Note: Descriptions are shown in the official language in which they were submitted.
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OSCILLATING HYDROFOIL, TURBINE, PROPULSIVE SYSTEM AND METHOD
FOR TRANSMITTING ENERGY
FIELD OF THE INVENTION
The present invention relates to the field of turbines and more specifically
concerns turbines with oscillating foils.
BACKGROUND OF THE INVENTION
The prospect of harvesting water flow energy with hydrokinetic turbines is
becoming more attractive than ever among renewable forms of energy, due to the
high energy density of flowing water, to its predictability with both tidal
and river
applications, and the minimal environmental and human impact.
Known to the Applicant are the following publications and patent documents:
[1] The European Marine Energy Centre Ltd (EMEC), (2010):
http://www.emec.org.uk/tidal_devices.asp
[2] Bernitsas, M., Raghavan, K., Ben-Simon, Y., and E.M.H., G., (2008). VIVACE
(Vortex Induced Vibration Aquatic Clean Energy): A new concept in the
generation
of clean and renewable energy from fluid flow. ASME Journal of Offshore
Mechanics and Arctic Engineering, 130(4), November, p. 041101.
[3] Bernitsas, M., Ben-Simon, Y., Raghavan, K., and E.M.H., G., (2009). The
VIVACE Converter: Model tests at high damping and Reynolds number around
105. ASME Journal of Offshore Mechanics and Arctic Engineering, 131(1),
February, p. 011102.
[4] Jones, K., Lindsey, K., and Platzer, M. (2003). An investigation of the
fluid-
structure interaction in an oscillating wing micro-hydropower generator. Fluid
Structure Interaction II, Chakrabarti, Brebbia, Almorza, and Gonzalez-Palma,
eds.
WIT Press, Southampton, UK, pp. 73-82.
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[5] Kinsey, T. and Dumas, G. (2010). Testing and Analysis of an Oscillating
Hydrofoils Turbine Concept. ASME 2010 3rd Joint US-European Fluids
Engineering Summer Meeting, Paper FEDSMICNMM2010-30869, Montreal,
Canada
[6] Kinsey, T. and Dumas, G. (2008). Parametric Study of an Oscillating
Airfoil in a
Power-Extraction Regime. AIM Journal , 46 (6), pp. 1318-1330
[7] McKinney, W. and DeLaurier, J. (1981). The Wingmill: An Oscillating-Wing
Windmill. Journal of Energy, Vol. 5, No. 2, pp. 109-115
[8] Pulse Tidal Limited, (2010): http://www.pulsegeneration.co.uk.
io [9] The Engineering Business Limited, (2002). Research and development
of a
150 kw tidal stream generator. Tech. rep., Crown Copyright.
[10] The Engineering Business Limited, (2003). Stingray tidal energy device -
phase 2. Tech. rep., The Engineering Business Limited.
[11] The Engineering Business Limited, (2005). Stingray tidal energy device -
is phase 3. Tech.rep., Crown Copyright.
[12] Anderson, J. M. et al., (1998). Oscillating Foils of High Propulsive
Efficiency.
Journal of Fluid Mechanics, Vol. 360, Apr. 1998, pp. 41-72.
doi:10.1017/S0022112097008392
[13] Dumas, G. (2010). HAO-Laval: Le projet d'hydrolienne 5 ailes oscillantes.
20 Journal de l'AQME, septembre 2010, Vol.25 (3), pp. 8-10.
[14] Kinsey, T., Dumas, G., Lalande, G., Ruel, J., Mehut, A., Viarouge, P.,
Lemay,
J. and Jean, Y. (2011). Prototype Testing of a Hydrokinetic Turbine Based on
Oscillating Hydrofoils. Renewable Energy, 36 (6), pp. 1710-1718.
Also known to the Applicant are these related patents:
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US 7,493,759 B2 2/2009 Bernitsas et al. (VIVACE); WO 2004110859A1 6/2004
Lambert-Bolduc (tolo); WO 2005108781A1 5/2005 Paish (Pulse Tidal); US
20060275109 Al 12/2006 Paish (Pulse Tidal); WO 2008053167A1 5/2008 Paish
(Pulse Tidal); WO 2010015821A2 2/2010 Paish (Pulse Tidal); WO 2008144938A1
Referring to FIG.1, the use of oscillating rectangular lifting surfaces 10a,
10b,
referred to as hydrofoils, where the pitching and heaving motions of the
hydrofoils
are perpendicular to the flow, is advantageous and has been shown to be as
io efficient as rotating blades turbines, especially when compared to
horizontal axis
rotor blades 12, such as the ones used in most modern wind turbines.
