GB2337305A - A tidal power generator with a vertical axis transverse flow rotor - Google Patents
A tidal power generator with a vertical axis transverse flow rotor Download PDFInfo
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- GB2337305A GB2337305A GB9911140A GB9911140A GB2337305A GB 2337305 A GB2337305 A GB 2337305A GB 9911140 A GB9911140 A GB 9911140A GB 9911140 A GB9911140 A GB 9911140A GB 2337305 A GB2337305 A GB 2337305A
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- vertical axis
- rotor
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- stream
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F03—MACHINES OR ENGINES FOR LIQUIDS; WIND, SPRING, OR WEIGHT MOTORS; PRODUCING MECHANICAL POWER OR A REACTIVE PROPULSIVE THRUST, NOT OTHERWISE PROVIDED FOR
- F03B—MACHINES OR ENGINES FOR LIQUIDS
- F03B17/00—Other machines or engines
- F03B17/06—Other machines or engines using liquid flow with predominantly kinetic energy conversion, e.g. of swinging-flap type, "run-of-river", "ultra-low head"
- F03B17/062—Other machines or engines using liquid flow with predominantly kinetic energy conversion, e.g. of swinging-flap type, "run-of-river", "ultra-low head" with rotation axis substantially at right angle to flow direction
- F03B17/065—Other machines or engines using liquid flow with predominantly kinetic energy conversion, e.g. of swinging-flap type, "run-of-river", "ultra-low head" with rotation axis substantially at right angle to flow direction the flow engaging parts having a cyclic movement relative to the rotor during its rotation
- F03B17/067—Other machines or engines using liquid flow with predominantly kinetic energy conversion, e.g. of swinging-flap type, "run-of-river", "ultra-low head" with rotation axis substantially at right angle to flow direction the flow engaging parts having a cyclic movement relative to the rotor during its rotation the cyclic relative movement being positively coupled to the movement of rotation
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F03—MACHINES OR ENGINES FOR LIQUIDS; WIND, SPRING, OR WEIGHT MOTORS; PRODUCING MECHANICAL POWER OR A REACTIVE PROPULSIVE THRUST, NOT OTHERWISE PROVIDED FOR
- F03B—MACHINES OR ENGINES FOR LIQUIDS
- F03B13/00—Adaptations of machines or engines for special use; Combinations of machines or engines with driving or driven apparatus; Power stations or aggregates
- F03B13/12—Adaptations of machines or engines for special use; Combinations of machines or engines with driving or driven apparatus; Power stations or aggregates characterised by using wave or tide energy
- F03B13/26—Adaptations of machines or engines for special use; Combinations of machines or engines with driving or driven apparatus; Power stations or aggregates characterised by using wave or tide energy using tide energy
- F03B13/262—Adaptations of machines or engines for special use; Combinations of machines or engines with driving or driven apparatus; Power stations or aggregates characterised by using wave or tide energy using tide energy using the relative movement between a tide-operated member and another member
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E10/00—Energy generation through renewable energy sources
- Y02E10/30—Energy from the sea, e.g. using wave energy or salinity gradient
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- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Combustion & Propulsion (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Life Sciences & Earth Sciences (AREA)
- General Life Sciences & Earth Sciences (AREA)
- Oceanography (AREA)
- Other Liquid Machine Or Engine Such As Wave Power Use (AREA)
Abstract
A tidal power generator comprises a vertical axis transverse flow rotor and a cam ring pump where the power is taken off the rotor via the cam ring which communicates with the rim of the rotor. The rotor may be neutrally or positively buoyed and fixed to the seabed by mooring lines. The ring cam (figure 2) may be annular and comprise separate lobes tensioned together; the lobes projecting in up to four directions, each to drive a set of pumps. The rotor may further comprise variable pitch blades where the pitch angle is controlled by the moment of the blades around a pitch angle and generated by a fluid pressure in a manifold common to all blades. The pumps and ring cam may be housed in a toroid located above the rotor at the rim. The rotor itself may be 50m in diameter, 20m deep, have 3 banks of blades and be stiffened by streamlined diagonal ties.
