Wing Wave: Feasible, Alternative, Renewable, Electrical Energy Producing Ocean Floor System

Mark Christian, Billy Wells, Sitara Baboolal, Patrick Maloney, Stephen Wood. Ph.D., P.E. Ocean Engineering

Florida Institute of Technology Melbourne, Florida, USA

swood@fit.edu

Abstract—Wing-Wave is an ocean, alternative energy system to convert the circular motion of ocean waves as they propagate through the sea into electrical energy. The system consists of planes, called “wings”. The wings are mounted on the sea floor and move in a radial motion as a result of the passing waves. The mechanical energy is translated into electrical energy by means of an electrical generator. Three Wing-Wave prototype systems were built at Florida Institute of Technology (Florida Tech) and deployed November 17th, 2010, June 23rd, 2011, and June 6th, 2012, respectively. Each deployment provided valuable information that lead to modifications in subsequent versions and deployment techniques, culminating in the demonstration of a fully functioning and feasible alternative, renewable, electrical energy producing subsea system.

Index Terms—ocean energy, wave energy, wave energy converter, WEC, electrical energy, alternative energy, hydrokinetic energy, hydroelectric, green energy.

I. INTRODUCTION The Wing-Wave system (Fig. 1) is an alternate energy

generation device designed to capture energy from ocean waves at a depth of 10 to 15 meters and produce electricity. This paper explores this production of electricity through the oscillatory motion of water particles instead of through the traditional combustion of fossil fuels. The development of such technology is important given the increasing demand and the steadily decreasing supply of conventional resources for electricity generation with the added benefit of not producing greenhouse gasses associated with the combustion of fuels used in electrical turbines.

There has been significant exploration into the harvesting of renewable resources for the purpose of the creation of electrical energy; however one of the primary concerns with this is the consistency of the source of power. Two of the leading renewable energy sources wind and conventional hydro-electrical are constrained to small areas of applicability given their requirement for resource intensity and regularity. Conventional hydroelectric generators currently produce 6% of the energy demand of the United States, all rivers within the United States that have potential for large scale energy production have already been dammed, preventing further expansion of this field [1]. Wind turbines are primarily located in the Mid-West of the United States and further exploration of

is limited by the 3.86-m/s (7.5-knot) minimum wind speed required to turn a majority of wind turbines [2].

Due to the primary population densities residing on the coasts of the United States the harvesting ocean wave energy is ideal. It is projected that wave energy has the potential to produce 252 billion kilowatt-hours of electrical energy each year along the coasts of the United States alone [3]. The proximity of the ocean to major population centers combined with predictability of wave action allows for a broad use of the Wing-Wave technology. The main constraint on the Wing-Wave is the depth at which water particles cease to move in elliptical orbits.

II. BACKGROUND There are many variations in the types and effectiveness of

wave energy converters (WEC). Usually, WECs are grouped by the location of the wave in which energy is extracted. The most common types of WECs include terminators, attenuators, point absorbers, and overtopping devices. • Terminator WECs gather a wave’s energy and stop the

forward propagation of the wave. These types of WECs usually exist on the shoreline, since the wave terminates there anyway.

• Attenuator WECs either float on the ocean surface or are partially submerged. They usually contain some sort of hinge mechanism and body section, which move independently from one another about the hinge. As the wave passes the attenuator, energy is harvested, and the wave continues propagation further along the surface of the ocean.

Fig. 1. 2012 Wing-Wave System

• Point Absorbers are usually stationary and work on differences in pressure and/or elevation in the surface of the ocean and after the energy is absorbed from a wave, the wave itself continues on its journey across the ocean.

• Overtopping Devices collect water as it passes over some sort of boundary, essentially filling with water and using the pressure created to produce energy.

