WO2015082871A1

WO2015082871A1 - A module and modular apparatus for efficiently producing waves in a body of water

Info

Publication number: WO2015082871A1
Application number: PCT/GB2014/000505
Authority: WO
Inventors: John Baxendale
Original assignee: Wave-Master Systems Limited
Priority date: 2013-12-07
Filing date: 2014-12-08
Publication date: 2015-06-11
Also published as: GB201506699D0; GB201321688D0; GB2533440B; GB2533440A

Abstract

This invention relates to apparatus for the energy-efficient production of non-turbulent waves in a body of water and capable of producing a discrete wave or a succession of waves having a repetition rate and size that is suitable for surfing. The wave-making apparatus comprises a plurality of wave-making modules arranged side by side in parallel in a body of water (5) having an opposing beach (4) on which the waves may break. Each wave-making module comprises a reservoir (2) and a piston (1), the piston suspended so as to be able to move freely in a horizontal direction within the reservoir. Waves are generated in the body of water by the withdrawal (6) and forward (7) motions of the piston 1 when driven by an actuator. The design of the apparatus makes use of the resonant cavity that is formed between the piston (1) and the back wall of the reservoir (9), and makes use of the otherwise wasted wave energy from the withdrawal stroke of the piston, when reflected from the back wall of the reservoir (9), to supplement the forward, wave-generating stroke of the piston and thereby produce large non-turbulent waves with a high energy efficiency that are suitable for surfing and recreation. By energizing each wave-generating module in a sequence from one end to the other avoids the very high power requirement that would result from their simultaneous activation.

Description

A Module and Modular Apparatus for Efficiently Producing Waves in a Body of Water

Field of the Invention

This invention relates generally to a module and modular apparatus for efficiently producing non-turbulent waves in a body of water. The apparatus is assembled from a plurality of the modules to generate waves in a body of water. The apparatus is for use in the field of recreational surfing and generates waves in a body of water either in isolation or with a high repetition rate and which are of a size and repetition rate that are suitable for surfing.

Background

Waves that are generated artificially for surfing or recreation in a body of water known as a wave-pool must meet a number of criteria:

1. They must be of sufficient size and preferably exceed one metre in height.

2. They must travel at their natural velocity from the wave-making apparatus towards a shelving beach where they may break and dissipate their energy without being reflected.

3. For the installation to be economically viable, they must be produced at a high repetition rate, preferably in excess of 180 waves per hour.

4. The waves should be essentially monochromatic, i.e. of a single frequency and without any significant smaller intermediate waves or harmonics.

5. The waves should have 'laminar flow' characteristics as opposed to 'turbulent flow'.

By controlling the bottom profile of the wave-pool, or the direction of the waves, or a combination of both, the waves should be caused to break or peel progressively from one end to the other, thereby creating waves that are of interest to surfers. Prior Art

Existing wave-making apparatus include water reservoir apparatus, whereby water is pumped into one or more vertical tanks located at one end of a wave-pool. When full of water, rapid-action valves are opened to evacuate the stored water into the wave-pool by gravity and thus generate a wave. The two principal problems with this method are that the waves are turbulent and also the waves can only be produced at a rate of 30 to 40 per hour depending on the power and capacity of the pumps.

Another example of a wave-pool utilises a paddle or flap which is hinged at the bottom of the pool and described in U.S Patent No. 4,062,192 and U S Patent No. 4,976,570. Actuators are arranged to move the paddle to and fro in order to generate waves. Due to the smaller volume of water displaced by the paddle, the waves produced by this method are smaller than those produced by a piston.

A third type of wave-making apparatus is typified by U.S. Patent No. 6,716,107 and U.S. Patent No. 5,564,859 and U.S. Patent No. 5,171 ,101. A wide, thin jet of pumped water is directed horizontally against a fixed, curved profile in order to simulate a breaking wave. Though popular, a problem is that these do not behave like ocean waves and are regarded by surfers as an entirely different sport.

Afourth type of wave-making apparatus is described in U.S. Patent No. 2012/00 17951 A1. This apparatus moves an underwater profile on tracks along the bottom of a wave-pool. The water thus displaced forms a breaking wave. The principal problem with these pools is that because the underwater profile has to be moved back and forth along the bottom of the wave-pool, a wave repetition rate of only about 120 per hour can be achieved.

A fifth type of wave-making apparatus is in a scientific journal article 'Accuracy of Solitary Wave Generation by a Piston Wave-Maker' by Katell Guizien and Eric Barthelemyn, Journal of Hydraulic Research, Vol. 40, 2002, No. 3. The article describes mathematical basis for an experimental procedure to generate solitary waves in a flume using a piston type wave maker.

