WO2009137884A1

WO2009137884A1 - Improved ocean wave energy converter

Info

Publication number: WO2009137884A1
Application number: PCT/AU2009/000611
Authority: WO
Inventors: Dullaway Glen
Original assignee: Perpetuwave Power Pty Ltd
Priority date: 2008-05-15
Filing date: 2009-05-15
Publication date: 2009-11-19
Also published as: EP2313646A4; US8536724B2; US20110068579A1; AU2009246060A1; BRPI0912623A2; EP2313646A1

Abstract

An ocean wave energy converter comprising a structure that is supported above the water and has means to stabilise the structure, an array of guided independently operated elongate floats that operate from the structure above via two or more guidance arms, each guidance arm is attached to the structure so that the floats pivot about the horizontal axis parallel the length of the floats, each float is attached to the guidance arms at the centre of buoyancy of the float, and the floats are substantially parallel to the wave fronts.

Description

IMPROVED OCEAN WAVE ENERGY CONVERTER

TECHNICAL FIELD

The proposed invention relates to a much improved design of ocean wave energy converter suitable for extracting energy from ocean waves. The energy converter uses an oscillating or reciprocating motion of a number of independently operated elongated floats to produce electrical or other form of useful energy including to power a desalination plant or pumping plant etc. The floats are guided by two or more guidance arms for each float. BACKGROUND and PRIOR ART

Designing a successful ocean wave converter or power plant is truly a complex issue, and a large number of designs have been trialled over a hundred years but still none are in commercial production and none have proved beyond doubt via the public release of actual performance levels (which is the standard in the established wind turbine and solar industries) that the design can make commercial levels of power output let alone at an acceptable cost. The reality is there is a limited amount of energy in the oceans waves with average wave height of about 1 metre prevalent in most oceans of the world, and the energy is very difficult to extract being a pulsing type energy available about every ten seconds being an average wave period, and some 50 + metres between consecutive waves. This makes it extremely difficult to produce commercial levels of consistent electricity and for a design to be successful in this environment requires a very specific design that is tailored to the energy source. The prior art shows many different ocean wave energy converter designs have used floats or buoy type designs to extract the energy from the waves, and these are either independently operated or non independently operated and are either round or cylindrical designs or those that are elongated or rectangular. The present invention relates to those ocean wave energy converters that use an array of elongated floats that are independently operated.

In U.S. Patent No 1,925,742 a single trailing arm has a float thereto a fixed and as such the design is very low in power production and has a very small buoyancy volume to move up a wave, and is totally different to the current invention. In U.S. Patent No. 3,957,398, two telescopic arms are fixed to an elongated float that are operated independently of each other. The small buoyancy volume offered by these cylindrical floats and the large distance between the floats is very inefficient at extracting energy from the waves and again results in low performance per square meter of the energy converter and is very different from the current invention. Ih U.S. Patent No. 4,560,884 two trailing arms are pivotally attached to each elongated independently operated float but these floats are to small and are spaced to far apart for the wave energy converter to make sufficient power for each square metre of energy converter, and thus again the design has a low power output and is not economical. As a result none of the above prior art have the right mix of features required to produce a high energy density/acceptable cost ocean wave power energy converter such as is disclosed herein. Object of the Invention

The object of the present invention is to disclose and protect a novel float based ocean wave energy converter as disclosed herein that provides far superior performance through the optimal shape, sizing, spacing, design and operation of an array of independently operated and guided elongated floats that results in an efficient, robust, high power density and cost effective power plant to be produced.

