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An oscillating foil turbine has a foil having a first fluid dynamic surface for producing lift in a fluid flow, a support for the foil, and a second fluid dynamic surface, wherein the support allows for cyclic motion of the first and second surfaces with respect to each other. A driven member is pro

An oscillating foil turbine has a foil having a first fluid dynamic surface for producing lift in a fluid flow, a support for the foil, and a second fluid dynamic surface, wherein the support allows for cyclic motion of the first and second surfaces with respect to each other. A driven member is provided to tap energy from flow throughout each cycle. Throughout at least part of the cyclic translation, the fluid dynamic surfaces are oriented sufficiently parallel, and separated by a distance that is sufficiently small, to achieve a substantial wing-in-ground effect.

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1. An oscillating foil turbine for tapping fluid kinetic energy from a reversible flow comprising: a first foil having a chord length and a first fluid dynamic surface designed to produce lift, mounted to a support for cyclic oscillation in the flow, with substantial motion in a first direction perp

1. An oscillating foil turbine for tapping fluid kinetic energy from a reversible flow comprising: a first foil having a chord length and a first fluid dynamic surface designed to produce lift, mounted to a support for cyclic oscillation in the flow, with substantial motion in a first direction perpendicular to the flow, the first fluid dynamic surface having first and second sides, and the first foil is a reversible foil equally operable in flows in two opposite directions;a second fluid dynamic surface operating in the flow to produce an effective ground parallel to a direction of the flow and perpendicular to the first direction; anda member coupled directly or indirectly to the first foil, adapted to use the motion in the first direction to perform work,wherein throughout a portion of the cycle the first side of the first fluid dynamic surface is separated from the effective ground by less than about 20% of the chord length, and the effective ground has an extent such that at least 80% of the first foil is projected onto the effective ground in the first direction. 2. The oscillating foil turbine of claim 1 wherein the flow is a reversing marine flow or a wind. 3. The oscillating foil turbine of claim 1 wherein the second fluid dynamic surface is a wall defining the ground, the wall having an extent such that at least 90%, more preferably 95-295%, more preferably 100-150%, and more preferably still about 105-125% of the first foil is projected onto the effective ground in the first direction. 4. The oscillating foil turbine of claim 1 wherein the first foil is a cambered foil, and the first side of the first fluid dynamic surface is a flat side of the first foil. 5. The oscillating foil turbine of claim 1 wherein the support comprises a frame including a pair of slits through which a pair of rigid protrusions disposed at opposite ends of the first foil pass to define a pivot axis of the first foil, the slits and rigid protrusions providing translational or revolute translational joints for coupling the first foil to the pair of slits, the joints substantially preventing the first foil from roll, sway, or yaw motion. 6. The oscillating foil turbine of claim 1 wherein the second fluid dynamic surface is on a second foil moved to operationally provide the effective ground with the first foil, and the first and second fluid dynamic surfaces are both suction surfaces, or both pressurized surfaces of the first and second foils, the first and second foils: being similar in size and contour, moving at the same rates throughout the portion of the cycle; and having similar angles of attack throughout the portion of the cycle, to provide a mirror symmetry between the first and second foils. 7. The oscillating foil turbine of claim 1, further comprising a sidewall extending normal to the pitch axis of the first foil. 8. An oscillating foil turbine for tapping fluid kinetic energy from a flow comprising: a first foil having a chord length and a first fluid dynamic surface designed to produce lift, mounted to a support for cyclic oscillation in the flow, with substantial motion in a first direction perpendicular to the flow, the first fluid dynamic surface having first and second sides, wherein the support comprises a guideway through which rigid protrusions of the foil pass, providing a translational joint for coupling the foil to a frame, the guideway oriented substantially in the first direction;a second fluid dynamic surface operating in the flow to produce an effective ground parallel to a direction of the flow and perpendicular to the first direction; anda member coupled directly or indirectly to the first foil, adapted to use the motion in the first direction to perform work,wherein throughout a portion of the cycle the first side of the first fluid dynamic surface is separated from the effective ground by less than about 20% of the chord length, and the effective ground has an extent such that at least 80% of the first foil is projected onto the effective ground in the first direction. 9. The oscillating foil turbine of claim 8 wherein the work done drives an electrical power generator, or a pump. 10. The oscillating foil turbine of claim 8 wherein the flow is a marine flow or a wind. 11. The oscillating foil turbine of claim 8 wherein the second fluid dynamic surface is a wall defining the ground, the wall having an extent such that at least 90%, more preferably 95-295%, more preferably 100-150%, and more preferably still about 105-125% of the first foil is projected onto the effective ground in the first direction. 