U.S. patent application number 11/794700 was filed with the patent office on 2009-10-29 for vortex induced vibration optimizing system.
Invention is credited to Donald Wayne Allen, Dean Leroy Henning, Li Lee.
Application Number | 20090269143 11/794700 |
Document ID | / |
Family ID | 36021758 |
Filed Date | 2009-10-29 |
United States Patent
Application |
20090269143 |
Kind Code |
A1 |
Allen; Donald Wayne ; et
al. |
October 29, 2009 |
Vortex Induced Vibration Optimizing System
Abstract
There is disclosed a system comprising a structure, a vortex
induced vibration monitoring system, adapted to monitor a vortex
induced vibration level of the structure, a tensioner connected to
the structure, and a controller adapted to calculate a tension on
the structure to optimize the vortex induced vibration value of the
structure.
Inventors: |
Allen; Donald Wayne;
(Houston, TX) ; Henning; Dean Leroy; (Needville,
TX) ; Lee; Li; (Houston, TX) |
Correspondence
Address: |
SHELL OIL COMPANY
P O BOX 2463
HOUSTON
TX
772522463
US
|
Family ID: |
36021758 |
Appl. No.: |
11/794700 |
Filed: |
January 6, 2006 |
PCT Filed: |
January 6, 2006 |
PCT NO: |
PCT/US06/00336 |
371 Date: |
February 19, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60642085 |
Jan 7, 2005 |
|
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Current U.S.
Class: |
405/211 ;
405/212 |
Current CPC
Class: |
G01M 5/0025 20130101;
E21B 19/002 20130101; G01M 5/0033 20130101; G01M 5/0066 20130101;
B63B 2021/504 20130101; E21B 17/01 20130101; B63B 21/502 20130101;
G01H 1/08 20130101; G10K 11/161 20130101; B63B 39/005 20130101 |
Class at
Publication: |
405/211 ;
405/212 |
International
Class: |
E02D 31/00 20060101
E02D031/00 |
Claims
1. A system comprising: a structure; a vortex induced vibration
monitoring system, adapted to monitor a vortex induced vibration
level of the structure; a tensioner connected to the structure; and
a controller adapted to calculate an optimal tension value on the
structure to minimize the vortex induced vibration value of the
structure, and adapted to adjust the tensioner to the optimal
tension value.
2. The system of claim 1, further comprising a vessel connected to
the structure, wherein the vessel is floating in a body of
water.
3. The system of claim 1, wherein the structure is selected from
the group consisting of risers and mooring lines.
4. The system of claim 1, wherein the vortex induced vibration
monitoring system comprises a plurality of sensors on the
structure.
5. The system of claim 1, further comprising a vessel connected to
the structure, wherein the vessel comprises an oil platform.
6. The system of claim 1, wherein the structure comprises one or
more strakes and/or fairings adapted to lower the vortex induced
vibration value of the structure.
7. The system of claim 1, wherein the tensioner is adapted to be
manually adjusted.
8. The system of claim 1, wherein the tensioner is adapted to be
automatically adjusted based on the tension value calculated by the
controller.
9. A method of controlling vortex induced vibration of a structure
comprising: monitoring a level of vortex induced vibration in the
structure; adjusting the tension in the structure to minimize the
level of vortex induced vibration; and calculating an optimal
tension value for the structure.
10. The method of claim 9, wherein the method is an iterative
process that continues for a plurality of time cycles.
11. The method of claim 9, wherein the structure is selected from
the group consisting of risers and mooring lines.
12. The method of claim 9, wherein monitoring the vortex induced
vibration comprises measuring a value from a plurality of sensors
on the structure.
13. The method of claim 9, wherein the structure comprises one or
more strakes and/or fairings adapted to lower the vortex induced
vibration value of the structure.
14. The method of claim 9, wherein the method is an iterative
process that continues for time cycles of 0.5 to 5 minutes, for
example 1 minute.