Thus the major object of this invention is to protect an ocean wave energy converter where, an array of two or more closely spaced elongated floats are pivotally attached to two guidance arms operating from the structure above and the guidance arms are suitably disposed so that, as the floats move up they also to a smaller extent move backwards in the direction of wave travel which has the affect of increasing the energy that can be converted by the float and guidance arm system, especially the energy in a breaking wave and thus reduces the maximum destructive loadings on the floats and associated structure etc as the energy of the moving water in a breaking wave can be harnessed to assist in forcing the float up and backwards to produce more energy. In the preferred design the above said guidance arms are trailing arms and preferably by means disclosed herein allow for the said floats to be positioned closely together and operate in extreme conditions without interfering with adjacent floats and the most preferred design also allows for any float to be raised for maintenance without inhibiting the operation of any other float. In the broadest scope of this invention the elongated floats are shaped and sized so that maximum energy extraction from a normal wave can occur, and in the preferred design the front of the floats is substantially angled back at the bottom or is rounded at the lower front corner so that they work better in severe conditions and assist in extracting energy from the breaking component of the waves energy. In its broadest scope there are not means provided to freely allow for the float to move on an angle if required, but in the preferred design there is means provided to freely allow the for the floats to operate well on an angle if waves are approaching from either side of parallel to the long side of the elongated floats, or if the waves are higher on one end to the other end.

Various other aspects of the invention also disclosed herein relate to the design of and method of operation of other crucial mechanical and structural aspects of the wave energy converter required to realise the energy efficiency and power density required for a viable wave energy converter.

Description of the Invention

The invention that I seek protection for is described as having; a structure that is supported above the water and is stabilised by means to at least substantially reduce rocking of the structure as an array or plurality of two or more floats extract energy from the waves, the floats are independently operated elongated floats that are guided from the structure above by two or more guidance arms each to extract energy from the waves at least on the upward stoke, the guidance arms may in the broadest scope be of the reciprocating telescopic type design that leans backwards less than 40 degree or they may be of the trailing arm type of design that pivots from the structure and in the preferred design improved operation is shown by the disclosure of various improvements, with reference to the length of the float each guidance arm is pivotally attached equidistantly to the elongated floats from above so that the floats pivot about the horizontal axis parallel to the elongated sides of the floats and with reference to the width of the float the guidance arms are attached at or about the average centre of buoyancy (+ or — 15 % of the width of the float from the centre of buoyancy), the floats are at least substantially parallel to the wave fronts when at rest meaning the structure may or may not have yaw with the floats being parallel to the mean wave direction if the structure does not yaw, the guidance arms cooperate with the structure and provide for the floats to move up and down in a repetitive motion as the waves pass and to transfer energy from the floats to the drive means being any form of hydraulic fluid or gas or direct drive means that results in a useful application of the energy, The floats are substantially four sided, rectangular or elliptical or any combination thereof with the weight of the combined guidance arms and float upon the float at rest being between 5 % and 50 % of the buoyancy offered by the float. The average height of a float is between 10 % and 80 % of the average width of the float and the length of a float is more than 250 % of the average width of the float, The average gap between the elongated sides of the floats at rest is less than 200 % of the average width of the floats, and in the most preferred design the gap is between 15 % and 70% of the average width of the float

In the preferred design at least in larger wave height conditions the float is caused to become at least partially submerged into a wave front before or as the float moves up over the wave, and then the said float at least substantially retains its extent of submergence for at least a substantial part of its upward stroke. The combined weight of the guidance arms on the floats and floats at rest is between 10 % and 35 % of the buoyancy offered by the float and the length of the elongated floats is more than 300 % of the average width of the floats and less than 2000 % of the average width of the floats, the average height of the floats is between 20 % and 50 % of the average width of the floats, the front side of at least some of the floats are shaped like the front lower half of an eclipse, or angled back from the top so the average angle of the rounded or angled portion of the said front &ce from horizontal is between 20 degree and 70 degrees from the front upper corner looking back and with the most preferred design the said angle is between 35 degrees and 55 degrees. In the preferred design the guidance arm to float pivot allows for limited sideways outward movement of the swing arm relative to the float of up to 20 % of the width of a float from its state of rest position so the float can operate well on an angle to the wave, or if the wave is lower at one end to the other end. In the preferred design the extent to which the float is forced to become submerged into the wave and as the float moves up over the wave is at least greater when the average wave height is between 2 to 3 metres than when the average wave height is about a half metre, and in the most preferred design the float is submerged into the wave by more than 30 % more when the average Hsig wave height is between 2 to 3 metres than when the average wave height is between .5 and .7 metre. Further preferences have the guidance arm being a trailing arm and the trailing arms and float do not interfere with adjacent floats or adjacent trailing arms while operating, the width of the float being sized relative to the length of the trailing arms and the trailing arms being attached between about the average centre of buoyancy of the float and 15 % of the width of the float behind the average centre of buoyancy,

