The effect of time-varying axial tension on VIV suppression for a flexible cylinder attached with helical strakes

The time-varying effect of axial tension has recently attracted increasing focus when investigating vortex-induced vibration (VIV) for flexible cylinders. This paper applies an alternative time domain force–decomposition model to predict VIV response, in which the structural stiffness will be updated at each time step to take the tension variation into account. Firstly, the adopted numerical model is compared against the latest published experimental results of a small-scale cylinder with constant and time-varying tensions. Then, extensive cases of a long flexible cylinder are designed to investigate the tension time-varying effect on structural response and fatigue damage respectively. Several new response characteristics different from the constant tension case are analyzed from the VIV mechanism level. Fatigue analysis also reveals the influence laws of the amplitude and frequency of varying tension. Mathieu-type resonance between VIV and time-varying tension excitation is captured, under which structural response as well as fatigue damage will enlarge significantly. Some conclusions drawn by this research can provide reference at the engineering design stage of marine slender structures.

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The Effectiveness of Two- versus Three-start Helical Strakes in Suppressing VIV of Flexible Cylinder

10.4043/24774-ms ◽

2014 ◽

Author(s):

Lee Kee Quen ◽

Aminudin Abu ◽

Pauziah Muhamad ◽

Naomi Kato ◽

Asnizah Sahekhaini ◽

...

Keyword(s):

Flexible Cylinder ◽

Helical Strakes

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Practical Design Considerations for Managing Marine Growth on VIV Suppression Devices

Volume 2: CFD and VIV ◽

10.1115/omae2015-41237 ◽

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.

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Experimental Investigation on the Suppression Device of VIV of a Flexible Riser

Volume 2: CFD and VIV ◽

10.1115/omae2014-23427 ◽

2014 ◽

Cited By ~ 1

Author(s):

Yun Gao ◽

Shixiao Fu ◽

Leijian Song ◽

Tao Peng ◽

Runpei Lei

Keyword(s):

Fatigue Damage ◽

Experimental Results ◽

Experimental Investigations ◽

Flexible Riser ◽

Excited Mode ◽

Response Characteristics ◽

Helical Strakes ◽

Uniform Current ◽

Viv Suppression ◽

Synchronization Regime

Experimental investigations were conducted on a flexible riser with and without helical strakes. A uniform current was obtained by towing a riser model in a tank, and the vortex-induced vibration (VIV) suppression of strakes with different heights and pitches was studied. The results of the bare riser show that the characteristics of the synchronization of the VIV for a flexible riser have many orders, and the excited mode jumps from one to another abruptly. During the high order synchronization regime, the VIV response decreases with the increased order of the synchronization. The experimental results also indicate that the response characteristics of a bare riser can be quite distinct from those of a riser with helical strakes, and the suppression performance depends on the geometry of the helical strakes. The fatigue damage in the CF direction is of the same order as that in the IL direction for the bare riser. However, for the riser fitted with helical strakes, the fatigue damage in the CF direction is much smaller than that in the IL direction. The experimental results also confirmed that strake height has a greater influence on the VIV response than the strake pitch, and the drag exerted on the riser increases with strake pitch and height.

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Fairing Evaluation Based on Numerical Simulation

Volume 5: Ocean Engineering; CFD and VIV ◽

10.1115/omae2012-83883 ◽

2012 ◽

Cited By ~ 2

Author(s):

Juan P. Pontaza ◽

Mohan Kotikanyadanam ◽

Piet Moeleker ◽

Raghu G. Menon ◽

Shankar Bhat

Keyword(s):

Fluid Dynamics ◽

Numerical Simulation ◽

Current Speed ◽

Full Scale ◽

Attractive Alternative ◽

Element Analysis ◽

Vortex Induced Vibrations ◽

Helical Strakes ◽

Computational Fluid Dynamics Cfd ◽

Viv Suppression

It is well established that strakes are effective at suppressing vortex-induced vibrations (VIV). Fairings are an attractive alternative to helical strakes, because they are a low drag VIV suppression solution. The paper presents an evaluation of a fairing design, based on numerical simulations — to be complemented at a later stage with current tank testing. This paper documents the computational fluid dynamics (CFD) and finite element analysis (FEA) of the evaluation: (1) 3-D CFD in the laboratory scale: 4.5 inch pipe, 3 ft/s current speed, (2) 3-D CFD in the full scale: 14 inch riser, 4 knots current speed, and (3) 3-D FEA of the full-scale fairing module latching mechanism, under service loads corresponding to 4 knots current speed. The analysis results show that the fairing design (1) is effective at suppressing VIV, (2) yields a low drag coefficient (0.52 at Re ∼ 106), and (3) its latching mechanism is adequate for use in calm sea states with 4 knots current speeds.

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

Volume 5: Polar and Arctic Sciences and Technology; CFD and VIV ◽

10.1115/omae2009-79081 ◽

2009 ◽

Cited By ~ 1

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.

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