GB2198553A - Vessel positioning system - Google Patents
Vessel positioning system Download PDFInfo
- Publication number
- GB2198553A GB2198553A GB08725050A GB8725050A GB2198553A GB 2198553 A GB2198553 A GB 2198553A GB 08725050 A GB08725050 A GB 08725050A GB 8725050 A GB8725050 A GB 8725050A GB 2198553 A GB2198553 A GB 2198553A
- Authority
- GB
- United Kingdom
- Prior art keywords
- vessel
- forces
- sensors
- geographical area
- predetermined geographical
- 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.)
- Withdrawn
Links
- 230000007613 environmental effect Effects 0.000 claims abstract description 9
- 238000000034 method Methods 0.000 claims description 5
- 230000000694 effects Effects 0.000 abstract description 4
- 239000003129 oil well Substances 0.000 abstract 1
- 230000033001 locomotion Effects 0.000 description 11
- 238000004519 manufacturing process Methods 0.000 description 6
- 238000006073 displacement reaction Methods 0.000 description 3
- 239000012530 fluid Substances 0.000 description 2
- 238000002347 injection Methods 0.000 description 2
- 239000007924 injection Substances 0.000 description 2
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 2
- 241000132536 Cirsium Species 0.000 description 1
- 230000003466 anti-cipated effect Effects 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 230000008878 coupling Effects 0.000 description 1
- 238000010168 coupling process Methods 0.000 description 1
- 238000005859 coupling reaction Methods 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 239000000446 fuel Substances 0.000 description 1
- 238000012423 maintenance Methods 0.000 description 1
- 239000003921 oil Substances 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 230000036647 reaction Effects 0.000 description 1
- 230000000452 restraining effect Effects 0.000 description 1
- 238000005096 rolling process Methods 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
- 239000010496 thistle oil Substances 0.000 description 1
Classifications
-
- G—PHYSICS
- G05—CONTROLLING; REGULATING
- G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
- G05D1/00—Control of position, course, altitude or attitude of land, water, air or space vehicles, e.g. using automatic pilots
- G05D1/02—Control of position or course in two dimensions
- G05D1/0206—Control of position or course in two dimensions specially adapted to water vehicles
- G05D1/0208—Control of position or course in two dimensions specially adapted to water vehicles dynamic anchoring
Landscapes
- Engineering & Computer Science (AREA)
- Aviation & Aerospace Engineering (AREA)
- Radar, Positioning & Navigation (AREA)
- Remote Sensing (AREA)
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Automation & Control Theory (AREA)
- Control Of Position, Course, Altitude, Or Attitude Of Moving Bodies (AREA)
Abstract
To maintain a floating vessel 1 within a predetermined geographical area, a plurality of sensors 6 are positioned on the surface on which the vessel floats at a distance from the vessel so as to sense environmental conditions such as winds and currents which will in due course exert forces on the floating vessel. Those forces are predicted by a model on the basis of information provided by the sensors, and forces are applied to the vessel to adjust the position of the vessel relative to the predetermined geographical area in dependence upon the predicted forces so as to counteract those forces. The system thus anticipates the arrival of waves or other environmental effects so as to enable those effects to be counterbalanced by relatively small forces. As shown the vessel 1 is moored by a cable 2 to a buoy 3 connected to a riser of an oil well (not shown). <IMAGE>
Description
VESSEL POSITIONING SYSTEM AND METHOD
The present invention relates to a system and method for maintaining a floating vessel within a predetermined geographical area.
It is known in the offshore oil industry tn a floating production vessel to a single buoy so as to enable the vessel to weather-vane around the buoy. This weather-vaning minimises forces but not motions. The buoy is geneially to connected to a production riser the base of which is moored to the sea bottom and pipes extend up through the riser, through swivel joints between the riser and the buoy and thence from the buoy to the production vessel.
In order to avoid the forces applied tn the system exceeding acceptable limits it is necessary to limit the maximum displacement of the vessel relative to a datum position. Gererally hecSuse the vessel is weather-vaning its bows will point towards the wind and waves and therefore the bow can be at any point along a generally circular path. The position of the bow relative to a datum position is sensed and when the bow moves beyond a predetermined distance fro the datum position forces are applied to tc- vessel to prevent it moving too far away from the dat@@ position.The force generated b the weather is restrained by the mooring load onto the buoy, movement of the buoy causing it to submerge and generate a restraining force, and the use of powerful thrusters mounted on the vessel.
Because the system essentially reacts to forces acting on the vessel after those forces have caused the vessel to move, the dynamic thrusters must be able to respond rapidly to demands made upon them and must be able to deliver very large forces. This means that the capital cost of the equipment is nigh and also the operating costs are high, requiring continuous maintenance and often operating inefficiently as the thrusters rarely operate at maximum capacity.