The Ocean Engineering Department at Florida Institute of Technology under the direction of Stephen L. Wood Ph.D., P.E., has since 2007 the goal to construct a sub-surface energy pump system to collect and analyze its power output. In recent years there have been several studies concerning the validity of using ocean waves as an energy source. Although most of these studies have been on the power output of surface waves the Wing-Wave takes it deeper. It works with the concept that particles orbiting under a shallow water wave follow an elliptical path. As depth increases the horizontal movement of the particles’ rotation remains the same while the vertical movement decreases. This causes the motion of the ocean floor to oscillate in an almost exclusively horizontal direction. The Wing-Wave system was designed to capture this horizontal motion to pump the wings of the system, ultimately pumping a working fluid to a generator via a hydraulic ram.

The Wing-Wave WEC concept came from several private commercial designs. One in particular is the AW-Energy Wave Roller (Fig. 2). Original concepts for the Wave Roller date back to 1999, when the first prototypes were designed and the first patents were applied for. The Wave Roller is fixed to the sea floor, and as waves pass overhead, the particle velocities impart a force over the presented surface area normal to the wave propagation [4]. Another private design is the Oyster Wave Energy Converter (Fig. 3). Mechanically, this WEC works in the same fashion as the Wave Roller. The main difference is that the fluid in the hydraulic system is transferred onshore to a hydroelectric power plant. Current and plausible testing sites for the Oyster include Scotland, Ireland, and the west coast of the United States [5].

At Florida Tech, in order to determine the best design for the wing, models were built and their efficiencies compared by observing their range of motion when placed in a wave tank (Fig. 4). The range of motion were compared on a flat wing, a flat wing with a top panel (T-shaped), a triangular wing and the flat panel with top and side panels. The least effective model was the T-shaped wing where as the most effective was the wing with top and side panels. This model testing finalized the design for the prototype wing.

In 2010, the next task took the most effective wing design proven during testing and applied it to a full-scale prototype (Fig. 5). Sitting on a 6.1-m x 4.6-m (20-ft x 15-ft) based constructed of 6061 Aluminum, with four 0.6-m (2-ft) triangular extensions for stability two 4.6-m x 2.4-m (15-ft x 8-ft) tall aluminum wings were placed one in front the other connected to the frame via stainless steel hinges. A piston system was attached to the wings to transfer the pumping motion caused by the horizontal movement of the wave (wave energy) to a generator to produce power. This system was

however not connected to a data recorder and its energy output was not recorded while at sea.

In 2011 Clean and Green Enterprise Ltd, a sponsor for the 2010 version, built and deployed with Florida Tech a single flat composite wing 1.8-m x 1.2-m (6-ft x 4-ft), connected to a smaller aluminum frame and equipped with accelerometers and its movement was recorded (Fig. 6). This version showed the Wing-Wave is a viable means of producing ocean energy.

The 2012 Wing-Wave design (Fig. 1) is based on two of the 1.8-m x 1.2-m (6-ft x 4-ft) wings, made of 1.27-cm (½-in) thick composite panel that with alternating prism support beams, 20.3-cm (8-in) wide base and 15.2-cm (6-in) wide top. The approximate weight of each panel is 68-kg (150-lbs) in air and positively buoyant in water. The wings are attached to the metal frame and bolted directly to the sea floor via sand screws. The hydraulic ram is attached to the wings and the metal frame to pumps fluid to the Power Take-Off system on the surface where the accumulator and generator reside.

III. DEPLOYMENT LOCATION The Wing-Wave Energy System was deployed in 2010

4.83-km (3-mi) northeast of Fort Pierce, Florida and in 2011 and 2012 3.22-km (2-mi) southeast of Fort Pierce. These locations were selected because of the wave data previously gathered, the clarity of the water, and have optimal depth and bottom sediment consistency for the chosen method of anchoring. Compilation and analysis of the oceanographic data ensured that accurate wave forces were calculated. Data from NOAA’s National Data Buoy Center buoy #134 near to the deployment location was used; even though located in 16-m (52-ft) of water, the wave forces can be projected at the deployment location.

