Abstract:
An apparatus and method for converting wave energy using the relative rotational movement between two interconnected float assemblies and the relative rotational movement between each of the float assemblies and a spar which extends from a connection with the float assemblies at the water surface into the water.

Description:
BACKGROUND OF INVENTION 
     The present invention relates to the extraction of energy from water waves found in oceans or other large bodies of water and, in particular, the conversion of wave energy into electrical energy. Water waves that form in large bodies of water contain kinetic and potential energy that the device and methodology of the present invention is designed to extract. More specifically, the object of the present invention is to provide structures and methods to efficiently convert the hydrodynamic surge (horizontal component) and heave (vertical component) of ocean wave energy into rotary shaft motion for use in direct drive rotary generation. 
     SUMMARY OF INVENTION 
     We describe a unique approach for converting wave motion to mechanical rotary motion. A wave energy converter (WEC) that extracts energy from both the heave and surge energy contained in an ocean wave so as to allow for twice the energy extraction potential of other systems that only extract energy from heave motion in the waves. 
     We also describe a wave energy converter that provides a wave to rotary energy approach that will work with a DDR generator or any other power take off (PTO) driven by a mechanical rotary drive shaft. The system may allow, but is not limited to, the use of large diameter, high torque and low speed direct driven rotary (DDR) generators in wave energy applications and may allow for a more cost effective and efficient conversion of wave energy as compared to other methods of conversion. 
     We also describe a method by which the ocean wave forces can be coupled to create low speed high torque rotation. This rotation can then be coupled to the DDR generator or other PTO. This PTO may include all forms of rotary power conversion; such as a large direct driven rotary electric generator, a gear box driven electric generator, a belt driven electric generator, water pumping systems, water desalination, pneumatic pumping systems and even hydraulic pumps, and similar devices. 
     The structure and methodology includes mechanical implementations that, among other things, allow for an increase in the rotary speed of the main drive shaft. They also provide for methods of implementation that increase the magnetic flux velocity in the generator air gap. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The invention will become more readily appreciated by reference to the following detailed descriptions, when taken in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is an isometric view of a wave energy converter; 
         FIG. 2  is a representational drawing of an ocean wave; 
         FIG. 3  is a cross-sectional view of an example wave energy converter; 
         FIGS. 4A-4C  are isometric views of an example wave energy converter; 
         FIG. 5  is an isometric view of an example wave energy converter; 
         FIG. 6  is an isometric view of an example wave energy converter; 
         FIG. 7  is a cross-sectional view of fore and aft floats showing exemplary connecting bearing shafts; 
         FIG. 8  is a partial cut-away view of an embodiment of an example wave energy converter; 
         FIG. 9  is an isometric view of an embodiment of an example wave energy converter; 
         FIG. 10  is an isometric view of an example wave energy converter; 
         FIG. 11  is a side view of an embodiment of the wave energy converter of the present invention; 
         FIG. 12  is an isometric view of an example wave energy converter; 
         FIG. 13  is an isometric view of an example wave energy converter; 
         FIG. 14  is a partial isometric view of the present inventions; 
         FIG. 15  is an isometric view of an example wave energy converter; 
         FIG. 16  is an isometric view of an example wave energy converter; 
         FIG. 17  is an isometric view of an example wave energy converter; 
         FIG. 18  is a partial isometric view of an example wave energy converter; and 
         FIG. 19  is an isometric view of an example wave energy converter. 
     
    
    
     DETAILED DESCRIPTION OF INVENTION 
     A wave energy converter  10 , shown in  FIG. 1 , is comprised of a fore float  11  and an aft float  12 . These floats  11 ,  12  are rotably attached to spar  13 . The floats  11 ,  12  are attached through drive shafts  18  and  19  (shown in  FIG. 3 ) to a mechanical rotary system that utilizes the speed or torque to perform mechanical work (electric generation, water pumping, or similar function). As seen in  FIG. 1 , the outer body is comprised of three components: the spar  13 ; the fore float  11 ; and the aft float  12 . The floats  11  and  12  are connected together by bearing shafts  16  and  17  (the latter of which is shown in  FIG. 3 ) such that fore float  11  and aft float  12  can rotate relative to each other. 
