WO2013007975A1

WO2013007975A1 - An underwater vehicle for installation, maintenance of wave, tidal or water current power generating devices

Info

Publication number: WO2013007975A1
Application number: PCT/GB2012/000592
Authority: WO
Inventors: Stephen Hugh Salter
Original assignee: Aquamarine Power Limited
Priority date: 2011-07-14
Filing date: 2012-07-13
Publication date: 2013-01-17
Also published as: GB201112105D0; GB201115206D0

Abstract

An apparatus for movement along the bed of a body of water comprises a plurality of legs and a controller for controlling operation of the legs, wherein the controller may be configured to control operation of the legs so that in operation on a bed of the body of water the apparatus moves along the bed of the body of water.

Description

AN UNDERWATER VEHICLE FOR INSTALLATION, MAINTENANCE OF WAVE, TIDAL OR WATER CURRENT POWER GENERATING DEVICES

Field of the invention The present invention relates to an apparatus that can move over the bed of the body of water. The invention also relates to the installation and/or maintenance of wave, tidal or water current devices

Background of the invention

There has been a great deal of activity in development of renewable energy sources in recent years. Much activity has been directed to the development of wave and tidal stream plant for extracting energy from waves or tides. In many cases, wave and tidal plant must be installed on the seabed. The sub-sea environment can be harsh and can be subject to a wide variety of conditions, which can present significant technical difficulties. The condition of the seabed itself varies widely from location to location, with the rocks, sand, mud, vegetation and other materials that make up the seabed being distributed unpredictably and often shifting due to the action of tides and currents. In areas of interest close to the shore, the seabed is often bare rock due to the action of waves or currents, and can present significant obstructions, for example steps or inclines of significant steepness and size.

The absence of equipment for working on the seabed is a severe impediment for both wave and tidal stream plant. Seabed operations may require intricate movements of tools or components with accuracy to the order of a millimetre. Work might involve moving chain saws to cut shapes in rock, putting retainer pins into holes, making electrical, hydraulic or pneumatic connections, drilling holes, pumping flushing liquids, placing explosives, detonators and air tubes, fitting nuts to threaded post-tensioning bar, inspecting corrosion, removing bio-fouling, cutting rock, digging cable trenches, laying cables, placing instrument packages and aligning bearings.

The oil industry has developed jack-up platforms for work in shallow seabeds.

A typical design has four vertical legs which can be lowered to the seabed to lift a barge clear of wave action or raised to the barge so that it can be towed. Intricate activities are more difficult from a base above wave height and so there is a need for a vehicle which can function on the seabed.

Tracked seabed vehicles such as those developed by the Norwegian company Scanmudring and Blade Offshore are already in use for dredging and sediment removal and pile attachment. Track propulsion is excellent for the fairly straight line movements needed for military and agricultural applications over soft ground and Scanmudring claim to work in bed pressures down to 6 kPa. A 70 kg person wearing a 300 by 100 mm boot exerts a ground pressure of 3.8 times greater. However, tracked vehicle rotations are awkward and direct side movements impossible. Wave and tidal stream plant will often be placed in areas where small, loose material has been removed by scouring, and where the presence of irregular rock can present significant difficulties. If a tracked vehicle has to cross a hard ridge there can be an acute stress concentration over a short length of track.

There is also a need for robotic machine-tools for work on the seabed attachment. It may be desired to cut cavities of a wide range of shapes and sizes and drill holes at any angle. It may also be desired to insert explosives, detonators, post-tension stands and grout, or to direct chain-saws, water jets or abrasive wheels to cut away unwanted outcrops of rock. In addition, it may be desired to insert pins and tighten nuts with a controlled torque, dig cable trenches and align power cables in them.

it is desirable for subsea vehicles to be easy to transport on land and to be stable in large waves even in shallow water and in the highest current speeds.

Summary of the invention

In a first, independent aspect of the invention there is provided an apparatus for movement along the bed of a body of water, the apparatus comprising a plurality of legs and a controller for controlling operation of the legs, wherein the controller may be configured to control operation of the legs so that in operation on a bed of the body of water the apparatus moves along the bed of the body of water. The controller may be configured to control movement of the legs so that the apparatus moves with a walking motion.

An apparatus that is capable of moving along the bed of a body of water using a walking motion is particularly suitable for operation in environments where the bed of the body of water is rocky or unstable, for example due to strong tidal forces, waves or currents that remove or reduce sedimentary deposits. Such environments are often ones in which it is desired to install wave or tidal stream systems, and the apparatus may be particularly useful in the installation and maintenance of such systems.

The apparatus may comprise an actuation system, or other actuation means, for moving the legs under control of the controller. The apparatus may comprise user input means, for example a user interface, to provide instructions to the controller. The user input means may comprise a connection (for example a wired connection) to a user terminal that is operable by a user to provide instructions to the controller. The instructions may comprise instructions to move the apparatus in a selected direction or at a selected speed, or may comprise instructions to perform a step operation using a selected one or more of the legs. The instructions may comprise one or more instructions to perform at least one tool operation.

The controller may be configured to control movement of the legs so as to perform a sequence of step operations, wherein each step operation comprises lifting at least one leg off the ground, moving the at least one leg and replacing the at least one leg on the ground.

Each leg may comprise a respective foot. The step operation for a leg may comprise lifting the foot of the leg off the ground, moving the leg and replacing the foot on the ground.

The step operation for a leg may comprise a substantially vertical movement of the leg and/or a substantially horizontal movement of the leg. The substantially horizontal movement of the leg may comprise a substantially horizontal movement of the leg in any desired direction. The substantially vertical movement and the substantially horizontal movement may be performed at least partly simultaneously or may be performed sequentially.

The controller may be configured to control movement of the legs so that, at a given time or at substantially all times, a vertical line passing through the centre of gravity of the apparatus passes inside a polygon that would be obtained by drawing straight lines between each of the feet that are in contact with the ground.

The plurality of legs may comprise at least three legs, optionally between 3 and 20 legs, optionally between 4 and 16 legs.

Each leg may have a length of between 1m and 10m, optionally between 2m and 6m. In operation, each leg may be liftable above the ground by a distance of at least 1m, optionally between 1m and 10m, optionally between 2m and 5m.

