GB2612792A - Wave-propelled vehicles - Google Patents

Abstract

A wave-propelled vehicle 102 adapted to float at the surface 106 of a body of fluid. The vehicle comprises a hull 104 defining at least one concavity (214, 216, Fig 2). The hull comprises an upper hull portion 118 and a lower hull portion 120 and has an asymmetrical transverse profile to generate thrust in response to waves on the body of fluid. The vehicle may have a plurality of modes of operation including one or more of wave propulsion, underwater gliding flight, underwater powered flight or aerial gliding flight.

Description

WAVE-PROPELLED VEHICLES

[0001] The present application relates to wave-propelled vehicles, in particular, to vehicles that generate forward thrust from the action of surface gravity waves present at the surface of a body of fluid.

[0002] Several wave-propelled vehicles are known. These vehicles exploit the approximately orbital motions of near-surface fluid particles induced by surface gravity waves travelling across a body of fluid, such as wind-induced waves travelling across an ocean, to produce forward thrust.

[0003] Both manned and unmanned wave-propelled vehicles have been developed. In the case of the latter, it is common to restrict the size of a given vehicle to a few metres for reasons of cost, safety, stealth, and ease of deployment and recovery. Unmanned vehicles of this sort have application in oceanography, hydrocarbon exploration, and defence and security.

[0004] Two main types of vehicle are known.

[0005] In the first type (see, for example, W02014009683), a floating body oscillates in any of its six degrees of freedom (but typically pitch) under the action of waves. A hydrodynamic device attached to the body at the bow or stern experiences a motion relative to the fluid locally, from which thrust may be produced. For example, an oscillating or "flapping" foil mounted to the bow or stern may be allowed to pivot relative to the body about a spanwise pitching axis in response to the local relative flow between the fluid and the body, with end stops, springs, or a combination of end stops and springs adapted to influence the foil's angle of attack to the local flow in order to generate thrust. In some embodiments of this type, the floating body has a canoe-like hull form, and the hydrodynamic device is a flapping foil of a conventional planar shape, akin to an aeroplane's wing.

[0006] In the second type (see, for example, US7641524), a floating body subjected to waves experiences oscillatory motion in any of three degrees of freedom (typically heave) leading to vertical displacement of a point on the body, and an elongate member attached to and projecting downward from this point hosts a hydrodynamic device, such as a foil or an array of foils, at a distal position that moves up and down as the attachment point on the body moves up and down at the surface. Typically, the elongate member is much longer than the floating body. Because the orbital particle motions due to a surface gravity wave decay with depth (exponentially in the case of a deep body of fluid), the hydrodynamic device in this type of mechanism may experience a periodic vertical velocity different to the surrounding vertical velocity of the fluid, with the relative velocity related to the length of the elongate member. Implementations of this type of mechanism may feature a floating body designed to closely follow the surface of the fluid, i.e., a body with high hydrodynamic stiffness, such as a low-density, surfboard-like body. The elongate member may be a flexible tensile member, such as a tether.

[0007] In relation to vehicles of the first type, it will be appreciated that such vehicles may require implementation at very long lengths in order to produce oscillatory motion that is out of phase with orbital particle velocities at the mounting location of a hydrodynamic device, and hence produce thrust, at higher periods/wavelengths. For example, out-of-phase pitching motions sufficiently vigorous for thrust production in 4s waves could be expected to require a hull length on the order of 25m.

[0008] A vehicle of the first type can be approximately conceptualised as a forced springmass-damper system, whereby the spring force (or spring torque in the case of a rotational mode of oscillation) is provided by hydrostatic pressure acting on the displaced volume of the hull, mass (or inertia) is provided by the floating body, and damping forces are provided by any thrust-producing hydrodynamic device attached to the hull, as well as parasitic effects such as skin friction and radiation damping due to the oscillatory motion of the vehicle relative to the fluid. One skilled in the art will appreciate that in such a system damping is crucial, having the potential to greatly reduce out-of-phase oscillation. Therefore, an overly ambitious implementation of the hydrodynamic device, or a poor floating body design, can be highly detrimental to thrust production.

[0009] In relation to vehicles of the second type, one skilled in the art will appreciate that the introduction of an elongate member (necessary to ensure an adequate vertical velocity differential between particles at the surface and particles at the hydrodynamic device) will introduce considerable drag to the system. It will also be appreciated that where such a member is made flexible there will be scope for fouling between elements of the system; alternatively, where such a member is made rigid, there will be scope for bending and torsional failure.

[0010] A disadvantage of both types of vehicle in ocean-going applications is their general lack of suitability for operation from time to time as underwater vehicles. For example, in some applications, such as oceanography or hydrocarbon exploration, it would be advantageous at times to operate a wave-propelled surface vehicle as an underwater glider or as an underwater powered vehicle. Current wave-propelled surface vehicles typically feature a large amount of excess buoyancy within the floating body to achieve favourable dynamics in their surface-bound wave-propelled mode, which is undesirable for an underwater vehicle. Furthermore, hydrodynamically efficient surface hull shapes typically perform poorly underwater (and vice versa). Vehicles of the second type are particularly disadvantaged in this regard.

[0011] A further disadvantage of both types of vehicle is their general lack of suitability for aerial gliding flight. This mode of operation is desirable for rapid aerial deployment of one or more vehicles to a specific location or locations on the surface, for example, for the purposes of monitoring large scale features in oceanographic applications, or for rapidly assessing large areas in defence and security applications.

[0012] Finally, both types of vehicle employ moving parts, such as flapping foils, within hydrodynamic devices that convert local relative motion into thrust. Disadvantages of employing such moving parts include lower reliability (especially relevant when a vehicle is deployed on long endurance missions in the open ocean) and greater noise (especially relevant when the vehicle is configured to conduct acoustic sensing).

[0013] Examples will now be described, by way of example only, referring to the accompanying drawings.

[0014] FIG. 1 depicts isometric, front, side, top and bottom views of a vehicle adapted to float at the surface of a body of fluid; [0015] FIG. 2 depicts isometric, side, top and rear views of a wave-propelled vehicle; [0016] FIG. 3 depicts isometric, side, top and rear views of a wave-propelled vehicle; [0017] FIG. 4 depicts isometric, side, top and rear views of a wave-propelled vehicle; [0018] FIG. 5 depicts isometric, side, top and rear views of a wave-propelled vehicle; [0019] FIG. 6 depicts isometric, side, top and rear views of a wave-propelled vehicle; [0020] FIG. 7 depicts isometric, side, top and rear views of a wave-propelled vehicle; [0021] FIG. 8 depicts a side view of a wave-propelled vehicle; [0022] FIG. 9 depicts a wave-propelled vehicle moving in waves; [0023] FIG. 10 depicts a vehicle with a square side profile; [0024] FIG. 11 depicts a vehicle with a rectangular side profile; [0025] FIG. 12 depicts a vehicle with a staggered or swept side profile; [0026] FIG. 13 depicts a vehicle with a staggered or swept side profile; [0027] FIG. 14 depicts wave propulsion in a head sea; [0028] FIG. 15 depicts wave propulsion in a beam sea; [0029] FIG. 16 depicts a wave-propelled vehicle bearing control surfaces; [0030] FIG. 17 depicts a wave-propelled vehicle bearing solar panels and control surfaces; [0031] FIG. 18 depicts a wave-propelled vehicle with an associated empennage; [0032] FIG. 19 depicts a wave-propelled vehicle comprising a pressure hull and thrusters; [0033] FIGs. 20-24 depict respective side, front, rear, top and bottom views of the wave-propelled vehicle of FIG. 19.

[0034] FIG. 25 depicts buoyancy control of the wave-propelled vehicle of FIG. 19.

[0035] FIG. 26 depicts a control system of a wave-propelled vehicle.

[0036] Referring to FIG. 1, there is shown a view 100 of a vehicle 102 comprising a hull 104 adapted to float at the free surface 106 of a body of fluid. There are defined axes X, Y and Z, originating at the vehicle's centre of gravity 108. At equilibrium, the hull 104 has a centre of buoyancy 110 disposed directly above the centre of gravity 108, and the X-axis coincides with the longitudinal axis of the hull 104. When travelling (generally forwards in direction 112), the axes remain pinned to the centre of gravity 108, the X-Y plane remains horizontal, the Z-axis remains vertical, and the projection of the hull's longitudinal axis onto the X-Y plane coincides with the X-axis. The hull may oscillate in or about the X, Y and Z axes. Oscillations about the X-axis are termed "roll" oscillations; oscillations about the Y-axis are termed "pitch" oscillations; oscillations about the Z-axis are termed "yaw" oscillations; oscillations in the X-axis are termed "surge" oscillations; oscillations in the Y-axis are termed "sway" oscillations; and oscillations in the Z-axis are termed "heave" oscillations.