IV. THEORY This type of energy system is based on the elliptical motion

of water particles (Fig. 7) as wave energy is transferred through the ocean. Water particles are not transmitted though the ocean along with the waves; instead the energy of the wave is transmitted though the physical collision of particles. The sinusoidal shape of an ocean wave is caused by the friction between the wind and sea forcing the affected water particles to move. Because of each particle’s resistance to movement, as particles collide affected particles move upward. At the surface the vertical movement is the greatest and decays with depth as water pressure increases. In deep water (depth/wavelength ratio is greater than 0.5) the amount of vertical and horizontal displacement are nearly equal causing the orbit of the particle to be spherical in nature. In intermediate to shallow water however (depth/wavelength ratio is less than 0.5) the orbits are also affected by the drag force of the sea floor. This drag force causes the orbits to elongate at they near the sea floor while at the same time there is a corresponding decrease in the vertical displacement (Eqns. 1 and 2).

It can be observed in Fig. 8 that both the velocity and the acceleration of the water particle vary sinusoidal with respect to location in the orbital. At the minimum displacement the water particle has the highest velocity and no acceleration, conversely at the maximum extent of the orbital the velocity is negligible and the acceleration is at its highest point.

Fig. 6. 2011 Acceleration data

A. Water Particle Modeling The average wave height varies from 0 to 2 meters and has

a period ranging from 6 to 12 seconds, which provides the required data to accurately predict the movements of the water particles at a variety of depths. To accomplish this, a series of equations are used to determine the vertical and horizontal particle displacements, velocities and accelerations as a function of time. The initial parameters that are required to determine these values are: the angular velocity (m/s); the wavelength (m); the celerity (m/s), and the wave number. These values (Eqns. 1-4) are a function of wave height (m): H, wave period (s): T, wave number: k, wavelength (m): L, acceleration due to gravity (m/s2): g, water depth (m): h, angular velocity (m/s): σ, wave celerity (m/s): C, time (s): t, particle depth (m): z. Using these values that describe the motion of the wave it is possible to determine the internal motion of the wave. This motion is best described by modeling the motion of a theoretical particle at the depth in question. Equations 5-7 describe the horizontal displacement, velocity, and acceleration correspondingly and similarly Eqns. 8-10 describe the vertical movement. In all the equations the water particle is modeled as a function of time, wave characteristics and depth.

To ensure the accuracy of the calculations it is important to note that the origin of the particle depth located at the sea surface and the value becomes progressively negative as depth increases; this culminates at the sea floor where the addition of the water depth and the particle depth is zero.

Fig. 2. Wave roller [4]

Fig. 3. Oyster wave energy converter [5]

Fig. 4. Wing models

Fig. 5. 2012 Full scale prototype

Fig. 7. Water Particle Orbitals [6]

Fig. 8. Per Unit Velocity and Acceleration of Water Particles [7]

Horizontal Calculations

Vertical Calculations

Figure 9 is a visual reference for the geometry of the oscillation of the water particle subjected to wave conditions. It is important to note, however, that these calculations are based on linear wave theory. This form of calculation does not take internal friction into account; however this greatly simplifies wave modeling, and the discrepancy that exists between linear and non-linear wave theory are minor when compared to the projected forces of the waves. The largest oscillations in water particle position was calculated to occur at a wave height of 3-m at a period of 10 seconds the results of this are displayed in Table 1.

TABLE I. WATER PARTICLE DATA FOR 10-SEC. PERIOD & 3-METER WAVE HEIGHT

Mean Particle Depth

(m) Velocity

(m/s) Acceleration

(m/s2) Displacement

(m) Hor. Vert Hor. Vert. Hor. Vert.

