GB2133151A - Surveying positions of mooring lines - Google Patents
Surveying positions of mooring lines Download PDFInfo
- Publication number
- GB2133151A GB2133151A GB08400029A GB8400029A GB2133151A GB 2133151 A GB2133151 A GB 2133151A GB 08400029 A GB08400029 A GB 08400029A GB 8400029 A GB8400029 A GB 8400029A GB 2133151 A GB2133151 A GB 2133151A
- Authority
- GB
- United Kingdom
- Prior art keywords
- support
- mooring line
- transducer assembly
- water bottom
- mooring
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S15/00—Systems using the reflection or reradiation of acoustic waves, e.g. sonar systems
- G01S15/02—Systems using the reflection or reradiation of acoustic waves, e.g. sonar systems using reflection of acoustic waves
- G01S15/06—Systems determining the position data of a target
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S15/00—Systems using the reflection or reradiation of acoustic waves, e.g. sonar systems
- G01S15/88—Sonar systems specially adapted for specific applications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S5/00—Position-fixing by co-ordinating two or more direction or position line determinations; Position-fixing by co-ordinating two or more distance determinations
- G01S5/18—Position-fixing by co-ordinating two or more direction or position line determinations; Position-fixing by co-ordinating two or more distance determinations using ultrasonic, sonic, or infrasonic waves
Landscapes
- Engineering & Computer Science (AREA)
- Radar, Positioning & Navigation (AREA)
- Remote Sensing (AREA)
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Acoustics & Sound (AREA)
- Computer Networks & Wireless Communication (AREA)
- Measurement Of Velocity Or Position Using Acoustic Or Ultrasonic Waves (AREA)
Abstract
Positions of mooring lines (4A-H) extending between a moored structure (1) and anchors (5A-H) in the water bottom are surveyed by means (12) comprising a rotatable submarine transducer assembly including acoustic pulse transmitting means and an array of acoustic receivers, a support for locating the transducer assembly at a predetermined level above the water bottom and actuator means for rotating said assembly about a vertical axis relative to the support. During operation the transmitting means produce a beam (20) of acoustic pulses (21). Pulse reflections originating from mooring line sections that are successively scanned by said beam are received by the acoustic receivers, and the position of each scanned mooring line section is calculated by a processor unit on the basis of the time intervals at which said pulses are received after transmission. The support may be suspended from the moored structure or located on the water bottom. Two or more transducer assemblies may be mounted to monitor several mooring line sections simultaneously. A plurality of surveying systems may be used. <IMAGE>
Description
SPECIFICATION
Method and means for surveying positions of mooring lines
The invention relates to a method and means for surveying positions of mooring lines extending between a moored structure and anchors in the bottom of a body of water.
The current use in deep water areas of permanently moored structures, such as floating platforms carrying drilling or oil and gas production facilities, has introduced safety problems associated with the positioning of mooring lines in relation to underwater facilities such as well heads and flow lines on the water bottom. Detailed instructions for the deployment and operation of such moorings exist which permit satisfactory theoretical mooring patterns to be devised to minimise accidents due to anchor dragging etc. However, during the entire anchoring period measurements must still be carried out to check whether the touch points of the mooring lines onto the water bottom and the clearance between the mooring lines and the underwater installations meet the operating requirements.Such measurements, required under both long-term static conditions and during short-term movements of the vessel, are currently carried out by measuring the direction of each mooring line in relation to the vessel and by calculation of the mooring line catenary, using measured values of the mooring line tension. This known surveying technique has been found to be time consuming and insufficiently accurate.
The primary object of the present invention is to provide a method and means for continuously monitoring mooring line positions during extended periods of time, without affecting the operations performed on the moored structure. In particular to provide a method and means for detecting the location of each of the touch points of the mooring lines onto the water bottom with an accuracy considerably superior to that of the technique currently employed.
A further object of the present invention is to provide a surveying method that is able to respond quickly to changes in mooring line positions, for instance effects caused by oscillating movements of the moored structure due to wind, waves, tides and currents.
The method according to the present invention comprises the steps of:
a) arranging a transducer assembly including acoustic pulse transmitting means and an array of acoustic receivers at a predetermined submarine level above the water bottom by means of a support;
b) transmitting a beam of acoustic pulses by means of said transmitting means;
c) receiving pulse reflections by means of the array of acoustic receivers, said reflections originating from a mooring line section scanned by said beam;
d) transferring the received reflections to a processor unit and calculating the position of the scanned mooring line section on the basis of the time intervals at which said pulses are received after transmission;
e) rotating the transducer assembly relative to the support about a substantially vertical axis of rotation and repeating the sequence of steps b through e.
