SYSTEMS AND METHODS FOR A PLURALITY OF NESTED REACTION STRUCTURES IN WAVE GENERATORS

BACKGROUND

This disclosure relates generally to wave energy systems. More specifically, this disclosure relates to harnessing wave energy to power water vehicles such as unmanned underwater vehicles utilizing multiple nested reaction structures.

SUMMARY

The subject matter of the present application has been developed in response to the present state of the art, and in particular, in response to the problems and disadvantages associated with conventional deposition that have not yet been fully solved by currently available techniques. Accordingly, the subject matter of the present application has been developed to provide embodiments of a system, an apparatus, and a method that overcome at least some of the shortcomings of prior art techniques.

Disclosed herein is a system. The system includes an unmanned underwater vehicle (UUV), a first reaction structure configured to deploy from a body of the UUV, and a second reaction structure configured to deploy between the first reaction structure and the body of the UUV. The system further includes one or more tendons connecting the first and second reaction structures to the body of the UUV, wherein the first reaction structure deploys at a depth below the second reaction structure. The preceding subject matter of this paragraph characterizes example 1 of the present disclosure.

A top major surface of the first reaction structure is configured to mate to a bottom major surface of the second reaction structure when the first reaction structure and the second reaction structure are undeployed from the body of the UUV. The preceding subject matter of this paragraph characterizes example 2 of the present disclosure, wherein example 2 also includes the subject matter according to example 1, above.

The first reaction structure comprises a plurality of perforations. The preceding subject matter of this paragraph characterizes example 3 of the present disclosure, wherein example 3 also includes the subject matter according to any one of examples 1-2, above.

The first reaction structure comprises a plurality of flaps configured to cover the plurality of perforations. The preceding subject matter of this paragraph characterizes example 4 of the present disclosure, wherein example 4 also includes the subject matter according to any one of examples 1-3, above.

The flaps are configured to move to an open position which uncovers the perforations when the first reaction structure moves in a first direction relative to water. The preceding subject matter of this paragraph characterizes example 5 of the present disclosure, wherein example 5 also includes the subject matter according to any one of examples 1-4, above.

The flaps are configured to move to a closed position which covers the perforations when the first reaction structure moves in a second direction relative to water, wherein the second direction is different from the first direction. The preceding subject matter of this paragraph characterizes example 6 of the present disclosure, wherein example 6 also includes the subject matter according to any one of examples 1-5, above.

The first and second reaction structures are configured to move from an undeployed position to a deployed position. The preceding subject matter of this paragraph characterizes example 7 of the present disclosure, wherein example 7 also includes the subject matter according to any one of examples 1-6, above.

The undeployed position includes both reaction structures touching the body of the UUV, and the deployed position includes the first and second reaction structures separated from the body of the UUV. The preceding subject matter of this paragraph characterizes example 8 of the present disclosure, wherein example 8 also includes the subject matter according to any one of examples 1-7, above.

The second reaction structure comprises a plurality of perforations. The preceding subject matter of this paragraph characterizes example 9 of the present disclosure, wherein example 9 also includes the subject matter according to any one of examples 1-8, above.

The second reaction structure comprises a plurality of flaps configured to cover the plurality of perforations. The preceding subject matter of this paragraph characterizes example 10 of the present disclosure, wherein example 10 also includes the subject matter according to any one of examples 1-9, above.

The flaps are configured to move to an open position which uncovers the perforations when the second reaction structure moves in a first direction relative to water. The preceding subject matter of this paragraph characterizes example 11 of the present disclosure, wherein example 11 also includes the subject matter according to any one of examples 1-10, above.

The flaps are configured to move to a closed position which covers the perforations when the second reaction structure moves in a second direction relative to water, wherein the second direction is different from the first direction. The preceding subject matter of this paragraph characterizes example 12 of the present disclosure, wherein example 12 also includes the subject matter according to any one of examples 1-11, above.

