This invention relates to sub-aquatic generators which are direction sensitive and, as such, are required to be rotated underwater to be oriented in a desired way. In particular, this invention relates to sub-aquatic generators for utilisation in bidirectional water flows such as tidal waters. The invention may be advantageously utilised with non-buoyant or so called heavy sub-aquatic generators.

Background of Invention

Sub-aquatic power generating apparatuses are generally well known and currently the subject of much research and development. One type of sub-aquatic power generating apparatus is the tidal turbine generator 10 shown in Figure 1. This generator 10 includes a turbine 12 mounted on a support structure 14 which is fixed, either by gravity or some other suitable fixing means, to the sea bed 16. The turbine 12 includes a rotor 18 having a plurality of turbine blades 20 which are arranged to provide rotative force about a principal axis 22 when placed in an appropriate flow of water 24. The rotor 18 is used to drive an electrical machine in the form of an electromagnetic generator (not shown) which is housed within the so-called nacelle or casing 26 of the turbine 12. The electromagnetic generators currently used in tidal turbines are typically conventional in that it simply converts the rotational mechanical movement provided by the rotor into electrical energy. The generated electrical energy is exported into an electrical network or grid by a suitable arrangement and connection of cables (not shown).

As will be appreciated by the skilled person, the efficiency of many sub-aquatic turbine arrangements, and other types of sub-aquatic power generators, is affected by the direction of the flow 24 relative to the orientation of the power generating equipment. Hence, it is generally desirable to provide a power generating apparatus with some functionality to allow for varied orientation of the machine in respect to the flow conditions. Such requirements may be minor changes in a particular flow or bidirectional changes in tidal waters.

The present invention seeks to provide an improved arrangement for rotation of a sub- aquatic generator. Statements of Invention

In a first aspect the present invention provides a power generating apparatus, comprising: a support structure; a power generating module, wherein the power generating module is adaptably attached to the support structure so as to have a fixed configuration and rotatable configuration; and, a release actuator for placing the power generating module in the rotatable configuration from the fixed configuration.

Providing a releasing actuator to move the power generating module from the fixed configuration to the rotatable configuration allows a heavy turbine to be used whilst still allowing for rotation of the power generating module. It may also be advantageously used with a neutrally or slightly buoyant turbine structure.

The power generating apparatus may generate electricity. The power generating module may include a turbine. The turbine may include one or more bladed rotors. The power generating module may be for use in any directional waters. The directional water may be bidirectional, such as tidal waters. By bidirectional, it is to be understood that the waters may only be generally bidirectional and not necessarily separated by 180 degrees. Further, the rotation may account for minor fluctuations in a general flow direction.

The support structure and power generating module may be physically connected in the fixed and rotatable configurations. The physical connection may be provided by one or more bearing arrangements. Thus, the lifting device may be arranged to urge, drive, push or thrust the support structure and power generating module apart thereby reducing the friction between one or more contacting surfaces but without physical separation. Alternatively, the lifting device may be arranged to physically separate the mating surfaces between the support structure and power generating module when moving into the rotatable

configuration.

The power generating apparatus may further comprise a clamping device arranged to place the power generating module in the fixed configuration from the rotatable configuration, so as to prevent rotation. The clamping device may be a clamp or other arrangement which provides an attachment between the support structure and power generating module which prevents relative rotation between the two components.

The lifting device may include a resilient bias. The resilient bias may be a sprung

arrangement. The spring arrangement may include one or more springs arranged in an array. The springs may be Belleville springs or the like. The lifting device may urge the power generating module and support structure apart by a distance. The distance may be in the order of a few millimetres.

The clamping device may have three configurations. The three configurations may be a fixed configuration in which relative rotation between the support structure and power generating apparatus is not possible, a rotatable configuration in which the relative rotation is possible, and a free configuration in which the support structure and power generating apparatus may be separated for deployment or retrieval purposes.

The power generating module may be negatively buoyant or heavy. By heavy it is meant that relative density with respect to water (saline or otherwise) is greater than 1. That is, the power generating module has a greater density than the water in which it is immersed.

