U.S. patent application number 09/727272 was filed with the patent office on 2002-05-30 for dimpled marine seismic fairing.
Invention is credited to Barker, Glen P..
Application Number | 20020062777 09/727272 |
Document ID | / |
Family ID | 24922005 |
Filed Date | 2002-05-30 |
United States Patent
Application |
20020062777 |
Kind Code |
A1 |
Barker, Glen P. |
May 30, 2002 |
DIMPLED MARINE SEISMIC FAIRING
Abstract
An apparatus and method for improving the efficiency of marine
cable tow operations. Indentations such as dimples in the exterior
surface of cable fairings reduce cable strumming and reduce
frictional drag forces as the cables and fairings are towed through
the water. The size, configuration and orientation of the
indentations can be selected to control the desired water flow
parameters, and overall tow efficiency is increased.
Inventors: |
Barker, Glen P.;
(Friendswood, TX) |
Correspondence
Address: |
WESTERNGECO INTELLECTUAL PROPERTY DEPARTMENT
P.O. BOX 2469
HOUSTON
TX
77252-2469
US
|
Family ID: |
24922005 |
Appl. No.: |
09/727272 |
Filed: |
November 29, 2000 |
Current U.S.
Class: |
114/243 |
Current CPC
Class: |
Y02T 70/121 20130101;
B63B 21/663 20130101; Y02T 70/10 20130101 |
Class at
Publication: |
114/243 |
International
Class: |
F15D 001/10 |
Claims
What is claimed is:
1. An apparatus for reducing friction acting against a marine cable
towable through water, comprising: a fairing body engagable with
the cable, wherein said body has an exterior surface in contact
with the water; and a plurality of indentations in said body
exterior surface for reducing friction as said body is towed
through the water.
2. An apparatus as recited in claim 1, wherein said indentations
comprise dimples.
3. An apparatus as recited in claim 1, wherein said indentations
are symmetrically configured.
4. An apparatus as recited in claim 3, wherein at least one of said
indentations is configured in a round dish shape.
5. An apparatus as recited in claim 3, wherein at least one of said
indentations is configured in a polygonal shape.
6. An apparatus as recited in claim 3, wherein at least two
different shapes of indentations are formed in said body exterior
surface.
7. An apparatus as recited in claim 1, wherein said indentations
are oriented in a particular pattern on said body exterior
surface.
8. An apparatus as recited in claim 1, wherein at least two of said
indentations have different sizes.
9. An apparatus as recited in claim 1, further comprising a
splitter plate attached to said body.
10. A fairing for reducing drag on a cable towable through water,
comprising: a body having an exterior surface in contact with the
water, wherein said body has a lead end and a tapered second end;
and a plurality of indentations in said body exterior surface for
reducing friction as said body is towed through the water.
11. An apparatus as recited in claim 10, wherein said indentations
are symmetrically configured.
12. An apparatus as recited in claim 10, wherein at least two
different shapes of indentations are formed in said sheath exterior
surface.
13. An apparatus as recited in claim 10, wherein said indentations
are oriented in a particular pattern on said sheath exterior
surface.
14. An apparatus as recited in claim 10, wherein said cable
comprises a marine seismic cable.
15. An apparatus as recited in claim 1, further comprising a
splitter plate attached to said body.
16. A method for towing a cable in water, comprising the steps of:
attaching a fairing to the cable, wherein said fairing has an
exterior surface having a plurality of indentations; deploying a
cable and attached fairing in the water behind a tow vessel; and
moving the tow vessel to tow said cable through the water.
17. A method as recited in claim 16, further comprising the step of
deploying a fairing in the water wherein at least two of said
indentations have different configurations.
18. A method as recited in claim 16, further comprising the step of
deploying a fairing in the water wherein at least two of said
indentations have different sizes.
19. A method as recited in claim 16, further comprising the steps
of attaching a plurality of fairings to the cable.
20. A method as recited in claim 16, further comprising the step of
connecting marine seismic equipment to said cable before said cable
and fairing are deployed in the water.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to the field of marine seismic
exploration. More particularly, the invention relates to an
improved apparatus and method for improving marine cable tow
efficiency by improved fairings attached to a marine cable.
[0002] Cables are towed through water in marine seismic operations
to pull acoustic energy sources, flotation buoys, hydrophones, and
other marine seismic equipment through the water. For large seismic
vessels, multiple cables are simultaneously towed in a large swath
through the water. The cables may extend thousands of meters behind
the seismic tow vessel.
[0003] Large drag forces are generated as the cables are towed
through the water. The drag forces are caused by friction between
the water and cable exterior surface and increase exponentially as
the vessel speed increases. Uneven water flow around the cables
produces alternating shedding forces which cause transverse
vibrations, known as "strumming", in the cables. Strumming creates
turbulent flow within the water and generates acoustic noise
interfering with seismic data collection operations. Strumming
further generates stresses at equipment connection points and
accelerates equipment failure.
[0004] Numerous techniques have been developed to reduce frictional
drag forces acting on a cable towed through water. One technique
uses multiple fibers or "hairs" to interrupt vortex shedding and
other friction inducing processes. For example, U.S. Pat. No.
4,084,065 to Swenson (1978) disclosed yarn or fiber incorporated
into a braided cable for providing a plurality of polyester fiber
hairs for reducing low velocity cable strumming in water. U.S. Pat.
No. 4,756,270 to Boscov (1988) disclosed cable fairing comprised of
fairing hairs formed with a filamentary yarn woven into a
cable.
[0005] Another technique uses protrusions extending outwardly from
the cable to interrupt drag inducing eddies. U.S. Pat. No.
4,190,012 to Rispin et al. (1980) disclosed a cable fairing having
a plurality of stubs formed in a spiral pattern about the exterior
surface of a cable. U.S. Pat. No. 5,214,244 to Cummings et al.
(1993) disclosed a flexible jacket having a helically displaced
phase shifter for decoupling a seismic cable from strumming induced
by von Karmen vortex sheets. Each of the phase shifting sections
had a length less than one quarter the coherence length of the
flexible jacket.
[0006] Other friction reducing techniques attach fairings to cables
to reduce cable strumming in the water. U.S. Pat. No. 4,075,967 to
Silvey (1978) disclosed a hydrodynamic fairing having a plurality
of parallel vanes. U.S. Pat. No. 4,470,651 to Hale (1987) disclosed
a fairing having a relatively large clearance relative to the cable
to permit frictionless rocking and consequential wear between the
fairing and the cable. U.S. Pat. No. 4,655,155 to Folb et al.
(1987) disclosed a faired towline having a rectangular leading
edge. U.S. Pat. No. 5,275,120 to Ruffa et al. (1994) disclosed a
tow cable fairing having a plurality of radially extending tab
members indexed in a helical pattern longitudinally along the
cable.
[0007] Various fairing configurations have been developed. U.S.
Pat. No. 5,335,620 to Small (1993) disclosed a continuous,
longitudinally extending fairing comprised of a single plastic
extrusion and fastening means for providing shock and impact
protection to seismic array sensors and cables. U.S. Pat. No.
5,367,971 to Carpenter et al. (1994) disclosed an outer cable layer
having a twisted surface to create ridges for minimizing vortex
shedding and cable strumming. U.S. Pat. No. 5,678,504 to Toplosky
(1997) disclosed a towing cable fitted with fairings having
negative lift vanes.
[0008] Improvements to fairings and the connection mechanisms
between fairings and cables were shown in U.S. Pat. No. 4,542,708
to Holcombe et al. (1985), which disclosed a fairing cable segment
having a rotatable spring steel clip for minimizing interfacial
friction between the fairing and cable.
[0009] As the size of marine seismic arrays and the tow speed
increases, a need exists for improved techniques for reducing drag
forces. The techniques should reduce strumming noise interfering
with acoustic data collection and should increase tow efficiency
through the water.
SUMMARY OF THE INVENTION
[0010] The invention provides an apparatus and method for reducing
friction acting against a marine cable towable through water. The
apparatus comprises a fairing body engagable with the cable,
wherein the body has an exterior surface in contact with the water,
and a plurality of indentations in the body exterior surface for
reducing friction as the body is towed through the water. In
different embodiments of the invention, the indentions can comprise
dimples, can be symmetrically shaped, can be oriented in a selected
pattern, and can have different sizes and configurations.
[0011] The method of the invention comprises the steps of attaching
a fairing to the cable, wherein the fairing has an exterior surface
having a plurality of indentations, of deploying a cable and
attached fairing in the water behind a tow vessel, and of moving
the tow vessel to tow said cable through the water.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 illustrates a seismic tow vessel in water.
[0013] FIG. 2 illustrates indentations formed in the exterior
surface of a fairing.
[0014] FIG. 3 illustrates different shapes and forms of
indentions.
[0015] FIG. 4 illustrates one pattern of indentations.
[0016] FIG. 5 illustrates test data of a dimpled pipe under
different test conditions.
[0017] FIG. 6 illustrates test data comparing dimpled pipe to hairy
fairings.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0018] The invention uniquely reduces frictional drag acting
against a towed cable and components attached to the cable.
Referring to FIG. 1, tow vessel 10 is positioned in water 12 and
deploys cable 14 from drum or spool 16. Marine seismic equipment
such as acoustic energy source gun 18, buoy 20, and hydrophone 22
is attached to cable 14.
[0019] As shown in FIG. 2, fairing 24 generally comprises body 26
and exterior surface 28. Body 26 can be formed with a metallic or
extruded or wrapped plastic or composite sheath material resistant
to damage. A plurality of indentations 30 are formed in exterior
surface 28 for the purposes of reducing drag forces between fairing
24 as cable 14 and fairing 24 are towed through water 12, for
reducing the amount of tow energy expended by vessel 10, for
reducing strumming of cable 14 and the undesirable noise generated
by such strumming, and for reducing the wear on cable 14 at
connections between cable 14 and marine seismic equipment such as
that identified above.
[0020] Indentations 30 are formed in the exterior surface 28 in
contact with water 12. The term "dimple" as used herein means a
slight depression in exterior surface 28, and can be dish-shaped,
polygonal, or of another configuration. Each indentation 30 or
dimple can be formed with a symmetric or asymmetric configuration
as shown in FIG. 3 by symmetric indentation 32 and by asymmetric
indentation 34. FIG. 3 also shows geometric indentations 36 and 38
having selected configurations of different shapes, and indentation
40 is formed in a different size. Many different indentation 30
shapes, sizes, and configurations are possible within the scope of
the invention, and different combinations of different indentations
30 can be provided to provide different flow dynamics. The size and
depth of indentations 30 can be varied to accomplish different flow
characteristics. One or more splitter plates 42 can be attached to
body 26 to vary the flow dynamics of fairing 24 and cable 14
through water 12.
[0021] FIG. 4 illustrates a plurality of indentations 30 in a
selected pattern. Although one pattern is illustrated in FIG. 4,
many different patterns and configurations of indentations 30 are
possible to accomplish different flow dynamics between fairing 24
and cable 14 and water 12. A plurality of indentations 30 resist
formation of turbulent flow between fairing 24 and water 12 and the
correspondent shedding vortexes causing strumming and other
undesirable fluid dynamics.
[0022] Indentations 30 can be added to sheath exterior surface 28
before or after sheath 26 has been formed. Rollers or other
mechanisms can form indentations 30 such as dimples in exterior
surface 28. Indentations 30 can also be added to cable 14 to reduce
friction and to provide traction against spool 16 or cable pullers
for deploying and retrieving cable 14 from water 12 which lessens
the radial gripping force necessary to grasp cable 14.
[0023] As fairing 24 is pulled through water 12, indentations 30
break up the water flow and reduce strumming of cable 14. Drag
forces acting on fairing 24 and cable 14 are accordingly reduced,
resulting in less tow energy required to pull fairing 24 and cable
14 and associated seismic equipment through water 12.
[0024] FIG. 5 illustrates drag tests under different test
conditions. Typical tow ranges for seismic cables range between a
Reynolds Number of 50,000 with a 1.45 inch diameter cable at 3.5
knots, and a Reynolds Number of 100,000 with a faired 2.0 inch vane
tag line at 4.5 knots. Within this selected Reynolds Number range,
which is not limiting to the scope of the invention, different
cavitation tunnel and liquid tow tank tests provided substantially
similar results for cylindrical cable sections. Larger sized
dimples reduce the drag coefficient. FIG. 6 illustrates test
results for the invention when compared to a conventional hairy
fairing lead. As shown, indentations on exposed surfaces provided
superior results in drag reduction.
[0025] As previously noted, splitter plate 42 can be attached to
fairing 24 to further reduce the drag coefficient. The combination
of splitter plate 42 and dimples 30 on cable 14 reduced the drag
coefficient to a range between 0.5 and 0.7.
[0026] The invention uniquely provides a drag reducing solution not
anticipated by conventional systems. Although protrusions and other
devices can cooperate with the indentations to accomplish different
results, the indentations uniquely provide drag reducing
characteristics for marine tow operations.
[0027] Although the invention has been described in terms of
certain preferred embodiments, it will become apparent to those of
ordinary skill in the art that modifications and improvements can
be made to the inventive concepts herein without departing from the
scope of the invention. The embodiments shown herein are merely
illustrative of the inventive concepts and should not be
interpreted as limiting the scope of the invention.
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