15. The method of claim 9, wherein calculating an optimal tension
value for the structure is an iterative process that continues for
time cycles of 0.5 to 5 minutes, for example 1 minute.
16. An apparatus for minimizing vortex induced vibration in a
structure, comprising: a means for calculating the level of vortex
induced vibration of the structure; a means for calculating an
optimal level of tension in the structure to minimize the vortex
induced vibration; and a tensioner means adapted to apply the
optimal level of tension.
17. The apparatus of claim 16, wherein the means for calculating
the level of vortex induced vibration comprises a plurality of
sensors on the structure.
18. The apparatus of claim 16, wherein the means for calculating
the level of vortex induced vibration comprises calculating the
level of vortex induced vibration from a level of tension of the
structure.
19. The apparatus of claim 16, wherein the means for calculating
the level of vortex induced vibration comprises calculating the
level of vortex induced vibration from a level of current or wind
about the structure.
20. The apparatus of claim 16, wherein the means for calculating
the level of vortex induced vibration and the means for calculating
an optimal level of tension are adapted to iteratively calculate,
for example every 0.5 to 5 minutes.
Description
FIELD OF INVENTION
[0001] The present disclosure relates to systems and methods for
optimizing the vortex induced vibration of a substantially
cylindrical structure in a body of water.
BACKGROUND
[0002] U.S. Pat. No. 6,695,540 discloses a vortex induced vibration
suppressor and method. The apparatus includes a body that is a
flexible member of a polymeric (e.g. polyurethane) construction. A
plurality of helical vanes on the body extend longitudinally along
and helically about the body. A longitudinal slot enables the body
to be spread apart for placing the body upon a riser, pipe or
pipeline. Adhesive and/or bolted connections optionally enable the
body to be secured to the pipe, pipeline or riser. U.S. Pat. No.
6,695,540 is herein incorporated by reference in its entirety.
[0003] U.S. Pat. No. 6,561,734 discloses a partial helical strake
system and method for suppressing vortex-induced-vibration of a
substantially cylindrical marine element, the strake system having
a base connected to the cylindrical marine element and an array of
helical strakes projecting from the base for about half or less of
the circumference of the cylindrical marine element. U.S. Pat. No.
6,561,734 is herein incorporated by reference in its entirety.
[0004] U.S. Pat. No. 6,223,672 discloses an ultrashort fairing for
suppressing vortex-induced vibration in substantially cylindrical
marine elements. The ultrashort falling has a leading edge
substantially defined by the circular profile of the marine element
for a distance following at least about 270 degrees thereabout and
a pair of shaped sides departing from the circular profile of the
marine riser and converging at a trailing edge. The ultrashort
fairing has dimensions of thickness and chord length such that the
chord to thickness ratio is between about 1.20 and 1.10. U.S. Pat.
No. 6,223,672 is herein incorporated by reference in its
entirety.
[0005] Referring to FIG. 1, there is illustrated system 100. X axis
102, Y axis 104, and Z axis 106 are all defined. System 100
includes vessel 110 floating in water 112. Cylindrical structure
114 is connected to vessel 110, and cylindrical structure 114 goes
to bottom 116 of water 112. Current 118a, 118b, and 118c are all
traveling in the X direction, and encounter cylindrical structure
114. Vortexes 120a, 120b, and 120c are caused by the interaction of
currents 118a-118c with cylindrical structure 114. Vortex induced
vibrations (VIV) 122a, 122b, and 122c are caused by interaction of
currents 118a-118c with cylindrical structure 114.
[0006] There is a need in the art for systems and/or methods to
optimize VIV of structures exposed to a current or wind.
SUMMARY OF THE INVENTION
[0007] One aspect of the invention includes a system comprising a
structure, a vortex induced vibration monitoring system, adapted to
monitor a vortex induced vibration level of the structure, a
tensioner connected to the structure, and a controller adapted to
calculate a tension on the structure to optimize the vortex induced
vibration value of the structure.
