WO2008144938A1

WO2008144938A1 - Mechanism for the control of an oscillating wing

Info

Publication number: WO2008144938A1
Application number: PCT/CA2008/001054
Authority: WO
Inventors: Guy Dumas; Clément GOSSELIN; Louis-Alexis Allen-Demers; Jean Lemay; Jean Ruel
Original assignee: Universite Laval
Current assignee: Universite Laval
Priority date: 2007-05-30
Filing date: 2008-05-30
Publication date: 2008-12-04
Anticipated expiration: 2009-11-30

Abstract

An oscillating-wing mechanism comprises two oscillating wings. A heaving sub-mechanism has an arm being pivotally connected at a central portion to a base with the oscillating wings being connected at opposed ends of the arm by rotational joints. The heaving sub-mechanism has constraining members between the base and the arm to constrain the arm to an oscillating motion in which the oscillating wings move along a heaving degree of freedom. A pitching sub-mechanism is connected between the rotational joints and the base to constrain the oscillating wings to a pitching degree of freedom. Actuators are provided on the base and connected to the heaving sub-mechanism and the pitching sub-mechanism to control the pitching and heaving degrees of freedom. The oscillating-wing mechanism is used to extract power from a fluid flow or to produce propulsive forces.

Description

MECHANISM FOR THE CONTROL OF AN OSCILLATING WING

CROSS-REFERENCE TO RELATED APPLICATION

The present patent application claims priority on United States Provisional Patent Application No. 60/940,825, filed on May 30, 2007.

BACKGROUND OF THE APPLICATION

1. Field of the Application

The present application relates to oscillating-wing systems, and more particularly to mechanisms supporting oscillating wings to extract power from a fluid flow, or to produce propulsive forces from the fluid flow.

2. Background Art In order to produce more green energy, a steadily increasing number of wind turbines are being installed. Unfortunately, they radically change the landscape and are quite noisy. One promising concept could change this situation, since it relies on the use of oscillating wings simultaneously heaving and pitching below water as power extraction devices, as set forth by Kinsey, T., and Dumas, G. ("Parametric study of an oscillating airfoil in power extraction regime, " 24^th AIAA Applied Aerodynamics Conference, 2006) . An oscillating wing is defined as an airfoil experiencing simultaneous pitching θ(t) and heaving h(t) motions as shown in Fig. 1. Referring to a pitching axis located on a chord line at position x_p from the leading edge, the airfoil motion may be expressed as in: θ(t) = 0₀ sin (γf) h(t) = H₀ sin (yt + φ) where θo and Ho are respectively the pitching and heaving amplitudes, γ the angular frequency (=2πf) and φ the phase difference between the two motions. The free stream velocity far upstream of the oscillating airfoil, U_∞, is also indicated in Fig. 1.

Results of suitable efficiency have been reached for a pitch amplitude, θo, of 76.3° and for a heaving amplitude of one chord, H₀=C, where c stands for the length of the^' airfoil (Fig. 1), for symmetric airfoils with φ kept constant at 90°. It is desirable to find a mechanism that can guide an oscillating wing in producing this kind of motion while, at the same time, transmitting the kinetic energy of the wing to an alternator/power generator with efficiency.

SUMMARY OF THE APPLICATION

It is therefore an aim of the present application to provide a novel mechanism for controlling motion of an oscillating wing that addresses issues associated with the prior art. Therefore, in accordance with a first embodiment of the present application, there is provided an oscillating-wing mechanism comprising: at least two oscillating wings adapted to be positioned in a fluid flow; a heaving sub-mechanism having an arm being pivotally connected at a central portion to a base with the oscillating wings being connected at opposed ends of the arm by rotational joints, the heaving sub-mechanism having constraining members between the base and the arm to constrain the arm to an oscillating motion in which the oscillating wings move along a heaving degree of freedom; a pitching sub-mechanism connected between said rotational joints and the base to constrain the oscillating wings to a pitching degree of freedom; and at least one actuator on the base and connected to the heaving sub-mechanism and the pitching sub-mechanism to control the pitching and heaving degrees of freedom.

Further in accordance with the first embodiment of the present application, the heaving sub- mechanism and the pitching sub-mechanism are connected so as to couple the pitching degree of freedom and the heaving degree of freedom in a single degree of freedom.