The power generating module is rotatably mounted on at least one bearing arrangement when in the rotatable configuration. The power generating module may be rotatably mounted on the at least one bearing arrangement when in the fixed configuration. However, the bearing arrangement may not be effectively operable due to the clamping device.

The lifting device may include one part of the at least one bearing arrangement.

The power generating apparatus may be rotatable about a vertical axis.

The power generating apparatus and support structure may include respective intimately contacting mating surfaces when in the fixed configuration and the lifting device may separates the mating surfaces when moving from the fixed configuration to the rotatable configuration.

The clamping device may be arranged to constrict around respective parts of the power generating apparatus and support structure so as to clamp the mating surfaces together.

The lifting device may be an active device comprising one or more actuators. The actuators may be one or more taken from the group comprising: hydraulic, pneumatic or electrical. The actuators may be individually operable.

The lifting device may be operable to tilt the power generating module and move the yawing axis away from vertical such that the power generating module yaws under its own weight. By yawing axis it is meant the axis about which the power generating module yaws or rotates in the water so as to be orientated in a different direction.

The power generating apparatus may further comprise a ballast system which is actively controllable to move the centre of gravity of the power generating apparatus. The ballast system may include one or more tanks. The tanks may be controllably floodable with water or a gas. In a second aspect, the present invention provides a method of rotating a power generating apparatus having: a support structure; a power generating module, wherein the power generating module is adaptably attached to the support structure so as to have a fixed configuration and rotatable configuration; and, a lifting device for placing the power generating module in the rotatable configuration from the fixed configuration, the method comprising the steps of: generating power in a first orientation with the power generating module; placing the power generating module in the rotatable configuration using the lifting device; rotating the power generating module to a second orientation; placing the power generating module into the fixed configuration; and, generating power in the second orientation.

Where the power generating apparatus includes a clamping device to place the power generating apparatus in the fixed configuration, the method may further comprise the steps of: releasing the clamp such that the lifting device can place the power generating module in the second configuration; and, tightening the clamp to place the power generating module in a fixed configuration.

The method may further comprise the steps of: controlling the lifting device so as to differentially lift the power generating module so as to tilt the yawing axis away vertical to allow gravitational yawing.

The lifting device may be a hydraulic arrangement. Where the power generating module and support structure include respective intimately contacting mating surfaces in the fixed configuration the hydraulic arrangement may include a fluid path for introducing fluid between the mating surfaces so as to create lift.

The mating surfaces may define an interface between the support structure and power generating module. The interface may include at least one cavity for receiving the fluid.

The fluid may be provided to the cavity and may exit the interface via at least one exhaust.

The interface may include at least one resilient seal which is configured to restrict the exhaust flow to the exhausts.

The pressurised fluid may be provided by an accumulator which is configured to be charged by the power generating module.

The pressurised fluid may be provided by a pump. The pump may be connected to the power generation module. The power generating apparatus may comprise a plurality of cavities linked by

interconnecting conduits. The power generating apparatus may further comprise a hydraulic arrangement configured to provide a hydraulic bearing between the support structure and power generating module.

Description of Drawings

Embodiments of the invention will now be described with the aid of the following drawings of which:

Figure 1 shows a conventional sub-aquatic tidal generator

Figures 2a and 2b show a sub-aquatic tidal generator according to the present invention in a first orientation and a second orientation.

Figures 3a, 3b and 3c show schematic cross sectional details of the sub-aquatic generator shown in Figures 2a and 2b in respective fixed, rotatable and releasable configurations.

Figures 4a, 4b, 4c show an alternative embodiment of the invention.

Figure 5 shows a hydraulic lifting arrangement.

Detailed Description of Invention

Figures 2a and 2b show a sub-aquatic power generating apparatus which is similar in many respects to the turbine shown in Figure 1. Thus, with reference to Figure 2a, there is shown a sub-aquatic generator 210 having a support structure 214 which is attached to the sea bed 216 and a power generating module having a turbine 212 and a support 213 for attaching it to the anchored support structure 214. The turbine 212 includes a bladed rotor 218 which is rotatably driven about the principal axis 222 of the generator 212 when placed in a flow of water 224 such as, for example, a tidal flow 224. The rotational power generated between the interaction of the flow 224 and the rotor 218 is harnessed within the housing 226 of the turbine 212 by driving an electrical machine, thereby generating electricity for export into a network or grid (not shown).