[0008] Another aspect of the invention includes a method of
controlling vortex induced vibration of a structure in a body of
water comprising monitoring a level of vortex induced vibration in
the structure, and adjusting the tension in the structure to
minimize the level of vortex induced vibration.
[0009] Another aspect of the invention includes an apparatus for
minimizing vortex induced vibration in a structure comprising a
means for calculating the level of vortex induced vibration of the
structure, a means for calculating an optimum level of tension in
the structure to minimize the vortex induced vibration.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 illustrates a vessel floating in water connected to a
cylindrical structure.
[0011] FIG. 2 illustrates a vessel floating in water connected to a
cylindrical structure.
[0012] FIG. 3 illustrates a close-up view of the vessel and
cylindrical structure of FIG. 2.
[0013] FIG. 4 illustrates an example of tension values over
time.
[0014] FIG. 5 illustrates an example of tension values over
time.
DETAILED DESCRIPTION OF THE INVENTION
[0015] Referring now to FIG. 2, in one embodiment of the invention,
System 200 is illustrated. X axis 202, Y axis 204, and Z axis 206
are all defined. System 200 includes vessel 210 connected to
cylindrical structure 214, and cylindrical structure 214 is
connected to bottom 216 of water 212. Currents 218a, 218b, and 218c
encounter cylindrical structure 214, causing vortexes 220a, 220b,
and 220c, and VIV 222a, 222b, and 222c. Vessel 210 includes tension
monitor 230, tensioner 232, and controller 240. Sensors 234a, 234b,
and 234c are provided on cylindrical structure 214, which measure
VIV and/or current.
[0016] Vortex induced vibration (VIV) is defined herein is a
vibration having a given displacement and frequency of a structure
caused by the vortexes which are caused by an ambient current. The
VIV "level" is a function of the displacement and the frequency of
the vibrations, with higher displacements and higher frequencies
causing higher tensions, stresses, and/or strains, and lower
displacements and lower frequencies causing lower tensions,
stresses, and/or strains. It is generally desirable to lower the
displacement and/or the frequency of VIV in a structure, for
example to extend the structure's fatigue life.
[0017] In some embodiments, the level of VIV is calculated by
averaging the acceleration of the structure over the length of the
structure. For example, for a structure having a single
accelerometer providing an output of 2 meters per second squared
(m/s.sup.2), the VIV value would be 2 m/s.sup.2. In another
example, for a 50 m structure having five accelerometers (every 10
m) providing outputs of 1, 2, 3, 4, and 5 m/s.sup.2, the VIV value
would be the average of 3 m/s.sup.2. In some embodiments, the
acceleration can be calculated from an accelerometer. In some
embodiments, the acceleration can be calculated from one or more of
the bending stress, velocity, displacement, wind or current, and/or
dynamic tension.
[0018] In some embodiments, the level of VIV is calculated at a
given location of the structure, for example at location with high
stress concentration factors and/or substandard welds. For example,
for a 50 m structure having five accelerometers (every 10 m)
providing outputs of 1, 2, 3, 4, and 5 m/s.sup.2, the given
location with a high stress concentration factor registers the
value of 4, so the VIV value would be 4 m/s.sup.2. This location
with the stress concentration factor would be the location to
reduce the VIV level.
[0019] In some embodiments, the level of VIV is calculated at a
given area of the structure, for example at an area that has had
more fatigue damage than the rest of the structure, in order to
balance the fatigue damage along the length of the structure and
improve the overall life of the structure. For example, for a 50 m
structure having five accelerometers (every 10 m) providing outputs
of 1, 2, 3, 4, and 5 m/s.sup.2, the given area that has had more
fatigue damage registers the value of 2, so the VIV value would be
2 m/s.sup.2. This area that has had more fatigue damage would be
the area to reduce the VIV level.
