Experimental Investigation of Vortex-Induced Vibrations of a Flexibly Mounted Circular Cylinder in Combined Current and Wave Flows

2021 ◽  
Author(s):  
Pierre-Adrien Opinel ◽  
Narakorn Srinil
Keyword(s):  
Experimental Investigation ◽  
Circular Cylinder ◽  
Cross Flow ◽  
Wave Flow ◽  
Regular Wave ◽  
Regular Waves ◽  
Vortex Induced Vibrations ◽  
Flow Frequency ◽  
The Cross ◽  
Wave Flows

Abstract This paper presents the experimental investigation of vortex-induced vibrations (VIV) of a flexibly mounted circular cylinder in combined current and wave flows. The same experimental setup has previously been used in our previous study (OMAE2020-18161) on VIV in regular waves. The system comprises a pendulum-type vertical cylinder mounted on two-dimensional springs with equal stiffness in in-line and cross-flow directions. The mass ratio of the system is close to 3, the aspect ratio of the tested cylinder based on its submerged length is close to 27, and the damping in still water is around 3.4%. Three current velocities are considered in this study, namely 0.21 m/s, 0.29 m/s and 0.37 m/s, in combination with the generated regular waves. The cylinder motion is recorded using targets and two Qualisys cameras, and the water elevation is measured utilizing a wave probe. The covered ranges of Keulegan-Carpenter number KC are [9.6–35.4], [12.8–40.9] and [16.3–47.8], and the corresponding ranges of reduced velocity Vr are [8–16.3], [10.6–18.4] and [14–20.5] for the cases with current velocity of 0.21 m/s, 0.29 m/s and 0.37 m/s, respectively. The cylinder response amplitudes, trajectories and vibration frequencies are extracted from the recorded motion signals. In all cases the cylinder oscillates primarily at the flow frequency in the in-line direction, and the in-line VIV component additionally appears for the intermediate (0.29 m/s) and high (0.37 m/s) current velocities. The cross-flow oscillation frequency is principally at two or three times the flow frequency in the low current case, similar to what is observed in pure regular waves. For higher current velocities, the cross-flow frequency tends to lock-in with the system natural frequency, as in the steady flow case. The inline and cross-flow cylinder response amplitudes of the combined current and regular wave flow cases are eventually compared with the amplitudes from the pure current and pure regular wave flow cases.

Laboratory Experiment of Two-Degree-of-Freedom Vortex-Induced Vibrations of Circular Cylinder in Regular Waves

2020 ◽  
Author(s):  
Pierre-Adrien Opinel ◽  
Narakorn Srinil
Keyword(s):  
Circular Cylinder ◽  
Cross Flow ◽  
Wave Theory ◽  
Degree Of Freedom ◽  
Water Tank ◽  
Regular Waves ◽  
Flow Directions ◽  
Line Cross ◽  
Flow Frequency ◽  
Two Degree Of Freedom

Abstract This paper presents new laboratory experiments of two-degree-of-freedom vortex-induced vibration of a flexibly mounted vertical circular cylinder in regular waves. A new experimental model has been developed and tested in the Wind, Wave & Current Tank at Newcastle University. The system mass ratio is close to 3 and the cylinder aspect ratio based on its submerged length is close to 27. The Stokes first-order wave theory is considered to describe the depth-dependent, horizontal velocity amplitude of the wave flow in the circulating water tank. This wave theory is satisfactorily validated by the wave probe measurement. The effects of cylinder stiffness affecting system natural frequencies are also investigated by using a combination of different spring setups in in-line and cross-flow directions. For each set of springs, VIV tests are performed in regular waves, with flow frequency ranging from 0.4 to 1 Hz and amplitude from 0.01 to 0.09 m. The associated Reynolds number at the water surface is in a range of 1.7 × 103–1.5 × 104. The surface Keulegan-Carpenter number (KC) is in the range of 2 < KC < 28 while the surface reduced velocity (Vr) is in the range of 0.5 < Vr < 16 depending on the implemented spring stiffness. Combined in-line/cross-flow oscillations of the cylinder are measured using two non-intrusive Qualisys cameras and the associated data acquisition system. The spring forces are also acquired using four load cells. Results reveal that, depending on KC and Vr, the cylinder primarily oscillates at the flow frequency in the in-line direction and at an integer (mainly 2, 3 and 4) multiple of the flow frequency in the cross-flow direction. Such occurrence of multi frequencies corroborates other experimental and numerical results in the literature. Several peculiar trajectories are observed, including infinity, butterfly, S and V shapes. The present experimental data of vibration amplitudes and oscillation frequencies in in-line/cross-flow directions as well as response patterns provide new results and improved understanding of VIV in oscillatory flows. These will be useful for the development of an industrial tool in predicting offshore structural responses in waves.

