TITLE OF INVENTION

SEA BARRIER SYSTEM

BACKGROUND OF THE INVENTION

In some existing embodiments of ocean turbines, a plurality of open turbines may be mounted on a top-surface of a base for converting the kinetic energy of moving water associated with the breaking wave into electricity. The turbine should stay within the top part of the wave, where highest concentration of kinetic energy is present to maximize the energy efficiency.

One potential problem with this arrangement is that the tidal change will make difficult to meet the above-mentioned conditions, i.e., at low tide, the wave will pass underneath of the turbine without rotating it, or at high tide, the turbine stays within lower portion of the wave where the water moves slow, and as a result, rotation speed of the turbine becomes slow.

Another potential problem with open turbine operating in the breaking-wave zone is that once the wave breaks, it creates vortex flows and foam mixture of water and air, where the wave energy is dissipated through heat by the friction loss through the viscosity, and as a result, the power output from the turbine becomes fairly low.

Also known is an Oscillating Water Column (OWC). A typical OWC arrangement comprises two key elements: a collector chamber, which takes power from the waves and transfers it to the air within the chamber, and a power take off (PTO) system, which converts the pneumatic power into electricity. The pressure in the collector chamber is alternately pressurized as the water column rises and falls as the water column falls. The OWC is probably the most studied and best developed of the various embodiments of ocean turbines. In shore-based operations, OWCs have demonstrated sufficient reliability to be somewhat viable. Unfortunately, the size of the OWC collector chamber has to be big enough, because OWC uses sinuous up- down motion of the wave, i.e., OWC uses arriving wave at deeper place at shore where the waveform has not been deformed into short pulse wave. Therefore, in theory, to make the conversion efficiency maximum, the size of the chamber should be near to the half wavelength, i.e., 25 m long (at near shore, the wavelength has been reduced roughly 50% of the deep-sea value). This is practically too long to make.

The height of the collecting chamber should be also high enough to avoid upward running water colliding to the chamber celling, where the expensive turbine is running with highspeed air. Once the seawater directly runs into the turbine, the turbine will be crashed into by the water because the water has roughly 1000 times higher mass density than air. Therefore, to lower the risk, the collecting chamber needs to be high enough, i.e., for example 3 meter deep and 10 meter high in Mutriku wave energy test site.

The cost of the resulting power generated by OWC systems is still too high.

Consequently, an improved ocean turbine system is desired.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a side view of an embodiment herein, while FIG. 1B shows a wave and some of the energy concentrated therein;

FIG. 2 shows a perspective view of a frame according to the embodiments herein;

FIG. 3A shows an embodiment of a wave energy conversion system sitting on dry land;

FIG. 3B shows a joining brace according to the embodiments herein; FIG. 4 shows a bracket according to the embodiments herein;

FIG. 5 is a plan view of a portion of the frame and bracket;

FIG. 6 shows the bracket with a turbine installed therein;

FIG. 7 shows a pair of contrasting frame shapes used in the embodiments herein;

FIGS. 8A and 8B show a wave simulation within the frame shapes of FIG. 7;

FIGS. 9A, 9B, and 9C show the wave energy conversion system in use;

FIG. 10 shows a potential method of manufacture of an embodiment herein;

FIG. 11 shows a grouping of wave energy conversion systems;

FIG. 12 is a water- velocity diagram;

FIG. 13 shows some example simulation results;

FIG. 14A shows example total power during three periods of waves is shown in FIG.A, while FIGS. 14B and 14C show close-up views of two half periods;

FIG. 15A shows an example effective power during three periods of waves, while FIGS.B and 15C show close-up views of two half periods;

FIG. 16A shows an example kinetic power during three periods of waves, while FIGS.B and 16C show close-up views of two half periods;

FIG. 17A shows an example pressure power during three periods of waves, while FIGS.B and 17C show an example close-up of two half periods from FIG. 17A;

FIG. 18 shows an example stream wise volumetric flow rate;

FIG. 19 shows an example stream wise velocity;

FIG. 20 shows examples of a spatial integration probe;

FIG. 21 shows a ducted wave energy converter installation;

FIG. 22 shows a sea wall integration; FIG. 23 shows a breakwater constructed with piles;

FIG. 24 shows a hexagonal shaped pile integration;

FIG. 25 shows output voltage from half-scale WEC;

FIG. 26 shows the rms output voltage;

FIG. 27 shows output voltage from half-scale WEC;

FIG. 28 shows output voltage from half-scale WEC; and

FIG. 29 shows a power conditioner.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

To solve the above problems, this invention uses a funnel structure, which will focus the moving water in the wave into a turbine, as a result, the power conversion efficiency becomes less sensitive to the tidal change.