A sixth type of apparatus and method for generating waves in a body of water is revealed in US Publication 4976570 (Walter R. Davis, Todd H. Nahraup). A moveable wave-generating member is cyclically reciprocated in the body or water to make waves. A disadvantage of this device is that a chamber and a baffle positioned adjacent the wave generating member dissipates energy from the return stroke. As the dissipated energy can do no useful work, the apparatus is inefficient for producing waves.

Further methods and mechanisms for generating waves suitable for surfing such as US Patent Publication 4062192 and US Patent Publication US53421 5 are known, but like the aforementioned methods and mechanisms they suffer from not being able to efficiently produce waves suitable for surfing.

Summary of the Invention

According to one aspect of the invention there is a wave generating module for a wave-making apparatus comprising a flume which is flooded with water through an open end, a back wall which blocks the flume, and a barrier constrained to move along the flume intermediate the back wall and the open end, characterised by a reciprocating means arranged to displace the barrier towards the back wall to generate a wave toward the back wall that is reflected from the back wall to assist subsequent displacement of the barrier away from the back wall in generating a wave through the open end. Advantageously energy from the reflected wave is added to the energy input by the reciprocating means in displacing the barrier away from the back wall. The effect is that the height of the wave that is generated through the open end is increased by the additional energy.

Preferably the reciprocating means is arranged to vary the rate of displacement of the barrier with a substantially sinusoidal cycle. Advantageously the sinusoidal cycle substantially minimizes the amount of energy required to be input by the reciprocating means since the barrier speed and direction of the barrier varies smoothly so that little if any turbulence is generated in the water in the flume. The movement of water in the flume corresponding to the generated waves is laminar flow movement which dissipates less energy than turbulent flow. Preferably the reciprocating means is arranged to pause the cycle momentarily before starting the displacement of the barrier toward the back wall. A full cycle of the reciprocating means starts with the displacement of the barrier towards the back wall. The cycle ends with barrier coming to rest after the reciprocating means has displaced the barrier to a furthest position away from the back wall. Advantageously by pausing the reciprocating means at the end of the cycle, a preselected distance and time interval between waves generated through the open end is possible. The end of the cycle just before the reciprocating means starts the displacement of the barrier again towards the back wall. The preselected distance and time interval is selectable to accommodate the preferences of surfers who surf the wave generated through the open end. It is also selectable to vary the total amount of energy used by the apparatus per hour. In other words the length of the preselected pause is selectable for the preference of surfers and to limit the amount of power required by the wave making apparatus. Preferably the reciprocating means is arranged such that the period of the cycle coincides with a natural frequency of a standing wave in the flume reflected from the back wall. There is a natural frequency for a wave that travels though the water in the flume. By reciprocating the barrier at the natural frequency of the wave, the reciprocating displacement of the barrier is reinforced by the wave. The reciprocating displacement of the barrier also reinforces the height of the wave generated through the opening. The height of the wave is increased by the resonance of the wave with the barrier displaced by the reciprocating means.

Preferably the reciprocating means is arranged such that the speed that the barrier is displaced away from the back wall such that it coincides with the speed of the wave reflected from the back wall. Advantageously the reciprocating movement of the barrier is thereby in phase with the wave reflected from the back wall so as to capture the maximum amount of energy from the back wall.

Preferably in use the depth of water in the flume is substantially uniform where the barrier is furthest from the back wall. The wave reflected from the back wall impacts against the barrier. The wave is damped by the barrier because the speed of the barrier away from the back is slows as the reflected wave catches up to the barrier and impacts against it. The barrier slowed to capture the energy to the barrier rather than simply reflect the wave off the barrier. Advantageously by capturing the energy in the wave reflected from the back wall into the barrier, the captured energy is in turn transferred to the energy of the wave generated from the opening. The height of the wave generated through the opening is thereby increased by the energy of the reflected wave. As the barrier takes the energy out the reflected wave it damps out the wave in the flume. Advantageously the wave making machine may be tuned to generate high waves though the opening by observing the cyclic speed and period of the barrier required to make the depth of water in the flume substantially uniform where the barrier is furthest from the back wall because this is an indication that the energy of the reflected wave has been damped out of the water in flume and transferred to the barrier.

Preferably the reciprocating means comprises a pantograph to which the barrier is connected. Advantageously a pantograph extends linearly and therefore is a strong structural mechanism for reciprocating the barrier within the flume toward and away from the back wall.

