The present description relates generally to a watercraft including a lifting body.
Hydrodynamic lifting bodies are used to generate dynamic lift during watercraft motion. Hydrodynamic lifting bodies have the ability to decrease drag and increase watercraft speed. Certain lifting bodies generate both static and dynamic lift. In lifting bodies that generate static lift, watercraft wave excitation may be reduced. Watercrafts utilizing lifting bodies may, in some cases, achieve greater watercraft efficiency as well as seakeeping and sea-kindliness, which may be particularly desirable in locations with rough prevailing seas, for instance.
U.S. Pat. No. 9,944,356 B1 to Wigley discloses a shape shifting fluid foil with a sliding link that is designed to dynamically alter the profile a skin wrapping the foil. However, the inventors herein have recognized potential issues with the fluid foil taught in U.S. Pat. No. 9,944,356 B1 as well as other types of lifting bodies. For example, the foil's wrapping skin and sliding link may be susceptible to degradation, thereby decreasing the foil's durability which may constrain the foil's applicability. The inventors have further recognized certain issues with hydrofoils designed to generate elliptical lift distributions. The tips of the elliptical hydrofoils, during forward motion, experience relatively heavy hydrofoil tip loading and high yaw instability. This may result in diminishment of the hydrofoil's handling performance. Hydrofoils with elliptical lift distributions may also generate comparatively high drag which is span dependent and may pose design constraints on the hydrofoil.
The inventors have recognized the abovementioned drawbacks with previous fluid foils and developed a watercraft system to resolve at least some of the drawbacks. The watercraft system, in one example, includes a lifting body designed to generate dynamic lift during watercraft operation. The lifting body structurally includes a central portion and two opposing lateral sides with lateral edges and exhibits twist from the central portion to the opposing lateral sides. The lifting body further includes a chord and a fore-aft cross-section. Each of the chord and the fore-aft cross-section decrease in directions that extend from a center of the lifting body to the lateral edges. Designing a lifting body with twist and a profile that tapers the chord and fore-aft cross-section decreases drag for a given lift and root bending moment. To elaborate, the lifting body may have greater hydrodynamic efficiency in comparison to a lifting body with an elliptical lift distribution that generates the same amount of lift and results in the same root bending moment. Utilizing the lifting body with a twist (e.g., a twist range between five degrees and ten degrees, in one use-case example) in conjunction with a tapered chord and fore-aft cross-section in the watercraft, enhances aspects of the watercraft's handling performance, such as yaw stability. The watercraft's customer appeal may be expanded as result of the handling performance gains.
Further in one example, the lift distribution curve generated by the lifting body during motion may taper to zero at each of the body's lateral tips and, in some instances, have a bell shaped profile. Structural characteristics of the lifting body such as twist (from the root to either tip), the fore-aft chord, and/or the foil shape may be blended to attain the bell shaped lift distribution. In this way, the lifting body's efficiency may be further increased for a given lift and bending moment or for a fixed amount of material. The bell shaped lift distribution may further improve the watercraft's handling performance, if so desired.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.
A watercraft system designed to achieve increased efficiency (e.g., increased lift to drag ratio), increased seakeeping, and enhanced watercraft control (e.g., yaw control stability) in comparison to previous lifting bodies that generate elliptical lift distributions is described herein. To achieve the aforementioned benefits, a watercraft is provided with a lifting body having a lift distribution that tapers lift near the lateral tips of the lifting body to form a bell shape. To achieve this lift distribution, the lifting body may exhibit a desired amount of twist along with a chord that tapers from a center of the lifting body to its tips. The inventors, through rigorous computational fluid dynamics (CFD) modeling, found that the bell shaped lift distribution increases the lifting body's lift to drag ratio and decreases tip vortices. To elaborate, this type of lifting body has a higher lift to drag ratio (L/D) for a given lift and root bending moment with a fixed amount of lifting body structural material. Further, this type of lifting body creates inboard vortices which result in upwash at the tips. The tip upwash tilts the lift vector forward so that the component of lift at the tips produce thrust, resulting in increased yaw stability. The lifting body may further be profiled to induce inboard vortices that create an upwash at the tips that tilt the lift vector to produce thrust. Further, the lifting body may be profiled to decrease fluid cavitation. To achieve these characteristics, the lifting body's root chord may be relatively large and the lifting body twist may be relatively small to decrease the cavitation while retaining the bell-shaped lift distribution, in one use-case embodiment. For instance, the deviation of the twist may be 6° or less and the root chord to tip chord ratio may be equal to or greater than 0.2, in one specific example. Further in some examples, the location of maximum camber of the lifting body may be shifted further aft to redistribute the pressure over a larger area to prevent highly localized pressure drop around the leading edge that may cause cavitation.