Still further in accordance with the first embodiment of the present application, one said actuator is connected to the single degree of freedom.

Still further in accordance with the first embodiment of the present application, the constraining members of the heaving sub-mechanism are a link interconnected by a revolute joint to a crank, the link and the crank being respectively connected to the arm by a revolute joint and to the base.

Still further in accordance with the first embodiment of the present application, the pitching sub- mechanism has a beveled wherein the pitching sub- mechanism has a beveled gear transmission connecting the rotational joints of the oscillating wings to the base to control the pitching degree of freedom.

Still further in accordance with the first embodiment of the present application, a gear and link sequence couple the beveled gear transmission to the crank so as to couple the pitching degree of freedom and the heaving degree of freedom in a single degree of freedom.

Still further in accordance with the first embodiment of the present application, the pitching sub- mechanism has a gear transmission connecting the rotational joints of the oscillating wings to the base to control the pitching degree of freedom.

Still further in accordance with the first embodiment of the present application, the gear transmission has at least one shaft within the arm, with beveled gears at the ends of the at least one shaft meshing with beveled gears at the rotational joints and at the base to couple the oscillating wings in a single rotational input/output at^' the base. Still further in accordance with the first embodiment of the present application, an oscillation axis of the arm on the base and an axis for the single rotational input/output at the base are coincident.

Still further in accordance with the first embodiment of the present application, the base is a post supporting the heaving sub-mechanism and the pitching sub-mechanism.

Still further in accordance with the first embodiment of the present application, an alternator is provided for each said actuator to extract energy from fluid flow forces on the oscillating wings.

In accordance with a second embodiment of the present application, there is provided an oscillating- wing mechanism comprising: at least one oscillating wing adapted to be positioned in a fluid flow; a mechanism having at least a pair of parallel sequences of links and revolute joints, the mechanism being between a base and the at least one oscillating wing and constraining motion of the at least one oscillating wing to a pitching degree of freedom and a heaving degree of freedom; and at least one actuator on the base and associated with the' mechanism to control the pitching and heaving degrees of freedom.

Further in accordance with the second embodiment of the present application, the parallel sequences constrain the motion of the oscillating wing to the heaving degree of freedom, and wherein the mechanism has a sub-mechanism constraining the motion of the oscillating wing to the pitching degree of freedom. Still further in accordance with the second embodiment of the present application, the sub-mechanism is any one of a pulleys and belt transmission, a gears and chain transmission, and a parallelogram linkage.

Still further in accordance with the second embodiment of the present application, the parallel sequences constrain the oscillating to motion in the heaving degree of freedom and the pitching degree of freedom.

Still further in accordance with the second embodiment of the present application, coupling means are associated with said mechanism so as to couple the pitching degree of freedom and the heaving degree of freedom in a single degree of freedom.

Still further in accordance with the second embodiment of the present application, an alternator is provided for each said actuator to extract energy from fluid flow forces on the at least one oscillating wing.

BRIEF DESCRIPTION OF. DRAWINGS

Fig. 1 is a schematic view of pitching and heaving motions of an oscillating wing; Fig. 2 is a schematic view of an oscillating- wing mechanism in accordance with a preferred embodiment of the present application, with actuation of heaving and pitching decoupled;

Fig. 3 is a schematic view of a simplified configuration of the oscillating-wing mechanism of Fig. 2;

Fig. 4 is a schematic representation of the architecture of the oscillating-wing mechanism of Fig. 3; Fig. 5 is schematic view of an oscillating- wing mechanism in accordance with another embodiment of the present invention, with actuation of heaving and pitching coupled; Fig. 6 is a schematic view of a simplified configuration of the oscillating-wing mechanism of Fig. 5;

Fig. 7 is a schematic representation of the architecture of the oscillating-wing mechanism of Fig. 6; and

Fig. 8 is the schematic representation of the architecture of Fig. 7, with additional information;

Fig. 9 is a schematic perspective view of an oscillating-wing mechanism in accordance with another preferred embodiment of the present application, with the DOFs coupled; and

Fig. 10 is another schematic perspective view of the oscillating-wing mechanism of Fig. 9.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring now to the drawings, and more particularly to Fig. 2, an oscillating-wing mechanism in accordance with a first embodiment is generally shown at 10. The mechanism 10 has a parallel sub-mechanism 12 supporting an oscillating wing 14 so as to extract power from a fluid flow by controlling the pitching and heaving of the wing 14, as described previously, or to produce propulsive forces from the fluid flow, amongst numerous other possibilities. The parallel sub-mechanism 12 constrains the wing 14 to movement along a heaving degree of freedom (DOF) (Fig. 1) .