     Water waves  20  are comprised of rotational particle motions that are grossly depicted in  FIG. 2 , heave, which creates vertical up force  21  and vertical down force  22  on bodies exposed to the wave, and surge which creates horizontal force  23 , that a wave imparts to a body. The magnitude of the rotational forces  22  and  23 , depicted in  FIG. 2 , are highest at the water&#39;s surface, and diminish as the water depth increases. The floats  11  and  12  of  FIG. 1  experience vertical forces due to the heave of wave  20 . 
     In  FIG. 3 , the floats  11  and  12  interconnect through bearing shafts  16  and  17  so as to permit relative movement between them. Driveshaft  19  connects float  11  to driveshaft flange  31  by passing through a motor housing  30  mounted to the top of spar  13 . Rotation between the driveshaft  19  and motor housing  30  is accommodated by a sealed spar bearing  33 . The sealed spar bearing  33  permits rotation of driveshaft  19  relative to housing  30  but keeps water out of the motor housing  30 . In similar fashion, driveshaft  18  connects float  12  to driveshaft flange  32  by passing through motor housing  30 . Rotation between the driveshaft  19  and motor housing  30  is accommodated by sealed spar bearing  34 , which also seals the housing  30  so as to keep out water. Driveshaft flange  31  is mounted to a stator assembly of a generator and driveshaft flange  32  is mounted to a rotor assembly of a generator. Alternatively, driveshaft flanges  31  can connect to a rotor assembly of a first generator and driveshaft flange  32  can connect to a rotor assembly of a second generator, with the stator of each being fixedly mounted inside motor housing  30 . In one embodiment, two  80  ton generators are employed. 
     As shown in  FIG. 3 , the float surface area is maximized by staggering the fore float  11  and aft float  12  about an axis of rotation. The bearing shaft  17  and bearing shaft  16  of  FIG. 3  are axis centric on opposite sides of wave energy converter  10 . The placement of these bearing shafts allow for only relative rotational motion about the axis between the fore float  11  an aft float  12 . While this approach of coupling the fore float  11  and aft float  12  with a bearing system that is independent of the spar is not essential for function of the system, it allows for reduction of forces on the spar bearings  33  and  34 . 
     The spar heave plate  14  shown in  FIG. 1  is exposed to smaller heave forces due to its depth below the water surface. The placement of that plate below the surface encourages the spar  13  to remain relatively stationary in the vertical direction and resist the vertical motion of the floats  11  and  12 . 
     A Power Take Off (PTO) can be mounted in the spar  13  or floats  11  and  12 , and may be mounted in any location as appropriate for the specific design considerations. A first and second direct drive rotary generation PTO  35  and  36  are shown in  FIG. 8 , but any mechanical power transfer system such as a DDR generator (previously mentioned), a gear box driven electric generator, a belt driven electric generator, water pumping systems, water desalination, pneumatic pumping systems, even hydraulic pumps, or similar can be used. 
     In one embodiment, the first PTO  35  is connected to drive shaft  19  through flange  31 . The second PTO  36  is connected to drive shaft  18  through flange  32  (not shown in  FIG. 8 ). The relative rotational motion between the spar  13  and the floats  11  and  12  drives the first and second PTO to convert wave motion to useable power. As described earlier, the pitching action of the spar (surge energy) and the pitching action of the float (heave energy) are combined to create a net sum that is complementary and produces a combined speed and force that is greater then the individual float or spar energies. This net energy is transferred to the PTO to perform work such as electrical generation, water pumping, air pumping, or similar effort. 
     In another embodiment, a single PTO can be connected to drive shafts  18  and  19 , such that a rotor (not shown) is attached to the fore float  11  and the stator is attached to the aft float  12  (or visa-versa). The heave motion of this system creates relative rotational motion between the floats  11  and  12 . By connecting the PTO only between the floats, the only energy captured is the energy from the relative motion between the floats. Hydrodynamic modeling has shown that the motion between the floats is increased by the addition of the spar system and its contribution of pitch heave response on the float bodies. However, an advantage to this arrangement is the increased rotary speeds and reduced generator costs. Because the stator and rotor are both turned in opposite directions by the float motion, the relative speed between the rotor and stator is twice that of a spar mounted stator. It is well known in the art of generator design that increased speed, in general, allows for reduced cost. 