Description
2337305 Plant to Generate Ener-gy from Tidal Streams This invention
relates to the larg"cale generation of power by a Vertical- Axis Rotor positioned in a tidal str - - More specifically it relates to the general structure and construction of sudb-,a device, the method of power take-off and methods for ensuring maximum eftiency of tidal power collection.
The Oceans represent a large' natural energy reserve, and methods of harnessing this energy can make an important contribution to sustainable supplies, which it is essential to develop if long-term environmental goals are to be met.
io In addition to the power from waves, another route to power extraction from the oceans is to harness the energy WT1dal Streams. The tidal stream resource is not as large as the deep-sea wa ource on the western side of a continent, but it is still substantial and the ouW is totally predictable. Several tidal-stream turbine designs have been proposed in the past. Axial propeller types have shown some promise, but higher theoretical efficiencies are available from the Darrieus type turbine. However, deployment of the latter has largely been discounted, due to the difficulty oflidning access for repairs, and in transferring the torque to a drive shaft and gerr.
1 Although there are some simila"- between wind-turbines and tidal-stream ones there are several differen.-The velocities in the best tidal streams are about one fifth of typical wind cut peeds, but over the time-scale of tens of minutes they are much steadier elso accurately predictable. There is less need of storage and easier integr with network planning. Blades in water can suffer cavitation damage thatrely limits tip-speed ratios. Water rotors will therefore have higher solidity modern wind-turbine designs. The lower rotor-to-current speed ratios enfWe the need for both variable- pitch and variable-speed if stall is to be avd'-'. Gravity loads are a major problem for wind but in water they can be acc opposed by buoyancy.
Aliv The transport of parts of the largest wind turbines on land is a major problem but floating objects of any likely size can be moved very cheaply. Centrifugal effects are important in wind energy but are negligible for tidal streams. Wind plant in good coastal European sites will be subject to rain and salt spray and so corrosion problems will be similar. Indeed sea spray that has partly evaporated will have a higher salt concentration than the seawater from which it came. However bio-fouling of water turbine blades will be serious. The slower speeds mean that enormous torque's, of the order of 10' Nm, and very high bearing loads are needed.
Although the efficiency of turbines in an open tidal stream will be about half that of those in a barrage, the technique avoids the financial hazards of a very large investment and of a long construction period. The design can evolve making use of experience from early prototypes rated at a few megawatts.
Both ring-cams and gears could be considered for the power take-off for such devices.
The simplest spur gear pair puts all the power through one line of contact. In an epicyclic gear-train the power goes equally through three lines. Some very special epicyclic machines with controlled compliance spindles can use five. But in a very large ring-cam machine the power would go through many hundreds, or even thousands of lines of contact, in parallel. Gear teeth have to combine hardness and tensile strength but cams need only hardness. Gears must mesh accurately with correct centre distances and tooth profiles, even under heavy load. Ring-cams need smooth surfaces but can have tens of millimetres of initial geometrical error and distortion under load, provided only that Hertzian fatigue limits are not exceeded. High torques twist long gears thereby changing line contacts to points but do no harm to ring cams.
A noise sensor can detect early damage to rollers and cam lobes in a ringcam machine. The control-computer can arrange that followers can skip damaged lobes. However a single damaged gear tooth will rapidly infect all the others.
Gears have fixed velocity ratios. Ring-cam pumps can give the infinitely variable 1 ratios which are needed to connect variable water velocities to synchronous generators. Selective use of the pumping modules can allow a ring cam to provide the function of the main rotor bearing and still be tolerant of gross changes of dimensions.
These factors allow ring-cams to achieve the very high torques (well over 108 Nm) with surprisingly low weights of machinery.
Existing ring cam machines use -displacement ring-cam motors with a single ring, and are made by several cnies. Such machines have for many years provided slow, accurate drives in marine uses. Their casings have inward-facing io lobes that impart a radial movement to a number of roller cam- followers driving pistons. Hydraulic connections aT made with rotating kidney-port valves, close to the axis, which act like the commutator of an electric motor. In each rotation of the machine, every cam lobe ddM every cam-follower. The cost depends on the sum of lobes and followers b output depends on their product. Thus machines give better value for money as size increases.