-9.75 1.766 0.173 0.713 0.109 1.807 0.275 -10.97 1.750 0.086 0.707 0.054 1.791 0.138 -12.2 1.745 0.000 0.705 0.000 1.786 0.000 As our ability to forecast weather patterns becomes more

advanced, so does forecasting the incoming energy from waves. Wave characteristics can be estimated as a function of the weather patterns that generate the waves. In order to fully assess the energy potential, an investigation of the amount of energy flux must be introduced. The summation of energies per unit volume can be given by the basic Bernoulli’s equation (assuming irrotational inviscid flow of propagating waves) Wave Energy per Unit Volume Eqn. 11.

(11)

where = velocity potential, V = water particle velocity, g = acceleration of gravity = 9.81-m/s2, p = pressure, and ρ = density of fluid

The local energy per meter length of wave crest transmitted can be calculated and estimated using the wave energy Eqn. 12. (12)

where ρ = density of seawater = 1025-kg/m3, g = acceleration of gravity = 9.81-m/s2, T = wave period in seconds, H = wave height in meters.

When considering a wave propagating toward shore with respect to harvesting its energy, the main focus is on the horizontal presentation of the wave energy as it arrives normal to the affected shoreline. This is the energy flux, which in general terms is the time rate of change of energy per unit area normal to the flow direction. In mathematical terms, the energy flux can be determined by multiplying the energy per unit volume by the individual particle velocities (Eqn. 13 Wave Energy Flux).

(13)

Fig.9. Orbital Geometry [7]

By describing the velocity potential in terms of wave height, water depth, horizontal distance over a given period, and wave length, and by integrating this over the wave period and the water depth, the average wave energy flux is described in Eqn. 14.

(14) Upon investigation of waves entering shallow water, it must

be noted that the motion of the wave orbitals that transmit the energy of the wave, cease their vertical movement and are restricted to a near horizontal motion (Fig. 10). For the Wing-Wave system, these horizontal velocities provide the energy to be harvested, because the velocity component ω is parallel to the vertical plane, the integral of the k term is equal to zero [8]. Theses energy calculations provide a reasonable estimate as to what sort of energy is available along our coastal zones, where these specific WECs are placed for deployment testing.

The basis for design parameters is the wave characteristics that the WECs encounter during testing. The National Wave Buoy Data Center collects wave spectral analysis from various buoys moored throughout the world. Historical wave data for specific locations is available online at the National Wave Buoy Data homepage. Types of data available are wave heights, periods, and direction of swell (see Figs. 11 and 12).

Swell and sea height data are extremely important for determining the amount of movement expected from each WEC. In conjunction with the National Data Buoy Center, Scripps Institute hosts the Wave Rider Buoy [Station ID: 41114, Location: 27.551° N, 80.225° W]. Through the use of Fast Fourier Transforms, spectral analysis of the raw data collected from the buoy is made into a useable form for predicting significant wave heights. By analyzing historical data, a legitimate estimation of wave heights during the proposed deployment window is determined. The efficiency of the design relies on the spatial orientation with respect to incoming ground swells. By knowing the direction of average swell, the system is oriented for maximum energy conversion. This wave data is the beginning of the power output calculations, due mostly in part to the fact that these criteria cannot be changed.

V. 2010 WING WAVE CONSTRUCTION The 2010 system consisting of two parallel planes, or

“wings” mounted on the sea floor was funded by Clean and Green Enterprises and deployed on November 17th, 2010 for a four day deployment. However, due to extended record storm conditions the system was deployed for thirty days in seas the system was not designed for. The system was observed to be fully functional by the deployment divers with the oscillations of the wings coinciding with the projected movement based on the surface wave height and wavelength. The system was found to be severely damaged at recovery.

The system’s primary design concern is the oscillatory force that passing waves subject the wings to. While there are many approximate equations the most accurate method of determining the applied force is by calculating the body and

surface forces that act on the control volume. For these purposes the control volume is defined as the physical area in which the wing moves through. As such it is important to note the primary difference that exists between both wings. One of the wings had the physical constraint acting on it in the form of a hydraulic piston, limiting the wing to a 60 degree range of motion; the other wing had free motion.

