GB1596053A - Apparatus for extracting engergy from waves - Google Patents

Description

(54) APPARATUS FOR EXTRACTING ENERGY FROM WAVES (71) I, SECRETARY OF STATE FOR DEFENCE, LONDON, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to apparatus for converting energy from liquid waves, particularly ocean or sea waves.

According to the present invention apparatus for converting energy from liquid waves includes at least two parallel plates arranged generally vertically one behind the other in a body of liquid, float means biassing the plates upwardly in the liquid, and pump means connected to adjacent plates, the plates being disposed substantially normally to the direction of wave movement in the liquid such that wave movement induces a relative horizontal motion of adjacent plates which actuate the pump means.

Preferably the pump means includes an intake for the liquid in which the plates are immersed.

The pump may include a piston and cylinder arrangement with inlet and outlet valves, and may be double acting. Alternatively the pump may be in the form of a flexible bellows connected between the plates.

In one form of the invention two plates are positioned half a wavelength apart.

Another form of the invention has three plates, two trailing plates fixed relative to one another with a horizontal spacing of half a wavelength and a leading plate moveable about a mean spacing one quarter wavelength from the adjacent trailing plate.

One form of the invention using flexible bellows includes at least two plates arranged generally vertically in a body of liquid. float means for maintaining the top of the plates on or above the liquid surface, at least one bellows extending between the or each pair of plates and at least two non-return valves associated with each bellows for permitting flow through the bellows in one direction only, the arrangement being such that in use, wave movement of the liquid induces relative to and fro movement between each pair of plates thereby to pump a fluid through the bellows. The pumped fluid is preferably the liquid in which the apparatus is located.

Preferably each plate includes at least one hole in which a non-return valve is fitted and preferably each bellows interconnects a corresponding pair of such holes in adjacent plates.

There may be a multitude of plates arranged parallel to one another and each plate may include two or more such holes and have two or more bellows connected thereto on either side of the plate.

Preferably the first plate in the direction of travel of the waves is anchored in a manner which does not restrict the to and fro movement of the plate.

Preferably each plate is supported by a float attached to the plate at approximately one fifth of its depth.

The liquid (which will almost invariably be water) may be pumped into an elevated lake for later use, or may be used directly, for example to drive a turbine which way be used to drive a generator to produce electricity.

Mooring of the apparatus relative to the liquid in which it is immersed may be such as to prevent any relative vertical movement of adjacent plates. However in many embodiments of the invention mooring means to prevent such movement might be inordinately complicated. This is especially so when the apparatus is immersed in ocean or sea water where the mooring means will preferably be of a type which automatically compensate for tide effects. Where significant relative vertical movement occurs it may be profitable to convert it into energy to supplement the energy obtained from the longitudinal movement. Conversion may be by use of pumps having cylinders secured to fixed structure (such as mooring shackles) and pistons actuated by vertical movement of the plates, or vice versa.Alternatively pumping means may be secured to adjacent plates in such a manner that they are actuated by relative vertical movement, horizontal movement, or both.

Some embodiments of the invention will now be described, by way of example only, with reference to the accompanying Drawings, of which Figures 1 to 4 were filed with Application 8734/78, and Figures 5 to 9 were filed as Figures 1 to 5 of the drawings filed with Application 27271/77, and of which: Figure 1 shows in elevation an embodiment of the invention having two plates.

Figure 2 shows in elevation an embodiment of the invention having three plates.

Figure 3 shows the forces acting on the plates of the embodiment of Figure 2 as a wave passes them.

Figure 4 shows in elevation a method of attaching two plates together.

Figure 5 is a plan view of an embodiment of apparatus according to the invention utilising bellows.

Figure 6 is an elevation view of the apparatus of Figure 5 Figures 7, 8 and 9 are plan views of further embodiments of the invention, and Figure 10 is an elevation of an embodiment of the invention arranged to convert vertical as well as horizontal wave motion.

An apparatus for converting energy from liquid waves (Figure 1) includes an upstream (that is, first contacted by a wave) plate 10 and a downstream plate 11 each having one end supported on the surface of a liquid 12 by a float 13 and being maintained substantially vertical by the floats 13 and ballast weights 14. Secured to the downstream plate 11 is a cylinder 15 of a double acting pump, the cylinder 15 having inlet valves 16 opening to the liquid 12 and outlet valves 17 connected to an outlet pipe 18. A piston 19 of the pump is connected by an actuating rod 20 to the upstream plate 10.

