Patent Publication Number: US-2009235660-A1

Title: Device for converting wave energy

Description:
The present invention relates to a device for absorption of wave energy according to the ingress of the following claim  1 . 
     Such a device is known from the applicants own Norwegian patent application no. 2003 2883. In this application a device for use in a wave powered generator is described. The device comprises a floating body adapted to float in or near the surface of the water. A piston rod extends from the floating body to a cylinder, which in turn is clamped in a fixture. This fixture is placed on a floater. 
     Additionally, from the applicants own PCT-application WO 2004/113718 it is known a platform construction equipped with devices for absorption of wave energy of the above mentioned type. This application is hereby incorporated by reference. The platform construction consists generally of a platform above water and a number, for example four, of legs extending down in the water and that has sufficient buoyancy to hold the platform stable above water. 
     A test platform (“Buldra”) according to the principles in  FIG. 10  in WO 2004/113718 was built in the last half of 2004 and was first used in February 2005. This turned out to work in a satisfactory way. Work has been done on several improvements of the devices that absorb wave energy and the platform construction itself based on the test results that are produced by the testing of “Buldra”. The present invention relates to some of these improvements and is particularly aimed at the energy transmission means. 
     Another known solution for wave powered generators is disclosed in U.S. Pat. No. 6,256,987 where a number of units placed on the bottom of shallow water are described. Every unit comprises a hood adapted to move vertical in relation to a frame. The interior of the hood is filled with gas. When waves pass over the unit the hood will move up and down according to the waves, i.e. the hood moves upwards when a trough of wave passes and it will move downwards when a wave crest passes. The lower part of the unit is filled with water. This water volume can be varied and suppress gas so that the gas volume and thereby resonant frequency can be adapted to the wave frequency. 
     The largest disadvantage of this solution is that it must be placed on the bottom of the sea. Thereby one gets difficult access to the units for maintenance and repair. The units must in addition be placed on shallow water and will therefore constitute danger to ships and fishery. 
     It is an object of the present invention to avoid the fastening problems that exists when a heavy moveable rod shall be moveable supported in a structure, such as for example shown in the  FIGS. 1   a  and  1   b  in the above mentioned WO 2004/113718. This is achieved by arranging the floating body moveable on a guide rod, which guide rod is flexible supported in the structure. 
     It is further an additional object of the present invention to be able to utilize horizontal wave forces. This is achieved by that the guide rod is attached to energy absorption devices adapted to absorb horizontal forces from the guide rod. 
     Additional preferable embodiments of the invention are disclosed in more detail in the dependent claims. 
    
    
     
       The invention will be described in more detail below with reference to the example embodiment shown in the enclosed drawings, where: 
         FIG. 1  shows a wave absorption device according to the invention, 
         FIG. 2  shows a modifies floating body, and 
         FIG. 3  shows the floating body in  FIG. 2  seen from below. 
         FIG. 4  shows an alternative embodiment of the present invention, 
         FIG. 5  shows a wave absorption device in  FIG. 4  as a wave crest is passing, 
         FIG. 6  shows a wave absorption device in  FIG. 4  as a trough of waves is passing, 
         FIG. 7  shows a segment of the energy transmission devices in  FIG. 4 , 
         FIG. 8  shows a platform construction comprising a number of wave energy absorption devices, and 
         FIG. 9  shows a segment of the legs of the platform construction with a secondary energy absorption device. 
     
    
    
       FIG. 1  shows a wave energy absorption device according to the invention. It comprises a guide rod  1  along which a floating body  2  can move. The guide rod  1  is a tube formed body which at its upper end is clamped to an upper deck  3 . The guide rod  1  extends with a certain clearing through a lower deck  4 . Four horizontal cylinders  5  are clamped between the lower deck  4  and the guide rod  1 . The cylinders  5  stand in a right angle on each other. Thereby, the horizontal cylinders  5  can take up side forces which the guide rod  1  is influenced by from the waves. These side forces generate hydraulic pressure in the horizontal cylinders  5  that can be transformed to electrical energy by means of a not shown generator. 