The Motion and Internal Reactions of a Vessel in Regular Waves

1958 ◽  
Vol 2 (01) ◽  
pp. 5-14
Author(s):  
James A. Fay
Keyword(s):  
Cross Flow ◽  
Bending Moment ◽  
Force Distribution ◽  
Experimental Measurements ◽  
Wave System ◽  
Regular Wave ◽  
Regular Waves ◽  
The Cross ◽  
Vessel Motion ◽  
Theory And Experiment

An analysis of the force distribution on a vessel moving into a regular wave system is presented, starting with a "cross-flow" hypothesis similar to that proposed by Munk (15) 2 for airships and applied to various aspects of vessel hydrodynamics by Weinblum and St. Denis (9), Grim (3), and Korvin-Kroukovsky (11). Expressions for the vessel motion (pitch and heave) and internal reactions (bending moment and shear) are obtained and compared with experimental measurements by Lewis (12). The agreement between theory and experiment for the motion is quite good, but for the bending moment is poor. Remarks concerning the justification of the cross-flow hypothesis are appended.

An Experimental Investigation on Cylinder VIV Trajectories Under Different Model Scale

2014 ◽  
Author(s):  
Zh. Kang ◽  
Yunhe Zhai ◽  
Ruxin Song ◽  
Liping Sun
Keyword(s):  
Experimental Investigation ◽  
Vibration Frequency ◽  
Degrees Of Freedom ◽  
Natural Vibration ◽  
Cross Flow ◽  
Small Scale ◽  
Natural Vibration Frequency ◽  
Test Results ◽  
The Cross ◽  
Initial Research

In this paper, model tests were carried out to investigate two degrees of freedom VIV of horizontally-laid cylinders with diameters of 5cm, 11cm, 20cm and length 120cm and compared their vibration trajectories. The test results showed that the in-line and cross-flow vibration frequency of different scale cylinders demonstrate “multi frequency” phenomenon, that is, the in-line vibration frequency is not only twice but also once or four times as much as the cross-flow vibration frequency in some scale, natural frequency and reduced velocity conditions. Also, the cross-flow multi-frequency vibration phenomenon occurred. The trajectory of the vibration cylinder differentiated from the traditional “8” shape accordingly. The vibration trajectory, especially of small-scale cylinder, changed in most conspicuous manner. Through the initial research and analysis, it was found that in addition to in-line and cross-flow natural vibration frequency and the flow velocity, the shape of cylinders was also one of the main causes leading to different vibration trajectory forms.

On the Coupling Between In-Line and Cross-Flow VIV Response

2002 ◽  
Author(s):  
Martin So̸reide
Keyword(s):  
Limit State ◽  
Preliminary Investigation ◽  
Cross Flow ◽  
Design Criterion ◽  
Wave Loads ◽  
Flow Response ◽  
Large Current ◽  
Vortex Induced Vibrations ◽  
The Cross ◽  
Fatigue Limit State

As offshore installations are moving into deeper water, engineers have to face new challenges in design of structures. Risers and free-span pipelines, subjected to heavy wave loads and large current velocities, are important components of these installations. Vortex induced vibrations (VIV) is a well known subject for most offshore engineers. VIV can cause large stresses and fatigue damage of slender marine structures. Hence, large safety factors are applied to the fatigue limit state design criterion (FLS), due to uncertainties regarding VIV. The present paper describes the preliminary investigation into the coupling between in-line and cross-flow VIV response. Most experimental data so far has been concentrated on predicting the cross-flow response. However, in-line displacements can make a valuable contribution. In fact, it has been proved that in-line responses may decrease the cross-flow response significantly when allowing the pipe to oscillate in both directions. The paper is based on a master of science thesis at the Norwegian University of Science and Technology (NTNU).