[0020] Referring now to FIG. 3, a more detailed view of vessel 210
and cylindrical structure 214 is provided. Tension monitor 230 is
connected to cylindrical structure, and is adapted to monitor the
level of tension on cylindrical structure 214 over time.
[0021] Tensioner 232 is also connected to cylindrical structure
214, and is adapted to selectively increase or decrease the tension
on cylindrical structure 214. Sensors 234a, 234b, and 234c are
provided on cylindrical structure 214, and are adapted to provide a
measurement of the movements of cylindrical structure 214 (for
example VIV) and/or a measurement of currents 218a, 218b, and 218c.
Sensor 234d is adapted to provide a measure of movement of vessel
210, and/or the ambient current. Controller 240 is adapted to
receive input from tension monitor 230, sensors 234a-234d, and to
provide output to tensioner 232, to selectively increase and/or
decrease the tension on cylindrical structure 214, as necessary, to
control VIV.
[0022] In operation, the VIV is calculated, for example by using
sensors 234a-234d, and/or from tension monitor 230. In some
embodiments, VIV may be calculated by controller 240 from the
movement of sensors 234a-234d relative to a stationary object such
as bottom 216 of water 212. In some embodiments, VIV may be
estimated by controller 240 from the current measurements of
sensors 234a-234d. In some embodiments, a suitable method of
calculating VIV from the dynamic tension measurements from tension
monitor 230 and/or calculating an optimum tension value to minimize
VIV is VIV calculation software commercially available from Shell
Oil Company or one of its affiliates of Houston, Tex. Controller
240 then outputs an optimum tension value. In some embodiments,
optimum tension value may be sent to tensioner 230 which either
increases or decreases tension on cylindrical structure 214. In
some embodiments, the tension may be manually adjusted on
cylindrical structure 214 based on optimum tension value from
controller 240.
[0023] For example, referring to FIG. 4, an optimal tension value
for the system 200 is 3025 newtons (N) in order to minimize the VIV
on cylindrical structure 214, starting with an initial value of
tension of 10,000 N, one suitable algorithm would be to start off
adding 1000 N of tension and determining whether the VIV is
improved or worsened. In the example illustrated in FIG. 4, since
the VIV value is worsened by adding tension from 10,000 to 11,000
N, then controller 240 would adjust the tension by subtracting 1000
N of tension each time cycle until subtracting 1000 N creates a
worse value of VIV than the previous cycle's tension value.
[0024] In this example, the tension at each cycle would be reduced
from 11,000 to 10,000 to 9,000 all the way down to 2,000 N, as the
values were consistently improving from 4,000 to 3,000. The VIV
value only worsened when moving from 3,000 to 2,000 N. Next, the
tensioner would adjust upwards at half the previous value, in this
case 500 N, using the same logic until the VIV value is worsened by
adding an additional 500 N. In this case, the tension would be
adjusted from 2,000 to 2500 to 3000 to 3500, at which point the
tensioner would stop adjusting upwards as moving from 3000 to 3500
N worsens the VIV value. The process continues by then subtracting
250 N increments, adding 125 N increments, subtracting 62.5 N
increments, adding 31.25 N increments, etc., until the optimal
tension value of 3025 N is reached, or the system restarts.
[0025] In some embodiments, using this example, the tension
adjustments continue until such time as the VIV value (a function
of the displacement and frequency, discussed above) changes by at
least 2 times the change caused by the previous tension adjustment
increment, so that controller 240 restarts and the initial change
made is adding 1000 N, and starting the cycle over. This may
indicate a change in the subsea environment or other conditions
which would require a new optimal tension value to be iterated. For
example, if changing the tension from 3500 to 3250 N changes the
VIV value by 2%, and then changing the tension from 3250 to 3000
changes the VIV value by 4%, then the system would reset, and the
next change in tension would be to add 1000 N tension to the
previous value of 3000.