Ih the most preferred design, means are so disposed so that any one of the trailing arms may be raised while the wave energy converter is in operation without reducing the stroke angle of the adjacent swing arms, and in the preferred design the said means to allow the swing arm to be lifted without interference of any other float or trailing arm is by having the trailing arms of each later float going back, being offset to the outside of the previous trailing arms and the trailing arm float pivot is located off the end of the float and may be located above or below the top of the float It is also preferred that each subsequent float going back is longer than the previous float by about the distance needed to clear the previous trailing arm, so that the distance from the said float to the trailing arm float pivot is maintained. It is further preferred that the structure is supported above the water by pontoons or hulls and these may be partly filled or emptied with water by pump means to adjust the height of the energy converter or to compensate for high side winds.

©RAWING FIGURES.

Fig — 1. is a end view of an array of floats according to the present invention.

Fig — 2. is a top view of the array of floats as shown in Fig - 1.

Fig — 3. Is a front view of a float and attached guidance arms and showing the guidance arm float pivot.

Fig — 4 is a partial cutaway side view of a floating version of an ocean wave energy converter that has yaw.

DESCRIPTION REFERENCED TO THE DRAWINGS.

FIG - 1 and FIG - 2 show respectively an end view and top view of an array of floats 1 that shows some of the various possible combinations of float 1 shape and guidance arm float bracket 4 are shown that fall within the scope of this invention. The length (L) of the floats 1 is about six hundred percent of the width (W) of the float 1. The float 1 on the left in FIG - 1 and FIG - 2 is the forward float 1 of the array and has a rectangular back section and an elliptical front lower section with the guidance arm float brackets 4 located in from the end of the float as shown. In the centre float lof FIG's - 1 and FIG - 2 the float 1 has a rectangular rear section and an angled front section for eighty percent of the height of the front side as shown on an angle of fifty degree from the top. On the float on the left and the float in the middle of FIG -1 and FIG - 2 the guidance arm float bracket 4 is wider than the width of the guidance arm so the guidance arm may slide sideways relative to the float. In the float 1 on the right hand side of FIG' s — 1 and 2 the float 1 has a rectangular section on the top and the underside is convex being the bottom half of an eclipse, and the guidance arm float bracket 4 is located below the top of the float, and the respective guidance arm float brackets 4 are shorter than on the other two floats and only located pivotal movement of the floats is provided. Adjacent floats 1 have a gap (g) between the elongated sides of the floats 1 of between forty and fifty five percent of the float width (W), as the floats 1 are spaced at essentially the same distance apart but the difference in (G) comes about due to (W) being taken as the average width of the float 1. For the same reason the height of the floats is between thirty percent and forty percent of the width of the floats. Also the float guidance arm 2 location relative to the width of the floats 1 is between the centre of buoyancy and ten percent of the float width behind the centre of buoyancy.

