U.S. patent application number 17/219261 was filed with the patent office on 2021-12-30 for submerged wave energy converter for deep water operations.
The applicant listed for this patent is The Regents of the University of California. Invention is credited to Mohammed-Reza ALAM, Thomas BOERNER, Nigel KOJIMOTO, Marcus LEHMANN, Bryan MURRAY.
Application Number | 20210404436 17/219261 |
Document ID | / |
Family ID | 1000005840071 |
Filed Date | 2021-12-30 |
United States Patent
Application |
20210404436 |
Kind Code |
A1 |
LEHMANN; Marcus ; et
al. |
December 30, 2021 |
SUBMERGED WAVE ENERGY CONVERTER FOR DEEP WATER OPERATIONS
Abstract
A submergible wave energy converter and method for using the
same are described. Such a wave energy converter may be used for
deep water operations. In one embodiment, the wave energy converter
apparatus comprises an absorber having a body with an upper surface
and a bottom surface and at least one power take-off (PTO) unit
coupled to the absorber and configured to displace movement of the
absorber body relative to a reference, where the power take-off
unit is operable to perform motion energy conversion based on
displacement of the absorber body relative to the reference in
response to wave excitation, and where the power take-off unit is
operable to return the absorber body from a displaced position to a
predefined equilibrium position and to provide a force acting on
the absorber body for energy extraction.
Inventors: |
LEHMANN; Marcus; (Berkeley,
CA) ; ALAM; Mohammed-Reza; (Berkeley, CA) ;
BOERNER; Thomas; (Berkeley, CA) ; KOJIMOTO;
Nigel; (Berkeley, CA) ; MURRAY; Bryan;
(Berkeley, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
The Regents of the University of California |
Oakland |
CA |
US |
|
|
Family ID: |
1000005840071 |
Appl. No.: |
17/219261 |
Filed: |
March 31, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
15960336 |
Apr 23, 2018 |
11002243 |
|
|
17219261 |
|
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|
|
62489386 |
Apr 24, 2017 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F05B 2270/18 20130101;
F03B 13/187 20130101; F05B 2250/72 20130101; F05B 2260/406
20130101; F03B 13/148 20130101; Y02E 10/20 20130101; F03B 13/10
20130101; F03B 13/186 20130101; F05B 2250/22 20130101; Y02E 10/30
20130101 |
International
Class: |
F03B 13/10 20060101
F03B013/10; F03B 13/18 20060101 F03B013/18; F03B 13/14 20060101
F03B013/14 |
Goverment Interests
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] This invention was made with Government support under
DE-AC02-05CH11231, awarded by the Department of Energy. The
Government has certain rights in the invention.
Claims
1.-25. (canceled)
26. A method for operating a wave energy converter comprising an
absorber body, a plurality of power takeoff units coupled to the
absorber body, and a plurality of mooring lines, wherein each of
the plurality of mooring lines couples a power takeoff unit of the
plurality of power takeoff units to a seafloor, the method
comprising: receiving, at a controller, data from one or more
sensors integrated into the wave energy converter; determining, by
the controller, a tension on a first mooring line of the plurality
of mooring lines to manage a load exerted on the wave energy
converter based on the data from the one or more sensors; and
adjusting the tension of the first mooring line to the tension
determined by the controller.
27. The method of claim 26, wherein adjusting the tension is
performed by a winch of a first power takeoff unit of the plurality
of power takeoff units, wherein the first mooring line is coupled
to the first power takeoff unit via the winch.
28. The method of claim 26, further comprising determining, by the
controller, a tension on a second mooring line of the plurality of
mooring lines to manage the load exerted on the wave energy
converter based on the data from the one or more sensors; and
adjusting the tension of the second mooring line based on the
tension determined by the controller.
29. The method of claim 28, further comprising independently
adjusting the tension in the first mooring line and the tension in
the second mooring line.
30. The method of claim 26, wherein the data from the one or more
sensors is indicative of the load exerted on the wave energy
converter.
31. The method of claim 26, wherein the data from the one or more
sensors is indicative of a motion of the absorber body.
32. The method of claim 26, wherein determining the tension on the
first mooring line comprises determining a tension on the first
mooring line that prevents the load exerted on the wave energy
converter from exceeding a predetermined maximum load.
33. The method of claim 26, wherein each of the plurality of
mooring lines is arranged diagonally relative to the seafloor.
34. A method for operating a wave energy converter comprising an
absorber body, a power takeoff unit coupled to the absorber body,
and a mooring line that couples the power takeoff unit to a
seafloor, the method comprising: determining, by the controller, an
adjustment of a tension on the mooring line and of a submergence
depth of the absorber body in order to regulate motion of the
absorber body and maximize power generation; and adjusting the
submergence depth and the tension in the mooring line based on the
adjustment determined by the controller.
35. The method of claim 34, wherein adjusting the submergence depth
comprises adjusting a length of the mooring line via a winch of the
power takeoff unit to which the mooring line is coupled.
36. The method of claim 34, further comprising: receiving, by the
controller, data from one or more sensors integrated into the wave
energy converter, wherein the adjustment is determined at least in
part based on the data received from the one or more sensors.
37. The method of claim 36, wherein the data from the one or more
sensors is indicative of energy capture by the wave energy
converter.
38. The method of claim 34, further comprising receiving an input
from an operator, wherein the adjustment is determined at least in
part based on the input from the operator.
39. The method of claim 34, wherein determining the adjustment
comprises a machine-learning algorithm.
40. The method of claim 34, wherein determining the adjustment
comprises comparing the data received from the one or more sensors
to a lookup table.
41. The method of claim 34, wherein the adjustment comprises
regulating the motion of the absorber body such that a frequency of
the absorber body corresponds to a frequency of ocean waves.
42. A method for operating a wave energy converter comprising an
absorber body, a power takeoff unit coupled to the absorber body,
and a mooring line that couples the power takeoff unit to a
seafloor, the method comprising: determining, by the controller, an
adjustment of one or more of: a tension in the first mooring line,
a submergence depth of the absorber body, and a geometry of the
absorber body, in order to regulate motion of the absorber body to
maximize power generation; and adjusting at least one of the
tension in the mooring line, the submergence depth of the absorber
body, or the geometry of the absorber body, respectively, based on
the adjustment determined by the controller.
43. The method of claim 42, wherein the absorber body comprises an
aperture having a movable closure, and wherein adjusting the
geometry of the absorber body comprises adjusting a position of the
closure.
44. The method of claim 42, further comprising receiving data from
one or more sensors integrated into the wave energy converter, and
wherein the adjustment is determined at least in part based on the
received data.
45. The method of claim 42, wherein the adjustment comprises each
of the tension in the first mooring line, the submergence depth of
the absorber body, and the geometry of the absorber body.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 15/960,336, filed Apr. 23, 2018, which claims
priority to provisional patent application Ser. No. 62/489,386,
titled, "Submerged Wave Energy Converter for Deep Water
Operations," filed on Apr. 24, 2017. Each of these applications is
incorporated herein by reference in its entirety.
NOTICE OF MATERIAL SUBJECT TO COPYRIGHT PROTECTION
[0003] A portion of the material in this patent document is subject
to copyright protection under the copyright laws of the United
States and of other countries. The owner of the copyright rights
has no objection to the facsimile reproduction by anyone of the
patent document or the patent disclosure, as it appears in the
United States Patent and Trademark Office publicly available file
or records, but otherwise reserves all copyright rights whatsoever.
The copyright owner does not hereby waive any of its rights to have
this patent document maintained in secrecy, including without
limitation its rights pursuant to 37 C.F.R. .sctn. 1.14.