Preferably the barrier is supported solely by the pantograph. Advantageously the pantograph fulfills the role of supporting the barrier as well as reciprocating the barrier. The barrier does not need to be supported by the bottom of the flume or any wall of the flume. Such a support contributes to frictional drag on the reciprocating motion of the barrier. Since the barrier is supported solely by the pantograph, there is no frictional drag by the flume and so the wave making apparatus is efficient.

Preferably the barrier is connected to two linked parts of the pantograph at a location on each part which remains fixed with respect to the other, so as to maintain the same orientation of the barrier relative the back wall as the barrier is displaced. The effect is that the barrier does not swing in flume like a door on hinge; rather it simply reciprocates back and forth in the flume. Advantageously a face of the barrier is maintained throughout the motion in the same orientation to push water in the flume toward the back wall and subsequently for a face on the reverse side of the barrier to push water in the opening toward the opening. The barrier is thereby efficient and effective at producing a wave throughout the entire cycle of reciprocal motion.

Preferably the barrier is connected to two linked parts of the pantograph at locations on each part which moves with respect to the other, such that in use horizontal displacement of the top of the barrier is further than horizontal displacement of the bottom of the barrier to emulate movements of water particles in the wave. Advantageously the barrier swings as it is displaced. This combination of motions causes the barrier to produce waves very efficiently with very little turbulence caused by moving the barrier through the water in the flume.

Preferably the module comprises a motor and crankshaft acting upon a structural member of the pantograph. Advantageously the barrier is displaced with near sinusoidal motion. Preferably the crankshaft is connected to a structural member that is pivotally connected to the flume. Advantageously the other parts of the pantograph do not have to be as heavy or massive which reduces cost and means that the amount of energy required to move the inertia of the pantograph is kept low so that the energy of the motor goes the barrier supported by the pantograph and the wave it generates. Preferably in use the height of the top of the barrier above the mean surface level of water in the flume is substantially 30 % to 45 % of the length of the barrier such that the barrier has neutral buoyancy.

Preferably substantially 30 % to 45 % of the length of the barrier extends above the mean surface level of water in the flume in use such that the barrier has neutral buoyancy. Preferably in use the height of the top of the barrier above the mean surface level of water in the flume is substantially 30 % to 45 % of the length of the barrier such that the barrier has neutral buoyancy. Thus preferably the height of the top of the barrier above the mean surface level of the water is substantially 30 % to 45 % of the length of the barrier. Preferably the reciprocating means supports the barrier so that substantially 30 % to 45 % of the length of the barrier extends above the mean surface level of water in the flume. Preferably the barrier is so supported by its connection to a pantograph.

In use the barrier generates a wave. The crest of the wave raises the height of the water pushed against the barrier. About 30 % to 45 % of the length of the barrier extends above the mean level of water in the flume in use. The density of the barrier is such that with the bottom 55 % to 70 % of the barrier in water the barrier has neutral buoyancy. Advantageously a barrier with neutral buoyancy does not need to be held up by the reciprocating means or by any connection to a wall of the flume. The barrier also does not need to be supported by the bottom of the flume. The reciprocating means does not have to be as massive or as heavy or expensive since it does not need to hold up the barrier. The reciprocating means only needs to move the barrier to move with reciprocal motion along the flume. Since there is no connection of the barrier to the flume and no friction such as could otherwise be caused by the barrier sliding along the bottom of the flume.

Preferably the barrier has a length in the direction of the depth of the flume predetermined to be substantially 160 % of the mean depth of a water in which the flume is to be flooded, so that in use substantially 35 % to 40 % of the length of the barrier extends above the mean surface level of the water. Advantageously as the barrier generates a wave the crest of the wave does not overflow the top of the barrier so the full power of the reciprocating means and reflected wave is used. Advantageously the barrier is not longer or heavier than it needs to be since the maximum height of a crest of a wave produced by the barrier is about 160 % of the mean depth of the water.

Preferably the flume is formed by a pair of lateral walls. Advantageously this simple construction of the flume is achieved by metal, polymer, or cement panels. Preferably the lateral walls are substantially parallel flat panels. Advantageously the flume that is formed by parallel flat panels is a straight trough which a reciprocating means such as a hydraulic ram or pantograph can extend and retract straight along.