In this invention, the funnel structure acts as a rectifier, which converts the vortex flow into the parallel flow, and thus the power conversion efficiency becomes higher. In the electrical circuitry, the rectifier component converts the AC voltage (vortex flow in the breaking wave) into DC voltage (parallel flow of water). The narrowing cross-section in the funnel limits freedom and all moving water can only move in forward direction where the turbine captures the energy.

Funnels with a tapered structure require that the length of the taper should be sufficiently long as quarter wavelength (e.g. ~25 meters) in a deep sea case. If the length of the taper is too short, the power of the wave will be reflected backward (rather than forward) and thus the wave energy not converted into electricity by the turbine generator. This results in lower power output from the turbine generator. On the other side, if the length of the taper is sufficiently long, this requires the size of the overall structure being so large as to not be economically feasible.

In this invention, we place the wave energy converter at the wave-breaking zone, l~2 meter depth, where the wave form is deformed through interaction with the seafloor in shallow water, and it forms a short pulse wave: like soliton wave. The physical length of the upper wave portion of such short pulse wave becomes less than 10 meters, which is much shorter than the wavelength of ocean wave in deep sea; -100 meters. As a result, the required length of the taper funnel structure in shallow water becomes about 2 ~ 4 m.

FIG. 1A shows an embodiment of a wave energy conversion system 100. The breaking waves arrive to the wave energy conversion system 100 and portions of the wave enter at a tapered surface 120. Some portions of the wave come in, preserve their kinetic energy and accelerate (accelerated flow 116) near to the nozzle 1 12. Meanwhile, other portions of the wave become part of the vortex flow 136 where their kinetic energy is reduced.

It is an object of the embodiments herein to preserve as much kinetic energy as possible, and ensure that these preserved portions reach the propeller blades 108 and thus the turbine, including going all the way through the system 100. In order to achieve this object and optimize power conversion, tapered surfaces (e.g. taper 120) can be located at a variety of heights and angles, partly by varying the length of the legs 208, as well as numerous other adjustments. In an embodiment, the specific locations, sizes, and contours of these surfaces 120 are chosen partly on the basis of computer simulation, manufacturing advantages, and also testing and verifying during use. The power generated by the turbine is moved along an energy transfer path 132 to some type of energy storage 124, where it may be stored or may be transferred in some proportion to some type of energy consumption 128, either on-shore, off-shore, or nearer to shore.

FIG. 1B shows a diagram of a wave, including a location of the highest concentration of kinetic energy. This location is the target of the embodiments herein, and is the portion of the wave desired to be accelerated and reach the propeller blades 108.

FIG. 2 shows a perspective view of a frame 204. A tapered pipe structure is located inside one or more of the box caissons. The taper structure typically has a nozzle 112 (FIG. 1) located at a distal end, and within that nozzle 112 are propeller blades 108. This combination results in the system 100 having a semi-tubular or box caisson shaped. Breaking waves create a high intensity impact force, which can stress and degrade mechanical equipment located in water. Consequently, the embodiments herein, including the frame 204, incorporate solid mechanical design aimed at resisting this type of force, including being joined together by welding. Further, one or more on-device and near-device sensors 216 and accelerometers 218 are also helpful in becoming aware of and quickly addressing potential damage, impacts, and structural damages. In an embodiment, the frame 204 is made by aluminum plate, welded together using for example tig welds. The example locations of the on-device and near-device sensors 216 and

accelerometers 218 shown in FIG. 2 are for example only, and should not be considered limiting. The on-device and near-device sensors 216 and accelerometers 218 are hardened and ruggedized to work in heavy salt, heavy water, and heavy sun conditions, and can also be equipped with various anti-seagull and anti-barnacle concealment mechanisms.