FIELD OF THE INVENTION
[0004] The technology of this disclosure pertains generally to
renewable electricity generation, and more particularly to a system
and platform for wave energy extraction using an absorber actuating
one or more power take-off units.
BACKGROUND
[0005] The oceans of the world have long been recognized as a
potential continuous and abundant source of natural mechanical
energy. Increasing global demand for electricity and the need for
alternatives to fossil fuel production make harnessing wave energy
to produce electricity an attractive endeavor. Energy from the
ocean could help to relieve the electricity generation load in many
heavily populated regions of the world as well as to reduce the
volume of environmentally harmful emissions.
[0006] However, successful harvesting of energy from waves for
conversion into electrical energy has been generally limited to
small scale applications, and few existing systems are capable of
providing electricity to established power grids. There are a
number of reasons for the lack of utilization of wave energy in
spite of over 200 years of innovations. One significant reason for
the slow utilization of the available energy from the oceans is the
damage and destruction that can occur to generating devices from
exposure to wave energy from storms, rogue waves and exposure to a
high salt marine environment. Many conventional wave energy
converters extract power from the surface of the ocean and must be
engineered to survive the power of the harshest ocean storms, which
increases the design complexity as well as capital costs.
[0007] In addition to being unable to withstand rough weather, the
performance of many generating devices will drop significantly
during rough weather. Surface wave energy converters rely on
regular and consistent wave formation using vertical motion (heave)
to convert the wave energy and rely on the shape of the incident
wave. Irregular wave behavior during storms or areas without a
consistent flow of powerful waves results in power generation that
is unpredictable and erratic and therefore unsuitable as a source
for existing power grids. Other surface wave energy converters
produce highly distorted power due to the reciprocal motion induced
by the ocean waves.
[0008] Wave energy converters may also be location limited. Surface
devices may interfere with the activity of commercial and private
vessels and therefore cannot be placed in shipping lanes.
Generating systems must also be in close proximity to the shore
because it is difficult to transfer generated energy a great
distance from the shore. Therefore, wave energy is not a viable
power source in all settings because of the location of
generation.
[0009] Capital costs, maintenance costs and repair costs have been
another barrier to widespread installation of fields of wave energy
converters. The useful lifetime, reliability and maintenance
requirements of wave energy devices are important economic factors
considered in such electrical generation investments. Devices that
frequently break down produce unacceptable electricity production
losses, income losses and increased operational costs. Furthermore,
as the demand for renewable energy technologies increases, the cost
of investment and construction of wave energy extraction generating
systems and devices is expected to decrease.
[0010] Successful harvesting of energy from waves for conversion
into electrical energy has also been problematic because the power
quality that is produced by these devices is poor due to the
irregular velocity of the power generating structures as a result
of the irregular spectral nature of the incoming ocean wave.
Consequently, the generator is not able to operate at a constant
speed for optimum efficiency. Rather, the output power is
continuously, fluctuating from zero to a peak and back in every
wave where the device absorber linkage is directly connected to its
generator.
[0011] Although devices for extracting wave energy to perform work
in some form have been developed since the 1700's, only a few full
scale wave energy projects have been constructed. Wave energy
technologies that have been developed tend to be variations of
three general schemes: wave capture devices, oscillating water
column devices and wave profile devices.
[0012] Accordingly, there is a need for a reliable way to harness
wave power to produce electrical energy in remote marine
environments that is efficient, easy to maintain and low in
cost.
SUMMARY OF THE DISCLOSURE
[0013] A submergible wave energy converter and method for using the
same are described. Such a wave energy converter may be used for
deep water operations. In one embodiment, the wave energy converter
apparatus comprises an absorber having a body with an upper surface
and a bottom surface and at least one power take-off (PTO) unit
coupled to the absorber and configured to displace movement of the
absorber body relative to a reference, where the power take-off
unit is operable to perform motion energy conversion based on
displacement of the absorber body relative to the reference in
response to wave excitation, and where the power take-off unit is
operable to return the absorber body from a displaced position to a
predefined equilibrium position and to provide a force acting on
the absorber body for energy extraction.
[0014] Further aspects of the technology described herein will be
brought out in the following portions of the specification, wherein
the detailed description is for the purpose of fully disclosing
embodiments of the technology without placing limitations
thereon.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] The present invention will be understood more fully from the
detailed description given below and from the accompanying drawings
of various embodiments of the invention, which, however, should not
be taken to limit the invention to the specific embodiments, but
are for explanation and understanding only.
[0016] FIGS. 1A-C illustrate side, front and top views,
respectively, of one embodiment of a wave energy converter
apparatus for converting wave energy to usable power.
[0017] FIGS. 2A-C illustrate side, front and top views,
respectively, of an alternative embodiment of a wave energy
converter apparatus.
[0018] FIGS. 3A-C illustrate side, front and top views,
respectively, of another alternative embodiment of a wave energy
converter apparatus.
[0019] FIGS. 4A-C illustrate side, front and top views,
respectively, of another alternative embodiment of a wave energy
converter apparatus.
[0020] FIGS. 5A-C illustrate side, front and top views,
respectively, of another alternative embodiment of a wave energy
converter apparatus.
[0021] FIGS. 6A-C illustrate side, front and top views,
respectively, of another alternative embodiment of a wave energy
converter apparatus.
[0022] FIGS. 7A-C illustrate side, front and top views,
respectively, of an embodiment of a wave energy converter apparatus
that includes an absorber without a platform.
[0023] FIGS. 8A-C illustrate side, front and top views,
respectively, of another embodiment of a wave energy converter
apparatus that includes an absorber without a platform.
[0024] FIGS. 9A-C illustrate side, front and top views,
respectively, of another embodiment of a wave energy converter
apparatus that includes an absorber without a platform.
[0025] FIGS. 10A-C illustrate side, front and top views,
respectively, of yet another embodiment of a wave energy converter
apparatus that includes an absorber, a platform and one or more
mooring chains.
[0026] FIGS. 11A-C illustrate side, front and top views,
respectively, of a further embodiment of a wave energy converter
apparatus absorber aspect ratios, geometries and shapes.
[0027] FIG. 12 is a block diagram of one embodiment of an interface
controller for a wave energy converter apparatus including
interaction between controller input and output sources,
functionalities and data.
[0028] FIG. 13-16 are active and passive aperture opening and
closing control mechanisms that includes apertures that may be
opened and closed.
[0029] FIG. 17 illustrates a block diagram of a power conversion
chain containing one or more PTOs.
[0030] FIGS. 18A-G, 19A-B, 20A-B, and 21A-B illustrate examples of
PTO subsystems that may be used for PTO subsystems of FIG. 1-11
(and the other wave energy converter apparatuses described herein
referencing a cylinder or winch).
[0031] FIGS. 22A-B illustrate examples of interfaces used to
interface hydraulic cylinders to a hydraulic motor and generator,
including the coupling in between.
[0032] FIGS. 23A-23B illustrate examples of an electrical subsystem
that may be used to interface the converted wave energy to the
grid.
DETAILED DESCRIPTION
[0033] In the following description, numerous details are set forth
to provide a more thorough explanation of the present invention. It
will be apparent, however, to one skilled in the art, that the
present invention may be practiced without these specific details.
In other instances, well-known structures and devices are shown in
block diagram form, rather than in detail, in order to avoid
obscuring the present invention.
[0034] A system and method for converting wave energy of ocean
waves to a motive force derived from pressure differentials created
by the system's interaction with ocean water are described. In one
embodiment, the system comprises at least one submersible wave
energy harvesting body, at least one power take-off unit, at least
one restoring force mechanism, and a reaction mechanism providing
force acting on the absorber body for energy extraction. In one
embodiment, the body includes a system for managing structural
loads to maintain energy extraction at a high, and potentially
maximum, level while mitigating damaging loads.