Preferably the lateral walls support the back wall between them. Advantageously as a result the lateral walls and the back walls form a stabile flume structure. According to another aspect of the invention there is wave making apparatus comprising an array of wave making modules as described herein; the wave making apparatus comprising a plurality of the wave-making modules arranged side by side with their flumes in parallel and energized from end to end in sequence to require less power than would result from simultaneous activation. Advantageously the modular construction of the wave making apparatus permits modules to be manufactured at factory remote to a construction site. The modules are conveniently transported in a vehicle over the road the construction site and at the construction site each module is taken off the vehicle and put in place side by side.

Preferably the reciprocating means of a second module is arranged to displace the barrier of the second module so that it follows the displacement of the barrier of the first module by a predetermined time interval. The direction of the crest of the wave with respect the array of modules is controllable by preselecting the time interval between cycles of reciprocating means of adjacent modules. This is also the time lag difference of cycles which corresponds to the phase difference of cycles. According to another aspect of the invention there is a wave-making module immersed in a body of water and comprising a water reservoir and a piston that is constrained to move horizontally within the reservoir when driven by an actuator such that the wave generated by the piston's withdrawal stroke is reflected from the back wall of the reservoir and thereby assists the forward stroke of the piston in generating a discrete wave or a succession of waves.

Preferably the suspension and horizontal movement of the piston is facilitated by means of a pantograph mechanism.

Preferably the piston is activated by means of a motor and gears and a crank acting upon a structural member of the pantograph. Preferably the pantograph mechanism is modified such that the horizontal displacements of the upper part of the piston are greater than the horizontal displacements of the bottom of the piston and thereby more closely emulates the movement of water particles in a natural wave.

According to another aspect of the invention there is a wave making apparatus comprising a plurality of wave-making modules according to claim 1 which are arranged side by side in parallel and energised from end to end in sequence in order to avoid the very high power requirement that would otherwise result from their simultaneous activation.

The advantages of the present invention overcome aforementioned problems of the prior art. This invention comprises a plurality of wave-making modules arranged in line in a body of water having an opposing beach on which the waves may break. Each wave-making module comprises a piston and actuator contained within a four-sided rectangular reservoir having an open end and an open top. These modules make use of otherwise wasted wave energy from the withdrawal stroke of the pistons in order to supplement the forward, wave generating strokes of the pistons and thereby produce large non-turbulent waves with a high energy efficiency and also with a high repetition rate that are suitable for surfing and recreation.

The invention will now be described, by way of example only, with reference to the accompanying drawings in which:

Brief Description of the Figures

Figure 1 is a side view of the module wherein a piston 1 is shown at its furthest rest position according to the invention. Figure 2 shows a graph of the piston displacement with time.

Figure 3 shows the side view of a single unbroken wave passing a fixed point and moving from left to right.

Figure 4 shows a cutaway view of a module in a body of water at the start of the cycle with the piston in its furthest rest position from the back wall. Figure 5 shows a cutaway view of a module in a body of water when the piston is half way through its withdrawal stroke.

Figure 6 shows a cutaway view of a module in a body of water when the piston at its maximum withdrawal towards the back wall of the reservoir where it has momentarily stopped at its closest rest position to the back wall. Figure 7 shows a cutaway view of a module in a body of water when the piston half way through its forward stroke. Figure 8 shows a cutaway view of a module in a body of water, the piston now having returned to its rest position.

Figure 9 shows a preferred embodiment of the piston wave-making apparatus in side view. Figure 10 shows a wave making apparatus comprising a plurality of wave-generating modules.

Figure 11 shows an isometric view of the module shown in Figure 1.

Detailed Description of the Invention Referring to a side view of the module 1000 in Figure 1 , a piston 1 is shown at its rest position. The piston is located within a five-sided reservoir 2 that is open at the piston end and at the top. The piston is also known as a barrier 1 because it blocks water from flowing from the within the reservoir 2 out through the open end 50 of the reservoir. The reservoir is also known as a flume because it has the form of a trough with an open end.

The reservoir is located at one end of the body of water, the bottom of the pool 3 gradually shelves towards a beach 4 at the furthest end. The piston 1 extends from the bottom of the reservoir to a height sufficient to prevent it from being over-topped by the waves. The piston is mounted so as to move freely in a horizontal direction. The piston need not be a perfect fit against the internal surfaces of the reservoir but allow for sufficient water to leak between the reservoir 2 and the main body of the wave pool 5 and achieve equilibrium within a few minutes.

An actuator, omitted for clarity, is provided in order to move the piston 1 into the reservoir in an initial withdrawal stroke 6 and then to return the piston to the rest position in a forward stroke 7. The volume of water thus displaced equals the displacement of the piston stroke multiplied by the depth of the water 8 and the width of the piston.