When submitted to a fluid flow, an oscillating foil undergoes a combined
sinusoidal, or quasi-sinusoidal, heave-pitch motion. It is known that the
efficiency
of a turbine is improved when the heaving, or translational, motion is leading
the
15 pitching, or angular motion.
With reference to FIGs. 2A to 2C, an implementation of a hydrokinetic turbine
14
based on oscillating hydrofoils 10 is shown. The cyclical heaving motion of a
pair
of tandem foils 10 is transformed and transmitted to a rotating shaft 16,
using long
aluminum rods 18a connected to crankshafts 20a. The pitching motion of the
foils
20 10 is coupled to their heaving motion into a one degree-of-freedom
system by the
use of chains and sprockets driven by an additional set of rods 18b and
crankshafts 20b connected to the rotating shaft 16.
Although functional, this implementation has some drawbacks. One of them
comes from the use of the elongated rods 18a, 18b oscillating into the flowing
25 water which causes a loss of energy. Another drawback is that the
hydrodynamic
forces on the rods generate vibrations which contribute to premature wear of
the
bearings. Also, the phase difference between the oscillating motions of both
hydrofoils is 180 . This means that they reach their zero-production points,
at top
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and bottom positions, at the same time, which results in an undesirable
fluctuating
power output.
There is therefore a need to transmit energy from a fluid flow with increased
efficiency. It would also be desirable to provide a transmission system or
method
which limits mechanical losses, improves robustness and resistance to wear,
and
evens out the output power curve.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a turbine, a propulsive
system, a
method or a hydrofoil addressing at least one of the above-mentioned needs.
According to a first aspect of the invention, a turbine is provided. The
turbine is for
converting kinetic energy from a fluid flow into mechanical energy by driving
a
rotatable shaft.
The turbine comprises a support structure, first and second hydrofoils, a
heaving-
to-pitching assembly and a linear-to-rotary transmission system.
The first and second hydrofoils extend from the support structure, each
hydrofoil
being slidably and rotatably connected to the structure, to allow each of the
hydrofoils to move linearly in a heaving motion and to oscillate about a
spanwise
axis in a pitching motion.
The heaving and pitching motions are quasi-sinusoidal, wherein for a given one
of
the hydrofoils, the heaving and pitching motions are out of phase by a pitch-
heave
motion phase, and wherein the respective heaving motions of the first and
second
hydrofoils are out of phase by an inter-hydrofoil phase.
The heaving-to-pitching assembly is for coupling the heaving motions of the
first
and second hydrofoils to the pitching motions of the second and first
hydrofoils
respectively, the pitch-heave motion phase being substantially equal to the
inter-
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hydrofoil phase, the heaving motion of one of the hydrofoils thereby drives
the
pitching motion of the other hydrofoil.
The linear-to-rotary transmission system is operatively connected to the first
and
second hydrofoils and to the rotatable shaft. The heaving motions of the first
and
5 second hydrofoils therefore drive a rotational motion of the shaft.
According to another aspect of the invention, there is provided a method for
converting kinetic energy from a fluid flow into mechanical energy. The method
comprises the steps of:
a) providing a turbine including first and second hydrofoils, each of the
hydrofoils being able to move linearly in a heaving motion, and being able
to oscillate about a spanwise axis in a pitching motion. The heaving and
pitching motions are quasi-sinusoidal, wherein :
¨ for a given one of the hydrofoils, the heaving and pitching motions are
out of phase by a pitch-heave motion phase, and
- the respective heaving motions of the first and second hydrofoils are out
of phase by an inter-hydrofoil phase;
b) coupling the heaving motions of the first and second hydrofoils to the
pitching motions of the second and first hydrofoils respectively, with the
pitch-heave motion phase being substantially equal to the inter-hydrofoil
phase, the heaving motion of one of the hydrofoils thereby driving the
pitching motion of the other hydrofoil; and
c) transforming the heaving motions of the hydrofoils into a rotational
movement of a rotatable shaft, with linear-to-rotary transmission means.
According to yet another aspect of the invention, there is provided a
propulsive
system for transmitting mechanical energy from a rotatable driving shaft. The
system comprises a support structure, first and second hydrofoils, a heaving-
to-
pitching assembly and a rotary-to-linear transmission system.