[0026] In another example, referring to FIG. 5, an initial tension
value is 3000 N, and an optimal tension value is 7750. As before,
controller 240 controls tensioner 232 by adding 1000 N of tension
at a time, until such time as adding 1000 N of tension worsens
rather than improves the VIV value. In this case, tensioner 232
with each cycle moves from 3000 to 4000 to 5000, all the way to
9000 N, as moving from 8000 to 9000 N is the first time that the
VIV value worsens by adding 1000 N. Next, 500 N increments are
subtracted, here until the tension value reaches 7000 N, as the
change from 7500 to 7000 N is the first time that the VIV value was
worsened by subtracting 500 N. Next, 250 N increments are added,
then 125 N increments are subtracted, then 62.5 N increments added,
etc, until the optimal value of 7750 N of tension is reached.
[0027] In some embodiments of the invention, the system will reset
at such time as the VIV value changes by greater than 2 times the
previous incremental change made by adjusting the tension value.
This could indicate a change in subsea conditions, such as a change
in the currents.
[0028] In some embodiments of the invention, the cycle time between
increments is set at about 0.5 to 5 minutes, for example at about 1
minute, to allow sufficient time to take VIV measurements, and to
allow the change in tension to take effect on cylindrical structure
214.
[0029] In some embodiments of the invention, cylindrical structure
214 may change its response modes of vibration due to very small
changes in currents 218a-218c. In some embodiments, small changes
in tension can cause changes in the response mode of vibration of
cylindrical structure 214. These changes in mode may be accompanied
by a period of low displacement while cylindrical structure 214
transitions from one mode to another, akin to the vibration
stopping and then restarting in a different response mode.
[0030] In some embodiments of the invention, active tension control
may be used to control/reduce VIV for significant durations to
substantially improve the fatigue life of cylindrical structure 214
immersed in currents 218a-218c.
[0031] In some embodiments of the invention, cylindrical structure
214 has a natural frequency of f.sub.n, where n is the mode number
(i.e. f.sub.1 is the natural frequency of the first bending mode in
a given direction). The natural frequency is controlled by an
equation that consists of a tension term as well as a material
stiffness term. For a long structure (such as deepwater risers,
cables, umbilicals, tendons, etc.), the tension term is usually
significantly larger than the material stiffness term, so that
changes in the tension significantly affect the natural frequency.
In this case, if the change in tension is sufficient, it will cause
a change in the response mode number. When the mode number changes
the VIV may be temporarily reduced.
[0032] In some embodiments of the invention, VIV 222a-222c can be
measured by a) measurement of structural motions; b) measurement of
dynamic tension; c) measurement of an ocean current thought to
produce VIV; or d) a combination of a) through c). Using a), both
the frequency and displacement (at least at the measurement points)
are known. If only b) is used, then the frequency may be known and
the displacements may be inferred from the dynamic tension range.
An analytical or computational model of the riser can be used to
relate the dynamic tension to the riser displacement, for example,
VIV calculation software commercially available from Shell Oil
Company or its affiliates.
[0033] In some embodiments of the invention, a method for active
control of VIV thru tension control includes: (1) Input of the
structural motion measurement and/or dynamic tension measurement,
for example sampled at a frequency sufficient to approximate the
vibration. (2) Conversion of the structural motion measurements or
dynamic tension measurements to estimates of vibration amplitude
and/or frequency (frequency is not necessary), if the frequency is
known, a structural dynamics model of the riser is used to estimate
the mode number (optional). Note that a current measurement can
also be used to estimate the mode provided an accurate VIV model is
used. (3) The required tension is then computed. (4) The tension is
then adjusted. Steps 1-4 are repeated as often as deemed necessary
or desired.