Further, a plurality of spatial integration probes 2004 are used for obtaining the volumetric flow rate and the power of the fluid passing through an arbitrary surface. FIG. 20 shows some example positions of a surface of the probe 2004, which in FIG. 20 are shown in the inlet, middle and outlet of the frame 204. However, the arrangement of FIG. 20 is but for suggestion and example only, so that the embodiments herein should not be considered as limited exclusively thereto.

FIG. 3 A shows an embodiment of the wave energy conversion system 100 but not in water, instead sitting on dry land. For simplicity, various elements of the turbine 104 are not shown in FIG. 3 A. The frame 204 has legs 208, and has a turbine 104 attached. The turbine 104 comprises propeller blades 108, among other things.

FIG. 3B shows a joining brace 304 connected to a leg 208 according to the embodiments herein. FIG. 4 shows an exploded view of a portion of the frame 204 near to a bracket 308.

FIG. 5 is a plan view of a portion of the frame 204 and bracket 308, and how they are joined together. The legs 208 are also shown. FIG. 6 shows the bracket 308 with a turbine 104 installed therein. Specifically, the turbine 104 has propeller blades 108, a transfer cable 604, and active electronics 608. The active electronics 608 can include a diode arrangement, suitable for preventing current from flowing backwards. All current should flow from the system 100 to the energy storage and/or the energy consumption 128, and never flow in reverse. Further, in an embodiment, the system 100 continues to flow at least some minimal power even when the tide is flowing out.

Continuing with the concept of optimizing for energy conversion, it is a well-known problem of devices that only work when the tide is in a certain position. That is, for a fixed- height system, permanently mounted into a specific location and not varying in height, such a device may only capture wave energy for a fraction of a given day. That is, many hours of a day, e.g. when the tide is up, a device may be entirely submerged and thus not able to capture waves. Similarly, there may be hours where a device is entirely above the surface of the water, dry, and not capturing any wave energy whatsoever. To address this, an embodiment of the system 100 exists which is free-floating and buoyant, although still anchored to a specific spot. Such a device is arranged to still hold its position, capture and convert wave energy, regardless of the state of the tide.

FIG. 7 shows a pair of contrasting frame shapes used in the embodiments herein. A funnel caisson shape 704 is uniformly tapered throughout the entire frame, using a long tapered surface 712. Meanwhile, a pool caisson shape 708 has a flat horizontal portion, and then a short tapered surface 716. When waves pass through a system based on the pool caisson shape 708, there is a reverse flow zone before the outlet of the pool caisson shape 708, which makes the overall flow velocity smaller than the funnel caisson shape 704. However, this also acts to minimize the negative effects of the vortex flow 136.

In the Computer Fluid Dynamics (CFD) simulation referenced in FIGS. 7-8, the turbines 108 are not included. Performance of two types of the tapered waveguides 704/708 were evaluated by the CFD.

FIG. 8 shows a wave simulation within the frame shapes of FIG. 7, including approximate locations of vortex flow 1 16 and accelerated flow 136. As stated earlier, some of the wave hitting the wave energy conversion system 100 is reflected, which is unwanted.

Consequently, further optimization on the parameter matching such as the taper slope, turbine size, and rotation speed is implemented in order to minimize reflection. For example, effective results were achieved both with turbines 104 having a diameter of 35cm, and also with 60cm.

FIGS. 9A, 9B, and 9C show the wave energy conversion system in use. As shown in FIGS. 9A-9C, one or more wave energy conversion systems 100 are located at what is perceived to be a suitable surf-wave zone. The specific location of these systems 100 is chosen according to pre-determined criteria. Measurements taken from the sensors 216 and accelerometers 218 (discussed earlier w/ respect to e.g. FIG. 2) show that water speed (front foam) flowing around the tapered surface 712Y716 is roughly 4 m/sec, while the water speed inside the tapered surface 712, 716 was 6~8 m/sec.

FIG. 10 shows a potential method of manufacture of an embodiment herein.