The plurality of legs may be arranged in a plurality of rows. The plurality of rows may comprise between two and eight rows, optionally four rows. Each row may comprise at least two legs, optionally between two and 10 legs, further optionally each row may consist of two legs.

The controller may be configured to perform a step operation for each leg of at least one of the rows whilst substantially simultaneously maintaining the legs of one or more other rows in contact with the ground. The controller may be configured to perform a step operation for legs of at least two rows, whilst substantially simultaneously maintaining each leg of at least one, optionally at least two, other rows in contact with the ground.

The controller may be configured to control operation of the legs to perform a step operation using each leg of at least one of the rows whilst substantially simultaneously maintaining each at least one leg, optionally each leg, of each other row in contact with the ground.

The controller may be configured to repeat the step operation using the legs of each other row in turn.

The controller may be configured to make the apparatus walk by performing a step operation using one leg at a time.

The controller may be configured to perform step operations in sequence to move the apparatus in any desired direction, for example forwards, backwards, sideways or diagonally. The walking motion may be in any desired direction, for example forwards, backwards or sideways.

The controller may be configured to control operation of the legs to rotate the apparatus, for example to rotate the apparatus in yaw about a vertical axis, or to rotate the apparatus by a desired pitch angle or roll angle. Rotation of the apparatus can be useful, for example, to position tools mounted on the apparatus to be in a desired position to perform desired operations, for example drilling or assembly operations.

After each step operation the controller may be configured to perform a push operation that comprises pushing at least one leg towards the ground, and determining a response to the push operation.

The controller may be configured to alter the position of at least one leg, for example by performing a step operation, dependent on the response to the push operation.

The controller may be configured to perform step operations alternately in respect of different ones of the rows.

The controller may be configured to alternately perform step operations in respect of the legs or the rows of legs in a sequence.

The apparatus may further comprise, for each leg, a respective at least one ram operable to move the leg. The apparatus may comprise, for each leg, a respective two, or more, rams operable to move the leg.

The apparatus may comprise, for each leg, a pair of rams, one ram of the pair positioned on one side of the leg and the other ram of the pair positioned on the other side of the leg. The pair of rams maybe arranged to move the leg in a substantially horizontal direction.

For each leg, the at least one ram may comprise a ram arranged to move the leg in a substantially vertical direction.

The apparatus may comprise, for each leg, a linkage, optionally a quadrilateral linkage, for transmitting force from at least one of the rams, for example the further pair of rams, to the leg. The linkage may be arranged to transmit force to move the leg in a horizontal direction.

Each ram may be a hydraulic ram. At least one, or each, of the rams may be a double-acting ram.

The apparatus may further comprise an actuation system for actuating the rams. The actuation system may comprise a motor and at least one pump, for example at least one radial piston machine. Each radial piston machine may comprise a plurality of pumping chambers. Each pumping chamber may be selectively operable using a respective at least one valve to apply pressure to a ram, optionally to one side of a double acting ram.

The actuation system may further comprise at least one accumulator.

The apparatus may further comprise at least one sensor for sensing pressure. Optionally the or each sensor is arranged to sense pressure associated with a respective one of the rams. The at least one sensor may sense hydraulic pressure. The controller may be operable to control operation of the rams, for example to vary pressure applied to the rams, in response to signals from the at least one sensor. The controller may vary pressure applied to the rams. The variation in pressure applied to the rams may be to counteract forces and/or movement experienced by the apparatus. The variation in pressure may comprise pulses of pressure, for example correcting pulses of pressure to counteract forces and/or movement experienced by the apparatus.

The apparatus may comprise a frame. The legs may be mounted to the frame. The frame may be a substantially open frame. The frame may comprise a substantially open floor. By providing a substantially open frame, water is able to flow freely upwards and downwards through the apparatus. That can be particularly important in areas of high current, as if the apparatus included a body which did not allow such flow of water through the apparatus then pressure differentials (for example pressure differentials in a direction perpendicular to the bed of the body of water) could develop across the apparatus, causing the apparatus to become less stable and, in extreme cases, toppling the apparatus. The frame may be configured so that at least 30%, optionally between 10% and 90%, optionally between 30% and 70%, optionally between 60% and 80%, optionally around 70% of the area of the apparatus in a direction perpendicular to the bed of the body of water, when the legs are in contact with the bed of the body of water, is open and/or allows passage of water.

The apparatus may be substantially open at the sides. The apparatus may be configured so that at least 50%, optionally between 50% and 95%, further optionally between 70% and 90% of the area of the apparatus in a direction parallel to the bed of the body of water, when the legs are in contact with the bed of the body of water, is open and/or allows passage of water.

The apparatus may comprise a plurality of attachment regions. The attachment regions may be arranged for attachment to lifting gear to enable lifting of the apparatus, in whole or part, by lifting gear, for example lifting gear for lifting containers. The attachment regions may be spaced and configured in accordance with a standard arrangement for containers, for example the ISO R668 standard. Each attachment region may comprise a mounting point. Each attachment region may comprise a fitting for stacking, loading or interconnection with other apparatus. Each attachment region may comprise a twistlock fitting.

The attachment regions may be configured to enable attachment of the apparatus to another apparatus of the same or similar type. The controller may be configured to control the apparatus and at least one other apparatus of the same or similar type, for example in a master-slave mode of operation. By attaching several apparatus of the same or similar type together an underwater walking apparatus with greater stability or able to carry greater loads can be provided. That may be useful for particular tasks, for example carrying drills or other items longer than a certain length, or carrying supplies of grout.

The apparatus may comprise a load platform or other load attachment means for carrying a load.

The apparatus may comprise at least one tool. The apparatus may comprise at least one mounting means for mounting at least one tool.

The at least one tool may comprise at least one of a drill; a cutting tool, for example a chainsaw; a digging tool; a welding tool; or a grouting tool.

The at least one tool may be mounted on a linkage. The mount may comprise the linkage. The linkage may comprise a parallelogram linkage. The tool may comprise a cutting tool, for example a chainsaw.

The controller may be operable to control operation of the at least one tool. The controller may be configured to operate to control operation of the apparatus, and of the at least one tool, in combination thereby to move the apparatus and/or tool and to perform at least one tool operation. The movement of the apparatus and/or tool and the at least one tool operation may be performed in a sequence, for example a predetermined sequence and/or a sequence selected or otherwise instructed by a user.

