Summary
Two sets of tests have been conducted on short fairings with a
chord-to-pipe-diameter ratio of approximately 1.5 partially covering a long
pipe that was towed under a rotating arm at Reynolds numbers equivalent to
those experienced by many production risers. From the first set of tests,
results for pipes with continuous fairings over various lengths of the outer
end of the pipe are presented, as well as for two configurations with partial
coverage. From the second set of tests, results for a series of partial fairing
coverage tests are presented that consisted of a more systematic variation of
fairing density on the outer two joints. The results produced several practical
conclusions that can be used for more economical marine tubular designs.
Introduction
Short fairings are a popular vortex-induced vibration (VIV) suppression
device for marine tubulars, including deepwater risers and tendons. Their
growth in popularity stems from several advantages they possess over helical
strakes, including better performance on downstream tubulars, lower sensitivity
to marine growth (provided they weathervane effectively), larger damping, and
lower drag (Allen and Henning 2003; Lee et al. 2004, 2006). Fig. 1
presents diagrams of a sample fairing and a sample helical strake.
Numerous experiments have been conducted on fairings to ascertain their
performance. Many of these experiments have consisted of a tubular experiencing
first-mode VIV. Tests of this type can be quite effective at examining the
reduction of dynamic lift forces on a cylinder, but do not necessarily indicate
global or damping effects of fairings on long risers and tendons.
Experiments on long tubulars at low Reynolds numbers are much easier to
accomplish than similar tests at high Reynolds numbers because of (in the case
of a tow test) the energy required to move the test cylinder through the water
or, in the case of a flume test, the energy required to circulate water past
the test cylinder. Thus, most experiments on long tubulars have been conducted
at low Reynolds numbers.
This paper presents results from experiments on a long cylinder, equipped
with fairings, towed in a sheared flow in the subcritical and critical Reynolds
number ranges. For production risers, this represents the prototype Reynolds
number range for all but the largest of risers in very high currents. Various
distributions of fairings were examined, and the displacements, drag
coefficients, and accelerations are reported herein.
© 2007. Society of Petroleum Engineers
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History
- Original manuscript received:
25 January 2007
- Meeting paper published:
30 April 2007
- Revised manuscript received:
11 September 2007
- Manuscript approved:
24 September 2007
- Version of record:
20 December 2007
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