FIG. 11 shows a grouping of wave energy conversion systems 100. The drawings herein mostly show a single wave energy converter 100, but as shown in FIG. 1 1, the wave energy converters 100 can be grouped together.

In operation, a breaking wave runs into the tapered surface 120, and the resulting water flow is focused and the water flow speed is in turn accelerated. This water flow drives the propeller blade 108 attached to the turbine 104 that is located inside of the nozzle 1 12, which in turn results in electricity being generated. Because the blade is located inside the nozzle 1 12, the power conversion efficiency becomes roughly twice as much as an open water turbine.

FIG. IB shows a typical surf- wave, in which kinetic energy located is localized at the top of the wave. Accordingly, the top part of a wave runs faster than the bottom that wave, resulting in the wave“breaking”. At the portion of the wave that breaks, the top part of the wave crushes the bottom part, and mixes, so that some kinetic energy is lost as heat through friction. Some change in viscosity of the resulting water-mixture also occurs.

If the wave-breaking described above can be induced to occur inside the tapered structure 120, and if amount of bottom-water within the wave energy conversion system 100 can be reduced, more of the kinetic energy at the upper portion of the wave can be captured and not lost/dissipated. This is partly because the surfaces of the wave energy conversion system 100 reflect and direct the water in an axial direction towards the propeller blade 108 and nozzle 1 12 (as shown by the arrows within FIGS. 1 A and 2). The water flow is thus improved, so that more kinetic energy is preserved and available to drive the propeller blade 108 within the turbine 104.

FIG. 3 shows a flowchart describing some potential methods of achieving the steps described above.

The embodiments herein can achieve continuous (non-pulsing) power, not merely an occasional surge due to a wave, but instead at least some minimal amount of power even during “lull” periods of the tide, both micro and macro.

MEASUREMENT

The amounts of this power are measured (not the voltage amount, the current amount), and accurate determinations can be made of how much current is being generated. This is a nastier requirement than mere voltage, because with current, the current-measurement instrument must be introduced directly into the circuit.

To address this, an analyzer port 612 can be located at some point within the transfer cable 604, and measure actual current flowing from the turbine 104. The analyzer port 612 can be used to connect a variety of measurement devices, work with the active electronics 608, and obtain a wide variety of substantive information about the performance of the turbine 104 as well as the overall system 100. Further, all features mentioned in FIG. 6 and all Figures herein can be encased in protective materials such that they continue to function and convey useful information even when the system 100 is entirely submerged in water, and also when the system 100 is entirely above the water. SIMULATIONS

This Appendix will discuss how the performances of two types of the taper waveguides 712, 716 were evaluated by Computer Fluid Dynamics Simulation (CFD). Within the

simulations herein, the turbines 104 are not included, thus the water smoothly passes through exit of the taper. Accordingly, an actual system 100 may work differently than what is shown in these simulations, but for the purpose of effective computer simulation, it was necessary to not include the turbine 104. This is because the purpose of these simulations is mainly to show which shapes, sizes, and surfaces of the system 100 would be optimal. The discussions and analysis within this Appendix (simulations) will thus be turbine-neutral, and turbine-agnostic.

The main targets of this simulations were evaluating the energy passing through caissons and comparing the performance of two types of caisson shapes 704, 708. One of the factors in performing a computer simulation is known as a blockage ratio. When the blockage ratio B =

5%, the breaking waves are created at the same position between two simulations. Such a low blockage ratio leads to an increase in the computational domain, which increases the calculation time (32 million grids, 17 cores, 96 hours for 3 period of waves). Therefore, in running the evaluations/simulations, it became helpful to use the slip boundary condition both sides domain with the periodic boundary condition. The calculation grid was reduced by one-third, and the calculation time was also reduced.

The following simulations were calculated by SURGE (Free-Surface Flow Solver for Gravity-Driven Hydraulic Events), which is a computational fluid dynamics (CFD) assessment resource for measuring free-surface flow. As a numerical approach, the volume-of-fluid (VOF) method based on the finite difference method (FDM) is employed to model the free surface flow. In addition, a nesting grid system is implemented for combined multi-scale hydraulic phenomena such as shoaling waves and their attacking on a coastal structure.

