Experimental Investigations of the Efficiency of Round-Sectioned Helical Strakes in Suppressing Vortex Induced Vibrations

2011 ◽  
Vol 133 (4) ◽  
Author(s):  
Raed K. Lubbad ◽  
Sveinung Løset ◽  
Geir Moe
Keyword(s):  
Flow Direction ◽  
Cross Flow ◽  
Experimental Investigations ◽  
Outer Diameter ◽  
Reference Case ◽  
Test Cylinder ◽  
Vortex Induced Vibrations ◽  
Helical Strakes ◽  
Flow Directions ◽  
The Cross

Vortex induced vibrations (VIVs) may cause a large amount of damage to deep water risers. Helical strakes are used as a mitigating measure to suppress these vibrations. The purpose of this paper is to verify the efficiency of round-sectioned helical strakes in suppressing VIV. It is believed that round-sectioned helical strakes can be more readily mounted on risers for intervention and maintenance compared with sharp-edged strakes that may have to be welded onto the risers. Systematic experimental investigations including 28 configurations of round-sectioned helical strakes were tested in an attempt to find the most suitable strake configuration. The experiments were performed in a steady flow flume with an elastically mounted rigid circular cylinder of 500 mm in length and 50 mm in outer diameter. The test cylinder was spring-supported in both the inline and cross-flow directions. The measurements were limited to mapping the displacement of the cylinder. First, the cylinder was tested without strakes as a reference case. The best configuration among the tested round-sectioned helical strake configurations was found to reduce the amplitude of oscillation relative to the bare cylinder case by 96% in the cross-flow direction and by 97% in the inline direction. The main features of this configuration are the number of starts (3), the pitch (5D), and the diameter of the strake (0.15D), where D is the outer diameter of the test cylinder. Additionally, this paper investigates the effects of varying pitch, the effects of surface roughness, and the effects of the ratio between the cross-flow and inline natural frequencies of the test rig on the efficiency of the suggested configuration of round-sectioned helical strakes.

Comparison of Calculated In-Line Vortex Induced Vibrations to Model Tests

2012 ◽  
Author(s):  
Elizabeth Passano ◽  
Carl M. Larsen ◽  
Halvor Lie
Keyword(s):  
Cross Flow ◽  
Added Mass ◽  
Model Tests ◽  
The Finite Element Method ◽  
Response Frequency ◽  
Flow Response ◽  
Vortex Induced Vibrations ◽  
Flow Directions ◽  
The Cross ◽  
Semi Empirical

The purpose of the present paper is to compare vortex-induced vibrations (VIV) in both in-line and cross-flow directions calculated by a semi-empirical computer program to experimental data. The experiments used are the Bearman and Chaplin experiments in which a model of a tensioned riser is partly exposed to current and partly in still water. The VIVANA program is a semi-empirical frequency domain program based on the finite element method. The program was developed by MARINTEK and the Norwegian University of Science and Technology (NTNU) to predict cross-flow response due to VIV. The fluid-structure interaction in VIVANA is described using added mass, excitation and damping coefficients. Later, curves for excitation, added mass and damping for pure in-line VIV response were added. These curves are valid for low current levels, before the onset of cross-flow VIV response. Recently, calculation of response from simultaneous cross-flow and in-line excitation has been included in VIVANA. The in-line response frequency is fixed at twice the cross-flow response frequency and the in-line added mass is adjusted so that this frequency becomes an eigenfrequency. A set of curves based on forces measured during combined cross-flow and inline motions are used. At present, the in-line excitation curves are not dependent on the cross-flow response amplitude. In the paper, in-line and cross-flow response predicted by VIVANA will be compared to the Bearman and Chaplin model tests. The choice of added mass and excitation coefficients will be discussed.

Influence From Helical Strakes on Vortex Induced Vibrations and Static Deflection of Drilling Risers

2005 ◽  
Author(s):  
Carl M. Larsen ◽  
Gro Sagli Baarholm ◽  
Halvor Lie
Keyword(s):  
Dynamic Response ◽  
Test Data ◽  
Oscillation Amplitude ◽  
Cross Flow ◽  
Current Profile ◽  
Dynamic Stresses ◽  
Drag Forces ◽  
Vortex Induced Vibrations ◽  
Bending Stresses ◽  
Helical Strakes