It is an object of the present invention to provide an improved system and method for maintaining a floating vessel within a predetermined geographical area.
According to the present invention there is provided a system for maintaining a floating vessel within a predetermined geographical area, comprising a plurality of sensors spaced from the vessel for sensing environmental conditions which will in due course exert forces on the floating vessel, means for predicting those forces on the basis of information provided by the sensors, means for applying forces to the vessel to adjust h@ position cf the vessel relative to the predetermined geographical area, and means for controlling the force applying means in dependence upon the predicted forces to counteract those forces.
The present invention also provides a methoo for m intainina a floating vessel within a predetermineo eographical area, wherein environmental condit which will in due course exert forces on the floating vessel are sensed by a plurality of sensors spaced from the vessel, a prediction of what those forces will be at any particular time is made on the basis of the information provided by the sensors, and forces are applied to the vessel in dependence upon the predicted forces so as to counteract those forces.
An embodiment of the present invention will now be described by way of example with reference to the accompanying drawing.
The drawing is a plan view of a vessel 1 moored by a cable 2 to a floating buoy 3. The floating buoy is connected to the top of a riser structure extending from a fixed mooring point on the sea bottom. Flexible joints are provided in the riser structure to enable the buoy to move within a relatively limited area in response to forces applied to it by the environmental conditions and more significantly by .ht vessel as a @esult ui the effects of the environmental conditions on that vessel.
The general structure of a riser and buoy system of the type to which the accompanying drawing relates is illustrated and described in British Patent No.
2099894.
Assuming that the prevailing wind and the direction of motion of waves on the sea surface corresponds to the direction indicated by arrow A the vessel 1 will assume the position illustrated by weather-vaning around the buoy 3. In these conditions roll of the vessel and the force on the vessel required to counteract the effect of wind and waves is minimised. If however the wind direction w-s to change relatively rapidly to correspond to the direction iraicatea by arrow 5 a relatively large force would be applied to the vessel and transmitted through the cable 2 to the buoy 3.To counteract this forces would have to be applied to the vessel by a combination of controlling the tension in the cable 2 and controlling the force applied to the vessel by thrusters (not shown). In conventional systems the counteracting forces are generated as a result of a detected movement of the vessel relative to a datum position defined by an accurate position sensing system. Thus the counteracting forces are generated in react Ion to movements of the vessel and considerable energy must be expended in a relatively short time to overcome a momentum imparted to the vessel before the position sensing system has detected significant movement of the vessel.
In accordance with the present invention sensors 6 are moored in relatively stable positions around the vessel. In the illustrated example four sensors die showr. put depeding on conditions an alternative greater or larger number could be provided. The sensors detect at least wind, speed and direction and preferably also detect current speed and direction and wave height, speed and direction. The data derived by the sensors is transmitted by radio to a data processing system on the vesscl in which is programmed a model of the response of the vessel to various conditions. The response can be determined from response amplitade operators which can be generated in full scale tests.
The computing system monitors the outputs of the sensors and predicts from those outputs the forces which will be exerted on the vessel when environmental conditions affecting rne sensors t.
reach the vessel. Tnus for example n t he
lustrateq in the accompanying drawing the sensor a the bottom righthand corner would be the first to detect the change in wind direction from the direction of arrow 4 to the direction of arrow 5.
The computing system would then be able to predict that a force would be exerted on the vessel 1 in a direction correspondlna to the arrow 5. To minimise tne forces required to be applied to the vessel and the pitchina and rolling of the vessel forces car be applied to the vessel before the vessel has in fact moved in response to the change in wind direction so as to initiate a movement of the vessel which counteract the results of the change in wind direction. This means that the best heading for the vessel can be selected to minimise roll and pitch and that movements of the vessel away from position can be minimised.
Conventional thrusters as used in prior art vessel positioning systems may be used but alternatively a modlfiea rudder system tor example a double rudder) and a constant tension winch driven by an auxiliary power system of the vessel could be used.
The sensors 6 are preferably 500 to 1000 metres away from the vessel so as to give adequate time for the vessel positioning system to respond to incoming changing conditions whilst at the same time enabling the effect of those conditions on the vessel to be accurately predicted.
In more detail, in one possible system an existing aframax 80,000 dwt tanker may be converted to operate as a floating production facility. A mooring tower similar in design to that installed in the Thistle oil field but excluding the use of fluid swivels would be installed. mooring towers of the type known in the Thistle field are generally kncwn as SALM (single ancnor leg mooring). In the proposei example of the present invention the tower would be capable of supporting flexible production risers in a catenary and would be capable of allowing an emergency mooring load of 350 metric tons.
Vessel motion is controlled as described above.