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The first and second hydrofoils extend from the support structure, each
hydrofoil
being slidably and rotatably connected to the structure, to allow each of the
hydrofoils to move linearly in a heaving motion, and to oscillate about a
spanwise
axis in a pitching motion. The heaving and pitching motions are quasi-
sinusoidal,
whereby for a given one of the hydrofoils, the heaving and pitching motions
are out
of phase by a pitch-heave motion phase, and the respective heaving motions of
the first and second hydrofoils are out of phase by an inter-hydrofoil phase.
The heaving-to-pitching assembly is for coupling the heaving motions of the
first
and second hydrofoils to the pitching motions of the second and first
hydrofoils
respectively. The pitch-heave motion phase being substantially equal to the
inter-
hydrofoil phase, the heaving motion of one of the hydrofoils thereby drives
the
pitching motion of the other hydrofoil.
The rotary-to-linear transmission system is operatively connected to the
rotatable
shaft and to the first and second hydrofoils, the rotational motion of the
driving
shaft thereby driving the heaving and pitching motions of the hydrofoil.
Yet another aspect of the invention concerns a hydrofoil. The hydrofoil
comprises
a pair of foils extending in parallel, the foils being connected via rigid
links.
Other features and advantages of the present invention will be better
understood
upon a reading of the preferred embodiments thereof with reference to the
appended drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a schematic view of two oscillating hydrofoils and a turbine with
a
horizontal axis rotor blade (PRIOR ART).
Figures 2A, 2B and 2C are perspective side views of a turbine shown in three
different positions, respectively (PRIOR ART).
Figure 3 is a side perspective view of a turbine according to a preferred
embodiment of the invention.
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Figure 4 is a side perspective view of a turbine according to another
preferred
embodiment of the invention.
Figure 5 is a side perspective view of a turbine according to yet another
preferred
embodiment of the invention. Figure 5A is a front view of the hydrofoil of
Figure 5,
according to an embodiment of the invention. Figure 5B is a side view of the
hydrofoil of Figure 5.
Figure 6A is a schematic view of a heaving-to-pitching assembly in combination
with hydrofoils. Figure 6B is a graph representing the pitching and heaving
motions of the hydrofoils of Figure 6A.
Figure 7 is a schematic view of part of the heaving-to-pitching assembly of
Figure
6A. Figure 7A is a schematic view of a hydrofoil and its corresponding rotary
actuator. Figure 7B is an alternative embodiment for the rotary actuator of
Figure
7.
Figure 8 is a schematic view of part of a heaving-to-pitching assembly,
according
to another preferred embodiment. Figure 8A is an alternative embodiment for
the
rotary actuator of Figure 8.
Figure 9 is a schematic view of part of a linear-to-rotary transmission
system,
according to a preferred embodiment. Figures 9A and 9B are schematic views of
another part of a linear-to-rotary transmission system, according to two
preferred
embodiments.
Figure 10 is a schematic view of components of a linear-to-rotary transmission
system, according to another preferred embodiment.
Figure 11 is a side perspective view of a turbine, according to a preferred
embodiment of the invention. Figure 11A is a schematic view of components of
the
turbine of Figure 11.
Figure 12 is a side perspective view of a turbine, according to another
preferred
embodiment of the invention. Figure 12A is a schematic view of components of
the
turbine of Figure 12.
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Figure 13 is a side perspective view of a turbine, according to a yet another
preferred embodiment of the invention. Figures 13A and 13B are schematic views
of alternative embodiments of rotary actuators.
Figure 14 is a schematic view of a propulsive system, according to another
preferred embodiment of the invention.
DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
In the following description, similar features in the drawings have been given
Hi similar reference numerals. In order to preserve clarity, certain
elements may not
be identified in some figures if they are already identified in a previous
figure.
Referring to Figure 3, a first embodiment of a turbine 30 is shown, for
converting
kinetic energy from a fluid flow, represented by arrow 32, into mechanical
energy.
The mechanical energy can be used to drive a rotatable shaft from an
electrical
generator for example. The fluid can be of any type, such as air or water, but
the fluid
flow is preferably the current of an ocean or of a river.