Helical strakes are known to reduce and even eliminate the oscillation amplitude of vortex induced vibrations (VIV). This reduction will increase fatigue life, and also reduce drag magnification from cross-flow vibrations. But sections with strakes will also have a larger drag coefficient than the bare riser. Hence, the extension of a section with strakes along a riser should be large enough to reduce oscillations, but not too long in order to limit drag forces from current and waves. The optimum length and position for a given riser will therefore vary with current profile. Dynamic response from waves should also be taken into account. The purpose of the present paper is to illustrate the influence from strakes on VIV, as well as on static and dynamic response for a drilling riser. Hydrodynamic coefficients for a cylinder with helical strakes are found from experiments and applied in an empirical model for the analysis of VIV. The result from the VIV analysis is used for a second calculation of drag forces that are applied in an updated static analysis. Dynamic stresses from regular waves are also presented, but VIV are not considered for these cases. A simple study of length and position of the section with strakes is carried out for some standard current profiles. Results are presented in terms of oscillation amplitudes, fatigue damage, bending stresses and riser angles at ends. The study is based on test data for one particular strake geometry, but the analysis method as such is general, and the computer programs used in the study can easily apply other test data.

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.

VIV Response and Drag Measurements of Circular Cylinders Fitted With Permeable Meshes

2015 ◽  
Author(s):  
Murilo M. Cicolin ◽  
Gustavo R. S. Assi
Keyword(s):  
Reynolds Number ◽  
Long Range ◽  
Flow Direction ◽  
Cross Flow ◽  
Circular Cylinders ◽  
Peak Response ◽  
Vortex Induced Vibrations ◽  
Different Types ◽  
Cylindrical Tubes ◽  
Low Mass

Experiments have been carried out on models of rigid circular cylinders fitted with three different types of permeable meshes to investigate their effectiveness in the suppression of vortex-induced vibrations (VIV). Measurements of amplitude of vibration and drag force are presented for models with low mass and damping which are free to respond in the cross-flow direction. Results for two meshes made of ropes and cylindrical tubes are compared with the VIV response of a bare cylinder and that of a known suppressor called the “ventilated trousers” (VT). All three meshes achieved an average 50% reduction of the peak response when compared with that of the bare cylinder. The sparse mesh configuration presented a similar behaviour to the VT, while the dense mesh produced considerable VIV response for an indefinitely long range of reduced velocity. All the three meshes have increased drag when compared with that of the bare cylinder. Reynolds number ranged from 5,000 to 25,000 and reduced velocity was varied between 2 and 15.

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

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.

The Importance of Mode Number on In-Line Amplitude of Vortex-Induced Vibration of Flexible Cylinders

2008 ◽  
Author(s):  
Susan B. Swithenbank ◽  
Carl Martin Larsen
Keyword(s):  
Natural Frequencies ◽  
Flow Direction ◽  
Empirical Relationship ◽  
Cross Flow ◽  
Bending Stiffness ◽  
Mode Number ◽  
Flow Mode ◽  
Physical Parameters ◽  
Complex Data ◽  
The Cross

Most empirical codes for prediction of vortex-induced vibrations (VIV) has so far been limited to cross-flow response. The reason for this is that cross-flow amplitudes are normally larger that in-line amplitudes. Additionally the in-line response is considered to be driven by the cross-flow vibrations. However since the in-line frequency is twice the cross-flow frequency, fatigue damage from in-line vibrations may become as important and even exceed the damage from cross-flow vibrations. A way to predict in-line vibrations is to apply traditional methods that are used for cross-flow VIV and establish an empirical relationship between the cross-flow and in-line response. Previous work suggests that the ratio between the in-line and cross-flow amplitudes depends on the cross-flow mode number, Baarhom et al. (2004), but the empirical basis for this hypothesis is not strong. The motivation for the present work has been to verify or modify this hypothesis by extensive analysis of observed response. The present analysis uses complex data from experiments with wide variations in the physical parameters of the system, including length-to-diameter ratios from 82 to 4236, tension dominated natural frequencies and bending stiffness dominated natural frequencies, sub-critical and critical Reynolds numbers, different damping coefficients, uniform and sheared flows, standing wave and traveling wave vibrations, mode numbers from 1–25th, and different mass ratios. The conclusion from this work is that the cross-flow mode number is not the important parameter, but whether the frequency of vibration in the cross-flow direction is dominated by bending stiffness of tension.