[0035] FIGS. 1A-C illustrate side, front and top views,
respectively, of one embodiment of a wave energy converter
apparatus for converting wave energy to usable power. The apparatus
converts wave energy to mechanically usable power such as, for
example, a torque on a rotary shaft that can drive an electric
generator, hydraulic pump or other consumers. The wave energy is
captured by utilizing a submerged body, referred to as an absorber
herein, that is excited by incident waves, creating a pressure
differential between the top and bottom sides of the absorber. This
pressure differential leads to alternating area loads across the
area of the absorber and ultimately to oscillating relative motion
of the absorber predominantly in heave, surge, and pitch degrees of
freedom (DOF) but also the sway and roll DOF for off-neutral-axis
incident waves.
[0036] Referring to FIGS. 1A-C, in one embodiment, the wave energy
converter apparatus has two main structural elements: 1) an upper,
slender, horizontally oriented absorber 101, with the main function
of a fluid-structure interaction for high performance wave to
mechanical energy conversion; and, 2) a lower base 103, that is
responsible for providing a reaction point for the damping and
restoring force elements allowing for energy extraction of the
absorber 101 from waves.
[0037] In one embodiment, the body of absorber 101 is rigid,
semi-rigid or flexible and the structure is able to extract energy
from water waves by surge, heave, pitch, roll, yaw, and/or sway
excitation. In one embodiment, absorber 101 is rectangular in shape
with dimensions of 20 m by 40 m. Note that other shapes and sizes
of absorbers may be used, such as those shown, for example, in
FIGS. 11A-11C. In one embodiment, absorber 101 comprises a
composite of steel beams, steel or fiberglass plates and has a
frame profile that is reinforced by main and minor beams and load
distributing cross beams and partially filled with polyurethane
foam or sealed pressure vessels and a ballast system to create a
body with neutral or controlled positive buoyancy.
[0038] The top surface of the body of absorber 101 is preferably
planar. However, the top surface may also be altered in a way that
induces desired drag and turbulence leading to an improved fluid
structure interaction (FSI), and thus improved energy transfer from
wave to structure. This could be in a form of surface roughness or
vertical structures blocking or redirecting water flow over the
surface. For example, in one embodiment, winglet extensions may be
attached to prevent neutralization of the dynamic pressure
difference on the side edges of absorber 101.
[0039] In one embodiment, absorber 101 comprise a plate that is
constrained to split the water particles' orbital motions induced
by ocean waves, thus creating independent locally-varying and
time-varying pressures above and below the body of absorber 101,
thereby inducing a motive force from the local and total pressure
differential. The motion is then transferred to one or more power
take-off units (PTOs), which include, in one embodiment, hydraulic
cylinders 102, which transform the motion of absorber 101 into a
standard form of mechanical power. A restoring force is provided to
ensure absorber 101 oscillates about a set equilibrium. A reaction
mechanism is used to oppose the displacement of the power takeoff
and thus transfer energy to a new mechanical form but is also
capable of aiding the displacement of the PTO for increased net
power extraction.
[0040] Absorber 101 is excited by the dynamic pressure difference
created by overpassing waves, which produces a dynamic area load on
the absorber. The horizontally oriented absorber 101 horizontally
splits the pressure gradient underneath incident waves, creating a
pressure differential across it. This pressure differential leads
to alternating area loads across the absorber area and ultimately
to oscillating relative motion of absorber 101 predominantly in
heave, surge, and pitch degrees of freedom (DOF) but also the sway
and roll DOF for off-neutral-axis incident waves. The main function
of absorber 101 is to increase, and potentially maximize, the
oscillating motion in heave, surge and pitch induced by the wave
excitation load/water particle motion around the structure for
on-neutral-axis waves and also in sway and roll for
off-neutral-axis waves.
[0041] In one embodiment, lower base platform 103 comprises a set
of ballast tanks that provide neutral or controllable positive
buoyancy. Restoring forces that react to oppose the compression of
cylinders 102 of the PTOs are enabled by the positive buoyant
ballast system integrated into platform 103.
[0042] In one embodiment, the body of absorber 101 and lower base
platform structure 103 are mechanically connected through joints
with four hydraulic cylinders 102 that serve as power take-off
(PTO) units in the embodiment shown in FIG. 1A-1C. Although four
hydraulic cylinders 103 are preferred, it will be seen that fewer
than four or more than four cylinders as well as alternative force
mechanisms can be used as power take off units. Cylinders 103 can
be single or double acting damping elements acting as a power
take-off system extracting energy from absorber 101. Cylinders 102
can also be individually actuated and/or excited independently and
each can be adjusted in their damping characteristics.
[0043] In one embodiment, hydraulic cylinders 102 are connected on
one end to the body of absorber 101 by a joint 104 and to the lower
base platform 103 on the other with the joint, where the joints can
be universal, gimbal or other type of mechanical joint providing
the same degrees of freedom with the desired reduction of degree of
freedom in obtained. The placement of the hydraulic cylinders in
relation to absorber 101 and base platform 103 allows the absorber
to predominantly operate in the surge, heave, and pitch degrees of
freedom (DOF). This is enabled by placing the joints on the
absorber 101 in a way that creates a lever with respect to the two
neutral symmetry axis of the absorber, e.g. the surge extraction is
affected by the lever distance from the neutral axis of the
absorber that is perpendicular to the wave propagation
direction.
[0044] In one embodiment, one function of the base platform 103 is
to reduce, and potentially minimize, motion induced by 1) wave
excitation load/water particle motion around the structure and 2)
the reaction forces of hydraulic cylinders 102. A secondary
function of base platform 103 is to house the hydraulic power
conversion chain in a central concealed chamber including the
accumulators, hydraulic motors and mechanical consumers such as,
for example, a generator.
[0045] In one embodiment, platform 104 provides the reaction forces
for extending PTO units through four taut mooring lines 105 into
anchors 106 that are embedded in the seafloor. The four corners of
platform 103 house winches (not shown) that are connected to the
taut mooring lines 105 that are spread out diagonally and connect
to anchors 106. In one embodiment, all mooring lines 105 are
connected to base platform 104 via submersible lock winches,
thereby allowing the adjustment of active line lengths to change
the operating depth of the device. The winches can also be locked
for high holding capacity during operation. Suitable anchors 106
include a direct embedment anchor, a vertical load anchor, a
suction anchor, a driven pile or micro pile anchor or a gravity
anchor, etc.
[0046] To enable efficient power extraction, one task of base
platform 103 is to provide the opposing force for the double acting
hydraulic cylinder 102 of the PTO units attached to it. In one
embodiment, while positive PTO forces (e.g., a positive heave, PTO
extension) are guided along the shortest path into taut mooring
lines 105 and anchors 106, the negative PTO counter forces (PTO
compression) are provided by the mass and hydrodynamic inertia as
well as the net positive buoyancy from the platform's integrated
ballast tanks, ultimately enabling double acting power extraction.
Shadowed by absorber body 101, platform 103 operates deeper and is
designed to show a reduced, potentially minimal, hydrodynamic
response to the occurring wave spectrum. Hence, wave excitation
forces acting on base platform 103 may be orders of magnitude
smaller than for absorber body 101 in any degree of freedom.
[0047] The forces of hydraulic cylinders 102 on base platform 103
have vertical and horizontal components. In one embodiment,
hydraulic cylinders 102 are mounted to face each other in a way
that a positive horizontal force vector of a front hydraulic
cylinder opposes the negative horizontal force vector of a back
hydraulic cylinder. Residual horizontal forces can be transferred
through the angled taut mooring lines 105 into the anchors 106 and
the ocean floor. Positive vertical force vectors induced by
cylinders 102 on platform 103 are also transferred through taut
mooring lines 105 into the anchors 106. Negative vertical force
vectors induced by cylinder 102 on platform 103 are opposed by the
positive vertical force caused by buoyancy created by the ballast
system as well as the mass and hydrodynamic inertia of platform
103.