[0037] Waves travelling through the body of fluid may disturb the free surface, and in turn cause the hull 104 to oscillate in or about any of the axes defined above. At various times during relative motion between the hull 104 and the surface 106, parts of the hull may alternately be submerged or broach the surface 106. An upper extent 114 and a lower extent 116 of this "dynamic immersion" of the hull may be defined, thus defining an upper portion 118 of the hull; a lower portion 120 of the hull may be defined as that portion of the hull below the lower extent 116 of dynamic immersion. Together, the upper portion 118 and the lower portion 120 of the hull define the operative volume 122 of the hull. It will be appreciated that, in this example, the operative volume of the hull has no transverse plane of appreciable symmetry, i.e., it has an asymmetrical transverse profile.

[0038] The upper hull portion 118 has a centre of volume 124 disposed above the centre of gravity 108.

[0039] The upper hull portion 118 may be projected onto the X-Y plane at equilibrium; this projected area 126 has a centroid 128; the projected area is shown in dashed-line form and expanded for clarity purposes.

[0040] The lower hull portion 120 may be projected onto the X-Y plane at equilibrium; this projected area 130 has centroid 132; the projected area is shown in dashed-line form and expanded for clarity purposes.

[0041] The upper hull portion 118 has a leading position 134; a leading position is a forward-most location in a sagittal plane of the hull. In the example depicted, the sagittal plane is the median or mid-sagittal plane. However, examples can be realised in which the sagittal plane is a parasagittal plane. Examples can be realised in which the leading edge comprises multiple leading positions such as, for example, one per sagittal plane according to at least one, or both, of the plan profile and side profile of a leading edge.

[0042] The lower hull portion 120 of the hull has a trailing position 136; a trailing position is an aft-most location in a sagittal plane of the hull. In the example depicted, the sagittal plane is the median or mid-sagittal plane. However, examples can be realised in which the sagittal plane is a parasagittal plane. Examples can be realised in which the trailing edge comprises multiple trailing positions such as, for example, one per sagittal plane according to at least one, or both, of the plan profile and side profile of a trailing edge.

[0043] The observations made above relating to the vehicle 102 of FIG. 1 are also applicable to any and all vehicles described herein mutatis mutandis.

[0044] Referring to FIG. 2, there is shown a view 200 of a wave-propelled vehicle 202 comprising an upper hull portion 204 and a lower hull portion 206. The upper hull portion 204 comprises a hydrofoil portion 208 spanning a vertical extent. The lower hull portion comprises a hydrofoil portion 210 spanning a vertical extent, and a hydrofoil portion 212 spanning a horizontal extent. The hydrofoil portions 210 and 212 define concavities 214 and 216 when viewed from the front or rear.

[0045] One skilled in the art will appreciate that as the upper hull portion 204 experiences dynamic immersion under the action of waves, it will experience time-varying forces due to static and dynamic pressure exerted by the fluid (i.e. hydrostatic and hydrodynamic forces respectively), and these forces will be transmitted to the lower hull portion 206, thus influencing the motion of the lower hull portion 206 relative to the surrounding fluid.

[0046] It will also be appreciated that the concavities 214 and 216 may act to influence or enhance the added mass or added inertia (that is, mass or inertia due to ambient fluid that is periodically accelerated in response to oscillation of the hull in or about the axes previously defined, and which thereby influences the oscillatory motion), and so enhance the oscillatory response of the vehicle to certain wave conditions. It will be further appreciated that the added mass or added inertia due to the concavities 214 and 216 may differ according to the axis in or about which an oscillation takes place. It will be further appreciated that, since the concavities are defined in the frontal plane and generally allow free passage of ambient fluid in the longitudinal direction, drag in the direction of travel is not unduly increased with the introduction of added mass or inertia for oscillatory motions in or about various of the axes. [0047] It will be further appreciated that, as the vehicle 202 experiences oscillatory motions relative to the surrounding fluid, the hydrofoil portions of the vehicle may generate thrust. For example, a hydrofoil portion may experience a time-varying angle of attack and velocity relative to the surrounding fluid such that, on average, the hydrofoil portion generates thrust in the direction of travel, as one skilled in the art will appreciate from steady-state aerodynamic and hydrodynamic theory. Alternatively, thrust production by the oscillating hydrofoil portions may be considered as being due to the creation of a favourable (i.e., thrust-producing) unsteady wake, such as a reverse von Karman street of shed vortices.

[0048] Referring to FIG. 3, there is shown a view 300 of a wave-propelled vehicle 302 comprising an upper hull portion 304 and a lower hull portion 306. The upper hull portion 304 comprises a streamlined surface of revolution 308 in addition to a hydrofoil portion spanning a vertical extent, in contrast to the upper hull portion 204 of vehicle 202, which does not. The lower hull portion comprises a hydrofoil portion 310 spanning a vertical extent, and a hydrofoil portion 312 spanning a horizontal extent. The hydrofoil portions 310 and 312 define concavities 314 and 316 when viewed from the front or rear.

[0049] It will be appreciated that the upper hull portion 304 of vehicle 302 may modify the onset of hydrostatic and hydrodynamic forces (but chiefly hydrostatic forces) in response to, for example, heave, pitch and roll oscillations, relative to forces generated by the upper hull portion 204 of vehicle 202 in response to equivalent oscillations of vehicle 202.

[0050] Referring to FIG. 4, there is shown a view 400 of a wave-propelled vehicle 402 comprising an upper hull portion 404 and a lower hull portion 406. The upper hull portion 404 comprises a hydrofoil portion 408 spanning a horizontal extent in addition to a hydrofoil portion spanning a vertical extent, in contrast to vehicle 202, which does not. The lower hull portion comprises a hydrofoil portion 410 spanning a vertical extent, and a hydrofoil portion 412 spanning a horizontal extent. The hydrofoil portions 408, 410 and 412 define concavities 414 and 416 when viewed from the front or rear.

[0051] It will be appreciated that the upper hull portion 404 of vehicle 402 may modify the onset of hydrostatic and hydrodynamic forces (but chiefly hydrodynamic forces) in response to, for example, heave, pitch and roll oscillations, relative to forces generated by the upper hull portion 204 of vehicle 202 in response to equivalent oscillations of vehicle 202.

[0052] It will also be appreciated that the hydrofoil portion 408 acts to increase the size of the concavities 414 and 416 relative to the equivalent concavities 214 and 216 of vehicle 202, which may further enhance the added mass or added inertia provided by the fluid in oscillatory motions in or about certain of the axes, and so enhance the oscillatory response of the vehicle to certain wave conditions.

[0053] Referring to FIG. 5, there is shown a view 500 of a wave-propelled vehicle 502 comprising an upper hull portion 504 and a lower hull portion 506. The upper hull portion 504 comprises a hydrofoil portion 508 spanning a horizontal extent as well as a vertical extent, in contrast to vehicle 202, which does not. The lower hull portion comprises hydrofoil portions 510 and 510' spanning vertical extents, and a hydrofoil portion 512 spanning a horizontal extent. The hydrofoil portions 508, 510, 510' and 512 define a concavity 514 when viewed from the front or rear.

[0054] It will be appreciated that, unlike hydrofoil portions 408 and 412 of vehicle 404, none of the hydrofoil portions 508, 510, 510' and 512 of vehicle 502 expose tips to the ambient fluid, i.e., each hydrofoil portion is terminated at each of its spanwise ends by another hydrofoil portion, and the hydrofoil portions together form a closed profile when viewed from the front or rear. It will be appreciated that this may reduce parasitic (i.e., non-thrust-producing) damping of wave-induced oscillatory motions in or about certain of the axes, e.g., roll motion about the X-axis. Further benefits of non-planar lifting systems such as that provided by way of the example of vehicle 502 will be apparent to one skilled in the art. For example, in generating lift, non-planar systems offer at least one, or both, of a more compact arrangement than planar systems and generate less induced drag.

[0055] It will be appreciated that the single concavity 514 may further enhance the added mass or added inertia provided by the fluid in oscillatory motions in or about certain of the axes such as, for example, all motions except a surge motion in the X-axis, and so enhance the oscillatory response of the vehicle to certain wave conditions, relative to the previously described examples of wave-propelled vehicles.

[0056] Referring to FIG. 6, there is shown a view 600 of a wave-propelled vehicle 602 comprising an upper hull portion 604 and a lower hull portion 606. The upper hull portion 604 comprises a hydrofoil portion 608 spanning a horizontal extent as well as a vertical extent. The lower hull portion comprises hydrofoil portions 610 and 610' spanning vertical extents, and a hydrofoil portion 612 spanning a horizontal extent.