The controller may be configured to operate the legs and/or the at least one tool to cut a trough in the bed of the body of water. The trough may comprise a trough that is at least partially prism shaped.

The controller may be configured to operate the legs and/or the at least one tool to cut at least one notch in the bed of the body of water, for example at one or more predetermined positions with respect to the or a trough. The controller may be configured to operate the apparatus to install at least one chock device on the bed of the body of water. The controller may be configured to operate the apparatus to install the at least one chock device in the at least one notch.

Each chock device may comprise at least one cushion device, for example for cushioning a component, for example a flap, of an apparatus, for example a wave power apparatus, during installation of the component on the bed of the body of water.

The apparatus may comprise a watertight housing wherein the controller is within the watertight housing.

Electrical connections between the controller and each other component of the apparatus may be located within water-tight packaging, so that there is no contact between any of those electrical connections and the sea or other body of water in operation.

The apparatus may further comprise at least one fairing.

Alternatively or additionally each leg may be shaped so as to reduce or minimize hydrodynamic drag. The apparatus may comprise a body portion and the legs may be attached to the body portion. The body portion may comprise the frame. The body portion may comprise a fairing.

Each fairing may be arranged so as to reduce hydrodynamic drag on at least one leg.

Each leg may include a respective fairing. Each fairing may extend over at least 10% of the length of the leg, optionally at least 20% of the length of the leg, optionally at least 50% of the length of the leg. Each fairing may be located at the top of a respective leg.

Each fairing may be shaped as a hydrofoil to reduce drag. Each fairing may be substantially neutrally buoyant and/or may be free to rotate. Each fairing may have substantially neutral buoyancy moment. For each hydrofoil, an axis of rotation may be forward of a centre of pressure.

In a further independent aspect of the invention there is provided a method of performing operations at the bed of a body of water, comprising controlling operation of an apparatus comprising a plurality of legs, the control of operation of the apparatus comprising controlling the legs so that the apparatus moves over the bed of the body of water, for example using a walking motion.

The method may comprise, performing any of the operations described herein in relation to the or a apparatus

The apparatus may comprise an apparatus as claimed or described herein.

The apparatus may comprise at least one tool and the method may comprise moving the apparatus and performing at least one operation using the at least one tool. The operation may form part of an installation or maintenance procedure of a wave power, or tidal power or water current power system.

In another independent aspect of the invention there is provided a method of installing a component of an apparatus, for example a wave power apparatus, at the bed of the body of water. The component may comprise a flap. The method may comprise installing at least one chock device, placing the component into contact with the at least one chock device, and subsequently attaching the component to the bed of the body of water when the component is in a desired position.

The at least one chock device may comprise at least one cushioning means for example for cushioning the component of a wave power apparatus, for example the flap, during installation of the component on the bed of the body of water.

The cushioning means may comprise at least one valve controlling fluid pressure within the cushion means. The method may comprise selectively operating the least one valve, for example in response to at least one of movement of the component, measured force, or wave motion. The method may comprise selectively operating the at least one valve to move the component towards the desired position.

There may also be provided an apparatus or method substantially as described herein with reference to the accompanying drawings.

Any feature in one aspect of the invention may be applied to other aspects of the invention, in any appropriate combination. For example, apparatus features may be applied as method features and vice versa. Detailed description of embodiments Embodiments of the invention are now described, by way of non-limiting example, and are illustrated in the following figures. -

Figure 1 is a schematic top-view of an apparatus for movement along the bed of a body of water in accordance with an embodiment;

Figure 2 is a schematic side view of the apparatus of Figure 1 ;

Figure 3 is a schematic front-view of the apparatus of Figure 1 in operation;

Figures 4a to 4f are schematic side-views of the apparatus of Figure 1 when performing a variety of tasks;

Figure 5 is a side view of the apparatus of Figure 1 installing a flap device; and

Figure 6 is a schematic illustration of a chock used in installation of a device.

Described embodiments can be used for any suitable operation performed at the bed of a body of water, and may be particularly useful in the installation or maintenance of a wave power apparatus, or a component of such apparatus. The wave power apparatus may, by way of non-limiting example comprise an Oyster (RT ) device produced by Aquamarine Power Limited, and/or may comprise a wave power apparatus as described in one or more of GB2476274, WO2011/073628, GB 2472093, WO 2011/010102, US 2011/0006005, GB 2467011 , WO 2010/084305, WO 2010/049708, WO 2009/044161 , or WO 2006100436, each of which is in the name of Aquamarine Power Limited and each of which is incorporated herein by reference.

An apparatus 2 for movement along the bed of a body of water is illustrated schematically in Figure 1.

The apparatus 2 comprises a chassis 4, which is a steel framework made from tubular steel with lifting points 5 at each corner which conform to the ISO R668 standard for 40 foot or 1AA shipping containers. The total weight does not exceed the ISO limit of 30.48 tonnes so that it can be moved easily by commonplace container-handling equipment almost anywhere in the world. In the embodiment of Figure 1, the chassis has outer dimensions of 12.4m by 2.4m by 2.8m. The apparatus 2 may comprise a load platform for carrying loads in some embodiments.

The apparatus 2 comprises eight legs 6a, 6b, 6c, 6d, 6e, 6f, 6g, 6h in four rows. The maximum spacing of any two legs of the apparatus, for example the most rearward and most aftward legs, in this case is 8 m. The bottom part of each leg, which contacts the ground, is referred to as a foot.

It is a feature of the embodiment of Figure 1 that the floor of the chassis 4 is open such that water can flow upwards and downwards through the chassis 4 during underwater operation. The apparatus also comprises two hydraulic rams 8a-8h, 10a-10h for each leg. Each pair of hydraulic rams 8a-8h, 10a-10h is placed as close as possible on either side of each leg 6a-6h and fed with the same pressures to avoid side loads and bending moments. Each leg 6a can be moved vertically by operation of the associated pair of hydraulic rams 8a, 10a using an actuation system. In the embodiment of Figure 1 , each leg can be moved vertically for a distance of around 2m relative to the chassis 4, enabling the apparatus to clear obstacles of 2m in height. That makes the apparatus particularly suitable for operation on the sea bed, particularly in near-shore, areas of interest where obstacles of such size may commonly be found.