Disclosed herein is a system. The system includes a body, a first reaction structure configured to deploy from the body, and a second reaction structure configured to deploy between the first reaction structure and the body. The system further includes one or more tendons connecting the first and second reaction structures to the body of the UUV, wherein the first reaction structure deploys at a depth below the second reaction structure, and one or more power take-out (PTO) units coupled to or between the first and second reaction structure and the body, the one or more power take-out (PTO) units configured convert energy from relative motion between the first and second reaction structures to the body. The preceding subject matter of this paragraph characterizes example 13 of the present disclosure.

A top major surface of the first reaction structure is configured to mate to a bottom major surface of the second reaction structure when the first reaction structure and the second reaction structure are undeployed from the body of the UUV. The preceding subject matter of this paragraph characterizes example 14 of the present disclosure, wherein example 14 also includes the subject matter according to example 13, above.

The first reaction structure comprises a plurality of perforations. The preceding subject matter of this paragraph characterizes example 15 of the present disclosure, wherein example 15 also includes the subject matter according to any one of examples 13-14, above.

The first reaction structure comprises a plurality of flaps configured to cover the plurality of perforations. The preceding subject matter of this paragraph characterizes example 16 of the present disclosure, wherein example 16 also includes the subject matter according to any one of examples 13-15, above.

The flaps are configured to move to an open position which uncovers the perforations when the first reaction structure moves in a first direction relative to water. The preceding subject matter of this paragraph characterizes example 17 of the present disclosure, wherein example 17 also includes the subject matter according to any one of examples 13-16, above.

The flaps are configured to move to a closed position which covers the perforations when the first reaction structure moves in a second direction relative to water, wherein the second direction is different from the first direction. The preceding subject matter of this paragraph characterizes example 18 of the present disclosure, wherein example 18 also includes the subject matter according to any one of examples 13-17, above.

The first and second reaction structures are configured to move from an undeployed position to a deployed position. The preceding subject matter of this paragraph characterizes example 19 of the present disclosure, wherein example 19 also includes the subject matter according to any one of examples 13-18, above.

The undeployed position includes both reaction structures touching the body of the UUV, and the deployed position includes the first and second reaction structures separated from the body of the UUV. The preceding subject matter of this paragraph characterizes example 20 of the present disclosure, wherein example 20 also includes the subject matter according to any one of examples 13-19, above.

Other aspects and advantages of embodiments of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrated by way of example of the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the advantages of the subject matter may be more readily understood, a more particular description of the subject matter briefly described above will be rendered by reference to specific embodiments that are illustrated in the appended drawings. Understanding that these drawings depict only typical embodiments of the subject matter and are not therefore to be considered to be limiting of its scope, the subject matter will be described and explained with additional specificity and detail through the use of the drawings, in which:

FIG. 1 depicts an unmanned underwater vehicle (UUV), according to one or more embodiments of the present disclosure;

FIG. 2 depicts an unmanned underwater vehicle (UUV) with one reaction structure beginning to deploy, according to one or more embodiments of the present disclosure;

FIG. 3 depicts an unmanned underwater vehicle (UUV) with two reaction structures deployed, according to one or more embodiments of the present disclosure;

FIG. 4 depicts a plurality of reaction structures of an unmanned underwater vehicle (UUV), according to one or more embodiments of the present disclosure;

FIG. 5 depicts a plurality of reaction structures of an unmanned underwater vehicle (UUV), according to one or more embodiments of the present disclosure;

FIG. 6 depicts a reaction structure with a plurality of perforations, according to one or more embodiments of the present disclosure;

FIG. 7 depicts an unmanned underwater vehicle (UUV), according to one or more embodiments of the present disclosure;

Throughout the description, similar reference numbers may be used to identify similar elements.

DETAILED DESCRIPTION

It will be readily understood that the components of the embodiments as generally described herein and illustrated in the appended figures could be arranged and designed in a wide variety of different configurations. Thus, the following more detailed description of various embodiments, as represented in the figures, is not intended to limit the scope of the present disclosure, but is merely representative of various embodiments. While the various aspects of the embodiments are presented in drawings, the drawings are not necessarily drawn to scale unless specifically indicated.

The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by this detailed description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.

Reference throughout this specification to features, advantages, or similar language does not imply that all of the features and advantages that may be realized with the present invention should be or are in any single embodiment of the invention. Rather, language referring to the features and advantages is understood to mean that a specific feature, advantage, or characteristic described in connection with an embodiment is included in at least one embodiment of the present invention. Thus, discussions of the features and advantages, and similar language, throughout this specification may, but do not necessarily, refer to the same embodiment.