The turbine 30 includes first and second hydrofoils 34a, 36a extending from a
support structure, in this case a post 38, which is preferably in an upright
vertical
orientation. The hydrofoils 34a, 36b extend from one side of the post, and are
substantially parallel to one another. Preferably, when the support structure
38 is a
single post, another pair of first and second hydrofoils 34b, 36b extend on
the
opposite side of the post, such as to maximize the lifting surfaces of the
turbine 30.
Although shallower configurations are achieved when the post is in an upright
or
vertical orientation, the post may also be positioned in a horizontal
orientation, the
hydrofoils thus extending in a vertical orientation. The hydrofoils 34, 36
have an
elongated and substantially planar body. Each of the hydrofoils 34, 36 also
has an
extending curved profile. They also have a symmetrical transversal cross-
section.
Now referring to Figure 4, a second embodiment of a turbine 30 is shown. In
this
case, the support structure comprises two spaced-apart posts 38a, 38b, the
first and
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the second hydrofoils 34, 36 extending between them. Each hydrofoil 34, 36 is
slidably and rotatably connected to the structure, allowing each of the
hydrofoils to
move linearly in a heaving motion, and to oscillate about a spanwise axis in a
pitching motion. In this configuration of the turbine 30, the heaving motion
is
vertical and each hydrofoil 34, 36 oscillates about a horizontal axis.
Preferably, the
hydrofoils 34, 36 each have a rectangular or untwisted configuration. Still
preferably, the cross-section of each hydrofoil is symmetrical and its surface
is
curved.
Now turning to Figures 5, 5A and 5B, yet a third embodiment of a turbine 30 is
shown. In this case, the hydrofoils 34, 36 each comprises a pair of foils 40a,
40b
extending in parallel between the posts. The foils 40a, 40b are rigidly
connected
via rigid links, in this case reinforcement plates 42, which are distributed
along the
span of the hydrofoil. The ends of the hydrofoils are also provided with end
plates
44a, 44b, which may facilitate the connection of the hydrofoils with other
components of the turbine while reducing the undesirable effects of wingtip
vortices. As best shown in Figure 5A, the multi-surface hydrofoil 34 is
composed of a
closely-spaced pair of foils, thus becoming a bifoil. Such a configuration
increases
the rigidity of the hydrofoil 34, allowing the use of higher aspect ratios,
which is the
ratio of length (span) to width (chord) of the hydrofoil. A hydrofoil with a
higher aspect
ratio has increased lifting and thrusting capabilities while preserving its
width and
thus the compactness of the system. Best shown in Figure 5B, the two foils
40a,
40b are located on each side of the pitching axis 46 of the hydrofoil.
This configuration of the hydrofoil also favours a modular fabrication, where
the
overall length of the hydrofoil can be adapted, that is, increased or
decreased,
according to specific applications, using the same basic components. This
modular configuration can also facilitate transport of the hydrofoil.
As will be appreciated, a hydrofoil 34, 36 can be composed of a single lifting
surface, or alternatively incorporates multiple lifting surfaces rigidly
connected to
each other.
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The mechanism involved in the oscillating motion of the hydrofoils can be
divided
in two main parts, according to their respective tasks. The first task implies
the
coupling of a linearly-oscillating or heaving-oscillating motion into an
alternating
rotary motion or pitching-motion. This first task is achieved with a heaving-
to-
5 pitching assembly, in which pitch-heave couplings are used to obtain a 1
degree-
of-freedom system. The second part relates to the coupling of a linearly-
oscillating
motion into a rotary motion. This second part is achieved with a linear-to-
rotary
transmission system, using a power transmission link between the cyclical
heaving
motions of the hydrofoils and a rotating shaft.
10 The heaving-to-pitching assembly
Figures 6A to 8A show alternatives which can be considered in order to perform
this first task, while Figures 9, 9A and 9B show alternatives to perform this
second
task. Figures 10 to 13 show the turbine with the components of the heaving-to-
pitching assembly and of the linear-to-rotary transmission system when
combined.
Referring now to Figures 6A, a schematic representation of a heaving-to-
pitching
assembly 48 in combination with the first and second hydrofoils 34, 36 is
shown.
The hydrofoils 34, 36 can slide and rotate, allowing them to move linearly in
a
heaving motion yl, Y2, and to oscillate about a spanwise axis in a pitching
motion
81, 82. The heaving-to-pitching assembly allows the coupling of the heaving
motions Vi, y2 of the first and second hydrofoils 34, 36 to the pitching
motions 02,
81 of the second and first hydrofoils 36, 34, respectively.