12. The oscillating foil turbine of claim 8 wherein the first foil is a cambered foil, and the first side of the first fluid dynamic surface is a flat side of the first foil. 13. The oscillating foil turbine of claim 8 wherein the guideway comprises a pair of slits through which a pair of rigid protrusions disposed at opposite ends of the first foil pass to define a pivot axis of the first foil, the slits and rigid protrusions providing translational or revolute translational joints for coupling the first foil to the pair of slits, the joints substantially preventing the first foil from roll, sway, or yaw motion. 14. The oscillating foil turbine of claim 8, further comprising a sidewall extending normal to the pitch axis of the foil. 15. The oscillating foil turbine of claim 8 wherein the second fluid dynamic surface is on a second foil moved to operationally provide the effective ground with the first foil, and the first and second fluid dynamic surfaces are both suction surfaces, or both pressurized surfaces of the first and second foils, the first and second foils: being similar in size and contour, moving at the same rates throughout the portion of the cycle; and having similar angles of attack throughout the portion of the cycle, to provide a mirror symmetry between the first and second foils. 16. The oscillating foil turbine of claim 15 wherein the first and second foils are both coupled to a frame for controlled variation of angles of attack of the foils during the cycle. 17. The oscillating foil turbine of claim 15 wherein the first and second foils are both coupled to a frame for controlled variation of angles of attack of the foils during the cycle. 18. The oscillating foil turbine of claim 15 wherein the first and second foils are both coupled to a frame by a mechanical controller that controls variation of angles of attack of the foils during the cycle. 19. The oscillating foil turbine of claim 15 wherein each of the first and second foils are coupled to a frame via an axle of a rotary motor embedded in the foil for controlled variation of an angle of attack of the foil during the cycle, the axle meeting a rotationally bearing surface of the frame or of a drive train for grounding the pitching of the foil. 20. The oscillating foil turbine of claim 15 wherein each of the first and second foils are coupled to a frame via an axle of a rotary motor embedded in the foil for controlled variation of an angle of attack of the foil during the cycle, the axle meeting a rotationally bearing surface of the frame or of a drive train for grounding the pitching of the foil, wherein a locking mechanism is set at a fixed angle of attack at a beginning of each stroke and released at the end of each stroke, whereby the rotary motor operates only during pitching intervals between strokes. 21. An oscillating foil turbine for tapping fluid kinetic energy from a flow comprising: a first foil having a chord length and a first fluid dynamic surface designed to produce lift, mounted to a support for cyclic oscillation in the flow, with substantial motion in a first direction perpendicular to the flow, the first fluid dynamic surface having first and second sides;a second fluid dynamic surface operating in the flow to produce an effective ground parallel to a direction of the flow and perpendicular to the first direction; anda reciprocating pushrod extending from the first foil substantially in the first direction and adapted to use the motion in the first direction to perform work,wherein throughout a portion of the cycle the first side of the first fluid dynamic surface is separated from the effective ground by less than about 20% of the chord length, and the effective ground has an extent such that at least 80% of the first foil is projected onto the effective ground in the first direction. 22. The oscillating foil turbine of claim 21 wherein the reciprocating pushrod extending is coupled to a crankshaft for continuous rotation of the crankshaft, and the work is done by the crankshaft. 23. The oscillating foil turbine of claim 21 wherein the work done drives an electrical power generator, or a pump. 24. The oscillating foil turbine of claim 21, further comprising a sidewall extending normal to the pitch axis of the foils. 25. The oscillating foil turbine of claim 21 wherein the flow is a marine flow or a wind. 26. The oscillating foil turbine of claim 21 wherein the second fluid dynamic surface is a wall defining the ground, the wall having an extent such that at least 90%, more preferably 95-295%, more preferably 100-150%, and more preferably still about 105-125% of the first foil is projected onto the effective ground in the first direction. 27. The oscillating foil turbine of claim 21 wherein the first foil is a cambered foil, and the first side of the first fluid dynamic surface is a flat side of the first foil. 28. The oscillating foil turbine of claim 21 wherein the guideway comprises a pair of slits through which a pair of rigid protrusions disposed at opposite ends of the first foil pass to define a pivot axis of the first foil, the slits and rigid protrusions providing translational or revolute translational joints for coupling the first foil to the pair of slits, the joints substantially preventing the first foil from roll, sway, or yaw motion. 29. The oscillating foil turbine of claim 21 wherein the second fluid dynamic surface is on a second foil moved to operationally provide the effective ground with the first foil, and the first and second fluid dynamic surfaces are both suction surfaces, or both pressurized surfaces of the first and second foils, the first and second foils: being similar in size and contour, moving at the same rates throughout the portion of the cycle; and having similar angles of attack throughout the portion of the cycle, to provide a mirror symmetry between the first and second foils. 30. The oscillating foil turbine of claim 29 wherein the first and second foils are both coupled to a frame for controlled variation of angles of attack of the foils during the cycle. 31. The oscillating foil turbine of claim 29 wherein the first and second foils are both coupled to a frame for controlled variation of angles of attack of the foils during the cycle. 32. The oscillating foil turbine of claim 29 wherein the first and second foils are both coupled to a frame by a mechanical controller that controls variation of angles of attack of the foils during the cycle.