In the embodiment of Fig. 1, the parallel sub- mechanism 12 has links 20, 21 and 22 forming a parallelogram linkage. Links 20 and 21 are respectively connected to a base by revolute joints 2OA and 2IA, and to link 22 by revolute joints 2OB and 21B. Link 22 extends beyond the intersection with link 20 and has its end connected to the wing 14 by revolute joint 22A. Links 23 and 24 form a two- link sub-mechanism that is operatively connected to the revolute joint 21B of the parallelogram linkage. Link 23 is connected to the base by revolute joint 23A, and is connected to the link 24 by revolute joint 23B. Link 24 is operatively connected to the revolute joint 2IB.

In a preferred embodiment, a degree of actuation is provided at the base to actuate a rotation of the link 23 about the revolute joint 23A. The rotational actuation of the link 23 results in the decoupled movement of the wing 14 in the heaving DOF and, likewise, heaving forces resulting from the effect of the fluid flow on the wing 14 are used to actuate a power generator associated with the revolute joint 23A. In order to control the pitching motion of the oscillating wing 14, pulleys 25 and 26 are respectively provided on the joints 2OA and 2OB, but rotate independently from the joints 2OA and 2OB, so as to form a pitching sub-mechanism. A link 27 is connected at a first end to the pulley 26 by revolute joint 26A. The link 27 is connected at a second end to the wing 14 by revolute joint 27A. The pulley 26, the links 22 and 27 and the wing 14 form a parallelogram linkage.

Belt 28 interconnects the pulleys 25 and 26, whereby motion is transmitted between the pulleys 25 and 26. Although a belt and pulley assembly is shown in Fig. 2, it is considered to use a chain and gear assembly or equivalent. The axes of all revolute joints described above for the parallel mechanism 12 are parallel to one another.

In a preferred embodiment, a degree of actuation is provided at the base to actuate a rotation of the pulley 25 -about its axis. The rotational actuation of the pulley 25 results in the decoupled movement of the wing 14 in the pitching DOF and, likewise, pitching forces resulting from the effect of the fluid flow on the wing 14 are used to actuate a power generator associated with the pulley 25.

For clarity purposes, base is used herein to define the ground or a structure supporting the oscillating-wing mechanism. The base is immovable with respect to the embodiments of the oscillating-wing mechanism.

Referring to Fig. 3, a simplified version of the oscillating-wing mechanism 10 of Fig. 2 is illustrated as 10'. The oscillating-wing mechanism 10' has an architecture equivalent to that of the oscillating-wing mechanism 10 of Fig. 2, whereby the following input-output equations apply to both mechanisms 10 and 10' . In the parallel sub-mechanism 12, input θ₂ is placed coaxially with D, the third fixed joint 2OA. By doing so, a parallelogram is obtained to direct the angle θ, so the latter is now equal to θ₂.

Referring concurrently to Figs. 3 and 4, one obtains the following input-output equations:

Λ cosøi + # sin0! = C where :

A = 2a (XQ + c cosφ) B = 2a (yo + c sinφ) C = x²o + y² ₀ + a² - b² + c²

+2c (xo cosφ + yo sinφ)

Since this sub-mechanism 12 decouples the pitching and the heaving, the angular position of the oscillating wing is now equal to the second input: θ = θ₂

Referring to Fig. 5, an oscillating-wing mechanism in accordance with an alternative embodiment is generally shown at 30. The mechanism 30 is similar to the oscillating-wing mechanism 10, whereby like elements will bear like reference numerals. The mechanism 30 has a parallel mechanism 12' and the wing 14.

The parallel sub-mechanism 12' is similar to the parallel sub-mechanism 12 of Fig. 2, in that links 20, 21, 22, 23 and 24 are arranged in a similar manner. On the other hand, the pitching-control assembly of the parallel sub-mechanism 12 (pulleys 25 and 26) has been replaced by additional linkages. More specifically, the wing 14 is pivotally connected to link 27' by revolute joint 27A. The link 27' is connected to the base by a pair of links, namely links 31 and 32. Link 31 is pivotally connected to the base by revolute joint 3IA, and is connected to link 32 by revolute joint 31B. Link 32 is pivotally connected to the link 27' by revolute joint 32A.