     A first bracket  6  is arranged at the upper end of the floating body  2 . Two linear rods  7  are attached to the bracket. The linear rods  7  are attached to a second bracket  8  at their upper ends. The second bracket  8  is slidable on the guide rod  1 . The second bracket  8  is connected to two drive belts  9 ,  10 , one on each side. The drive belts  9 ,  10  are led over respective lower re-control roller  11  (ornstyrningsruller) and respective upper re-control roller  12   a  and  12   b.    
     On each side of the upper re-control rollers  12 , gear systems  13 ,  14 ,  15 ,  16  are arranged which the re-control rollers are attached to. The gear systems  13 ,  14 ,  15 ,  16  are attached to help rollers  17 ,  18 . The gear systems  13 ,  14 ,  15 ,  16  are configured to transfer the rotation of the re-control rollers  12   a ,  12   b  to a rotation in the same direction independent of the rotational direction of the re-control rollers  12   a ,  12   b . This is done by that when the floating body  2  is moving downwards the rotation of the re-control roller  12   a , which is happening in the direction of the clock, is transferred to the gear system  13  and lead to rotation of the help roller in the direction of the clock. In addition, the rotation of the re-control roller  12   b , that will be in the opposite direction of the clock, is transferred via the gear system  15  to the help roller  18  and lead to rotation of this in the opposite direction of the clock. The gear systems  14  and  16  will then function as a free wheel and not transfer any rotation. 
     When the floating body is moving upwards, the rotation from the re-control roller  12   a  will, which now will be in the opposite direction of the clock, be transferred via the gear system  16  to a rotation in the opposite direction of the clock by the help roller  18 . The rotation of the re-control roller  12   b , which is now rotating in the direction of the clock, will be transferred via the gear system  14  to a rotation in the direction of the clock by the help roller  17 . The gear systems  13  and  15  will now run as free wheels. 
     In this way the help roller  17  will rotate in the direction of the clock all the time and the help roller  18  in the opposite direction of the clock. By arranging a flywheel (not shown) in the gear systems or on the help rollers one can get the help rollers  17 ,  18  to rotate with approximately constant speed even though the power supply happens intermittic. The load on the drive belts will be symmetric by the above mentioned configuration. 
     The rotational energy from the help rollers  17 ,  18  can be taken out on a not shown shaft from each of the help rollers  17 ,  18 . The shaft can be connected to an electrical generator. 
     The lower re-control rollers  11  are preferably arranged on a horizontal movable bracket and connected to the guide rod  1 . 
     When the floating body  2  is moving, for example upwards as a result of influence from a wave crest, the body  2  will be held back by that the generators are exposed to a load constituting in the order of 10% less than the upward directed force of the wave crests. Thereby, the floating body  2  will be held more submerged in the water than the buoyancy would require and the force that acts against the body  2  will thereby increase. 
     In the same way the floating body  2  can also be held back by downward directed movement with a force in the order of 10% less than the body&#39;s  2  effective weights (gravity minus buoyancy). 
     In the above mentioned WO 2004/113718 it is described in detail how such an attachment of a floating body can be done at a hydraulic system. However, in the hydraulic system described here the floating body will be held completely still under parts of the wave motion. However, with an electrical system it is simpler to control the force that the floating body is held back with. A person skilled in the art of current control will immediately understand how this should be done. 
     In  FIG. 1  the floating body is shaped with a lower part that has gradually tampering diameter against the lower end  19 . This shape causes the floating body to let the water go easier if it is moving completely out of the water and cuts easier down in the water when it moves back to the water again. 
       FIG. 2  shows an alternative floating body  2 . This floating body  2  is equipped with vertical fins  20  extending along the surface of the floating body  2  from top to bottom. In  FIG. 2 , eight fins are shown extending orthogonal out from the floating body  2 , but the number can be different from this. The width of the fins, measured from the surface of the floating body  2  to the outmost edge of the fins, can also be varied. However, the size of the fins will be limited by the weight, as the fines do not give net buoyancy to the floating body and thereby should not comprise a too large part of the weight. 