[0057] When viewed from above, it can be observed that the projection of the lower hull portion 608 onto the X-Y plane has a tapered shape, i.e., the width of the projection is narrower at the trailing position 616 than at a leading position 618. In the example, the projection follows an approximately parabolic profile. It will be appreciated that such tapering may favourably influence the coupling between various modes of oscillation, e.g., the coupling between the heave and pitch modes of oscillation, promoting large vertical excursions of the trailing position.

[0058] The hydrofoil portions 608, 610, 610' and 612 form part of an annular hull profile, which defines a concavity 614 when viewed from the front or rear.

[0059] It will be appreciated that, in contrast to vehicle 502, vehicle 602 has no corners in its frontal profile. One will appreciate that this may act to further reduce parasitic (i.e., non-thrustproducing) damping of oscillatory motion in or about certain of the axes, e.g., roll motion about the X-axis. It will be further appreciated that a wide variety of frontal profiles with this characteristic may be effected, as an alternative to the substantially circular frontal profile of vehicle 602, for example, an oval, squircle or rectangular frontal profile. Examples can be realised in which the frontal profile has a major axis and a minor axis such that the major axis is greater than the minor axis. Examples can be realised in which the major and minor axis are perpendicular to one another and parallel to the Y-axis and the Z-axis. Examples can be realised in which the major axis is parallel to the Y-axis while the minor axis is parallel to the Z-axis or vice versa.

[0060] Referring to FIG. 7, there is shown a view 700 of a wave-propelled vehicle 702 comprising an upper hull portion 704 and a lower hull portion 706. The upper hull portion 704 comprises a hydrofoil portion 708 spanning a horizontal extent as well as a vertical extent. The lower hull portion comprises hydrofoil portions 710 and 710' spanning vertical extents, and a hydrofoil portion 712 spanning a horizontal extent. The hydrofoil portion 708 has a very thin cross-section relative to the other hydrofoil portions. The thin cross-section has thickness

S

that is less than the thickness of the hydrofoil 712 spanning the horizontal extent. One will appreciate that, relative to the hydrofoil portion 608 of vehicle 602, which has a thickness similar to other hydrofoil portions of vehicle 602, the hydrofoil portion 708 of vehicle 702 may experience an increase in hydrodynamic forces relative to hydrostatic forces in response to dynamic immersion, and so influence the oscillatory response of the vehicle to certain wave conditions. For example, the dynamics of a vehicle can be adapted or otherwise tuned to anticipated wave conditions by, for example adjusting a parameter of a vehicle. An example of changing a parameter of a vehicle can comprise adjusting the buoyancy of the upper portion to change the balance of hydrodynamic and buoyant forces acting on the upper portion that will, in turn, increase at least one, or both, of the net thrust or oscillation amplitude.

[0061] Referring to FIGs. 2 to 7, it will be appreciated that, as any of the vehicles 202, 302, 402, 502, 602 and 702 experience oscillatory motions relative to the surrounding fluid, the hydrofoil portions of a given vehicle may generate thrust in the manner attributed to the hydrofoil portions of the vehicle 202. It will be further appreciated that a hydrofoil portion of any of the example vehicles may have an aerofoil cross-section, for example, a NAGA symmetrical aerofoil cross-section, such as a NACA0015 aerofoil cross-section. It will be further appreciated that a hydrofoil portion of any of the vehicles may have some other fine cross-section, that is, a cross-section that has a low ratio of thickness to chord, such as a thin plate cross-section. Such cross-sections may, for example, have thickness to chord ratios of 2% to 30%.

[0062] Referring to FIG. 8, there is shown a side view 800 of the vehicle 402. In this figure and the associated description, the vehicle 402 is used as an example, but one skilled in the art will appreciate that the observations are also applicable mutafis mutandis to any and all other wave-propelled vehicles described in this specification and/or shown in the figures.

[0063] The vehicle 402 has a centre of gravity 802, and an equilibrium centre of buoyancy 804 disposed directly above the centre of gravity 802 by a distance BZ.

[0064] The upper hull portion 404 has a leading position 806 disposed, at equilibrium, above the X-Y plane by a distance ULZ, and longitudinally from the centre of gravity 802 by a distance ULX. The upper hull portion 404 has a centre of volume 808 disposed above the X-Y plane by a distance UVZ, and longitudinally from the centre of gravity 802 by a distance UVX. The projection of the upper hull portion 404 onto the X-Y plane has a centroid 810 that, at equilibrium, is longitudinally offset from the centre of gravity 802 by a distance UCX. The upper hull portion 404 has a trailing position 812 disposed, at equilibrium, above the X-Y plane by a distance UTZ, and longitudinally from the centre of gravity 802 by a distance UTX. It will be appreciated that although the dimensions ULZ and UTZ are depicted as being equal in this particular example, examples may be realised where these differ. Examples can be realised in which ULZ>UTZ or vice versa.

[0065] The lower hull portion 406 has a leading position 814 offset, at equilibrium, from the X-Y plane by a distance LLZ, and longitudinally from the centre of gravity 802 by a distance LLX. The projection of the lower hull portion 406 onto the X-Y plane has a centroid 816 that, at equilibrium, is longitudinally offset from the centre of gravity 802 by a distance LCX. The lower hull portion 406 has a trailing position 818 offset, at equilibrium, from the X-Y plane by a distance LTZ, and longitudinally from the centre of gravity 802 by a distance LTX. It will be appreciated that although the dimensions LLZ and LTZ are depicted as being equal in this particular example, examples may be realised where these differ. Examples can be realised in which LLZ>LTZ or vice versa.

[0066] The above distances and ratios, that is ULZ, UTZ, LLZ, LTZ, ULX, [LX, UTX, LTX, BZ can be applicable to any and all of the vehicles described herein.

[0067] It will be appreciated that, in this particular example, the leading position 806, the centre of volume 808 of the upper hull portion 404, and the centroid 810 of the projection of the upper hull portion 404 onto the X-Y plane are all disposed forward of the centre of gravity 802. However, examples may be realised where any of these are disposed longitudinally aligned with, ahead of or behind the centre of gravity 802, in any and all combinations.

[0068] An example has been realised, based on the vehicle depicted in FIG. 6, in which the following relationships hold: [0069] ULZ = UTZ [0070] LLZ = LTZ [0071] U LX = LLX = 81m m [0072] ULZ + LLZ = 252mm [0073] LLZ = 41mm [0074] U LX + UTX = 126mm [0075] [LX + LTX = 252mm [0076] BZ = 20mm.

[0077] Referring to FIG. 9, there is shown a view 900 of a sequence of side views 902-912 of the vehicle 402 moving in a head (oncoming) wave 914. The head wave 914 is travelling from right to left, as indicated by the arrow 916. The vehicle 402 is moving generally from left to right. The motion of various positions on the vehicle 402 are indicated by arrows, such as the arrows 918 and 920, which indicate the motions of the centre of volume 808 of the upper hull portion 404 and the centre of gravity 802 respectively. The velocity of a particle at the free surface is indicated by arrows such as 922, at various positions on the wave. Position 924 is the falling surface of the wave; position 926 is the trough of the wave; position 928 is the rising surface of the wave; and position 930 is the crest of the wave.

[0078] View 902 shows the vehicle 402 gliding down along with or relative to the falling surface 924 of the wave. In this condition, the upper hull portion 404 and the lower hull portion 406 are advancing with approximately the same velocity in an absolute frame of reference, as depicted by the arrows representing their motion.

[0079] View 904 shows the vehicle 402 arriving at the trough 926.

[0080] View 906 shows the upper hull portion 404 plunging into the bottom of the rising surface 928. At this point a change in hydrostatic forces, hydrodynamic forces, or a combination of hydrostatic and hydrodynamic forces acting on the upper hull portion 404 encourages the lower hull portion 406 to effectively swing up underneath the upper hull portion 404 in a pendular motion. Hydrodynamic forces acting on the lower hull portion 406 may further encourage this swinging motion. The swinging motion is indicated by arrows emanating from various positions on the hull in view 906. It will be observed that these describe a motion into a "nose-up" attitude with a centre of rotation located approximately at the centre of volume 808 of the upper hull portion 404, but one will appreciate that the motion may not be a pure rotation, and may be expressed as an approximate rotation about another position associated with the upper hull portion 404. One will further observe that the centre of gravity 802 may experience a smooth transition into the swinging motion, that the lower hull portion 406 may not experience significant damping due to, for example, flow separation for the motion shown, and that the upper hull portion 404 may not experience significant rotational damping, due to the relatively short spacing between the leading and trailing positions of the upper hull portion 404.

[0081] View 908 shows the vehicle 402 in a resultant nose-up attitude, rising along with or relative to the rising surface 928. Hydrostatic forces, hydrodynamic forces, or a combination of hydrostatic and hydrodynamic forces acting on the immersed portions of the hull may encourage the vehicle 402 to rise along with or relative to the wave. One skilled in the art will appreciate that the vehicle 402 may not be making appreciable headway in an absolute reference frame at this point, whilst acquiring potential energy from the wave.