Although all present ring-cam machines use fixed displacement, it is possible to achieve variable displacement bydisabling a selected proportion of pumping modules by holding open some 1 valves. The modules can be enabled by signals from a computer to a mac coil on each valve. The technique has been described in previous work ("r 1993).
The tidal stream application n 7k variable-displacement and the abi diameters it is better to react the ring-cam diameter the same as the rotor, g-A - OD take bearing loads. At these much larger on the cam through its thickness rather than round its circumference. In such a design it becomes possible to situate the 25 ring cam pump system in a watergotoroid which lies at the surface of the sea.
T As the spars of the rotor rotate reh to the toroid, the circular ring cam moves past an array of ring cam followers& drive pistons.
Clusters of individual tidal streanerators that approach the size of the channels in which they are installedwill behave differently and potentially better 1 than those in an open flow field. It gets harder for water to flow around the rotors and so they will behave more like a ducted turbine, unrestricted by the Betz limit. We need to understand the 'output impedance' of the channel and the forcing function of its excitation in order to make the best match with the rotor. We also need to be sure that the higher water level upstream of the rotor does not cause flooding. The rectangular window of the vertical axis configuration allows it to have a higher packing fraction than the horizontal one. The ideal arrangement may be to use two contra-rotating vertical-axis rotors side by side to cancel each other's torque, down-stream vorticity and side thrust.
io According to the present invention there is provided a vertical axis tidal stream power generator comprising a variable pitch, vertical axis, rotor, and a power take-off consisting of a ring cam pump at the rim.
In a preferred embodiment, the rotor has sets of symmetrical vertical blades supported at both ends by bearings in horizontal rings (Figure 1). In one possible design configuration, the rings have streamlined elliptical sections with for example, but not restricted to a chord -to-th i ck ness ratio of five. This gives a large reduction in bending moments and bearing loads relative to a cantilevered support and allows a much greater total depth.
Also in a preferred design embodiment, the rotor rings are braced between the spars to increase torsional strength and stiffness, by diagonal ties of high-tensile cable, for example but not necessarily of steel construction, fitted with rotating fairings to minimise drag (Figure 1). In one possible design, for convenient transport in sea containers, a single rotor blade would not exceed 10 metres length and 2.4 meters chord.
In a preferred embodiment of the current invention, variable pitch is achieved by rotating the blades about spars that join the horizontal rings.
In a preferred embodiment, the moment of the blades is fixed, rather than the angle, ensuring that the pitch actuation is made much easier.
1 Each blade is preferably driven by one hydraulic changeover valve with a central locked position, but the fluid pressure is derived from a manifold common to all of the blades. The drive to the power take-off can therefore be instantly removed by reducing the pressure in the blade pitch manifold. In one preferred design configuration the blades rotate on hydrostatic bearings which allow frame distortion by means of a plurality of bearing pads which control the flow of fluid to said pads in proportion to their displacement from the unloaded position, while at the same time giving the opposite control of flow to pads on the opposite side of the bearing, the flow control being implemented by spool valves moved by io master pads.
In the current invention, the upper-part of the rotor drives a ring-cam of the same diameter running through a floating torus shown in Figures 2 and 3. In one possible design configuration, the torus is at least 3.4 metres in diameter to allow maintenance staff to stand comfoftbiy. The lower part of the torus is preferably divided into many separate wateffight compartments. Since the cam cannot pass through the generators, so these will preferably be in enlarged sections of the power torus. The ring cam is preferably made from separate lobes that are tensioned together. In a preferred configuration, the displacement of the ring cam pumps is controlled by poppe tvalves (Figure 2), especially where a fraction T of the valves can be disabled by oids operated under computer control.
The proposed vertical-axis coration allows convenient entry to an atmospheric generation chamber in a preferred embodiment use is made of _MW zero-pressure gutter seals (Figuiu" and 3).
In one possible deployment geo, in a tidal channel, a plurality of turbines are packed closely so as to block a 1 -fraction of the channel and so improve on the Betz efficiency limit.
It is also preferred that the tidi ' C-am generator is neutrally, or positively buoyant and in operation, tension leg moorings (Figure 4). In a W preferred implementation, cables M attached to the power torus at the surface "tf and the horizontal component of tension in the cables must equal the resultant horizontal forces on the rotor.
