EP2921445A1

EP2921445A1 - Connecting an underwater vehicle to a tether

Info

Publication number: EP2921445A1
Application number: EP15250004.7A
Authority: EP
Inventors: Julian Paul Askew; Mark John Guinan
Original assignee: Seadrift Holdings Ltd
Current assignee: Seadrift Holdings Ltd
Priority date: 2014-03-01
Filing date: 2015-02-26
Publication date: 2015-09-23
Anticipated expiration: 2035-02-26
Also published as: EP2921445B1; GB201403694D0; US20150246713A1; GB2523600B; GB2523600A

Abstract

The connection of an underwater vehicle by a tether and apparatus for such connection is disclosed. The apparatus comprises a drum which has a helical surface and which stores the tether so that the tether is unwound from the drum to allow the underwater vehicle to move away from the apparatus. The apparatus also includes a pulley system which engages with the tether and which also unwinds the tether from the drum. The apparatus further includes a pulley-drive and a drum-drive. The pulley-drive is operable in a forward mode to drive the pulley system for the unwinding of the tether and operable in a braking mode to resist the re-winding of the tether and the drum-drive is operable in a forward mode to drive the drum for the re-winding of the tether and operable in a braking mode to resist the unwinding of the tether.

Description

The present invention relates to an apparatus for connection to an underwater vehicle by a tether. The present invention also relates to a method of unwinding a tether connected to an underwater vehicle from an underwater drum to allow movement of the vehicle. The present invention also relates to a method of re-winding a tether connected to a underwater vehicle onto an underwater drum.
It is known to use a tether management system (TMS) in which a buoyant tether is winched onto a submersed drum, so that an underwater vehicle may travel freely around the tether management system, performing required duties without being subject to movements occurring to a support vessel and without requiring the support vessel to move.
Given that the tether is buoyant in water, the underwater vehicle does not apply tension to the tether, therefore the spooling of the tether may become difficult. In known systems, additional mechanisms are deployed to position the tether upon a particular region of the cable drum. However, these mechanisms are subject to failure and a degree of expertise is required during a reconnection process.
According to a first aspect of the present invention, there is provided an apparatus for connection to an underwater vehicle by a tether, comprising: a drum configured to store said tether such that said tether is unwound from said drum to allow said vehicle to move away from the apparatus; a pulley system configured to engage with said tether and unwind the tether from said drum; a pulley-drive operable in a forward mode to drive said pulley system for the unwinding of the tether and operable in a braking mode to resist the re-winding of said tether; and a drum-drive operable in a forward mode to drive said drum for the re-winding of said tether and operable in a braking mode to resist the unwinding of the tether, characterised in that: said drum has a continuous groove defining a substantially helical surface.
In an embodiment, the tether conveys power, control signals and communication signals.
According to a second aspect of the present invention, there is provided a method of unwinding a tether connected to an underwater vehicle from an underwater drum to allow movement of said vehicle, said method comprising the steps of: driving a pulley system configured to engage with said tether so as to unwind said tether from said drum; and activating said drum so as to maintain transported tether between the drum and said pulley system in tension, characterised in that: said drum has a continuous groove defining a substantially helical surface.
In an embodiment, the pulley system includes a primary pulley defining a radius of curvature for the tether and configured to engage on an internal surface of the tether; and a plurality of support pulleys configured to engage with an external surface of the tether in opposition to said primary pulley.
According to a third aspect of the present invention, there is provided a method of rewinding a tether connected to an underwater vehicle, onto an underwater drum, said method comprising the steps of: driving said drum so as to rewind said tether onto the drum; and activating a pulley system configured to engage with the tether so as to maintain transported tether between the pulley system and the drum in tension, characterised in that: said drum has a continuous groove defining a substantially helical surface.
The invention will now be described by way of example only with reference to the accompanying drawings, of which:

Figure 1 shows a tether management system embodying the present invention;
Figure 2 shows the tether connected to an underwater vehicle;
Figure 3 details the tether management apparatus;
Figure 4 shows a cross-section of the tether management apparatus;
Figure 5 shows a hydraulic circuit; and
Figure 6 details a portion of a pulley in contact with a tether.

Figure 1

An apparatus 101 is shown in Figure 1, and may be identified as a tether management system (TMS) for tethering an underwater vehicle 102, possibly taking the form of a remotely operated vehicle receiving control signals from a control station within a support vessel 103.
In the configuration shown in Figure 1, the tether management system 101 appears as if sitting on top of the underwater vehicle 102 and as such is sometimes referred to as a "tophat". The support vessel 103 includes a launch and recovery system 104, including a drum 105, a swinging frame 106 and an umbilical cable 107. A winch is configured to lift and load apparatus 101 off and on the support vessel 103 and in use the apparatus may operate at depths of up to four kilometre (4km).
Within the apparatus 101, a drum 108 is configured to store a tether 109, such that the tether 109 is unwound from the drum 108 to allow the vehicle 102 to move away from the apparatus. The vehicle 102 may travel in any direction away from the apparatus 101, typically up to a distance of one thousand five hundred metre (1500m).

Figure 2

As illustrated in Figure 2, the support apparatus 101 is connected to the support vessel 103 by an umbilical cable 107. The weight of apparatus 101, even when submerged, is sufficient to maintain the umbilical cable 107 in tension, thereby facilitating the spooling and unspooling of the umbilical cable 107 onto and off from the drum 105.
The tether management drum 108 has been activated thereby allowing tether 109 to be removed, such that the underwater vehicle 102 may move away from the tether management apparatus 101.
Remotely operated underwater vehicles, such as vehicle 102, are often built with a large floatation pack on top of an aluminium chassis to provide buoyancy while tasks are being performed. A tooling skid may be fitted to the bottom of the vehicle to accommodate a variety of sensors and tooling packages. Light components tend to be raised towards the top of the vehicle, with heavy components being at the bottom. Electrical components are contained within oil-filled watertight containers to protect them from water corrosion and water pressure.
In the oil industry, crews typically work two twelve-hour shifts and the vehicle 102 itself may be underwater for most of this time. Failure of the tether management apparatus 101 is highly undesirable, given that facilities for effecting repairs at sea are limited and system downtimes incur significant costs. It is therefore highly undesirable for problems to occur due to the mis-spooling of tether 109 when the underwater vehicle 102 is being brought back to the tether management apparatus 101 at the end of a shift.
As shown in Figure 2, the re-winding of tether 109 is made problematic due its buoyancy. Unlike umbilical cable 107, the tether 109 will often be slack, due to the vehicle 102 going out to an extreme distance and then retracting back towards the tether management apparatus. Thus, this slack must be taken up before the tether 109 is again placed in tension. This problem does not occur with the umbilical cable 107 because this always remains substantially in tension due to the weight of the tether management apparatus 101.
The tether 109 is not merely a link between the tether management apparatus 101 and the vehicle 102. The umbilical 107 provides a voltage of anything up to four kilovolts (4kv) and experience suggests that a voltage of one kilovolt per kilometre (1kv/km) of cable is required in order to guarantee the availability of power at the tether management system 101 and the remote vehicle 102.
The tether also conveys control signals to the vehicle 102, relayed via the umbilical 107 and the tether management apparatus 101 and returns data and images back to the support vessel 103. Thus, the tether 109 represents a complex assembly of materials but given the requirement for buoyancy, the tether 109 tends to be less robust than the umbilical cable 107. Furthermore, it is undesirable for excessive unnecessary lengths of tether to be released, given that this will cause additional drag when underwater currents are present.
In many applications, it is not possible to use a free swimming underwater vehicle connected directly to the support vessel 103. The tether management system allows better access to plant without bringing the support vessel 103 too close. Furthermore, in some installations a minimum distance must be maintained between vessels and operational plant. Furthermore, the tether management system reduces the extent to which the support vessel 103 is required to move. Its presence also isolates the remote vehicle 102 from natural movements of the support vessel 103, possibly due to swell.

Figure 3

A frame 301 of the tether management system 101 is illustrated in Figure 3. Tether drum 302 has been located within the frame 301. In this embodiment, drum 302 has a helical surface 303. In this embodiment, the helical surface is provided by a helical sleeve applied over a substantially smooth drum.