Furthermore, the described features, advantages, and characteristics of the invention may be combined in any suitable manner in one or more embodiments. One skilled in the relevant art will recognize, in light of the description herein, that the invention can be practiced without one or more of the specific features or advantages of a particular embodiment. In other instances, additional features and advantages may be recognized in certain embodiments that may not be present in all embodiments of the invention.

Reference throughout this specification to “one embodiment,” “an embodiment,” or similar language means that a particular feature, structure, or characteristic described in connection with the indicated embodiment is included in at least one embodiment of the present invention. Thus, the phrases “in one embodiment,” “in an embodiment,” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.

There are a variety of ocean-based systems that can benefit from incorporation of built-in energy harvesting solutions to extend or expand at least one of the following, among others: performance capabilities, lifetime, range, communication capability, and/or remote operation/control capability. These include, but are not limited to floating or submerged buoys, floating or sub-surface platforms that support various types of equipment, surface or under-water vehicles, including unmanned underwater vehicles (UUVs). While the description below focuses on UUVs, it should be understood the embodiments of the inventions described below may be incorporated into any one of the systems described in the previous sentence, or any other ocean-based system.

In addition to UUVs, embodiments described herein may apply to other types of Wave Energy Converters (WEC) other than just UUV's. Wave Energy Converters (WEC) are subject to very large differences in incident wave power. If this high variability is transferred to the electrical generator, this will be challenging to maintain an efficient and low-cost electrical system. The end effect is that variability becomes a significant driver for the cost and weight of the generator, which is compounded with direct drive approaches. It has been suggested that the PTO peak power can be limited to less than 20 times the average.

UUVs, which include autonomous underwater vehicles (AUVs) and Remote Operated underwater Vehicles (ROVs), are gaining increasing acceptance and starting to be applied to several uses. Adoption of UUV technology has recently experienced rapid growth, fueled by possibilities opened up through technology advances and growing awareness of these capabilities by users and customers. Coupled with advances in modern robotics, UUVs are performing maritime tasks in days that used to take fleets of ships months to complete. UUVs are particularly useful as unmanned survey platforms, and typically have an array of on-board sensors to collect data for a variety of applications. They are used widely for a variety of commercial applications including persistent ocean remote condition monitoring, marine search and rescue, marine wildlife monitoring, underwater construction, aquaculture, surveillance, and inspections of subsea infrastructure. In addition, there are a number of critical military operations that are increasingly reliant on UUVs including mine countermeasures, surveillance, submarine detection, etc. In both commercial and military arenas, UUVs offer the potential to be cheaper, less complex, safer and more reliable than human-powered vehicles. The US Navy, in particular, is starting to restructure its operations significantly to take advantage of the resilience, surveillance, cost savings, and stealth benefits of operating many small UUVs, as compared to large ships.

Although UUVs are seeing increasing adoption, they have not yet reached their full potential. While ROVs draw power from an umbilical connection and are remotely operated from a surface vessel, AUVs are autonomous and untethered systems and require a power source to be carried onboard. Available power is therefore a key constraint for most AUVs. The power draw from various sensors that may be carried on an AUV is indicated in Table 1 and it is clear that an increase in available power by even a small amount can be game-changing for AUV applications. It has been shown that should greater power be available on board AUVs the most desired increase in functionality is longer mission durations, higher sampling rate, more sensing capability and improved communication capability.

Generally, an on-board battery is used for all power demands, including propulsion, communication, sensors, and data acquisition. Lithium batteries are the most common type of battery used in AUVs, and they can allow operation for a number of hours, with the mission duration greatly influenced by the vehicle speed or data collection rate. An AUV is typically built around a given battery capacity which can occupy up to 75% of the interior of the AUV. Extended duration missions require the AUV to be recovered and batteries to be recharged or swapped, generally requiring the intervention of a support vessel. Reducing the number of recoveries & redeployments for a given mission duration is an obvious driver to reduce costs and increase safety.