The body forces acting on the system are gravitational and buoyant, which can be calculated simultaneously with Eqn. equation 15.

(15)

Where: FBuoyancy is the total buoyant force, g the acceleration due to gravity, ρ is the density of seawater, VSea is the volume of displaced seawater and MWing is the mass of the wing.

The horizontal forces that the wings are subjected to due to wave action can be simplified (Eqn. 16).

(16) Where: F is the total force on the wing, Fvirtual mass is the

force required to move the water particles, Fbasset is the Basset Force, FDrag is the drag force. The drag force is the actual force that induces motion in the wings, this occurs as the water particles strike and move around the wings. This is a function primarily of the wing shape and the velocity of the water particles. For ease of modeling the wing will be modeled as a 2.44-m x 4.57-m (8-ft x 15-ft) flat plane (Eqn. 17).

(17)

Where: ρ is the density of seawater (kg/m3), U is the water particle velocity (m/s), A is the cross sectional area (m2), CD is the coefficient of drag. The coefficient of drag (CD) is a coefficient multiplier that describes the level to which the shape in question influences the amount of drag force exhibited. The larger the number the greater amount drag force will be. For a flat plane with dimensions of the wings the drag coefficient is 1.2 [11].

The Basset Force describes the lagging boundary layer caused by viscous effects as the wing moves. However given the complexity of the equations and the relatively small impact that the Basset Force will have on the structure due to the low acceleration this force can be regarded as negligible when compared to the other forces [12].

The Added-Mass force refers to the force that is imparted as the structure is accelerated through the surrounding fluid. The particles come in contact with the structure and are accelerated to move from the path of motion [13]. This is the primary force that resists the motion of the wing. The coefficient of Added-Mass is 0.765 for the wings and is determined experimentally from the shape of the wing in reference to the water particle flow (Eqn. 18) [11].

(18)

Where: FAdded-Mass is the Added-Mass force, ρ is the density of sea water, Cm is the coefficient of Added-Mass, V is the

Fig. 10. Wave Orbital Motions [9]

Fig. 11. Wave Buoy Data, Ft. Pierce FL [10]

Fig. 12. Wave Rose, Ft Pierce Florida [10]

Fig. 13. 2010 Wing Wave System

volume of Added-Mass, A is the acceleration of the wing. The volume of the Added-Mass is found using Eqn. 19.

(19)

Where: W is the width of the wing and H is the height of the wing.

When performing these calculations it is important to note that the energy production unit will provide an additional force on the wing and because of the uncertain nature of this generator unit, the primary values that are displayed are simply imparted from the water to the wings. Additionally, the calculations were performed for a simple 2.4 x 3.048-m (8x10-ft) rectangle to simplify the force calculations. From the archived data it is known that the wave height varies from zero to three meters during the approximate time of deployment. Using the particle velocity values that were determined for a range of depths and wave conditions the values found in Table 2 were determined. These values were only displayed for an 8 second period given this had the highest Force Values.

VI. 2010 WING DESIGN The “Wings” (Fig. 13) were constructed from 6061-T6

aluminum sheets mounted to a skeleton composed of 1.9-cm (¾-in) 6060-T6 aluminum angle iron. The angle iron was placed horizontally on one side and as an “X” on the other to resist bowing and flexing of the wings. The flexing of the wing inwards was a primary design concern given the moment arm existing between mounting points. Using the calculated distributed forces the overall forces the wings are subjected to is determined. Modeling the wings first as individual sections is done to assess the forces and load flow through the structure. Unfortunately, due to the complexity of the wings simplifications were performed to allow the structure to be modeled using ANSYS Workbench; the original geometry is pictured in Fig. 14.