The means according to the present invention comprises:
a transducer assembly including acoustic pulse transmitting means for producing a beam of acoustic pulses and an array of acoustic receivers;
a support for locating the transducer assembly at a predetermined submarine level above a water bottom;
actuator means for rotating the transducer assembly relative to the support about a vertical axis of rotation; and
data transfer means for transferring data from the transducer assembly to a processor unit.
In a suitable embodiment of the invention the processor unit is programmed to calculate the location of the touch point of each mooring line onto the water bottom and/or the position of each of the mooring lines at each point of the relevant mooring line catenary on the basis of the information gathered by the acoustic receiving means about the azimuth and elevation of a series of points along the length of each mooring line catenary.
The invention will now be explained in more detail by way of example with reference to the accompanying drawings, wherein
Figure 1 shows a top view of a mooring system for an offshore structure together with mooring line surveying means according to the present invention;
Figure 2 shows the mooring system and the mooring line surveying means of Fig. 1 in elevation on an enlarged scale; and
Figure 3 shows in detail a vertical section of the mooring line surveying means of Fig. 1 and Fig. 2.
In Figures 1 and 2 a moored structure is indicated by the reference numeral 1. The structure 1 floats at the surface of a body of water 2 and is moored to the water bottom 3 by means of a mooring system 4 comprising eight mooring lines 4A through 4H that are connected to anchors 5A through 5H, respectively, which anchors are positioned in the water bottom 3. The structure 1 is a floating semi-submersible platform a carrying (not shown) facilities for the production of oil and/or gas. These production facilities are in communication with submarine oil and/or gas walls (not shown) via flow lines 8 that are arranged on the water bottom 3 and that communicate with a substantially vertical riser system 10 being suspended from the platform 1.
In order to detect the positions of the mooring lines 4A-H and especially the positions of the touch points 7A-H of these lines 4 onto the water bottom 3, a submarine mooring line surveying means 12 is placed on the water bottom 3.
The mooring line surveying means 1 2 is located centrally with respect to the locations of the anchors 5A-5H, and the means 12 (see also Fig.
3) includes a transducer assembly 13 that is rotatably mounted on a support 1 5. Furthermore a cable 14 including a plurality of data transfer and power supply leads provides communication between the transducer assembly 1 3 and a processor unit (not shown) on the platform 1.
The support 1 5 includes a support member 15A (see Fig. 3) and a ballast member 15B which members are interconnected by four substantially parallel tension legs 15C. The tension legs 15C are kept in an upright position by positive buoyancy force acting on the support member 15A, which force is obtained by a buoyancy element 1 6 that is connected to the support member 15A by means of a tensioning cable 1 8.
Actuator means 1 7 are arranged in a watertight shell 19 on top of the support member 1 5 for rotating the transducer assembly 1 3 relative to the support 15 about a substantially vertical axis of rotation V. The actuator means 1 7 comprise an electric motor (not shown) for rotating the transducer assembly 1 3 in a reciprocating mode (see arrows I and II in Fig.1) through a horizontal arc sector of about 3600.
The transducer assembly 1 3 consists of a transducer panel that comprises acoustic pulse transmitting means for generating a beam of acoustic pulses. The assembly 1 3 further comprises an array of horizontally and vertically separated acoustic receivers. Acoustic pulse transmitters as well as acoustic pulse receivers of the above type for submarine use are known per se and do not require a detailed description thereof.
The operation of the mooring line surveying means 12 will now be explained with reference to
Figs. and 3.
During operation the acoustic pulse transmitters of the assembly 13 transmit a beam 20 of acoustic pulses 21, said beam 20 being of suitable geometry (such as a diffraction limited beam). The beam 20 is transmitted in such elevated direction that the lower boundary 22 of the beam 20 is approximately parallel to the water bottom 3 so as to restrict reverberations from the water bottom 3 to an acceptable value.
