Note: Descriptions are shown in the official language in which they were submitted.
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1
WET BUOYANCY ENGINE
BACKGROUND OF THE INVENTION
Technologies such as stealth buoys and underwater gliders need to modify
their own buoyancy in order to operate. Strategies such as pumping fluid are
typically
used to change the device's net volume. This in turn requires a mechanically
sophisticated (and consequently expensive) apparatus. This document introduces
the
concept of a buoyancy engine that exploits the enormous volume and pressure
changes accompanying the reversible electrochemical interconversion of water
to
hydrogen and oxygen gases. Named the Water Electrolytic Transformation (WET)
buoyancy engine, this device promises to deliver a new, efficient, and very
inexpensive means to control buoyancy in remote sensing and surveillance
devices.
Stealth buoys are surveillance devices that record data while they lie on the
ocean floor where they are virtually undetectable and are less prone to
drifting
problems. When it becomes necessary to notify its deployer, the buoy inflates
an
elastic collar and rises to the surface in order to transmit its data to some
receiving
station. It then retracts the collar and descends to the bottom where it
gathers new
data. These buoys have obvious military applications such as tracking hostile
ships
and submarines, but also civilian applications such as detection of smuggling
and
monitoring marine life.
Underwater gliders are autonomous submarine vehicles that direct vertical
force (buoyancy) to horizontal translation using wings. These devices have
been
showing promise in recent years as a means of collecting oceanographic data
inexpensively (Rudnick et al., 2004, Marine Technology Society Journal 38: 73-
84).
There also exists the military potential for using fleets of gliders for
autonomous
remote sensing and surveillance over a large patrol area.
US Patent 5,596,943, entitled 'Apparatus and method for floating a towed
device from a submerged vehicle' teaches a method of surfacing a vehicle towed
by a
submerged vehicle by displacing water from within the towed vehicle with gases
evolved by electrolysis. The towed vehicle has interior balloons or bladders
for
capturing evolved gases which are situated such that when empty, the towed
vehicle
CA 02678224 2016-10-04
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is neutrally buoyant. As the internal bladders fill with evolved gases,
positive
buoyancy is produced, causing the towed vehicle to surface. Thus, this patent
in
effect teaches a method for modifying the hydrodynamic properties of a towed
body.
Published US Patent Application 2008/0088133 entitled Wave activated power
generation device and wave activated power generation plant' teaches a wave
activated power generation device comprising a cylindrical floating body
anchored on
water and extending in a vertical direction relative to a surface of the water
which
includes a buoyancy control chamber that allows the floating body to
vertically float in
the water so as to adjust its position relative to the surface of the water.
The floating
body includes an air chamber and an air turbine which converts air flow into
electrical
power. Thus, this document in effect describes a method for harvesting energy
from
waves and wind by adjusting the position of the apparatus to an optimal depth.
It is important to remember that air is a fluid, as is sea water, and buoyancy
is
simply the difference in weight between an object and the volume of
surrounding
media it displaces. Since water is denser than air, it provides a much greater
buoyant
force for a given volume.
SUMMARY OF THE INVENTION
According to a first aspect of the invention, there is provided a method for
effecting vertical movement of a vessel within a body of water comprising:
providing a vessel comprising a housing containing a buoyancy engine,
the engine comprising a compartment within the housing for storing water
therein, said compartment having a water valve for allowing water into the
water
storage compartment and a gas valve for allowing gas to exit the water storage
compartment;
a source of electrical energy within the housing, said source external to the
water storage compartment and a pair of electrodes electrically connected to
the
electrical energy source and positioned within the water storage compartment;
placing the vessel into a water column;
decreasing the buoyancy of the vessel by opening the water valve such that
CA 02678224 2016-10-04
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water enters the water storage compartment via the water valve and gas escapes
the
water storage compartment via the gas valve;
closing the water valve and the gas valve once the vessel has reached a first
depth within the water column; and
increasing the buoyancy of the vessel by electrolyzing a quantity of the water
within the water storage compartment thereby generating hydrogen and oxygen
gases which are retained, thereby increasing the buoyancy of the vessel and
causing
the vessel to rise to a second depth within the water column.