[0082] View 910 shows the vehicle 402 broaching at the crest 930. At this point, the vehicle 402 experiences a change in hydrostatic forces, hydrodynamic forces, or a combination of hydrostatic and hydrodynamic forces, acting on the upper hull portion 404.

[0083] View 912 shows the vehicle 402 rotating as it passes the crest 930. At this point, the change in hydrostatic forces, hydrodynamic forces, or a combination of hydrostatic and hydrodynamic forces, acting on the upper hull portion 404 as a result of the broaching depicted in view 910, encourages the upper hull portion 404 to swing over the lower hull portion 406. Hydrodynamic forces acting on the lower hull portion 406 may further encourage this swinging motion. In view 912 the swinging motion is depicted as a pure rotation about the centre of gravity 802, but one will appreciate that the motion may not be a pure rotation, and may be expressed as a rotation about another position associated with the lower hull portion 406.

[0084] As the vehicle 402 completes the swinging motion depicted in view 912, it assumes a position and attitude relative to the wave similar to that depicted in view 902, and commences gliding down along with or relative to a falling surface of the next wave. One skilled in the art will appreciate that the motion depicted by views 902-912 may be a repeated motion across several waves leading to long term headway of the wave-propelled vehicle 402.

[0085] One will appreciate that the swinging motion depicted in view 906 of FIG. 9 may be encouraged by arranging the upper hull portion 404 and the lower hull portion 406 such that low resistance to swinging is encountered by the lower hull portion, allowing efficient conversion of kinetic energy from the preceding glide into potential energy as the centre of gravity 802 rises during the swing, resulting in a nose-up attitude of the vehicle 402. As the upper hull portion plunges into the rising surface of the wave, hydrostatic forces, hydrodynamic forces, or a combination of hydrostatic and hydrodynamic forces, may act to create an approximate centre of rotation for the pendular swinging motion. Such an approximate centre of rotation may arise in the vicinity of a leading position 806 of the upper hull portion, the centre of volume 808 of the upper hull portion, the centroid 810 of the projected area of the upper hull portion longitudinally, but at or near the elevation of the centre of volume 808, or another nearby position associated with the upper hull portion. One will appreciate that a centre of gravity 802 may be arranged relative to this location to encourage the transition from the previous gliding motion to the pendular swinging motion; in particular one will appreciate that a centre of gravity 802 arranged at a suitable distance from the approximate centre of rotation, and such that its velocity during the glide is substantially tangential to its subsequent orbit about the approximate centre of rotation, may minimise the kinetic energy lost to resistance during the swing.

[0086] One will appreciate that the swinging motion depicted in view 912 of FIG. 9 may be encouraged by arranging the upper hull portion 404 and the lower hull portion 406 such that the upper hull portion has a centre of volume 808 ahead of the centre of gravity 802. In such an arrangement, as the upper hull portion broaches the surface near the crest of the wave, the instantaneous centre of hydrostatic pressure acting on the vehicle will move rearward, encouraging the vehicle to pitch nose-down; heave and pitch motions may be coupled in this way. One will further appreciate that a long, or increasing, distance between leading and trailing positions of the lower hull portion may encourage the, or an increasing, swinging motion due to hydrodynamic forces acting on the lower hull portion, encouraging the lower hull portion to align with the horizontal orbital particle velocities at the crest of the wave. A low centre of gravity 802 may also help to encourage the swinging motion of view 912. The position of the centre of gravity may influence the swinging motion.

[0087] One will appreciate that the motion described with reference to FIG. 9 may be considered at least partly pendular, with at least a pendular swinging motion repeated with each wave. Consequently, it may be possible to arrange the vertical distance from a position associated with the upper hull portion to the centre of gravity 802, corresponding to the characteristic length of an equivalent pendulum, to suit the period of ambient waves, and so amplify the resulting motions and the production of thrust. One will appreciate that a vehicle may be configured to adapt this distance dynamically, for example through the use of any of a number of internal weight shift mechanisms known to one skilled in the art.

[0088] Referring to FIG. 10, there is shown a view 1000 of a vehicle 1002 without the transverse asymmetrical profile of vehicle 402, but otherwise sharing many of the latter's features, including hydrofoil portions of the upper and lower hull portions spanning respective horizontal and vertical extents. It can be observed that leading positions of the upper hull portion 1004 and the lower hull portion 1006 are longitudinally offset from the centre of gravity 1008 by the same distance, and that trailing positions of the upper hull portion 1004 and the lower hull portion 1006 are longitudinally offset from the centre of gravity 1008 by the same distance. The centre of volume 1010 of the upper hull portion is disposed substantially directly above the centre of gravity 1008.

[0089] Views 1012 and 1014 show swinging motions corresponding to those described with respect to vehicle 402 in views 906 and 912 of FIG. 9 respectively. Each view of FIG. 10 depicts the vehicle 1002 subjected to the same swinging motion as depicted in the corresponding view in FIG. 9. One will appreciate that the arrows indicating particle velocities at the surface of wave 914 depicted in FIG. 9 are also applicable to the particle velocities of equivalent wave 1016, travelling in direction 1018, at equivalent positions on the wave. Such arrows have been omitted in FIG. 10 for clarity.

[0090] Referring to view 1012, it can be seen that the vehicle 1002 is undergoing a swinging motion at the trough of wave 1016. Whilst one may appreciate from the arrows indicating the swinging motion of view 1012 that resistance to rotation due to the lower hull portion may be similar to that of vehicle 402 with respect to view 906, resistance to rotation due to the motion of leading and trailing positions of the upper hull portion 1004 may be significantly higher. One will appreciate that this may suppress such swinging motions and cause a breakdown in the vehicle's ability to make headway.

[0091] Referring to view 1014, it can be seen that vehicle 1002 is undergoing a swinging motion at the crest of wave 1016. One will appreciate that because the centre of volume 1010 of the upper hull portion has a smaller longitudinal offset from the centre of gravity 1008 (relative to the equivalent offset of vehicle 402), the broaching of the upper hull portion 1004 of vehicle 1002 will tend to encourage nose-down pitching to a lesser degree than one may infer for vehicle 402 from view 906. One will appreciate that this may suppress such swinging motions and cause a breakdown in the vehicle's ability to make headway. More generally, the reduced coupling between heave and pitch motions of vehicle 1002 relative to vehicle 402, arising at least partially from the substantial transverse symmetry of the operative portion of the hull of vehicle 1002, may interfere with the vehicle adopting an attitude conducive to thrust production in various phases of motion, e.g., an attitude conducive to gliding down the falling surface of a wave.

[0092] Referring to FIG. 11, there is shown a view 1100 of a vehicle 1102 sharing many of the characteristics of vehicle 1002 described with reference to FIG. 10 above. However, it can be seen that, compared to vehicle 1002, vehicle 1102 has a longer upper hull portion 1104 and a longer lower hull portion 1106 relative to the overall height of the operative portion of the hull. Consequently, the centre of gravity 1108 of the vehicle and the centre of volume 1110 of the upper hull portion are closer together, relative to the lengths of the upper and lower hull portions.

[0093] Views 1112 and 1114 show swinging motions corresponding to those described with respect to vehicle 402 in views 906 and 912 of FIG. 9 respectively. Each view of FIG. 11 depicts the vehicle 1102 subjected to the same swinging motion as depicted in the corresponding view in FIG. 9. One will appreciate that the arrows indicating particle velocities at the surface of wave 914 depicted in FIG. 9 are also applicable to the particle velocities of equivalent wave 1116, travelling in direction 1118, at equivalent positions on the wave. Such arrows have been omitted in FIG. 11 for clarity.

[0094] Referring to view 1112, it can be seen that the vehicle 1102 is undergoing a swinging motion at the trough of wave 1116. One will appreciate from the arrows indicating the swinging motion of view 1112 that resistance to rotation due to the lower hull portion may be greater than one may infer for vehicle 402 from view 906, and resistance to rotation due to the motion of leading and trailing positions of the upper hull portion 1104 may be also be significantly higher. One will appreciate that this may suppress such swinging motions and cause a breakdown in the vehicle's ability to make headway.

[0095] Referring to view 1114, it can be seen that vehicle 1102 is undergoing a swinging motion at the crest of wave 1116. As for vehicle 1002, the smaller longitudinal offset of the centre of volume 1110 of the upper hull portion of vehicle 1102 from its centre of gravity 1108 will tend to encourage nose-down pitching to a lesser degree than one may infer for vehicle 402 from view 906. One will appreciate that this may suppress such swinging motions and cause a breakdown in the vehicle's ability to make headway.