In wave-making apparatus such as that described in U.S. Patent No. 4,976,570 the waves and water movement produced behind the piston or within the reservoir represent wasted energy and considerable effort is devoted to dissipating this energy safely. It is a feature of this invention that the back wall of the reservoir 9 acts to reflect wave energy from the withdrawal stroke of the wave-generating piston in such a way as to supplement the wave-generating piston's forward stroke and thereby to increase overall efficiency. Therefore the water reservoir between the piston and the back wall acts as a resonant cavity with the piston being a node and the back wall an anti-node whose dimensions are dependent upon the water depth and the dimensions of the reservoir. Referring to Figure 2, the graph of the desired piston displacement with time is shown. From the rest position, the piston is withdrawn at a uniform velocity represented by the straight portion of the line 108 until the maximum piston displacement is achieved. The piston then commences its forward stroke at a uniform velocity represented by the straight portion of the line 109 until the piston has returned to its rest position. The wave period is represented by the time 110 which is the period between two successive waves.

Figure 3 illustrates the side view of a single unbroken wave passing a fixed point and moving from left to right. As the wave 1 11 approaches the fixed point, the water in the pool 112 starts to flow to the left and towards the approaching wave whilst the water level decreases. As the face of the wave 111 reaches the fixed point, the water level increases and rapidly flows from left to right and which then slows to a halt prior to the approach of the next wave.

The water velocities backwards and forwards are at their maxima near the water surface but decrease with depth until they are at their minima near to the bottom of the wave pool 113.

Figures 4 to 8 show side views of the situation at several instants during the wave generating cycle. Figure 4 shows the situation at the start of the cycle with the piston 114 in its rest position. The actuator and piston suspension are omitted for clarity. The water on the pool side of the piston 1 15 is at the same depth as the water within the reservoir 116. Figure 5 shows the piston half way through its withdrawal stroke. The water level in the pool adjacent to the piston 1 15 is falling due to the piston withdrawal, whilst the water level in the reservoir 116 is rising and a wave has started to move towards the back wall 117. Figure 6 shows the piston at its maximum withdrawal towards the back wall of the reservoir 117 where it has momentarily stopped. The reservoir wave 16 has reached its maximum amplitude against the back wall.

Figure 7 shows the piston half way through its forward stroke. The wave in the pool has reached its maximum amplitude and is travelling forwards into the pool. The wave that was reflected from the back wall now assists the forward movement of the piston.

Figure 8 shows the piston now having returned to its rest position, the water level in the reservoir has returned to normal and the wave that has been generated is propagating into the pool.

The dimensions given for the following wave generating apparatus are by way of example only. A preferred embodiment of the piston wave-making apparatus is illustrated in the side view of Figure 9. A reservoir 18 is positioned and anchored to a pool bed 19 in two metres of water depth. The piston 1 is suspended from a horizontal pantograph arrangement 22, by means of bearings 23 fixed to the sides of the reservoir and bearings 24 fixed to the rear of the piston. The piston thus suspended is free to move horizontally in the reservoir from a rest position indicated by arrow 25 to a maximum withdrawal position indicated by arrow 26. With a reservoir width of one metre and a maximum piston displacement of two metres, in a water depth of two metres, the volume of water that is displaced by a cycle of movement of the piston in this example is four cubic metres. The length of the reservoir is the distance from the piston rest position 25 to the back wall 9 of the reservoir and is approximately five metres.

An alternative piston mounting arrangement may be devised in which the piston moves freely, parallel to the bottom of the wave pool and where the displacement at the top of the piston is greater than the displacement at the bottom of the piston. For reasons of simplicity, this embodiment does not illustrate this arrangement. In this embodiment, the piston is activated by means of a motor-driven crank 29 connected to an attachment point 30 on the pantograph by means of a crankshaft 31. The speed of the motor and the dimensions of the crank and the crankshaft are arranged such that from its rest position, the piston reaches its maximum withdrawal displacement and returns to its rest position in approximately four seconds, with a piston displacement of 2 metres. Each cycle of operation may be repeated every 15 seconds, or less.

Reviewing Figure 11 shows an isometric view of the wave making module 1000 shown in Figure 1. The module for a wave-making module comprises a flume 2 flood-able through an open end 50, a back wall 9 which blocks the flume, and a barrier 1 constrained to move along the flume intermediate the back wall and open end, characterised by a reciprocating means 70 arranged to displace the barrier toward the back wall to a closest position 26 and subsequently displace the barrier away from the back wall to a farthest position 25 in synchronization with a wave reflected from the back wall so as to urge a wave through the open end.