In FIG — 3 a float is shown with the guidance arms 2 shown extending from the pivot point with the float (1) to guide the floats 1. The pivot point comprises a float guidance pin (3) that is secured at both ends by the guidance arm float bracket 4 which is firmly fixed to the float 1, and the respective guidance arm 2 which pivots about the float guidance pin (3). On the left hand side of the float 1 a located pivot design is used while on the right hand end the float guidance pin (3) can be seen to be extended and this allows the guidance arm 2 to slide along the shaft for a short distance. On the right hand end of the float 1 the hole in the end of the guidance arm 2 that goes around the float guidance pin 3 is five percent larger than the diameter of the float guidance pin 3 to allow for the float 1 to have limited movement to slide back and forth along the guidance arm 2 as it moves to change its angle on a wave. The broken lines show the extent of possible movement of the guidance arm 2 about the float 1 when a float 1 is caused to operate on an angle due to the variations in wave conditions. Figure 4 shows a side view of an ocean wave energy converter wife an array of floats 1 and guidance arms 2 according to the present invention. The ocean wave energy converter has its structure 5 being rectangular and made of steel and supported above the water by a hull or pontoon 6 at each corner. The structure 5 is secured by first mooring means at the centre of the front of the structure being a permanent anchor and chain 8 attached to the structure 5 and the said structure is also secured at the front and rear of each side by respective mooring means and a respective chain 9 which extends thereto. The length of the side mooring chains 9 is adjustable by an anchor winch that extends the length of one side while reducing the length of the chain on the other side so the ocean wave energy converter can yaw and always operates at the correct angle to the waves 11 which is with the elongated floats 1 parallel to the waves 11. The energy converter is shown with a wave 11 passing along it towards the rear as shown by the arrow 10. The guidance arms 2 are of the trailing arm type of design and the pivot point 7 is at the forward end of the guidance arms 2 where they pivot from the structure 5 above and have limited pivotal movement along the horizontal axis parallel to the wave 11 front, with the pivot point 7 using bearings a housing and an axle. Two guidance arms 2 are pivotally attached to each float 1 from above and the design of float 1 and guidance arms 2 allow for any floats to be removed from the water without interrupting any adjacent floats 1. The guidance arms 2 of the first float 1 to the left of the drawing, pivots from a lower point on the structure than the other guidance arms and the said first guidance arm 2 has a dog leg downwards approximately halfway along to improve movement of the respective float 1. The guidance arms of the first float 1 are located in from ten percent in from the end of the float 1. The guidance arms 2 of the second float 1 are located off the end of the float 1 with both first and second floats 1 being the same length. With reference to the third float 1 from the front and every float 1 thereafter is five percent longer than each previous float 1 and the guidance arms 2 are straight and pivot off the end of each float 1 as shown in FIG - 3. The guidance arm float brackets 4 in combination with the guidance pin 3 and guidance arms 2 allow the floats 1 to have limited pivotal movement about the horizontal axis, and also allows for the guidance arms 2 of each respective float 1 to slide along the guidance pin 3 for a limited distance of up to ten percent. The length of the floats 1 is nine hundred percent of the average width of each float 1 and the average height of the floats 1 is forty percent of the average float 1 width. The floats 1 are rectangular in section at the rear and the lower front is like an eclipse with the average angle being about forty five degrees from the top of the float 1. At rest the elongated sides of the floats 1 are located fifty percent of the width of a float 1 apart. The ocean wave energy converter only extracts energy from the waves 11 as the elongated floats 1 are moving up a wave 11 front. A fresh water based hydraulic system provides for the power transfer from the float 1 and guidance arm 2 combination to a common accumulator which then provides a steady consistent flow of water for a hydroelectric type water turbine and attached generator. A water based hydraulic ram 12 is pivotally attached to each guidance arm 2 at one end about halfway along each guidance arm 2, and the hydraulic ram 12 is pivotally attached to the structure 5 at the other end. As the floats 1 are forced to move up over the wave 11, the attached guidance arm 2 and hydraulic ram 12 are forced upwards and pumps water out of the upper end of the cylinder of the hydraulic ram under a high pressure to charge an accumulator which in turn supplies a consistent flow of water under pressure to drive the water turbine and attached generator. The hydraulic rams 12 are refilled with fresh water as the floats 1 are moving down. The lower end of the cylinder of the hydraulic ram 12 is vented to atmosphere. A separate front resistant plates 13 and a rear underwater resistance plate 14 are located under the respective front and rear ends of the energy converter. The front resistance plate 13 is fixed horizontally and extends out either side of the energy converter and is not located under or in front of the array of floats 1, and is located about nine metres below the surface of the water. The rear resistance plate 14 is located directly under the rear section of the array of floats 1 and adjustable up or down at the front and back of it so the angle of it from horizontal may be raised up at the rear of it to increase wave height when wave height is small, or to be horizontal when wave height is high. The hulls 6 are elongated and located at each comer of the structure and the front hulls 6 are substantially perpendicular to the long sides of the floats while the rear hulls 6 are each on an angle of thirty degrees so they are spaced at a greater distance apart at the front than at the back and assist to direct waves into the most rear floats not shown. Some of the irrelevant features have been left from the drawings to reduce cluttering and to disclose more clearly what is protected. In an alternative preferred design which is not shown in the drawings, the ocean wave energy converter is a tri-maran with three hulls the central hull being a much larger hull and taking the wave energy converter is secured for limited yaw about a large pylon fixed to the ocean floor about the front of the wave energy converter. The pylon substantially stabilises the front of the energy converter. The guidance arms are telescopic type arms that reciprocate up and down via a linear slide type design that is attached to the structure. The float guidance pin is not extended and the guidance arm pivot point does not provide for the guidance arm to slide back and forth along the float guidance pin. The guidance arm float bracket are fixed to the float about twenty percent of the length of the float in from the end of the floats. The guidance arms are angled back from vertical going up at an angle of fifteen degrees in the rear direction from vertical. Direct drive means is used to transfer energy from the guidance arm to the generator and this system uses a flexible cable that is attached to the top end of the guidance arm to then go about an idler pulley and then the said flexible cable goes around a drive pulley to cause a one way mechanism on a shaft to turn a rotating output shaft which drives an electrical generator. Energy is extracted from the waves on only the up stroke of the floats. Only a rear resistance plate is used, this is adjustable in height and angle.