[0096] Referring to FIG. 12, there is shown a view 1200 of a vehicle 1202 sharing many of the characteristics of vehicle 1002 described with reference to FIG. 10 above. It can be seen that vehicle 1202 has a swept or staggered side profile. Consequently, upper hull portion 1204 is disposed generally behind lower hull portion 1206, and the centre of gravity 1208 lies ahead of the centre of volume 1210 of the upper hull portion 1204.

[0097] Views 1212 and 1214 show swinging motions corresponding to those described with respect to vehicle 402 in views 906 and 912 of FIG. 9 respectively. Each view of FIG. 12 depicts the vehicle 1202 subjected to the same swinging motion as depicted in the corresponding view in FIG. 9. One will appreciate that the arrows indicating particle velocities at the surface of wave 914 depicted in FIG. 9 are also applicable to the particle velocities of equivalent wave 1216, travelling in direction 1218, at equivalent positions on the wave. Such arrows have been omitted in FIG. 12 for clarity.

[0098] Referring to view 1212, it can be seen that the vehicle 1202 is undergoing a swinging motion at the trough of wave 1216. One will appreciate from the arrows indicating the swinging motion of view 1212 that resistance to rotation due to the lower hull portion may be greater than one may infer for vehicle 402 from view 906. One will appreciate that this may suppress such swinging motions and cause a breakdown in the vehicle's ability to make headway.

[0099] Referring to view 1214, it can be seen that vehicle 1202 is undergoing a swinging motion at the crest of wave 1216. Since the centre of volume 1210 of the upper hull portion 1204 is behind the centre of gravity 1208 of the vehicle in this case, one will appreciate that the broaching of the vehicle 1202 at the crest of the wave may discourage a nose-down swinging motion such as that depicted. One will appreciate that this may suppress such swinging motions and cause a breakdown in the vehicle's ability to make headway.

[0100] Referring to FIG. 13, there is shown a view 1300 of a vehicle 1302 sharing many of the characteristics of vehicle 1002 described with reference to FIG. 10 above. It can be seen that vehicle 1302 has a swept or staggered side profile. Consequently, upper hull portion 1304 is disposed generally ahead of lower hull portion 1306, and the centre of gravity 1308 lies behind the centre of volume 1310 of the upper hull portion 1304.

[0101] Views 1312 and 1314 show swinging motions corresponding to those described with respect to vehicle 402 in views 906 and 912 of FIG. 9 respectively. Each view of FIG. 13 depicts the vehicle 1302 subjected to the same swinging motion as depicted in the corresponding view in FIG. 9. One will appreciate that the arrows indicating particle velocities at the surface of wave 914 depicted in FIG. 9 are also applicable to the particle velocities of equivalent wave 1316, travelling in direction 1318, at equivalent positions on the wave. Such arrows have been omitted in FIG. 13 for clarity.

[0102] Referring to view 1312, it can be seen that the vehicle 1302 is undergoing a swinging motion at the trough of wave 1316. One will appreciate from the arrows indicating the swinging motion of view 1312 that resistance to rotation due to the lower hull portion may be greater than one may infer for vehicle 402 from view 906. One will appreciate that this may suppress such swinging motions and cause a breakdown in the vehicle's ability to make headway.

[0103] Referring to view 1314, it can be seen that the vehicle 1302 is undergoing a swinging motion at the crest of wave 1316. Since the centre of volume 1310 of the upper hull portion 1304 is ahead of the centre of gravity 1308 of the vehicle in this case, one will appreciate that the broaching of the vehicle may encourage a nose-down swinging motion such as that depicted. One skilled in the art will further appreciate, however, that suppression of the swinging motion described in relation to view 1312 may be sufficient to cause a breakdown in the vehicle's ability to make headway.

[0104] Considering FIGs. 8-13 and their associated descriptions together, it will be appreciated that relationships between the dimensions shown in FIG. 8 may determine or influence a vehicle's ability to realise appreciable wave propulsion in head waves.

[0105] It will be appreciated that an upper hull portion of shorter, or decreasing, longitudinal extent than a lower hull portion may encourage corresponding increasing swinging motion at the trough of a wave as part of a thrust-producing cyclical motion.

[0106] It will be appreciated that a low centre of gravity, and a large, or increasing, vertical offset between the upper hull portion and the centre of gravity, may encourage a respective, or increasing, swinging motion at the trough of a wave as part of a thrust-producing cyclical motion.

[0107] It will be appreciated that excessive significant stagger or sweep in the side profile of the operative region of a hull may discourage swinging motion at the trough of a wave and so prevent thrust-producing cyclical motion.

[0108] It will be appreciated that a pivot position associated with the upper hull portion, created by hydrostatic forces, hydrodynamic forces, or a combination of hydrostatic and hydrodynamic forces, acting on the upper hull portion, if disposed at a location on the upper hull that is substantially longitudinally aligned with the centre of gravity, may encourage swinging motion at the trough of a wave as part of a thrust-producing cyclical motion.

[0109] It will be appreciated that a centre of volume of an upper hull portion ahead of the centre of gravity of a vehicle may encourage swinging motion at the crest of a wave as part of a thrust-producing cyclical motion.

[0110] It will be appreciated that a lower hull portion with a large longitudinal extent, such as, for example, the chord of a hydrofoil portion spanning a horizontal extent, may encourage swinging motion at the crest of a wave as part of a thrust-producing cyclical motion.

[0111] Referring to FIG. 14, there is shown a view 1400 of a response of the vehicle 602 to a wave 1402. In the illustrated example, the wave 1402 is a head wave. The direction of travel of the head wave 1402 is indicated by a respective arrow 1404. The wave, when interacting with the vehicle 602, causes the vehicle 602 to move, in particular, to vary its orientation in a flapping motion. The flapping motion comprises heaving and pitching motions. The relative motion of the vehicle 602 within the wave bearing body of fluid 1406 generates thrust in the direction indicated by the arrow 1408.

[0112] The heaving and pitching of, in particular, the lower hull portion 606 of the vehicle 602 generates thrust. Examples can be realised in which the thrust is associated with an unsteady wake such as, for example, a reverse von Korman street of vortices, four of which vortices 1410 to 1416 are shown in FIG. 14.

[0113] Also shown in FIG. 14 is an indication of the draft 1418 associated with the vehicle 602. At equilibrium, the vehicle 602 is arranged to have a predetermined draft. Examples can be realised in which the predetermined draft is such that the volume of fluid, in use, within the concavity of the vehicle 602 would have a mass that is greater than the mass of the vehicle. The fluid occupying the concavity would typically be water, in particular, sea water. Alternatively, or additionally, the predetermined draft is such that the volume of fluid within the concavity encompasses a predetermined portion of the volume of the concavity such as, for example, at least 50% of the volume of the concavity. Examples can be realised in which more than 50% of the volume of the concavity can be occupied by the fluid. For example, the vehicle may be configured with a load state such that 90% or more of the concavity is filled at equilibrium.

[0114] Referring to FIG. 15, there is shown a front and top view 1500 of the vehicle 602 in a beam sea, that is, interacting with a beam wave 1506. The beam wave has a direction of travel that is perpendicular to the longitudinal axis of the vehicle 602 as indicated by the arrow 1508. The beam wave, when interacting with the vehicle 602 causes the vehicle to oscillate about a centre of gravity 1510. The oscillation illustrated in FIG. 15 is a roll oscillation indicated by the arrow 1512. The roll oscillation has a respective angular amplitude 1514. The respective amplitude 1514 is related to the incident wave 1506. The oscillation results in forward thrust being generated. The forward thrust is indicated by the arrow 1516. One will appreciate that secondary oscillations (not shown) in or about any of the axes of the vehicle may occur concurrently with the roll oscillation illustrated, and that such secondary oscillations may enhance the thrust produced.

[0115] Examples can be realised in which the thrust is associated with an unsteady wake from at least one hydrofoil portion of the hull, such as, for example a reverse von Karmen street of vortices, two examples 1518 and 1520 of which are shown in FIG. 15.

[0116] Referring to FIG. 16, there is shown a view 1600 of front 1602, top 1604, and side 1606 views of a wave-propelled vehicle 1608. The vehicle 1608 is an example of the above-described vehicle 602. The vehicle 1608 comprises one or more than one hydrodynamic control surface. The one or more than one hydrodynamic control surface is used to steer the vehicle while in motion. For instance, examples can be realised in which the vehicle 1608 comprises a hydrodynamic control surface 1612 that is disposed beneath, or forms part of, the lower hull portion 1610 of the vehicle 1608. Alternatively, or additionally, a symmetrically disposed hydrodynamic control surface can be included within the cavity. Such an internally contained hydrodynamic control surface 1614 is illustrated. Still further, the vehicle 1608 may comprise a set of hydrodynamic control surfaces. In the example depicted the set of hydrodynamic control surfaces may comprise a pair of control surfaces 1616 and 1618 positioned on, or at, the trailing edge 1620 of the lower hull portion 1610 of the vehicle 1608. One skilled in the art will appreciate that various arrangements of control surfaces may be realised to steer the vehicle.