     The function of the fins  20  is to capture horizontal forces from the waves that act against the floating body. One has found that the horizontal wave forces can contain twice as much energy as the vertical wave forces. It is therefore an objective of the embodiment according to  FIG. 2  to collect a larger part of these forces. Since the fins  20  stand out in several directions from the floating body  2 , the waves will meet approximately the same area independent of which direction the waves have. 
     As seen from  FIG. 3 , the fins  20  have inclined side surfaces  21 ,  22  that function to deviate the water flow and reduce turbulence. Thereby one also will reduce the loss of force influence from the waves that arise because of turbulence. 
     The horizontal wave forces are transferred from the floating body  2  to the guide rod  1 . Since the guide rod  1  is permitted to move slightly horizontal (approximately 100 mm measured at the lower deck  4 ) the forces will be further transferred to horizontal cylinders  5 . From here, hydraulic energy can be taken out which in turn can be converted to electrical energy. 
     The vertical wave forces are transferred from the floating body to the linear rods  7  that move together with the floating body. Since the linear rods  7  are connected to the drive belts  9 ,  10  via the upper bracket  8  the vertical forces are transferred further to the drive belts  9 ,  10 , and from these to the gear systems  13 ,  14 ,  15 ,  16 . As mentioned above, rotational energy can be collected from the gear system, which in turn can be converted to electrical energy. The gear system has an exchange that increases the rotational velocity to a velocity that is optimal for the following electrical generator. 
     Chains, wires, straps or other flexible extended drive means can also be used in stead of drive belts. 
     To avoid transfer of large voltages from the guide rod  1  to the upper deck  3 , the guide rod  1  is preferably flexible suspended in the upper deck  3 , for example by a spherical layer (not shown). By going through the lower deck  4  it can be installed an elastic damper material that absorbs the forces from the guide rod  1  if the movement becomes so large that the horizontal cylinders  5  are not capable of absorbing all the forces. The same is valid for the linear rods  7  when they go through the lower deck  4 , where it also can be installed an elastic damper material. 
     In an alternative embodiment, not shown in the figure, the drive belts  9 ,  10  and the gear systems  13 ,  14 ,  15 ,  16  can be replaced with linear generators directly connected to the linear rods  7  by that the stators are connected to the upper deck  3  and the linear rotators (in English also called “mover”) are attached to the linear rods  7 . The linear generators can transfer the linear kinetic energy directly to electrical energy. 
     Linear generators can here also be used in stead of the hydraulic horizontal cylinders  5 . 
     It is preferably arranged for the floating body  2  to be brought completely out of the water under the vertical movement. Thereby the guide rod  1  will straighten up to vertical position due to the gravity so that even though the wave side forces only act in one direction the guide rod  1  will not be hanging out on the side. 
       FIG. 4  shows an alternative embodiment of the invention. Here it is an extra set of linear rods  30  extending through a tunnel in the floating body  2  and are connected with a bracket  31 . The bracket  31  is in turn connected with a vessel in the shape of a cylinder  32  closed at its upper end and open at its lower end. The cylinder  32  is slidable on the guide rod  1 . 
     The cylinder  32  is partially filled with water so that the upper part of the cylinder  32 , close to the closed top, is filled with air. This cylinder  32  will move in anti-phase with the floating body  2  when the device is placed in the waves.  FIG. 5  shows the device as it is passed by a wave crest. The floating body  2  is forced up by the wave crest. At the same time the pressure that acts on the air in the cylinder  32  will increase so that more water flows through the lower open end of the cylinder  32 . Thereby the weight of the cylinder  32  will increase and the cylinder will sink in the water.  FIG. 6  shows the device as it is passed by a trough of waves. In this case the cylinders&#39; down diving depth will be reduced. Thereby the air in the cylinder will press out water from the cylinder and reduce the weight of the cylinder so that it rises in the water. The principle with this is the same that is used to get the hood to move in step with the waves according to U.S. Pat. No. 6,256,985. 