At the inlet surface of computational domain, the mean water depth is h— 5m, which is at transitional-water zone, and assumed period T = lOs wave height H) = 0.75m wave length L) = 60m to generate the target breaking waves. Next, for clarity, within this disclosure, various power identifiers will be referred to as follows: power PJKJ, effective power PYZZ, kinetic power PE, and pressure power Pbc. The pressure power Pbc = PYZZ (effective) - PE (kinetic).

Additionally, potential dimensions of the tapered surfaces 712, 716 can be varied by a wide variety of factors, including but not limited to length, size of input window, size of output window, and distance from the taper bottom to the sea floor.

FIG. 13 shows a simulation result, stating that the power at the output window reaches 90 kW peak by the funnel caisson 704 and 70 kW by the pool caisson 708. The average power for a three second interval shown in FIG. 13 is roughly 10 kW for both cases, while funnel caisson, the power obtained is higher at the front end. The simulation results indicate the taper waveguide enhances wave power effectively. With the turbine 104 integrated, the energy contained in the front peak will be delayed (reflected) and build up later plateau, so that the resulting waveform would likely be other than what is shown in FIG. 13.

FIG. 20 shows examples of a spatial integration probe 2004, which is used for obtaining the volumetric flow rate and the power of the fluid passing through an arbitrary surface. As shown in FIG. 20, a face of the probe 2004 can be located at for example an inlet, middle and outlet of caisson, such as but not limited to caissons 712, 716. However, the probe 2004 could have other shapes and other locations than what is shown in FIG. 20, which is for example only. Consequently, the embodiments herein should not be considered as limited solely to that within

FIG. 20.

TABLE 1

TABLE 1 shows some example parameters that can be obtained partly through use of a spatial integration probe.

Some example parameters that can be obtained by the spatial integration probe 2004 are shown in TABLE 1, where F is the VOF function, which is the water percentage of grid volume, Ax, Ay, Az are the grid width, and DAΐ is the projected area of the grid in the i direction. /? = p' + pgz is the static pressure, which is the sum of pressure and gravitational potential. From the Bernoulli's theorem, the total power is given by the following equation . . . where h _z is the water depth specified by the probe surface. However, the gravitational potential power cannot be captured by the electric generator, the effective power is given by the following equation;

The total power P _tot at the outlet surface of two types of caissons is shown in FIGS. 14A-C. The total power during 3 period of waves is shown in FIG. 14A, and the zoom figure of two half period is shown in FIGS. 14B-C.

The effective power eff at the outlet surface of two types of caissons is shown in FIGS. 15A-C. The effective power during 3 period of waves is shown in FIG. 15 A, and the zoom figure of two half period is shown in FIG. 15B-C.

The kinetic power PK at the outlet surface is shown in FIG. 16. The kinetic power during 3 periods of waves is shown in FIG. 16A, and the zoomed figure of two half period is shown in FIGS. 16B-C.

The pressure power P _p · = P _ef r - P _K at the outlet surface is shown in FIGS. 17A-C. The pressure power during 3 period of waves is shown in FIG. 17 A, and the zoomed figure of two half period is shown in FIG. 17B-C. Finally, an example stream wise volumetric flow rate is shown in FIG. 18, and an example stream wise velocity is shown in FIG. 19.

In conclusion, the simulations herein results suggest the power at the output window of a caisson reaches 90 kW peak by the funnel caisson 704 and 70 kW by the pool caisson 708. The average power for three second is roughly 10 kW for both cases, while with the funnel caisson 704, the power is higher at front end. Accordingly, the simulations herein suggest the tapered waveguide optimizes and concentrates waves power effectively. WEC INSTALLATION

