The influence of the yaw angle on the VIV fatigue damage of a yawed cylinder with or without helical strakes

Vortex-induced vibration (VIV) excited by current is a major contributor to the fatigue accumulation of marine risers. For deepwater operations, several risers are often arranged together in an array configuration. In this study, a set of four identical flexible pipes of a rectangular arrangement were tested in a water tunnel. By comparing the dynamic responses of a pipe in an array with that of a single isolated pipe, the effects of the current speed and the center-to-center distance between the up-stream and downstream pipes on their dynamic responses were investigated. Fatigue damages accumulated on each pipe in an array was calculated and a factor, termed “fatigue damage amplification factor”, was defined as a ratio between the fatigue damage rate of pipe in an array and the fatigue damage rate of a single pipe at a same current condition. The results showed that for bare pipes (i.e., without helical strakes), the downstream pipes in an array configuration may have larger dynamic responses and fatigue damage rates than those of a single pipe; and, it is not always conservative to assume that the fatigue damage rate estimated for a single pipe can be used to represent the fatigue damage rates of pipes in an array. This preliminary study provided some meaningful results for the design, analysis and operation of marine riser arrays.

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The effect of yaw angle on VIV suppression for an inclined flexible cylinder fitted with helical strakes

Applied Ocean Research ◽

10.1016/j.apor.2017.07.014 ◽

2017 ◽

Vol 67 ◽

pp. 263-276 ◽

Cited By ~ 24

Author(s):

Wanhai Xu ◽

Yingsen Luan ◽

Qinghua Han ◽

Chunning Ji ◽

Ankang Cheng

Keyword(s):

Flexible Cylinder ◽

Helical Strakes ◽

Viv Suppression ◽

Yaw Angle

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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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Performance of helical strakes in suppressing the FIV fatigue damage of two long flexible cylinders in a tandem configuration

Ocean Engineering ◽

10.1016/j.oceaneng.2021.109836 ◽

2021 ◽

Vol 239 ◽

pp. 109836

Author(s):

Wanhai Xu ◽

Yuhan Li ◽

Kun Jia ◽

Qicheng Wang

Keyword(s):

Fatigue Damage ◽

Tandem Configuration ◽

Helical Strakes

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Numerical Examination on the Effect of Internal Fluid Presssure on the Hydrodynamic Response of a Marine Riser

International Journal of Innovative Technology and Exploring Engineering - Special Issue ◽

10.35940/ijitee.k1265.09811s19 ◽

2019 ◽

Vol 8 (11S) ◽

pp. 1310-1315

Keyword(s):

Fatigue Damage ◽

Numerical Study ◽

Ansys Fluent ◽

Drag Forces ◽

Hydrodynamic Loading ◽

Sea Bed ◽

Exploration And Production ◽

Helical Strakes ◽

Initial Work ◽

Lift And Drag

Marine risers are long slender structures which links the floating vessel on the sea surface and its manifold on the sea bottom. It acts as a transportation means for the hydrocarbon resources underneath the sea bed. A riser mainly undergoes hydrodynamic loading which leads to Vortex induced vibrations (VIV) or Flow induced vibrations. These are motions induced on bodies interacting with an external fluid flow producing periodic irregularities on the flow which leads to fatigue damage of offshore oil exploration and production risers. Therefore, suppressing of VIV by providing helical strakes, fairings etc. is necessary in order to reduce the fatigue damage of risers due to hydrodynamic loading. The present paper deals with the numerical study on the response of a marine riserdue to the effect of internalfluid pressure. The initial work is carried out in ANSYS ICEM CFD software. The CFD solution after analysis is obtained from ANSYS FLUENT. The hydrodynamic effects like lift and drag forces along with motion responses is obtained.

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Research on Typical Vibration Accelerations of Wind Wheel Changing with Yaw Angle

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.599-601.426 ◽

2014 ◽

Vol 599-601 ◽

pp. 426-433

Author(s):

Jian Long Ma ◽

Jian Wen Wang ◽

Bo Dong ◽

Hai Jiao Wei

Keyword(s):

Wind Turbine ◽

Fatigue Damage ◽

Constant Load ◽

Exciting Force ◽

Symmetric Vibration ◽

Vibration Acceleration ◽

Horizontal Axis Wind Turbine ◽

First Order ◽

Axial Movement ◽

Yaw Angle

Dynamic and static frequency of the rotor about diameter of 1.4m small horizontal axis wind turbine was tested by using PULSE16.1 structural vibration analysis system., through combining the data of static frequency to identify rotor Dynamic frequency using spectrum analysis method. The conclusions found that, at a yaw condition of constant rotor speed, vibration acceleration of axial movement, disc effect and first order vibration of rotor increased with the increase of the yaw angle. The reason was that yaw exciting force which generated by the yaw behavior increased with the increase of yaw angle. At a constant load yaw, vibration acceleration of axial float, disc effect increased with the increase of the yaw angle. At the yaw condition of constant load R=82Ω、R=118Ω and the yaw angle 25°,30°,the acceleration value sharp increased and occurred the machine resonance phenomenon due to the tower instability. First order symmetric and anti symmetric vibration acceleration of rotor decreased with the increase of the yaw angle. The reason was that after the wind turbine yaw, the speed decreased of rotor caused the centrifugal force of the blades decreased, the impact of the centrifugal load changed was far greater than yaw exciting force for the first order vibration acceleration. The study also found that vibration acceleration values of rotor first order anti symmetric was greater than axial movement, disc effect and first order symmetric vibration acceleration values, which shows that stress concentration in root of blade was large and the blade fatigue damage was more serious. This paper related research results can provided a new analytical thinking for rotor fatigue damage or breakage occurred frequently in wind turbine operation process, and may provide a reference for the vibration characteristics of rotor in the process of yaw.

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