A possible anchoring system is for a post-tensioned pile design such as the one shown in the Figure 6.
Design and Construction Details with Example Calculations Variable pitch blades have been shown by hydrodynamic analysis to be required in order to implement the invention efficiently. Fixed-pitch blades would spend too much time stalled at the, necessarily low, tip- speed ratio and would have a performance coefficient of only 0.2 whereas variable pitch can achieve over 0.4, io which is comparable with vertical axis wind machines. In one possible embodiment, the pitch bearings could use self-aligning hydrostatic master- andslave pads fed with filtered sea water, like those proposed for ram guides of the Budal and Falnes buoy (Salter 1993). These bearings would preferably be placed at about 0.05 of chord forward of the centre-of- pressure so that they would need a small but positive moment to move away from the local angle of incidence. If the bearing surfaces are made from the marine version of Glacier DU they can operate for a few weeks with no feed.
Pitch actuation is made much easier if we do not attempt to fix the angle but instead fix the moment on the blades. The blades will then take up whatever angle gives the right moment and we do not have to be concerned about the change of direction of current flow. At lower angles of incidence the blade chords would be tangential but once the angle of incidence exceeds the value of maximum lift-to-drag ratio (about 9 degrees) the blades should track the angle of incidence to keep it at the optimum value. Each blade would preferably use one hydraulic changeover valve with a central locked position. Two common fluid lines can control all the blades. The maximum pitch angle during normal operation would preferably not exceed 30 degrees. However after any damage to moorings it might be convenient if the actuator allowed angles up to 90 degrees either side of the rotor tangent line to reduce drag.
V\fith the rotor rings braced between the spars by diagonal ties of hightensile steel cable fitted with rotating fairings drag is minimised. Without these fairings the drag of the ties would be enormous, wasting about one third of the power. For the very largest rotor sizes it may be further preferable to cross-brace the rings with ties running from each "r attachment to a point on the opposite side of the rotor so as to improve elastbility on the upstream arc of the rotor.
Sections of the power torus enk to house the generators would make convenient attachment points for tM moorings.
In one embodiment of the design, small, identical components can be assembled i o to make different rotor diameters. All items, including the half- sections of the power torus, will then fit in a sea iner. None need weigh more than say 20 tonnes.
A possible design for the complete _Wstem is shown in Figure 1.
In a particular design, 3 banks of 6.7 metre blades with chord of 1.9 metres have been chosen.
The blade thickness of the hydrofoil sections is decided by the need for it to act as an efficient beam for the high dbuted loading and also for it to have near neutrally buoyancy. If we restrict to maximum stress in the steel to 180 MPa and keep to one thickness of stAM".rdate over the whole blade surface then the section thickness will need to be,- of chord. The preference is for a new section designed by Rodewald (1QM which has been optimised for a smaller negative pressure coefficient.
The forces on the cam are best red throuqh its thickness rather than round its circumference. The ring wou&-spift int-o many separate lobes with scarf joints at the troughs. The separalobes would be pulled together by a cable running through their centre like ts in a necklace. The final cam surface would be ground after assembly in" power torus. In one embodiment of the invention, each lobe section weighs-Willy 45 kg.
-X-E A cruciform combination of 4 cam tracks as shown in Figure 2 can also provide the functions of geometrically-tolerant radial and thrust bearings which are not available as catalogue items at 50 meters diameter. Extra pumping stroke can accommodate thermal expansion. The cam is contained in a power torus with dry manned access. The gap between the power torus and the rotor has flowrestricting labyrinth flaps forming a gutter seal as shown in Figures 2 and 3.
We need quite large power-torus diameters to make the system stable in pitch and roll and to allow comfortable manned access. The initial design study suggests that cost per kilowatt falls gently with rotor increasing diameter to at io least 100 metres. Provided that the system design allows the isolation of faulty pumping modules, there seems to be no limit to the size of ring cam pumps.
The limit to rotor diameter may be imposed by the elastic stability of the rotor rings which will suffer compressive forces on the upstream side. Downstreamonly generation is possible and might suit very big units.