The positions 25, 26 and the rate of displacement of the barrier control the height of wave urged though the open end and the amount of energy required to generate the wave. The reciprocating means fitted with pantograph mechanism 22 described herein allows for a wave to be generated and urged through the open end with a low ratio of energy required to generate the wave to height of the wave generated.

In some embodiments the module comprises water level detector arranged to detect the level of water in the flume and adjust the closest and furthest positions according to a preselected level of water that the flood-able flume is to be flooded. The reciprocating means in some embodiments is arranged to stop reciprocating if the water level falls below a preselected level to prevent module being damaged by running dry.

As mentioned the barrier preferably has neutral buoyancy when partially submerged in water. The neutral buoyancy allows the reciprocating means such as a pantograph to support and displace the barrier without the bottom of the barrier scraping the bottom of the flume. Preferably the water level detector is arranged to work the reciprocating means to stop the reciprocating means if the water level in the flume drops below a level which results in a loss of neutral buoyancy of the barrier. This prevents the bottom of the barrier scraping the floor of the flume due to loss of buoyancy and advantageously prevents damage to the barrier and the flume.

In some embodiments the module comprises a first pressure sensor on a face 41 of the barrier 1 directed towards the back wall and a second pressure sensor on a face 42 directed toward the opening 50.

In some embodiments the reciprocating means 70 is adapted to adjusts the displacement cycle parameters 108, 109, and 110 as shown in Figure 2 and/or positions 25, 25 according to the detected level of water in the flume and/or pressure detected by the sensors to generate a wave through the opening with preselected characteristics such as wave height, wave speed, or wave energy.

The reciprocating means 70 is arranged to displace the barrier 1 to the closest position 26 to the back wall 9 so as to cause a predetermined height, speed, or energy of the wave reflected from the back wall. The reciprocating means is arranged to displace the barrier 1 to the furthest position 25 so as to cause a predetermined height, speed, or energy of the wave urged through the open end.

The reciprocating means 70, 26 is arranged to displace the barrier to a preselected furthest position 25, and to vary the rate of displacement of the barrier 1 in a preselected manner so that in use the surface level of water in the flume 2 is uniform between the back wall 9 and barrier 1 as the barrier reaches the furthest position 25.

The reciprocating means 70, 26 displaces the barrier 1 so as to reach a maximum speed where the barrier is located at a position that is intermediate forty percent of the maximum distance it travels from the closest and furthest positions. This is where barrier is located substantially midway between the closest and furthest positions.

The reciprocating means continuously increases the speed of the barrier from the closest 26 and furthest 25 positions to the position of maximum speed and continuously decreases the speed of the barrier from the position of maximum speed the closest and furthest positions. The reciprocating means 70 shown in Figure 11 is as a hydraulic ram. In other embodiments the reciprocating means comprises a rod pivotally connected to a rotatable crank and the barrier 1.

In some embodiments the reciprocating means comprises a pantograph 22 as shown in Figure 9. The pantograph 22 has a pair of stationary pivot points 23 fixed relative to the back wall 9. The pantograph also has a pair of linear moving points 24. These linear moving points are constrained by the pivotally connected parts 36, 37, 38, and 39 to move to move straight along the flume 20 intermediate the back wall and open end. This movement of the linear moving points 24 is relative to the back wall while during said movement the linear moving points 24 are in fixed positions relative to each other.

The barrier is joined to the pantograph by pivot connections to the pair of linear moving points 24 so as to maintain the same orientation of the barrier relative the back wall as the barrier is displaced toward the back wall and subsequently displaced away from the back wall. This embodiment of the pantograph and barrier is shown in Figure 9.

In an alternative embodiment not shown the barrier 1 is joined to a first one of the moving points 24 and also joined to a point on the pantograph that moves relative to the first one as the barrier is displaced so that the orientation of the barrier swings relative the back wall as the barrier is displaced toward the back wall and subsequently displaced away from the back wall. This composite motion of the barrier closely emulates the motion of particles in a natural wave. The composite motion allows the barrier to generate waves efficiently.

As shown in Figure 9 the reciprocating means comprises a pantograph 22 that comprises a first pair of parts 36, 39 connected together by a first pivot 40 and a second pair of parts 37, 38 connected together by a second pivot 41 , wherein a first part 36 of the first pair and a first part 37 of the second pair are connected to an object that is fixed relative to the back wall by pivots 23, and the second part 39 of the first pair and the second part 38 of the second pair are connected to the movable barrier 1 by pivot connections 24. The reciprocating means comprises a rod or crankshaft 31 pivotally connected to a crank 29 rotatable by motor, The crank 29 rotates about an axis that is relative to the back wall 9. The crankshaft is also connected to the first 36 or second 37 part of the first pair of parts.