The approach we describe to mitigate this problem is to incorporate some self-recharging capability within the AUV. This allows the AUV to extract energy from its surrounding environment and eliminates the need to recover the vehicle for recharging until the mission is complete, thereby allowing a significant increase to the physical range of operation. Furthermore, this can result in an increased availability of power for internal systems which can allow greater capabilities to be incorporated or utilized within the AUV. A number of approaches have been attempted to incorporate on-board energy harvesting on AUVs with limited success.

Wave energy could be an attractive solution for AUV powering. Wave energy has a high energy density, is available anywhere in the ocean, can potentially be harnessed without rising above the ocean surface, and is available 24 hours a day. Wave generated propulsion is demonstrated on commercially available systems, e.g., waveglider. However, the efforts on electricity generation for AUV's from wave energy to date have focused on rocking or gyroscopic systems and resulted in less than 1 Watt of average power, an order of magnitude less power than the described approach.

By including a wave powered recharging capability this will allow the AUV to operate for significantly longer periods of time, potentially indefinitely. This reduces the cost per mission, allows additional sensors and communications, enables more complex missions, and most importantly, will allow substantially more ocean science to be completed. The approach described is scalable and adaptable and can potentially be applied to any AUV. This approach is described for a torpedo shaped AUV as this is the dominant form of AUV in use, however the described principle is applicable to any arbitrary shaped AUV.

Under nominal operations the AUV would operate normally and with an identical external profile. When the AUV desires to recharge, the AUV body will reconfigure into a two-body, wave energy converter through the lowering of a reaction structure. While the reaction structure may be internal to, external to, or part of the body of the AUV, in one embodiment, the reaction structure may be part of or align with the exterior casing of the AUV.

Disclosed herein is a wave energy converter (WEC) system, which may be part of a UUV (configured to go under the surface). The system may include a float (or may be referred to as a body), a drivetrain, and a plurality of reaction structures coupled to the drivetrain by at least one tendon. The reaction structures are configured to nest together and into the body when not in use (not deployed) and when deployed are configured to cause relative movement of each of the reaction structures and the body which will create changing forces on the tendons and ultimately power a drivetrain or other energy harvesting machinery.

Disclosed herein are variations on the reaction structures where they include perforations and/or flaps which with the plurality of reaction structures (that are deployed in series above/below each other) creates a wider range of oscillation amplitudes.

In previous work it was assumed (but not clearly shown) that the drag would asymptote to a constant value as the amplitude increased. However, the data was limited to a small range of amplitude values. Many embodiments utilize a general U-shape for the reaction structure (although this is not necessary).

In work done by the inventors, it was shown how the power produced is strongly dependent upon the hydrodynamic properties of the reaction plate, specifically, added mass (Ca) and drag (Ca). It was identified that maximum power can be produced by maximizing added mass while minimizing drag. However, both these properties display nonlinear, amplitude, and period-dependent behavior. Previous work in this space has found that by nondimensionalizing the amplitude and the period of oscillation into two parameters, KC and Re respectively, makes the interpretation of the hydrodynamic non-linearities somewhat more straightforward. The former of these parameters, KC, is also known as the “Keuligan Carpenter” number and is effectively a ratio of the amplitude of motion to the object size. Larger KC numbers effectively mean a larger amplitude of oscillation. The second parameter, Re or Reynolds number is a well-known non dimensional parameter and ostensibly (in this case) refers to the speed of the oscillation.

The primary objective behind hydrodynamic testing was to identify a reaction structure that would maximize the power generated, and which could be stowed against the body of the AUV when not in use or nested. It is understood that the reaction structure must maximize its added mass increase, while it should also minimize drag forces. In some embodiments, the baseline shape for this reaction structure is a semicircular U-shape (Baseline U) as this will nest against the lower hull of the AUV.

Following direction from work completed, initial work was focused along two primary directions. The first approach focused on incorporating multiple streamwise ribs of various width, i.e. longitudinal fins along the length of the reaction structure (described below and depicted in the figures). The intent is that that these fins will not impede normal streamwise flow when the AUV is operating, while enhancing the reaction structure's vertical added mass when in charging mode. The second approach focused on incorporating multiple tandem U-shaped reaction structures that ‘nest’ together when stowed (described below and depicted in the figures).

