Phasing mechanisms between the in-line and cross-flow vortex-induced vibrations of a long tensioned beam in shear flow

The fluid-structure energy transfer of a tensioned beam of length to diameter ratio 200, subject to vortex-induced vibrations in linear shear flow, is investigated by means of direct numerical simulation at three Reynolds numbers, from 110 to 1,100. In both the in-line and cross-flow directions, the high-wavenumber structural responses are characterized by mixed standing-traveling wave patterns. The spanwise zones where the flow provides energy to excite the structural vibrations are located mainly within the region of high current where the lock-in condition is established, i.e. where vortex shedding and cross-flow vibration frequencies coincide. However, the energy input is not uniform across the entire lock-in region. This can be related to observed changes from counterclockwise to clockwise structural orbits. The energy transfer is also impacted by the possible occurrence of multi-frequency vibrations.

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Vortex-induced vibrations of a long flexible cylinder in shear flow

Journal of Fluid Mechanics ◽

10.1017/jfm.2011.90 ◽

2011 ◽

Vol 677 ◽

pp. 342-382 ◽

Cited By ~ 80

Author(s):

REMI BOURGUET ◽

GEORGE E. KARNIADAKIS ◽

MICHAEL S. TRIANTAFYLLOU

Keyword(s):

Shear Flow ◽

Vortex Shedding ◽

Cross Flow ◽

Maximum Velocity ◽

Travelling Wave ◽

Transition To Turbulence ◽

Wave Component ◽

Flexible Cylinder ◽

Vortex Induced Vibrations ◽

Lock In

We investigate the in-line and cross-flow vortex-induced vibrations of a long cylindrical tensioned beam, with length to diameter ratio L/D = 200, placed within a linearly sheared oncoming flow, using three-dimensional direct numerical simulation. The study is conducted at three Reynolds numbers, from 110 to 1100 based on maximum velocity, so as to include the transition to turbulence in the wake. The selected tension and bending stiffness lead to high-wavenumber vibrations, similar to those encountered in long ocean structures. The resulting vortex-induced vibrations consist of a mixture of standing and travelling wave patterns in both the in-line and cross-flow directions; the travelling wave component is preferentially oriented from high to low velocity regions. The in-line and cross-flow vibrations have a frequency ratio approximately equal to 2. Lock-in, the phenomenon of self-excited vibrations accompanied by synchronization between the vortex shedding and cross-flow vibration frequencies, occurs in the high-velocity region, extending across 30% or more of the beam length. The occurrence of lock-in disrupts the spanwise regularity of the cellular patterns observed in the wake of stationary cylinders in shear flow. The wake exhibits an oblique vortex shedding pattern, inclined in the direction of the travelling wave component of the cylinder vibrations. Vortex splittings occur between spanwise cells of constant vortex shedding frequency. The flow excites the cylinder under the lock-in condition with a preferential in-line versus cross-flow motion phase difference corresponding to counter-clockwise, figure-eight orbits; but it damps cylinder vibrations in the non-lock-in region. Both mono-frequency and multi-frequency responses may be excited. In the case of multi-frequency response and within the lock-in region, the wake can lock in to different frequencies at various spanwise locations; however, lock-in is a locally mono-frequency event, and hence the flow supplies energy to the structure mainly at the local lock-in frequency.

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Fatigue damage from time domain simulation of combined in-line and cross-flow vortex-induced vibrations

Marine Structures ◽

10.1016/j.marstruc.2015.02.005 ◽

2015 ◽

Vol 41 ◽

pp. 200-222 ◽

Cited By ~ 25

Author(s):

M.J. Thorsen ◽

S. Sævik ◽

C.M. Larsen

Keyword(s):

Fatigue Damage ◽

Time Domain ◽

Cross Flow ◽

Time Domain Simulation ◽

Vortex Induced Vibrations ◽

Flow Vortex

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Forced Vibration Tests for In-Line Vortex-Induced Vibration to Assess Partially Strake-Covered Pipeline Spans

Journal of Offshore Mechanics and Arctic Engineering ◽

10.1115/1.4048660 ◽

2020 ◽

Vol 143 (3) ◽

Author(s):

Jie Wu ◽

Decao Yin ◽

Elizabeth Passano ◽

Halvor Lie ◽

Ralf Peek ◽

...