Flexible joints 21 allow some degree of relative vertical movement between the plates 10, 11. Preferably the apparatus includes means for varying the separation between the plate 10, 11. For clarity no such means are illustrated but they may consist, for example, of a telescopic actuating rod 20 and means for varying the length of the rod 20.

In operation the apparatus is placed in liquid 12 which is subjected to wave motion with the plates 10, 11 normal to the direction of wave movement. The distance between the plates 10, 11 is adjusted to be half a wavelength. As waves pass the plates 10, 11, horizontal movement of the liquid induces relative horizontal movement of the plates 10, 11, which results in reciprocation of the piston 19 in the cylinder 15 and causes liquid 12 to be pumped along the outlet pipe 18. The liquid can be pumped to a higher level, or can be used directly for example to drive a turbine.

It will be appreciated that the action of pumping liquid 12 will inhibit relative movement of the plate and means (not shown) must be incorporated, for example in the output pipe 18, to control the output pressure in order to obtain a reasonable output.

In the case where the apparatus of Figure 1 is operated at an infinitely high pressure, corresponding to an arrangement where plates 10, 11 are rigidly maintained at a separation of half a wavelength, each incoming wave is almost wholly reflected and almost no wave energy passes the plates. An apparatus utilising this fact is illustrated in Figure 2 where plates 110, 111 having floats 113 and ballast weights 114 are held in position half a wavelength apart by tie rods 130, some degree of relative vertical movement being allowed by flexible joints 121.

Upstream of plate 110 is a plate 131 having a float 113 and ballast weight 114, movable relative to plate 110 about a mean position one quarter of a wavelength ahead of plate 110. Plate 131 is connected by pumP actuating rod 120 (having flexible joints 121) to the piston (not shown) of a pump 115, the construction and operation of the pump being as described for the apparatus illustrated in Figure 1. Means such as telescopic rods 130,120 (not shown) are preferably incorporated for adjusting the distances between plates 131,110 and 111.

Operation of the apparatus as illustrated in Figure 2 is roughly as for the apparatus as illustrated in Figure 1. However, as illustrated in Figure 3, because plates 110 and 111 are rigidly maintained half a wavelength apart the wave forces on them are always equal and opposite and as a result neither moves horizontally. Any wave passing plate 131 is totally reflected by plate 110 and a standing wave is set up between plate 131 and 110. In its position a quarter wavelength ahead of plate 110, plate 131 is at an antinode for the horizontal motion of liquid particles, and the liquid between plates 131 and 110 presents very little resistance to the motion of plate 131. By suitable adjustment of the pump output pressure a large fraction of the total wave energy can be converted into useful energy. Preferably the output pressure is made proportional to the velocity of plate 131 so that the resistance to the motion of plate 131 imposed by the pump means is also proportional to the velocity.

This may be achieved by the installation of hydraulic amplifiers and switches in the output pipe.

Whilst the embodiments described above, with reference to Figure 1 and to Figure 2 have referred to only a single pump it will be realised that, in practice, a plurality of pumps will be positioned between pairs of plates 10,11 or 131, 110.

The relative motion of the plates need not be strictly horizontal. For example in one method of maintaining the mean spacing of adjacent plates, as illustrated in Figure 4, a bracket 50 secured to the base of a plate 10 is connected by a tie rod 51 and flexible links 21 to the top of a plate 11. Plate 10 will now rock about a point C which is the point at which extended lines along the lengths of Plate 10 and tie rod 51 meet. A plate 131 as in the apparatus described with reference to Figure 2 may be attached to plate 110 in a similar manner. Plates 10,11;131,110 respectively will be attached to pumping means as has already been described. With this arrangement the separation of the plates can be adjusted to some extent, to allow for variation in wavelength, by adjusting the buoyancy of the floats 13 or 113 or the weight of the ballasts 14 or 114.

Some further embodiments of the invention will now be described as being installed in the sea.