According to a further aspect of the invention, there is provided a method for
effecting vertical movement of a vessel within a body of water comprising:
providing a vessel comprising a housing containing a buoyancy engine,
the buoyancy engine comprising a compartment within the housing for storing
water therein, said compartment having a water valve for allowing water into
the water
storage compartment and a gas Valve for allowing gas to exit the water storage
chamber; and
a source of electrical energy within the housing, said source being external
to
the water storage compartment and a pair of electrodes electrically connected
to the
electrical energy source and positioned within the water storage compartment;
placing the vessel into a water column;
decreasing the buoyancy of the vessel by opening the water valve such that
water enters the water storage compartment via the water valve and gas escapes
the
water storage compartment via the gas valve;
closing the water valve and the gas valve once the vessel has reached a first
depth within the water column; and
causing the vessel to rise to a second depth within the water column by
increasing the buoyancy of the vessel by electrolyzing a quantity of the water
within
the water storage compartment thereby generating hydrogen and oxygen gases
which are retained, thereby increasing the buoyancy of the vessel and causing
the
vessel to rise to the second depth within the water column.
According to another aspect of the invention, there is provided a method for
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effecting vertical movement of a vessel within a body of water comprising:
providing a vessel comprising a housing containing a buoyancy engine,
the buoyancy engine comprising:
a compartment within the housing for storing water therein, said
compartment having a water valve at a base thereof for allowing water into the
water
storage compartment, said compartment including a barrier which separates
headspace above the compartment into a hydrogen chamber and an oxygen
chamber, said hydrogen chamber comprising a hydrogen gas valve for releasing
hydrogen gas from the water storage compartment, said oxygen chamber
comprising
an oxygen gas valve for releasing oxygen gas from the water storage
compartment,
said barrier comprising a fuel cell;
a source of electrical energy external to the water storage compartment
and a pair of electrodes electrically connected to the electrical energy
source and
positioned within the water storage compartment such that the cathode of the
electrolysis device is in the hydrogen chamber and the anode of the
electrolysis
device is in the oxygen chamber; and
a plurality of sensors powered by the source of electrical energy;
placing the vessel into a water column;
decreasing the buoyancy of the vessel by opening the water valve such that
water enters the water storage compartment via the water valve and gas escapes
the
water storage chamber via the gas valves until the vessel rests at the bottom
of the
body of water;
carrying out readings within the body of water via the sensors;
in response to a specific condition being met, increasing the buoyancy of the
vessel by electrolyzing a quantity of the water within the water storage
compartment
thereby generating hydrogen and oxygen gases which are retained, thereby
increasing the buoyancy of the vessel and causing the vessel to rise to the
surface of
the body of water,
wherein some of the energy of electrolysis is recovered by the fuel cell and
is
transferred to the source of electrical energy and stored.
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According to yet another aspect of the invention, there is provided a method
for
effecting vertical movement of an autonomous vessel within a body of water,
said ,
body of water having a floor and a surface, said method comprising:
providing an autonomous vessel comprising a housing comprising logic
5 circuitry and a buoyancy engine,
the buoyancy engine comprising a compartment within the housing for storing
water therein, said compartment having a water valve for allowing water into
the water
storage compartment and a gas valve for allowing gas to exit the water storage
compartment and a source of electrical energy within the housing, said source
being
external to the water storage compartment and a pair of electrodes
electrically
connected to the electrical energy source and positioned within the water
storage
compartment;
placing the autonomous vessel into a water column;
the logic circuitry instructing the buoyancy engine to decrease the buoyancy
of
the autonomous vessel by opening the water valve such that water enters the
water
storage compartment via the water valve and gas escapes the water storage
compartment via the gas valve;
the logic circuitry instructing the buoyancy engine to close the water valve
and
the gas valve once the autonomous vessel has reached the floor of the body of
water
within the water column; and
the logic circuitry causing the autonomous vessel to rise to the surface of
the
body of water within the water column by increasing the buoyancy of the
autonomous
vessel by electrolyzing a quantity of the water within the water storage
compartment
thereby generating hydrogen and oxygen gases which are retained, thereby
increasing the buoyancy of the autonomous vessel and causing the autonomous
vessel to rise to the surface of the body of water within the water column.