Figure 6B illustrates the heaving and pitching motions of the hydrofoils 34,
36
which are sinusoidal, or quasi-sinusoidal. In this graph, the heaving motion
of the
first hydrofoil 34 is represented by curve yi and its pitching motion by curve
01.
Similarly, for the second hydrofoil 36, its heaving motion is represented by
curve Y2
and its pitching motion by curve 82.
As can be appreciated, for a given hydrofoil, its heaving and pitching motions
are
out of phase by a pitch-heave motion phase, which is equal to Pi/2, or 90
degrees
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which corresponds to T/4. It can also be observed that the heaving motion yi
of
the first hydrofoil 34 is out of phase relative to the heaving motion y2 of
the second
hydrofoil 36, by an inter-hydrofoil phase. While the pitch-heave phase for a
hydrofoil is typically Pi/2, the heaving-to-pitching assembly 48 sets the
inter-foil
phase between yi and yz to be also equal to Pi/2, making it possible to use
the
heaving motion of each foil to drive the pitching motion of its neighbour
foil.
Back to Figure 6A, the heaving-to-pitching assembly 48 includes a pair of
first and
second linear actuators 50, 52, a pair of first and second rotary actuators
54, 56,
and a heaving-to-pitching coupling system 58.
lo The first linear actuator 50 is connected to the first hydrofoil 34, and
the second
linear actuator 52 is connected to the second hydrofoil 36. When a hydrofoil
34, 36
moves linearly, in a heaving motion induced by water current for example, the
corresponding linear actuator 50, 52 is driven by this heaving motion. In this
case,
the first and second linear actuators 50, 52 are hydraulic cylinders.
Similarly, the first rotary actuator 54 is connected to the first hydrofoil 34
and the
second rotary actuator is connected to the second hydrofoil 36. The heaving-to-
pitching coupling system 58, which preferably consists of hydraulic conduits,
serves to couple the first linear actuator 50 to the second rotary actuator
56, and to
couple the second linear actuator 52 to the first rotary actuator 54.
When the first hydrofoil 34 moves linearly under the flow of current, fluid is
pushed
outside the cylinder 50 through the conduits 58, the fluid in turn actuating
the
rotary actuator 56, thereby driving the pitching motion of the hydrofoil 36.
The
same relationship exists between the hydrofoil 36, the cylinder 52, and the
rotary
actuator 54. The hydraulic cylinders 50, 52 and rotary actuators 54, 56 are
sized
and configured such that the inter-foil phase is equal to the heaving-to-
pitching
phase, which is 90 degrees.
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Preferably, as shown in Figures 3, 4 and 5, the hydraulic cylinders 50, 52,
the
rotary actuators 54, 56, and the coupling system 58 are housed within the base
structure, in this case the post(s) 38.
In order to lower the operating pressure of the hydraulic cylinders, it is
possible to
double the components of the heaving-to-pitching assembly. In this case,
embodiments such as those shown in Figures 4 and 5, ie with two posts 38,
allow
a first post 38a to house a first pair of linear actuators 50, 52, a first
pair of rotary
actuators 54, 56 and a first heaving-to-pitching assembly. The turbine also
comprises a second post 38b that houses a second pair of linear actuators 50,
52,
a second pair of rotary actuators 54, 56 and a second heaving-to-coupling
system
58.
Referring now to Figures 7, the connection between the first hydrofoil 34, the
first
linear actuator 50 and the second rotary actuator 56 are shown. The pitching
axis
46 of the hydrofoil 34 is rigidly connected to the double-sided cylinder 50
and to
the rotary actuator 56. Both outlets 60a, 60b of the double-sided hydraulic
cylinder
50 are connected to the inlets 62a, 62b of the rotary actuator 56. In this
case, the
rotary actuator 56 is a single vane actuator. In Figure 7, the second
hydrofoil 36 is
not shown for more clarity, but of course, the second hydrofoil 36 is indeed
connected to the second rotary actuator 56, as shown in Figure 7A.
Preferably, the heaving-to-pitching assembly comprises a pitch-controlling
mechanism 74 for controlling the pitching amplitude of the corresponding
hydrofoil.