A further alternative design shares some similar features to that shown in FIG - 4 but the structure is permanently fixed to pylons located about the four corners of the structure. No hulls are used and the structure is raised up or down the pylons to the changing tide height by large hydraulic rams. The floats are substantially as shown in FIG - 4 except that both the upward and down ward stroke of the float is used to generate useful power and this is achieved by the lower side of the hydraulic rams being used to pump water out under pressure as the floats move down and they refill with water as the float moves up. The guidance arms are also of the trailing arm type, however the guidance arms and the respective pivot points are located about twenty percent of the width of a float in from the end of the respective float, and the trailing arms are of the dog leg design shown on the forward most float in FIG - 4. Adjacent guidance arms are offset so the guidance arms allow uninterrupted movement of the floats. There are no resistance plates used on this version and the structure is stabilised by the pylons.

These different types of ocean wave energy converter and float operation/ guidance are shown to illustrate that this invention may be successfully operated in a number of different design variations, and it is obvious to one skilled in the art that other changes and variations are protected by this patent application.

Claims

CLAIMSWhat is claimed is,

1. An ocean wave energy converter comprising, a structure that is supported above the water and has means to at least substantially stabilise the structure, an array of guided independently operated elongated floats that operate from the structure above via guidance arms that cooperate with the structure and with the float at the other end, each float is guided by two or more guidance arms each to move substantially up and down in a repetitive manner and to extract energy at least on the upward stoke, with reference to the length of the float each guidance arm is pivotally attached equidistantly from above so that the floats pivot about the horizontal axis parallel to the elongated sides of the floats and with reference to the width of the float the floats are attached at or about the average centre of buoyancy of the float, the floats are at least substantially parallel to the wave fronts when at rest, the combined weight of the guidance arms on the floats and floats at rest is between 5 % and 50 % of the buoyancy offered by the float, the length of the elongated floats is more than 250 % of the width of the floats, the gap between the elongated sides of the floats at rest is less man double me average width of the float, the average height of the floats is between 10 % and 80 % of the average width of the said float,

2. The invention described in Claim 1 wherein, the floats extract energy from the ocean waves at least substantially on the upward movement of the float, means are provided to cause the float to become at least partially submerged into a wave front before or as the float begins to move up over the wave and at least substantially retaining its extent of submergence as it continues to move up over at least most of the wave.

3. The invention described in Claim 2 wherein, the height of the floats is between 20 % and 50 % of the width of the float, the combined weight of the guidance arms and float on the floats at rest is between 10 % and 50 % of the buoyancy offered by the float, the gap between the elongated sides of the float is less than 125 % of the width of the adjacent floats.