A 50 m diameter pump suitable for use with a 20 m deep rotor and able to act as a bearing would weigh only 52 tonnes, of which much is lowprecision structural steel. Design calculations have been implemented as a Mathcad document that can quickly recalculate values for any other input values.
Torque can be calculated from the product of pressure, number of cam lobes, number of pumping modules, piston area and piston stroke divided by 27r.
Pumping modules are disabled by holding open plastic poppet-valves made from carbon-fibre filled poiyether-ether-ketone which we have tested to full fatigue life. They have an annular shape and very low flow losses when they are disabled, about 0.2% of the energy of a working stroke. Losses will be dominated by the shear and leakage of the hydrostatic bearing between the rollers and the pads that drive the pistons of each pumping module. The Mathcad analysis uses the standard equations for leakage and shear and shows that losses should not exceed 1 % of the instantaneous power, with perhaps a further 1 % if the pump is used for bearing duty.
Large turbines will need economical ways to resist the very large (> 10 MN) down-stream and cross-stream forces. It is possible to perform all the mooring function with tension-leg cables as shown in Figures 4 and 5.
Cables must be attached to the power torus at the surface. The horizontal component of tension in the cables must equal the resultant horizontal forces on the rotor. The vertical component of the cable tension is opposed by a change of depth of immersion of the torLM-which must have enough plan area and freeboard. If cables were attached to the most upstream point then the entire system will tend to pitch nose down. If they were attached to the downstream io point then it would pitch nose up. There must therefore be some intermediate attachment point that is neutral in pitch. It will be the point that allows the line of action of all the cables to pass d"ugh the intersection of a vertical line through the centre of buoyancy and a horti line through the centre of pressure of all the blades.
The plan view of the cables musthe rotated from the stream direction to take account of the cross current force. - Some slack in the downstream lines (which will tauten when the flow direction Mverses) allows the torus to follow the rise and fall of the tide. This is likely to be small at a point of especially high stream velocity because this point shou at a tide node. In some sites it may be possible to make a cable attachnto rock anchors on land, which would have many attractions, compared with ones. However this would remove the vertical component of cable tensk- W-and might require careful attention to pitch stability.
It is likely but not certain that tt-eabed at a good tidal stream site will be 25 scoured down to bare rock. This -vMid make it suitable for a post-tensioned pile design such as the one shown in.#p Figure 6. A conical crater with roughly a ex--- sixty-degree cone angle is made rock by the detonation of a sequence of charges. Underwater explosionsin. rock produce undesirably shallow craters and, without suppression, kill all fish to great distances. We propose to suppress the effects using a slow pyrotechrde- propulsion charge lasting about a second to make a protective gas bubble. When the bubble is formed a sequence of A&P lw- blasting charges will be fired at increasing depths down to about 3 metres. (The gas-to-water interface has a very high reflection coefficient and the speed of sound in a water/gas mixture can be as low as 20 mlsec.) A final propellant charge will throw the debris clear of the crater which would be about 2.7 metres in diameter. A hole about 100 mm diameter and 20 metres long will then be drilled into the bottom of the crater.
A stack of parallel triangular steel plates spaced apart by about 30 mm will be lowered into it and some steel post-tensioning wire lowered through the gaps between the plates to reach the bottom of the hole. The bottom three-quarters of io the hole will be filled with grout. Concrete will then be poured round the steel plates to bed them into the crater. After the concrete has reached full strength, the wires will be tensioned up to their constant working stress and so will suffer no fatigue. An increase of mooring force will change the compressive rock preload.
The stream velocities at a good site are above the safe levels for divers except for a few minutes either side of slack water. The sediment entrained in high velocity streams may well reduce visibility to zero. The drilling and placement of charges and installing of the pile hardware will therefore have to be done from a jack-up platform, or a purposedesigned remotely operated vehicle. In installing the power-generating device, it may possible to take advantage of local Channel Hydrodynamics. It is possible that the combined resonance of the channel and the ocean driving it can be enhanced by changing the phase of generation in the manner of the latching and reactive loading being developed for wave energy.