Experimental Investigation of Vortex-Induced Vibration Responses of Tension Riser Transporting Fluid

2009 ◽  
Author(s):  
Yongbo Zhang ◽  
Fanshun Meng ◽  
Haiyan Guo
Keyword(s):  
Experimental Investigation ◽  
Frequency Spectrum ◽  
Cross Flow ◽  
Internal Flow ◽  
Strain Gauges ◽  
Test Results ◽  
Amplitude Response ◽  
Flowing Fluid ◽  
Vortex Induced Vibrations ◽  
Vibration Responses

This paper presents the test results of a vertically tensioned riser model under vortex-induced vibrations. The influence of internal flowing fluid and top tensions on the riser behavior is investigated. Twelve strain gauges were mounted on the riser and both the in-line and cross-flow responses at locations were measured. The frequency spectrum and amplitude response were derived from the strain date. The influences of internal flow and top tensions on two kinds of model risers are analyzed and some conclusions are drawn.

Simplified Model for Evaluation of Fatigue From Vortex Induced Vibrations of Marine Risers

2004 ◽  
Author(s):  
Gro Sagli Baarholm ◽  
Carl M. Larsen ◽  
Halvor Lie ◽  
Kim Mo̸rk ◽  
Trond Stokka Meling
Keyword(s):  
Fatigue Damage ◽  
Cross Flow ◽  
Mode Shapes ◽  
Design Stage ◽  
Response Frequency ◽  
Lower Mode ◽  
Marine Risers ◽  
Vortex Induced Vibrations ◽  
Well Yield ◽  
The Cross

This paper presents a novel approach for approximate calculation of the fatigue damage from vortex-induced vibrations (VIV) of marine risers. The method is based on experience from a large number of laboratory tests with models of full-length risers, large-scale tests and also full-scale measurements. The method is intended to provide a conservative result and be used for screening purposes at the early design stage. The model is in particular aimed at predicting fatigue for risers that respond at very high mode orders (above 10), but may as well yield valid results for lower mode numbers. The model will, however, not be adequate for free span pipelines or other structures that normally will respond at first and second mode. The riser will be defined in terms of some key parameters like length, weight, tension, hydrodynamic diameter and stress diameter. A current profile perpendicular to the riser in one plane must be known. The program will apply a simple model for calculation of eigenfrequencies and mode shapes, and these are sorted into in-line (IL) and cross-flow (CF) bins. An effective current velocity and excitation length can be defined from the profile and will be applied to identify the dominating cross-flow response frequency and the total displacement rms value. The dominating in-line response frequency is taken as twice the cross-flow frequency, and inline response rms is taken as a given portion of the cross-flow rms value. A set of contributing modes is defined from an assumed frequency bandwidth that reflects observed bandwidths, but also modal composition for cases with discrete frequency response. A simple mode superposition technique is then used to find the set of modes that gives the identified rms values. Bending stresses will be found directly from the curvature of the mode shapes. Fatigue damage will be found from stress rms values, user defined stress concentration factor and given SN curves. The model has been implemented in a simple computer program and verified by comparing results to measurements. The ambition has not been to obtain an exact match between computed results and observations, but to verify that the model gives reasonable but conservative results in almost all cases. However, an unrealistic over prediction of the fatigue damage is not desired. The results are promising, but the need for more information from measurements and response analyses with programs like VIVANA and SHEAR7 is still obvious.

The Effect of Rotational Friction on the Stability of Short-Tailed Fairings Suppressing Vortex-Induced Vibrations

2011 ◽  
Author(s):  
Gustavo R. S. Assi ◽  
Peter W. Bearman ◽  
Michael A. Tognarelli ◽  
Julia R. H. Rodrigues
Keyword(s):  
Circular Cylinder ◽  
Lift Force ◽  
Flow Direction ◽  
Fluid Dynamic ◽  
Cross Flow ◽  
Critical Limit ◽  
Vortex Induced Vibrations ◽  
Equivalent Length ◽  
Low Mass ◽  
The Stability

Experiments have been carried out on a free-to-rotate short-tail fairing fitted to a rigid length of circular cylinder to investigate the effect of rotational friction on the stability of this type of VIV suppressor. Measurements of the dynamic response are presented for models with low mass and damping which are free to respond in the cross-flow and streamwise directions. It is shown how VIV can be reduced if the fairing presents a rotational friction above a critical limit. In this configuration the fairing finds a stable position deflected from the flow direction and a steady lift force appears towards the side the fairing has deflected. The fluid-dynamic mechanism is very similar to that observed for a free-to-rotate splitter plate of equivalent length.

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