4. The invention described in Claim 3 wherein, the guidance arms are trailing arms with the forward end pivoting from the structure above, adjacent trailing arms are located closer together than the combined length of a trailing arm and a half of the width of the attached float, the trailing arms at least substantially do not interfere with adjacent floats whilst operating, the axis of the guidance arm float pivot is located between about the average centre of buoyancy of the float and 15 % behind the average centre of buoyancy of the float

5. The invention described in Claim 4 wherein, adjacent trailing arms and their respective pivot point are offset from the adjacent trailing arms and pivot points, the relative width of the floats is between 25 % and 90 % of the length of the trailing arm, the gap between the elongated sides of the floats is between 10 % and 80 % of the average width of the float.

6. The invention described in Claim 5 wherein, the relative width of the floats is between 30 % and 80 % of the length of the trailing arms, the floats are forced to become submerged into the wave and as the float moves up over the wave, the extent of the submergence is at least greater when the average wave height is between two and three metres high than when the average wave height is about half a meter.

7. The invention described in Claim 6 wherein, the float is substantially rectangular or four sided in cross sectional view except for the front side and lower front corner which is at least substantially angled back or is rounded like the lower front of an eclipse so that at least a substantial portion of the front side is between 20 degree and 70 degree from horizontal.

8. The invention described in Claim 7 wherein, the trailing arms are so disposed so that a float may be at least substantially lifted from operation without interfering operation of any adjacent floats, the length of the elongated floats is between 250 % and less than 2000 % of the width of the float

9. The invention described in Claim 8 wherein, the float trailing arm pivot and trailing arm are by means so disposed that the float easily operates on an angle if a wave is arriving at an angle or is lower at one end than the other end, the pivot points of adjacent trailing arms are closer together than the length of the trailing arm, the length of the elongated floats is between 300 % and less than 1500 % of the width of the float.

10. The invention described in Claim 9 wherein, the means of allowing the float to easily operate well on an angle is provided within the pivoting connection of the float and trailing arm with the trailing arm being suitable disposed to slide along an extended float pivot shaft which it is secured to, for a limited distance of less than 50 % of the width of the float.

11. The invention described in Claim 10 wherein, the float is caused to be submerged more than 30 % more into a wave at least when the average wave is between 2 and 3 metres high than when the average wave is between .5 and .7 meters.

12. The invention described in Claim 11 wherein, the trailing arms of each later float are offset to the outside of the previous trailing arm with the float and attached trailing arms being shorter in length than the distance between the insides of the later two trailing arms so that the trailing arm and attached float can be swung through its entire stroke while not interfering with the adjacent floats or trailing arms.

13. The invention described in Claim 12 wherein, each later float is longer than the previous float in the array so that the distance from the float to the trailing arm float pivot remains substantially the same.

14. The invention described in Claim 13 wherein, the structure is supported above the water by its own pontoons or hulls and large horizontal stabilizer plates are located more than 1 metre down in the water off to either side of the front of the energy converter and at the rear of the ocean wave energy converter, the angle of the front face of the floats is between 35 degree and 55 degree from the horizontal top.

15. The invention described in Claim 14 wherein, the pontoons or hulls that support the structure above the water have water pump means to pump water into and out of any one or all of the pontoons or hulls to adjust the height of the energy converter as required.

16. The invention described in Claim 15 wherein, at least under part of the rear half of the array of floats an adjustable plate that can be angled upwards in the rear direction and which may be the stabiliser plates, is adjustable in height from one or both ends so that the adjustable plate acts like a false shoreline to reduce the depth of the water as the waves move further along and thereby force the waves upwards at least when the average wave height is less than 1 metre.

17. The invention described in Claim 16 wherein, The trailing arm float pivot is located lower on the float than the average top of the float.

18. The invention described in Claim 7 wherein, the trailing arms are of the dog leg type guiding the front float in FIG - 4.

19. The invention described in Claim 8 wherein, the trailing arm float pivot point is a located pivot that only allows for the float to pivot about the trailing arm.

20. The invention described in Claim 7 wherein, the design is substantially as disclosed and described in FIG -4.