A link 33 is pivotally connected between the links 22 and 27' via revolute joints 21B and 32A, and therefore forms a parallelogram linkage. In order to control the heaving and pitching motion of the oscillating wing 14, the link 23 and the link 31 each have a degree of actuation provided at the base to actuate their rotations about the revolute joint 23A and the revolute joint 3IA, respectively. The coupled rotational actuations of the links 23 and 31 result in the movement of the wing 14 in the heaving DOF and/or pitching DOF. Likewise, heaving and pitching forces resulting from the effect of the fluid flow on the wing 14 may be used to actuate a power generator associated with the revolute joints 23A and/or 31A.

Referring to Figs. 6 to 8, a simplified version of the oscillating-wing mechanism 30 of Fig. 5 is illustrated as 30'. The oscillating-wing mechanism 30' has an architecture equivalent to that of the oscillating-wing mechanism 30 of Fig. 5, whereby the following input-output equations apply to both mechanisms 30 and 30 ' .

Ref erring to Figs . 6 and 7 , one obtains the following input - output equations : A_\ cosøi

C\ where :

A\ = 2αi(xo + c cosφ)

+2c (x₀ cosφ + y₀ sinφ) and

A₂ cos0₂ + B₂ sin0₂ = C₂ where :

A₂ = 2a₂(xo - X₂ + c cosφ + d cosø) B₂ = 2a₂ (yo -y₂ + c smφ + d sinθ)

C₁ = (X₀ - X₂)² +Oo - _y₂)² + α² ₂ - ό² ₂ +c² +d² + 2c ((X₀ - x₂) cosφ + yo - y₂) sinφ) + 2d ((X₀ - X₂) + c cosφ) cosø

The above equations can readily be used to solve for the input coordinates G₁ and θ₂ for given values of the input variables .

To find the dynamic relations of the mechanism 30' to obtain the moment acting at the inputs, the approach based on the principle of virtual work (Wang, J., and Gosselin, CM., "A new approach for the dynamic analysis of parallel manipulators," Multibody System Dynamics, 2, pp. 317-334, 1998) is used: riδøi + τ₂δ0₂ = Miδøi + M₂δ0₂ + M₃δ,8i + M₄δβ₂ + M₅δφ + M₆Θ + Mδθ +/iδ, +/₂δ₂

+fsδ+f₄δ₄ +f₅δ₅ +f_(>δ₆ + Fδc

Using two simple cases, (δ0i = 1, δ0₂ = 0) and (δ0i = 0, δ0₂=l), the torque at the inputs become: Ti = Mi + M₃δβι + M₄δβ₂ + M5δφ + M₆δθ + Mδθ

+/,δi +/₃δ₃ +/₄δ₄ +/₅δ₅ +/₆δ₆ + Fδc T₂ = M₂ + M₄δβ₂ + M₆δθ + Mδθ +f₂δ₂ +/₄δ₄ +/₆δ₆

Where inf initesimal displacements of the bars may be found from Fig . 8 as :

δχ = δθ_xEr _x δ₂ = δθ₂E?₂ δ₃ = δθιEl ι+ δβιEr ₃ δ₄ = δθ₂El ₂+ δβ₂Er₄

δ(, = δφEΪ₅+ δθEr ₆ δc = δφEl ₅

As we only have the angular displacement δθ_\ and δ0₂, we can differentiate the input and output equations to obtain relations between the different angular displacements .

—b_x sinβ, c sinφ a_x sin θ, δθ,

— b_x cosβ, c cosφ δβ a_x cos θ, δθ, -ό₂ sinβ₂ t/ sinθ δβ₂ a₂ sin θ₂δθ, - csinφδφ -b₂ cosβ₂ d cosθ δθ a₂ cosθ₂δθ₂ -ccosφδφ

In order to be able to be able to determine the dynamic equations governing the mechanism of Fig. 5, we must describe mathematically the forces and moments acting at the centre of mass of each frame. Initially, the formula that will be used to calculate the forces is: f,= In₁Ci₁ + m, g

Then, it is necessary that the inertia tensor of each moving body be known . cosθ, -sinθ₍ 0

/o, = QJ₁Q ₁ with Q₁ sinθ, cosθ, 0

0 0 1

, I²,

Assuming that all the bars are cylindrical, the inertia tensor takes the form shown previously.