FIG. 21 shows an example of a ducted wave energy converter (WEC) device 2100 fixed into the ground 21 10. The size of this device is about 2m x 2m x 4m and is a box made of concrete (sometimes called a caisson) which is placed on the ground 21 10. Since the mass of this device is about 20 000 kg, it is stable against waves 2115. However, depending on the seafloor, other options may be possible. For example, in the case of a sand beach, prior to installation, stones or concrete blocks may be placed on the sand floor to make a flat and stable base. The location of the device 2100 depends on where the wave breaking zone is at mean tide level. A wave breaking zone moves back and forth depending on the tidal change. In this embodiment, directly fixing this device 2100 on the ground is suitable to a beach where the tidal change is small. Most of the islands in the Pacific and Indian Ocean, beaches in the Mediterranean Sea and Gulf Coast satisfy this condition. However, European coasts have a high tidal range, for example, Normandy France, where this embodiment is not suitable. In this device 2100, the ocean wave runs into the water pool 2120, the taper section 2125 and then the turbine 2130 at the exit. A maintenance person 2135 can stand behind the concrete caisson, and beside the generator, where the wave cannot reach and the maintenance person can safely check equipment.

Furthermore, electrical components 2140 (power breaker switch, power cable connections) can be stored inside an electrical hutch (groove), where no wave can reach and thus workers can safely maintain the electrical components.

FIG. 22 shows an example of a plurality of wave energy converters integrated into a seawall 2200. Such seawalls are commonly prepared to protect shipping ports and harbors from waves. This device integrates the taper 2205 (funnel structure) and turbines 2210 inside the seawall which has a dual function of costal protection and renewable energy. Multiple arrays of funnels at different vertical levels for different tidal conditions may be installed. For example, one series for high tide and another series for low tide may be installed. The incoming waves 2215 from the ocean hits the seawall where there are multiple taper openings. This generates high speed water flow into the turbines to generate electricity. Furthermore, the water level inside the port is lower than the sea level, thus this device can act as a temporal water dam. Thus, the return water flow 2220 will be created at the open gap between seawalls. According to the concept of the energy conservation law in physics, if energy is taken from the water flow, the kinetic energy of the water becomes lower, and as a result, the outgoing water from the turbines becomes slow, or gentle. Therefore, this integrated seawall with wave energy converters becomes an ideal barrier to reduce waves inside a port or harbor. The size and design of the seawall are compatible to the commonly used designs for port and harbor seawall protection.

FIG. 23 shows an example of integration of multiple wave energy converters into a breakwater 2300 supported by piles 2305. Breakwaters are structures constructed near coasts as part of coastal management. In some places, because of the impact of waves or tidal current, it is difficult to keep structures on the seabed stably. This embodiment becomes a suitable choice in such situations. The breakwater installed with funnels 2310 and turbines 2315 may be supported by piles 2305 standing on the seafloor. Due to the physics of the wave 2320, the water movement in the ocean wave is localized at the surface. Thus, it is efficient to place the breakwater on the surface and the lower structure can be made of piles. In this case, the amount of concrete or stones can be reduced to make the base of the breakwater. According to the concept of energy conservation laws in physics, if energy is taken from water flow, the kinetic energy of the water becomes lower. As a result, the outgoing water flow after the breakwater becomes slow or gentle. Therefore, this integrated breakwater with wave energy converters becomes an ideal barrier to reduce wave impact to the land.

FIG. 24 shows an example of installing wave energy converters into a hexagonal pile 2400 and stacking vertically as a breakwater. In this application, funnels 2405 are integrated inside the hexagonal pile which is made of concrete. The turbine and generator 2410 are installed at the end of the hexagonal structure. A plurality of hexagonal piles are stacked to form a breakwater. The hexagonal shape has a self-alignment function. For example, although wave impact sometimes move such a pile, the hexagonal pile will re-align naturally and gaps will be filled to improve mechanical stiffness of the breakwater. The outer size of the hexagonal pile is close to the tidal range, for example, 2 to 3 m. This breakwater is also placed at the wave breaking zone, and the depth is chosen at the water level where low tide at the center of the lower array, so that the output power becomes maximum for the lower array. At high tide, the water level will come to the center of the upper array, so that the output power becomes maximum at the upper array. Due to this design, fabrication cost becomes lower. Also, due to the self- alignment function, installation of the breakwater is easier.

A floating embodiment is also possible. In principle, a funnel could be integrated with a floating buoy. However, the water speed of a deep sea wave is slower, thus the short funnel cannot effectively capture a wave and thus it will not be economically feasible.