[0117] Referring to FIG. 17, there is shown a view 1700 of a wave-propelled vehicle in isometric 1702, top 1704, side 1706 and rear 1708 views. The vehicle 1710 is an example of the above-described vehicle 602. It can be appreciated that the vehicle comprises a set of solar energy harvesting panels 1712. The set of solar energy harvesting panels 1712 can comprise a set of solar panels. The set of solar energy harvesting panels are disposed on the upper half of the vehicle 1710. The solar energy harvesting panels can comprise, for example, photovoltaic panels or cells. The vehicle 1710 may additionally comprise a set of hydrodynamic control surfaces. In the illustrated example, a pair 1714 and 1716 of hydrodynamic control surfaces is provided. The pair 1714 and 1716 of hydrodynamic control surfaces are substantially the same as the above-described pair 1616 and 1618 of hydrodynamic control surfaces. The vehicle 1710 can also comprise an internal hydrodynamic control surface 1718 comparable to the above-described hydrodynamic control surface 1614. [0118] The set of solar energy harvesting panels 1712 is arranged to generate and store electricity from sunlight in a battery (not shown). The stored energy can be used to drive any onboard electrical or electronic systems of the vehicle 1710.

[0119] Referring to FIG. 18, there is shown a view 1800 of a vehicle 1802. The vehicle 1802 is an example of the above-described vehicle 602. It can be appreciated that the vehicle additionally comprises an empennage referred to generally by the reference numeral 1804. The empennage 1804 is arranged to allow the vehicle 1802 to be aerially launched from, for example, a large aeroplane. The vehicle, given the empennage, can glide or fly a number of miles according to the altitude of launch. The empennage comprises a number of control surfaces and actuating mechanisms of a kind apparent to one skilled in the art (not shown) to control or otherwise steer the vehicle 1802 towards its destination during flight. Although the example shown in FIG. 18 has been described with reference to the vehicle 602 shown in or described with reference to FIG. 6, any vehicle described herein can have such an associated empennage. Optionally, once a vehicle comprising an empennage 1804 lands in a body of fluid, the empennage 1804 may be ejected from the vehicle.

[0120] Referring to FIG. 19, there is shown a view 1900 of front 1902 and rear 1904 perspective views of a wave-propelled vehicle 1906. The vehicle 1906 is an example of the above-described vehicle 602. The vehicle 1906 additionally comprises at least one, or both, of a pressure hull 1908 and one or more than one supplementary thruster. In the example shown, three supplementary thrusters 1910, 1912 and 1914 are provided. The one or more than one supplementary thruster represents a set of supplementary thrusters. The one or more than one thruster 1910-1914 can be powered by the above-described battery (not shown).

The vehicle 1906 also comprises the above-described solar energy harvesting panels 1712, and a symmetrically disposed control surface 1918.

[0121] The supplementary thrusters 1910-1914 can be used to at least one of drive, control or steer, taken jointly and severally in any and all permutations, the vehicle 1906, including when the vehicle is fully submerged, especially when sufficiently removed from the surface waves, the influence of which progressively decreases with depth from the surface. The thrusters 1910-1914 may be used to steer the direction of the vehicle 1906. Alternatively or additionally, the control surface 1918 may be used to steer the vehicle.

[0122] Examples may be realised whereby the hydrofoil portions of the vehicle's hull act as lifting surfaces in underwater powered or gliding flight. In underwater gliding flight, the control surface 1918 may be used to steer the vehicle.

[0123] The pressurised hull 1908 forms part of a buoyancy control system, described with reference to FIG. 25, which is used to influence the buoyancy of the vehicle 1906. Buoyancy is controlled to support the vehicle 1906 in diving and returning to the surface following such a dive. The vehicle 1906 also comprises an antenna or antennas 1916 to support communications.

[0124] FIGs. 20 to 24 depict respective views of the vehicle 1906 shown in, and described with reference to, FIG. 19.

[0125] FIG. 20 depicts a side view 2000 of the vehicle 1906.

[0126] FIG. 21 depicts a front view 2100 of the vehicle 1906.

[0127] FIG. 22 depicts a rear view 2200 of the vehicle 1906.

[0128] FIG. 23 depicts a top view 2300 of the vehicle 1906.

[0129] FIG. 24 depicts a bottom view 2400 of the vehicle 1906.

[0130] Referring to FIG. 25, there is shown a view 2500 of a buoyancy control system associated with any of the vehicles described herein and/or as shown in the figures. The view 2500 is a frontal cross-sectional view of the hull of the vehicle 1906. It can be appreciated that the hull has been divided into a number of compartments 2502 to 2512. The following description refers to water as the fluid in which the vehicle floats, and air as the fluid above the free surface, but one skilled in the art will appreciate that the description can equally be applied to a range of fluid combinations.

[0131] The upper-most compartment, that is compartment 2502, may contain water or air. When the vehicle 1906 is at the surface of a body of water, water may be exchanged for air and vice-versa through a simple valve and pump (not shown).

[0132] A pair of middle compartments 2504 and 2506 is provided to give buoyancy to the vehicle 1906. The compartments 2504 and 2506 can be filled with a foam such as, for example, a syntactic foam. The foam can have a density that is lower than that of water to provide positive buoyancy.

[0133] A pair 2508 and 2510 of further compartments is provided. The compartments 2508 and 2510 are free-flooding compartments. The free-flooding compartments 2508 and 2510 may contain either water or a buoyancy control working fluid. The buoyancy control working fluid can comprise a mineral oil, or other liquid that is substantially incompressible and preferably less dense than water. The buoyancy control working fluid may be pumped into or out of a bladder 2514 to populate or evacuate corresponding bladders (not shown) in the compartments 2508 and 2510. When the buoyancy control working fluid is pumped into the bladder within each of the compartments 2508 and 2510, water within the compartments 2508 and 2510 is displaced into the ambient water surrounding the vehicle 1906.

[0134] The lowest compartment 2512 is a pressure hull. The pressure hull 2512 is filled with air but for the bladder 2514, which is arranged to store a volume of buoyancy control working fluid. The buoyancy control working fluid stored in the bladder 2514 can be pumped into the bladders (not shown) within the compartments 2508 and 2510. Conversely, the buoyancy control working fluid may be evacuated from the bladders (not shown) within the compartments 2508 and 2510 into the storage bladder 2514.

[0135] When the vehicle is operating at the surface, the upper compartment 2502 is filled with air, and the buoyancy control compartments 2508 and 2510 are filled with water. The vehicle 1906 is arranged to be positively buoyant in this condition.

[0136] "Mien the vehicle 1906 is required to dive, the upper compartment 2502 is filled with water, that is, the air is discharged and the vehicle 1906 becomes negatively buoyant. The negative buoyancy allows the vehicle 1906 to dive. The direction of travel during the dive can be controlled by the supplementary thrusters and/or hydrodynamic control surfaces.

[0137] When the vehicle is required to ascend, the buoyancy control working fluid stored within the storage bladder 2514 is pumped into the bladders within the buoyancy control compartments 2508 and 2510, which displaces any water within those compartments 2508 and 2510 into the surrounding environment. The resulting effect is that the vehicle 1906 becomes positively buoyant. Once the vehicle broaches the surface, the upper compartment 2502 can be filled with air by expelling the water it contains into the surrounding environment, which further increases the overall buoyancy of the vehicle 1906. The buoyancy control working fluid can then be pumped out of buoyancy control compartments 2508 and 2510 into the storage bladder 2514, which allows the buoyancy control compartments 2508 and 2510 to be filled with water again. Any example vehicle described herein can be arranged to dive and operate beneath the thermocline of a body of fluid.

[0138] Referring to FIG. 26, there is shown a view 2600 of a control system 2602 for controlling any of the wave-propelled vehicles described herein. The control system 2602 comprises a processor 2604 for controlling or otherwise orchestrating all of the control and operational functions associated with the vehicle. The position of a vehicle is determined using a GPS system 2606. The GPS system is arranged to provide position information to a navigation system 2608. The navigation system is arranged to make or execute operational actions or decisions according to desired actions of the vehicle. For example, the navigation system can influence a control surface system 2610. The control surface system 2610 is arranged to control the hydrodynamic control surfaces described above and/or any thrusters if present. The control system 2602 also comprises a sensor system 2612. The sensor system is arranged to monitor, for example, the depth or pressure of the environment of a vehicle. The sensor system 2612 can also be arranged to carry sensors for taking measurements or readings associated with the environment such as, for example, sonar sensors for performing sonar sensing such as, for example sonar imaging. The control system 2602 also comprises a buoyancy/dive control system 2614. The buoyancy/dive control system 2614 is arranged to control diving of the vehicle; that is, to control descent, depth maintenance and ascent operations in response to commands from the processor 2604. A power management system 2616 is provided to distribute power according to current operational demands of a vehicle and to control charging of a battery 2618 to harvest solar energy using the above-described solar energy harvesting panels. A communication system 2620 is also provided to manage communications with a command and control centre (not shown).