There are two primary loading conditions that the wings were subject to (see Figs. 15, 16), the first condition being the drag force. Two ANSYS model scenarios are presented: under typical conditions (1-m wave height) and storm conditions (3-m wave height). The second condition is with respect to the wing with the hydraulic piston attached to it. As the wing oscillates there is a cyclical impact load imparted as the wing is stopped short. It can be observed that this stress is significantly more local and intense despite that this loading being derived from the lower Added-Mass force.

Table 2: Induced Wave Force for 8 second Period and 1, 2

and 3 meter Wave Height

A. Base Design The base acts as a mounting platform for both the wings. It

is comprised of a network of 6061-T6 “C” and “I” beams. The decision was made to separate the wings as far as possible to reduce dampening effects and prevent turbulent flow from developing between the wings. The wings were placed 1.22-m (4-ft) from the end of the base to reduce the chance of the structure tipping. Also to reduce tipping the base was designed with triangular “Feet” that protrude from the sides of the structure. These “Feet” also serve as an attachment point for the gravity anchor system and have the additional benefit of shielding the system.

B. Anchoring System The anchoring system comprised of a gravity and screw

anchor system. The gravity anchor resists vertical motion of the system induced by wave motion whereas the screw anchors are meant to resist lateral motion. The combined anchor system provided 9,072-kg (20,000-lb) of resistance to vertical motion, with the screw system using four galvanized anchor screws each with a 1814-kg (4000-lb) pullout resistance [14]. These 1.5-m (5-ft) screws were attached to each corner of the base and driven into the seabed approximately 1.82-m (6-ft) away. The gravity anchors consisted of four 470-kg (1037-lb) [15] concrete anchors that were attached to the Feet and the Base.

C. Systems Failure Analysis The loss of the wings can be directly attributed to the high

seas for the extended period of time. This specifically caused two items that, in concert, caused the loss of the wings: the repetitive impact of the wing against the hydraulic piston and a failure of the welds due to inexperienced student welding. While all instrumentation was lost with the wings analysis of bio-fouling on the exposed metal shows that the wing with the hydraulic was lost during the first storm and the second wing a week later during the second storm.

D. 2010 Wing-Wave - Conclusion The Wing-Wave was ultimately successful in harvesting

energy from the motion of waves. This prototype was designed to gain information for the optimization of subsequent systems. As such many critical issues were discovered or determined, primarily the strength and durability required in the hinges and the power generation system since both the high cycle rate and the wide variation in forces occur in the ocean.

The following suggestions from this test were applied to the 2011 and 2012 versions: 1) the wings be composed of fiberglass-epoxy laminate to greatly increase the strength of the wing while having a relatively small increase in weight, 2) the hinges be significantly stronger as the combination of storm load forces and repeated oscillations caused the hinge system to fail 3) the energy conversion system requires significant investigation as it was not entirely addressed in the 2010 system, 4) the system should be simplified and to have a minimum of components, 5) the system must have a structure able to accept large loads for an extended period of time.

VII. 2012 WING-WAVE CONSTRUCTION The 2012 Wing-Wave design is centered around two 1.22-

m x 1.82-m (4-ft x 6-ft) fiberglass wings placed side by side on the 6.1-m x 4.6-m (20-ft x 15-ft) 2010 base. The panels on the sides were tapered from top to bottom, and the panel on top of the wing was rectangular. With the use of a hydraulic ram, the pivoting motion of the wing is converted into hydro-mechanical energy. When mounted on the wing and frame, the pivoting motion causes the ram to expand and contract. The movement of the wing pumps the hydraulic ram, pushing fluid into the accumulator via hydraulic lines.

A. Design Decisions The most important criteria for design consideration were

twofold; simplicity and efficiency. The research brought together two main types of systems: a mechanical system and a hydraulic system to find a way to generate electricity from the ocean. At Florida Tech multiple ocean energy systems are being investigated so with only one generator on hand and with different wave energy converters to be tested, the choice was made to run a closed hydraulic system. The generator needed the capability to work with different systems without compromising its original function to generate electricity. The WECs are connected to the power take off unit via hydraulic lines.