[0048] In one embodiment, the volume of the ballast system is
designed in a way that the highest negative vertical force, wave
and PTO induced moments in all directions on base platform 103 does
not exceed a positive vertical force ensuring taut mooring lines
105 stay taut at all times to prevent snapping loads caused by a
slack taut mooring line 105.
[0049] Positive and negative moments on platform 103 created by
cylinder induced loads with a lever from the neutral axis of the
platform are also compensated through taut mooring lines 105 into
anchors 106 as well as the distributed positive load of the
buoyancy.
[0050] Relative motion between the absorber 101 and base platform
103 results in the conversion of mechanical to hydraulic energy
through the cylinders 102 of the PTO units which charge a
closed-loop hydraulic circuit. In one embodiment, the hydraulic
circuit is housed in an isolated chamber (not shown) that is
integrated into platform 103 and is accessible during maintenance
through a hatch integrated in absorber 101 that can be opened and
passed when locked to base platform 103 to access the chamber.
[0051] In one embodiment, the generated hydraulic flow at the given
operating pressure inside each cylinder 102 is rectified with
hydraulic check valves that feed into a closed loop hydraulic
circuit and the pressurized fluid is collected in an accumulator
bank (not shown). Since the time-series of the flow that is
generated by the cylinders is directly coupled to the sum of the
relative displacement of the pistons of cylinders 102, the produced
flow fluctuates similar to the irregular motion of the absorber
induced by the irregular motion of the ocean. In one embodiment,
one function of the accumulators is to smooth out this irregular
flow to a steady flow at set operating pressure and another
function is to temporarily store the mechanical power as energy in
the form of pressurized fluid.
[0052] In one embodiment, the irregular hydraulic fluid flow is
rectified through check valves and the variable PTO flow of
cylinder 102 is smoothened using a bank of hydraulic accumulators,
which maintain a constant system pressure difference between the
high and low pressure sides. The high pressure side is used to
drive a hydraulic motor which in turn drives a mechanically coupled
consumer such as, for example, a generator or pump, thereby
converting hydraulic flow into mechanical torque and ultimately
electricity or flow of a different fluid such as ambient seawater
in the final conversion step. That is, the accumulators are
discharged over a hydraulic motor that generates the desired
consumer torque. The low pressure side includes a reservoir that
back feeds the cylinders through the check valves. In one
embodiment, the accumulators also include a control system with a
processor and programming that is configured to monitor and control
hydraulic system pressures and power generation.
[0053] In an alternative embodiment, energy is stored in an
intermediate stage in capacitors or batteries. One function of
these electrical energy storage devices is to smooth power flow
from the PTO to the power export cable. Another possible function
is to store energy to be returned to the PTO to control the force
acting on the absorber according to a control signal provided by a
controller.
[0054] In one embodiment, the control system also monitors and
controls the absorber load through aperture, hydraulic pressure and
winch control. The controller may also monitor resonance and
overall apparatus buoyancy.
[0055] In one embodiment, an umbilical cable is used to transfer
electricity to the shore and the grid. In another embodiment,
pressurized fluid is transported to the shore where it can perform
work such as generating electricity.
[0056] For towing, installation and failure cases, absorber 101 and
platform 103 can be mechanically locked creating a hydrodynamic
stable system. In one embodiment, this is accomplished by having
the hydraulic cylinders actively pulled in to their shortest
extension, causing absorber to be pulled into a lock. In this mode,
the wave energy converting apparatus is not converting wave energy
to mechanical power, the motion and excitation load is desired to
be reduced to its minimum.
[0057] A number of alternative embodiments of a wave energy
converter apparatus are described below. These embodiments have
some similarly named and numbered components that operate and/or
function as other like named components in other embodiments except
where noted.
[0058] FIGS. 2A-C illustrate side, front and top views,
respectively, of an alternative embodiment of a wave energy
converter apparatus. Referring to FIGS. 2A-C, two downstream
located hydraulic cylinders 202A and 202B are oriented diagonal
outwards from platform 203 to the upper body of absorber 101 and
connected via joints while one upstream hydraulic cylinder 202C is
located in the geometric center (or substantially near the
geometric center). At the same mounting points as the cylinder
joints on the body of platform 203, the taut mooring winches are
located resulting into shortest possible force flow through the
platform structure from cylinder to mooring line.
[0059] FIGS. 3A-C illustrate side, front and top views,
respectively, of another alternative embodiment of a wave energy
converter apparatus. Referring to FIGS. 3A-C, one downstream
located hydraulic cylinder 302B is oriented diagonal outwards from
platform 303 to absorber 301 and connected via joints and one
upstream hydraulic cylinder 303A is located in the geometric center
(or substantially near the geometric center).
[0060] FIGS. 4A-C illustrate side, front and top views,
respectively, of another alternative embodiment of a wave energy
converter apparatus. Referring to FIGS. 4A-C, one hydraulic
cylinder 402 connects platform 403 and absorber 401 via joints in
the geometric center of both. Three taut mooring line winches (not
shown) are coupled to three taut mooring lines 405 and are oriented
diagonally outwards to provide stability of the platform in all
directions.
[0061] FIGS. 5A-C illustrate side, front and top views,
respectively, of another alternative embodiment of a wave energy
converter apparatus. Referring to FIGS. 5A-C, the wave energy
converter apparatus has a configuration with 1, 2, 3 or 4 PTOs such
as, for example, hydraulic cylinders similar to the embodiments in
FIGS. 1A-4C, and have not been shown to avoid obscuring other
aspects of the wave energy converter apparatus. The cylinders
connect platform 503 and absorber 101 via joints. A rigid mounting
structure 511A with legs such as, for example, mooring tendons,
truss, or pile structures 510A is connected to an anchor on the
seafloor that provides stability to the platform in all directions
including positive and negative vertical loads. No buoyancy in the
platform is needed as the tendons can act in tension and
compression. A mechanical link connects a docking mount 511B to the
mounting 511A. Platform 511B is the mounting point for cylinders
and contains the power conversion chain and the cable
connection.
[0062] In one embodiment, absorber 101 and platform 511B can be
disconnected from the rigid mounting platform 511A together for
installation, maintenance and decommissioning.
[0063] FIGS. 6A-C illustrate side, front and top views,
respectively, of another alternative embodiment of a wave energy
converter apparatus. Referring to FIGS. 6A-C, the wave energy
converter apparatus has a configuration with 1, 2, 3 or 4 PTOs such
as, for example, hydraulic cylinders similar to the embodiments
depicted in FIGS. 1A-4C, and have not been shown to avoid obscuring
other aspects of the wave energy converter apparatus. The cylinders
connect platform 603 and absorber 101 via joints. One or multiple
mono piles or truss structures 620 provide stability to platform
611 in all directions including positive and negative vertical
loads. In one embodiment, no buoyancy in platform 611A is needed as
the pile/truss 620 can react in tension and compression. In one
embodiment, a mechanical link connects a platform of mono pile 611A
and docking 611B. Docking platform 611B is the mounting point for
cylinders and contains for power conversion chain and cable
connection.
[0064] In one embodiment, absorber 101 and docking platform 611B
can be disconnected from the platform of mono pile 611A together
for installation, maintenance and decommissioning. No anchor is
needed as mono pile 620 also acts like an anchor.
[0065] In one embodiment, each power takeoff unit of the wave
energy converting apparatus, such as those of FIGS. 1A-C to 6A-C,
comprises linear generators or rack and pinion mechanical
assemblies connected to rotary generators and provide restoring
force and damping forces acting on the body of absorber 101.