Prior art systems have used a turret mooring system or thruster-based dynamic positioning system to head the vessel into the weather and to minimise fuel consumption whilst staying at a given location with an accuracy of plus or minus 1% of water depth. This generates large vessel forces, and high operal iflo costs. In contrast in accordance with the present invention the remote sensors are used to enable the motions of the vessel to be anticipated in terms of roll, pitch, wave and longitudinal and latera displacement. This ensures that the correct heading is chosen to minimise roll and pitch and also ensures that displacements do not exceed the limitations of the catenary riser. Further, the conventiona weather-vaning operation requires the use of fluid swivels which in practice are pressure limited.
Therefore the ability to subject the catenary riser to torque and remain on station with a monohull allows large fields or those requiring reservoir support in the form of water injection, artificial lift or gas injection to be developed cheaply, i.e.
without the use of a specialist vessel.
A suitable constant te.isior: indless working on the cable linking the vessel to the tower might work in the range of 10 to 200 metric tons, this capacity being assisted by a Becker-type rudder and a controllable pitch propellor. Four 3,500 BHP azimuthina thrusters may oe fitted to provide odditional redundancy, and a greater degree of operational control for wireline well servicing.
The vessel may comprise a bow arrangement incorporating a control room for controlling the movement of the floating production facility, quick connect/disconnect riser couplings, and a chain stopper.
Claims (7)
1. A system for maintaining a floating vessel within a predetermined geographical area, comprising a plurality of sensors spaced from the vessel for sensing environmental conditions which will in due course exert forces on the floating vessel, means for predicting those forces on the basis of information provided by the sensors, means for applying forces the vessel to adjust the position of the vessel relative to the predetermined geographical area, and means for controlling the force applying means in dependence upon the predicted forces to counteract those forces.
2. A system according to claim 1, comprising four sensors moored in a rectangular pattern around the vessel.
3. A system according to claim 1 or 2, wherein each sensor detects wind speed and direction
4. A system according to claim 3, wherein each sensor detects current speed and direction.
5. A method for maintaining a floating vessel within a predetermined geographical area, wherein environmental conditions which will in due course exert forces on the floating vessel are sensed b) a plurality of sensors spaced from tb: vessel, a predict ion of what those forces will be at any particular time is made on the basis of the information provided by the sensors, and forces are applied to the vessel in dependence upon the predicted forces so as to counteract those forces.
6. A system for maintaining a floating vessel within a predetermined geographical area substantially as hereinbefore described with reference to the accompanying drawing.
7. A method for maintaining a floating vessel within a predetermined geographical area substantially as hereinbefore described with reference to the accompanying drawing.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB868625766A GB8625766D0 (en) | 1986-10-28 | 1986-10-28 | Vessel positioning system |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB8725050D0 GB8725050D0 (en) | 1987-12-02 |
| GB2198553A true GB2198553A (en) | 1988-06-15 |
Family
ID=10606430
Family Applications (2)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB868625766A Pending GB8625766D0 (en) | 1986-10-28 | 1986-10-28 | Vessel positioning system |
| GB08725050A Withdrawn GB2198553A (en) | 1986-10-28 | 1987-10-26 | Vessel positioning system |
Family Applications Before (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB868625766A Pending GB8625766D0 (en) | 1986-10-28 | 1986-10-28 | Vessel positioning system |
Country Status (1)
| Country | Link |
|---|---|
| GB (2) | GB8625766D0 (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102455708A (en) * | 2010-10-28 | 2012-05-16 | 上海振华重工(集团)股份有限公司 | System and method for on-line recognition and control of ship model for ship power positioning |
| CN104850125A (en) * | 2015-05-26 | 2015-08-19 | 中国海洋石油总公司 | Cable release control method and system |
Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1492654A (en) * | 1974-04-06 | 1977-11-23 | Voith Gmbh J M | Method of and apparatus for the dynamic positioning of a floating body |
-
1986
- 1986-10-28 GB GB868625766A patent/GB8625766D0/en active Pending
-
1987
- 1987-10-26 GB GB08725050A patent/GB2198553A/en not_active Withdrawn
Patent Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1492654A (en) * | 1974-04-06 | 1977-11-23 | Voith Gmbh J M | Method of and apparatus for the dynamic positioning of a floating body |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102455708A (en) * | 2010-10-28 | 2012-05-16 | 上海振华重工(集团)股份有限公司 | System and method for on-line recognition and control of ship model for ship power positioning |
| CN104850125A (en) * | 2015-05-26 | 2015-08-19 | 中国海洋石油总公司 | Cable release control method and system |
| CN104850125B (en) * | 2015-05-26 | 2018-06-19 | 中国海洋石油总公司 | A kind of cable releasing control method and system |
Also Published As
| Publication number | Publication date |
|---|---|
| GB8725050D0 (en) | 1987-12-02 |
| GB8625766D0 (en) | 1986-12-03 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |