EP2330027A1

EP2330027A1 - Remotely operated submersible vehicle with adjustable tether mounting terminal

Info

Publication number: EP2330027A1
Application number: EP09178230A
Authority: EP
Inventors: Andrew Hunt
Original assignee: Soil Machine Dynamics Ltd
Current assignee: Soil Machine Dynamics Ltd
Priority date: 2009-12-07
Filing date: 2009-12-07
Publication date: 2011-06-08

Abstract

A remotely operated submersible vehicle (100) is disclosed. The vehicle (100) comprises a housing (102), positioning means (104, 106, 108, 110, 112, 114, 120, 122) adapted to control a position and/or orientation of the remotely operated submersible vehicle and a mounting apparatus (116) adapted to be connected to a tether cable (118) to enable a position at which a towing force is applied from the cable (118) to the apparatus to be adjusted.

Description

FIELD OF THE INVENTION

The present invention generally relates to underwater vehicles such as remotely operated vehicles (ROVs) for underwater applications, and relates particularly, but not exclusively, to a remotely operated vehicle having an adjustable tether mounting terminal for operation in high-speed and low-speed water flows.

BACKGROUND OF THE INVENTION

Remotely operated vehicles, generally referred to as ROVs, are tethered underwater robots mainly used in the offshore industry and for marine research. ROVs are unoccupied, maneuverable and operable by a user aboard a vessel or platform.
Typical work-class ROVs have a buoyancy block or system that is mounted to a rigid frame to which several independently driven and controlled thrusters are attached. The ROV is connected to the vessel or platform by means of a tether or umbilical cable through which power, information signals and control signals are passed. Some tethers or umbilicals may also contain hoses for delivery of hydraulic or pneumatic services etc. ROVs may be equipped with cameras, lights, sonars, magnetometers, tooling manipulators and/or cutting arms, water samplers and other instruments for measuring, for example, water clarity, light penetration and temperature.
An example of a typical work-class ROV is shown in Figure 1 . A buoyancy tank or block 2 is mounted to a frame 3 and adapted to provide sufficient buoyancy for the ROV 1. Thrusters 4 are mounted to the frame 3 allowing the ROV 1 to maneuver underwater. Tooling 5 such as manipulators and grabbers can be used for carrying equipment and for performing maintenance tasks and are located at one end of the frame 3. The ROV 1 is connected to the vessel or platform (not shown) by means of a tether or umbilical cable 6 that is usually attached to a top-side terminal 7 of the frame.
However, as shown in Figure 2 , these typical work-class ROVs 1 cannot operate effectively in high-flow conditions, i.e. typically in water flows of speed in excess of about 2 knots (≈ 1 m/s), because the flow resistance of the top-side tether cable 6 and the ROV 1 causes drag that may move the ROV 1 out of the desired position. Thus, thrusters and hydrofoils provide forces F_d, F_t and moment M to counteract the flow induced additional forces arising from the combination of ROV drag F _rd and cable force F_ch and F_CV that affect the ROV's position and maneuverability.
Figure 3 shows a typical work-class ROV 1 when operating in low-flow conditions, i.e. substantially no water flow or water flow significantly less than 2 knots (≈ 1 m/s), with only forces F_C, F_d, F_t and F_rd acting on the ROV 1.
As a result, the necessary additional compensatory maneuvers make the ROV in the configuration shown in Fig 2 sluggish and less responsive and sometimes unable to maintain position, and the additional use of thrusters and/or hydrofoils increases the power consumption of the ROV.

SUMMARY OF THE INVENTION

Preferred embodiments of the present invention seek to overcome one or more of the above disadvantages of the prior art.
According to an aspect of the present invention, there is provided a remotely operated submersible vehicle, comprising:

a housing;
positioning means adapted to control a position and/or orientation of said remotely operated submersible vehicle;
a mounting apparatus adapted to be connected to a tether cable to enable a position at which a towing force is applied from the cable to the apparatus to be adjusted.

This provides the advantage that the towing force to the tether cable is always in a hydro-dynamically optimal position for the vehicle (ROV), therefore minimizing any additional forces that may affect the position of the vehicle due to cable drag in high-flow conditions and weight/cable slack in low-flow conditions. Thus, fewer compensatory manoeuvres by the positioning means are necessary to maintain a desired vehicle position, requiring less power and therefore minimizing energy consumption of the vehicle.
A position at which a towing force is applied by a cable to the apparatus may include at least one first position above the centre of gravity of the vehicle in use.
A position at which a towing force is applied by a cable to the apparatus may also include at least one second position upstream of the centre of gravity of the vehicle when in use in the direct flow of fluid in which the vehicle is submerged
The vehicle may further comprise detachment means for enabling remote detachment of a tether cable.
This provides the advantage that the tether cable could be detached instantly in case of an emergency or to allow autonomous operations of the remotely operated vehicle.
The positioning means may comprise at least one thruster and/or at least one hydrofoil and/or at least one variable buoyancy chamber.
At least one said hydrofoil may be remotely controllable.
At least one said thruster may be positioned adjacent an edge region of the housing
A combination of advantageously positioned and remotely controllable thrusters, hydrofoils, variable buoyancy chambers and weight provide the advantage that the manoeuvrability of the remotely operated submersible vehicle is maximized allowing more accurate operations.
The remotely operated submersible vehicle may further comprise at least one tool.
At least one said tool may comprise at least one manipulator.
At least one said tool may be adapted to be located downstream of the centre of gravity of the vehicle in use in the direction of flow of fluid in which the vehicle is submerged.
This provides the advantage that a tooling package e.g. manipulators are protected from the full force of the water flow and do also not interfere with the optimized hydro-dynamic characteristics of the remotely operated submersible vehicle.
The remotely operated submersible vehicle may further comprise a protection frame adapted to provide protection to at least one hydrofoil and/or at least one thruster.
This provides the advantage that crucial parts for the manoeuvrability of the remotely operated submersible vehicle are protected from external forces making it more hardwearing and increasing its lifetime, thereby reducing cost of repairs.
The remotely operated submersible vehicle may further be adapted for operation without using a tether cable.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred embodiment of the present invention will now be described, by way of example only and not in any limitative sense, with reference to the accompanying drawings, in which:

Figure 1 schematically illustrates a typical known ROV in use;
Figure 2 schematically illustrates the forces affecting the vehicle of Figure 1 with a top-side tether cable in high-flow conditions;
Figure 3 shows the vehicle of Figure 1 in low-flow conditions;
Figure 4 shows a perspective side-front view of an embodiment of the invention including part of the tether cable and a clump weight;
Figure 5 shows a perspective side-rear view of an embodiment of the invention including part of the tether cable;
Figure 6 schematically illustrates a mechanism of a first mounting apparatus for the present invention;
Figure 7 schematically illustrates a mechanism of a second mounting apparatus for the present invention;
Figure 8 schematically illustrates a mechanism of a third mounting apparatus for the present invention;
Figure 9 schematically illustrates an embodiment of the invention in high-flow mode when in use; and
Figure 10 schematically illustrates an embodiment of the invention in low-flow mode when in use;

DETAILED DESCRIPTION OF EMBODIMENT

Referring to Figures 4 and 5 , a remotely operated submersible vehicle 100 embodying the present invention comprises a hydrodynamic chassis 102 that houses the components making up the vehicle 100. The components may also include a structural frame, motors, pumps, valve packs, control equipment, tooling packages, attachments for payloads etc. within the streamlined shape.
Furthermore, hydrofoils 104, 106, 108 are located at various positions around the vehicle 100 to control not only the gross position of the vehicle 100 in the water column but also its orientation.
In addition to the hydrofoils, high power steerable thrusters 110 may be orientated in such a way to enable control of the gross position of the vehicle 100 in the water column, or to provide lift capacity for payloads carried by the vehicle 100. Also, in low-flow mode, which is used when operating the vehicle in water flow with flow speeds significantly less than about 2 knots (1 m /s), the high-power steerable thrusters 110 would primarily be used for manoeuvring the vehicle 100 in conjunction with the vertical 112 and vectored horizontal thrusters 114.
Additional vertical thrusters 112 and vectored horizontal thrusters 114 are fitted to augment the vehicle's gross and fine position,
Two variable buoyancy tanks 122 maybe provided on the vehicle 100, which are adapted to provide a variable weight to the vehicle 100 by either filling or emptying the tanks 122 using a suitable pump and valve system (not shown). The weight of the vehicle 100 may also be adjusted by other means such as adding/removing ballast.
Furthermore, a protection frame 124 is provided to minimise risk of damage to the hydrofoils 104, 106, 108 and high-power steerable thrusters 110. Tooling and manipulators 126 may be fitted to the rear of the vehicle 100 in order to protect them, for example, from the full force of the water flow. The tooling or manipulators 126 may also be located at any of the other sides of the vehicle 100.
The tether cable 118 may either be a simple wire or fibre rope, providing the remotely operated submersible vehicle has onboard power, or an electrical lifting umbilical cable adapted to provide electrical power and allowing signal transfer or more complicated umbilical containing hoses as well as electrical cables. The umbilical cable 118 may be detachable so the vehicle can be disconnected for autonomous operations or in case of an emergency. The umbilical cable 118 can also be used to lift the vehicle 100 into and out of the water.
Since the location of the cable 118 on the housing 102 is crucial to the stability of the vehicle's position when operating in high-flow or low-flow conditions, the position where the cable 118 is coupled to the vehicle 100 is adjustable to suit the mode of operation.
Figure 4 shows the present invention in high-flow mode, where the mounting apparatus 116 provides for the tether cable 118 to be positioned near the front of the vehicle 100 with regard to the flow direction of the vehicle 100, i.e. the front of the vehicle 100 faces the flow direction of the vehicle when pulled behind a vessel 200 or the flow of a water column 210 that is directed towards the vehicle 100. The tether cable or umbilical cable 118 is coupled to the mounting apparatus 116 and a suitable single or a plurality of clump weights 120, or other means that are adapted to apply a downward force to the tether cable 118, is/are coupled to the tether cable 118 in order to assist the gross positioning of the tether cable 118 and subsequently the vehicle 100 in the water column.
Figure 5 shows the present invention in low-flow mode, where the mounting apparatus 116 provides for the tether cable or umbilical cable 118 to be located in a more conventional manner at the top-side of the vehicle 100, with regards to the operating position of the vehicle 100.

Tether mounting terminal mechanism

A detailed example of a first mechanism 117 for the mounting apparatus 116 is shown in Figure 6 . The umbilical cable 118 is attached to a chain or conveyor belt 126 that is moved by one or two hydraulically or electrically driven sprockets 128. The chain or conveyor belt 126 may be supported by supporting rollers 130 or edge guides 131. This bridle mechanism may be locked in position by a lock 132 in order to fix the umbilical cable 118 in the desired position.
Figure 7 shows a detailed example of a second mechanism 119 of the mounting apparatus 116. The umbilical cable is coupled to rollers 136 that run within a rail system 134 allowing movement along the housing 102 of the vehicle 100. The rollers 136 are moved by a remotely controlled hydraulic arm 138 that may also lock the umbilical cable 118 in the desired position.
Figure 8 shows a detailed example of a third mechanism 121 of the mounting apparatus 116. Similar to the second mechanism 119, the umbilical cable is coupled to rollers 140 that run within a rail system 142 allowing movement along the housing 102 of the vehicle 100. The rollers 140 are coupled to a first remotely controlled hydraulic ram 144 via a first cable 148 on one side of the rail 142, and to a second remotely controlled hydraulic ram 146 via a second cable 150 on the other side of the rail 142. Through activation of either the first or second hydraulic ram 144, 146, the rollers 140 may be moved into various positions along the housing 102 of the vehicle 100.

High-flow mode operation

During a typical operation in high-flow mode, the remotely operated submersible vehicle 100 uses a combination of the high-power steerable thrusters 110, the vertical and vectored horizontal thrusters 112, 114, the tether cable's length and position, the hydrofoils 104, 106, 108 and the variable weight provided by the buoyancy tanks 122 and/or clump weight 120 to maintain the desired position in the water column.
For most operations the support vessel 200 is likely to maintain its position. However, the vehicle 100 may simply be towed behind the vessel 200 for, for example, survey operations. The support vessel 200 could be any suitable structure in the tidal flow onto which the associated deck equipment for the vehicle 100 is installed.
As shown in Figure 9 , the vehicle 100 is connected to a suitable tether winch 220 on the surface support vessel 200 or any other structure (not shown). The clump weight's 120 position and its mass are adjusted to move the vehicle 100 in the desired position within the water column. Then, the mounting apparatus 116 moves the cable 118 towards the front of the vehicle 100 so that when the vehicle 100 is deployed into the water flow the drag force F _drag is minimised. Subsequently, the water flow has a tendency to align the vehicle 100 and tether cable 118 behind the surface support vessel 200. The tether cable 118 is then paid out to the desired length and the vehicle operates its hydrofoils 104, 106, 108 to move the vehicle into the desired vertical and lateral position and orientation. Any of the thrusters 110, 112, 114 and variable buoyancy tanks 122 may also be used in conjunction / or on their own to help positioning the vehicle 100.
When the vehicle 100 is in the desired position, the required task is completed. Typical tasks may include (i) reversing and connecting onto a structure to deliver services, e.g. electrical, hydraulic, air etc., (ii) deploying payloads to an accurate location on the seabed, e.g. ACDP, (iii) manipulation work such as connecting electrical connectors or cleaning, or (iv) inspection.

Low-flow mode operation

Figure 10 shows an embodiment of the present invention during a typical operation in low-flow mode.
The remotely operated submersible vehicle 100 is connected to a suitable tether winch 220 on the surface support vessel 200. The mounting apparatus 116 moves the cable position towards the top of the vehicle 100 like in a more conventional work-class ROV. The tether cable 118 is then paid out to the desired length and the vehicle 100 operates its thrusters 104, 106, 108 and variable buoyancy tanks 122 to manoeuvre the vehicle into position.
When the vehicle 100 is in the desired position, the required task is completed. Typical tasks may include (i) reversing and connecting onto a structure to deliver services, e.g. electrical, hydraulic, air etc., (ii) deploying payloads to an accurate location on the seabed, e.g. ACDP, (iii) manipulation work such as connecting electrical connectors or cleaning, or (iv) inspection.
It will be appreciated by persons skilled in the art that the above embodiments have been described by way of example only, and not in any limitative sense, and that various alterations and modifications are possible without departure from the scope of the invention as defined by the appended claims.

Claims

A remotely operated submersible vehicle, comprising:
a housing;

positioning means adapted to control a position and/or orientation of said remotely operated submersible vehicle;

a mounting apparatus adapted to be connected to a tether cable to enable a position at which a towing force is applied from the cable to the apparatus to be adjusted.
A vehicle according to claim 1, wherein said position at which a towing force is applied by a cable to said apparatus includes at least one first position above the centre of gravity of said vehicle in use.
A vehicle according to claim 1 or 2, wherein said position at which a towing force is applied by a cable to said apparatus includes at least one second position upstream of the centre of gravity of said vehicle when in use in the direct flow of fluid in which said vehicle is submerged.
A vehicle according to any one of the preceding claims, further comprising detachment means for enabling remote detachment of a tether cable.
A vehicle according to any one of the preceding claims, wherein said positioning means comprises at least one thruster and/or at least one hydrofoil and/or at least one variable buoyancy chamber.
A vehicle according to claim 5, wherein at least one said hydrofoil is remotely controllable.
A vehicle according to claim 5 or 6, wherein at least one said thruster is positioned adjacent an edge region of said housing.
A vehicle according to claim 7, wherein the orientation of at least one said thruster is remotely adjustable.
A vehicle according to any one of the preceding claims, further comprising at least one tool.
A vehicle according to claim 9, wherein at least one said tool comprises at least one manipulator.
A vehicle according to claim 9 or 10, wherein at least one said tool is adapted to be located downstream of the centre of gravity of said vehicle in use in the direction of flow of fluid in which said vehicle is submerged.
A vehicle according to any one of the preceding claims, further comprising a protection frame adapted to provide protection to said at least one hydrofoil and/or at least one said thruster.
A vehicle according to any one of the preceding claims, wherein the vehicle is adapted for operation without using a tether cable.