Examples of power takeoff units that may be used in the embodiments
described herein are shown in FIGS. 18-21. Note that PTOs with
belts or mooring lines can only be used for single acting, and
double acting configurations can also be used in single acting
fashion.
[0066] FIGS. 10A-C illustrate side, front and top views,
respectively, of yet another embodiment of a wave energy converter
apparatus that includes an absorber, a platform and one or more
mooring chains. Referring to FIGS. 10A-C, absorber 1101 may be
configured with 1, 2, 3 or 4 cylinders 1102 similar to the
embodiments described above. Each of the cylinders 1102 is coupled
platform 1103 and absorber 1101 via joints. Three or more catenary
mooring chains 1105 are coupled to platform 1103. In one
embodiment, platform 1103 is buoyant and rests in the mid water
column in equilibrium between weight of the chains 1105 and
buoyancy.
[0067] In one embodiment, one or more drag plates (not shown) are
coupled to platform 1103 to increase the hydrodynamic added mass of
platform 1103. The mass and added mass inertia of platform 1103
provide the reaction force to cylinders 1102 in operations and
stability to platform 1103 in all directions including positive and
negative vertical loads.
[0068] FIGS. 7A-C illustrate side, front and top views,
respectively, of an embodiment of a wave energy converter apparatus
that includes an absorber without a platform. Referring to FIGS.
7A-C, the wave energy converter apparatus can be configured to
include 1, 2, 3 or 4 hydraulic cylinders 702, which are similar to
those described above, and that are part of PTOs that are connected
to a single absorber body 701 through hinges on one side and
connected to taut mooring lines 105 on the other side. In one
embodiment, each mooring line 105 is pointed diagonally downwards
and connected to an anchor 106 (e.g., a direct embedment anchor, a
vertical load anchor, a suction pile, etc.).
[0069] In one embodiment, each taut mooring line 105 is connected
to at least one PTO unit, referring to FIGS. 18A-G, which includes
a restoring force mechanism and a damping mechanism that operate in
parallel. This configuration allows energy extraction from multiple
degrees of freedom, primarily heave, surge, and pitch motion. The
restoring force mechanism integrated into each of the PTO units
provide a restoring force to bring absorber 701 back to its neutral
position once displaced.
[0070] FIGS. 8A-C illustrate side, front and top views,
respectively, of another embodiment of a wave energy converter
apparatus that includes an absorber without a platform. Referring
to FIGS. 8A-C, the wave energy converter apparatus can be
configured to include 1, 2, 3 or 4 hydraulic cylinders 802, which
are similar to those described above, and that are part of PTOs
that are embedded into a single absorber body of an absorber 801
and connected to taut mooring lines 105. In one embodiment, each
mooring line 105 is pointing downwards to the seafloor and
connected to an anchor 106 (e.g., a direct embedment anchor, a
vertical load anchor, a suction pile, etc.).
[0071] In one embodiment, each taut mooring line 105 is connected
to at least one PTO unit, which includes a restoring force
mechanism and a damping mechanism that operate in parallel. This
configuration allows energy extraction from multiple degrees of
freedom, primarily heave, surge, and pitch motion. A restoring
force mechanisms integrated into each of the PTO units connected to
the cylinders provides a restoring force to bring absorber 801 back
to its neutral position once displaced.
[0072] FIGS. 9A-C illustrate side, front and top views,
respectively, of another embodiment of a wave energy converter
apparatus that includes an absorber without a platform. Referring
to FIGS. 9A-C, the wave energy converter apparatus can be
configured to include 1, 2, 3 or 4 hydraulic cylinders 902, which
are similar to those described above, and that are part of PTOs
that are embedded into a single absorber body of an absorber 901
and connected to taut mooring lines 105. Two or four of cylinders
902 are aligned in a downwards pointing orientation and the taut
mooring lines connect to a junction point leading to one shared
vertical mooring line 905 that connects to one or two anchors, such
as anchor 106.
[0073] In one embodiment, each taut mooring line 905 is connected
to at least one PTO unit, which includes a restoring force
mechanism and a damping mechanism that operate in parallel. This
configuration allows energy extraction from multiple degrees of
freedom, primarily heave, surge, and pitch motion. In one
embodiment, the restoring force mechanism integrated into each of
the PTO units coupled to the cylinders provides a restoring force
to bring absorber 901 back to its neutral position once
displaced.
[0074] FIG. 12 illustrates one embodiment of a control system for a
wave energy converter apparatus, such as the various embodiments of
a wave energy converter apparatus disclosed herein. The control
units and modules of FIG. 12 are described in more detail
below.
[0075] FIG. 13 through FIG. 16 are active and passive aperture
opening and closing control mechanisms. In one embodiment, the one
or multiple of these aperture control mechanisms is embedded into
the absorber.
[0076] The use of the apertures of FIGS. 13-16 enable the area of
the wave energy converter apparatus subject to wave excitation to
be controlled to both avoid sudden, extreme spikes in structural
loads as well as to optimize energy harvesting conditions. Given
the complex interactions and changing requirements for ideal energy
harvesting, the apparatus includes a mechanism for adjusting to
changing wave conditions and to handle sudden, extreme load spikes.
This mechanism helps manage the highly variable loading imposed on
the apparatus at several time scales by changing sea states,
superposition of waves, and the relative position of the
apparatus.
[0077] More specifically, in one embodiment, one or more absorber
body apertures, such as shown in FIGS. 13-16, are included in the
absorber. The motive force created on the absorber is principally
due to the locally-varying and time-varying propagating pressure
field differences between the regions above and below the absorber.
These pressure differences exist only because of the separation
imposed by the absorber. Locally canceling this pressure
difference, for example, by use of controlled apertures in the
absorber can effectively and substantially reduce the overall
structural load on the absorber, thereby also reducing the load on
the supporting structural elements of the wave energy converter
apparatus. Once opened, the apertures allow a direct pressure
exchange between fluid above and underneath the absorber body. In
the case of passive (e.g., pressure activated) apertures, different
passive cracking pressures limit when to actuate the mechanisms and
the time to actuate the mechanisms can be set differently for
different aperture units. Note that in one embodiment, for passive
apertures, no input from pressure sensors is required for
activation. In one embodiment, a passive activation mechanism to
control the opening and closing of the passive apertures comprise a
mechanism driven directly by environmental parameters such as wave
pressure compared to signal sent from central controller.
[0078] Active aperture closures include controlled rotary closures
or linear closure mechanisms. Passive and active mechanisms can be
implemented in the same aperture mechanism or independently.
[0079] By varying coverage of at least one aperture embedded in the
absorber, the pressure differential can be effectively short-cut
with varying intensity. Through immediate and active control of one
or more apertures in the absorber body, the body hydrodynamics can
be tuned to increase, and potentially maximize performance, in a
given sea state. Additionally, this load control strategy,
implemented in the primary conversion stage, allows for lean
apparatus structural designs and device components by allowing load
bearing elements to be sized according to the demands of the energy
absorbing operating states, rather than by storm conditions.
Moreover, this control mechanism enables effective wave energy
absorption for variable significant wave height. By actively
controlling the active area of the absorber actuation of such
control apertures of FIGS. 13-16, the wave energy converter
apparatus can achieve improved performance without the accompanying
risk of overload conditions and peak loads.
[0080] In one embodiment, the wave energy converting apparatus
includes other control mechanisms to manage loads, including but
not limited to, control over physical settings of the damping and
restoring elements of the power conversion chain system; control
over the dynamic responses of damping and restoring elements of the
power conversion chain system; and control over the operating depth
of the wave energy converting apparatus, or portion thereof.