       FIG. 7  shows a detail of an alternative energy transmission device. This differs from the embodiment in  FIG. 1  by that the linear rods  7  are led all the way up through the upper deck  3 . This is also the linear rods  30 , which are connected to the cylinder  32 . Two generators  33 ,  34  are placed on the upper deck  3 . The first generator  33  is attached to the linear rods  30  via a shaft  35 , on which two wheels  36 ,  37  are arranged, which lies against a respective one of the linear rods  30 . A respective support wheel  38 ,  39  is arranged on the opposite side of the linear rods  30 . 
     The second generator  34  is attached to the linear rods  7  via a shaft  40 , on which two wheels  41 ,  42  leaning against one of the respective linear rods  7  are arranged. A respective support wheel  43 ,  44  is arranged on the opposite side of the linear rods  7 . 
     Each of the generators will be sat in rotation in the direction of the clock when the floating body  2 , respectively cylinder  30  moves downwards and in the opposite direction of the clock when the floating body, respectively cylinder  30  moves upwards. It is thereby generated an electric current form each of the generators that alternates with the wave period. By means of conventional power control technique, this alternating current can be transformed to direct current or alternating current with a fixed frequency. 
     The previously described fixing of the floating body, and possibly also the cylinder  32 , can be performed very simple by means of the generators  33  and  34 . This can be secured against over load by the components by that the wheels  36 - 38  and  41 - 44  are allowed to skid towards the linear rods  7 ,  39  if the forces exceeds certain values. 
     The floating bodies  2  are preferably produced in a rubber material or a rubber like plastic material which is light and at the same time handles a certain amount of hits. For this, one can use the same material used in fenders. The cylinder  32  can be produced in steel or concrete. The cylinder  32  should have neutral buoyancy when it is half filled with water respectively air/gas and when there are no waves. 
       FIG. 8  shows a platform construction  50  that uses several wave absorption devices according to the  FIGS. 5 and 6 . In principle, the platform construction itself is the same as disclosed in WO/2004/113718, particularly  FIG. 9 , where the wave energy absorption devices are attached to a deck construction  51  comprising two decks  3  and  4  (in accordance with the decks  3  and  4  in the preceding). By each of the corners of the deck constructions  51 , a leg  52  which is filled with air to give buoyancy is attached. 
     The legs  52  are connected with each other by a frame work  53  at their lower end. The frame work is also intended to comprise a control for the guide rods  1  of the wave energy absorption devices. A damper device  56  is arranged at the lower ends of the legs  52 , which can be shaped in the same way as described in WO/2004/113718. 
     A secondary wave energy absorption device  54  is arranged approximately on the middle of each leg  52 . This consists of a blade wheel  55  rotatably supported on the leg  52 . The blades of the blade wheel  55  can be curved, as shown in  FIG. 8 . Such a wave energy absorption device  54  will absorb energy from the waves independent of which direction they have. For further transmitting the energy the blade wheel  55  can be in connection with roller or similar placed between the blade wheel  55  and the leg  52 , where the rollers in turn are in connection with a generator. 
       FIG. 9  shows an alternative embodiment of the blade wheel  55 . In this embodiment the blade wheel  55  has straight blades  57 , which however are curved abeam the length axis. The blades  57  are fastened between two rings  58  and  59  at a shaft extension  60  at each end of the inner long side of the blade  57 . A pin  61  is arranged at each end of the outer long side of the blade  57 , which is led in a track  62 . Thereby, the blade can swing from one position, as shown by the blade  57   a  where the blade stands out from the leg  52 , to a position shown by the blade  57   b , where the blade lays approximately parallel with the surface of the leg  52 . In the example shown in  FIG. 8  the wave direction is shown by the arrow  63 . The blades  57  located on the right side of the leg (seen in the direction of the arrow  63 ) will then lay out so that they extend out form the leg  52 , while the blades  57  located on the left side of the leg  52  (seen in the direction of the arrow  63 ) will lay approximately parallel with the surface of the leg  52 . Thus, the resistance from these blades will be reduced. The blade wheel  55  will thereby rotate in the opposite direction of the clock (seen from above) independently of the flow direction. 
     The blade wheel  55  is supported on a number of rollers  64 , which in turn are rotatably supported in brackets  65  attached to the leg  52 . A generator (not shown) can be arranged in connection with each roller  64 .