Good tidal stream sites are likely to be in the channels between a large mainland and a smaller island. If there are alternative routes for shipping it may be possible to add a flat upper surface to the power torus and use it as a roadway. The following design parameters have been calculated from a Mathcad worksheet for an initial reference design Diameter 50 m Maximum stream 4 misec- velocity Maximum design 180 Mpa stress Tip-speed ratio 2.67 Rotor tip speed 10.7 mlew' maximum Solidity -Idd 0.121 Blade number 10 Blade span 3 x 6.67 Chord 1.9 M, Foil section Rodewald OM JU Optimum incidence 9 deg.
angle Pitch change angle 11 de g.
Theoretical 40% efficiency Mooring force 6.5 MN Mooring cables 8 by 64 Torus minor 3.4 m diameter Hertzian cam stress 750 MPa Roller diameter 98 mm Roller width 100 mm Lobe number 307 Follower number 720 Pump bore 44 mm Pump stroke 65 mm Pressure 400 bar Delivery per rev. 17 m3 Pump strokes per 221,040 rev.
Computer decision 88 E-6 sec time Maximum torque 139 E6 Nm Total pump weight 52 tonne Torque per ú 273 Nm Torque per kg 2162 pump 7 Cost per kg pump ú7.9 Cost per total kg ú6.97 Total weight 640 tonne Power at 4 mlsec 12 MW Harwell parametric ú4.5 m cost Cost per peak kW ú375 Useful torque would be reduced if some modules are used for bearing duty.
Particular care has been taken in this design example to make sure that all the parts of the rotor will fit into a sea container so that they can be moved by road or sea to any site. Assembly can take place in a sheltered bay which can be given additional protection from a ship (perhaps one about to be scrapped) moored across the bay entrance. The ship can store sub-assemblies and house the workforce.
The starting point would be to add flotation bags to each section of the lower ring, float them into place, and bolt them together with the shorter bearing-sections io between them. Roundness can be set with floating cables running across the diameter. When the ring is sufficiently true, the sections can be welded together and a hoop-wire tensioned round the ring to bias the welds into compression. The lower ends of the diagonal ties would be attached to the rings with their upper ends tied to floats.
The floating ring can be rotated to bring each part in turn under lifting gear on the ship or gantries sitting on the sea bed so that the arrangement is effectively a circular production line moving past aligning, welding, painting and inspection points.
The lower hydrostatic bearings will be attached to the bearing sections and the lower set of spars and blades lowered into place. The bearings can have up to 2 degrees of misalignment and this allows the spars to be deliberately splayed outwards from the ring like a crown but retained at the outward tilt by guy ropes tied to points further round the ring. Although 2 degrees does not sound much, a 1.75 metre high wave would be needed to tilt a 50 metre rotor through this angle.
Air would then be released from the ring flotation bags and the first stage lowered until flotation bags at the top of the blades reach the water. The next set of bearings would be added and the next set of ring sections assembled as before.
When the upper ends of the diagonal ties are connected we will have a strong and sufficiently stiff structure which can be handled with less delicacy. It can be raised to any height at any time for painting or anti-fouling by means of the flotation bags. These could so useful that it may be worth building them in to the lower ring.
The halves of a section of the power torus can be floated into place inside and outside the upper ring, bolted together with temporary jigs and then joined together with the G-frames, which will hold the pumping modules.
Circularity can be set for all 20 sections with the radial floating cables aided by laser measurements from a central datum point. They will then welded together.
The power torus will then be bolted to the upper ring of the rotor with removable attachments.
At this point the structure will still have an open roof making it easy to lower parts r into the power torus but not yet gMhg the clean working conditions desirable for 2o hydraulic assembly.
The cam lobes will be lowered into their correct places, which will be defined by rolling bearings with Vee pulleys tW locate machined surfaces between the cam humps. Groups of about 20 lobes will be threaded over the internal tensioning wires and tension set on the entire circle. We now have a fairly flexible cam ring 25 running on temporary Vee rollers butwith unfinished lobe surfaces.
The cam will be rotated past an optical scanning head that will record the variations in the cam surfaces and so allow the most efficient grinding to be planned. The grinding heads will be assembled in the space later to be used for the generators. The cam will be drawn past them and ground until all the lobe surfaces have been covered. Note that is not necessary for the lobes to have the same height or wave length so that the precision is far less daunting than in making big gears.