The apparatus also includes two further hydraulic rams 12a-12h, 14a-14h associated with each leg 6a-6h, each pair of hydraulic rams, for example 12a, 14a, being operable by an actuation system to move a respective leg, for example 6a, in a horizontal direction. Each pair of hydraulic rams 12a-12h, 14a-1 h is connected to a respective quadrilateral linkage 16a-16h. Movement of a leg 6a in the horizontal plane is controlled by the two rams 12a, 14a driving the mid-points of the quadrilateral linkage 16a.

If both rams 12a, 14a are extended the linkage 16a moves its leg 6a outwards. If the forward ram 12a is contracted and the aft one 14a is extended the leg 6a moves forward. The quadrilateral linkages 16a-16h are made as deep as possible, (for example 2.26 metres, nearly the full height, 2.59 metres, of the ISO container in the embodiment of Figure 1 ) to minimize the loading on its bearings, which are the SKF TX spherical plain type in the embodiment of Figure 1.

By appropriate movement of the rams, each of the legs 6a-6h can be placed in a desired position, within a range of possible positions, relative to the chassis 4. In Figure 1 , by way of example, leg 6b is shown in the position in which it is closest to the chassis 4, and leg 6c is shown in the position in which it is furthest away from the chassis 4. Leg 6a is shown in a mid-way position between furthest out and closest in positions. Leg 6e is shown in its further forward position relative to chassis 4 and leg 6f is shown in its furthest back position relative to the chassis. Thus the separation between legs 6e and 6f is shown at its maximum in Figure 1. Leg 6d is shown in both its furthest out and closest in positions in Figure 1 , and leg 6h is shown in both its furthest forward and furthest back positions. It will be understood that there is a single leg 6d and a single leg 6h in the embodiment of Figure 1 , and the different positions of those legs 6d, 6h are shown overlaid in Figure 1 purely for the purposes of illustration. The separation between the two positions of leg 6d shown in Figure 1 is 525 mm, and the separation between the two positions of leg 6h shown in Figure 1 is 835 mm.

The movements of 8 legs 6a-6h, each with double-acting rams 8a-8h, 10a- 10h, 12a-12h, 14a-14h to give movement in both directions, requires the actuation system to provide 48 separately-controlled hydraulic services in the embodiment of Figure 1.

In the embodiment of Figure 1 , the hydraulic actuation system comprises an Artemis Digital Displacement (RT ) hydraulic system pump/motor 20 powered by a Raser P-200 100 kW induction motor 18, and connected via hydraulic connections to the rams 8a-8h, 10a-10h, 12a-12h, 14a-14h.

The Artemis Digital Displacement (RTM) hydraulic system allows one induction motor 18 running at just less than 1500 or 1800 rpm to drive multiple banks of radial-piston machines on a common shaft. Each bank has six pumping chambers and each chamber is controlled by two electronically-operated poppet valves. The timing of valve operations allows each chamber to idle, to pump or to motor with an option to change these modes every time a piston approaches bottom-dead-centre and to terminate pumping or motoring before the end of the stroke.

If a chamber is idling the oil of the system never comes under pressure but is returned to the low-pressure tank and the energy wasted is about 1/500 of the energy which would have been delivered if that chamber had been enabled. This makes the machines very efficient at part load and able to react much faster than a variable geometry swash-plate or bent-axis design. They are also excellent at recovering nearly all the energy put into, say, the lifting of a leg when the time comes for it to be lowered again. The number of banks can be reduced if one side of each ram is connected to a constant pressure accumulator which is maintained at a pressure slightly less than half the maximum system pressure of 400 bar. The 6 chambers of one bank can also be divided into two services of three chambers. The choice of ram diameter and chamber displacement sets the resolution of leg movement.

The apparatus 2 of Figure 1 includes a controller 22 for controlling operation of the motor 18, radial piston machines 20 and hydraulic rams 8a-8h, 10a-10h, 12a- 12h, 14a-14h, in such a way as to control movement of the legs. Valve timing in many modes of operation has to be precise to less than a millisecond, which is achieved using the controller 22, which includes a microprocessor. The controller 22 is operable to control the legs to perform step operations in sequences thereby to cause the apparatus to move using a walking motion. One digital bit in the microprocessor can move a leg by as little as one millimetre and it is possible to have split-cycle operation to reduce this even further. This means that the main body 2 of the vehicle can move at a steady velocity along any chosen course while the microprocessor/computer of the controller 22 solves the geometrical equations for the quadrilateral linkages 16a-16h.

Any suitable controller 22 can be used, for example the controller 22 may comprise a suitably programmed PC or may comprise dedicated circuitry, for example an ASIC. The controller 22 may be provided in a watertight housing. Electrical connections between the controller 22 and other components may be provided in watertight packaging.

A user interface may also be provided, and connected to the controller 22, thereby allowing a user to provide instructions to the controller to control operation of the apparatus. The user interface may comprise a PC or other computer terminal, for example located above water, or may comprise a dedicated control panel. The control panel may comprise a joystick or one or more buttons enabling a user to control direction and speed of movement of operation of the apparatus, and may be watertight and operable underwater.

Energy for movement and subsequent operations can be supplied as three- phase electricity through a drum 24 of cable at the rear of the vehicle. The drum fits inside the frame 4 and the cable is able to deliver 100 kW at 415 volt three-phase over a length of around half the width of the Pentland Firth, when the cable is fully paid out from the drum 24. Thus, the apparatus 2 of Figure 1 has a range such that it can be used for installing seabed attachments for tidal stream plant in that location. The maximum range from shore of the apparatus 2 is around 5 km, but the range can be increased by increasing the length of cable and/or the size of the drum. More power can be delivered in alternative embodiments in which a rotary transformer is fitted inside the drum 24.

It is a feature of the embodiment of Figure 1 , that the controller is able to control operation of the motor 20, hydraulic system 18 and rams 8a-8h, 10a-10h, 12a-12h, 14a-14h thereby to control operation of the legs 6a-6h and to cause the apparatus to move along the bed of a body of water, for example the sea bed.