In the present case, this mechanism 74 consists of stoppers 64a, 64b and of
relief
valves 66a, 66b. The fluid volume of the actuator 56 is designed to be
slightly less
than the fluid volume displaced by the hydraulic cylinder 50. This results in
an
automatic referencing system which operates when necessary. The extra fluid
ensures that the vane 68 reaches the stoppers 64a, 64b, such that the preset
maximum pitching amplitude is reached. Once the vane 68 touches one of the
stoppers 64a, 64b, pressure rises and the extra fluid, which is preferably eco-
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friendly, such as surrounding water that has been filtered, is ejected through
the
relief valves 66a, 66b.
Figure 7B illustrates another embodiment of a pitch-controlling mechanism 74.
In
this case an active device is used. The volumetric pump 76, which is
mechanically
or otherwise controlled with a controller 78, periodically resets the pitch-
heave
motion phase.
Back to Figure 7, mechanical friction should be avoided wherever possible, in
order to reduce maintenance. Preferably, hydrostatic bearings 70a, 70b are
used
instead of contact seals in every hydraulic cylinder and actuator. The
hydrostatic
113 bearings 70a, 70b are fed by an external pump 72 operating at a higher
pressure
than the hydraulic fluid. In addition to providing guidance and contactless
operation of the hydraulic cylinder 50, the hydrostatic bearings ensure the
replacement of any hydraulic fluid losses in the system. Alternatively, the
vane 68
of the rotary actuator may also be equipped with a low-friction sealant, such
as
Teflon, UHMW, or the like.
Now turning to Figure 8, another type of rotary actuator is shown. In this
case, the
rotary actuator 56 includes a drum-and-cable mechanism. In such a mechanism,
the pitching axis 47 of the second hydrofoil 36 is rigidly connected to the
axis of
the drum 82b. A cable 84 is rigidly connected to the drums 82a, 82b and is
driven
by a linear double rod hydraulic cylinder 86. Stoppers 64a, 64b and relief
valves
66a, 66b can also be used with this type of rotary actuator 56, to control the
pitching amplitude of the hydrofoil. Alternatively, as shown in Figure 8A, a
controlled volumetric pump 76 can be used instead.
The linear-to-rotary transmission system
With reference to Figures 9, 9A and 9B, part of a linear-to-rotary
transmission
system 88 is shown. This part of the linear-to-rotary transmission system 88
operatively connects the first hydrofoil 34 and to the rotatable shaft 90,
such that
the heaving motion of the first hydrofoil can drive a rotational motion of the
shaft
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90. Of course, another part of the linear-to-rotary transmission system
connects to
the second hydrofoil 36, but this is not shown in the drawing for clarity
purposes.
As shown in either one of the embodiments of Figures 9A and 9B, the linear-to-
rotary transmission system 88 linked to the first hydrofoil 34 comprises a
transmission actuator 92 operatively connected to said hydrofoil 34, which in
this
case is an hydraulic cylinder 92. This cylinder 92 is rigidly connected to the
hydrofoil 34. The system 88 also includes linear-to-rotary transmission links
94, for
transforming the linear motion of the transmission actuators 92 into the
rotational
motion of the shaft 90.
As can be appreciated, both embodiments of the linear-to-rotary links 94 shown
in
Figures 9A and 9B allow to couple the transmission actuator 92, and thus
indirectly the hydrofoil 34, to the rotating shaft 90. The heaving power from
the
hydrofoil 34 is transformed in a rotational motion of the shaft, which can be
part of
an electrical generator, generating electricity.
With reference to Figure 9A, the transmission link 94 comprises two single-
sided
hydraulic cylinders 96a, 96b connected to crankshafts 98a, 98b. In the
alternative
embodiment shown in Figure 9B, the hydraulic cylinders 96a, 96b are connected
to a hydraulic axial piston engine 100. Of course, other types of transmission
links
94 may also be considered.
Back to Figure 9, the displaced volume of the double-sided hydraulic cylinder
92
preferably matches the total volume of the single-sided hydraulic cylinders
96a,
96b. However, to account for any mismatch in fluid volumes, relief valves
102a,
102b are added to each conduit.
Preferred embodiments of turbines and propulsive systems
Figure 10 shows another preferred embodiment of the linear-to-rotary
transmission
system 88 where the first and second transmission actuators 92, 93, and the
first
and second rotary actuators 54, 56 are connected to double-sided hydraulic
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cylinders 104a, 104b, 104c, and 104d. The cylinders 104a, 104c are connected
to
the same rod 106. Similarly cylinders 104b, 104d share rod 108.
