U.S. patent application number 13/563087 was filed with the patent office on 2012-11-22 for wave energy converter.
This patent application is currently assigned to PROTEAN ENERGY AUSTRALIA PTY LTD. Invention is credited to Sean Derek MOORE.
Application Number | 20120292910 13/563087 |
Document ID | / |
Family ID | 38922835 |
Filed Date | 2012-11-22 |
United States Patent
Application |
20120292910 |
Kind Code |
A1 |
MOORE; Sean Derek |
November 22, 2012 |
WAVE ENERGY CONVERTER
Abstract
A wave energy converting apparatus and tension mooring system
are described. The apparatus comprises an elongate support
structure designed to extend above a mean water level in the ocean.
The support structure has a submerged member below the mean water
level. A float member of positive buoyancy is slidably mounted on
the support structure so as to be movable in a vertical direction.
The apparatus also comprises a linear electric generator having a
stator provided in connection with the support structure and a
translator integrated into the body of the float member.
Differential motion of the float member relative to the support
structure results in the generation of electrical power by the
electric generator. The mooring system comprises a cable extending
from a ballast to a counterbalancer suspended from the submerged
member via a pulley mechanism. The mooring system allows the
apparatus to be "tuned" to prevailing ocean conditions.
Inventors: |
MOORE; Sean Derek;
(Gosnells, AU) |
Assignee: |
PROTEAN ENERGY AUSTRALIA PTY
LTD
Subiaco
AU
|
Family ID: |
38922835 |
Appl. No.: |
13/563087 |
Filed: |
July 31, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12373421 |
Jan 12, 2009 |
8264093 |
|
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PCT/AU2007/000940 |
Jul 9, 2007 |
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13563087 |
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Current U.S.
Class: |
290/53 |
Current CPC
Class: |
F05B 2240/917 20130101;
Y02E 10/30 20130101; F03B 13/1845 20130101; B63B 35/44 20130101;
B63B 2035/4466 20130101; F05B 2210/18 20130101; F05B 2220/707
20130101; E02B 9/08 20130101 |
Class at
Publication: |
290/53 |
International
Class: |
F03B 13/14 20060101
F03B013/14 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 11, 2006 |
AU |
2006903707 |
Claims
1-13. (canceled)
14. An apparatus for converting ocean wave energy into a more
usable form, the apparatus comprising: an elongate support
structure designed to extend above a mean water level, having a
submerged member provided in connection therewith below the mean
water level and a buoyant means to enable the support structure to
float in the ocean in a generally upright orientation; a float
member of positive buoyancy slidably mounted on the support
structure so as to be movable in a vertical direction, the float
member being provided with a hydroplane surface that converts a
horizontal component of the wave motion into a vertical movement of
the float member, thus enhancing the energy extracting capacity of
the float member; and, an energy extraction means provided in
connection with the support structure and the float member, so that
when wave motion causes a suitable differential motion between the
float member and the support structure said energy extraction means
converts the incident energy into a more usable form.
15. An apparatus for converting ocean wave energy as defined in
claim 14, wherein the energy extraction means comprises a linear
electric generator in which a stator is provided in connection
therewith the support structure and a translator is provided in
connection therewith the float member.
16. (canceled)
17. An apparatus for converting ocean wave energy as defined in
claim 14, wherein the submerged member is provided with a
hydroplane surface adapted to convert a horizontal component of the
wave motion into a vertical movement of the submerged member, thus
enhancing the energy extracting capacity of the submerged
member.
18. An apparatus for converting ocean wave energy as defined in
claim 14, wherein the submerged member is provided with a variable
buoyancy hydrostatic pressure chamber adapted to convert a
variation in the hydrostatic pressure at a constant altitude into a
decrease or increase in the member's buoyancy leading to an
associated vertical movement of the submerged member, thus causing
the submerged member to descend as the wave height increases and
ascend as the wave height decreases.
19. An apparatus for converting ocean wave energy as defined in
claim 14, wherein the float member has an elongate horizontal
cross-section with a front end and a rear end, the front end being
adapted to face into the general direction of an approaching
wave.
20-21. (canceled)
22. An improved float member in an apparatus for converting ocean
wave energy into usable energy, the float member comprising: a
positively buoyant member slidably mounted on a support structure
so as to be movable in a vertical direction responsive to wave
motion, and having a hydroplane surface that converts a horizontal
component of the wave motion into a vertical movement of the float
member, thus enhancing the energy extracting capacity of the float
member.
23. An apparatus for converting ocean wave energy as defined in
claim 14, the apparatus further comprising a mooring system for
mooring the structure to the seabed.
24. An apparatus for converting ocean wave energy as defined in
claim 23, wherein said submerged member and buoyant means are
adapted to have substantially positive buoyancy in use, and said
mooring system comprises a dampening means for applying a dampening
action to the support structure via the mooring system.
25. An apparatus for converting ocean wave energy as defined in
claim 24, wherein said dampening means is adapted to increase the
dampening action when the energy extracted by the energy extraction
means increases, whereby the differential motion between the float
member and the support structure can be maximised and the amount of
energy extracted optimised.
26. An apparatus for converting ocean wave energy as defined in
claim 25, wherein, when little or no energy is being extracted by
the energy extraction means said dampening means applies no
dampening action and mechanical stresses on the support structure
can be minimised as the mooring system freewheels.
27. An apparatus for converting ocean wave energy as defined in
claim 25, wherein, said mooring system comprises a cable extending
from a ballast means to a counterbalancing means suspended from the
support structure via a pulley mechanism.
28-29. (canceled)
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Continuation of application Ser. No.
12/373,421, filed Jan. 12, 2009, which is a U.S. National Stage of
PCT/AU2007/000940 filed Jul. 9, 2007, which applications are
incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The present invention relates to wave energy converters for
converting ocean wave energy into electrical energy and relates
particularly, though not exclusively, to such wave energy
converters that operate on the principles of buoyancy, hydrodynamic
pressures, and oscillation. The invention relates more particularly
to a tension mooring system for a wave energy converter.