As shown in Figure 9 the barrier 1 is supported solely by the pantograph 22. As shown in Figure 9 there is a floor 3 arranged to shield the barrier 1 in the flume 2 in use from any object below the flume. In some embodiments the floor 3 is an integral part of the module 1000. The floor comprises a panel supported by a wall 61 , 62 of the flume.

In other embodiments the floor 3 is a foundation slab which is part of the bed of the body of water. The module is transported to a construction site where the floor 3 is in place. The module is connected to the floor that is in place.

In the embodiment shown in Figure the module 1000 comprises a pair of lateral walls 61 , 62 that define side walls of the flume 2. The lateral walls 61 , 62 support the back wall 9 between them. The lateral walls 61 , 62 are also joined by the floor 3 of the flume 2 between them.

Although it is not shown in any figure in some embodiments at least one of the lateral walls 61 , 62 is designed to be driven into the bed of a body of water and thereby act as a piling to support the module.

The barrier 1 has a length 210 in the direction of the depth of the flume predetermined to be substantially 160 % of the mean depth of a water in which the flume is to be flooded, so that in use substantially 35 % to 40 % of the length of the barrier extends above the mean surface level of the water.

The barrier has neutral buoyancy as partially submerged so that substantially 35 % to 40 % of the length of the barrier extends above the mean surface level of the water. The reciprocating means 70, 22 is arranged to displace the barrier 1 so that the distance between the closest position 26 and the back wall 9 is between substantially 75 % and 100 % of the length 210 of the barrier in the direction of the depth of the flume. The reciprocating means 70, 22 is arranged to displace the barrier 1 so that so that the distance between the furthest position 25 and the back wall 9 is between is between substantially 75 % and 160 % of the length 210 of the barrier in direction of the depth of the flume. The distance that the furthest position 25 is from the closest position 26 is substantially 55 % to 70 % of the length 210 of the barrier in the direction of the depth of the flume.

The length of the back wall 9 is substantially 100 % to 125 % of the length 210 of the barrier in the direction of the depth of the flume. In Figure 9 the back wall 9 is shown about 25 % longer that the barrier 1. In some embodiment the module comprises a piling to be driven into the bed of a body of water and thereby support the module above the bed.

The module 1000 is weighted so as to rest submerged on a bed of a body of water with the flume oriented in position for use.

The piston wave-maker module described above comprises a single one metre wide wave-generating module. However, in order to provide an effective wave pool installation, as illustrated in Figure 10, a plurality of wave-making modules are installed along one bank of the body of water to make a wave making apparatus 82. The number of modules may be extended left 83 and right 84 to any desired extent.

In order to avoid the momentary very high power requirement caused by the simultaneous activation of all the wave-generating modules, it is preferable that there should be a phased time delay in the activation of each of the plurality of wave-generating modules illustrated in Figure 10. This results in a smooth and continuous power demand. An additional secondary benefit is that, with computer control of the timing, it is possible to produce waves that converge, or diverge, and are thus made more interesting to surfers.

As shown in Figure 0 the wave making apparatus 82 comprises an array of wave making modules 1000 wherein the modules are submerged in a body of water and oriented with respect to each other so that the flumes 22 are parallel. Each module of the apparatus rests on the bottom of the body of water. In the wave making apparatus the back wall of a second module is arranged intermediate the closest 26 and furthest 25 positions of the barrier 1 of an adjacent first module.

In the wave making apparatus, the reciprocating means of a second module is arranged to displace the barrier of the second module so that it follows the displacement of the barrier of the first module by a predetermined time interval.

The wave making apparatus and the module for the apparatus are suitable for situation in and operation in a body of water. An example of body of water is a modified swimming pool, a surfing pool on a cruise ship, a man-made lake, a natural bay, coves, and lagoon in the sea or a lake. The wave making apparatus is usually situated near a boundary of the water such as a natural or artificial shoreline because the depth of water decreases as the shoreline is approached which encourages the waves generated through the open end of the flumes of the modules to curl over and break as they approach the shore.