This embodiment can be advantageous for applications where several turbines 30
are deployed together, such as in tidal farms, also called hydrokinetic
turbine
5 parks, where the linear-to-rotary transmission system of each turbine
unit 30
connects to a same rotating shaft and electrical generator, with the relative
motion
phases between the turbines set in such a way as to further smoothes out the
applied torque and rotation velocity.
Preferably, the hydraulic fluid used is low-pressure, around 150 psi, and
consists
io of conditioned water or vegetable oil which limits energetic losses
(minimal friction
in hoses and minimal leaks in the ambient water) and ensures an
environmentally
friendly operation.
It should also be noted that the inter-foil phase of 90 degrees in a basic
unit pair of
hydrofoils implies a relative motion of each foil with its neighbouring foil.
As a
is consequence, the hydraulic hoses interconnecting the hydraulic cylinders
and the
rotary actuators need to allow for this relative motion.
Advantageously, an inter-foil phase of 90 degrees allows avoiding that both
hydrofoils 34, 36 reach their zero-production point, at top and bottom
positions, at
the same time, which effectively smoothes out the torque signal at the
generator
and makes the whole turbine self-starting at low water current velocity.
Preferably,
the heaving-to-pitching assembly and the linear-to-rotary transmission system
88
are compact enough so that most of the components fit inside the two side
posts
38a, 38b forming the base structure. By doing so, most of the components are
shielded from the flowing water, while the hydrofoils remain exposed.
With reference to Figure 11 and 11A, the heaving-to-pitching coupling system
58,
which includes hydraulic conduits inter-connecting the linear actuators 50, 52
and
rotary actuators 54, 56, may incorporate some length of coaxial sliding
conduits
110, 112, 114, 116, so that the hydraulic circuit can account for the relative
motion
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between both hydrofoils 34, 36 while maintaining a constant overall fluid
volume.
Figure 11A also provides a complete overview of the preferred mechanism with
the rotary actuators 54, 46 rigidly connected via rigid links 118, 120 to
their
respective pitch-heave coupling hydraulic cylinders 50, 52, to their linear-to-
rotary
transmission cylinders 92, 93 and to their associated sliding conduits 110,
112,
114, 116.
Referring to Figure 12, in order to facilitate the alignment of the hydraulic
cylinders
which are part of the heaving-to-pitching assembly and of the linear-to-rotary
transmission system, and in order to further improve the compactness of the
entire
io mechanism, it is possible to rely on the use of coaxial hydraulic
cylinders 122, 124.
The coaxial cylinders 122, 124 can also be used in combination with sliding
coaxial conduits, similar to the embodiment shown in Figure 11.
Referring to Figure 13, the turbine 30 can be further simplified by combining
the
hydraulic cylinders associated with a hydrofoil 34 or 36, for the heaving-to-
pitching
assembly and for the linear-to-rotary transmission system, within a single
hydraulic
cylinder 126 or 128.
In this embodiment of the turbine 30, linear-to-rotary transmission links 94
are
connected to the shaft 90 and the two transmission cylinders 126, 128 are each
connected to the linear-to-rotary transmission links 94.
The first hydraulic cylinder 126 comprises a rod 130 and two pistons 134a,
134b
located at both ends of the rod 130, each piston marking the boundaries of
first
and second chambers on both sides of the cylinder 126. The second hydraulic
cylinder 128 has a similar configuration with rod 132, and pistons 136a, 136b.
The
rods 130, 132 are preferably articulated, to facilitate their alignment and
displacement. Each rod 130, 132 is connected to a corresponding one of the
hydrofoils 34, 36. For a given cylinder 126 or 128, the first chamber 138 is
connected to its corresponding rotary actuator 56, 54 via the coupling means,
and
the second chamber 140 is connected to the transmission cylinders 96a, 96b.
The
rotatable shaft 90, moving in a constant rotational movement, can be coupled
with
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any means 142 to an electric generator 144. In this preferred embodiment of
the
turbine 30, the hydraulic cylinders 126, 128 are part of both the heaving-to-
pitching
assembly and of the linear-to-rotary transmission system. Figures 13A and 13B
show alternatives for the rotary actuators 54, 56. In Figure 13A, a rotary
vane
actuator 67 is represented, while in Figure 13B, a drum-and-cable mechanism 75
is shown.
Referring to Figure 14, an adaptation of the embodiment shown in Fig. 10
yields
yet another embodiment of the invention, consisting of a propulsive system
146.