[0034] In some embodiments of the invention, an active control VIV
mitigation system 200 includes: (1) a floating or fixed structure
210 for producing hydrocarbons (the offshore platform); (2) one or
more long structures/tubulars 214 in tension; (3) a tensioner
system 232 for controlling/adjusting the tension of the tubular;
(4) a measurement of the tension 230 that is fed electronically
into a computer; (5) a computer 240 that determines the required
amount of tension adjustment to mitigate the vortex-induced
vibration motion of the tubular(s) using a preset automatic
algorithm; and (6) a mechanism 240 to feed the required tension
adjustment back to the tensioner system 232.
[0035] In some embodiments of the invention, structure 214 may have
different natural frequencies for different directions of
vibration. In some embodiments, vessel 210 will have more than one
tubular. In some embodiments, a single computer 240 can compute the
required amount of tension adjustment needed for VIV mitigation for
multiple tubulars. In some embodiments, a measurement of currents
218a-218c may also be fed into computer 240 to improve system
accuracy. In some embodiments, local measurements of tubular strain
may also be fed into the computer 240 to improve system accuracy.
In some embodiments, tension adjustments are done automatically. In
some embodiments, system 200 may have safety precautions in the
form of mechanical or electrical hardware that restricts the
magnitude and/or rate of the tension adjustments to safe
levels.
[0036] In some embodiments of the invention, vessel 210 may be a
floating oil platform, for example a fixed platform, a tension leg
platform, a spar, or a drilling rig.
[0037] In some embodiments of the invention, structure 214 may be a
mooring line, riser, a tubular, or any other structure subject to
current or wind. In some embodiments, structure 214 may have a
diameter of about 0.1 to about 5 meters, and a length of about 10
to about 10,000 meters (m). In some embodiments, structure 214 may
have a length to diameter ratio of about 100 to about 100,000. In
some embodiments, structure 214 may be composed of about 50 to
about 300 threaded tubular sections, each with a diameter of about
10 cm to about 60 cm and a length of about 5 m to about 50 m, and a
wall thickness of about 0.5 cm to about 5 cm.
[0038] In some embodiments of the invention, tension monitor 230
may be a commercially available load cell.
[0039] In some embodiments of the invention, tensioner 232 may be a
commercially available ram style tensioner.
[0040] In some embodiments of the invention, controller 240 may be
a commercially available topside computer.
[0041] In some embodiments, the VIV level may be minimized by
periodically changing the tension by at least about 5%, for example
about 10%. For example, a riser system having an acceptable tension
range of 80 to 125 kN may start with a tension of 100 kN. In the
first time period, the tension can be increased to 115 kN, then in
the second time period, decreased to 90 kN, then increased to 110
kN, and then subsequently decreased and increased by at least about
10% in each time period to minimize VIV, for example by changing
the mode of the riser. The controller 240 may be programmed to stay
within the acceptable range, increase or decrease by a minimum
percentage, and make an increase or decrease each time the VIV
level increases over a given threshold.
[0042] In some embodiments, vessel 210 may have multiple structures
214 attached, for example about 5 to 30, or about 10 to 20. For
example, if system 200 has twenty structures attached, vessel 210
has a maximum tension which can be applied to all twenty structures
while still maintaining a safe environment. If the maximum tension
which can be applied to vessel 210 is 10,000 kN, then the average
maximum tension per structure is 500 kN. Controller 240 may be
programmed to keep total tension on vessel 210 under 10,000 kN,
while minimizing the VIV level on all 20 structures.
[0043] In some embodiments of the invention, there is disclosed a
system comprising a structure in a body of water, a vortex induced
vibration monitoring system, adapted to monitor a vortex induced
vibration level of the structure, a tensioner connected to the
structure, and a controller adapted to control the tensioner to
adjust the tension on the structure to optimize the vortex induced
vibration value of the structure. In some embodiments, there is a
vessel connected to the structure, where the vessel is floating in
the body of water. In some embodiments, the structure is selected
from the group consisting of risers and mooring lines. In some
embodiments, the vortex induced vibration monitoring system
includes a plurality of sensors on the structure. In some
embodiments, the vessel includes an oil platform. In some
embodiments, the structure includes one or more strakes and/or
fairings adapted to lower the vortex induced vibration value of the
structure.