[0139] Examples can be realised in which any of the vehicles described herein has a centre of volume of the operative region, a centre of volume of the lower hull portion, or an equilibrium centre of buoyancy disposed at a predetermined position along an axis transverse to a longitudinal axis to induce an oscillatory motion about the centre of gravity having an associated period. The associated period can be arranged to accommodate, or be resonant with, a respective wavelength, or range of wavelengths, of waves in the body of a fluid.

[0140] The examples described herein can be deployed and left in theatre or on task for long durations since the movement is wave-powered. Being wave-powered allows the vehicles to autonomously perform a task on site and then drift to a collection point or base under wave-power.

[0141] Examples can be realised according to any of the following clauses: [0142] Clause 1: A wave-propelled vehicle adapted to float at the surface of a body of fluid, wherein the vehicle comprises a hull defining at least one concavity; the hull comprising an upper hull portion and a lower hull portion; the hull having an asymmetrical transverse profile to generate thrust in response to waves on the body of fluid.

[0143] Clause 2: The vehicle of clause 1, comprising a centre of gravity (802) and an equilibrium centre of buoyancy (804) disposed above centre of gravity (802) by a distance BZ; the centre of gravity defining an origin of a cartesian reference frame with the X-axis being, or being parallel to, the longitudinal, or roll, axis of the vehicle, the Z-axis being, or being parallel to, the transverse, or yaw, axis of the vehicle and the Y-axis being, or being parallel to, a further transverse, or pitch, axis of the vehicle.

[0144] Clause 3: The vehicle of clause 2, in which the upper hull portion comprises a centre of volume (808) disposed, at equilibrium, above the X-Y plane of the reference frame by a distance UVZ, and longitudinally from the centre of gravity (802) by a distance UVX.

[0145] Clause 4: The vehicle of any of clauses 2 or 3, in which the upper hull portion (404) has a projection onto the X-Y plane of the reference frame such that, at equilibrium, the centroid (810) of the projection is longitudinally offset from the centre of gravity (802) by a distance UCX.

[0146] Clause 5: The vehicle of any of clauses 2 to 4, in which the lower hull portion (406) has a projection onto the X-Y plane such that, at equilibrium, the centroid (816) of the projection is longitudinally offset from the centre of gravity (802) by a distance LCX.

[0147] Clause 6: The vehicle of any of clauses 2 to 5, in which the lower hull portion (406) has a trailing position (818) that, at equilibrium, is offset longitudinally from the centre of gravity by a distance [TX.

[0148] Clause 7: The vehicle of clause 1 comprising at least one or more than one of the following taken jointly and severally in any and all permutations: a. a centre of gravity (802) and an equilibrium centre of buoyancy (804) disposed above the centre of gravity (802) by a distance BZ; the centre of gravity defining an origin of a cartesian reference frame with the X-axis being, or being parallel to, the longitudinal, or roll, axis of the vehicle, the Z-axis being, or being parallel to, the transverse, or yaw, axis of the vehicle and the Y-axis being, or being parallel to, a further transverse, or pitch, axis of the vehicle; b. a centre of volume (808) of the upper hull portion disposed, at equilibrium, above the X-Y plane of the reference frame by a distance UVZ, and longitudinally from the centre of gravity (802) by a distance UVX; c. an upper hull portion (404) having a projection onto the X-Y plane of the reference frame such that, at equilibrium, the centroid (810) of the projection is longitudinally offset from the centre of gravity (802) by a distance UCX; d. a lower hull portion (406) having a projection onto the X-Y plane such that, at equilibrium, the centroid (816) is longitudinally offset from the centre of gravity (802) by a distance LCX; or e. a trailing position (818) of the lower hull portion (406) that, at equilibrium, is offset longitudinally from the centre of gravity (802) by a distance [TX.

[0149] Clause 8: The vehicle of any preceding clause, comprising at least one or more than one of the following features taken jointly and severally in any and all permutations: a. the ratio (UTX+ULX)/(LTX+LLX) is less than 1.0, for example, 0.5; b. at least one or more than one of the ratios LLZ/ULZ and LTZ/UTZ, taken jointly and severally in any and all permutations, is less than 1.0, for example, 0.15; c. at least one, or all, of a leading position (806) of the upper hull portion (404), the centre of volume (808) of the upper hull portion (404), the centroid (810) of the projected area of the upper hull portion (404), and a trailing position (812) of the upper hull portion (404), is disposed, at equilibrium, behind a leading position (814) of the lower hull portion (406); d. at least one, or all, of a leading position (806) of the upper hull portion (404), the centre of volume (808) of the upper hull portion (404), the centroid (810) of the projected area of the upper hull portion (404), and a trailing position (812) of the upper hull portion (404), is disposed, at equilibrium, ahead of a trailing position (818) of the lower hull portion (406); e. at least one or more than one of the ratios ULX/UVZ, UVX/UVZ, UCX/UVZ, taken jointly and severally in any and all permutations, is less than 1.0, for example, 0.15; f. the centre of volume (808) of the upper hull portion (404), is disposed, at equilibrium, ahead of the centre of gravity (802).

[0150] Clause 9: The vehicle of any preceding clause, wherein the upper hull portion comprises a hydrofoil portion having a fine cross-section, optionally a thin plate cross-section, or an aerofoil cross-section, such as, for example, a NACA symmetrical aerofoil cross-section. [0151] Clause 10: The vehicle of clause 9, wherein the cross-section of a hydrofoil portion of the upper hull portion has a thickness between 2% and 30% of the chord of the cross-section, optionally 15%.

[0152] Clause 11: The vehicle of clause 9 or 10, wherein a hydrofoil portion of the upper hull portion spans a longitudinal or horizontal extent.

[0153] Clause 12: The vehicle of any preceding clause, wherein the lower hull portion comprises a hydrofoil portion having an aerofoil cross-section, such as, for example, a thin plate cross-section, or an aerofoil cross-section, optionally a NACA symmetrical aerofoil cross-section.

[0154] Clause 13: The vehicle of clause 12, wherein the aerofoil cross-section of a hydrofoil portion of the lower hull portion has a thickness between 8% and 30% of the chord of the cross-section, optionally 15%.

[0155] Clause 14: The vehicle of clause 12 or clause 13, wherein a hydrofoil portion of the lower hull portion spans a longitudinal or horizontal extent.

[0156] Clause 15: The vehicle of any preceding clause, wherein the hull comprises a hydrofoil portion spanning a vertical extent, said hydrofoil portion having a fine cross-section, optionally a thin plate cross-section, or an aerofoil cross-section, such as, for example, a NACA symmetrical aerofoil cross-section.

[0157] Clause 16: The vehicle of clause 15, wherein the cross-section of the hydrofoil portion has a thickness between 2% and 30% of the chord of the cross-section, such as, for example, 15%.

[0158] Clause 17: The vehicle of any preceding clause, wherein a hydrofoil portion of the hull produces thrust due to wave-induced motion.

[0159] Clause 18: The vehicle of clause 17, wherein the thrust-producing hydrofoil portion is shaped to experience, in use, a time-varying angle of attack and velocity relative to the surrounding fluid of the body of fluid such that, on average, the hydrofoil portion generates thrust in the direction of travel.

[0160] Clause 19: The vehicle of clause 17 or clause 18, wherein the thrust-producing hydrofoil portion oscillates relative to the surrounding fluid such that it generates a thrust-producing unsteady wake, such as, for example, a reverse von Karmen street of shed vortices. [0161] Clause 20: The vehicle of any preceding clause, in which the hull defines a duct or conduit forming the concavity with a closed shape.

[0162] Clause 21: The vehicle of clause 20, in which the closed shape is an annulus defining the concavity.

[0163] Clause 22: The vehicle of clause 20 or 21, in which the closed shape is a squircle defining the concavity.

[0164] Clause 23: The vehicle of any preceding clause, in which the hull defining the concavity defines fluid ingress and fluid egress apertures; such as, for example, ingress and egress apertures that are longitudinally disposed.

[0165] Clause 24: The vehicle of any preceding clause, comprising a plurality of modes of operation; the plurality of modes of operation comprising at least one or more of a. wave propulsion, b. underwater gliding flight, c. underwater powered flight, or d. aerial gliding flight taken jointly and severally in any and all permutations.