Additionally,
The watercraft system 102 may include a fore lifting body 116 and an aft lifting body 118. However, the watercraft system may include an alternate number of lifting bodies such as more than two lifting bodies, in one example, or a single lifting body, in another example. As described herein, a lifting body is a hydrodynamic element which generates dynamic lift. Further in some examples, the lifting body may additionally generate static lift. Alternatively, in another example, the lifting body may primarily generate dynamic lift. In the alternate example, the lifting body may be referred to as a hydrofoil.
The fore and the aft lifting bodies 116, 118 are designed to generate lift distribution profiles which taper near the lateral sides of the lifting bodies. The tapered lift distribution increases lifting body efficiency, increases the watercraft's seakeeping ability, and handling performance. Structural features which allow the lifting bodies to realize these the efficiency and handling performance gains are expanded upon herein.
The fore lifting body 116 may be coupled to the hull 104 via a strut 120 and the aft lifting body 118 is correspondingly coupled to the hull via strut 122. In one example, the strut 120 may remain substantially fixed with regard to the hull 104 and fore lifting body 116. Further, the strut may extend in a fore-aft direction, in some instances. Still further in one example, the strut may exhibit symmetry about a longitudinal axis, include a curved leading edge, and include a tapered trailing edge. These geometric characteristics of the strut may be selected to reduce flow separation generated by the strut during watercraft motion to reduce drag.
An angle of attack of the fore lifting body 116 may be in the range of 6°-10°, in one embodiment. It will be appreciated that increasing the lifting body's angle of attack may correspondingly increase the chance of the lifting body generating pressure cavitation. The lifting body's angle of attack may be selected based on factors such as the watercraft's hull profile, the watercraft's expected operating environment, dynamic lift objectives, etc.
Further in one example, the strut 122 may include an adjustment mechanism 124, shown in
The fore and aft lifting bodies 116, 118 are designed to taper the lift generated during forward motion of the lifting body near the tips. In one embodiment, the fore and aft lifting bodies 116, 118 may have a similar geometry. When the lifting bodies have similar geometries, manufacturing cost reductions may be realized. However, in an alternate embodiment, the profile of the fore and aft lifting bodies 116, 118 may be differ. In such an example, the profile of the lifting bodies may be selected to reduce flow interference between the lifting bodies.
The watercraft 100 may further include a control system 250 with a controller schematically depicted at 252. The controller 252 may include memory 254 and a processor 256. The memory 254 may store instructions executable by the processor 256 to perform control strategies, such as maneuvering strategies. Furthermore, the controller 252 may further receive control inputs from a watercraft operator to maneuver the watercraft as well as various watercraft sensors. The memory may include known data storage mediums such as volatile and non-volatile memory, such as random access memory (RAM) and read only memory (ROM), respectively, and the like. Further, the processor may include one or more microprocessors. The controller 252 may send control signals, commands, etc. to controllable components such as the adjustment mechanism and receive signals from sensors and/or components in the watercraft. It will therefore be understood that the controller 252 may be in electronic communication (e.g., wired and/or wireless communication) with the sensors and controllable components. For instance, the controller 252 may send commands to the adjustment mechanism 124. Responsive to receiving the control command, an actuator in the adjustment mechanism 124 may adjust the angle of attack of the lifting body 118. To elaborate, the angle of attack may be adjusted based on operating conditions such as watercraft speed, operator input, etc. However, in other embodiments, the adjustment mechanism 124 may be manually adjusted via the watercraft operator.
The adjustment mechanism 124 may be manually or automatically adjusted, as previously indicated. To accomplish said adjustment, the mechanism 124 may include an adjustable piston 302, pivots 304, linkage 306, and/or other suitable components. Thus, the piston 302 may be retracted and extended to alter the lifting body's angle of attack. The piston may therefore be arranged at an angle with regard to a horizontal plane. The angle of the piston may be selected based on the piston's stroke length, the targeted range of attack adjustment, the hull's profile, etc. The adjustment mechanism 124 may further include a rudder 310 which pivots to adjust watercraft yaw.