Fatigue Analysis of Free Spanning Pipelines Subjected to Vortex Induced Vibrations

2013 ◽  
Author(s):  
F. Van den Abeele ◽  
F. Boël ◽  
M. Hill
Keyword(s):  
Fatigue Damage ◽  
Oil And Gas ◽  
Flow Direction ◽  
Cross Flow ◽  
Fatigue Analysis ◽  
Sensitivity Analyses ◽  
Vortex Induced Vibration ◽  
Vortex Induced Vibrations ◽  
Offshore Industry ◽  
Girth Welds

Vortex induced vibration is a major cause of fatigue failure in submarine oil and gas pipelines and steel catenary risers. Even moderate currents can induce vortex shedding, alternately at the top and bottom of the pipeline, at a rate determined by the flow velocity. Each time a vortex sheds, a force is generated in both the in-line and cross-flow direction, causing an oscillatory multi-mode vibration. This vortex induced vibration can give rise to fatigue damage of submarine pipeline spans, especially in the vicinity of the girth welds. In this paper, an integrated numerical framework is presented to predict and identify free spans that may be vulnerable to fatigue damage caused by vortex induced vibrations (VIV). An elegant and efficient algorithm is introduced to simulate offshore pipeline installation on an uneven seabed. Once the laydown simulation has been completed, the free spans can be automatically detected. When the fatigue screening for both inline and cross-flow VIV indicates that a particular span may be prone to vortex induced vibrations, a detailed fatigue analysis is required. Amplitude response models are constructed to predict the maximum steady state VIV amplitudes for a given pipeline configuration (mechanical properties) and sea state (hydrodynamic parameters). The vibration amplitudes are translated into corresponding stress ranges, which then provide an input for the fatigue analysis. A case study from the offshore industry is presented, and sensitivity analyses are performed to study the influence of the seabed conditions, where special emphasis is devoted on the selection of pipe soil interaction parameters.

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.

Interference in a three-dimensional array of jets

2015 ◽  
Vol 26 (5) ◽  
pp. 795-819
Author(s):  
P. E. WESTWOOD ◽  
F. T. SMITH
Keyword(s):  
Cross Sections ◽  
Flow Direction ◽  
Three Dimensional ◽  
Cross Flow ◽  
Longitudinal Vortex ◽  
Cross Sectional ◽  
Dimensional Array ◽  
Unsteady Jets ◽  
The Cross ◽  
Jet Cross Sections

The theoretical investigation here of a three-dimensional array of jets of fluid (air guns) and their interference is motivated by applications to the food sorting industry especially. Three-dimensional motion without symmetry is addressed for arbitrary jet cross-sections and incident velocity profiles. Asymptotic analysis based on the comparatively long axial length scale of the configuration leads to a reduced longitudinal vortex system providing a slender flow model for the complete array response. Analytical and numerical studies, along with comparisons and asymptotic limits or checks, are presented for various cross-sectional shapes of nozzle and velocity inputs. The influences of swirl and of unsteady jets are examined. Substantial cross-flows are found to occur due to the interference. The flow solution is non-periodic in the cross-plane even if the nozzle array itself is periodic. The analysis shows that in general the bulk of the three-dimensional motion can be described simply in a cross-plane problem but the induced flow in the cross-plane is sensitively controlled by edge effects and incident conditions, a feature which applies to any of the array configurations examined. Interference readily alters the cross-flow direction and misdirects the jets. Design considerations centre on target positioning and jet swirling.

The Numerical Research of Two-Degrees-of-Freedom Vortex-Induced Vibrations of Circular Cylinders

2012 ◽  
Vol 204-208 ◽  
pp. 4598-4601
Author(s):  
Jie Li Fan ◽  
Wei Ping Huang
Keyword(s):  
Degrees Of Freedom ◽  
Amplitude Ratio ◽  
Flow Direction ◽  
Cross Flow ◽  
Circular Cylinders ◽  
Two Degrees Of Freedom ◽  
Line Frequency ◽  
Ansys Cfx ◽  
Vortex Induced Vibrations ◽  
Lock In

The two-degrees-of-freedom of vortex-induced vibration of circular cylinders is numerically simulated with the software ANSYS/CFX. The VIV characteristic, in the two different conditions (A/D=0.07 and A/D=1.0), is analyzed. When A/D is around 0.07, the amplitude ratio of the cylinder’s VIV between in-line and cross-flow direction in the lock-in is lower than that in the lock-out. The in-line frequency is twice of that in cross-flow direction in the lock-out, but in the lock-in, it is the same as that in cross-flow direction and the same as that of lift force. When A/D is around 1.0, the amplitude ratio of the VIV between in-line and cross-flow in the lock-in is obviously larger than that in the lock-out. Both in the lock-in and in the lock-out, the in-line frequency is twice of that in cross-flow direction.

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