At this point the top roof will be welded on to give the torus its full strength. The 5 inside will be washed down with flushing oil passed through progressively finer filters so that the inside becomes clean enough for hydraulic assembly.
The proposed vertical-axis configuration allows convenient entry to an atmospheric generation chamber and the use of zero-pressure gutter seals. It also allows turbines to be packed closely so as to block a large fraction of some io channels and so improve on the Betz efficiency limit.
Cavitation imposes lower tip-speed ratios and so higher solidities than for wind turbines. It may be possible to design hydrofoil shapes such as the Rodewald foil which have a more even pressure distribution with lower negative pressure coefficients.
The low tip speed enforced by cavitation implies very large torques that would distort the geometry of conventional gearing.
Low tip-speeds also impose the need for variable pitch if we are to avoid stall at the most useful part of the rotation. This can conveniently be achieved by controlling the pitching-moment rather than the angle of the blade. Blades can be feathered in emergency.
Ring-cam pumps can provide the very large torques with greatly relaxed tolerances. This increases the maximum possible diameter of the rotor allowing generation at several tens of megawatts and making it more stable in tilt.
Disabling poppet-valves gives ring-cam pumps a continuously-variable 'gear25 ratio' so that a rotor moving at the correct tip-speed for any phase of the tidal cycle can drive a true synchronous generator.
time.
Energy losses of the ring-cam are dominated by the hydrostatic pads that support the cam rollers. They can be calculated from standard equations for leakage and shear and seem to be less than 1 % of output.
The use of a segmented cruciforrvv.cam with force reacted through the thickness 5 gives great economy of pump weight and allows it to act as a geometrically tolerant bearing.
Buoyancy can remove many of the.structural problems imposed by gravity which are suffered by wind turbines. If b are to be neutrally buoyant they must be quite short with thickness of at least 18% of chord.
io The transport of parts of the largest,Wind turbines on land is a major problem but floating objects of any likely size can be moved very cheaply. Indeed the proposed rotor design, with pairsUturbines used in reverse inthe manner of a Voith-Schneider propeller can be166sidered, making them self-propelled, with fuel tanks to give trans-ocean capability.
Maintenance and anti-fouling can be eased if air bags built into the lower ring can be used to lift the entire structure clear of the water without loss of tilt stability.
The proposed tension-leg localkik avoids bending moments associated with _A:
tower mountings. Seabed attachMents, at good tidal stream sites will be much harder than in the open sea because of zero visibility and very short diver access REFERENCES Salter SH. Power Take-off Systeme. Section B3 pp 101-151 DWII Preliminary Actions in Wave Energy R&D. CETAugust 1993.
v_ Salter SH, Rampen WHS. The ding cake Multi-eccentric Radial Piston Hydraulic Machine with Direct Cr Control of Displacement. pp 47-64. 1 Oth Lw International Conference on Flull ' d Power. Brugge April 1993. Mechanical Engineering Publications London 1W3.
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Claims (1)
1 A vertical axis tidal stream power generator comprising a variable pitch, vertical axis rotor, and a power take-off comprising a ring cam pump at the rim.
2. A vertical axis tidal stream power generator as claimed in Claim 1 with neutral or positive buoyancy such that it floats in water or seawater and is secured by tension leg moorings.
3.
A vertical axis tidal stream power generator as claimed in Claim 1 or Claim 2 where the ring cam is made from separate lobes tensioned together.
A ring-cam pump as claimed in Claim 1 and Claim 3 where the forces from the cam rollers work through the thickness of the cam ring in two or more directions.
A ring-cam pump as claimed in Claim 4 where the forces from the cam rollers work through the thickness of a quad cam ring in four directions.
6. A ring cam pump as claimed in Claim 1 and Claims 3 through 5 where the forces from the cam rollers can be regulated to provide the function of a geometrically tolerant bearing.
7. A vertical axis tidal stream generator as claimed in any preceding claim wherein the power take-off comprises ring cam pumps where the pump displacement is controlled by poppet valves.
8. A vertical axis tidal stream generator as claimed in Claim 7 in which a fraction of the valves can be disabled by magnetic coils driven by a computer.
9. A vertical axis tidal-stream generator as claimed in any preceding claim with a rotor comprising of variable pitch blades.