Figure 4

The management system 101 identified in Figure 1 is detailed in Figure 4. As previously described, a frame 301 supports a tether drum 302. The tether drum 302 supports a tether such that the apparatus may be connected to an underwater vehicle as shown in Figure 2. The tether drum 302 stores the tether 109 such that the tether 109 may be unwound from the tether drum 302 to allow an underwater vehicle (such as vehicle 102) to move away from the apparatus.
A pulley system 403 is configured to engage with the tether 109 so as to allow the tether to be unwound from the drum. A pulley-drive is provided, for driving the pulley system 403, in a forward mode to drive the pulley system for the unwinding of the tether thus moving the tether in the direction of arrow 401 and ultimately allowing the tether to exit the apparatus from an exit port 402. In addition, the pulley-drive is operable in a breaking mode to resist the re-winding of the tether.
A drum drive is operable in a forward mode to drive the tether drum 302 for the re-winding of the tether, thereby moving the tether in the direction of arrow 402. Furthermore, the drum-drive is also operable in a breaking mode to resist the unwinding of the tether. Thus, when the tether 301 moves in the direction of arrow 401, the pulley-drive is operable in its forward mode, thereby pulling the tether away from the drum. However, while this occurs, the drum 302 is in its breaking mode, applying force in the direction of arrow 402. The driving force of the pulley ensures that the tether does move in the direction of arrow 401, against the breaking force of the drum-drive. However, with these forces operating in opposite directions, the tether between the drum 302 and the pulley system 403 remains in tension, thereby ensuring that the tether is removed from the drum in a smooth operation.
With the drum-drive operable in a forward mode, the tether moves in the direction of arrow 402, thereby returning the tether to the drum. The pulley system 403 operates in its breaking mode, applying a reduced degree of force in the direction of arrow 401, thus resisting the movement of the drum 302. Drum 302 continues to move and the tether continues to be wound onto the drum. However, it is not possible for the tether to bunch or become slack, because the length of tether between the drum 302 and the pulley system 403 remains in tension.
The pulley system 403 includes a primary pulley 409 defining a radius of curvature 404 for the tether 109 as it moves. This radius of curvature is sufficient to ensure that the tether 109 does not experience excessive bending forces which may result in tether damage and failure.
A plurality of support pulleys are also provided which, in this embodiment, include a first support pulley 405 and a second support pulley 406. The support pulleys 405 and 406 are configured to engage with an external surface 407 of the tether 109 in opposition to the primary pulley 409. Thus, in operation, the tether 109 is held securely between the primary pulley 409 and the secondary pulleys 405, 406. This overall region of support may be referred to as a sheave and, given its driven nature, it may collectively be referred to as a power sheave.
The apparatus 101 provides for the tether to exit from exit port 402 in a substantially vertical direction. A flexible support conduit 408 supports the tether as it passes between the pulley system and the exit port 402. In an embodiment, the conduit 408 is fabricated from a plurality of interlocking portions, thereby facilitating flexibility during assembly and maintenance procedures.

Figure 5

In an embodiment, pulley-drive 403 is driven by a hydraulic motor 501. Similarly, drum 302 is driven by a second hydraulic motor 502. An electric motor receives electrical power from the umbilical 107 and uses this to apply pressure to a hydraulic fluid circulated within a hydraulic circuit; a schematic version of which is shown in Figure 5.
Hydraulic fluid from the hydraulic pump is supplied to a valve 503 from a main inlet 504. Valve 503 may receive a first pilot signal on an input line 505, resulting in pressure being supplied to line 506. The valve 503 may also receive a pilot signal on input line 507 resulting in pressure being applied to output line 508. The valve 503 may also remain in a rest condition, resulting in neither line 506 nor line 508 being energised.
A pilot signal on line 505 represents a spool out condition, forcing the tether out of orifice 401 through movement in the direction of arrow 401. A valve 509 directs high pressure fluid to the pulley-drive 501 causing the pulley-drive to pull tether away from drum 302. In addition, a further valve 510 supplies a lower breaking pressure to the drum-drive 502. Thus, the force applied to the pulley-drive 501 overcomes the force applied to the drum-drive 502 but with a positive pressure being applied to the drum-drive 502; the length of tether held between the drum 302 and the pulley system 403 remains in tension.
The application of a pilot signal to input line 507 results in pressure being applied to line 508. This in turn supplies driving pressure to drum-drive 502 via a valve 511. However, in addition, when the drum-drive receives a drive pressure, the pulley-drive 501 receives a lower breaking pressure via a valve 512. In this mode, the main drive pressure supplied to the drum-drive 502 results in a re-winding of the tether, with movement of the tether in the direction of arrow 402. However, given the breaking pressure supplied to the pulley-drive 501, via valve 512, the tether 109 between the pulley 403 and the drum 302 remains in tension. With the application of this tension, the tether 109 is forced to re-wind onto the drum 302 as intended, without the possibility of bunching or disruption.
Thus, the hydraulic system of Figure 5 allows the apparatus to be deployed in accordance with two methods of operation. During an unwinding method, a tether is connected to a underwater vehicle from an underwater drum 302 to allow movement of the vehicle. A pulley system 403 is driven, configured to engage with the tether so as to unwind the tether from the drum. Furthermore, the drum is also activated (at lower pressure) so as to maintain transported tether 109 between the drum and the pulley system in tension.
A second method of operation is provided for the re-winding of the tether, with the tether connected to an underwater vehicle. The tether rewinds onto underwater drum 302. The drum is driven so as to re-wind the tether onto the drum. Furthermore, pulley system 403 is also activated so as to engage with the tether, to maintain transported tether 109 between the pulley system 403 and the drum 302 in tension.
As shown in Figure 3, in an embodiment, the drum 302 has a continuous groove defining a substantially helical surface. In this way, a first layer of the rewound tether may be forced into this groove, due to the activation of the pulley system maintaining the tether in tension. After the first layer of the rewound cable has been positioned, due to the presence of the helical groove, a second layer may be rewound so as to fall within grooves defined by the first layer. Thus, this process may continue until all of the tether has been rewound onto the tether drum 302.
In an embodiment, the underwater vehicle is then restrained by a spring loaded device when the tether has been fully rewound. In this way, it is possible for the underwater vehicle to be restrained in the absence of power but for the vehicle to be released, activation of the spring loaded device is required. In an embodiment, hydraulic pressure is used to effect this release in response to the spool-out pilot signal being generated.