BACKGROUND TO THE INVENTION
[0003] At the beginning of the third millennium the concern of
people everywhere is increasingly on sustainability. As people
realise that fossil fuels are a finite energy resource, the search
for renewable, clean energy sources has become more urgent. Global
warming and climate change have focussed attention on the need to
reduce our dependence on fossil fuels. One of the most promising
renewable energy sources is wave energy. It has been estimated that
the worldwide energy potential of wave power is 2 Terawatts, which
is equivalent to a worldwide resource of about 2000 TWh per
year--sufficient for much of the world's electrical energy
requirements. Although there has been a desire to harness the
energy of waves for hundreds of years, past attempts have met with
limited success. The successes have been on a small scale, in the
order of tens to hundreds of kilowatts rather than the hundreds of
megawatts required.
[0004] One of the major difficulties in the past has been to design
a unit that is sufficiently robust to withstand the enormous power
that is possessed by the ocean's waves. In storm conditions the
wave energy can be massive, causing the destruction of many of the
prior art land- or shore-based systems. The typical prior art
approach to extracting wave energy has been to use a turbine or
hydraulic system. There have been some attempts to use a directly
driven rotary generator, as well as a directly driven linear
generator. However the most common prior art energy extraction
units are oscillating water columns
and hydraulic linked rotary generators. These are typically used in
near-shore, in-shore or on-shore installations. Another major
drawback of such prior art systems is the need to be close to shore
where the energy loss for shoreline waves is high due to frictional
losses, thus missing out on the majority of the wave energy present
in `deep` water.
[0005] The present invention was developed with a view to providing
a tension mooring system and a wave energy converter that can be
used either near-shore or offshore to extract a maximum amount of
ocean wave energy.
[0006] References to prior art in this specification are provided
for illustrative purposes only and are not to be taken as an
admission that such prior art is part of the common general
knowledge in Australia or elsewhere.
SUMMARY OF THE INVENTION
[0007] According to one aspect of the present invention there is
provided a tension mooring system for an apparatus for converting
ocean wave energy into a more usable form, the apparatus having a
structure with a submerged member provided in connection therewith
below the mean water level, the mooring system comprising:
an elongate flexible member extending from a ballast means to a
counterbalancing means adapted to be suspended from the submerged
member via a pulley mechanism; and a dampening means for applying a
dampening action to the motion of the submerged member, the
dampening means applying the dampening action to the elongate
flexible member via the pulley mechanism.
[0008] Preferably the counterbalancing means comprises a vessel
having a mass provided in connection therewith to provide a
counterbalancing force applied to the submerged member via the
elongate flexible member.
[0009] Preferably the counterbalancing means comprises an
adjustable buoyancy vessel having a mass provided in connection
therewith, wherein the buoyancy of the counterbalancing means can
be adjusted to vary the counterbalancing force applied to the
submerged member via the elongate flexible member. Preferably the
buoyancy of the counterbalancing means can be adjusted by pumping
air into the buoyancy vessel via an air hose.
[0010] Advantageously the mooring system further comprises a
mooring caddy, and the submerged member of the structure is adapted
to dock with the mooring caddy. Preferably the submerged member is
secured to the mooring caddy by a locking mechanism. Preferably the
dampening means and pulley mechanism are housed in the mooring
caddy.
[0011] According to another aspect of the present invention there
is provided an apparatus for converting ocean wave energy into a
more usable form, the apparatus comprising:
an elongate support structure designed to extend above a mean water
level, having a submerged member provided in connection therewith
below the mean water level and a buoyant means to enable the
support structure to float in the ocean in a generally upright
orientation; a float member of positive buoyancy slidably mounted
on the support structure so as to be movable in a vertical
direction; and, an energy extraction means provided in connection
with the support structure and the float member, so that when wave
motion causes a suitable differential motion between the float
member and the support structure said energy extraction means
converts the incident energy into a more usable form.
[0012] Preferably the float member is provided with a hydroplane
surface adapted to convert a horizontal component of the wave
motion into a vertical movement of the float member, thus enhancing
the energy extracting capacity of the float member. Typically the
float member has an elongate horizontal cross-section with a front
end and a rear end, the front end being adapted to face into the
general direction of an approaching wave. Preferably said front end
is narrowed to a tip. Preferably said hydroplane surface is one of
a plurality of substantially parallel hydroplane surfaces extending
substantially perpendicularly to and along respective first and
second sides of the floating member. Preferably said plurality of
hydroplane surfaces are inclined downwards from the front end to
the rear end of the float member, wherein water particles in a wave
are forced downwards by the hydroplane surfaces, creating
hydrodynamic forces acting upwards on the hydroplane surfaces which
are added to an upward force acting on the float member due to its
positive buoyancy.
[0013] According to another aspect of the present invention there
is provided an improved float member in an apparatus for converting
ocean wave energy into usable energy, the float member
comprising:
a positively buoyant member slidably mounted on a support structure
so as to be movable in a vertical direction responsive to wave
motion, and having a hydroplane surface adapted to convert a
horizontal component of the wave motion into a vertical movement of
the float member, thus enhancing the energy extracting capacity of
the float member.
[0014] Preferably the apparatus for converting wave, energy further
comprises a mooring means for mooring the structure to the seabed.
In one embodiment said submerged member and buoyant means are
adapted to have substantially neutral buoyancy in use, and said
mooring means comprises a tether adapted to prevent the apparatus
from drifting but still allow for automatic tracking of the
prevailing wave directions.
[0015] In another embodiment said submerged member and buoyant
means are adapted to have substantially positive buoyancy in use,
and said mooring means comprises a braking system for applying a
braking action to the support structure via the mooring means.
Preferably said braking system is adapted to increase the braking
action when the energy extracted by the energy extraction means
increases, whereby the differential motion between the float member
and the support structure can be maximised and the amount of usable
energy generated optimised. Conversely, when little or no energy is
being extracted by the energy extraction means the braking system
applies no braking action and mechanical stresses on the support
structure can be minimised as the mooring means freewheels.
[0016] In one embodiment said mooring means comprises a cable
extending from a ballast means to a counterbalancing means
suspended from the support structure via a pulley mechanism.
Typically said braking system applies a braking action to the cable
via the pulley mechanism. Preferably said braking system is
solenoid activated, electrical power for the solenoid being
supplied by the linear electric generator via a shunt circuit.
Preferably said braking system is computer controlled.
[0017] Throughout the specification, unless the context requires
otherwise, the word "comprise" or variations such as "comprises" or
"comprising", will be understood to imply the inclusion of a stated
integer or group of integers but not the exclusion of any other
integer or group of integers. Likewise the word "preferably" or
variations such as "preferred", will be understood to imply that a
stated integer or group of integers is desirable but not essential
to the working of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] The nature of the invention will be better understood from
the following detailed description of several specific embodiments
of the tension mooring system and wave energy converter, given by
way of example only, with reference to the accompanying drawings,
in which:
[0019] FIG. 1 is a top front perspective view of a first embodiment
of a wave energy converting apparatus in accordance with the
present invention;
[0020] FIG. 2 is a top front perspective view of the wave energy
converting apparatus of FIG. 1 with its associated tension mooring
system in accordance with the invention;
[0021] FIG. 3 is a front elevation of the wave energy converting
apparatus of FIG. 2;
[0022] FIG. 4 is a top front perspective view of the tension
mooring system employed with the wave energy converting apparatus
of FIG. 1;
[0023] FIG. 5 is a bottom rear perspective view of a mooring caddy
incorporated in the tension mooring system of FIG. 4;
[0024] FIGS. 6a and 6b illustrate the wave energy converting
apparatus of FIGS. 1 and 3 in the crest and the trough respectively
of an approaching wave;
[0025] FIGS. 7a and 7b illustrate the operation of the wave energy
converting apparatus of FIGS. 1 and 2 during variations in the mean
water level;
[0026] FIG. 8 is a top perspective view of a second embodiment of a
wave energy converting apparatus with its associated tension
mooring system in accordance with the invention;
[0027] FIG. 9 is a partially transparent, top perspective view of a
counterbalancing means which is part of the tension mooring system
associated with the wave energy converting apparatus of FIG. 8;
[0028] FIG. 10 is an enlarged perspective view of the wave energy
converting apparatus and the associated tension mooring system of
FIG. 8;
[0029] FIG. 11 is a partially transparent, top perspective view of
a first embodiment of a mooring caddy which is part of the tension
mooring system associated with the wave energy converting apparatus
of FIG. 8;
[0030] FIG. 12 is a partially transparent, top perspective view of
a second embodiment of a mooring caddy which is part of the tension
mooring system in accordance with the invention that may be
associated with a wave energy converting apparatus;
[0031] FIG. 13 is a top perspective view of a third embodiment of a
wave energy converting apparatus with its associated tension
mooring system in accordance with the invention;
[0032] FIG. 14 is a top perspective view of a fourth embodiment of
a wave energy converting apparatus with its associated tension
mooring system in accordance with the invention;
[0033] FIG. 15 is a bottom perspective view of a fifth embodiment
of a wave energy converting apparatus with its associated tension
mooring system in accordance with the invention; and,
[0034] FIG. 16 is a top perspective view of a sixth embodiment of a
wave energy converting apparatus with its associated tension
mooring system in accordance with the invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0035] The energy within an ocean wave is propagated via two
orthogonal energies, namely, the horizontal and vertical energies.
The vertical energy is contained within the vertical motion of the
water particles within the wave, known as heave, and possesses half
the available energy of the wave. The horizontal energy is
contained in the horizontal motion of the water particles within
the wave, known as surge, and also possesses half the energy of the
wave. For wave energy extraction to take place there needs to be
energy absorption from one or both of these orthogonal
energies.
[0036] The heave motion describes the z-axis (or up and down)
motion of the wave and as such it has a very high correlation with
the vertical energy within a wave. The amicability of heaving with
wave height makes it a popular and potentially efficient means to
extract the vertical energy from a wave. Extraction of the vertical
energy in a wave may be implemented in a Wave Energy Converter
(WEC) using a single heaving body or two heaving bodies. A single
heaving body uses a buoyant mass on top of the surface of the water
to extract the vertical energy of a wave. In order to extract
energy there needs to be differential motion, generally in the case
of a single heaving body the second frame of reference is the ocean
floor. By using the ocean floor as a frame of reference it is
possible to get the most amount of relative movement and as a
result the most amount of energy extracted over as wide a range of
frequencies as possible.
[0037] The implementation of a single heaving body design can be
achieved through two basic configurations. The first is as a buoy
floating on top of the water, with an attachment linking the buoy
to its reference frame; the buoy will then move with the waves on
the ocean's surface producing the differential motion relative to
the frame of reference. The second configuration uses a structure
fixed to the ocean floor, this structure is located either below or
above the mean water level and will have a buoy attached to it;
this buoy will then oscillate with the waves on the surface of the
water producing differential motion against the fixed reference
frame.
[0038] In a dual heaving body design the differential motion
between two oscillating bodies is used to generate energy; as
opposed to the relative motion of one body relative to a fixed
reference point, as in a single heaving body design. However an
analysis of the efficiency of the dual heaving body design as an
oscillating system, over the typical frequency range of ocean
waves, indicates that a dual heaving body design is not practical
for any serious wave energy extraction. This is further attested by
the fact that there are no commercial installations using this type
of differential motion. The existing commercial versions of a
heaving buoy use various implementations of a single oscillating
body.
[0039] The other aspect of wave motion pertinent to the present
invention is that of surge. As mentioned previously surge is motion
along the x-axis and is very amicable for the extraction of energy
from the horizontal energy of a wave. A surging body is capable of
extracting half of the wave energy, namely the horizontal energy
component of a wave. By combining surging and heaving it is
theoretically possible to extract 100% of the ocean wave energy.
Clearly there is a huge benefit in utilizing means capable of
extracting the energy from both of these vectors. This is really
only achievable in theory as other factors such as wave
non-linearities, multi-directional waves and other variables
influence the motion of the body. Preferred embodiments of the
present invention typically seek to harness both surging and
heaving in order to achieve optimum wave energy extraction.
Advantageously the WEC of the invention employ a hydrofoil or
hydroplane to access the horizontal energy in an ocean's wave. A
hydroplane can be used to divert the mass of water travelling in
the wave and thus produce a net force in any direction.
[0040] The preferred embodiments of the WEC of the present
invention typically employ a surging and heaving body design, which
uses multiple degrees of freedom to extract energy from the
travelling waves of the ocean. The WEC converts these heaving, and
surging motions of the water particles into vertical forces which
in turn move the translator of a linear electric generator in
differential motion with its stator. The linear electric generator
converts this differential motion to an induced potential
difference that can be applied to a load, thus allowing useful work
to be done with the chaotic energy of an ocean's wave.
[0041] In the preferred embodiments of the WEC of the present
invention heave response is not solely used to convert the energy
within a wave. In the present invention heave response may also be
used to `tune` the operational frequencies, such that frequencies
below its tuned frequency will experience minimal attenuation. A
tension mooring system in accordance with the invention is employed
in association with the WEC to achieve this tuneability. Such a
novel use of heave increases the survivability of the WEC without
sacrificing the efficiency of the energy extraction. This approach
is different to prior art devices, which only use the heave
response of the body(s) to generate their energy. For clarity, a
heave response is the vertical oscillation experienced by a body in
response to the heave of a wave. A heave response is an artefact of
buoyancy and mass only. A possible embodiment of the tension
mooring system in accordance with the invention may also itself be
used to extract energy from the heave of a wave, as will be
described in more detail below.
[0042] A preferred design of the WEC is such that it has only one
moving (or working) member, this member is located above the mean
water level within what is commonly termed the splash zone. The
system is an oscillatory system that uses forces derived from the
surge and heave of the water particles within the wave. These
forces are then used to drive the partially submerged structure
down, while the float is driven up. A tension mooring system is
preferably associated with the WEC to tension the submerged
structure relative to the ocean floor. The opposing motion of the
two bodies ensures the maximum amount of differential motion and
hence the maximum amount of energy extracted from the wave.
[0043] A first embodiment of the wave energy converting apparatus
10 of the present invention, as illustrated in FIGS. 1 to 7 of the
accompanying drawings, comprises an elongate support structure 12
designed to extend above a mean water level in the ocean. The
apparatus 10 uses surging, heaving, buoyancy and hydrodynamic
forces to extend the theoretical maximum energy extraction from 50%
for a single heaving body to 100%. The support structure 12 is in
the form of a frame having a submerged member 14 provided in
connection therewith below the mean water level. The support
structure 12 is also provided with a buoyant means to enable the
support structure to float in the ocean in a generally upright
orientation. In the illustrated embodiment the buoyant means is in
the form of a buoyancy tank 16 provided within the submerged member
14, as will be described in more detail below. In this embodiment
the buoyancy tank 16 is normally filled with sufficient air to give
the submerged member 14 an overall positive buoyancy. It will
therefore be referred to in this embodiment as a positively buoyant
submerged member (PBSM) 14. The buoyancy of the PBSM 14 extends
beyond the mean water level such that if the water level were to
rise the associated buoyancy force would also increase. In an
alternate embodiment the submerged member 14 is filled with
sufficient air to ensure that the submerged member has a total mass
equal to the mass of the water it displaces, i.e. it has neutral
buoyancy.
[0044] The apparatus 10 further comprises a float member 18 of
positive buoyancy slidably mounted in the support structure 12 so
as to be movable in a vertical direction within the support
structure 12. The apparatus 10 also comprises a linear electric
generator 20 having a stator 22 provided in connection with the
support structure 12 and a translator 24 provided in connection
with the float member 18. The stator 22 of this embodiment is of
planar, elongate construction and extends vertically along a
central plane of the support structure 12, from the positively
buoyant submerged member (PBSM) 14 below the mean water level to a
position above the mean water level. In this embodiment the
translator 24 is integrated into the body of the float member 18,
as will be described in more detail below. Electrical power
generated by the linear electric generator 20 is tapped off via an
electrical power terminal 26 provided at the top end of the stator
22, and may be carried to shore via a suitable underwater cable
(not shown) or by wireless (microwave) transmission.
[0045] The float member 18 of the PBSM 14 is a buoyant member and
has a density of half that of the water it displaces. It typically
also has a volume less than or equal to the volume of the submerged
member 14. The combination of these two parameters makes the mass
of the floating member 18 less than or equal to half the mass of
the PBSM 14. The buoyancy of the PBSM 14 provides an opposing force
sufficient to counter the downward force produced by the linear
electric generator 20 on its downward return stroke. The float
member 18 is free to move vertically along the stator 22 via low
friction guides. These low friction guides can typically be
implemented as a sealed bearing surrounded by a plastic or rubber
sleeve (not visible) located on the float member 18, with a
corresponding channel or guide located on the stator 22. Other
possible configurations for low friction guides will be evident to
persons skilled in the art. When wave motion causes a suitable
differential motion between the float member 18 and the support
structure 12, the translator 24 is translated relative to the
stator 22 and the linear electric generator 20 generates electrical
power.
[0046] Preferably the float member 18 is provided with a
hydrofoil/hydroplane surface 30 adapted to convert a horizontal
component of the wave motion into a vertical movement of the float
member 18, thus enhancing the energy extracting capacity of the
float member 18. The float member 18 has an elongate horizontal
cross-section, with a front end 32 and a rear end 34, the front end
32 being adapted to face into the general direction of an
approaching wave. The front end 32 is narrowed to a V-shaped tip.
Preferably the hydroplane surface 30 is one of a plurality of
substantially parallel hydroplane surfaces 30 extending
perpendicularly to and along respective first and second sides of
the float member 18. The hydroplane surfaces 30 are inclined
downwards from the front end 32 to the rear end 34 of the float
member 18. This configuration ensures that water particles in an
approaching wave are forced downwards by the hydroplane surfaces
30, creating hydrodynamic forces acting upwards on the hydroplane
surfaces 30 which are added to an upward force acting on the float
member due to its buoyancy.
[0047] The PBSM 14 also has an elongated horizontal cross-section,
with a front end 36 and a rear end 38, the front end 36 being
adapted to face into the general direction of an approaching wave.
The front end 36 is narrowed to a V-shaped tip and PBSM 14 has a
V-shaped hull like a boat, as can be seen most clearly in FIG. 1.
Preferably the PBSM 14 has a substantially planar upper surface 40
which is inclined upwards from the front end 36 to the rear end 38
of the submerged member, wherein water particles in a wave
approaching from the front are forced upwards by the planar upper
surface 40 creating a downward force acting upon the PBSM 14.
[0048] The PBSM 14 is designed such that resistance to downward
movement of the member is, to whatever extent possible, minimised.
On the other hand, upward movement of the PBSM 14 (and hence of the
entire support structure 12) is hindered by using hydrodynamic
forces derived from the viscous force of the planar upper surface
40 moving in an upward direction and the tethering force of the
tension mooring system. As water particles in the crest of a wave
encounter the float member 18 they are forced downwards by the
hydroplane surfaces 30. This produces an upward force on the float
member 18. On the other hand as the water particles encounter the
PBSM 14 they are forced upwards by the inclined upper surface 40.
This produces a downward force on the PBSM 14. Hence, when a wave
encounters the apparatus 10 there will be an upward force acting
upon the float member 18, and a downward force acting upon the PBSM
14, due to the wave's horizontal motion. The downward force applied
to the PBSM 14 will be opposed by the damping provided by the
linear electric generator 20. The result of the upward force
applied to the float member 18 via its hydroplanes 30 and buoyancy
is an upward movement of the translator 24 of the linear electric
generator 20. Through the interaction of these buoyant and
hydrodynamic forces it is possible to maximise the differential
motion between the float member 18 and the support structure 12 in
order to optimise the energy extracted from the wave by the
apparatus 10.
[0049] To counteract the upward buoyant force on the PBSM 14 a
novel tension mooring system has been invented, of which a
preferred embodiment, in the form of mooring means 60, is
illustrated in FIGS. 4 and 5. The mooring system 60 comprises a
ballast 62 for anchoring the device, and a counterbalancing means
64 for counteracting the excessive buoyancy of the PBSM 14. The
ballast 62 and the counterbalancing means 64 are connected via a
chain or cable 66, which passes through a pulley mechanism 68
located at the bottom of the PBSM 14 (see FIG. 5). A dampening
means in the form of a mechanical braking system 70 is provided in
connection with the pulley mechanism 68, though some other
dampening means such as an electrical or hydraulic or pneumatic
dampener can be used. The braking system applies a braking or
damping action to the cable via the pulley mechanism 68. The
braking system 70 effectively applies a braking action to the PBSM
14, and hence to the support structure 12 of the apparatus 10, via
the mooring means 60. The braking system 70 is typically solenoid
activated, electrical power for the solenoid (not shown) being
supplied by the linear electric generator 20 via a shunt circuit.
Therefore the braking system 70 will not engage if there is no
electricity being produced. The proportion of braking will be
dependent upon the amount of current being produced. If a small
power demand is being met, or the wave frequency is outside the
operational parameters of the linear electric generator 20, then
the braking system 70 will be off. However, as the power produced
increases so will the braking, thus maximizing the differential
motion between the two members and optimizing the amount of energy
produced. Preferably the braking system is computer controlled.
[0050] FIG. 6 illustrates the operation of the braking system 70.
When a wave of the desired frequency passes through the apparatus
10, the float member 18 will move upwards due to its positive
buoyancy and the hydrodynamic forces acting on the hydroplane
surfaces 30 (FIG. 6a). In this wave energy extracting mode, the
linear electric generator 20 is producing electrical power and this
will result in the application of a braking action via the braking
system 70 to the cable 66 of the mooring means 60. Hence
counterbalancing means 64 will not move and the PBSM 14 remains
stationary. On the other hand as the float member 18 returns to its
lowered position, as shown in FIG. 6b, it produces electrical power
due to the excess buoyancy of the PBSM 14 held in position by the
braking system 70. When the braking system 70 is off the
counterbalancing means 64 is able to move freely up or down on
cable 66.
[0051] By means of this simple control system it is possible to
implement an effective and adaptable means of controlling the
motion of the PBSM 14. By only engaging the braking system 70 when
energy is being produced, there will be a general decrease in
unnecessary stress on the system for times when no energy is being
produced. The braking system 70 may have a contact switch (not
visible) located at the top of the PBSM 14 which will be opened if
the float member 18 moves to the extent of its allowable movement.
Once the switch is opened the shunt to the solenoid will be opened,
thus allowing the PBSM 14 to rise in altitude and relieve the
upward stress provided by the float member 18. This altitude
adjustment will continue until such time as equilibrium is
achieved.
[0052] The mooring means 60 is designed to be a fully automatic
adjustment system, which will keep the mean water level of the
apparatus 10 at a consistent level. If the apparatus 10 moves away
from the shortest distance between the ballast and the PBSM, a
corrective force will come into play that will return the system to
the shortest distance between the two points. This corrective force
will be a fully automatic force due to the gravitational force. The
automatic control system of the apparatus 10 is such that all wave
frequencies outside of the predefined operational range will be
passed by the whole of the support structure 12 and not just the
float member 18. This approach will allow the system to
automatically calibrate itself to the prevailing mean water level,
thus allowing it to adjust to tidal fluctuations, storm surges and
other low frequency phenomenon, which if not planned for could lead
to the destruction of the wave energy converter.
[0053] FIG. 7 illustrates this automatic calibration of the
apparatus 10 to the mean water level. In this case, the wave
frequency is outside the predefined operational range of the
apparatus 10, and hence the float member 18 remains essentially
stationary relative to the PBSM 14 irrespective of the water level,
and there is no differential motion to produce electric power via
the linear electric generator 20. Hence the braking system 70
remains inactivated and the mooring system 60 freewheels. The
counterbalancing means 64 moves up and down with changes in the
mean water level, as shown in FIGS. 7a and 7b respectively.
[0054] In this embodiment the mooring means is implemented in the
form of a mooring caddy 72, in which the PBSM 14 of the support
structure 12 is adapted to dock in use. FIG. 5 illustrates a
preferred embodiment of the mooring caddy 72. The PBSM 14 is
secured in the mooring caddy 72 by a suitable locking mechanism,
which may automatically secure the PBSM 14 as it docks in the
mooring caddy 72. In the illustrated embodiment the PBSM 14 is
manually secured to the mooring caddy 72 via securing bolts 74. The
braking system 70 and pulley mechanism 68 are preferably housed in
the mooring caddy 72. All the components required to implement the
wave energy converting apparatus of this embodiment may be housed
in the mooring caddy 72. The mooring caddy 72 preferably has its
own buoyancy tank 76 (not visible) which can be filled or evacuated
with compressed air as required to lift or lower the caddy 72 in
the water during docking, maintenance or operational
situations.
[0055] The counterbalancing means 64 of the mooring means 60 will
essentially be a mass, though it is intended that the
counterbalance will not be a completely inert mass. Preferably the
counterbalancing means 64 comprises a denser-than-water substance
(e.g. concrete) and an air chamber within (not visible).
[0056] The air chamber is designed so that when filled it will
provide sufficient buoyancy to lift the counterbalancing means 64
to the surface of the water. When the air chamber is filled with
water it will add additional mass to the system thus increasing the
system's performance for lower frequencies. Another aspect of the
counterbalancing means 64 is the ability to refill the air chamber
within, either remotely and/or directly. When the air chamber is
re-filled the counterbalancing means will ascend to the surface of
the water in such a fashion that the caddy 72 will be located to
the top of the counterbalancing means 64, thus allowing for
extraction or maintenance to be performed on the PBSM 14.
[0057] A second use of the counterbalancing means 64 is as an
automatic commissioning system. The commissioning of the system
will be such that the mooring means 60 will be set, which includes
the ballast 62 and the counterbalancing means 64. The
counterbalancing means 64 will be left in its buoyant state until
such time as the apparatus 10 is ready to be commissioned. When the
apparatus 10 is to be commissioned it will be attached to the
exposed caddy 72, after which the counterbalancing means 64 will be
filled with water, thus automatically setting the apparatus 10 into
its correct working position, without the need for divers and
highly specialized equipment. This novel way of commissioning the
apparatus 10 will help to keep the commissioning, decommissioning,
repairs and maintenance costs to a minimum. An alternative
configuration is for the counterbalancing means 64 to be
constructed solely of denser than water material (such as concrete)
and that the caddy 72 is the adjustable buoyant chamber used to
raise and lower the counterbalancing means 64.
[0058] The linear electric generator 20 used by the apparatus 10 is
designed to provide the optimal frequency response and EMF to allow
the most amount of energy to be extracted from the waves of the
ocean. This optimization is achieved by matching the performance
parameters of the linear electric generator 20 to the damping
requirements of the mechanical system in such a way that critical
damping of the oscillating system will be achieved when the system
is under full load.
[0059] The linear electric generator 20 within the apparatus 10 is
such that the stator 22 is part of an oscillating body system which
is in a predominantly stationary reference frame, while the
translator 24 is attached to the predominantly moving reference
frame. In the illustrated embodiment the stator 22 is connected to
the submerged member 14, while the translator 24 is connected to
the float member 18. In reality both of these parts will be moving,
though for the sake of adhering to popular naming conventions, the
terms "stator" and "translator" will be used to refer to the
predefined WEC structures. As the motion of the stator 22 and the
translator 24 are subjective, the locations of the copper wire,
magnets, and magnetic permeable material can also be located on
either the stator or the translator. The location of these
materials will depend upon the specific requirements and design
criteria of the implementation of the apparatus.
[0060] The wave energy converting apparatus 10 is configured in
such a way to be easily towed behind a vessel, thus allowing it to
be readily and quickly commissioned. The V-shaped hull of the PBSM
14 facilitates effective towing of the wave energy converting
apparatus 10. To commission or decommission the apparatus 10
high-pressure air is applied to a valve 42 located above the mean
water level. In the illustrated embodiment the valve 42 is located
at the top of the stator 22 and is connected to a fluid passage
(not visible) that extends down through the stator 22 to the
buoyancy tank 16 in the body of the PBSM 14. High-pressure air
pumped into the buoyancy tank 16 via the valve 42 and through one
fluid passage expels ballast water from within the buoyancy tank 16
through the other fluid passage, thus causing the PBSM 14 to rise
above the mean water level. When the buoyant member 14 is above the
mean water level the energy production will stop and the entire
support structure 12 will behave as a boat thus enabling easy
transport of the apparatus 10.
[0061] When commissioning the apparatus 10, any excess buoyancy of
the buoyant member 14 is released by the reverse process thus
re-submerging the support structure 12 and re-instating the energy
production. This type of rapid deployment and retrieval aids in
keeping the cost of commissioning, repairs and maintenance to a
minimum, as well as ensuring the most reliable supply of
energy.
[0062] Another advantageous aspect of the apparatus 10 is that it
can be engineered to be responsive, for electric power generation,
to a specific wave frequency range. In the illustrated embodiment
the horizontal length of the apparatus 10 is approximately five
metres, which corresponds to a quarter wavelength of an ocean wave
of 20 metre wavelength. This feature is particularly useful when
applied to the ocean, as the energy available within ocean waves
increases the lower the frequency. In the past many wave energy
converters have been lost during storm conditions due to exposure
to excessive wave energy densities. With the frequency tuning
ability of the apparatus 10, it is possible to extract energy from
the predefined frequencies only, while simply letting the
destructive high energy density waves pass without attenuation.
[0063] The consequences for the survivability of the apparatus 10
are significant, not to mention the benefit of being able to
produce power when other wave energy converters would have to be
taken out of service to ensure their survival.
[0064] The wave energy converting apparatus 10 may be constructed
as a modular unit and may be one of a plurality of such modular
units that are connected together as a wave energy converting power
array or power matrix. In the illustrated embodiment the frame of
the support structure 12 is of substantially rectangular
configuration. This shape facilitates the interconnection of a
plurality of the modular units side by side in two orthogonal
directions.
[0065] FIGS. 8 to 11 illustrate a second embodiment of a wave
energy converting apparatus 44 and its associated tension mooring
system 50 in accordance with the invention. The wave energy
converting apparatus 44 comprises an elongate support structure 45
designed to extend above a mean water level in the ocean. The
support structure 45 is in the form of a vertically oriented column
having a submerged member 46 provided in connection therewith below
the mean water level. The support structure 45 of this embodiment
is also provided with a buoyant means to enable the support
structure to float in the ocean in a generally upright orientation.
In the illustrated embodiment the buoyant means is in the form of a
buoyancy tank 47 (not visible) provided within the submerged member
46. As with the previous embodiment, the buoyancy tank 47 is
normally filled with sufficient air to give the submerged member 46
an overall positive buoyancy.
[0066] The apparatus 44 further comprises a float member 48 of
positive buoyancy slidably mounted on the support structure 45 so
as to be movable in a vertical direction. In this embodiment the
float member 48 is of spherical configuration and is slidably
mounted on the vertical column of the support structure 45. The
apparatus 44 also comprises a linear electric generator 49 having a
stator provided in connection with the vertical column of the
support structure 45 and a translator integrated into the body of
the float member 48. Operation of the wave converting apparatus 44
of this embodiment, for converting ocean wave energy into
electrical power, is similar to that of the first embodiment 10 and
will not be described in detail again here. The hydrodynamic and
buoyant properties of the spherical float member 48 will produce a
differential motion of the translator of the linear electric
generator 49 relative to the stator, as in the previous embodiment.
Advantageously the upper surface of the submerged member 46 is of
substantially hemi-spherical configuration, so as to act as a
deflecting surface for the water (not unlike the upper surface 40
of the first embodiment), to further enhance this differential
motion.
[0067] The tension mooring system 50 of this embodiment comprises
an elongate flexible member in the form of a cable 51 extending
from a ballast means 52 to a counterbalancing means 53 adapted to
be suspended from the submerged member 46 via a pulley mechanism
54. The ballast means 52 may take the form of a large block of
concrete, or alternatively a suitable sea bed mooring may be
employed to anchor one end of the cable 51 to the ocean floor. The
counterbalancing means 53 comprises a mass having an adjustable
buoyancy tank provided in connection therewith, as illustrated in
FIG. 9.
[0068] The counterbalancing means 53 of this embodiment is in the
form of a hollow vessel 55 having a solid base 56 of a
predetermined mass to act as a counterweight for the submerged
member 46. The remaining volume of the vessel 55 can be filled with
compressed air via an air hose 57 to adjust the buoyancy of the
vessel 55. A valve 58 may be provided in a wall of the vessel 55 to
expel air to the ambient ocean. The other end of the cable 51 is
connected to the top of the vessel 55 and extends up to the pulley
mechanism 54, before it passes back down through a hollow passage
59 extending vertically along the central axis of the vessel 55 to
the ballast means 52.
[0069] By adjusting the buoyancy of the vessel 55 the
counterbalancing force applied to the submerged member 46 via the
cable 51 can be varied. In this manner the resonant frequency of
the wave energy converting apparatus 44 and its associated tension
mooring system 50 can be adjusted to "tune" it to the prevailing
ocean conditions. Preferably the mass of the base 56 of the vessel
55 is set to match the minimum desired operating frequency of the
system. This mass also helps to keep the wave energy converting
apparatus 44 in an upright orientation due to the low centre of
buoyancy and low centre of mass given to the system by the base 56.
As the mass of the vessel 55 decreases the resonant frequency of
the system increases.
[0070] The pulley mechanism 54 is housed in a mooring caddy 80,
which is illustrated with a transparent wall in FIGS. 11 and 12.
The mooring caddy 80 is of cylindrical shape in this embodiment to
match the shape of the submerged member 46, and may be permanently
or releasably attached to the bottom of the submerged member 46. As
can be seen most clearly in FIG. 11, the pulley mechanism 54
comprises a pulley 82 fixedly mounted on a shaft 84 which is
rotatably mounted between a pair of rotary electrical generators
86a and 86b. As the shaft 84 oscillates, the generators 86a and 86b
will generate an EMF and offer resistance to the rotary motion of
the shaft. The electrical generators 86 thus provide a dampening
means for applying a dampening action to the rotation of the shaft
84 and hence of pulley 82. When a load is applied to the electrical
generators 86, they effectively apply a dampening action to the
cable 51 via the pulley 82, and hence to the motion of the
submerged member 46 by virtue of the counterbalancing means 53.
[0071] If desired the electrical energy generated by the generators
86 can be stored in batteries 88 housed in the caddy 80. An
electronic energy conversion and control module 90 is provided for
converting the AC current generated by the generators 86 into a DC
current for storage in the batteries 88. The energy conversion and
control module 90 may also be configured to enable the caddy itself
to become the wave energy converter apparatus, as will be described
in more detail below. A microprocessor operated control system 92
is also provided within the mooring caddy 80, to provide automatic
control of all the components of the tension mooring system 50. The
control system 92 monitors the frequency of the waves and adjusts
the mass of the counterbalancing means accordingly.
[0072] An air compressor 94 is provided within the mooring caddy
80, for pumping air down to the counterbalancing means 53 via air
hose 57. Some of the power generated by the generators 86 can be
used to power the air compressor 94. Air compressor 94 is also
under the control of control system 92. An air conduit 96 supplies
air from atmosphere to the air compressor 94, and extends upwards
through the submerged body 46 to a point above the water line. Air
inside the hollow vessel 55 of the counterbalancing means 53 need
not be expelled to ambient ocean but could be pumped back up to a
pressure vessel (not shown) housed within the mooring caddy 80 or
submerged member 46.
[0073] A typical operating sequence for the tension mooring system
50 will now be described with reference to FIGS. 8 to 11:
[0074] Given a particular operational environment the control
system 92 will measure and calculate, via appropriate means such as
an accelerometer, the wave frequencies which are presented to the
system. The dominant and/or most energy dense frequencies will be
determined through calculation using well known formulae. Once the
optimal operational frequency has been selected, also from well
know formulae, the optimal system mass allowing for the most energy
to be extracted can be calculated.
[0075] The control system 92 will then calculate the current system
mass and determine the volume of water to be taken in, or removed
from, the system to achieve this optimal mass. If the mass needs to
be decreased, then the control system 92 will activate the air
compressor 94 to pump air into the hollow vessel 55 thus evacuating
the water present in the hollow vessel 55 through positive pressure
displacement as used in submarines. If the mass needs to be
increased, then the control system 92 will either open the air
valve 58 to expel the air within the hollow vessel 55 or activate
the air compressor 94 to pump the air into an alternate storage
tank thus allowing water to fill the evacuated volume and
increasing the mass of the system.
