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.

1.
Blevins
,
R. D.
, 1990,
Flow-Induced Vibration
, 2nd ed.,
Van Nostrand Reinhold
,
New York
.
2.
Zdravkovich
,
M. M.
, 1981, “
Review and Classification of Various Aerodynamic and Hydrodynamic Means for Suppressing Vortex Shedding
,”
J. Wind Eng. Ind. Aerodyn.
,
7
(
2
), pp.
145
189
.
3.
Jones
,
G. S.
, and
Lamb
,
W. S.
, 1993, “
The Suppression of Vortex Induced Vibration in Marine Risers
,”
Transactions-Institute of Marine Engineers
1358-3956,
105
(
5
), pp.
197
209
.
4.
Ruscheweyh
,
H.
, 1981, “
Straked In-Line Steel Stacks With Low Mass-Damping Parameter
,”
J. Wind Eng. Ind. Aerodyn.
,
8
(
1-2
), pp.
203
210
.
5.
Williamson
,
C. H. K.
, and
Govardhan
,
R.
, 2004, “
Vortex-Induced Vibrations
,”
Annu. Rev. Fluid Mech.
0066-4189,
36
, pp.
413
455
.
6.
,
R.
, 2006, “
Flow Induced Vibrations of Risers—Effect of Helical Strakes
,” MS thesis, Norwegian University of Science and Technology (NTNU), Trondheim, Norway.
7.
,
A.
, 2008, “
Vortex Induced Vibrations of Free Spanning Pipelines Using a Section Model Rig
,” MS thesis, Norwegian University of Science and Technology (NTNU), Trondheim, Norway.
8.
Moe
,
G.
, and
Overvik
,
T.
, 1983, “
Current Induced Motions of Multiple Risers
,”
Behaviour of Off-Shore Structures, Proceedings of the Third International Conference (BOSS 82)
, Vol.
1
, pp.
619
639
,
Hemisphere Publishing Corp.
,
Washington, D.C.
.
9.
Nakamura
,
Y.
, and
Tomonari
,
Y.
, 1982, “
The Effects of Surface Roughness on the Flow Past Circular Cylinder at High Reynolds Number
,”
J. Fluid Mech.
0022-1120,
123
, pp.
363
378
.
10.
Weaver
,
W.
, 1961, “
Wind-Induced Vibrations in Antenna Members
,”
J. Engrg. Mech. Div.
0044-7951,
87
(
EM 1
), pp.
141
165
.
11.
Woodgate
,
L.
, and
Maybrey
,
J. F. M.
, 1959, “
Further Experiments on the Use of Helical Strakes for Avoiding Wind Excited Oscillations of Structures of Circular or Nearly Circular Section
,” National Physical Laboratory, Aero Report No. 381.
12.
Wilson
,
J. F.
, and
Tinsley
,
J. C.
, 1989, “
Vortex Load Reduction: Experiments in Optimal Helical Strake Geometry for Rigid Cylinders
,”
ASME J. Energy Resour. Technol.
0195-0738,
111
(
2
), pp.
72
76
.
13.
Allen
,
D. W.
,
Henning
,
D. L.
, and
Lee
,
L.
, 2004, “
Performance Comparisons of Helical Strakes for VIV Suppression of Risers and Tendons
,”
Offshore Technology Conference (OTC)
, Houston, TX, OTC Paper No. 16186.
14.
Gartshore
,
I. S.
,
Khanna
,
J.
, and
Laccinole
,
S.
, 1978, “
The Effectiveness of Vortex Spoilers on a Circular Cylinder in Smooth and Turbulent Flow
,”
Proceedings of the Fifth International Conference on Wind Engineering
, Fort Collins, CO, pp.
1371
1379
.
15.
Tørum
,
A.
, 1995, “
MULTISPAN Vortex Induced Vibrations Tests
,” SINTEF, Trondheim, Norway, Report No. STF60 F95109.
16.
Mathiesen
,
M.
, 1995, “
MULTISPAN New Seabed Flow Characteristics in Macro Roughness Areas: Analysis of Current Data
,” SINTEF NHL, Trondheim, Norway, Report No. STF60 F94044.
17.
King
,
R.
, 1977, “
A Review of Vortex Shedding Research and Its Application
,”
Ocean Eng.
0029-8018,
4
(
3
), pp.
141
171
.
18.
Currie
,
I. G.
,
Hartlen
,
R. T.
, and
Martin
,
W. W.
, 1972, “
The Response of Circular Cylinders to Vortex Shedding
,”
IUTAM-IAHR Symposium in Flow-Induced Structural Vibrations
, Karlsruhe, Germany, pp.
128
142
.
19.
Griffin
,
O. M.
,
Skop
,
R. A.
, and
Ramberg
,
S. E.
, 1975, “
Resonant, Vortex-Excited Vibrations of Structures and Cable Systems
,”
Proceedings of the Offshore Technology Conference
, Houston, TX, pp.
731
744
, Paper No. 2319.
20.
Sarpkaya
,
T.
, 1978, “
Fluid Forces on Oscillating Cylinders
,”
J. Wtrwy., Port, Coast., and Oc. Div.
0148-9895,”
104
(
4
), pp.
275
290
.
21.
Iwan
,
W. D.
, and
Blevins
,
R. D.
, 1974, “
A Model for Vortex-Induced Oscillation of Structures
,”
ASME J. Appl. Mech.
0021-8936,
41
(
3
), pp.
581
586
.