The addition of streamwise ribs can be seen to increase both drag and added mass hydrodynamic coefficients as the width of the ribs is increased. This dependence seems to be linear with the cross-sectional area of the shape, however an increase of only around 50% is achieved with the test samples. A similar increase in hydrodynamic coefficients can be seen for the nested structures (U's), but the rate of increase is significantly higher with an added mass increase of over 300% seen with four nested U's.

An important observation between these two approaches is related to the drag. For the reaction structure with streamwise ribs the drag coefficient increases at the same rate as an added mass coefficient for both heave and pitch motion. However, for the nested U's, the added mass coefficient increases at much higher rate than the drag coefficient. As a result, it was determined that the tandem arrangement is superior to the shape with streamwise ribs. The further work was focused along this direction.

A further modification to the reaction structure that was investigated, was the incorporation of semi-circular ‘end-caps’ at the front and rear end of the reaction structure with the aim of entraining more fluid. Such end-caps would be hinged and spring-loaded so that they retract into the reaction structure when stowed against the AUV body. The testing, however, revealed that such modifications has very little effect on the hydrodynamic performance of the Baseline-U shape.

Referring now to FIG. 1, an unmanned underwater vehicle (UUV) as part of a system 200 is shown. Although the system 200 is shown and described with certain components and functionality in the following paragraphs, other embodiments of the system 200 may include fewer or more components to implement less or more functionality. The system 200 includes an unmanned underwater vehicle (UUV). In some embodiments, the UUV may be an AUV or a ROV. In the illustrated embodiment, the UUV includes a propeller to allow the UUV to maneuver through the water. The UUV may include other systems that require power to function including, but not limited to, sensors, propulsion systems, communication systems, data acquisition systems.

The system 200 also includes a plurality (at least two) reaction structures 204 configured to deploy from a body 202 of the UUV. In the illustrated embodiment, the outer reaction structure 204 aligns with an exterior casing of the UUV. The deployable reaction structures 204 allow the UUV to maneuver and perform functions either in a deployed or undeployed position. As shown, the outer reaction structure 204 aligns with the body 202 of the UUV for streamlined movement.

The system 200 also includes one or more tendons (not shown in FIG. 1). The one or more tendons connect the reaction structure 204 to the body 202 of the UUV. The reaction structure 204 may be configured to deploy at a depth below the body 202 of the UUV. In other embodiments, the reaction structure 204 may be configured to deploy above the body 202 of the UUV.

The system 200 further includes one or more power take-out (PTO) units or drivetrains (internal to the UUV). The PTO unit(s) may be coupled to the reaction structures 204, to the UUV or the body 202 of the UUV or coupled between the reaction structure 204 and the UUV.

The system further includes a control unit or a plurality of control units in some embodiments. The control unit (or controller) may include hardware or software that is capable of controlling the various features of the system 200 and performing functions of the system 200 as needed. In some embodiments, the control unit is coupled to the one or more PTO units. The control unit may be configured to harness and convert energy from the waves on a surface of a body of water. The relative positioning of the body 202 of the UUV and the reaction structure 204 connected by the tendons 206 (not shown in FIG. 1, see FIG. 3), and movement caused by the waves on the UUV allow for tensile forces (and other forces) to be harnessed from a PTO unit. The control unit may be configured to convert the wave energy for use in the other systems within the UUV.

Referring now to FIG. 2, the reaction structure 204 is beginning to be deployed and lowered from the body 202 of the UUV. As depicted, the outer reaction structure 204 is being deployed below the body 202 but can be deployed in other directions in other embodiments.

Referring now to FIG. 3, the reaction structure 204 is in a deployed position below the body 202 of the UUV. As shown, the system 200 can move back and forth between a deployed position (shown in FIG. 3) and an undeployed position (shown in FIG. 1) as needed. When recharging is needed, the UUV may deploy the reaction structure 204 and harness energy to recharge the UUV systems without requiring the UUV to return to base.

As depicted, the system includes two reaction structures 204 which are coupled to the body 202 of the UUV by tendons 206. As can be seen, there is a lower and an upper reaction structure 204. The reaction structures are generally the same shape such that they can nest (or fit together) and ultimately nest into body 202.

In some embodiments, the reaction plate 204 can be altered (after lowering) to a different shape that may provide additional benefits from a performance standpoint. In such embodiments, additional means may be included in the reaction structure to facilitate realignment, expansion, etc. so as to facilitate the reaction structure 204 to be altered from a baseline shape to form a more hydrodynamically desirable shape. In some embodiments of the invention, this shape may be one that provides an increased or lowered effective drag coefficient in the upward direction relative to the downward direction. In some embodiments of the invention, the altered shape may provide increased added mass relative to the baseline shape.

In some embodiments, the UUV body 202 will act as a float and will be connected to the deployable nested reaction structures below it, and use the wave generated relative movement of these bodies to generate power. Wave particle motion reduces by the square of the depth and therefore the wave loads on the UUV body 202 will be substantially greater than those on the upper reaction structure 204, deployed a few meters below, and even greater on the lower reaction structure 204. Accordingly, the UUV will generate the most power when the float is at the surface of a body of water, however this is not a requirement for operation and by positioning the UUV some distance below the surface, but still in the presence of waves. The UUV can still generate power if positioned below the surface.

In very large ocean waves where there is a risk of damage at the surface, the AUV can enter the recharging configuration at some depth below the surface, where the energy is reduced. The production of power from the relative motion the reaction plate and AUV body is similar to a two-body wave energy converter and will be described below. While charging, the AUV would be able to use its already existing systems, such as propulsion, buoyancy engine and navigation to autonomously maintain target charging depth, maintain heading and charge onboard batteries.

In the case where the UUV forms the reaction structure, the system may be capable of additional shape alterations that may allow it to function suitably as a reaction structure. In some embodiments, the PTO may be on the UUV body that forms the reaction structure.

In such embodiments, the system includes an unmanned underwater vehicle (UUV), a flotation structure that function as reaction structures and are configured to deploy from a body of the UUV, and one or more tendons connecting the flotation structure to the body of the UUV, wherein the flotation structure deploys above the body of the UUV. The system further includes one or more power take-out (PTO) units coupled to or between the flotation structure and the UUV. The system further includes a control unit coupled to the one or more PTO units to convert energy from waves on a surface of a body of water for use in other systems within the UUV.

In some embodiments, the two reactions structures 204 may be tethered together by a tendon 206. In some embodiments, each reaction structure 204 is independently tethered to the body 202. Although shown and described with two reaction structures 204, embodiments may include more than two reaction structures coupled to the body and deployed below.

As shown and depicted, the multiple or plurality of reaction structures are deployed “in series” or above and below each other such that one of the reaction structures is deployed between the other reaction structure and the body of the UUV.

In some embodiments, a top major surface 402 of the first reaction structure is configured to mate to a bottom major surface 404 of the second reaction structure when the first reaction structure and the second reaction structure are undeployed from the body of the UUV. In some embodiments, a top major surface 406 of the second reaction structure is configured to mate to a bottom major surface 408 of the body when the second reaction structure is undeployed. As can be seen, the reaction structures and the body of the UUV are configured to nest together with corresponding surfaces mating next to each other. This allows for a plurality of reaction structures to be used and deployed at varying depths.

Referring now to FIG. 4, the reaction structures of an unmanned underwater vehicle (UUV) is shown. Although the reaction structures 204 are shown and described with certain components and functionality in the following paragraphs, other embodiments of the reaction structures 204 may include fewer or more components to implement less or more functionality.

In the illustrated embodiment, the reaction structures 204 are coupled to the body of a UUV (not visible) via tendons 206. As can be seen a main tendon 206 runs vertical and would be coupled to the body of the UUV positioned above these reaction structures 204.