[0044] In some embodiments of the invention, there is disclosed a
method of controlling vortex induced vibration of a structure in a
body of water including monitoring a level of vortex induced
vibration in the structure, and adjusting the tension in the
structure to minimize the level of vortex induced vibration. In
some embodiments, the method is an iterative process that continues
for a plurality of time cycles. In some embodiments, the structure
is selected from risers and mooring lines. In some embodiments,
monitoring the vortex induced vibration includes measuring a value
from a plurality of sensors on the structure. In some embodiments,
the structure includes one or more strakes and/or fairings adapted
to lower the vortex induced vibration value of the structure. In
some embodiments, the method is an iterative process that continues
for time cycles of about 0.5 to about 5 minutes. In some
embodiments, the method also includes calculating an optimal
tension value for the structure. In some embodiments, calculating
an optimal tension value for the structure is an iterative process
that continues for time cycles of about 0.5 to about 5 minutes, for
example about 1 minute.
[0045] In some embodiments of the invention, there is disclosed an
apparatus for minimizing vortex induced vibration of a structure,
comprising a means for calculating a level of vortex induced
vibration in the structure, and a means for calculating a tension
in the structure to minimize the level of vortex induced
vibration.
[0046] In some embodiments of the invention, there is disclosed a
system for controlling vortex induced vibration, including a
cylindrical structure within a body of water, a means for
monitoring the level of vortex induced vibration of the cylindrical
structure, a means for optimizing the level of vortex induced
vibration of the cylindrical structure. In some embodiments, the
cylindrical structure is connected to a vessel is floating in the
body of water. In some embodiments, the cylindrical structure is
selected from the group consisting of risers and mooring lines. In
some embodiments, the means for monitoring the level of vortex
induced vibration includes a plurality of sensors on the
cylindrical structure. In some embodiments, the means for
monitoring the level of vortex induced vibration includes a system
for calculating the level of vortex induced vibration from a level
of tension of the cylindrical structure. In some embodiments, the
cylindrical structure includes one or more strakes or fairings, for
example about 10 to about 100, adapted to lower the vortex induced
vibration value of the structure. Suitable strakes are disclosed in
U.S. Pat. No. 6,561,734, which is herein incorporated by reference
in its entirety. Suitable fairings are disclosed in U.S. Pat. No.
6,223,672, which is herein incorporated by reference in its
entirety.
[0047] In some embodiments of the invention, there is disclosed a
system for optimizing vortex induced vibration of a cylindrical
structure in a body of water, including a system for measuring and
calculating vortex induced vibration values of the cylindrical
structure, a tensioner adapted to change the tension on the
cylindrical structure, and a controller adapted to change the
tension on the cylindrical structure in order to optimize the
vortex induced vibration value. In some embodiments, the
cylindrical structure is connected to a vessel is floating in the
body of water. In some embodiments, the cylindrical structure is
selected from the group consisting of risers and mooring lines. In
some embodiments, the system for measuring and calculating vortex
induced vibration values includes a plurality of sensors on the
cylindrical structure. In some embodiments, the system for
measuring and calculating vortex induced vibration values includes
calculating the level of vortex induced vibration from a level of
tension of the cylindrical structure. In some embodiments, the
cylindrical structure includes one or more strakes or fairings
adapted to lower the vortex induced vibration value of the
cylindrical structure.
[0048] Those of skill in the art will appreciate that many
modifications and variations are possible in terms of the disclosed
embodiments, configurations, materials and methods without
departing from their spirit and scope. Accordingly, the scope of
the claims appended hereafter and their functional equivalents
should not be limited by particular embodiments described and
illustrated herein, as these are merely exemplary in nature.
* * * * *