Referring to Figures 5 and 6 of the drawings, the apparatus 210 comprises a series of parallel plates 211, oriented more or less vertically and parallel to the waves (ie parallel to the wave fronts). Each plate 211 is supported by a float 212 fixed to the plate, so that most of the plate is below the water surface, about one fifth of the plate extending above the water surface. Each plate is provided with a number of holes (two as drawn) fitted with non-return valves 214 such that water can pass through in one direction, but not in the other. The nonreturn valves may be single flap valves as illustrated or any other suitable type. On each side of the valve 214, a flexible extensible bellows 215 is connected and joined to the corresponding holes on the neighbouring plate, the bellows preferably being below the water surface by the height of the waves.The whole structure thus comprises several parallel plates joined together by many lines of bellows connected in series. It extends for many wavelengths parallel to the waves (direction of the arrows 219 in Figure 5), and one or more wavelength perpendicular to the wavefronts (directions of the arrows 218). The structure is anchored by lines 217 attached to the end plate on the seaward side with sufficient play to allow the plate to follow the motion of the waves, which is indicated by the arrows 118. The anchoring lines 217 may be attached to a single point on the sea bed and may include means to automatically align the apparatus with the direction of wave travel.

The action of the apparatus is as follows.

A to and fro, more or less horizontal, motion of the plates 211 is induced by the waves, such that the bellows 215 are alternately expanded and compressed. As a result water enters each line of bellows at one end and is pumped through the nonreturn valves to the other end. It then enters a flexible pipe 220 and is used to do the useful work either ashore, or on another floating or fixed structure. The diameter of the pipe 220 is selected to reduce energy losses from the water passing through the pipe, and the pipe is arranged so that it does not restrict the freedom of movement of the plate to which it is attached.

The velocity of the water at the output of each line of bellows is approximately equal to half the peak horizontal particle velocity in the waves. The pressure of the water at the output is many times the dynamic pressure in the waves, approximately in the ratio of half the area of a plate to the total cross-sectional area of the bellows connected to it. As a result water can be pumped to heights many times the height of the waves. A substantial fraction of the wave power is transformed into hydraulic power in the form of water flow in pipes.

Other possible embodiments of apparatus are illustrated in Figures 7 to 9.

A pair of plates may be interconnected as shown in Figure 7. Tie rods 221 flexibly connected to a front plate 200 pass through holes 222 in a back plate 2001 and drive the small plates 223. Whereas the bellows 215 pump water when the front and back plates move together, the bellows 224 pump water when the plates move apart. This two-way pumping action enhances the efficiency of the device.

Gaps may be left between a series of front plates 212, as shown in Figure 8, so that the waves may reach the back plates 212' unhindered.

In this case the simple bellows 225 may be replaced by the arrangement 226, illustrated in Figure 9. Tie rods 227 are interconnected by pin or universal joints and are attached to the plates in a rhombus arrangement with the bellows forming the diagonals so that when the plates move towards each other bellows 228 are compressed, and when the plates move apart the bellows 229 are compressed. The water is pumped in the direction shown by the the arrows 230 into the outlet pipe 231. In this manner a two-way pumping action is achieved. Of course, in Figures 7 to 9 embodiments as in Figures 5 and 6, suitable non-return valves are included at either end of each bellows.

The number of plates in the device, the depth of each, and their spacing can be adjusted to optimize the performance. For example, in the apparatus illustrated in Figures 5 and 7, the vertical plates may be close together, but the depth of the plates below the water line may be roughly equal to the wavelength of the waves divided by 6.28 to achieve optimum performance. In the apparatus illustrated in Figures 8 and 9 the spacing of the plates in the direction of propagation of the waves may be one half wavelength to achieve the best efficiency. In particular, as the waves are absorbed their amplitude decreases from the seaward to the landward end of the device.To obtain optimum matching the diameter of the bellows may be gradually increased towards the landward end, so that the velocity of the water inside the bellows is progressively reduced to match the decreasing external particle velocity in the waves. The size of the plates may also increase towards the landward end.

Each plate may be a flat plate as shown in the drawings or may be a hollow plate in which water may be stored. In this case, the bellows leading in and out of such plates may be offset relative to each other.

The apparatus may be maintained in alignment by adjustment of mooring devices. Alternatively the hydraulic energy developed by the apparatus may be used to orientate the apparatus, or even to move the apparatus through the liquid medium.

Whilst the embodiments of the invention herein described have been described and illustrated as having floats 13,113,212 lying on the liquid surface, this need not be so.

The floats may be arranged to lie below the liquid surface by adjusting their buoyancy, the weight of ballast, or the configuration of mooring arrangements. This will involve the loss of some potential wave energy (depending on how far below the liquid surface the floats lie) but will reduce- the amount to which the apparatus is liable to damage by factors, such as gales, other than the waves themselves.

In many embodiments of the invention there will be some vertical movement of the plates accompanying the horizontal movement. Where the vertical movement is significant it may be profitable to convert it into energy to supplement the energy obtained from the longitudinal movement.