The support structure 214 is in the form of a columnar structure or pylon which extends from the sea bed 216 in a generally vertical direction so as to provide a platform to which the power generating module can be adaptably attached to when in use. The platform may also include facilities to connect various services and the like, such as connectors to transfer electrical power, control signals or performance data etc. The attachment of the support structure 214 to the sea bed 216 may be achieved by any suitable means such as piles buried into the sea bed 216 or it may be constructed so as to have a mass suitable for gravitational anchoring of the power generating apparatus. It will be appreciated that the support structure 214 may advantageously include suitable strengthening or support members and may be take a preferable geometric form such as a tripod for example.

The adaptable attachment between the turbine 212 and support structure 214 is such that the turbine 212 may be placed in a fixed configuration relative to the support structure 214, and thus the tidal flow, or in a rotatable configuration with the aid of a lifting device so that the turbine 212 may be rotated and orientated relative to a directional flow of water 224 in a predetermined way. Hence, the turbine can be held in a first orientation for a first flow direction, as shown in Figure 2a, before being placed in a second orientation, as shown in Figure 2b, in which the turbine 212 has been rotated by 180 degrees about the vertical axis of the support structure, to harness power from a second directional flow 224. In practice, the two flows may correspond to ebb and flood tides in a given location or more minor changes in a given directional flow. It will be appreciated that having a continuously variable rotation is particularly advantageous as it allows the orientation of the turbine to be adjusted to account tidal flows which do not come from directions of 180 degrees apart . Further, the rotation may account for minor fluctuations in the direction of a flow.

It is to be appreciated that by adaptably attached it is meant that the attachment of the power generating module 212 to the support structure 214 is such that it can be changed, altered or adjusted or the like to provide the fixed and rotatable configurations, but while the two components remain physically connected in some way. In one embodiment, the power generating module 212 is constructed so as to be negatively buoyant or heavy such that it sinks when placed in the water. Thus, to deploy the turbine 212, it would be placed in the water and lowered in a controlled way using an appropriate ship bourn crane or the like whilst being guided into place and correctly aligned with the platform and any connections. Once in place, the turbine 212 can be adaptably attached as required by a suitable mechanism, such as the clamp arrangement 228 described below. Negative buoyancy can be achieved by any known means such as the incorporation of ballast in the housing 226 of the turbine 212 or by flooding the housing 226 with water.

A clamp arrangement 228 for providing the adaptable attachment is shown in schematic cross-section in three different configurations in Figures 3a to 3c, respectively. With reference to Figures 3a-c, there is shown a turbine support in the form of a column 213 having a generally circular cross-section which extends down from the turbine housing 226 (as shown in Figure 2) and terminates in a flanged portion 230. The flanged portion 230 includes a flange 232 having a mating surface 234 on its distal, underside, and is constructed from a material and is dimensioned to provide the necessary strength and rigidity for the reliable attachment of the turbine 212 (as shown in Figure 2) to the support structure 214.

The upper side 236 of the flange generally and evenly tapers from the radially outer edge 238 of the flange 232 so as to provide an increased thickness towards the junction between the flange 232 and the turbine support column 213. The purpose of the flange 232, as is described below, is to provide a frictional engagement between the turbine 212 and support structure 214 with the aid of the clamp 250.

The mating surface 234 of flange 232 which is attached to the turbine support column 213 abuts a corresponding mating surface 240 provided on the opposing terminal end of the support structure 214, which also takes the form of a flanged, generally circular columnar tube.

The flanged portion of the support structure 214 is similar to that of the terminal end of turbine support 213 and is dimensioned such that the flange 244 has an approximately coincident radial outer edge 246 and corresponding angled taper 248 provided on the respective underside of the flange 248. Hence, when the mating surfaces 234, 240 are aligned and in intimate contact, the upper and lower flanges 232, 244 form, in cross section, a truncated isosceles triangle which diverges from the coincident outer radial edge 238 of the flanges 232, 244 having the major axis along the mating surfaces 234, 240. It will be appreciated that other formations and taper angles etc may be implemented whilst retaining the resultant axial compression functionality which is elaborated on below.