According to another aspect of the invention, there is provided a method for
effecting generally vertical movement of an autonomous vessel within a body of
water
comprising:
providing an autonomous vessel comprising a housing comprising logic
=
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circuitry and a buoyancy engine,
the buoyancy engine comprising:
a compartment within the housing for storing water therein, said
compartment having a water valve at a base thereof for allowing water into the
water
storage compartment, said compartment including a barrier which separates
headspace above the compartment into a hydrogen chamber and an oxygen
chamber, said hydrogen chamber comprising a hydrogen gas valve for releasing
hydrogen gas from the water storage compartment, said oxygen chamber
comprising
an oxygen gas valve for releasing oxygen gas from the water storage
compartment,
said barrier comprising a fuel cell;
a source of electrical energy within the housing, said source being
external to the water storage compartment and a pair of electrodes
electrically
connected to the electrical energy source and positioned within the water
storage
compartment such that the cathode of the electrolysis device is in the
hydrogen
chamber and the anode of the electrolysis device is in the oxygen chamber; and
a plurality of sensors powered by the source of electrical energy;
placing the autonomous vessel into a water column;
the logic circuitry instructing the buoyancy engine to decrease the buoyancy
of
the autonomous vessel by opening the water valve such that water enters the
water
storage compartment via the water valve and gas escapes the water storage
chamber
via the gas valves until the autonomous vessel rests at the bottom of the body
of
water;
carrying out readings within the body of water via the sensors;
in response to a specific condition being met, the logic circuitry instructing
the
buoyancy engine to increase the buoyancy of the autonomous vessel by
electrolyzing
a quantity of the water within the water storage compartment thereby
generating
hydrogen and oxygen gases which are retained, thereby increasing the buoyancy
of
the autonomous vessel and causing the autonomous vessel to rise to the surface
of
the body of water,
= 30 wherein some of the energy of electrolysis is recovered
by the fuel cell and is
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transferred to the source of electrical energy and stored.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 shows an overview of a single compartment WET buoyancy engine.
Figure 2 shows a double compartment WET buoyancy engine.
Figure 3 is a schematic diagram showing regenerative fuel cell operation.
Figure 4 is a diagram illustrating the operation of underwater gliders
incorporating WET buoyancy engines.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Unless defined otherwise, all technical and scientific terms used herein have
the same meaning as commonly understood by one of ordinary skill in the art to
which
the invention belongs. Although any methods and materials similar or
equivalent to
those described herein can be used in the practice or testing of the present
invention,
the preferred methods and materials are now described. All publications
mentioned
hereunder are incorporated herein by reference.
Technologies such as stealth buoys and underwater gliders need to modify
their own buoyancy in order to operate. Strategies such as pumping fluid are
typically
used to change the device's net volume. This in turn requires a mechanically
sophisticated apparatus, increasing the cost of the vehicle while diminishing
its
reliability.
Described herein is the concept of a buoyancy engine that exploits the
enormous volume and pressure changes accompanying the reversible =
electrochemical interconversion of water to hydrogen and oxygen gases.
Described herein is a Water Electrolytic Transformation (WET) buoyancy
engine which provides a new, efficient, and very inexpensive means to control
buoyancy in remote sensing and surveillance equipment. This in turn can be
used for
the production of inexpensive, disposable devices for numerous applications,
such as
the monitoring of shipping activity to early warning sensors for force
protection in
potentially hostile harbours. This buoyancy engine boasts the additional
advantage of
CA 02678224 2016-10-04
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interfacing well with environmental energy harvesting concepts.
To change its buoyancy, any underwater vehicle must necessarily change its
density. Since it is not practical to change mass, a net change in volume is
needed.