0

M₁ = -I₀, ^• ώ, - ω, X (I₀₁ ^■ ωj = 0

.

Using these equations, one may obtain the torque produced at the inputs as a function of the inertia of the links and the forces and moment acting on the wing. The power produced by each of these input- output may then be obtained by multiplying their angular velocity by the moment acting on them or needed by them. The total power virtually extracted is then the sum of the two curves .

Both mechanism 10 and 30 provide two DOFs, namely pitching and heaving. This feature allows better control of the oscillating wing 14, for instance to modify its trajectory.

As the oscillating-wing mechanisms 10 and 30 may be used as power generators, the mechanisms 10 and 30 advantageously have the actuators/alternators on the base/ground. This will also reduce the inertia of the mechanisms, for instance to stop the oscillating wing 14 at the end of a course and to accelerate the wing 14 in the other direction. This will allow the amount of energy used in controlling the movement of the oscillating wing 14 to be reduced, so as to increase the efficiency of the mechanism 10 and 30 in generating power.

Other configurations are considered, such as serial cable mechanisms, parallel cable mechanisms and the like. Moreover, although the wing 14 is symmetrical, asymmetrical wings could be used as well with the mechanisms 12 and 12' .

Referring to Figs. 9 and 10, an oscillating- wing mechanism in accordance with another embodiment is generally shown at 50. The oscillating-wing mechanism

50 is mounted to a post 51 that serves as the base, and has a heaving sub-mechanism 52 that supports a pair of oscillating wings 54.

The heaving sub-mechanism 52 has an arm 60 pivotally mounted to the post 51 at a central portion, with one of the wings 54 being mounted at each end with a rotational joint. The heaving sub-mechanism 52 is described hereinafter.

A pitching sub-mechanism is provided to constrain the motion of the oscillating wings 54 to a pitching degree of freedom. The pitching sub-mechanism is described hereinafter.

In the illustrated embodiment, a gear and link sequence is provided to couple the heaving sub-mechanism 52 to the pitching sub-mechanism, such that the oscillating-wing mechanism 50 may be controlled by a single degree of freedom. The gear and link sequence has links 61 (i.e., a crank), 62 and 63 interconnected by revolute joints. More specifically, the link 61 is mounted to the post 51 by joint 61A, whereas the links

61 and 62 are interconnected by joint 61B. The links 62 and 63 are interconnected by joint 62A.

The link 63 has a gear portion 63A distally positioned from the joint 62A and interconnected with the link 62. The link 63 is pivotally mounted to the post 51 by joint 63B. The gear portion 63A is therefore rotatable about its axis of rotation with respect to the post 51, while being constrained by the link assembly of links 61, 62 and 63. Actuation of the gear and link sequence through the rotation of the link 61 causes an oscillating motion of the gear portion 63A.

The pitching sub-mechanism has gear 64 that is operatively engaged with the gear portion 63A.

Moreover, by a transmission of beveled gears and shafts

(as partially seen in Fig. 9) or by a set of cables and pulleys, the gear 64 is connected to both oscillating wings 54. Accordingly, there is transmission of movements between the gear 64 and the oscillating wings 54, whether it is to control the pitching of the wings 54, or to extract energy from the fluid exerting forces on the wings 54.

The heaving sub-mechanism 52 has constraining members constraining the arm 60 to an oscillating motion. The constraining members feature a wheel 65 (or crank) that is rotatably mounted to the post 61. The wheel 65 is coaxially positioned with the link 61. The wheel 65 acts as a crank for link 66, with link 66 being connected to the wheel 65 by revolute joint 65A, and to the arm 60 by revolute joint 66A, via extension 67 of the arm 60. Therefore, rotation of the wheel 65 results in an oscillating motion of the arm 60, thereby constraining the oscillating wings 54 to the heaving degree of freedom. Other configurations are considered for the constraining' members .