Figure 6

An example of pulley 409 is illustrated in Figure 6. This primary pulley defines a groove 601 configured to make contact with tether 109 such that force may be applied in the direction of arrow 401 in order to remove tether from cable 107. In an embodiment, the pulley system effectively maintains a tight grip on the tether 109, given that the tether is being maintained in tension by the activation pressure applied to drum-drive 502.
In an embodiment, the profile of groove 601 is such that as the diameter of the tether 109 reduces, the tether is forced radially inwards, such that it is still held by the reducing width of groove 601. Furthermore, in an embodiment, pulley 409 is cast from polymer material, so as to enhance the frictional force between groove 601 and tether 109.

Claims

Apparatus (101) for connection to an underwater vehicle (102) by a tether (109), comprising:
a drum (108, 302) configured to store said tether such that said tether is unwound from said drum to allow said vehicle to move away from the apparatus;

a pulley system (403) configured to engage with said tether and unwind the tether from said drum;

a pulley-drive (501) operable in a forward mode to drive said pulley system for the unwinding of the tether and operable in a braking mode to resist the re-winding of said tether; and

a drum-drive (502) operable in a forward mode to drive said drum for the re-winding of said tether and operable in a braking mode to resist the unwinding of the tether, characterised in that:
said drum has a continuous groove defining a substantially helical surface (303).
The apparatus of claim 1, wherein said tether conveys power, control signals and communication signals.
The apparatus of claim 2, connectable to a surface device (103) by an umbilical cable (107) wherein said power and said control signal are received from said umbilical cable.
The apparatus of any of claims 1 to 3, wherein said underwater vehicle is a remotely controlled vehicle configured to receive control signal from said surface device.
The apparatus of any one of claims 1 to 4, wherein said helical surface is provided by a helical sleeve applied over a substantially smooth drum.
The apparatus of any of claims 1 to 5, wherein said pulley-drive includes a first hydraulic motor (501) and said drum drive includes a second hydraulic motor (502).
The apparatus of claim 6, wherein:
said pulley-drive receives a drive pressure and said drum-drive receives a lower braking pressure when unwinding the tether; and

said drum-drive receives a drive pressure and said pulley-drive receives a lower braking pressure when rewinding said tether.
A method of unwinding a tether (109) connected to an underwater vehicle (102) from an underwater drum (108, 302) to allow movement of said vehicle, said method comprising the steps of:
driving a pulley system (403) configured to engage with said tether so as to unwind said tether from said drum; and

activating said drum so as to maintain transported tether between the drum and said pulley system in tension, characterised in that:
said drum has a continuous groove defining a substantially helical surface.
The method of claim 8, wherein said pulley system includes:
a primary pulley (409) defining a radius of curvature (404) for the tether and configured to engage on an internal surface of the tether; and

a plurality of support pulleys (405, 406) configured to engage with an external surface of the tether in opposition to said primary pulley.
The method of claim 8 or claim 9, wherein said primary pulley defines a groove (601) and said groove is configured to maintain contact with the tether during tether shrinkage at depth.
The method of any of claims 8 to 10, including an exit port (402) for allowing the unwinding of the tether from the apparatus in a substantially vertical direction, and a flexible support conduit (408) for supporting the tether between the pulley system and said exit port.
A method of rewinding a tether (109) connected to an underwater vehicle (102), onto an underwater drum (108, 302), said method comprising the steps of:
driving said drum so as to rewind said tether onto the drum; and

activating a pulley system (403) configured to engage with the tether so as to maintain transported tether between the pulley system and the drum in tension, characterised in that:
said drum has a continuous groove defining a substantially helical surface (303).
The method of claim 12, wherein a first layer of rewound tether is forced into said groove due to the activation of said pulley system maintaining the tether in tension.
The method of claim 13, wherein said first layer of rewound tether defines a secondary helical groove and a second layer of rewound tether is forced into said secondary groove.
The method of any of claims 12 to 14, wherein said underwater vehicle is restrained by a spring-loaded device when the tether has been fully re-wound.