In the situation illustrated in Figs. 1 and 2 the
beam 20 of acoustic pulses 21 is directed towards
section S of mooring line 4A, which section S is
located close to the touch point 7A of said
mooring line 4A onto the water bottom 3. The
pulses 21 are transmitted at selected time
intervals and each pulse 21 that hits the mooring
line section S is subsequently reflected, so that a
train of pulse reflections 23 originating from
points along said section S travels back to the
transducer assembly 1 3. The arrival times of the
pulse reflections 23 at each of the receivers of the
assembly 1 3 are detected and transferred via the
cable 14 to the processor unit (not shown).The
processor unit subsequently calculates the
positions in the vertical plane of the points along
section S by comparing the time intervals at which each of said pulses is received by the vertically separated receivers of the assembly 1 3 after transmission of the relevant pulse by the transmitting means. Simultaneously therewith the processor unit calculates the positions in the horizontal plane of the points along section S by comparing the time intervals at which each of said pulses is received by the horizontally separated receivers of the assembly 1 3 after transmission of the relevant pulse by the transmitting means.
The processor unit subsequently calculates the position and shape of the entire mooring line 4A on the basis of the calculated data on the position of the scanned section S by means of known mathematical formulas for catenaries.
Simultaneously with the acoustic pulse transmission and receiving process the assembly 13 is rotated relative to the support 15 about the vertical axis V in a reciprocating mode (see arrows 1 and 11 in Fig. 1) over an arc sector of about 3600C so as to cover all eight of the mooring lines 4A-H during each scanning period. It will be understood that the position of each mooring line 4B-H may be calculated in the same manner as described hereinbefore with reference to mooring line 4A.
The calculated data on the positions of the mooring lines 4A-H are subsequently represented on a suitable display (not shown).
Optionally said display includes a screen such that the positions of the mooring lines can effectively be seen by operating personnel. If desired, the positions of the touch points 7A-H of the mooring lines 4A-H onto the water bottom 3 can be represented separately on the display (not shown).
It will be understood that the present invention is not limited to the surveyance of the positions of mooring lines of permanently moored structures.
In the example shown in the drawings, the acoustic surveying means 1 2 can be used for the surveyance of mooring lines of those supply vessels (not shown) that are temporarily anchored near the floating production platform 1.
Furthermore other submerged objects will be detected by the acoustic surveying means 12, such as the marine riser 10 and those parts of submarine production facilities (not shown) that are within the scope of the beam 20 of acoustic signals 21. The reflections obtained by these objects of known location can be used to measure the position of the transducer assembly 13 itself.
The invention is not restricted to the use of a support that is located on the water bottom. If desired the support may be suspended from the moored structure. Moroever all other types of support structures suitable for the purpose, such as frameworks, towers, etc. may be applied.
The use of a single surveying system to monitor all mooring lines of the mooring system requires that the system is approximately centrally located with respect to the locations of the anhchors so as to limit the distance between the mooring lines and the assembly to a minimum value. The invention, however, is not restricted to the use of a single surveying system. If desired a plurality of surveying systems may be positioned at different locations on the water bottom, wherein each system scans a sector of the mooring system.
The clearance between the mooring lines and submarine objects (such as pipelines and well heads) may be detected accurately by scanning the lower part of each mooring line. In order to position the transducer assembly such that it has uninterrupted "view" of the lower mooring line parts, the transducer assembly is to be located close to the water bottom. Depending on irregularities of the water bottom the distance between the transducer assembly and the water bottom will usually be between 5 and 25 m.
Furthermore the invention is not restricted to the use of a single transducer assembly in the acoustic surveying system. If desired two or more transducer assemblies may be mounted above each other, which assemblies transmit acoustic beams at different elevations so as to monitor simultaneously several sections of each mooring line in the manner as described hereinbefore with reference to the drawings. It will be appreciated that monitoring of several sections of each mooring line will improve the accuracy of the calculation of the positions of the mooring line catenaries.
The data that are continuously collected during the entire anchoring period by the surveying system according to the invention on the positions of the mooring line will enable operating personnel on the moored structure to adjust the mooring line pattern accurately in case the clearance between the mooring lines and the submarine facilities does not meet the operating requirements.
The mooring line surveying means according to the invention may be applied to monitor the shape of all kinds of mooring lines and tension legs, such as mooring chains, steel cables and mooring ropes. It will further be understood that the moored structure may be any type of offshore structure such as a floating platform, a guyed tower and a floating vessel.
Claims (16)
1. A method for surveying positions of mooring lines extending between a moored structure and anchors in the bottom of,a body of water, said method comprising the steps of:
a) arranging a transducer assembly including acoustic pulse transmitting means and an array of acoustic receivers at a predetermined submarine level above the water bottom by means of a support;
b) transmitting a beam of acoustic pulses by means of said transmitting means;
c) receiving pulse reflections by means of the array of acoustic receivers, said reflections originating from a mooring line section scanned by said beam,
d) transferring the received reflections to a processor unit and calculating the position of the scanned mooring line section on the basis of the time intervals at which said pulses are received after transmission;;
e) rotating the transducer assembly relative to the support about a substantially vertical axis of rotation and repeating the sequence of steps b through e.
2. The method as claimed in claim 1 , wherein step e is carried out simultaneously with steps b through d.
3. The method as claimed in any one of claims 1-2, wherein the support is positioned on the water bottom.
4. The method as claimed in any one of claims 1-2, wherein the support is suspended from the moored structure.
5. The method as claimed in any one of claims 1-4, wherein the transducer assembly is located approximately central with respect to the locations of the anchors.
6. The method as claimed in any one of claims 1-4, wherein the transducer assembly is located vertically below the moored structure.
7. The method as claimed in any one of claims 1-6, wherein said beam is transmitted at such elevation that the scanned section of each mooring line is located near the touch point of the relevant mooring line onto the water bottom.
8. The method as claimed in any one of claims 1-7, wherein said beam is transmitted at such elevation that the lower boundary of the beam is about parallel to the water bottom.
9. The method as claimed in any one of claims 1-8, wherein the location of the touch point of each mooring line onto the water bottom and/or the position of each of the mooring lines at each point of the relevant mooring line catenary curve is calculated by the processor unit on the basis of the data collected on azimuth and elevation of points along the scanned section of each mooring line catenary curve.
10. A method for surveying mooring line positions substantially as described hereinbefore with reference to Figs. 1, 2 and 3 of the accompanying drawing.
11. Means for surveying positions of mooring lines extending between a moored structure and anchors in the bottom of a body of water, said means comprising:
a transducer assembly including acoustic pulse transmitting means for producing a beam of acoustic pulses, and an array of acoustic receivers;
a support for locating the transducer assembly at a predetermined submarine level above a water bottom;
actuator means for rotating the transducer assembly relative to the support about a vertical axis of rotation; and
data transfer means for transferring data from the transducer assembly to a processor unit.
12. The means as claimed in claim 11, wherein the support comprises a ballast member for positioning the support on a water bottom.
13. The means as claimed in claim 12, wherein the support further comprises a support member carrying the transducer assembly, said members being interconnected by substantially parallel tension legs, and a buoyancy element being connected to the support member.
14. The means as claimed in claim 11, wherein the support is provided with means for suspending the support from a moored structure.
15. The means as claimed in any one of claims 11-14, wherein the actuator means are suitable for rotating the transducer assembly in a reciprocating mode about the axis of rotation through an arc sector of approximately 3600.
16. A means for surveying mooring line positions substantially as described hereinbefore with reference to Figs. 1, 2 and 3 of the accompanying drawing.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB08400029A GB2133151B (en) | 1983-01-05 | 1984-01-03 | Surveying positions of mooring lines |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB838300176A GB8300176D0 (en) | 1983-01-05 | 1983-01-05 | Surveying positions of mooring lines |
| GB08400029A GB2133151B (en) | 1983-01-05 | 1984-01-03 | Surveying positions of mooring lines |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| GB8400029D0 GB8400029D0 (en) | 1984-02-08 |