List of Features Referred to in the Description and Figures Barrier or Piston (1 , 14)

Face of barrier or piston directed toward open end of flume (42)

Barrier position versus time of barrier being displaced from closest to furthest rest position (108)

Barrier position versus time of barrier being displaced from furthest to closest rest position (109)

Rest position of barrier furthest from back wall (25) Rest position of barrier closest to back wall (26) Backward motion path of barrier (6) Forward motion path of barrier (7) Beach of body of water (4)

Body of water (5)

Mean depth of water in reservoir of flume (8)

Mean surface level of water in the reservoir or flume (20)

Module - (1000)

Pantograph (22)

Reciprocating means (70, 22, 31 , and 29)

Bearings connecting pantograph to side of reservoir/flume (23)

Bearings connecting pantograph to barrier (24)

Crank for reciprocating means (29)

Crankshaft for reciprocating means (31 )

Pivot connecting crankshaft to pantograph (30)

Reservoir or Flume (2, 18)

Back wall of reservoir or flume (9, 117)

Lateral walls of module forming lateral walls of flume (61 , 62)

Bottom or Bed of Pool or Reservoir (3, 19, 113)

Water - on pool side of barrier (115)

Water - in reservoir (116)

Apparatus comprising a plurality of wave generating modules (82) Wave making apparatus - Left end (83) Wave making apparatus - Right end (84)

Wave - Crest of wave generated by wave making apparatus (85)

Wave - Path of travel of wave generated by wave making apparatus (86)

Wave - Time Period (1 10) Wave - Lowest level of trough of wave (112)

The invention has been described by way of examples only. Therefore, the foregoing is considered as illustrative only of the principles of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the claims.

Claims

Claims:

1. A wave generating module for a wave-making apparatus comprising a flume which is flooded water through an open end, a back wall which blocks the flume, and a barrier constrained to move along the flume intermediate the back wall and the open end, characterised by a reciprocating means arranged to displace the barrier towards the back wall to generate a wave toward the back wall that is reflected from the back wall to assist subsequent displacement of the barrier away from the back wall in generating a wave through the open end.

2. A module according to claim 1 wherein the reciprocating means is arranged to vary the rate of displacement of the barrier with a substantially sinusoidal cycle.

3. A module according to claim 2 wherein the reciprocating means is arranged to pause the cycle momentarily before starting the displacement of the barrier toward the back wall.

4. A module according to claim 2 or 3 wherein reciprocating means is arranged such that the period of the cycle is coincides with a natural frequency of a standing wave in the flume reflected from the back wall.

5. A module according to claim 2 or 3 wherein reciprocating means is arranged such that the speed that the barrier is displaced away from the back wall coincides with the speed of the wave reflected from the back wall.

6. A module according to any preceding claim whereby in use the depth of water in the flume is substantially uniform where the barrier is furthest from the back wall.

7. A module according to claims 1 to 6 wherein the reciprocating means comprises a pantograph to which the barrier is connected.

8. A module according to claim 7 wherein the barrier is supported solely by the pantograph.

9. A module according to any preceding claim wherein the barrier is connected to two linked parts of the pantograph at a location on each part which remains fixed with respect to the other, so as to maintain the same orientation of the barrier relative the back wall as the barrier is displaced.

10. A module according to any of claims 6 to 9 wherein the barrier is connected to two linked parts of the pantograph at location on each part which moves with respect to the other, such that in use horizontal displacement of the top of the barrier is further than horizontal displacement of the bottom of the barrier to emulate movements of water particles in the wave.

11. A module according to any of claims 6 to 10 comprising a motor and crankshaft acting upon a structural member of the pantograph.

12. A module according to any preceding claim wherein in use the height of the top of the barrier above the mean surface level of water in the flume is substantially 30 % to 45 % of the length of the barrier such that the barrier has neutral buoyancy.

13. A module according to any preceding claim wherein the barrier has a length in the direction of the depth of the flume predetermined to be substantially 160 % of the mean depth of a water in which the flume is to be flooded, so that in use substantially 35 % to 40 % of the length of the barrier extends above the mean surface level of the water.

14. A module according to any preceding claim comprising a water level detector arranged to operate in conjunction with the reciprocating means to stop the reciprocating means from displacing the barrier if the level of water in the flume is below a predetermined level.

15. A module according to any preceding claim wherein the flume is formed by a pair of lateral walls.

16. A module according to claim 15 wherein the lateral walls support the back wall between them.

17. A wave making apparatus comprising an array of wave making modules according to any preceding claim comprising a plurality of wave-making modules arranged side by side with their flumes in parallel and energized from end to end in sequence to require less power than would result from simultaneous activation.

18. An apparatus according to claim 17 wherein the reciprocating means of a second module is arranged to displace the barrier of the second module so that it follows the displacement of the barrier of the first module by a predetermined time interval.

19. A body of water comprising a wave making apparatus according to claims 17 or 18.