10. A rotor as claimed in Claim 9 with variable pitch blades where the pitch angle is controlled by the moment of the blade around the pitch axis.
A vertical axis tidal-stream generator as claimed in Claims 1-9 where the moment of the rotor blades is generated by a controlled fluid pressure in pressure manifolds common to all blades.
12. A vertical axis tidal-stream generator as claimed in Claim 11 where the drive to the power take-off can be instantly removed by removing pressure in the blade pitch manifold.
13. A vertical axis tidal-stream generator as claimed in any preceding claim where the rotor blades rotalle on hydrostatic bearings which allow frame distortion by means of a pluraky of bearing pads.
14. A vertical axis tidal-stream generator as claimed in Claim 13 in which bearing pads control the " of fluid to pads in proportion to their displacement from the unloa position while at the same time giving the opposite control of flow to pads on the opposite side of the bearing.
15. A vertical axis tidal-stream generator as Claimed in Claim 14 where the flow control is implemented by spool valves moved by the master pads.
16. A vertical axis tidal-stream Onerator as claimed in any preceding claim where bending moments on blades are reduced by streamlined rings.
17. A vertical axis tidal-stream go,"--tor as claimed in Claim 16 where torsional strength and stiffness are inch- by diagonal ties.
18. A vertical axis tidal-stream gi -tor as claimed in Claim 17 where the ties have streamlined fairings in oMr to reduce drag loss.
19. A vertical axis tidal-stream rator as claimed in any preceding claim where an atmospheric press egeneration chamber is formed by use of a zeropressure seal.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB9911140A GB2337305B (en) | 1998-05-12 | 1999-05-14 | Plant to generate energy from tidal streams |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GBGB9810056.3A GB9810056D0 (en) | 1998-05-12 | 1998-05-12 | Plant to generate energy from tidals streams |
GB9911140A GB2337305B (en) | 1998-05-12 | 1999-05-14 | Plant to generate energy from tidal streams |
Publications (3)
Publication Number | Publication Date |
---|---|
GB9911140D0 GB9911140D0 (en) | 1999-07-14 |
GB2337305A true GB2337305A (en) | 1999-11-17 |
GB2337305B GB2337305B (en) | 2002-03-13 |
Family
ID=26313645
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
GB9911140A Expired - Fee Related GB2337305B (en) | 1998-05-12 | 1999-05-14 | Plant to generate energy from tidal streams |
Country Status (1)
Country | Link |
---|---|
GB (1) | GB2337305B (en) |
Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US8277168B2 (en) | 2006-10-27 | 2012-10-02 | Hardisty Jack | Tidal power apparatus |
GB2497272A (en) * | 2011-11-04 | 2013-06-12 | Seapower Gen Ltd | Transverse flow turbine with tensioned stays |
Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB305477A (en) * | 1928-02-04 | 1930-01-02 | Gaston Henri Vacquier | Improvements in apparatus for utilising tidal energy |
GB2002458A (en) * | 1977-08-13 | 1979-02-21 | Sandgaenger K | Power station |
US4239976A (en) * | 1977-03-29 | 1980-12-16 | Collard Louis Jean | Floating electric generator using the driving energy of water |
-
1999
- 1999-05-14 GB GB9911140A patent/GB2337305B/en not_active Expired - Fee Related
Patent Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB305477A (en) * | 1928-02-04 | 1930-01-02 | Gaston Henri Vacquier | Improvements in apparatus for utilising tidal energy |
US4239976A (en) * | 1977-03-29 | 1980-12-16 | Collard Louis Jean | Floating electric generator using the driving energy of water |
GB2002458A (en) * | 1977-08-13 | 1979-02-21 | Sandgaenger K | Power station |
Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US8277168B2 (en) | 2006-10-27 | 2012-10-02 | Hardisty Jack | Tidal power apparatus |
GB2497272A (en) * | 2011-11-04 | 2013-06-12 | Seapower Gen Ltd | Transverse flow turbine with tensioned stays |
Also Published As
Publication number | Publication date |
---|---|
GB9911140D0 (en) | 1999-07-14 |
GB2337305B (en) | 2002-03-13 |
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