Keyword(s):

Forced Vibration ◽

Hydrodynamic Force ◽

Cross Flow ◽

Added Mass ◽

Vortex Induced Vibrations ◽

Helical Strakes ◽

Vibration Tests ◽

Flow Vortex ◽

Hydrodynamic Data ◽

Mass Functions

Abstract Helical strakes can suppress vortex-induced vibrations (VIVs) in pipelines spans and risers. Pure in-line (IL) VIV is more of a concern for pipelines than for risers. To make it possible to assess the effectiveness of partial strake coverage for this case, an important gap in the hydrodynamic data for strakes is filled by the reported IL forced-vibration tests. Therein, a strake-covered rigid cylinder undergoes harmonic purely IL motion while subject to a uniform “flow” created by towing the test rig along SINTEF Ocean's towing tank. These tests cover a range of frequencies, and amplitudes of the harmonic motion to generate added-mass and excitation functions are derived from the in-phase and 90 deg out-of-phase components of the hydrodynamic force on the pipe, respectively. Using these excitation- and added-mass functions in VIVANA together with those from experiments on bare pipe by Aronsen (2007 “An Experimental Investigation of In-Line and Combined In-Line and Cross-Flow Vortex Induced Vibrations,” Ph.D. thesis, Norwegian University of Science and Technology, Trondheim, Norway.), the IL VIV response of partially strake-covered pipeline spans is calculated. It is found that as little as 10% strake coverage at the optimal location effectively suppresses pure IL VIV.

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Improved In-Line Vortex-Induced Vibrations Prediction for Combined In-Line and Cross-Flow Vortex-Induced Vibrations Responses

Journal of Offshore Mechanics and Arctic Engineering ◽

10.1115/1.4038350 ◽

2017 ◽

Vol 140 (3) ◽

Cited By ~ 1

Author(s):

Decao Yin ◽

Elizabeth Passano ◽

Carl M. Larsen

Keyword(s):

Cross Flow ◽

Hydrodynamic Coefficients ◽

Marine Structures ◽

Flexible Pipe ◽

Flexible Beams ◽

Forced Motion ◽

Pipe Model ◽

Vortex Induced Vibrations ◽

Flow Vortex ◽

Semi Empirical

Slender marine structures are subjected to ocean currents, which can cause vortex-induced vibrations (VIV). Accumulated damage due to VIV can shorten the fatigue life of marine structures, so it needs to be considered in the design and operation phase. Semi-empirical VIV prediction tools are based on hydrodynamic coefficients. The hydrodynamic coefficients can either be calculated from experiments on flexible beams by using inverse analysis or theoretical methods, or obtained from forced motion experiments on a circular cylinder. Most of the forced motion experiments apply harmonic motions in either in-line (IL) or crossflow (CF) direction. Combined IL and CF forced motion experiments are also reported. However, measured motions from flexible pipe VIV tests contain higher order harmonic components, which have not yet been extensively studied. This paper presents results from conventional forced motion VIV experiments, but using measured motions taken from a flexible pipe undergoing VIV. The IL excitation coefficients were used by semi-empirical VIV prediction software vivana to perform combined IL and CF VIV calculation. The key IL results are compared with Norwegian Deepwater Programme (NDP) flexible pipe model test results. By using present IL excitation coefficients, the prediction of IL responses for combined IL and CF VIV responses is improved.

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Interaction of In-Line and Cross-Flow Vortex Induced Vibrations in Risers

21st International Conference on Offshore Mechanics and Arctic Engineering, Volume 1 ◽

10.1115/omae2002-28303 ◽

2002 ◽

Cited By ~ 1

Author(s):

Erik Asp Hansen ◽

Mads Bryndum ◽

Stefan Mayer

Keyword(s):

Cross Flow ◽

Recent Model ◽

Experimental Investigations ◽

Numerical Tests ◽

Vortex Induced Vibrations ◽

Model Set ◽

Line Cross ◽

Set Up ◽

The Individual ◽

Flow Vortex

VIV in pipeline and risers has been studied through numerous experimental investigations using simplified model set-up, consisting of spring mounted rigid cylinders. Models have been constructed to allow in-line, cross-flow, or both in-line and cross-flow motions. Comparison of the model results shows overall agreement, although distinct differences exist between the individual model test series. Different explanation models have been established to try to improve the consistency, however, seldom definitive conclusions have been reached. The present paper presents the use of CFD to document the importance of the interaction of in-line and cross-flow motions on VIV response. 2D numerical tests have been performed using NS3 (DHI-CFD code) for a model undergoing in-line, cross-flow, combined in-line and cross-flow, and cross-flow in combination with forced in-line motions. The paper compares the results with some recent model tests and quantifies the significance of interaction.

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