Typically, this volume change is accomplished by pumping fluid to and from
bladders
or tanks. Described herein is an alternative electrochemical approach, named
the
Water Electrolytic Transformation (WET) buoyancy engine.
As shown in Figure 1, in some embodiments, there is provided a method for
effecting generally vertical movement of a vessel within a body of water
comprising:
providing a vessel 10 comprising a housing 20 containing a buoyancy engine
22,
the engine 22 comprising a compartment 24 within the housing 20 for storing
water 26 therein, said compartment having a water valve 28 for allowing water
into the
water storage compartment 24 and a gas valve 30 for allowing headspace gas 32
to
exit the water storage chamber;
a source of electrical energy 34 external to the water storage compartment 24
and a pair of electrodes (anode 36 and cathode 38) electrically connected to
the
electrical energy source 34 and positioned within the water storage
compartment 24;
placing the vessel into a water column;
decreasing the buoyancy of the vessel by opening the water valve 28 such that
water enters the water storage chamber 24 via the water valve 28 and headspace
gas
32 escapes the water storage chamber 24 via the gas valve 30;
to note that in other embodiments, the housing may be arranged such that
bladders
are arranged to collect oxygen and hydrogen gas evolved separately from the
respective subchambers.
=
As will be appreciated by one skill in the art, the use of bladders would
provide
a sealed system, where no new sea water (i.e., salt water) would need to enter
the
device in the course of its operation, which may help avoid contamination.
However, it
is important to note that bladders would not specifically affect the buoyancy
or energy
recovery.
As discussed herein, in some embodiments, the WET buoyancy engine
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includes a fuel cell for the recapture of the energy expended during
electrolysis. In
some embodiments, the WET buoyancy engine may include a single battery that
drives the electrolysis and powers the instruments and also stores the energy
recaptured by electrolysis. In other embodiments, there may be separate
batteries for
the electrolysis and for the sensors. In other embodiments, devices that
collect energy "
from the environment known in the art, for example, solar panels when surfaced
and/or a water turbine when submerged, may be added to recharge the
battery/batteries.
Sensors included in the stealth buoy include but are by no means limited to
acoustic sensors and electromagnetic detectors. As will be apparent to one of
skill in
the art, the stealth buoy must include a communication device for
communicating
when the device is surfaced. Radio waves are attenuated by water, which means
that
any kind of underwater communication would need to be done by an underwater
=
modem.
It is also of note that the engine's electrodes may be used as a depth gauge,
since the voltage of the water-gas reaction depends on pressure. As will be
known to
one of skill in the art, it is possible to estimate the depth of the vehicle
on the basis of
the pressure exerted by the surrounding water on the gases, since the "open
circuit
potential" (which means voltage at zero current) will change accordingly.
It is of note that while the stealth buoy incorporating the WET buoyancy
engine
may be used at any depth, in terms of targeted operation, relatively shallow
near-
shore waters such as harbours, bays and the like are probably the most likely.
Generally speaking, any unanchored body in the water will drift with the
current
(or under the influence of surface winds, if appropriate). Accordingly, the
stealth buoys
are arranged to sit on the bottom of the body of water while they gather
information.
In some embodiments, for example, as shown in Figure 3, the WET buoyancy
engine further comprises a regenerative fuel cell. In these embodiments, the
barrier
50 discussed above is a proton exchange membrane fuel cell as known in the
art. in
these embodiments, the oxygen and hydrogen gases are physically separated by a
membrane that allows the passage of protons only between the oxygen subchamber
CA 02678224 2016-10-04
54 and the hydrogen subchamber 52. In the example illustrated in panel A and
discussed below, water is produced from oxygen and hydrogen gases and
electrical
power is generated; in the example illustrated in panel B, application of
external
voltage, for example, stored electrical energy, drives the fuel cell in the
reverse
5 direction, producing oxygen and hydrogen gas from water, that is, in the
reverse
direction from panel A (electrolysis).