EXPERIMENTAL RESULTS

The following are the results from the field experiment on the aluminum made funnel taper.

1. Experimental setup Funnel taper: 1 m x 1 m upstream window, 2 m length, 0.4 m x 0.4 m downstream output window.

Turbine with funnel taper: Half-scale WEC 35 cm diameter, five blade.

Electrical generator: 550 Watt, 48 Vrms @ 330 rpm

1.4 kW, 120 Vrms (@600 rpm)

2. Measured Raw Data

Fig. 25 shows example output voltage from the half-scale WEC with funnel taper. Upper- right graph is an actual waveform from the generator three-phase AC voltage synchronous generator with permanent magnet array. The big two peaks correspond to two series of breaking waves at 12 second interval. The peak reached to 175 V. The load resistor was 31.4 ohm, so that the peak power was 1.73 x 175 x 175 / 31.4 = 1680 Watt, where 1.73 is a constant factor in three phase circuit. We have to note that this is peak output power, and it becomes zero right after the wave passes. For practical use, one needs to store these power into a battery, followed by power conditioner circuitry to connect to grid power system discussed below. The small output voltage between them is associated with backward flow of a wave. The bottom graph shows detailed structure inside the peak, which shows AC cycles. From this graph, we know the output voltage has short pulse waveform, and its peaks are varying pulse to pulse, i.e., breaking wave power always fluctuates.

3. RMS output voltage

RMS stands for root-mean-square, which is frequently used to measure the average power in randomly variating power, such as, this wave energy case. The peak voltage does not show the power output. If we have a load resistor, the terminal voltage v(t) is randomly changing. The current flow into the resistor is simply given by i (t) = v (t) /R, so that the instantaneous power flow into the resistor (which will be converted to heat in the resistor), p(t) = v(t) x i (t) = v(t) ² /R. When we talk about the power output from the wave energy system, we need to know the time average power (for example 1 hour). What we do is to integrate p(t) in time and then take average (dividing by time duration of integration, i.e., by T). If we define Vrms, we find that Vrms indicates time averaged effective voltage. Square of Vrm becomes normalized average power. We used digital data recorder connected to the electrical generator, which computes Vrms for every second, and send the data to a computer as a data series.

4. Average output power measurement.

We compared output from the wave energy converter with/without funnel taper.

FIG. 26 shows the rms output voltage without funnel taper (bare full-scale turbine 70 cm diameter), and half-scale (35 cm turbine) with funnel taper at the same location. As seen in the graph, the average voltage went up roughly 2.5 times with using funnel taper, which means, the power went up 2.5 x 2.5 = 6.3 times higher.

5. Tidal Change

Because the wave breaking zone moves back-and-forth (in-and-out), the power output is highly affected with water level change. FIG. 27 shows output voltage from bare Half-scale WEC for 14 hours. Non-dot line shows the tide change. The output power became zero at low tide during 6 to 8 hours. We took same data with taper funnel as follows in FIG. 28. In FIG. 28, it is clear that the output power became more stable against the tidal change, it did not go to zero. This is clear evidence this invention made wave energy converter system stable against tidal change. These two graphs above were taken with the same size turbine (35 cm diameter Half-scale WEC), thus comparison is fair. The output voltage was improved roughly three times with funnel taper, i.e., the power improvement was roughly 10 times, even through the wave height was lower in funnel taper case.

6. Power Grid Connection

The circuit diagram of FIG. 29 shows power conditioner 2900 for a wave power plant of 1 MWatt class. This configuration is same for smaller power -10 kW system. Series of WECs 2905 positioned by the beach, sending generated power through cables (a few hundreds meters) to the power conditioner system 2910 built in an onshore power house. We rectify the three phase AC power, convert into DC current, and temporally store them in a big capacitor bank (most probable we use EDLC: electric double layer capacitor or super capacitor), then sending out the power through DC-AC converter unit, which precisely matches the output frequency and voltage to the power grid system. This power conditioner is same technology used in solar PV system, so that it is well established, thus highly reliable system is available with low cost.