The controller 22 can control movement of the legs 6a-6h to perform a sequence of step operations, each step operation comprising lifting at least one leg off the ground, moving the at least one leg and replacing the at least one leg on the ground. The controller 22 can thus control the apparatus 2 to move with a walking motion. The maximum single step size of the embodiment of Figure 1 in a forward or backward direction is around 83 cm, and the maximum walking speed is around 28 cm/second. The maximum step sizes and maximum speeds can vary between different embodiments. Two-legged creatures can walk only with a series of controlled recoveries from falls. Small judo-fighters are trained to topple much larger opponents by preventing this recovery movement. For a walking vehicle to be unconditionally stable without continuous balance control it is necessary for a vertical line through the centre of gravity to pass inside a polygon drawn around the outside of the feet which are in contact with the ground. It is a feature of the embodiment of Figure 1 that, in certain modes of operation, action of the legs 6a-6h is controlled by the controller 22 in such a manner that the unconditional stability condition of the previous sentence is maintained.

During rapid movement on fairly level ground in one mode of operation, the weight of the apparatus 2 is taken at a first stage by the legs 6a, 6e, 6c, 6g of rows 1 and 3 whilst the legs 6b, 6f, 6d, 6h of rows 2 and 4 are advancing. At a second stage, the weight of the apparatus 2 is taken by the legs 6b, 6f, 6d, 6h of rows 2 and 4 whilst the legs 6a, 6e, 6c, 6g of rows 1 and 3 are advancing. The first and second stages are then repeated and the apparatus 2 moves across the bed of the body of water with a walking motion.

In more difficult conditions, such as climbing rough slopes, the weight will be taken by seven legs (for example, 6b-6h) while the eighth (for example, 6a) is moving to a new position and testing its grip before allowing all legs (6a-6h) to advance the vehicle by sequential operation of the legs. If the bed of the body of water consists of firm rock it is possible for the apparatus 2 to climb slopes of up to 45 degrees. While one advancing leg is moving forward it needs only enough forward force to overcome water drag, bearing friction and its own weight up any slope. However the legs on the ground generally exert a larger rearward force in those circumstances, enough to move the vehicle up a slope and recover energy on the way down.

In alternative modes of operation, faster movement may be obtained by operating four legs at a time. For example, step operations can be performed using the two legs of each of rows 1 and 3, whilst simultaneously each leg of rows 2 and 4 is pushed backwards against the ground. Thus, the legs of rows 1 and 3 can be off the ground moving forward to the next foothold whilst the legs of rows 2 and 3 are generating forward thrust. The step operations are then repeated using the two legs of each of rows 2 and 4, whilst pushing with each of the legs of rows 1 and 3. The centre of gravity of the apparatus 2 is always inside a quadrilateral formed by the feet that are in contact with the ground. Such a mode of operation is suitable for use on easy ground. Single leg movements and foothold checking may be used for tricky climbs or on poor ground as already described. It is a feature of the apparatus 2 that it can be operated to walk in any lateral direction, for example, forwards, sideways, backwards or diagonally by any desired distance by suitable operation of the legs 6a-6h. Such movement is not possible using tracked vehicles, without turning, and can be particularly useful when performing installation operations in confined areas or on rough ground.

The apparatus 2 can also be tilted by suitable operation of the rams 8a-8h, 10a-10h, 12a-12h, 1 a-14h. For example the body of the apparatus 2, to which the legs 6a-6h are attached, and comprising the frame 4, can be tilted in any desired direction by suitable operation of the rams 8a-8h, 10a-10h, 12a-12h, 14a-14h. The apparatus 2 can be rotated in yaw about a vertical axis around a point, and can also be pitched and rolled if desired. In a simple example, if the rams 8a-8d, 10a-10d are operated to lift all of the legs 6a-6d on one side of the apparatus 2, the body of the apparatus 2 will tilt towards that side. The pitch, yaw and roll angles of the body 2 can be set precisely by suitable operation of the rams 8a-8h, 10a-10h, 12a-12h, 14a- 14h to obtained a desired operating position. The apparatus 2 can then be held stationary in that position if so desired.

Rotation of the apparatus 2 can be particularly useful in positioning tools attached to the apparatus to a desired operating position, for example in order to perform drilling or assembly tasks. Again, such operations are difficult or impossible to perform using a tracked vehicle, as the body of the tracked vehicle is usually at a fixed height above the ground determined by the dimensions of the wheel and track arrangement.

It is a feature of the embodiment of Figure 1 that, as mentioned above in connection with the climbing of a slope, the controller 22 may test the grip of the apparatus once a leg (for example, 6a) has been moved to a new position, before allowing movement of further legs (6b-6h). Any suitable method for testing the grip of the apparatus 2 may be used, for example a push operation may be used that comprises pushing at least one leg towards the ground and determining a response to the push operation. For instance, in one embodiment, force is applied to one or more of the legs 6a-6h (for example to the leg that has been moved) by operation of the rams. The force may be applied, for example, in a substantially downward direction. Movement of the one or more legs 6a-6h in response to the applied force may be determined, for example, by way of a detected variation of the pressure within the hydraulic system. The controller 22 may alter the position of one or more legs 6a-6h in order to seek a more stable footing in response to the push operation, for example in response to detection of movement, or variation of pressure, above a threshold,. The apparatus 2 is able to move over the bed of a body of water in stable fashion over a variety of terrain by way of hydraulic control of operation of the legs 6a to 6h as described. The apparatus is also able to cope with a wide variety of sea conditions.

As mentioned above, the apparatus 2 is designed to have an open floor. In various embodiments, at least 10%, least 30%, between 10% and 90%, or between 30% and 70%, of the area of the apparatus in a direction perpendicular to the bed of the body of water, when the legs are in contact with the bed of the body of water, is open and/or allows passage of water.

The apparatus 2 is also substantially open at the sides. In various embodiments, the apparatus is configured so that at least 50%, between 50% and 95%, or between 70% and 90% of the area of the apparatus in a direction parallel to the bed of the body of water, when the legs are in contact with the bed of the body of water, is open and/or allows passage of water.

Even though the vehicle frame 4 is designed to be as open as possible and, additionally, its members can be given streamlined fairings, there will sometimes be substantial forces from waves and currents. Pressures in the rams 8a-8h, 10a-10h, 12a-12h, 14a-14h are a good measure of the forces on the frame and in some embodiments sensors are used to measure such pressures. The controller 22 in some such embodiments is configured to control the hydraulic system 18 in dependence on the measured pressures, for example to vary pressure applied to the rams in response to signals from the at least one sensor. For instance, the controller 22 may control the actuation system to supply correcting pulses of oil to maintain a desired position and orientation of the apparatus 2 with a desired geometrical accuracy. The apparatus 2 can therefore in practice be more stable than calculations of frame deflection under particular sea conditions might suggest.

Figure 3 shows a front view of the apparatus with wide leg separation and legs 6a-6h retracted to give a low centre of pressure. Sliding due to the combined effect of drag forces from waves and currents is unlikely on rough seabeds and stability calculations are dominated by the need to prevent toppling in roll due to the drag force from side currents. Ballast is added to the apparatus 2 of Figure 1 to bring the total weight to 30 tonnes, and thus roll should not occur at water velocities below 11 metres per second. A significant feature of the embodiment of Figure 1 is that the frame 4 of the apparatus 2 has an open floor so that stagnation pressure cannot act on a large area. Figure 3 shows the apparatus 2 laying cable from the cable drum 24 into a trench on the seabed, the trench having been cut using tools mounted on the apparatus 2.

The apparatus 2 of the embodiment of Figure 1 is able to move in stable fashion over the bed of a body of water in a variety of terrain and under a wide range of sea conditions. The apparatus 2 can be used for a wide range of applications, for example relating to the installation or maintenance of wave, tidal or water current devices. The stability of the apparatus 2 and its ability to place itself, in a stable configuration, in a range of different heights and linear and angular orientations makes it particular useful as a platform for the mounting and operation of a variety of tools for performing underwater operations.

In the embodiment of Figure 1 , a front face 30 of the chassis 4 can be used to mount, for example, a drill (for example, comprising an oblique drilling head for drilling inclined holes), a chain saw, a grout pump, or any other suitable tools. A mount for such tools can be attached to the front face 30, or the tools can be mounted to the front face 30 directly.

The apparatus 2 also includes a space 32 for installation of a vertical drill. The vertical drill can be mounted to parts of the frame of the chassis 4 surrounding the space 32. The apparatus also includes a space 34 for installation of a trench cutting disk, or a pair of trench cutting disk devices. The trench cutting disk device or devices can be mounted to parts of the frame of the chassis 4 surrounding the space 34. Each trench cutting disk device can comprise an inclined wheel with embedded diamond abrasive which can cut a V-shaped trench in rock.

A rear face 36 of the chassis 4 can be used to mount, for example, pulley arms for drum wrap or cable laying. Arms mounted to the rear face can be used, for example, to pick rock from the seabed (for example from a trench dug using the apparatus 2) or to lay cable. A mount for such tools can be attached to the rear face 30, or the tools can be mounted to the rear face 30 directly.

It will be understood that a variety of other tools can be mounted to the apparatus 2, which provides a stable platform that can be used to position accurately such tools. The tools that are used will depend on the particular tasks that are required to be performed.

In the case of installation of wave and tidal stream devices on the sea-bed, for example, there may be inconvenient outcrops on the sea-bed unsuitable for standard seabed attachment due to variations in the erosion rates of different rocks. Such outcrops may have to be removed. One way of removing outcrops of rock is by using chain saws. Copur et al, "Cutting Performance of Chain Saws in Quarries and Laboratory" (www.qarone.com/db/press/73670595684.pdf) reports cutting rates for chain saws. Saws are now available with cutting depths up to 3.4 metre, and average cutting rates in marble of nearly 10 square metres an hour from a 50 kW drive. Even longer saws could be used and better performance may be expected with full immersion underwater.

Chain saw cuts must be planned so that the gap cut does not close at the end of the operation and so jam the blade. This can be done for removing an outcrop if the first cut is horizontal and slightly less than a blade length below the top of the rock outcrop. This is followed by a series of vertical cuts with the slices falling away from the chain saw.

In an embodiment illustrated in Figures 4a to 4f, a hydraulically operated parallelogram linkage 42, similar to parallelogram linkages 16, is mounted to the front face 30 of the chassis 4. A chain saw 40 is mounted to the parallelogram linkage 42.

If a chain saw 40 is mounted on a parallelogram linkage 42 as shown in figures 4a to 4d it will be constrained to maintain a defined angle but will move in an arc. The arc offset can be compensated by the right amount of rearward motion of the apparatus to the point where the parallelogram angles are at 90 degrees followed by the right amount of advance. This allows the saw to remain in the cutting plane.

Two convenient shapes for seabed attachments are a cone, as proposed for example in relation to a vertical axis rotor by Salter & Taylor (Power Conversion Systems for Wave Energy, Proc. I. ech. E. Journal of Engineering in the Marine Environment, Part M, vol. 216, pages 1-27, 2003), and a prismatic trough suggested for a multiple plate attachment for Oyster. Appropriately shaped regions can be cut in the sea bed by the controlled movements of the apparatus 2 and operation of the chain saw 40, with the cone shape needing a small increase in the tooth clearance of the chain saw 40. Both cone and trough attachments are pulled down into position on the sea bed by post tensioning strands which are drilled into the rock.

Figures 4a to 4c illustrate the apparatus 2 cutting a cone shaped region in the rock using the chain saw 40. A cone-shaped attachment 44 is deposited in the region. The attachment 44 comprises 60 mm square hollow-section sections welded on each side of a triangular tongue.

In the embodiment of Figures 4a to 4f, the apparatus 2 also includes tilting frame 46 that includes a drill tool holder for holding a drill, which can be inclined at any angle. The drill is used to drill a 50 mm hole through the hollow sections of the attachment 44 and into the rock of the seabed. The apparatus 2 shown in Figures 4a to 4f also includes further tools, mounted on front face 30, including a tool for pushing 12 metre long Macalloy bars 48 into the rock holes, a grout hose for injecting grout leaving a suitable stretch length, a nut feeder for fitting nuts and a tensioner for tensioning the Macalloy bars to the chosen value. If necessary, longer bar lengths could be uncoiled from a drum. The result is an attachment in which tensile forces reduce the preload in the rock but not to zero while compressive forces increase it but not close to its crushing stress. The stretch length means that the post-tension bars are under constant tension and do not fatigue. The area of tongues or cones is maximum load divided by 0.15 times rock strength. For a 50 MW vertical-axis rotor in the Pentland Firth the maximum load on a tri-link leg could be 30 N. The three cones would have a diameter of 3.5 metres. The weight in water of the rock removed would be about 60 tonnes and so it could be floated away by an air-filled sphere 5 metres in diameter. The removed rock may, for example, be sliced up and deposited at a suitable location, for example to provide a lobster nursery or other shelter for marine organisms.

The embodiment shown in Figures 4a to 4f can be used to install a flap-type device for example an Oyster (RT ) device produced by Aquamarine Power Limited, and/or a device as described in one or more of GB2476274, WO2011/073626, GB 2472093, WO 2011/010102, US 2011/0006005, GB 2467011 , WO 2010/084305, WO 2010/049708, WO 2009/044161 , or WO 2006100436.

It is necessary to align the bearings of the flap with holes 59 in vertical plates 58 of the seabed attachment 44 described above. Conical dowels with acute angles will not be forced out of mating holes but must be aligned to a precision of a millimetre.

After cutting the trough shown in figures 4a to 4f the next step is to use the chainsaw tool to cut three notches 50 in the rock to either side of the installation 44 as shown in figure 5. The notches are at the corners of an isosceles triangle with its base perpendicular to the flap rotation axis. The outermost pair of notches have a 60 degree angle. The notches on the bases of the triangles have their outer slopes at 30 degrees outward of the vertical and their inner slopes at 60 degrees inwards of the vertical. This notch arrangement allows the location of a drum-shaped structure 52 which acts as a chock. The choice of slopes gives a strong resistance to outward movement. The apparatus 2 is able to locate notches 50 to within 100 mm of the installation position.

The top and sides of each chock 52 carry three stacks of flat rubber Vetter bags 54 which were designed for gentle lifting of aircraft and the more robust lifting main battle-tanks. The bags 54 are filled with water and some air. The height of stack of bags 54 will be chosen to suit the maximum wave amplitude for which we wish to install the flap device. The area and working pressure of the bags 54 is chosen to suit the maximum flap loads which will be expected to occur during the installation.

The chocks 52 have air compartments which make them neutrally buoyant.

Apparatus 2 carries chocks 52 to the installation site and place them in the notches 50. The air compartments in the chocks 52 can then be flooded to give a down force to resist wave loads.

The flap, part of which is shown in Figure 5 is forced into contact with the Vetter bags 54 by a reduction of flap buoyancy and/or ropes round fairleads on the seabed attachment. The initial placement accuracy of bag contact is of the order of 1.5 metres.

Valves (not shown) between bags 54 and from bags to the sea can be opened and closed according to the position of the flap 60 to its final location. If a wave force is in the required direction then bags 54 under pressure can release water to allow movement in the desired direction but will oppose motion in the unwanted direction. The controller 20 of the apparatus 2 can be used to control operation of the valves, or a separate controller can be used. All of the intelligence is directed at valve timing with power provided by wave action. Once the flap position is correct dowels can be inserted into tongue plates of the attachment 44, the chocks 52 restored to neutral buoyancy and removed for use with the next installation.

Walking vehicles are more suitable than tracked ones for work needing multiple degrees of freedom over rocky seabeds and can achieve sub-millimetre precision with digital hydraulics. Chain saw attachments can be used for seabed cosmetic surgery and for cutting troughs or cones for post-tens^'ioned seabed attachments. Designing vehicle frames to the envelope of ISO sea containers allows fast, low cost transport almost anywhere in the world. Vetter bags can take large contact forces spread over large areas and so low local stresses. Controlled operation of valves between bags can allow wave forces to give precise location of plant to seabed attachments. The vehicle of the described embodiments can act as a stable and accurately controllable platform for sub-sea operations.

Various alternative or additional features can be provided in variants of the described embodiment or in alternative embodiments.

For example, in one alternative embodiment a sonar apparatus is mounted to the walking apparatus 2 and is directed towards the area of the bed of the body of water in the vicinity of the apparatus. Sonar measurements are performed to determine regions of the bed of the body of water which seem to be relatively flat and/or stable enabling movement of the one or more legs to those areas. The results of the sonar measurements may be displayed to a user via a user terminal thus enabling the user to manually select areas to which to move the legs. Alternatively, the controller may automatically select areas to which to move the legs based on the sonar measurements.

Sequences of movements of the legs that result in a walking motion have been described, but embodiments of the apparatus are not limited to such sequences, and any suitable sequence of movement of the legs can be used.

As already mentioned, the apparatus 2 can include attachment regions in the form of lifting points or mounting points complying with the ISO R668 standard. The lifting points or mounting points can also be used to interconnect two or more apparatus of the described embodiment, for example using a fitting as used to attach together containers complying with ISO standards. The fitting may comprise a twistlock fitting. The fittings and attachment regions may be used to stack or load the apparatus or interconnect the apparatus with other apparatus. Each attachment region may comprise a twistlock fitting. By attaching several apparatus of the same or similar type together an underwater walking apparatus with greater stability or able to carry greater loads can be provided. That may be useful for particular tasks, for example carrying drills or other items longer than a certain length, or carrying supplies of grout.

In alternative embodiments other suitable attachment regions can be used to enable lifting, stacking, loading or interconnection.

Fairings can be provided, and any suitable type of fairing may be used. In certain embodiments, a fairing is provided for each leg to reduce drag forces on each leg. The fairings may be shaped as hydrofoils. Each fairing may extend over a desired proportion of the length of each leg, for example over 10% to 90% of the length of the leg, at least 20% of the length of the leg, at least 50% of the length of the leg, or between 20% and 50% of the length of the leg. Each fairing may be substantially neutrally buoyant and may be free to rotate, for example about low friction bearings, on a line through the centre of gravity of the fairing and forward of the centre of pressure of the fairing. The centre of pressure of most foil sections is about 0.25 of the chord of a foil aft of the nose. If the bearing is forward of the centre of pressure then the moment of the foil will tend to make it head into the flow and so reduce the drag to a minimum. A bearing might be 0.15 to 0.2 of chord aft of the nose. The drag on a hydrofoil can be about 1/40^th of the drag on a circular spar of diameter equal to the foil thickness. Thus, the use of hydrofoil-shaped fairings can greatly decrease the drag experienced by the legs in operation. In the embodiment of Figure 1 , each leg is moved by a combination of vertical and horizontal movements. That arrangement provides for a particularly stable configuration, and can be useful for stepping over large obstacles, but the apparatus is not limited to the use of such an arrangement. In alternative embodiments, the legs may be jointed or otherwise arranged to move in an arcuate path, without requiring a combination of individually controlled horizontal and vertical movements. In such embodiments, the controller may use polar coordinates in control algorithms used to control movement of the legs.

