicode[STIX]{x1D70C}_{f}$ are solid and fluid densities, respectively. The effect of sphere rotation on VIV was studied over a wide range of non-dimensional rotation rates: $0\leqslant \unicode[STIX]{x1D6FC}~(\equiv \unicode[STIX]{x1D714}D/(2U))\leqslant 2.5$, with $\unicode[STIX]{x1D714}$ the angular velocity. The flow satisfied the incompressible Navier–Stokes equations while the coupled sphere motion was modelled by a spring–mass–damper system, under zero damping. For zero rotation, the sphere oscillated symmetrically through its initial position with a maximum amplitude of approximately 0.4 diameters. Under forced rotation, it oscillated about a new time-mean position. Rotation also resulted in a decreased oscillation amplitude and a narrowed synchronisation range. VIV was suppressed completely for $\unicode[STIX]{x1D6FC}>1.3$. Within the $U^{\ast }$ synchronisation range for each rotation rate, the drag force coefficient increased while the lift force coefficient decreased from their respective pre-oscillatory values. The increment of the drag force coefficient and the decrement of the lift force coefficient reduced with increasing reduced velocity as well as with increasing rotation rate. In terms of wake dynamics, in the synchronisation range at zero rotation, two equal-strength trails of interlaced hairpin-type vortex loops were formed behind the sphere. Under rotation, the streamwise vorticity trail on the advancing side of the sphere became stronger than the trail in the retreating side, consistent with wake deflection due to the Magnus effect. This symmetry breaking appears to be associated with the reduction in the observed amplitude response and the narrowing of the synchronisation range. In terms of variation with Reynolds number, the sphere oscillation amplitude was found to increase over the range $Re\in [300,1200]$ at $U^{\ast }=6$ for each of $\unicode[STIX]{x1D6FC}=0.15$, 0.75 and 1.5. The VIV response depends strongly on Reynolds number, with predictions indicating that VIV will persist for higher rotation rates at higher Reynolds numbers.

scholarly journals Experimental and Numerical Study on Hydrodynamic Performance of an Underwater Glider

2018 ◽  
Vol 2018 ◽  
pp. 1-13
Author(s):  
Yanji Liu ◽  
Jie Ma ◽  
Ning Ma ◽  
Zhijian Huang
Keyword(s):  
Reynolds Number ◽  
Degrees Of Freedom ◽  
Numerical Study ◽  
Similarity Theory ◽  
Dynamics Simulation ◽  
Hydrodynamic Performance ◽  
Hull Design ◽  
Motion Characteristics ◽  
6 Degrees Of Freedom ◽  
Temperature Depth

The hydrodynamic coefficients are important parameters for predicting the motion of the glider and upgrading the hull design. In this paper, based on the Reynolds number similarity theory, 6 degrees of freedom (DOFs) of the fluid force and torque of a 1:1 full-scale glider model are measured. The present measurements were carried out at (2 - 14m/s) by varying attack angles and sideslip angles (-9 - 9°), respectively. The measurements were used to study the variation of the hydrodynamics of the glider, and the measurements have also been used to validate results obtained from a CFD code that uses RNG k-ε. The hydrodynamic force coefficients obtained from CFD accord well with the measurements. However, the torque coefficients difference is fairly large. Dynamics simulation results show that CFD results can be used to design and study the motion characteristics of gliders. In order to simplify the design process of gliders, we fit the empirical formula based on the experimental data and obtain a drag coefficient equation with Reynolds number. The influence of two kinds of appendages of the Conductance-Temperature-Depth (CTD) unit and thruster unit on the glider drag were studied by a contrast test. The analysis results can provide reference for design and the motion investigate of gliders.