Fig. 14. Actual 2010 Wing Geometry

Fig. 15. 1 & 3 meter Normal Stress

Fig. 16. 1 & 3 meter Hydraulic Impact Stress

B. Structural Designs The fiberglass wing consists of six separate fiberglass

pieces attached together. A second wing was replicated from the existing wing. Modifications were made to the structure of both wings, e.g., making the top of the wing wider than the bottom to form a triangular cross section and attaching both wings using a stainless steel plate. The triangular cross section allows the wing to catch most of the force from the wave orbitals. Attaching the wings together ensures they move in unison.

A critical aspect in determining the forces acting on the Wing-Wave system is the horizontal velocity of the waves. Using the dispersion relationship and historical wave data, velocities were calculated in the horizontal directions from a given depth of 10-m, wave period of 7.92 seconds, wavelength of 76.8-m, and a wave height of 0.304-m:

C. Piston The hydraulic ram has a stroke length of 0.6-m (24-in) and

was used to determine the placement on the wings and the frame. In order to gain maximum output, the wing pumps the entire piston length while not bottoming out, which would cause additional stress on the structure. From previous experimentation it was observed that a 1.22-m x 1.82-m (4-ft x 6-ft) wing moved ±35° with no resistance. With the modified geometry and the hydraulic ram dampening the motion it was decided that the range of motion should be considered as ±40° movement. To calculate how high up the wing the ram should be it was necessary to calculate the distance the wing would move at a certain height.

(15) This means the ram should be 0.437-m (173/16-in) above the

hinge and should allow for 40° of motion in each direction without exceeding the stroke travel length of the piston. To attach the ram to the wing it was necessary to take precautions so the ram did not create concentrated stress points; this meant using a reinforcing aluminum plate between the two wings as well as plates on either side and bolting them together. Ten bolts were used to decrease the stress on each bolt. This dispersed the stress throughout the height of the wing. After the ram was positioned on the wing it was set to half stroke and connected to the base when the wing was vertical. When tested it allowed for approximately 45° of motion in each direction and when bottomed out the cross member swayed but held under additional weight.

Because the horizontal component of the wave velocities changes as the water depth changes, the overall forces must be integrated over the water depth. At the same time, the surface area is going to change as the depth increases. The two variables (water depth and surface area) are combined as a single integral. For density of seawater, an average salinity is assumed, giving a density of 1,025-kg/m3. The drag coefficient for a rectangular body can be given as a dimensionless 3.0. The breadth of the wing is 1.37-m, and the height varies with water depth (-z-8.1712)-m. This variation accounts for changes in forces due to the change of surface area as the water depth (and

consequently wave orbital velocities) change. The parameters for the horizontal velocity shown above are used for the horizontal velocities below.

Horizontal Wave Velocities (16)

Horizontal Velocities on Wing-Wave (17)

D. Testing The Wing-Wave received structural testing by manual

methods on land, and was found to function as intended with the addition of the hydraulic systems and mechanical modifications. The main land test for the Wing-Wave was to find a range of motion due to the geometry of the hydraulic ram placement. Initially, the range of motion was approximately ±30°, but it was decided the ram should be moved in order to provide a range of motion of ±40°, based on historical wave data and previous prototype testing.

E. Deployment The entire wave energy system, including the Wing-Wave

and universal PTO (Fig. 17) was deployed off the central east coast of Florida, from June 8-10, 2012. The main research vessel for this deployment was the M/V Thunderforce, owned by American Vibracore Services. Each section of the wave energy system had significant results and many lessons were learned over the course of the deployment.