In order to couple the turbine column and support structure column, a circumferential clamp 250 is provided which extends around the opposing flanged portions 230, 242. The clamp 250 is made up from a plurality of arcuate sections which are movable relative to each other so as to constrict (or dilate) around mated flanged portions 230, 242 so as to bear upon and urge the respective flanges 232, 244 together. In this way, the friction between the components experienced at the mating surfaces 234, 240 is increased and the rotation of the turbine 212 is prevented. Hence, a fixed configuration is provided. The specific arrangement of the clamp and a suitable method of actuation are described in GB2448710, which is incorporated by reference, which shows various examples of multiple segmented clamps and hydraulic actuation means.

The clamp 250 achieves the axial compression across the mating surfaces 234, 240 by engaging with tapered surfaces of the flanges 232, 244 which act to translate the radial constriction of the clamp 250 into an axial compression across the joint. To achieve this in the present embodiment, the clamp 250 is of a generally annular construction having an approximate U-shaped cross-section, the inner surface of which is shaped to correspond to the truncated wedge shape of the flanges 232, 244. Thus, the inner surface of the clamp 250 and the tapered surfaces of the flanges 232, 244 may add to the frictional retention of the support structure 214 and turbine support column 213 if required but, in the present embodiment, the materials chosen for the tapered surfaces give a low friction interface so as to allow for easier rotation of the turbine and an increase in compressive load across the mating surfaces 234, 240. The general clamping arrangement 228 also includes a lifting device 252 in the form of a resilient bias 254 which is located between the turbine support column 213 and support structure 214. The lifting device is arranged to axially urge the two components apart against the compression provided by the clamp and/or the weight of the turbine 212 thereby allowing it to rotate more readily. Thus, in the described embodiment, releasing the clamp 250 allows the lifting device 252 to place the power generating module 212 in the rotatable configuration from the fixed configuration.

In this described embodiment, the resilient bias 254 is in the form of a plurality of springs, for example, one or more suitably dimensioned Belleville springs, which are arranged in an evenly distributed circular array between respective opposing faces 256, 258 of the turbine support 213 and support structure 214. However, the skilled person will appreciate other forms of resilient bias may be used as required to fulfil the described function.

The opposing faces 256, 258 of the embodiment are provided by a recess which is provided at the radially inner edge of the terminal end face of the support structure 214, and the corresponding terminal end face of the turbine support 213. However, the skilled person will appreciate that there are various ways to provide the opposing faces.

The power generating apparatus includes a bearing arrangement on which the turbine may rotate when in the rotatable configuration. The bearing arrangement in the described embodiment is part of the lifting device 252 . Hence, there are provided corresponding races 262, 264 on the opposing face of the turbine column 213 and at the distal end of the resilient bias 254 with a ball bearing 266 or similar located therebetween. Other low friction bearing arrangements, such as wheels or plain bearings may also be implemented.

The lifting device 252 is attached to the power generating module 212 such that it can be more readily serviced when the power generating module is scheduled for retrieval and repair. Hence, the turbine race 262 is fixedly attached to the turbine support, whilst the support race 264 is free to rotate either with, or independently to the resilient bias 254.

Hence, there can be relative movement between the resilient bias and the turbine support, but with the resilient bias 254 being free to move against the support structure so as to preventing any undesirable strain or wear between the respective components during a rotation. It will be appreciated that the position of the bearing arrangement and the resilient bias, or more generally, the lifting device, may be interchanged with respect to one another.

As shown in Figures 3a to 3c, the clamping arrangement 228 is actuable so as to have three different respective configurations: a fixed or clamped configuration; a rotatable

configuration; and, a free configuration.

The fixed configuration is achieved when the clamp is tightened so as to sufficiently axially compress and clamp the tapered portions and provide the associated restraining friction. The rotatable configuration is provided when the clamp 250 is opened slightly so as to allow the lifting device 252 to push against the turbine support, thereby urging the turbine in an upwards direction away from the support structure 214 and reducing the effective weight that bears down and the resulting friction between the mating surfaces 234, 240. The biasing force of the lifting device 254 can be such so as to reduce the friction to a predetermined amount but will typically result in a separation of the mating surfaces 234, 240 by a few millimetres. When in the rotatable configuration, the turbine can be rotated by an appropriate

mechanism, such as the thruster described in GB2441769, which is incorporated by reference.