Electrolytic phase transformation was first reported several years ago as an
alternative materials-based actuation strategy (Cameron and Freund, 2002, PNAS
USA 99:7827-7831; Cameron and Freund, 2003, Chem Eng Technol 26: 1007-
10 1011; Cameron and Freund, 2003, Proc SPIE 4878: 14-20). This technology
exploits
the enormous pressure and volume changes that accompany the electrochemical
interconversion between liquid water and hydrogen and oxygen gases:
energy +2 H20 (/) 4-4 2 H2 (g) + 02(g) (1)
Expressed as the two constituent half-cell reactions, (one occurring at each
of
15 two electrodes)
2 H20 (/)4-- 4 H+ (aq) + 02 (g) + 4e-= (2)
4 H+ (aq) + 4 e--4-* 2H2 (g) (3)
This implies that two molecules of water may be converted to three molecules
of gas, reversibly, with an accompanying flow of four electrons through an
external
20 circuit. This reaction occurs with a thermodynamic potential of 1.23 V
(Bard and
Faulkner, 2001 in Electrochemical Methods, 2nd ed). The reversibility of the
reaction
should be emphasized; the generation of gas requires the input of electrical
energy,
but the recombination is spontaneous and will produce electrical energy under
particular circumstances, i.e., a fuel cell.
The behaviour of the generated gases can be well described by the ideal gas
law:
PV = ngRT (4)
where P and V are the pressure and volume of ng moles of gas at temperature T,
and
R = 8.3145 m3 Pa ma.' K-1 is the gas constant.
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The volume Võ, of n,, moles of pure water (density p = 1.00 g/mL and molecular
weight M, 18 g/mol) is easily calculated:
= x Map (5)
The reaction stoichiometry of Equation 1 indicates that 3 moles of gas will
arise
from the electrolysis of 2 moles of water. Invoking the ideal gas law
(Equation 4), the
volume of gas Vg resulting from the electrolysis of n moles of water is:
Vg = (3/2)nRT/P (6)
The engine's buoyancy arises from the weight of water the gas can displace.
Since 1/9 >> 1360 at ambient temperature and pressure), the
volume of
water consumed can be neglected (and this may not be a consideration anyway,
depending on the device ,configuration). Keeping in mind that the total
pressure
experienced by the engine is equal to the sum of atmospheric and water depth
pressures (Path., and P
= water respectively) and that four moles of electrons ne are
required to create three moles of gas (see Equations 2 and 3), an expression
relating
the buoyant force B of a WET buoyancy engine device with electrical charge Q
may
be derived from Equation 6 and Faraday's constant F = 9.54 x 104 C
B Vgp/g (7)
(8)
(Patm Pwater)Q
= (3/4)neRTo (9)
(Patm Pwater)g
= (3/4)QRTP (10)
(Patm Pwater)Fg
For simplicity, force due to gravity g = 9.8 N kg-I may be omitted to express
-
buoyancy in, for example, grams-force instead of Newtons.
Since its operation is governed by the ideal gas law (Equation 4), the WET
buoyancy engine response is pressure and temperature dependent. At greater
depths
and colder temperatures, more electrical energy is required to reach a given
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buoyancy; the buoyancy will increase as a WET buoyancy engine equipped vehicle
ascends.
Stealth buoys are autonomous vehicles to transport sensor packages in an
aquatic environment, and have the unique ability to change their own buoyancy.
Doing so allows the vehicle to lie on the ocean floor and gather data over
extended
periods of time without detection and without suffering significantly from
drift due to
ocean currents. The data may include (i) acoustic information that identifies
shipping
and boat traffic, fishing, marine wildlife, (ii) electromagnetic information
that identifies
shipping and/or enemy military activity, (iii) oceanographic or seismic
records, and (iv)
any other information corresponding to the sensor suite deployed on the
vehicle.