The illustrated reaction structures 204 include various components that are intended to maximize added mass while minimizing drag. The reaction structures include a general longitudinal U-shape. This general U-shape is dictated by a skeletal frame 205. The frame 205 includes a plurality of perforations (or apertures) 214. The perforations allow for water to flow through the frame 205. Additionally, the reaction structures include a plurality of flaps 212. The flaps 212 are configured to flex between covering the perforations 214 (this would be a closed position) or flexing to an open position (as shown in the figure) where the perforations 214 are exposed on the upper side of the frame 205. As such, as water is flowing upwards relative to the reaction structures, the flaps 212 will flex open and allow water to pass through the perforations 214. As water flows downwards relative to the reaction structures, the flaps 212 may flex closed and restrict water from passing through the perforations 214 because the flaps 212 are covering the perforations. This, along with the general U-shape of the frame 205 will created a different drag upwards as opposed to downwards. In other embodiments, the flaps 212 may be cycled between open and closed by other means including by mechanical means powered by a power source.

As can be seen, each flap 212 covers a column of perforations 214. Each reaction structure 204 includes six flaps 212, each covering a plurality of perforations in a column along the longitudinal direction of the reaction structure. Some embodiments of the reaction structures include no perforations 214 or flaps 212. Some embodiments of the reaction structures include only perforations 214 but no flaps 212. Some embodiments of the reaction structures include flaps 212 but no perforations 214. Each of these variations are not shown but can be envisioned by understanding the entirety of this disclosure.

Also depicted are clamps 222 which are not described in detail herein but allow for the various tendons 206 to move relative to the clamps 222 and allow the reaction structures 204 to deploy below the body of the UUV. In the illustrated embodiment, there is a central tendon 206 that runs from the lower reaction structure 204 (coupled to the lower reaction structure at coupling 236) and runs through upper reaction structure 204 (specifically, the central tendon 206 goes through a thru hole 232 positioned at an end of the frame 205) and up through the clamp 222 and up to the body. The clamp 222 may release or clamp down on the tendon 206 as needed. Additionally, there are two outer tendons 206 that run from the clamp 222 through thru holes 233 and are coupled to the edges of the frame 205 at couplings 234. These tendons allow for the reaction structures 204 to be deployed in series. When pulling up the reaction structures, the clamp 222 can be released allowing the lower reaction structure to be pulled up and nested with the upper reaction structure and ultimately further pulled up until nested into the body of the UUV. As such, embodiments herein describe a wave energy converter with a plurality of nesting reaction structures.

Referring now to FIG. 5, the reactions structures are now shown with the flaps 212 in a closed position (or folded back down) such that they are covering the perforations 214. During the upward motion of the reaction structures, the flaps on the perforated U-shape are closed. The resultant reaction force that perforated U-shape can provide is identical to the force that a nonperforated U-shape can provide (as in a reaction structure without any perforations). During the downward motion (which corresponds to what is shown in FIG. 4), the flaps 212 are open and the maximum force acting on the perforated U-shape is lower as compared to the force acting on a nonperforated U-shape. Up to 50% reduction in drag force has been observed in the experiments.

Referring now to FIG. 6, a reaction structure with perforations and not flaps is shown, according to one or more embodiments of this disclosure.

In some embodiments of the invention, controls and body mechanics may be included to alter the physical shape of the UUV body 202 itself so that it can react more to the waves and capture a greater amount of energy from waves. In some embodiments, the water plane area of the structure may be increased by opening up one or more additional structures including, but not limited to fins, shields etc.

The reaction structure 204 and the UUV body 202 may be connected in many ways, including with tendons 206 or with rigid connections. One embodiment that utilizes one or more tendons is described below. When deployed, the recharging configuration would include either a single tendon 206 from the center of the UUV body 202 connected to the reaction structure 204, or alternatively, two tendons 206, located axially along the body 202 of the UUV connected to the reaction structure 204. The two-tendon configuration allows for both pitch and heave motion to be primary contributors to relative (power generating) motion. Additional motion in surge, sway and yaw will also result in some secondary power generation. Other embodiments may include more than two tendons 206.

In some embodiments, the reaction structures 204 will be stowed against the body 202 of the UUV when not in use and then lowered below the UUV body 202 to generate power. This naturally gives the reaction structure 204 a hemispherical or partial hemispherical shape when deployed. Similar shapes have been shown to provide greatly increased added mass compared to flat plates. Increasing the added mass of the reaction structure 204 greatly increases its performance.