The lifting body 400 includes a central portion 402 and two opposing side portions 404, 406. The side portions 404, 406 may each include a lateral edge 408. Furthermore, the lateral edge may have a substantially planar profile. However, concave, convex, and chamfered lateral edges have been contemplated. Furthermore, the lifting body 400 includes a leading edge 410 and a trailing edge 412. As shown in
The lifting body may further be profiled to induce inboard vortices that create an upwash. This upwash tilts the lift vector to achieve negative drag over at least a portion of the operating angles of attack, thereby increasing lifting body efficiency and handling performance. To expound, focusing more load inboard and taper the load to zero at the tips enables the lifting body span to be increased without increasing the root bending moment when compared to lifting bodies with elliptical lift distributions and shorter spans. Further, a reduction in the tip vortices is a consequence of the bell shaped lift distribution. As such, for a given lift and bending moment, the reduction in the tip vortices and an increase in the lifting body's span enables the lifting body's efficiency to be increased in comparison to a lifting body having an elliptical lift distribution with a shorter span.
The span of the lifting body 400 measured between the lateral edges 408 is indicated at 418. The tip chord is indicated at 420 and the root chord is indicated at 422. In one example, the span 418 may be less than or approximately equal to 2.2 meters (m), the root chord 422 may be less than or approximately equal to 0.75 m, and/or the tip chord 420 may be less than or approximately equal to 0.375 m. However, other relative dimensions of the lifting body have been contemplated. The dimensions of the lifting body may be selected based on a variety of factors such as watercraft size, watercraft performance targets, lifting body material construction, expected watercraft operating environment, and the like. As described herein, a chord is a straight longitudinal line joining the leading edge to the trailing edge of the lifting body, hydrofoil, and the like.
The lifting body 400 may have a parabolic nose 424. To elaborate, the parabolic nose 424 may form a body of revolution. Thus, the nose's parabolic cross-section may extend circumferentially around a section of the root chord 422 adjacent to the leading edge 410 of the lifting body 400.
Cutting planes A-A′ and B-B′ indicate the cross-sectional views illustrated in
In comparison to the second embodiment of the lifting body 1000, shown in
In
In
Conversely,
In another embodiment, a lifting body may be provided with a modified local cross-sectional shape to control cavitation and/or lift. For instance, a leading edge shape of the lifting body may be altered in specific sections to reduce pressure drops and associated cavitation. For instance, the curve of the leading edge may be more or less pronounced in selected areas to tune the cavitation and lift generated by the lifting body. Consequently, lifting body efficiency may be further increased.
The technical effect of providing a watercraft assembly with a lifting body that generates a lift distribution which tapers lift near lateral sides of the lifting body increases lifting body efficiency and handling performance, thereby increasing watercraft efficiency.
Further,
In the following paragraphs, the subject matter of the present disclosure is further described. According to one aspect, a watercraft system is provided which comprises a lifting body configured to generate dynamic lift during watercraft operation and including a central portion and two opposing lateral sides with lateral edges; wherein the lifting body has a chord and a fore-aft cross-section that each decrease from a center of the lifting body to each of the lateral edges; wherein the lifting body twists from the center to each of the lateral edges.
According to another aspect, a watercraft system is provided that comprises a hydrofoil configured to generate dynamic lift during watercraft operation and including a central portion and two opposing lateral sides with lateral edges; wherein the hydrofoil twists from the central portion to the lateral edges and is configured to generate a lift distribution curve during forward motion of the watercraft system that tapers to zero at the lateral edges.
In another aspect, a lifting structure in a fluid medium is provided that comprises a lifting body designed to generate dynamic lift in the fluid medium with cross-sectional area parallel to the water surface and decreases in thickness from a center of the lifting body to two opposing lateral edges.
In any of the aspects described herein or combinations of the aspects, the lifting body may generate a lift distribution curve that tapers to zero at each of the lateral edges.
In any of the aspects described herein or combinations of the aspects, the lift distribution curve may be bell-shaped.
In any of the aspects described herein or combinations of the aspects, the lifting body may twist from the center to the lateral edges.
In any of the aspects described herein or combinations of the aspects, an amount of a twist deviation of the lifting body may greater than or equal to five degrees.