When some condition is met, e.g., after a fixed period, or after some
particular event
has been detected, the buoy's logic circuitry instructs the engine to increase
buoyancy
so that the vehicle can rise to the surface, where it can upload its
information via a
radio link, or simply be collected for analysis and redeployment. Depending on
the
buoy's logic program, the vehicle may then be instructed to descend, and begin
the
cycle again.
Table 1 outlines the relationship between electrical energy at varying depths
of
sea water (p = 1.03 g m1-1) to reach an arbitrary 1 g of buoyant force. This
assumes a
driving voltage of 1.5 V, a water temperature of 10 C, and a pressure increase
of
10.08 kPa rril. For reference, a rechargeable 1.2 V 9500 mAh NiMH D-cell
contains
around 34.2 kC of charge and approximately 41 kJ of energy.
Table 1: Theoretical charge and energy requirements per gram of buoyant force
at various
depths, and the corresponding buoyant force that can be achieved by the energy
of single
D-cell
Buoyancy
Depth (m) Pressure (Pa) Charge (C) Energy (I) per D-cell (g)
0 1.01 x 105 5.28 7.93 5.17 x 103
1 1.11 x 105 5.81 8.71 4.70 x 103
10 2.02 x 105 10.5 15.8 2.59 x 103
100 1.11 x 106 57.9 86.8 4.72x 102
1000 1.02x 107 540 811 5.06 x 10'
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As will be apparent to one of skill in the art, the electrolysis cell is
simple in
design. A simple two-electrode configuration is satisfactory as there is no
need for a
precise measurement of electrode potentials, and hence a three-electrode cell
is not
required. Three fundamental design concepts are illustrated in Figures 1 and 2
in
order of increasing complexity. The key issues are: rigid compartment vs.
bladder,
and mixed vs. separated gases. For example, while electrodes made from
platinum or
palladium would offer superior electrochemical kinetics for the electrolysis
reaction,
less expensive materials (e.g., stainless steel or carbon) may also be used
with
satisfactory results.
The fundamental operation of these devices is straightforward, as illustrated
in
Figure 1. The pressure of gases resulting from the application of electrical
current can
be employed to change the density of the device either through expelling water
from
the system, or through inflating a float bladder. In the former case, sea
water would be
used as the electrolysis medium. In the latter, only on-board water could be
used
which may be useful in scenarios where salt water is undesirable, or if a low
solution
pH is desired. As will be appreciated by one of skill in the art, in those
embodiments
incorporating bladders, internal water is not expelled. Possible advantages of
this
arrangement are: (i) purer water used for electrolysis, avoiding possible
contamination, and (ii) operation in fresh water (e.g., a lake) which may not
be 'salty'
enough for the electrolysis. After the WET buoyancy engine powered vehicle has
surfaced, resubmerging is easily done by simply venting the gases.
A slightly more sophisticated design involves a physical barrier separating
the
hydrogen and oxygen gases, as shown in Figure 2, This configuration is
somewhat
safer, avoiding a potentially reactive combination of gases. The separation
leads to
the possibility of recapturing the chemical energy in a controlled manner.
There must
be some provision of ionic transport between the two compartments. This can be
a
simple hole, a porous material (e.g., fated glass) or a membrane.
The electrochemical reaction of hydrogen and oxygen forms the basis of the
hydrogen fuel cell, a concept of enormous economic importance. Already
prototype
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14
vehicles based on Proton Exchange Membrane (PEM) fuel cells are being
demonstrated.
The reaction in question is the same as presented earlier (see Equation 1),
but
in the direction opposite to electrolysis. The reaction is exothermic and
spontaneous
on a catalyst surface. By separating the half-reactions, it is possible to
recover the
chemical energy in the form of electricity. Figure 3a illustrates the PEM fuel
cell. At the
heart of this device lies a membrane that permits the passage of protons only.
This
serves to keep the electrochemical half-reactions separated. Hydrogen arriving
at the
anode (typically made of platinum or a platinum alloy) and is oxidized to free
protons.