     In another embodiment, two PTO&#39;s can be mounted within housing  30 , or mounted on the surface outside of the spar, encased in a water tight enclosure on the port and starboard sides of the system as shown in  FIG. 9 . In this second arrangement, PTO  37  has a rotor (not shown) attached to one float  11  and a stator (not shown) attached to the other float  12 . The reverse is true of the PTO  38 , which has a rotor (not shown) attached to float  12  and a stator (not shown) attached to float  11 . Both PTO&#39;s are driven by the relative motion between the floats  11  and  12 . The same advantage of increased generator speed is realized between stator and rotor, because each is being rotated in opposite directions. 
       FIGS. 4A-4C  depict various positions of the floats  11  and  12  relative to each other and relative to spar  13  as different wave conditions are encountered by the wave energy converter  10 . More specifically,  FIG. 4A  shows a situation in which the spar  13  is essentially perpendicular to the horizon and float  11  and float  12  have rotated downward. In  FIG. 4B , floats  11  and  12  have rotated about bearing shaft  16  so as to be roughly horizontal while spar  13  has rotated off of the vertical position. In  FIG. 4C , float  11  has rotated clockwise, above the horizon, float  12  has also rotated clockwise, but to an angle below the horizon, while spar  13  has rotated counterclockwise about seal bearings  33  and  34 . The movement of floats  11  and  12  and spar  13  being in reaction to wave forces acting upon them, with each movement leading to the potential conversion of wave energy by wave energy converter  10 . Floats  11  and  12  will rotate up and down with each wave&#39;s incoming crest and trough, experiencing rotational motion with respect to the spar  13  due to heave forces acting on the floats. 
     The floats  11  and  12  of  FIG. 1 , experience horizontal forces  21  and  22  due to wave surges shown in  FIG. 2 . The floats  11  and  12  are allowed to rotate with respect to the spar  13 .  FIG. 4B  depicts the floats  11  and  12 , and spar  13  being pulled by surge forces to the right. The surge forces are minimal at the bottom of the spar  13  and at the heave plate  14 . This difference in horizontal loading between the top of spar  13  and the bottom of that spar causes a moment about the spar body, so as to cause the spar to pitch right as depicted in  FIG. 4B . The system is ballasted and designed to achieve a desired pivot point  15  on spar  13 , this pivot point affects the speed of the pitching action and the amount of power absorbed. The optimization of this pitching action is the designers&#39; prerogative based on design priorities upon reading and understanding this disclosure, but ideally the pivot point  15  is between the motor housing  30  but above the heave plate  14 . As the spar  13  pitches fore and aft, the spar  13  and floats  11  and  12  experience relative rotational motion. 
     In both cases, surge and heave forces, the floats  11  and  12  rotate about spar  13  with speed and torque to transmit power through drive shafts  18  and  19 . The net affect of these heave and surge driven rotary motions is hypothesized and numerically modeled to be complementary (not opposing) in direction and force. The synthesis of these two motions is depicted in  FIG. 4C , where it is shown that the net effect of both heave and surge forces will act on the wave energy converter  10  and that converter will absorb power from both modes (heave and surge) of wave motion. The system may work in either mode of operation to capture energy by using heave motion or surge motion as depicted, or both. 
     As an electrical generating system, a reduced cost of energy (CoE) is expected to be an advantage over other approaches. The wave energy absorber has the potential to be half the size of a competing wave energy converter of the same power rating. That size reduction reduces capital costs and CoE. The CoE is further reduced by reducing the capital expenditure of the generator by optimizing the electromagnetic design using a large diameter generator when low-speed high-torque rotary motion is employed. Operating and maintenance costs are reduced by the systems operational design; there are minimal moving parts, and the parts that do move do so fluidly, with the incoming waves, so as to reduce the affect of snap loading often experienced by marine deployed bodies. This construction and approach reduces repair time and cost. The speed of rotation and driving torque are both increased by the extraction of both heave and surge energy. Increasing the speed of body motions helps to reduce generator capital costs and the system components may be designed to satisfy this priority. In some methods described in this disclosure, reliability is improved by the elimination of all intermediate conversion stages. The WEC Survivability is another advantage of this system. The combined effect of the design results in a fluid motion of the wave converter in the ocean which reduces structural loading, reduces mooring loading, and accommodates for tidal variation. 