[0166] Clause 25: The vehicle of any preceding clause in which at least one or more than one of the at least one concavity, the hull, the upper hull portion, the lower hull portion or the asymmetrical transverse profile, taken jointly and severally in any and all permutations, is arranged to add mass when moving in the body of fluid.

[0167] Clause 26: The vehicle of any preceding clause, in which the asymmetrical transverse profile comprises a trailing edge having a tapering profile.

[0168] Clause 27: The vehicle of any preceding clause comprising a centre of gravity disposed at a predetermined position along an axis transverse to a longitudinal axis to induce an oscillatory or pendulatory motion about that centre of gravity having a predeterminable period. [0169] The wave-propelled vehicles described and claims herein can generate thrust without having individually moveable parts. The fixed arrangements of hydrofoils are responsive to wave motion to generate thrust. Examples can be realised in which each vehicle described builds upon, adds to, or adapts features of previously described vehicles. To the extent that any such building, adding or adapting is incompatible with the features of previously described vehicles, the features of the later described vehicle prevail.

Claims (27)

1. CLAIMS1 A wave-propelled vehicle adapted to float at the surface of a body of fluid, wherein the vehicle comprises a hull defining at least one concavity; the hull comprising an upper hull portion and a lower hull portion; the hull having an asymmetrical transverse profile to generate thrust in response to waves on the body of fluid.
2. 2 The vehicle of claim 1, comprising a centre of gravity (802) and an equilibrium centre of buoyancy (804) disposed above centre of gravity (802) by a distance BZ; the centre of gravity defining an origin of a cartesian reference frame with the X-axis being, or being parallel to, the longitudinal, or roll, axis of the vehicle, the Z-axis being, or being parallel to, the transverse, or yaw, axis of the vehicle and the Y-axis being, or being parallel to, a further transverse, or pitch, axis of the vehicle.
3. 3 The vehicle of claim 2, in which the upper hull portion comprises a centre of volume (808) disposed, at equilibrium, above the X-Y plane of the reference frame by a distance UVZ, and longitudinally from the centre of gravity (802) by a distance UVX.
4. 4 The vehicle of any of claims 2 or 3, in which the upper hull portion (404) has a projection onto the X-Y plane of the reference frame such that, at equilibrium, the centroid (810) of the projection is longitudinally offset from the centre of gravity (802) by a distance UCX.
5. The vehicle of any of claims 2 to 4, in which the lower hull portion (406) has a projection onto the X-Y plane such that, at equilibrium, the centroid (816) of the projection is longitudinally offset from the centre of gravity (802) by a distance LCX.
6. 6 The vehicle of any of claims 2 to 5, in which the lower hull portion (406) has a trailing position (818) that, at equilibrium, is offset longitudinally from the centre of gravity by a distance LTX.
7. 7 The vehicle of claim 1 comprising at least one or more than one of the following taken jointly and severally in any and all permutations: a. a centre of gravity (802) and an equilibrium centre of buoyancy (804) disposed above the centre of gravity (802) by a distance BZ; the centre of gravity defining an origin of a cartesian reference frame with the X-axis being, or being parallel to, the longitudinal, or roll, axis of the vehicle, the Z-axis being, or being parallel to, the transverse, or yaw, axis of the vehicle and the Y-axis being, or being parallel to, a further transverse, or pitch, axis of the vehicle; b. a centre of volume (808) of the upper hull portion disposed, at equilibrium, above the X-Y plane of the reference frame by a distance UVZ, and longitudinally from the centre of gravity (802) by a distance UVX; c. an upper hull portion (404) having a projection onto the X-Y plane of the reference frame such that, at equilibrium, the centroid (810) of the projection is longitudinally offset from the centre of gravity (802) by a distance UCX; d. a lower hull portion (406) having a projection onto the X-Y plane such that, at equilibrium, the centroid (816) is longitudinally offset from the centre of gravity (802) by a distance LCX; or e. a trailing position (818) of the lower hull portion (406) that, at equilibrium, is offset longitudinally from the centre of gravity (802) by a distance [TX.
8. 8 The vehicle of any preceding claim, comprising at least one or more than one of the following features taken jointly and severally in any and all permutations: a. the ratio (UTX+ULX)/(LTX+LLX) is less than 1.0, for example, 0.5; b. at least one or more than one of the ratios LLZ/ULZ and LTZ/UTZ, taken jointly and severally in any and all permutations, is less than 1.0, for example, 0.15; c. at least one, or all, of a leading position (806) of the upper hull portion (404), the centre of volume (808) of the upper hull portion (404), the centroid (810) of the projected area of the upper hull portion (404), and a trailing position (812) of the upper hull portion (404), is disposed, at equilibrium, behind a leading position (814) of the lower hull portion (406); d. at least one, or all, of a leading position (806) of the upper hull portion (404), the centre of volume (808) of the upper hull portion (404), the centroid (810) of the projected area of the upper hull portion (404), and a trailing position (812) of the upper hull portion (404), is disposed, at equilibrium, ahead of a trailing position (818) of the lower hull portion (406); e. at least one or more than one of the ratios ULX/UVZ, UVX/UVZ, UCX/UVZ, taken jointly and severally in any and all permutations, is less than 1.0, for example, 0.15; f. the centre of volume (808) of the upper hull portion (404), is disposed, at equilibrium, ahead of the centre of gravity (802).
9. 9. The vehicle of any preceding claim, wherein the upper hull portion comprises a hydrofoil portion having a fine cross-section.
10. 10. The vehicle of claim 9, wherein the cross-section of a hydrofoil portion of the upper hull portion has a thickness between 2% and 30% of the chord of the cross-section, optionally 15%.
11. 11 The vehicle of claim 9 or 10, wherein a hydrofoil portion of the upper hull portion spans a longitudinal or horizontal extent.
12. 12 The vehicle of any preceding claim, wherein the lower hull portion comprises a hydrofoil portion having an aerofoil cross-section, optionally a thin plate cross-section, or an aerofoil cross-section, optionally a NAGA symmetrical aerofoil cross-section.
13. 13. The vehicle of claim 12, wherein the aerofoil cross-section of a hydrofoil portion of the lower hull portion has a thickness between 8% and 30% of the chord of the cross-section, optionally 15%.
14. 14. The vehicle of claim 12 or claim 13, wherein a hydrofoil portion of the lower hull portion spans a longitudinal or horizontal extent.
15. 15. The vehicle of any preceding claim, wherein the hull comprises a hydrofoil portion spanning a vertical extent, said hydrofoil portion having a fine cross-section, optionally a thin plate cross-section, or an aerofoil cross-section, optionally a NAGA symmetrical aerofoil cross-section.
16. 16. The vehicle of claim 15, wherein the cross-section of the hydrofoil portion has a thickness between 2% and 30% of the chord of the cross-section, optionally 15%.
17. 17. The vehicle of any preceding claim, wherein a hydrofoil portion of the hull produces thrust due to wave-induced motion.
18. 18. The vehicle of claim 17, wherein the thrust-producing hydrofoil portion is shaped to experience, in use, a time-varying angle of attack and velocity relative to the surrounding fluid of the body of fluid such that, on average, the hydrofoil portion generates thrust in the direction of travel.
19. 19. The vehicle of claim 17 or claim 18, wherein the thrust-producing hydrofoil portion oscillates relative to the surrounding fluid such that it generates a thrust-producing unsteady wake.
20. 20. The vehicle of any preceding claim, in which the hull defines a duct or conduit forming the concavity with closed shape
21. 21. The vehicle of claim 20, in which the closed shape is an annulus defining the concavity.
22. 22. The vehicle of claim 20 or 21, in which the closed shape is a squircle defining the concavity.
23. 23. The vehicle of any preceding claim, in which the hull defining the concavity defines fluid ingress and fluid egress apertures.
24. 24. The vehicle of any preceding claim, comprising a plurality of modes of operation the plurality of modes of operation comprising at least one or more of a. wave propulsion, b. underwater gliding flight, c. underwater powered flight, or d. aerial gliding flight taken jointly and severally in any and all permutations.
25. 25. The vehicle of any preceding claim in which at least one or more than one of the at least one concavity, the hull, the upper hull portion, the lower hull portion or the asymmetrical transverse profile, taken jointly and severally in any and all permutations, is arranged to add mass when moving in the body of fluid.
26. 26. The vehicle of any preceding claim, in which the asymmetrical transverse profile comprises a trailing edge having a tapering profile.
27. 27. The vehicle of any preceding claim comprising a centre of gravity disposed at a predetermined position along an axis transverse to a longitudinal axis to induce an oscillatory or pendulatory motion about that centre of gravity having a predeterminable period.