The protons pass through the membrane, while the associated electrons are
forced to
pass through an external electrical circuit. The electron then reach the
cathode (often
containing platinum or platinum-ruthenium alloys), where they combine with the
protons and oxygen gas, forming water. The reaction continues spontaneously
until
the fuel is exhausted or the external electrical circuit is interrupted.
The same cell can be operated in reverse, Figure 3b, which is the familiar
electrolysis reaction. Such a device operated both directions is a called a
regenerative
fuel cell (RFC), and is a useful means of storing energy. RFC units store
surplus
energy collected in daylight for night operation. The theoretical cycle
efficiency of
charging and discharging a RFC is approximately 80%.
The interconversion of gases and electrical energy has previously been
demonstrated as an actuation strategy (Cameron and Freund, 2002; Cameron and
Freund, 2003; Cameron and Freund, 2003). Here, the interconversion can be
exploited to control buoyancy reversibly and precisely. Being based on the
same
principles as RFCs, the WET buoyancy engine provides highly efficient
operation,
since part of the energy expended during the gas generation stage can be
recovered
in the reverse step. Furthermore, since this engine is in effect an energy
storage
device, it is very well suited to operating in conjunction with environmental
energy
harvesting schemes.
The WET buoyancy engine stands out for its simplicity. The lack of moving
parts (other than a vent valve if so configured) implies operational
robustness and
CA 02678224 2016-10-04
inexpensive assembly; a working engine can be built for dollars. Accordingly,
the
WET buoyancy engine is ideal for autonomous and disposable applications.
WET buoyancy engine technology is also well suited to driving inexpensive
stealth buoys. A buoy deployed on the ocean bed could be made positively
buoyant
5 through the electrolysis reaction. After the buoy has completed its radio
transmission
at the surface, venting the gas would cause the device to sink once again. As
an
example, using the information from Table 1, a stealth buoy lying on the sea
bed at a
depth of 100 m and needing 20 g of buoyant force to start its ascent' would
need
roughly 1.7 kJ of energy input. A single D-cell could provide sufficient
energy to power
10 at least 24 cycles. A regenerative system could improve this figure:
reacting the gases
in a RFC configuration would recoup a significant fraction of the energy. The
current
work on 11 kg A-size sonobuoys suggests that a minimum of 1.2 L of water
= displacement should be effected to lift the device off the bottom. From a
100 m
= deployment, the energy content of 2.5 D-cells would be expended per
ascent.
15 Realistically, an energy recapture scheme should lower this to between one
(representing 60% recapture) and two (20% recapture) D-cells.
Alternatively, an energy harvesting scheme could be used to drive the
= electrolysis reaction, allowing indefinite operation of the buoyancy
engine. A simple
turbine attached to a small DC generator would suffice to convert the kinetic
energy of
water due to tidal flow. For a turbine with rotor diameter r in water flowing
with a
current v, it is easy to derive an expression for kinetic energy E per unit
time t:
E/t = (1/2)pntr2v3 (11)
As an example using real-world parameters, the predicted peak tidal current
flow in Halifax harbour ranges from around 0.34 m/s (0.22 m/s average) under
the
MacDonald bridge to around 0.10 Ws (0.064 m/s average) in the vicinity of the
anchorage between George's and McNab's islands (an area commonly used by
visiting aircraft carriers). Assuming a generator with a turbine around the
size of a
compact disc (6 cm radius), in one 24-hour period over 1.6 kJ could be
collected from
CA 02678224 2016-10-04
16
tidal flow under the MacDonald bridge. Assuming an overall conversion
efficiency of
only 30%, such a device could provide 20 g of buoyant lift to a stealth buoy
sitting on
the bottom (around 20 m deep) every 24 hours.
Underwater gliders travel through the water by changing their buoyancy to
generate net upwards or downwards force accordingly. The force is translated
to
horizontal motion by the glider's "wings". The buoyancy change is accomplished
by
the glider changing its internal volume typically on the order of 100 cm3 via
the
pumping of fluids, and attitude is controlled by shifting internal weights
(usually the
battery tray).