     These methods described utilize rotary motion from a WEC to allow for a point absorber design that captures the heave and surge energy components of the incoming wave energy. By capturing both the surge and heave component, the maximum possible energy capture width of the wave energy device is λ/π (where λ=wave length) as compared to λ/2π for a device that captures only the heave component. This improvement in capture width is expected to reduce the size and cost of the wave energy converter. The exact generator, pump, or rotary mechanisms for this application is not essential to the claims of this invention because it is applicable to any mechanism or system that is driven by a rotary shaft. 
     In  FIGS. 5 and 6 , the spar  13  is shortened and the damper plate  9  is connected to the spar  13  using a cable or chain  31 . The shortening of the spar allows for increased pitch motion and increased relative speed between float and spar in the surge mode of operation. The heave plate  14  connected through the cable  31  still allows for heave reaction force in the heave mode of operation and allows the damper plate  9  to be lower in the water to increase the effectiveness of the damper plate operation. A shorter spar  13  also reduces the overall system cost, optimization of power absorption, and optimization of PTO speed, lowers the damper plate position and increases heave response. 
     The spar  13  is designed to be relatively fixed in heave so that it resists the upward and downward heave motion of the floats. The spar  13  may also be designed such that it has a ballast chamber that varies the spar buoyancy between either positively buoyant when the wave trough is above the spar, or negatively buoyant when the wave crest is above the spar. Spar  13  is designed to transition between positive buoyancy and negative buoyancy, while maintaining the buoyancy to avoid sinking. This condition causes the heave motion of the spar  13  to move opposite (180 degrees out of phase) to the heave motion of floats  11  and  12 . This diving and rising spar design is accomplished using a compressible ballast chamber in the lower section of the spar (not shown). When the wave crest is over spar  13 , the higher pressure from the wave causes the ballast chamber to compress and causes the spar  13  to sink until the floats reach equilibrium buoyant state. Conversely, when the wave trough is over spar  13 , the pressure on the buoyancy chamber is reduced, the ballast chamber expands, and spar  13  rises until the floats  11  and  12  reach an equilibrium buoyant state with the spar  13 . This diving and rising action amplifies the range of motion between floats  11  and  12  and spar  13 , and can be used to improve the wave converter performance. Additionally, it has been shown that proper ballast location in the spar can increase captured power and can also be used to optimize relative speed between the spar and floats. 
     A challenge to proper operation of this system is the control of directionality. The power extraction efficiency is improved by proper orientation of floats  11  and  12  and the rotation axes with respect to the incoming wave front. Generally, performance is maximized when the axis of rotation is parallel to the incoming wave front, and minimized when the axis of rotation is perpendicular to the incoming wave front. Depending on the incident wave energy the system performance can be optimized and stabilized by changing the float orientation with respect to the incoming waves. It is recognized that in very energetic sea states, it may be desirable to decrease performance by changing the float orientation to a less efficient position. 
     Directionality is affected by direction of water flowing past the device. The mean drift current of the incident wave climate is one source of current flow acting on the buoy. Another source of water flow acting on the body is the predominant ocean current acting on the buoy body. Wind acting on the buoy body above the water surface will also affect directionality. Directional vanes  39 , shown in  FIG. 10 , can be used to channel water on the underside of floats  11  and  12 . These vanes can be installed on the fore float  11 , the aft  12 , or both, depending on the preferred affect. Directional vanes  39  will cause floats  11  and  12  to align with the direction of flow acting on them. As depicted in  FIG. 10 , the directional vanes  39  are shrouded by the outer hull of the floats. By shrouding the directional vanes  39 , the directional effects from the wave action will be increased due to the wave acting from under the float body, while the effects from ocean current will be minimized. The size, length and aspect ratio of the directional vanes  39  may be varied to increase or decrease the magnitude of the effect of the vanes on directionality. Directional vanes  39  can alternatively be used on the aft float  12  only to provide a rudder effect to keep the device pointed into the wave. 
     In another embodiment, a rudder  40 , shown in  FIG. 11  can be used to control float orientation in the wave. More than one rudder may also be used. The rudder may be positioned in all 360 degrees of rotation. The rudder is statically positioned, manually controlled, or automatically controlled using existing technology similar to an automatic pilot used on numerous vessels. The control for the rudder takes into account the prevailing wave direction, prevailing currents, wind, and drift and sets the rudder to maintain the desired buoy direction. 