| GB2133151A true GB2133151A (en) | 1984-07-18 |
| GB2133151B GB2133151B (en) | 1986-04-03 |
Family
ID=26284833
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB08400029A Expired GB2133151B (en) | 1983-01-05 | 1984-01-03 | Surveying positions of mooring lines |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2133151B (en) |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0188303A1 (en) * | 1985-01-16 | 1986-07-23 | C. van der Lely N.V. | Implement for automatically milking an animal |
| EP0209202A1 (en) * | 1985-07-16 | 1987-01-21 | N.V. Nederlandsche Apparatenfabriek NEDAP | Method and apparatus for automatically applying a milking cluster |
| EP2351687A1 (en) * | 2010-01-12 | 2011-08-03 | Nederlandse Organisatie voor toegepast -natuurwetenschappelijk onderzoek TNO | Mooring system |
| NO20161116A1 (en) * | 2016-07-05 | 2018-01-08 | Tronstad Holding As | System for monitoring load on mooring lines of floating installations |
Citations (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB546202A (en) * | 1939-12-06 | 1942-07-02 | Helge Fabian Rost | Subaqueous sound transmission system |
| GB739370A (en) * | 1954-02-02 | 1955-10-26 | Joseph Francis Krause | Improvements in or relating to adjustable electro-acoustic transducers |
| GB1125152A (en) * | 1965-01-19 | 1968-08-28 | Marconi Co Ltd | Improvements in or relating to sub-aqueous pressure wave sonar systems |
| GB1238965A (en) * | 1968-03-20 | 1971-07-14 | ||
| GB1401731A (en) * | 1972-05-01 | 1975-07-30 | Texaco Development Corp | Wave height measuring device |
| GB1432952A (en) * | 1972-06-29 | 1976-04-22 | Westland Aircraft Ltd | Detection of underwater objects |
| GB1482608A (en) * | 1973-08-16 | 1977-08-10 | France Armed Forces | Sonar systems for detecting submerged objects |
| GB1509333A (en) * | 1975-02-03 | 1978-05-04 | Raytheon Co | Steered beam transducer system |
| GB1525206A (en) * | 1976-03-03 | 1978-09-20 | Westinghouse Electric Corp | Depth sounder |
| GB1546412A (en) * | 1975-08-11 | 1979-05-23 | Edo Western Corp | Combination sonar and television system for use in underwater exploration |
-
1984
- 1984-01-03 GB GB08400029A patent/GB2133151B/en not_active Expired
Patent Citations (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB546202A (en) * | 1939-12-06 | 1942-07-02 | Helge Fabian Rost | Subaqueous sound transmission system |
| GB739370A (en) * | 1954-02-02 | 1955-10-26 | Joseph Francis Krause | Improvements in or relating to adjustable electro-acoustic transducers |
| GB1125152A (en) * | 1965-01-19 | 1968-08-28 | Marconi Co Ltd | Improvements in or relating to sub-aqueous pressure wave sonar systems |
| GB1238965A (en) * | 1968-03-20 | 1971-07-14 | ||
| GB1401731A (en) * | 1972-05-01 | 1975-07-30 | Texaco Development Corp | Wave height measuring device |
| GB1432952A (en) * | 1972-06-29 | 1976-04-22 | Westland Aircraft Ltd | Detection of underwater objects |
| GB1482608A (en) * | 1973-08-16 | 1977-08-10 | France Armed Forces | Sonar systems for detecting submerged objects |
| GB1509333A (en) * | 1975-02-03 | 1978-05-04 | Raytheon Co | Steered beam transducer system |
| GB1546412A (en) * | 1975-08-11 | 1979-05-23 | Edo Western Corp | Combination sonar and television system for use in underwater exploration |
| GB1525206A (en) * | 1976-03-03 | 1978-09-20 | Westinghouse Electric Corp | Depth sounder |
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0188303A1 (en) * | 1985-01-16 | 1986-07-23 | C. van der Lely N.V. | Implement for automatically milking an animal |
| EP0209202A1 (en) * | 1985-07-16 | 1987-01-21 | N.V. Nederlandsche Apparatenfabriek NEDAP | Method and apparatus for automatically applying a milking cluster |
| US4748936A (en) * | 1985-07-16 | 1988-06-07 | N.V. Nederlandsche Apparateneabriek Nedap | Method and apparatus for automatically applying a milking cluster |
| EP2351687A1 (en) * | 2010-01-12 | 2011-08-03 | Nederlandse Organisatie voor toegepast -natuurwetenschappelijk onderzoek TNO | Mooring system |
| NO20161116A1 (en) * | 2016-07-05 | 2018-01-08 | Tronstad Holding As | System for monitoring load on mooring lines of floating installations |
| NO342704B1 (en) * | 2016-07-05 | 2018-07-16 | Tronstad Holding As | System for monitoring load on mooring lines of floating installations |
Also Published As
| Publication number | Publication date |
|---|---|
| GB2133151B (en) | 1986-04-03 |
| GB8400029D0 (en) | 1984-02-08 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 20030103 |