VIV and WIV Suppression With Parallel Control Plates on a Pair of Circular Cylinders in Tandem

2009 ◽  
Author(s):  
Gustavo R. S. Assi ◽  
Peter W. Bearman
Keyword(s):  
Circular Cylinder ◽  
Drag Reduction ◽  
Flow Direction ◽  
Cross Flow ◽  
Offshore Structures ◽  
Circular Cylinders ◽  
Parallel Plates ◽  
Tandem Cylinders ◽  
Helical Strakes ◽  
Viv Suppression

Experiments have been carried out on two-dimensional devices fitted to a rigid length of circular cylinder to investigate the efficiency of pivoting parallel plates as wake-induced vibration suppressors. Measurements are presented for a circular cylinder with low mass and damping which is free to respond in the cross-flow direction. It is shown how VIV and WIV can be practically eliminated by using free to rotate parallel plates on a pair of tandem cylinders. Unlike helical strakes, the device achieves VIV suppression with 33% drag reduction when compare to a pair of fixed tandem cylinders at the same Reynolds number. These results prove that suppressors based on parallel plates have great potential to suppress VIV and WIV of offshore structures with considerable drag reduction.

Minimum power consumption for drag reduction on a circular cylinder by tangential surface motion

2013 ◽  
Vol 715 ◽  
pp. 597-641 ◽  
Author(s):  
Ratnesh K. Shukla ◽  
Jaywant H. Arakeri
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Power Consumption ◽  
Drag Reduction ◽  
Drag Force ◽  
Potential Flow ◽  
Power Loss ◽  
Tangential Velocity ◽  
Two Dimensional ◽  
Tangential Surface

AbstractWe investigate the effect of a prescribed tangential velocity on the drag force on a circular cylinder in a spanwise uniform cross flow. Using a combination of theoretical and numerical techniques we make an attempt at determining the optimal tangential velocity profiles which will reduce the drag force acting on the cylindrical body while minimizing the net power consumption characterized through a non-dimensional power loss coefficient (${C}_{\mathit{PL}} $). A striking conclusion of our analysis is that the tangential velocity associated with the potential flow, which completely suppresses the drag force, is not optimal for both small and large, but finite Reynolds number. When inertial effects are negligible ($\mathit{Re}\ll 1$), theoretical analysis based on two-dimensional Oseen equations gives us the optimal tangential velocity profile which leads to energetically efficient drag reduction. Furthermore, in the limit of zero Reynolds number ($\mathit{Re}\ensuremath{\rightarrow} 0$), minimum power loss is achieved for a tangential velocity profile corresponding to a shear-free perfect slip boundary. At finite $\mathit{Re}$, results from numerical simulations indicate that perfect slip is not optimum and a further reduction in drag can be achieved for reduced power consumption. A gradual increase in the strength of a tangential velocity which involves only the first reflectionally symmetric mode leads to a monotonic reduction in drag and eventual thrust production. Simulations reveal the existence of an optimal strength for which the power consumption attains a minima. At a Reynolds number of 100, minimum value of the power loss coefficient (${C}_{\mathit{PL}} = 0. 37$) is obtained when the maximum in tangential surface velocity is about one and a half times the free stream uniform velocity corresponding to a percentage drag reduction of approximately 77 %; ${C}_{\mathit{PL}} = 0. 42$ and $0. 50$ for perfect slip and potential flow cases, respectively. Our results suggest that potential flow tangential velocity enables energetically efficient propulsion at all Reynolds numbers but optimal drag reduction only for $\mathit{Re}\ensuremath{\rightarrow} \infty $. The two-dimensional strategy of reducing drag while minimizing net power consumption is shown to be effective in three dimensions via numerical simulation of flow past an infinite circular cylinder at a Reynolds number of 300. Finally a strategy of reducing drag, suitable for practical implementation and amenable to experimental testing, through piecewise constant tangential velocities distributed along the cylinder periphery is proposed and analysed.

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

Water ◽  
2020 ◽  
Vol 12 (1) ◽  
pp. 171 ◽  
Author(s):  
Ruijia Jin ◽  
Mingming Liu ◽  
Baolei Geng ◽  
Xin Jin ◽  
Huaqing Zhang ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Numerical Model ◽  
Stokes Equations ◽  
Flow Direction ◽  
Great Influence ◽  
Large Reynolds Number ◽  
Vortex Induced Vibration ◽  
Force Coefficients ◽  
Submerged Floating Tunnel ◽  
Lock In

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.

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