It will be understood that the present invention has been described above purely by way of example, and modifications of detail can be made within the scope of the invention.

Each feature disclosed in the description, and (where appropriate) the claims and drawings may be provided independently or in any appropriate combination.

Claims

1. An apparatus for movement along the bed of a body of water comprising a plurality of legs and a controller for controlling operation of the legs, wherein the controller may be configured to control operation of the legs so that in operation on a bed of the body of water the apparatus moves along the bed of the body of water.

2. An apparatus according to Claim 1 , wherein the controller is configured to control movement of the legs so as to perform a sequence of step operations, wherein each step operation comprises lifting at least one leg off the ground, moving the at least one leg and replacing the at least one leg on the ground.

3. An apparatus according to Claim 1 or 2, wherein the controller is configured to control movement of the legs so that, at a given time or at substantially all times, a vertical line passing through the centre of gravity of the apparatus passes through a polygon that would be obtained by drawing straight lines between feet of each of the legs that are in contact with the ground.

4. An apparatus according to any preceding claim, wherein the plurality of legs comprises at least 3 legs, optionally between 4 and 16 legs, further optionally 8 legs

5. An apparatus according to any preceding claim, wherein the plurality of legs are arranged in a plurality of rows, optionally in four rows.

6. An apparatus according to Claim 5, wherein the controller is configured to control operation of the legs to perform a step operation using each leg of at least one of the rows whilst substantially simultaneously maintaining each at least one leg, optionally each leg, of each other row in contact with the ground.

7. An apparatus according to Claim 6, wherein the controller is configured to repeat the step operation using the legs of each other row in turn.

8. An apparatus according to any of Claims 1 to 5, wherein the controller is configured to make the apparatus walk by performing a step operation using one leg at a time.

9. An apparatus according to any preceding claim, wherein after each step operation the controller is configured to perform a push operation that comprises pushing at least one leg towards the ground, and determining a response to the push operation.

10. An apparatus according to Claim 9, wherein the controller is configured to alter the position of at least one leg, for example by performing a step operation, dependent on the response to the push operation.

11. An apparatus according to any preceding claim, comprising, for each leg, at (east one ram operable to move the leg.

12. An apparatus according to Claim 11, wherein, for each leg, the at least one ram comprises a pair of rams, one ram of the pair positioned on one side of the leg and the other ram of the pair positioned on the other side of the leg, and optionally the pair of rams may be arranged to move the leg in a substantially horizontal direction.

13. An apparatus according to Claim 11 or 12, wherein, for each leg, the at least one ram comprises a ram arranged to move the leg in a substantially vertical direction.

14. An apparatus according to any of Claims 11 to 13, further comprising, for each leg, a linkage, optionally a quadrilateral linkage, for transmitting force from at least one of the rams, for example the pair or rams to the leg.

15. An apparatus according to any of Claims 11 to 4, further comprising an actuation system for actuating the rams, wherein the actuation system comprises a motor and at least one pump.

16. An apparatus according to Claim 15, wherein the at least one pump comprises at least one radial piston machine, the or each radial piston machine comprises a plurality of pumping chambers and each pumping chamber is selectively operable using a respective at least one valve to apply pressure to a ram, optionally to one side of a double acting ram.

17. An apparatus according to Claim 15 or 16, wherein the actuation system comprises at least one accumulator.

18. An apparatus according to any preceding claim, further comprising at least one sensor for sensing pressure, wherein optionally the or each sensor is arranged to sense pressure associated with a respective at least one of the rams.

19. An apparatus according to Claim 18, wherein the controller is configured to control operation of the rams, for example to vary pressure applied to the rams, in response to signals from the at least one sensor.

20. An apparatus according to Claim 19, wherein the variation in pressure applied to the rams comprise pulses of pressure, for example correcting pulses of pressure to counteract forces and/or movement experienced by the apparatus.

21. An apparatus according to any preceding claim, further comprising a sonar apparatus for performing sonar measurements on the bed of the body of water.

22. An apparatus according to any preceding claim, further comprising a frame, wherein the legs are mounted to the frame and the frame has a substantially open floor thereby to allow flow of water through the frame, for example upwards and downwards through the frame during underwater operation.

23. An apparatus according to any preceding claim, further comprising at least one tool.

24. An apparatus according to any preceding claim, further comprising a mount for mounting at least one tool and, optionally, the mount comprises a parallelogram linkage and the tool comprises a cutting tool, for example a chainsaw.

25. An apparatus according to Claim 23 or 24, wherein the at least one tool comprises at least one of a drill; a cutting tool, for example a chainsaw; a digging tool; a welding tool; or a grouting tool.

26. An apparatus according to any of Claims 23 to 25, wherein the controller is operable to control operation of the at least one tool.

27. An apparatus according to Claim 26, wherein the controller is configured to operate to control operation of the apparatus and of the at least one tool in combination thereby to move the apparatus and/or tool and to perform at least one tool operation.

28. An apparatus according to any preceding claim, comprising a water-tight housing wherein the controller is within the water-tight housing

29. An apparatus according to any preceding claim, further comprising at least one fairing.

30. An apparatus according to Claim 29, wherein each fairing is arranged so as to reduce drag on at least one leg.

31. A method of performing operations at the bed of a body of water, comprising controlling operation of an apparatus comprising a plurality of legs, the control of operation of the apparatus comprising controlling the legs so that the apparatus moves over the bed of the body of water.

32. A method according to Claim 31 , wherein the apparatus comprises an apparatus according to any of Claims 1 to 30.

33. A method according to Claim 31 or 32, wherein the apparatus comprises at least one tool and the method comprises moving the apparatus and performing at least one operation using the at least one tool, wherein the operation forms part of an installation or maintenance procedure of a wave power, tidal power or water current power system.