The system 146 allows operating a first oscillating hydrofoil 34 with similar
compact means of transmission for propulsion, rather than for power
extraction.
Although not shown, the same types of components and connections are made to
a second hydrofoil, the two hydrofoils being coupled such as shown in Figure
10.
This propulsive system 146 allows the transmission of mechanical energy from
the
rotatable driving shaft 90. The propulsive system comprises the same
components
of the turbine 30, that is: a support structure, first and second hydrofoils,
a
heaving-to-pitching assembly and a rotary-to-linear transmission system. In
contrast with the turbine 30, in the propulsive system 146, it is the
rotational
motion of the driving shaft which in turn drives the heaving and pitching
motions of
the hydrofoil.
Method for converting kinetic energy from a fluid flow into mechanical
energy
With reference to Figures 1 to 13, the method for converting kinetic energy
from a
fluid flow into mechanical energy requires a turbine which includes first and
second hydrofoils, each being able to move linearly in a heaving motion, and
to
oscillate about a spanwise axis in a pitching motion, where the heaving and
pitching motions are quasi-sinusoidal. For a given one of the hydrofoils, the
heaving and pitching motions are out of phase by a pitch-heave motion phase,
and
the respective heaving motions of the first and second hydrofoils are out of
phase
by an inter-hydrofoil phase. The method requires the coupling of the heaving
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motions of the first and second hydrofoils to the pitching motions of the
second
and first hydrofoils respectively. This coupling is made with the pitch-heave
motion
phase being substantially equal to the inter-hydrofoil phase. This
advantageously
allows for the heaving motion of one of the hydrofoils to drive the pitching
motion
of the other hydrofoil. The method also requires the transformation of the
heaving
motions of the hydrofoils into a rotational movement of the rotatable shaft,
using
linear-to-rotary transmission means.
Preferably, the method includes the sub-steps of providing a pair of first and
second linear actuators, a pair of first and second rotary actuators and a
heaving-
to-pitching coupling system. The first linear actuator is connected to the
first
hydrofoil, and the second linear actuator to the second hydrofoil, each of the
first
and second linear actuators being driven by the heaving motion of the
corresponding hydrofoil. The first rotary actuator must also be connected to
the
first hydrofoil, and the second actuator to the second hydrofoil, each of the
first
and second rotary actuators driving the corresponding hydrofoil in the
pitching
motion. Finally, the first linear actuator is coupled to the second rotary
actuator,
and the second linear actuator to the first rotary actuator, using the heaving-
to-
pitching coupling system.
Still preferably, the method comprises a sub-step of providing two spaced-
apart
posts, the first and second hydrofoils extending between the posts. The first
and
second hydrofoils each comprises a pair of foils extending in parallel between
the
posts.
Performances are also improved when the pitch-heave motion phase, and the
inter-hydrofoil phase are approximately 90 degrees. Preferably, the method
further
includes a step of controlling the pitching amplitudes of the first and second
hydrofoils.
The turbine described above offers an obvious advantage in shallow water sites
due to its rectangular harvesting plane, allowing the possibility to scale up
the
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rated power by simply increasing the turbine hydrofoil span. Furthermore, the
untwisted rectangular hydrofoils in the oscillating concept have a much
simpler
geometry, and are easier to produce than typical rotor blades.
For tidal operation, in which the turbine should be able to operate with both
ebb
and flood tides, i.e. in both opposite directions, the system can be reversed
by
rotating the hydrofoils by 180 degrees. This can be performed by mounting each
foil's rotary actuator on an additional 0-1800 hydraulic actuator which can be
fed
on demand by the pump feeding the hydrostatic bearings. Alternatively, the
foil
pitching-center junction with its structural spar may incorporate a clutch
coupling.
In such an embodiment, the 1800 rotation of the foil may be initiated
passively from
the action of the water flow. To complete the turbine reversal, a change of
phase is
also necessary.
This is preferably accomplished by inverting the rotational motion of the
electrical
generator through the electrical drive.
Oscillating foils can generate efficient propulsive forces when operating with
the
proper pitching angles. The embodiment presented above may be used for
propulsion purposes in applications aiming to generate thrust from oscillating
hydrofoils. In such cases, the electrical generator would operate as a motor
and
work would be performed by the foils on the fluid, rather than energy being
extracted from the fluid flow.
Numerous modifications could be made to the embodiments above without
departing from the scope of the present invention.