When in the rotatable configuration, the clamp 250 is retained in close proximity to the flanged portions so as to provide a bearing surface and guide to help retain the axial alignment between the support structure 214 and turbine support column 213. It will be appreciated that additional friction reducing features may be introduced to the flanges 232, 244 or inner surface of the clamp 250. Such features may include bearings or the like. It will also be appreciated in some embodiments that the lifting device provides a restraining function to help keep the support structure and power generating module in axial alignment. In this case, it may not be necessary to have contact between the clamp and the flanges which may be advantageous in reducing the frictional contact and make rotation more readily achievable. Once in the desired orientation, the clamp 250 is tightened so as to compress the resilient bias 254 and place the power generating apparatus in the fixed configuration from the rotatable configuration. In this way, the power generating apparatus 212 is clamped so as to be prevented from being rotated. A further advantage of the described arrangement is that, when clamped, the bearing arrangement is not in the main load path of the power generating apparatus which reduces the requirements from the bearings allowing them to be less expensive and more readily maintained.

The free configuration is provided by fully opening the clamp 250 so as to allow the support structure 214 and turbine to be coupled and separated during deployment and retrieval operations respectively.

It is to be noted that the fixed and rotatable configurations in the above described arrangements do not necessarily require the physical separation of the power generating module 212 and support structure 214. In some situations it will be sufficient for the lifting device 252 to simply reduce the pressure on the mating surfaces 234, 240 and the associated frictional forces which help retain the power generating module 212 in the fixed configuration. In this instance, the rotatable configuration may be such that there is no physical contact between the clamp and either or both of the turbine support 213 and support structure 214.

An alternative arrangement is shown in Figures 4a-c in which the power generating apparatus 410 is broadly similar to those described above but which includes an active lifting device 452 rather than a passive one. The active lifting device 452 is in the form of a plurality of linear actuators 454 arranged to differentially lift the power generating module 412 which allows it to gravitationally yaw, that is, rotate under its own weight.

To enable this, the power generating module 412 of the described arrangement has a centre of gravity 468 which is offset from the vertical axis 430 of the support structure 414. This may be achieved by choosing the location of the turbine support 413 relative to the power generating module 412 such that the centre of gravity is offset, or by using an active system such as a ballast arrangement (not shown) which is flooded when rotation is required.

Having a ballast system is preferable as it reduces the moment which would otherwise act on the clamp 450 in the case where the centre of gravity is permanently offset relative to the support structure axis 430. It will be appreciated that the ballast system may be arranged to pump water between locations in the power generating module rather than simply flooding a single location. It will also be appreciated that the centre of buoyancy, which may be different to the centre of gravity, will need to be factored in to any given design to allow for effective rotation.

The linear actuators 454 of the described arrangement are hydraulic rams which are arranged in a circular array around the perimeter of the support structure 414 and turbine support interface, preferably being anchored to the turbine support for the aforementioned reason of servicing etc. The actuators are individually operable and of a number and distribution such that the power generating module 412 can be tilted such that the longitudinal axis 470 of the turbine support and yawing axis can be tilted from vertical so as offset 472 by a predetermined amount. This raises the heavier portion of the power generating module 412 which falls under gravity so as to yaw the turbine. The predetermined amount by which yawing axis 470 is tilted will depend on the speed of rotation required and the distribution of mass of the power generation module 412. However, a few degrees would be a typical figure for most applications. Further, it may be desirable to configure the actuators such that the direction of rotation can be chosen, for example, to avoid tangling of cables of the like.

In use, the turbine is oriented in a first direction for power generation. At a predetermined time, normally during a period of minimal flow or slack water, the clamp 450 is partially released and the actuators differentially operated so as to tilt the power generating module 412 and yawing axis 470. Once tilted, rotation will occur until the heavier portion is at the lowest point (taking any equilibrium between any frictional forces etc into account) at which point the actuators 454 may be lowered to realign the yawing axis 470 to vertical.