[0081] In one embodiment, PTO units are included in the absorber
and have restoring and dampening elements that are controlled. In
one embodiment, the PTO units are controlled by controlling the
hydraulic fluid flow. In one embodiment, the control over the
hydraulic fluid flow using a combination of check valves and
actively controlled solenoid valves, proportional valves and an
accumulator bank allows the system to maintain and control constant
pressures and thus constant cylinder damping forces. The two
chambers of a hydraulic cylinder can be directly shortcut leading
to a fast reduction of damping force on the shaft and absorber.
[0082] A scheme where multiple discrete pressure levels can be
achieved to approximate linear damping force characteristics that
are proportional to cylinder velocity may be achieved by using
accumulators at different pre-charge pressure levels. This allows
damping of multiple cylinders to be controlled independently while
centralized hydraulic components are still shared. Alternatively,
linear damping force characteristics can be approximated with a
single centralized accumulator pressure and varying active
hydraulic cylinder piston area in each PTO.
[0083] In addition to its load control capabilities, in one
embodiment, the PTO units are passively controlled. As waves excite
the absorber body, the constrained kinematics of the device setup
inherently alter the hydraulic cylinder angles and thus, restoring
force (k) and damping properties (c) in each of the main degrees of
freedom. This nonlinear effect facilitates a self-adapting device
response over a broad wave frequency and height spectrum. This
change in damping and restoring forces during one closed absorber
oscillation cycle can be specifically designed to contribute to the
efficient operation of the wave energy converter apparatus.
[0084] FIG. 17 illustrates a block diagram of a power conversion
chain containing PTOs. Referring to FIG. 17, PTO subsystem 1901 is
electrically connected to electrical subsystem 1902. Electrical
subsystem 1902 is electrically connected to grid 1903. In one
embodiment, electrical subsystem 1902 is part of a wave energy
converter apparatus that contains PTO subsystem 1901. In another
embodiment, all or a portion of electrical subsystem 1902 is not
part of an energy converter apparatus that contains PTO subsystem
1901.
[0085] FIGS. 18A-G illustrate one embodiment of a wave energy
converter apparatus that includes more than one PTO subsystem
(unit). Referring to FIGS. 18A-G, an absorber 701 contains four PTO
subsystems 702 coupled to taut mooring lines 105. PTO subsystems
702 may be used in wave energy converter apparatuses, such as
those, for example, described in FIGS. 7A-C, 8A-C and 9A-C.
[0086] Note there are a number of PTO subsystem variations that may
be employed. These include those acting on (e.g., pulling on) a
single mooring line for conversion of the linear relative motion
between mooring lines, wire or belt and absorber buoy to electrical
energy generator. Such generators often operate with short-term
energy storage such a, for example, flywheels, capacitors or
batteries, to store energy generated as a result of conversion.
[0087] Examples of PTO subsystems 102 or 702 include, but are not
limited to, those that execute: 1) a static spring; 2) a dynamic
spring (fixed or adjustable (e.g., a time frame of day, sea state,
etc.); 3) a dynamic damper (e.g., adjustable (e.g., a time frame of
day, sea state, etc.). In one embodiment, these PTO subsystems
operate by having mooring lines pulling over a drum. Examples of
these includes PTO systems with a drum direct drive to one
generator, a drum direct drive to multiple generators, a drum with
mechanical power transmission, via toothed gearbox or belt gearbox,
to one or multiple generators, etc. In other embodiments, these PTO
subsystems operate by having mooring lines pulling on rack and
pinion, mooring lines pulling on a lead screw, mooring lines
pulling on a linear generator, and mooring lines pulling on a
hydraulic cylinder.
[0088] Other examples of PTO subsystems 102 or 702 include those
where a gas spring (e.g., a hydraulic cylinder accumulator couple)
or mechanical spring provide the static offset spring force and
companying sub-system solutions provide 1) a dynamic spring force
(e.g., fixed restoring force coefficient or adjustable restoring
force coefficient or 2) a dynamic damping force. In one embodiment,
these PTO subsystems operate by having mooring lines pulling over a
winch drum. FIGS. 18A-C describes examples of PTO systems with a
drum direct drive to one generator, a drum direct drive to multiple
generators, a drum with mechanical gearbox or belt transmission to
one or multiple generators, etc., where all forces are provided by
the generator. FIGS. 18D-G and 19-21B describe configurations where
some component of the total PTO force is provided by a parallel gas
spring and the additional force control is executed either by a
rotary or linear generator or hydraulic cylinder. For the
configuration of FIG. 18D, a clutch is added to the shaft to allow
for depth adjustments. In other embodiments, referencing FIGS.
19-21, the PTO subsystems operate by having mooring lines pulling
on a rack and pinion, a lead screw, a linear generator, and a
hydraulic cylinder.
[0089] More specifically, FIGS. 18A-F, 19A-B, 20A-B, 21A-B and
22A-B illustrate examples of single acting (always in tension) PTO
subsystems that may be used for PTO subsystems 702, 802, 902 of
FIGS. 7, 8 and 9 respectively and the other wave energy converter
apparatuses described herein. The operation of these PTO subsystems
is well-known to those skilled in the art. The PTO configurations
of 19A-B, 20A-B, 21A-B and 22A-B can be used as double acting PTOs
for 102, 202, 302, 402 and 502. FIGS. 18E-G describe alternative
configurations of the configuration in FIG. 18A replacing the belt
with a synthetic mooring line that terminates on a winch drum
(FIGS. 18E-F) or a capstan (FIG. 18G) that takes of the tension
from the line and can be adjusted in length by a winch that is not
located on the sliding table guided by rails. The configuration in
FIGS. 18F-G can also be implemented without rails where only the
hydraulic damper and hydraulic gas spring shafts connect to a
mounting platform of the winch drum. Thus, the shafts constrain the
PTO displacement and provide the same functionality as the rail.
Furthermore, as commonly used in the offshore industry, one
cylinder can provide both functions of the hydraulic damper and gas
spring sharing the same stroke, reducing the number of cylinders in
each PTO to one.
[0090] The movements of absorber hydraulic cylinders are caused as
a result of heave, surge and pitch wave actions. As a result of the
wave energy converter apparatus configuration, every positive and
negative motion of the absorber in any degree of freedom leads to
relative motion between the absorber and the base platform. This
relative motion leads to a relative motion between the cylinder
shafts and the cylinder housing, respectively, resulting into a
displacement of the fluid inside the cylinder chamber in a double
acting reciprocating motion.
[0091] In one embodiment, a resting state of the power take off
units of the wave energy converter apparatus controlled by the
restoring force component (e.g., a mechanical spring, an air
spring, a virtual spring, etc.) is a position in which the absorber
is essentially parallel with the surface of the water and the
hydraulic cylinders are not compressed.
[0092] The vertical forces or heave that can be exerted on the
absorber and cause the absorber to move up and down and the
displacement of each of the hydraulic cylinders is essentially the
same. Horizontal forces known as surge forces exerted on the
absorber cause forward and backward movements of the absorber and
corresponding extensions and compressions of the cylinders. Pitch
movements are the rotational motion around a lateral axis of the
absorber and result in alternating compressions and extension of
the cylinders.
[0093] Motion occurring in all six degrees of freedom of the
absorber is transferred to one or more power takeoff units, which
transform the absorber motion into a standard form of mechanical
power. A restoring force is in place to ensure the absorber
oscillates about a set equilibrium.
[0094] The maximum energy extraction potential for any wave energy
converter is achieved when the primary absorbing body's natural
frequency matches the frequency of the principle energy-carrying
component of the sea state spectrum at a given moment. This
frequency matching is known as resonance.