In any of the aspects described herein or combinations of the aspects, an amount of a twist deviation of the lifting body may be within a range of five degrees to ten degrees.
In any of the aspects described herein or combinations of the aspects, the watercraft system may further comprise a strut coupled to the lifting body and a watercraft hull.
In any of the aspects described herein or combinations of the aspects, the strut may extend to a leading edge of the lifting body.
In any of the aspects described herein or combinations of the aspects, the lifting body may be configured to generate static lift.
In any of the aspects described herein or combinations of the aspects, the lifting body may be a hydrofoil.
In any of the aspects described herein or combinations of the aspects, a trailing edge of the lifting body may be straight in shape.
In any of the aspects described herein or combinations of the aspects, the lifting body may comprise a parabolic nose.
In any of the aspects described herein or combinations of the aspects, the parabolic nose may form a body of revolution.
In any of the aspects described herein or combinations of the aspects, a ratio of the chord at one of the lateral edges to the chord at the center of the lifting body may be in a range from 0.2 to 0.44.
In any of the aspects described herein or combinations of the aspects, the watercraft system may further comprise an adjustment mechanism coupled to the lifting body and configured to adjust an angle of attack of the lifting body.
In any of the aspects described herein or combinations of the aspects, the lift distribution curve may be bell-shaped and may comprise a central convex section and two lateral concave sections.
In any of the aspects described herein or combinations of the aspects, the hydrofoil may be configured to generate downwash in a central section and upwash in opposing lateral sections.
In any of the aspects described herein or combinations of the aspects, an amount of a twist deviation of the hydrofoil may be within a range of five degrees to ten degrees and wherein a central chord of the hydrofoil may be greater than or equal to 0.6 meters. The central chord may be selected based on vehicle characteristics such as the vehicle's size, weight, operating speed, etc.
In any of the aspects described herein or combinations of the aspects, the watercraft system may further comprise a strut coupled to the hydrofoil and a watercraft hull and an adjustment mechanism coupled to the lifting body and configured to adjust an angle of attack of the hydrofoil.
In any of the aspects described herein or combinations of the aspects, the strut may be coupled to a leading edge of a parabolic nose of the hydrofoil.
In any of the aspects described herein or combinations of the aspects, the lifting structure may include an intermediate body of revolution between the strut and lateral tips.
In any of the aspects described herein or combinations of the aspects, the lifting body may have a bell-shaped lift distribution curve for a given lift and root bending moment which increases lifting body efficiency via a reduction in cavitation and drag generated by the lifting body.
In any of the aspects described herein or combinations of the aspects, the lifting body has twist in the spanwise direction of cross-section that increases lift at the root and taper lift to zero at the tip.
In any of the aspects described herein or combinations of the aspects, the lifting body may provide lift to a payload-carrying body via a strut.
In another representation, a watercraft lifting body assembly is provided which comprises a lifting body coupled to a watercraft hull via a strut and having a cross-sectional area which decreases from a root of the lifting body to two opposing lateral tips of the lifting body and has a twisted shape from the root to the opposing lateral tips.
It will be appreciated that the configurations and routines disclosed herein are exemplary in nature, and that these specific embodiments are not to be considered in a limiting sense, because numerous variations are possible. For example, the above technology can be applied to jet boats, propeller boats, jet skis, and other types of watercraft. The subject matter of the present disclosure includes all novel and non-obvious combinations and sub-combinations of the various systems and configurations, and other features, functions, and/or properties disclosed herein.
The following claims particularly point out certain combinations and sub-combinations regarded as novel and non-obvious. These claims may refer to “an” element or “a first” element or the equivalent thereof. Such claims should be understood to include incorporation of one or more such elements, neither requiring nor excluding two or more such elements. Other combinations and sub-combinations of the disclosed features, functions, elements, and/or properties may be claimed through amendment of the present claims or through presentation of new claims in this or a related application. Such claims, whether broader, narrower, equal, or different in scope to the original claims, also are regarded as included within the subject matter of the present disclosure.
The present application claims priority to U.S. Provisional Application No. 63/107,378, entitled “WATERCRAFT WITH LIFTING BODIES”, and filed on Oct. 29, 2020. The entire contents of the above-listed application are hereby incorporated by reference for all purposes.
Number | Date | Country | |
---|---|---|---|
63107378 | Oct 2020 | US |