Referring to the tendons 206, they may be flexible like a rope or rigid. If the tendons are flexible, then the structure benefits from the different drag in opposite directions. This allows for the tendons 206 to remain in tension as force can only be applied when the flexible tendons are in tension.

Referring to FIG. 7, an unmanned underwater vehicle (UUV), according to one or more embodiments of the present disclosure is depicted with the reaction structures in a deployed position. This figure shows some of the internal components within the body 202 of the UUV. The UUV includes drive train or power take off units 300 that are positioned within the body and are coupled to the reaction structures 204 via the tendons 206.

Methods of deploying a plurality of reaction structures 204 from a UUV are also contemplated herein.

In some embodiments, the system includes an unmanned underwater vehicle (UUV), a first reaction structure configured to deploy from a body of the UUV, and a second reaction structure configured to deploy between the first reaction structure and the body of the UUV. The system further includes one or more tendons connecting the first and second reaction structures to the body of the UUV, wherein the first reaction structure deploys at a depth below the second reaction structure.

In some embodiments, a top major surface of the first reaction structure is configured to mate to a bottom major surface of the second reaction structure when the first reaction structure and the second reaction structure are undeployed from the body of the UUV. In some embodiments, a top major surface of the second reaction structure is configured to mate to a bottom major surface of the body when the second reaction structure is undeployed.

In some embodiments, the first reaction structure comprises a plurality of perforations. In some embodiments, the first reaction structure comprises a plurality of flaps configured to cover the plurality of perforations.

In some embodiments, the flaps are configured to move to an open position which uncovers the perforations when the first reaction structure moves in a first direction relative to water. In some embodiments, the flaps are configured to move to a closed position which covers the perforations when the first reaction structure moves in a second direction relative to water, wherein the second direction is different from the first direction.

In some embodiments, the first and second reaction structures are configured to move from an undeployed position to a deployed position. In some embodiments, the undeployed position includes both reaction structures touching the body of the UUV, and the deployed position includes the first and second reaction structures separated from the body of the UUV.

In some embodiments, the second reaction structure comprises a plurality of perforations. In some embodiments, the second reaction structure comprises a plurality of flaps configured to cover the plurality of perforations.

In some embodiments, the flaps are configured to move to an open position which uncovers the perforations when the second reaction structure moves in a first direction relative to water. In some embodiments, the flaps are configured to move to a closed position which covers the perforations when the second reaction structure moves in a second direction relative to water, wherein the second direction is different from the first direction.

In some embodiments, the system includes a body, a first reaction structure configured to deploy from the body, and a second reaction structure configured to deploy between the first reaction structure and the body. The system further includes one or more tendons connecting the first and second reaction structures to the body of the UUV, wherein the first reaction structure deploys at a depth below the second reaction structure, and one or more power take-out (PTO) units coupled to or between the first and second reaction structure and the body, the one or more power take-out (PTO) units configured convert energy from relative motion between the first and second reaction structures to the body.

Although the operations of the method(s) herein are shown and described in a particular order, the order of the operations of each method may be altered so that certain operations may be performed in an inverse order or so that certain operations may be performed, at least in part, concurrently with other operations. In another embodiment, instructions or sub-operations of distinct operations may be implemented in an intermittent and/or alternating manner.

Embodiments of the invention can take the form of an entirely hardware embodiment, or an embodiment containing both hardware and software elements. In one embodiment, the movements of the system are implemented via software.

Additionally, some or all of the functionality described herein might be implemented via one or more controllers, processors, or other computing devices. For example, a controller might be implemented to control the mooring lines, the tether(s) or tendon(s), or modes of the system.

In the above description, specific details of various embodiments are provided. However, some embodiments may be practiced with less than all of these specific details. In other instances, certain methods, procedures, components, structures, and/or functions are described in no more detail than to enable the various embodiments of the invention, for the sake of brevity and clarity.

Although specific embodiments of the invention have been described and illustrated, the invention is not to be limited to the specific forms or arrangements of parts so described and illustrated. The scope of the invention is to be defined by the claims appended hereto and their equivalents.

SYSTEMS AND METHODS FOR A PLURALITY OF NESTED REACTION STRUCTURES IN WAVE GENERATORS

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