In order to relate the heaving sub-mechanism 52 and the pitching sub-mechanism, the link 61 and the wheel 65, namely the cranks, are coupled and therefore rotate together, thereby causing motion and/or acceleration in the pitching and heaving DOFs. Accordingly, by associating an actuator/alternator to the wheel 65, the pitching and heaving of the wings 54 are controlled simultaneously as one DOF. Moreover, the fluid flow energy collected through the wings 54 generates power through a single location, for instance at the wheel 65. It is however considered to separate the two DOFs of the oscillating-wing mechanism 50 so as to control each separately.

Claims

CLAIMS :

1. An oscillating-wing mechanism comprising: at least two oscillating wings adapted to be positioned in a fluid flow; a heaving sub-mechanism having an arm being pivotally connected at a central portion to a base with the oscillating wings being connected at opposed ends of the arm by rotational joints, the heaving sub-mechanism having constraining members between the base and the arm to constrain the arm to an oscillating motion in which the oscillating wings move along a heaving degree of freedom; a pitching sub-mechanism connected between said rotational joints and the base to constrain the oscillating wings to a pitching degree of freedom; and at least one actuator on the base and connected to the heaving sub-mechanism and the pitching sub-mechanism to control the pitching and heaving degrees of freedom.

2. The oscillating-wing mechanism according to claim 1, wherein the heaving sub-mechanism and the pitching sub-mechanism are connected so as to couple the pitching degree of freedom and the heaving degree of freedom in a single degree of freedom.

3. The oscillating-wing mechanism according to claim 2, comprising one of said actuator, with said actuator being connected to the single degree of freedom.

4. The oscillating-wing mechanism according to claim 1, wherein the constraining members of the heaving sub-mechanism are a link interconnected by a revolute joint to a crank, the link and the crank being respectively connected to the arm by a revolute joint and to the base .

5. The oscillating-wing mechanism according to claim 4, wherein the pitching sub-mechanism has a beveled gear transmission connecting the rotational joints of the oscillating wings to the base to control the pitching degree of freedom.

6. The oscillating-wing mechanism according to claim 5, further comprising a gear and link sequence coupling the beveled gear transmission to the crank so as to couple the pitching degree of freedom and the heaving degree of freedom in a single degree of freedom.

7. The oscillating-wing mechanism according to claim 1, wherein the pitching sub-mechanism has a gear transmission connecting the rotational joints of the oscillating wings to the base to control the pitching degree of freedom.

8. The oscillating-wing mechanism according to claim 7, wherein the gear transmission has at least one shaft within the arm, with beveled gears at the ends of the at least one shaft meshing with beveled gears at the rotational joints and at the base to couple the oscillating wings in a single rotational input/output at the base .

9. The oscillating-wing mechanism according to claim 8, wherein an oscillation axis of the arm on the base and an axis for the single rotational input/output at the base are coincident.

10. The osciliating-wing mechanism according to claim 1, wherein the base is a post supporting the heaving sub-mechanism and the pitching sub-mechanism.

11. The oscillating-wing mechanism according to any one of claims 1 to 10, further comprising an alternator for each said actuator to extract energy from fluid flow forces on the oscillating wings.

12. An oscillating-wing mechanism comprising: at least one oscillating wing adapted to be positioned in a fluid flow; a mechanism having at least a pair of parallel sequences of links and revolute joints, the mechanism being between a base and the at least one oscillating wing and constraining motion of the at least one oscillating wing to a pitching degree of freedom and a heaving degree of freedom; and at least one actuator on the base and associated with the mechanism to control the pitching and heaving degrees of freedom.

13. The oscillating-wing mechanism according to claim 12, wherein said parallel sequences constrain the motion of the oscillating wing to the heaving degree of freedom, and wherein the mechanism has a sub-mechanism constraining the motion of the oscillating wing to the pitching degree of freedom.

14. The oscillating-wing mechanism according to claim 13, wherein the sub-mechanism is any one of a pulleys and belt transmission, a gears and chain transmission, and a parallelogram linkage.

15. The oscillating-wing mechanism according to claim 12, wherein said parallel sequences constrain the oscillating to motion in the heaving degree of freedom and the pitching degree of freedom.

16. The oscillating-wing mechanism according to claim 12, further comprising coupling means associated with said mechanism so as to couple the pitching degree of freedom and the heaving degree of freedom in a single degree of freedom.

17. The oscillating-wing mechanism according to any one of claims 12 to 16, further comprising an alternator for each said actuator to extract energy from fluid flow forces on the at least one oscillating wing.