     In another embodiment, a two point mooring system is used to control directionality. This system may be slack moored as depicted in  FIG. 12 . In  FIG. 12 , a slack mooring line  41  attaches to bearing shaft  16  and a second mooring line  42  attached to bearing shaft  17 . A mechanism such as a chain winch  43 , shown in  FIG. 14 , can be used to shorten or lengthen either mooring line. This will create a rotation on the float such that can be oriented in the desired direction. 
     In another embodiment, a three point mooring system is used to control directionality. This system may be slack moored as depicted in  FIG. 13 . Mooring lines  41 ,  42  and  44  can attach to the heave plate  14  of converter  10  by conventional means. In one embodiment, mooring lines  41  and  42  form a common connection point to the heave plate  14  through a chain winch  43  as shown in  FIG. 14 . By adjusting the direction of chain as shown in  FIG. 14 , the heave plate  14  can be forced to rotate into the desired direction so as to orient the converter  10  in the desired direction. 
     In another embodiment, the top surface area of float  11  and float  12  in  FIG. 1  are covered with an array of solar panels  52  and  53 . This is of particular interest due to the large and un-blocked surface area that is in direct line of sight with the sun. Complementing the wave power with solar power provides for a more continuous power delivery from each WEC especially when wave energy is low during summer months. 
     The geometry of system components can be optimized for use on different bodies of water during different seasons based on many factors. The floats  11  and  12  may be constructed with a narrow width to length ratio, or it might have a wide aspect ratio. Float geometry is optimized for wave height, wave period, seasonal wave spectral density, power capture, and directionality considerations. Float shape is not limited by the geometry depicted and may take on a more curved disc shape. The floats  11  and  12  might also be cylindrical or rectangular in shape. Similarly, the diameter or length of the spar  13  may be altered for performance enhancements. 
     Depending on the wave conditions, for example the distance between a wave peak and a wave trough, it may be advisable to separate floats  11  and  12 , using adjustable arms as shown in  FIG. 17 , alter the shape of the floats as shown in  FIG. 16 , reorient the floats as shown in  FIG. 17  and  FIG. 18 , add additional damper plates as shown in  FIG. 19 , or, in shallower waters, embed the spar in the sea floor. 
     With regard to  FIG. 16 , it should be noted that the side profile of floats  11  and  12 , shown here as a tear-dropped shape, can be mounted to arms  47  and  48 , respectively, such that they can rotate about of center axis of the arms. The shape of the float is not limited. Float shape is to be optimized for hydrodynamic performance. These floats can include cylinders, squares, triangles and any combinations of curves. Nor is the rotation axis limited, but can be varied. The rotation of the floats changes the hydrodynamic performance, including water plain stiffness of the float, the float&#39;s center of gravity, and float free-board. Variable ballasting of floats  11  and  12  could provide additional hydrodynamic optimization. 
     As shown in  FIG. 17 , the length of arms  47  and  48  can vary to suit the water conditions or to control the amount of energy being absorbed. In this embodiment of a wave energy converter, floats  11  and  12  are rotably connected to arms  47  and  48 , respectively, via mounting  49  and  50 , respectively. The yaw rotation of the floats allows the floats to rotate so as to be perpendicular to the axis of rotation of the PTO in housing  30 . The floats can also rotate on arms  47  and  48  so as to be parallel with the axis of rotation of that PTO, or somewhere in between the parallel and perpendicular positions. Indeed, the orientation of the two floats can differ as shown in  FIG. 17 . The floats can be automatically or manually adjusted to control the amount of energy being absorbed from a wave. 
     As shown in  FIG. 18 , it is also possible to add a rudder  51  to the bottom of heave plate  14  in lieu of, or in addition to, directional vanes  39  of  FIG. 10 , rudder  40  of  FIG. 11 , or a combination of the two. Rudder  51  may be automatically or manually positioned to control the direction of the wave energy converter relative to the direction of wave travel. 
     As shown in  FIG. 19 , it is also possible to suspend a damper plate  52  from heave plate  14  to stabilize spar  13 . For the same reason, it is also possible to suspend a damper plate  52  from damper plate  9 , or a second heave plate (not shown) from heave plate  14 , or a combination of these plates to stabilize the operation of the wave energy converter of the present invention. 
     As can be readily understood from the foregoing description of the invention, the preferred structure and method of operation have been described, but other structures and approaches can be substituted therefore without departing from the scope of the invention.