[0076] In this manner the control system 92 will move mass into and
out of the tension mooring system 50 thus changing the operational
characteristics of the system through mass variation and allowing
the system to be tuned to perform optimally in an ever-changing
environment.
[0077] Any suitable dampening means may be employed in the mooring
caddy 80 for applying a dampening action to the motion of the
submerged member 46. The electric generators 86 are particularly
advantageous as they can be used directly as a source of electrical
power. However, a hydraulic pump could also be used to provide the
dampening action. FIG. 12 illustrates an alternative embodiment of
the mooring caddy 80, which is substantially identical to the
embodiment of FIG. 11 except that the rotary electric generators 86
have been replaced with a pair of hydraulic pumps 98 to provide the
dampening means. Both hydraulic pumps 98a and 98b are operatively
coupled to the shaft 84 by a respective belt and pulley system 99a
and 99b. The hydraulic pumps 98 may be used, for example, to pump
hydraulic fluid (oil, sea water) via a hose to an hydraulically
operated electric generator or hydraulic accumulator. Pneumatic
pumps may be used instead of the hydraulic pumps 98.
[0078] The wave energy converting apparatus 44 shown in FIGS. 8 and
10 incorporates a wind turbine 100 mounted on top of the support
structure 45 of the apparatus. The wind turbine 100 provides a
means of capturing another source of renewable energy, namely ocean
winds. The turbine is oriented to rotate about a vertical axis and
is provided with a series of vanes 102 to capture the wind and
generate electrical power. A rotary electric generator (not
visible) is housed in the base of the wind turbine 100. Electrical
power generated by the wind turbine 100 can be stored in the
batteries 88, or transmitted to shore via cable or wirelessly using
a microwave transmitter (not shown). A dome 104 visible on top of
the turbine may be used to house the transmitter and/or a GPS or
some other form of positioning beacon.
[0079] The wave energy converting apparatus 44 will of course
operate perfectly satisfactorily without the wind turbine 100. An
embodiment of the apparatus 44 without the turbine is illustrated
in FIG. 13. If desired the wave energy converting apparatus 44 can
also be fitted with solar panels 108 to take advantage of a third
source of renewable energy, namely sunlight. FIG. 14 illustrates an
embodiment of the apparatus 44 with a plurality of solar panels 108
mounted on top of the wind turbine 100. In other respects the wave
energy converting apparatus 44 of this embodiment (and of the
previous embodiment) with its associated tension mooring system 50
is substantially identical to that of the embodiment illustrated in
FIGS. 8 to 11 and will not be describe again here.
[0080] FIG. 15 illustrates a fourth embodiment of the wave energy
converting apparatus 110, which is similar to the embodiment 44 of
FIGS. 8 to 11 and hence the same reference numerals will be used to
identify the similar parts.
[0081] In this embodiment of the apparatus 110, the housing of the
mooring caddy 80 is open at the bottom so as to allow sea water to
fill the space within the hollow interior not occupied by the
components of the tension mooring system 50. In each of the
foregoing embodiments all of the components of the tension mooring
caddy housed within the caddy 80 are encapsulated in an air-tight
and water-tight casing that protects them from the corrosive
effects of sea water.
[0082] The open bottom of the mooring caddy 80 creates an air
chamber 112 that can be partially filled with air so as to give the
mooring caddy neutral buoyancy. As the chamber 112 is open to the
ambient ocean its buoyancy will vary with hydrostatic pressure
variations due to wave motion. As each wave crest passes the
buoyancy of the neutrally buoyant mooring caddy 80 will drop to
negative buoyancy as the hydrostatic pressure increases. The
mooring caddy will then rise as positive buoyancy occurs when the
apparatus 110 enters the trough of the wave. These variations in
the buoyancy of the mooring caddy, which is directly connected to
the submerged member 46 will be 180.degree. out of phase with the
vertical motion of the float member 48, and hence will help to
further increase the differential motion of the stator and
translator of the linear electric generator 49.
[0083] As previously mentioned, the tension mooring system of the
present invention may itself be used as a wave energy converting
apparatus. FIG. 16 illustrates an embodiment of the tension mooring
system 120 which itself has been configured as a wave energy
converting apparatus. In this embodiment the mooring caddy 80 is
mounted directly to the underside of a buoyant canister 122. There
is no linear electric generator as in the previous embodiments. In
this embodiment the canister 122 has a wind turbine 100 mounted on
top, similar to the embodiment of FIGS. 8 to 11. The tension
mooring system 120 operates in a similar way to the embodiment of
FIGS. 8 to 11, except that in this case the control system is
configured to enable the electric generators 86 to operate at
maximum efficiency to generate electrical power as they are not now
required to act as dampening means. The tension mooring system 120
still operates as an oscillating system which can be tuned to the
frequency of the waves in the ocean to extract maximum energy from
the heave response of the canister 122.
[0084] Now that several embodiments of the wave energy converting
apparatus and tension mooring system have been described in detail,
it will be apparent that the described embodiments of the apparatus
provide a number of advantages compared with the prior art,
including the following: [0085] (i) The wave energy converter is
robust in design, being able to withstand most weather conditions
with minimal likelihood of damage. [0086] (ii) The tension mooring
system enables the wave energy converting apparatus to be tuned to
the prevailing ocean conditions to maintain maximum efficiency.
[0087] (iii) The tension mooring system can be adapted for use with
any buoyancy type wave energy converting apparatus to improve its
operating efficiency. [0088] (iv) It is versatile, being able to
extract energy from waves covering a large range of wave heights,
wave frequencies and wave directions. [0089] (v) It is very
efficient, using the principles of surge, heave, buoyancy
hydrostatic and hydrodynamic pressure to extract the maximum amount
of energy from the waves.
[0090] It will be readily apparent to persons skilled in the
relevant arts that various modifications and improvements may be
made to the foregoing embodiments, in addition to those already
described, without departing from the basic inventive concepts of
the present invention. For example, the stator need not be located
on a central plane or axis of the apparatus, but could be located
elsewhere in the support structure of the wave energy converting
apparatus. Therefore, it will be appreciated that the scope of the
invention is not limited to the specific embodiments described and
is to be determined from the appended claims.
* * * * *