Fig. 17. Wing-Wave & PTO Raft

VIII. 2012 WING WAVE RESULTS After initial deployment and securing of the frame to the

ocean floor, the wing started moving with full force. With calm sea conditions, 0.3 to 0.6-m (1 to 2-ft) with a 9 second period, the wing was observed to easily move ±42 degrees with an 8 to 10 second period. The hydraulic lines were set to loop within a separate closed system until it could be hooked into the Power Take-Off raft. Initially the system worked without difficulty, although upon returning the next day one of the lines had blown off the ram and another was under vacuum. After replacing a faulty one-way check valve, inevitably allowing sea water into the ram along with any floating particles, the system work again. It was connected to the PTO raft and was successful in pumping water through the check valve. After the sea conditions had increased to 1 to 1.22-m (3 to 4-ft) waves, cracks began to show on the cross member that the hydraulic ram was mounted to; after recovery these cracks became more apparent.

The only structure to begin to show signs of failure on the Wave-Wing was the cross member that the base of the hydraulic ram was mounted to. This was a 3.048-m (10-ft) section of aluminum C-channel with the ram mounted in the center and the only points of failure were stress cracks at the ends and near the mounting point. For the beam to fail, the hydraulic ram must have exerted forces exceeding the tensile strength of the aluminum. A ram with longer stroke length would have alleviated this problem.

There were two other areas of high stress, the connecting plate between the two wings and the aluminum brackets holding the stainless steel tube. The center plate was the focus of the stress, it held the wings and the ram, withstanding the stress and dispersing the stress throughout the fiberglass to prevent failure. Twelve bolts dispersed stress throughout the fiberglass, allowing for approximately 2722-kg (6,000-lbs) or 227-kg (500-lbs) per bolt. The ram was connected to five plates of aluminum, one of which was the center plate between the wings.

Hydraulic pressure data from Wing-Wave was recorded and monitored successfully through the PTO control Unit. A summary of collected two sample datasets and their time-series plots are shown in Table 3, and Figs. 18, 19.

The new wing design showed greater motion even while dampened by the hydraulic ram, showing that the design captures more energy than the previous thought and could ultimately provide greater pressure or higher volume.

Since the ram was bottoming out, it created concentrated stress on the cross member it was mounted to thus causing stress cracks in the frame. This could have been avoided either with a longer ram or by moving the mount on the wing lower so there wouldn’t be as much motion. The frame structure could also have been reinforced, but that would not have solved the issue of the ram bottoming out.

While the hydraulic lines were disconnected and the ram was pumping sea water in and out of each port, the velocity and force the water exiting was such that a hand could only be held approximately six inches away from the port before it was blown back. This proved the wing could pump the working fluid to high pressure.

Data recorded from Wing-Wave was very encouraging, showing a maximum record peak of 407-kPa (59-psi) and a

moving average between 138 to 172-kPa (20 to 25-psi). As per earlier lab testing of the Harris hydro-electric generator, the minimum pressure required for the electrical output generation is greater than 103-kPa (15-psi), thus implying there was sufficient pressure available for generator operation. After careful evaluation of all parameters in the system a faulty control algorithm was determined to keep the generator from starting despite sufficient pressure. Consequently, electrical output could not be generated, but the lab testing implies that there was sufficient pressure to generate output voltage around 30 Volts. Figure 20 shows the time series plot for the wing wave pressure with the moving average.

Table 3: Sample PTO Deployment Results

Fig. 18. Time Series Plot for Dataset 1 (Start-up)

Fig. 19. Time Series Plot for Dataset 2 (During continuous operation)

IX. WING WAVE CONCLUSIONS The data collected during deployment show that significant

energy can be harvested in ocean waves. The Wing-Wave has again been proven for efficiently harvesting of energy from waves. The construction was a major success as well as the performance while testing. With more funding and time the Wing-Wave could power our future.

As discussed above, data recorded from Wing-Wave was very encouraging and showed that the Wing-Wave performed as designed. Also there was sufficient output pressure generation from Wing-Wave that would have converted to electrical output if the control algorithm had operated correctly.

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Fig. 20. Hydraulic Inlet Pressures