[0095] In one embodiment, the movements of the absorber body are
preferably in resonance with the current wave conditions. The
absorber resonance frequency is a function of the 1) the absorber's
mass, 2) the absorber's buoyancy, 3) the restoring force of the
power takeoff unit(s) attached to the absorber, 4) the power
extracting characteristics of the power takeoff acting on the
absorber (damping), and 5) the absorber's hydrodynamic added mass
and radiation damping. The added mass and radiation damping is
itself a function of the absorber's depth and geometry, the latter
component is dominated by the area normal to the absorber's
motion.
[0096] Control of all these components may be coordinated to
achieve maximum power extraction or load reduction on the absorber
from incident waves. The system can include several redundant,
independent mechanisms for matching the response characteristics of
the apparatus to ocean wave conditions. For example, the same
controllable apertures described above for load management will
also affect the hydrodynamic absorber properties, and thus the
natural frequency of the absorber, by changing the shape of the
absorber. Submergence depth can be used as a parameter to change
the hydrodynamic absorber properties, and thus resonance frequency,
of the apparatus, and is also considered in calculations to set
other parameters for resonance control. The power takeoff units of
the apparatus can also affect the absorber resonance frequency in
all degrees of freedom through both the restoring force component
("spring") and energy extraction component ("damper").
[0097] The dominant wave energy frequency conditions change
continuously throughout the year and it is useful to tune the wave
energy converter apparatus to achieve the optimum energy production
from the system in a broad range of ocean conditions such as wave
height, wave period and spectral shape. The system can be tuned,
for example, by changing the operating depth and/or the aperture
opening, hydrodynamic coefficients. FIGS. 23A and 23B illustrate
examples of interfaces used to interface hydraulic cylinders to a
hydraulic motor and generator, including the coupling in between.
Both FIGS. 23A and 23B include control values (PTO_i, CV_main),
control value accumulators, check values, and accumulators for use
for short term energy storage and longer term energy storage that
interface to a generator. In more complex embodiments, additional
valves can be used to connect hydraulic power stored temporarily in
accumulators directly to ports of the hydraulic cylinder, allowing
for reactive power and active motion control. These elements
operate in a manner well-known to those skilled in the art.
[0098] FIG. 26 illustrates an example of an electrical subsystem
that may be used to interface the converted wave energy to the
grid. The operation of the depicted electrical subsystem is
well-known in the art.
[0099] Referring back to control mechanisms of the wave energy
converting apparatus to manage loads, in one embodiment, such
control mechanisms control the operating depth of the wave energy
converting apparatus, or portion thereof. The time-varying pressure
differentials which create the motive force on the absorber body
decrease in amplitude with increasing water depth. Thus, an
absorber that is lower in the water column will experience lower
overall absorber excitation and thus structural loads compared to
the same absorber configuration higher in the water column. In one
embodiment, the system maintains the ability to adjust its
submergence. Controllable operating depth is thus an important
parameter to the system for load management and optimal
operation.
[0100] In one embodiment, a base platform or absorber of a wave
energy converter apparatus is connected to the mooring lines via
submersible, lockable winches (e.g., four lockable winches), each
of which can operate independently on its associated mooring line.
The winches enable the platform to be pulled into an operating
location. Once in place, the winches lock and significantly
increase their holding capacity. In one embodiment, a ballasting
system in the platform body is adjusted to secure tension in the
taut mooring lines at all times while mooring winches on the
platform frame are used to equalize tension among mooring lines and
to change operating depth during operations, deployment,
maintenance, and recovery.
[0101] In one embodiment, the wave energy converter apparatus is
controlled by a holistic device control architecture as shown in
the Interface Control Chart (ICC) in FIG. 12. The control
architecture embraces a SCADA system 1409 receiving information in
the form of data from sensors integrated into the various
components of the device 1401-1408. This information may comprise,
but is not limited to, instantaneous, time history averaged, or
predictions of wave period and height, water level, tide, and
current environmental data 1401, PTO forces, strokes, velocities
1403, data from GPS and/or inertial measurement units (IMUS) 1402,
structural monitoring data from strain sensors installed on
load-bearing elements of the device, hull pressure data 1407, PTO
motor/generator voltage, torque and speed data 1406, accumulator,
capacitor, battery or other kind of energy storage information
1405, mooring tether or winch forces and position data 1404,
ballast system information 1408 and wave pressure relieve mechanism
state information.
[0102] In one embodiment the holistic control architecture receives
and sends additional information and/or commands from external
databases 1410 or user defined input via satellite 1412, radio
frequency, acoustic frequency, optical communication, or other
bi-directional communication lines.
[0103] In one embodiment of the holistic control architecture a
submergence depth supervisory controller, a PTO and electrical
conversion chain supervisory controller 1414, a WEC absorber
body/wave pressure relieve mechanism supervisory controller 1413,
and a ballast system supervisory controller receive commands from
the main holistic controller 1411 and send commands to the physical
mechanisms 1417-1418, 1416, 1420.
[0104] The supervisory controllers are capable of bidirectional
communication with the physical mechanism through sensors, as well
as bidirectional communication with each other and independently to
external monitoring systems, In one embodiment of the holistic
control architecture, machine learning algorithms might update the
control commands which are send through the holistic controller to
the supervisory controllers for different subcomponents of the
WEC.
[0105] The holistic control framework described herein enables
control of hydrodynamic properties of the apparatus by control of
one or many actuation methods, collected under the term HyTune
1411. HyTune embraces absorber structure and individual PTO load
management by controlling embedded physical mechanism 1417-1418,
1416, 1420 to alter wave excitation (Froude-Krylov and diffraction)
forces (e.g., exponential load decay with increasing apparatus
depth for effective load mitigation), absorber radiation damping
forces, and hydrodynamic added mass in such a way that optimal wave
power absorption conditions are met while considering control
limits imposed from the various component control subsystems.
[0106] In one embodiment of the holistic control framework
described herein, the framework embraces control means to alter PTO
characteristics such as damping behavior and restoring force
coefficients to match the sea state for optimal power absorption in
combination with hydrodynamic tuning means described above or to
accompany hydrodynamic control means described above for load
management (e.g., load mitigation in severe sea). For each energy
producing operation sea station condition, the purpose of the
holistic control approach is to control wave excitation on and
hydrodynamic properties of the absorber in such a way that the
device can extract energy out of the water waves in the most
efficient way while not exceeding structural or component design
load limitations. This control approach and enables effective load
management by means of relatively small operating depth adjustments
and absorber geometry changes and includes but is not limited to
highly responsive mitigation of extreme loads and peak stress
during storm events.
[0107] For severe storm conditions or harsh wave climates, which
only insignificantly contribute to available annual energy, the
holistic control framework can control the device to move deeper in
the water column to the required safety operating depth using the
mooring winches, while independently and in parallel the system can
adjust physically or virtually implemented PTO damping and
restoring force coefficients to decrease loads on the absorber.
Additionally, passive safety apertures or active safety apertures
(e.g., FIGS. 15 and 16) can decrease excitation force if a specific
local fluid pressure is reached or the actively controlled safety
apertures might be partially or fully opened. The holistic
controller can orient the absorber position in such a way wave
excitation loads are decreased.
[0108] Accordingly, the submerged pressure-differential design and
the accompanying load management system allow for operation within
specified limits to balance energy capture with the requirement to
avoid damaging loads throughout the life of the apparatus.
[0109] As discussed above, for load mitigation and management
purposes, winches and the aperture mechanisms represent
complementary systems which can be used to compensate a failure of
one or the other system. In the case of a loss of functionality of
the aperture load management system, the apparatus can be winched
down and the capabilities for reduced operation can then be
assessed. In the case of loss of a mooring winch, the apparatus can
still be brought to the surface by winching the remaining systems
and pivoting around the mooring point associated with the failed
winch.