Conversion may be by use of pumps having cylinders secured to fixed structure (such as mooring shackles) and pistons actuated by movement of the plates, or vice versa.

A particular embodiment of the invention designed to take full advantage of both relative vertical and relative horizontal movement of adjacent plates (Figure 10) is similar to the embodiment as described with reference to Figure 2. A plate 331 is connected by a bracket 350 and the rod 351 to a pair of plates 110,111, the plates 110 and 111 being spaced half a wavelength apart and the plate 331 being movable about a mean position a quarter wavelength ahead of plate 110. Pumps 315a and 315h are secured to the top and bottom respectively of plate 110, each inclined at an angle to the horizontal Pistons (not shown) are connected to pump actuating rods 320a and 320b- respectively, the rods 320a,320b being secured to a common mounting point 340 on the plate 331.In operation plate 331 will move relative to plates 110,111 in response to both vertical and horizontal movement of a wave which passes it, and operation of the pumps 315a 315b will be actuated via rods 310a,320b.

WHAT I CLAIM IS: 1. Apparatus for converting energy from liquid waves including at least two parallel plates arranged generally vertically one behind the other in a body of liquid, float means biassing the plates upwardly in the liquid, and pump means connected to adjacent plates, the plates being disposed substantially normally to the direction of wave movement in the liquid such that wave movement induces a relative horizontal motion of adjacent plates which actuates the pump means, the plates being spaced apart by one half of a wavelength.

2. Apparatus for converting energy from waves including three plates arranged generally vertically, two trailing plates fixed relative to one another with a horizontal spacing of half a wavelength and a leading plate moveable about a mean spacing one quarter wavelength from the adjacent trailing plate, float means biassing the plates upwardly in the liquid, and pump means connected to the leading plate and to the trailing plates, the plates being disposed substantially normally to the direction of wave movement in the liquid such that wave movement induces a horizontal motion of the leading plate relative to the trailing plates which actuate the pump means.

3. Apparatus as claimed in any one of claims 1 to 2 wherein the pump means include an intake for the liquid in which the plates are immersed.

4. Apparatus as claimed in any one of claims 1 to 3 in which the pump means include a piston and cylinder arrangement with inlet and outlet valves.

5. Apparatus as claimed in claim 4 wherein the pump means is double acting.

6. Apparatus as claimed in any one of claims 1 to 5 wherein the leading plate is connected to the adjacent plate by a tie rod which extends from a bracket at the base of the leading plate to the top of the adjacent plate.

7. Apparatus for converting energy

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (20)

**WARNING** start of CLMS field may overlap end of DESC **. depth of each, and their spacing can be adjusted to optimize the performance. For example, in the apparatus illustrated in Figures 5 and 7, the vertical plates may be close together, but the depth of the plates below the water line may be roughly equal to the wavelength of the waves divided by 6.28 to achieve optimum performance. In the apparatus illustrated in Figures 8 and 9 the spacing of the plates in the direction of propagation of the waves may be one half wavelength to achieve the best efficiency. In particular, as the waves are absorbed their amplitude decreases from the seaward to the landward end of the device.To obtain optimum matching the diameter of the bellows may be gradually increased towards the landward end, so that the velocity of the water inside the bellows is progressively reduced to match the decreasing external particle velocity in the waves. The size of the plates may also increase towards the landward end. Each plate may be a flat plate as shown in the drawings or may be a hollow plate in which water may be stored. In this case, the bellows leading in and out of such plates may be offset relative to each other. The apparatus may be maintained in alignment by adjustment of mooring devices. Alternatively the hydraulic energy developed by the apparatus may be used to orientate the apparatus, or even to move the apparatus through the liquid medium. Whilst the embodiments of the invention herein described have been described and illustrated as having floats 13,113,212 lying on the liquid surface, this need not be so. The floats may be arranged to lie below the liquid surface by adjusting their buoyancy, the weight of ballast, or the configuration of mooring arrangements. This will involve the loss of some potential wave energy (depending on how far below the liquid surface the floats lie) but will reduce- the amount to which the apparatus is liable to damage by factors, such as gales, other than the waves themselves. In many embodiments of the invention there will be some vertical movement of the plates accompanying the horizontal movement. Where the vertical movement is significant it may be profitable to convert it into energy to supplement the energy obtained from the longitudinal movement. Conversion may be by use of pumps having cylinders secured to fixed structure (such as mooring shackles) and pistons actuated by movement of the plates, or vice versa. A particular embodiment of the invention designed to take full advantage of both relative vertical and relative horizontal movement of adjacent plates (Figure 10) is similar to the embodiment as described with reference to Figure 2. A plate 331 is connected by a bracket 350 and the rod 351 to a pair of plates 110,111, the plates 110 and 111 being spaced half a wavelength apart and the plate 331 being movable about a mean position a quarter wavelength ahead of plate 110. Pumps 315a and 315h are secured to the top and bottom respectively of plate 110, each inclined at an angle to the horizontal Pistons (not shown) are connected to pump actuating rods 320a and 320b- respectively, the rods 320a,320b being secured to a common mounting point 340 on the plate 331.In operation plate 331 will move relative to plates 110,111 in response to both vertical and horizontal movement of a wave which passes it, and operation of the pumps 315a 315b will be actuated via rods 310a,320b. WHAT I CLAIM IS:

1. Apparatus for converting energy from liquid waves including at least two parallel plates arranged generally vertically one behind the other in a body of liquid, float means biassing the plates upwardly in the liquid, and pump means connected to adjacent plates, the plates being disposed substantially normally to the direction of wave movement in the liquid such that wave movement induces a relative horizontal motion of adjacent plates which actuates the pump means, the plates being spaced apart by one half of a wavelength.

2. Apparatus for converting energy from waves including three plates arranged generally vertically, two trailing plates fixed relative to one another with a horizontal spacing of half a wavelength and a leading plate moveable about a mean spacing one quarter wavelength from the adjacent trailing plate, float means biassing the plates upwardly in the liquid, and pump means connected to the leading plate and to the trailing plates, the plates being disposed substantially normally to the direction of wave movement in the liquid such that wave movement induces a horizontal motion of the leading plate relative to the trailing plates which actuate the pump means.

3. Apparatus as claimed in any one of claims 1 to 2 wherein the pump means include an intake for the liquid in which the plates are immersed.

4. Apparatus as claimed in any one of claims 1 to 3 in which the pump means include a piston and cylinder arrangement with inlet and outlet valves.

5. Apparatus as claimed in claim 4 wherein the pump means is double acting.

6. Apparatus as claimed in any one of claims 1 to 5 wherein the leading plate is connected to the adjacent plate by a tie rod which extends from a bracket at the base of the leading plate to the top of the adjacent plate.

7. Apparatus for converting energy

from liquid waves including at least two plates arranged generally vertically in a body of liquid, float means for maintaining the top of the plate on or above the liquid surface, at least one bellows extending between the or each pair of plates and at least two non-return valves associated with each bellows for permitting flow through the bellows in one direction only, the arrangement being such that, in use, wave movement of the liquid induces relative to and fro movement between each pair of plates thereby to pump a fluid through the bellows.

8. Apparatus as claimed in claim 7 wherein the pumped fluid is the liquid in which the apparatus is located.

9. Apparatus as claimed in claim 7 or in claim 8 in which each plate includes at least one hole in which a non-return valve is fitted.

10. Apparatus as claimed in claim 9 wherein a bellows interconnects a corresponding pair of holes in adjacent plates.

11. Apparatus as claimed in any one of claims 1 to 10 in which the first plate in the direction of travel of the waves is anchored in a manner which does not restrict the to and fro movement of the plate.

12. Apparatus as claimed in any one of claims 1 to 11 wherein each plate is supported by a float attached to the plate at approximately one fifth of its depth.

13. Apparatus as claimed in any one of claims 1 to 12 including means for converting relative vertical movement of adjacent plates into energy.

14. Apparatus as claimed in claim 2 wherein the leading plate is attached to the adjacent trailing plate in such a way as to also move vertically relative to the adjacent trailing plate in response to vertical wave movement, and the pump means are so disposed as to convert both vertical and horizontal relative movement into energy.

15. Apparatus as claimed in any one of claims 1 to 14 wherein the energy is converted into potential energy by pumping liquid into an elevated lake.

16. Apparatus as claimed in any one of claims 1 to 14 wherein the energy is converted by operation of a turbine.

17. Apparatus as claimed in any one of claims 1 to 16 wherein part of the energy is converted into means for moving the apparatus.

18. Apparatus constructed and disposed substantially as herein described with reference to Figures 1 to 3 as filed with Patent Application 8734/78.

19. Apparatus constructed and disposed substantially as herein described with reference to Figures 1 to 4 as filed with Patent Application 27271/77.

20. Apparatus constructed and disposed substantially as herein described with reference to the accompanying Figure 9.