It will be appreciated that, when a ballast arrangement is employed the ballast chambers may be flooded once the power generating module 412 has been tilted, thus reducing the load which needs to be initially lifted by the actuators 454. To this end, the lifting device 452 may include a suitable mechanical locking device which locks the actuators 454 in place once extended so as to more readily and safely accommodate the additional weight. Once the rotation is complete, the actuators 454 are lowered and the clamp 450 retightened.

In some embodiments it may be advantageous to control the yawing rate by altering the differential lift or the ballast. In this instance it will advantageous to include some form of sensing arrangement to track rotation of the turbine 412 as part of a feedback loop.

It will be appreciated that the number of actuators 454 and the distribution will depend on the lifting capability of each actuator 454 and the yawing accuracy and controllability required. In practice there will likely be three or more actuators. Preferably, there will be five or more. A further advantage of the differential lifting arrangement is that the height of the respective actuators 454 can be tailored to level the turbine 412 to account for minor intolerances in the vertical attitude of the support structure 414, thereby allowing a greater degree of alignment with a flow. The active lifting device of the above described arrangement may be any suitable actuator or other arrangement. Hence, the active lifting device may incorporate one or more actuators or arrangements taken from the group comprising: hydraulic, pneumatic or electrical. A pneumatic actuator may include some form of lifting bag or the like placed between the support structure and the power generating module.

Figure 5 shows a cross-section of one side of the co-terminal ends of the turbine support 513 and the support structure 514 which includes an example of a hydraulic lifting device 510. In this arrangement the lifting of the power generating module (not shown) is achieved by injecting pressurised water into a cavity 515 between the mating surfaces 534, 540 of the support structure 513 and the turbine support 514. In the described arrangement, the pressurised water is provided by a pump (not shown) which is part of or at least attached to the power generating module and fed into the cavity 515 via a conduit 517 which is shown as being located within the wall 519 of the turbine support 513 although other configurations will be possible.

In some embodiments it will be advantageous to provide a plurality of cavities 515 which may take various shapes and be distributed around the perimeter of the interface 521 as required. Therefore, there may be a plurality of cavities 515 each provided with individual feed conduits 517. Each of the cavities 515 may be linked by interconnecting conduits (not shown) which allow the pressure between the cavities 517 to be equalised when in use. Alternatively, it may be possible in some applications not to have a cavity per se, but to simply inject fluid in between the mating surfaces.

Exhausts 523 may also be included to provide a greater degree of control in the amount of lifting. It will be appreciated that water will also exhaust laterally out of the interface between the mating surfaces as the turbine is lifted.

A hydraulic arrangement such as this is particularly advantageous as the water can provide a film on which the power generating module can be more readily yawed. Thus, this arrangement may be used in conjunction with one or more of the previously described embodiments as a way to provide a low friction interface between the mating surfaces, thereby reducing the required separation and the amount of lift which may be required from the biasing device or other lifting means.

The pressure required of the water would depend on the specific design of the turbine and is therefore likely to be application specific. However, one example requires a pressure of approximately 32bar.

Other arrangements which require lower pressure are also envisaged. For example, instead of injecting water between the mating surfaces, water could be injected into the turbine support and support structure if sealed in an appropriate way. Alternatively, other cavities or chambers could be created within the supporting structure to provide the required lift. The cavities or chambers may also be advantageously sealed at the interface so as to provide an enclosed volume.

Some embodiments of the hydraulic arrangement include sealing devices which provide defined exhausts to aid the predictability of the flow paths and therefore rate, thereby increasing the controllability of operation. In one embodiment, the sealing device includes at least one resilient component in the form of a rubber seal which extends across the interface 521 between the support structure 514 and turbine support 513. It is also considered preferable in some applications to have the exhausts 523 directed to the exterior of the turbine support structure 513 by having a suitable arrangement of exhaust paths. For example, the exhaust paths may include differential resistance paths which may be controlled with partial seals or some other form of limiting restriction such as a valve or the like.

The pressurised water may be provided directly from a pump or possibly from an

accumulator which has been charged during a power generating phase of the power generating module. Although the above described embodiments relate to tidal turbines, it will be appreciated that the invention is applicable to other forms of aquatic power generating apparatus which are directionally sensitive.