[0110] One response to the loss of PTO control is to switch the
apparatus from operating to idle mode. The absorber aperture can be
fully opened as a safety mechanism to effectively mitigate wave
excitation load. The positive buoyancy of the platform can be
adjusted using the ballast system tanks to reduce mean mooring line
tension. If required, operating depth reduction can be executed to
further reduce wave excitation loads. A damaged PTO can be
disconnected modular from the absorber structure and replaced
during a maintenance procedure.
[0111] Although the description herein contains many details, these
should not be construed as limiting the scope of the disclosure but
as merely providing illustrations of some of the presently
preferred embodiments. Therefore, it will be appreciated that the
scope of the disclosure fully encompasses other embodiments which
may become obvious to those skilled in the art.
[0112] From the description herein, it will be appreciated that
that the present disclosure encompasses multiple embodiments which
include, but are not limited to, the following:
[0113] 1. A submerged wave energy converter apparatus, comprising:
(a) an absorber body with an upper surface and a bottom surface;
(b) a spring-damper mechanism in a Power Takeoff unit coupled to
and/or integrate into the absorber body, the spring-damper
mechanism configured to exert forces based on the movement of the
absorber body relative to the mooring line/reaction point and input
from sensors integrated into the absorber body's sub-components and
body hull; (c) at least one energy converter body connected to the
PTO; and (d) at least one restoring force mechanism in the PTO
units configured to return a displaced absorber body to a set
equilibrium position; (e) wherein displacement of the absorber body
relative to the equilibrium position as a response to wave
excitation actuates the Power Takeoff units.
[0114] 2. The apparatus of any preceding embodiment, further
comprising: A ballast system capable of increasing or decreasing
buoyancy of the apparatus; and a mooring system having one or a
plurality of mooring lines.
[0115] 3. The apparatus of any preceding embodiment, wherein that
mooring lines are anchored with an anchor (e.g., a vertical load
anchor, a dead-weight anchor, a direct embedment anchor, etc.).
[0116] 4. The apparatus of any preceding embodiment, wherein the
mooring system further comprises: a locking winch comprising one or
multiple of a spool, capstan, windlass, gearbox and motor/generator
coupled to each mooring line; and a winch controller.
[0117] 5. The apparatus of any preceding embodiment, wherein the
power takeoff unit(s) comprise: a cylinder with a piston; and a
closed hydraulic system, where linear movement of the piston of the
cylinder pressurized fluid in the hydraulic system.
[0118] 6. The apparatus of any preceding embodiment, wherein the
hydraulic system further comprises: an accumulator bank; a
hydraulic motor; and an electrical generator
[0119] The apparatus of any preceding embodiment, wherein the power
takeoff unit(s) comprise: a belt, a drum or spool, a rotary
electric machine, and a braking mechanism.
[0120] 7. The apparatus of any preceding embodiment, wherein the
linear motion energy converter comprises: a cylinder with an arm,
an armature and a stator, where linear movement of the armature in
relation to the stator generates electrical current.
[0121] 8. The apparatus of any preceding embodiment, wherein said
restoring force mechanism comprises a mechanism selected from the
group of a mechanical spring, an air spring and an electric machine
generating a restoring force.
[0122] Embodiments of the present technology may be described
herein with reference to flowchart illustrations of methods and
systems according to embodiments of the technology, and/or
procedures, algorithms, steps, operations, formulae, or other
computational depictions, which may also be implemented as computer
program products. In this regard, each block or step of a
flowchart, and combinations of blocks (and/or steps) in a
flowchart, as well as any procedure, algorithm, step, operation,
formula, or computational depiction can be implemented by various
means, such as hardware, firmware, and/or software including one or
more computer program instructions embodied in computer-readable
program code. As will be appreciated, any such computer program
instructions may be executed by one or more computer processors,
including without limitation a general purpose computer or special
purpose computer, or other programmable processing apparatus to
produce a machine, such that the computer program instructions
which execute on the computer processor(s) or other programmable
processing apparatus create means for implementing the function(s)
specified.
[0123] Accordingly, blocks of the flowcharts, and procedures,
algorithms, steps, operations, formulae, or computational
depictions described herein support combinations of means for
performing the specified function(s), combinations of steps for
performing the specified function(s), and computer program
instructions, such as embodied in computer-readable program code
logic means, for performing the specified function(s). It will also
be understood that each block of the flowchart illustrations, as
well as any procedures, algorithms, steps, operations, formulae, or
computational depictions and combinations thereof described herein,
can be implemented by special purpose hardware-based computer
systems which perform the specified function(s) or step(s), or
combinations of special purpose hardware and computer-readable
program code.
[0124] Furthermore, these computer program instructions, such as
embodied in computer-readable program code, may also be stored in
one or more computer-readable memory or memory devices that can
direct a computer processor or other programmable processing
apparatus to function in a particular manner, such that the
instructions stored in the computer-readable memory or memory
devices produce an article of manufacture including instruction
means which implement the function specified in the block(s) of the
flowchart(s). The computer program instructions may also be
executed by a computer processor or other programmable processing
apparatus to cause a series of operational steps to be performed on
the computer processor or other programmable processing apparatus
to produce a computer-implemented process such that the
instructions which execute on the computer processor or other
programmable processing apparatus provide steps for implementing
the functions specified in the block(s) of the flowchart(s),
procedure (s) algorithm(s), step(s), operation(s), formula(e), or
computational depiction(s).
[0125] It will further be appreciated that the terms "programming"
or "program executable" as used herein refer to one or more
instructions that can be executed by one or more computer
processors to perform one or more functions as described herein.
The instructions can be embodied in software, in firmware, or in a
combination of software and firmware. The instructions can be
stored local to the device in non-transitory media, or can be
stored remotely such as on a server, or all or a portion of the
instructions can be stored locally and remotely. Instructions
stored remotely can be downloaded (pushed) to the device by user
initiation, or automatically based on one or more factors.
[0126] It will further be appreciated that as used herein, that the
terms processor, hardware processor, computer processor, central
processing unit (CPU), and computer are used synonymously to denote
a device capable of executing the instructions and communicating
with input/output interfaces and/or peripheral devices, and that
the terms processor, hardware processor, computer processor, CPU,
and computer are intended to encompass single or multiple devices,
single core and multicore devices, and variations thereof.
[0127] In the claims, reference to an element in the singular is
not intended to mean "one and only one" unless explicitly so
stated, but rather "one or more." All structural, and functional
equivalents to the elements of the disclosed embodiments that are
known to those of ordinary skill in the art are expressly
incorporated herein by reference and are intended to be encompassed
by the present claims. Furthermore, no element, component, or
method step in the present disclosure is intended to be dedicated
to the public regardless of whether the element, component, or
method step is explicitly recited in the claims. No claim element
herein is to be construed as a "means plus function" element unless
the element is expressly recited using the phrase "means for". No
claim element herein is to be construed as a "step plus function"
element unless the element is expressly recited using the phrase
"step for".
[0128] In addition to any other claims, the
applicant(s)/inventor(s) claim each and every embodiment of the
technology described herein, as well as any aspect, component, or
element of any embodiment described herein, and any combination of
aspects, components or elements of any embodiment described
herein.
[0129] Whereas many alterations and modifications of the present
invention will no doubt become apparent to a person of ordinary
skill in the art after having read the foregoing description, it is
to be understood that any particular embodiment shown and described
by way of illustration is in no way intended to be considered
limiting. Therefore, references to details of various embodiments
are not intended to limit the scope of the claims which in
themselves recite only those features regarded as essential to the
invention.
* * * * *