First, the energy consumption in the conventional gliders to reach a certain
buoyancy is not strongly dependent on depth, since the same quantity of fluid
will be
pumped under all conditions. This is reflected in the poor efficiencies at
shallower
cycles. It can be concluded then that many of these gliders are inefficient
for
operations in other than deep sea conditions. Consequently, they are
ineffective for
the littoral applications that would be most useful for surveillance and
reconnaissance.
The WET buoyancy engines consume energy proportional to depth, and are
therefore
more efficient in shallower waters. A glider propelled by a WET buoyancy
engine
would be ideal for military operations. One arrangement for a WET buoyancy
engine-
based stealth glider is shown in Figure 4. In this embodiment, the underwater
glider
100 comprises three WET buoyancy engines 101, 102, 103, specifically, one self-
contained regenerative buoyancy engine in the nose 101 and one in each wing
102
and 103 and connected to a single power source (BAT). As can be seen in the
individual panels, the buoyancy of the underwater glider can be increased by
effecting
electrolysis (generating oxygen and hydrogen gases) in all three buoyancy
engines
101, 102, 103 while buoyancy can be decreased by reversing the electrolysis
process
in all three buoyancy engines 101, 102, 103. The glider can be pitched up or
down by
either effecting electrolysis or reversing electrolysis respectively within
the buoyancy
engine in the nose 101. Similarly, the underwater glider can be rolled left or
right using
the buoyancy engines in the wings, as shown in Figure 4. Specifically, a right
roll uses
activation of 101 and 103 whereas a left roll uses activation of 101 and 102.
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Second, the cost (and, presumably, reliability) of the vehicles is largely a
reflection of their mechanical nature. Pumps to change buoyancy and screw
motors to
change centre of gravity add expense and complexity to the apparatus. The WET
buoyancy engine has no moving parts. Buoyancy can be controlled by one cell.
Pitch
and roll can be controlled with two additional independent cells. Using
regenerative
cells, buoyancy, pitch, and roll (and thus yaw) can be controlled as a self-
contained
system, with "pumping" achieved by electrical means, as illustrated in Figure
4 and as
discussed above. In this arrangement, the battery can be thought of as a
reservoir for
the electricity-gas equivalency.
It is of note that other suitable arrangements of WET buoyancy engines for an
underwater glider will be readily apparent to one of skill in the art and are
within the
scope of this invention. That is, the three WET buoyancy engine underwater
glider is
an illustrative example and does not necessarily limit the invention.
In use, the glider may initially sit flat on the surface, positively buoyant.
For use,
the underwater glider changes its overall buoyancy so it sinks slowly. Now, if
the
glider pitches its nose down slightly, some of the vertical motion will be
translated to
horizontal motion. In this manner, the underwater glider moves downward like a
bird
or plane gliding down towards the ground but with a significant horizontal
component
to its motion owing to the effect of the wing. Now if the glider changes its
buoyancy to
become slightly positive, and tilts its nose up, it will float upwards, but
the wing effect
will cause the vehicle to travel horizontally at the same time.
Underwater gliders are autonomous underwater vehicles designed to travel
great distances underwater through changes in net buoyancy and pitch and/or
roll
angles. These Vehicles too are used to carry sensor packages, and are
frequently
used to gather oceanographic data. Currently, both stealth buoys and gliders
rely on
complicated, expensive engines to change their buoyancy. The WET engine
introduces a simple, inexpensive, and energy-efficient means to effect
buoyancy
changes, leading to the possibility of inexpensive -- perhaps disposable ---
stealth
buoys and underwater gliders.
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One further advantage of using RFC WET buoyancy engine units as shown in
Figure 4 is that gas can be continuously reconsumed during the ascent In order
to
maintain constant buoyancy. Additionally, the cell open circuit voltage will
be
proportional to the gas pressure, in accordance with the Nernst equation (Bard
and
Faulkner, 2003). Therefore, the RFC could serve as a redundant depth gauge.
Buoyancy control is a key element to the operation of autonomous underwater
vehicles. Stealth buoys and underwater gliders cannot function without a means
of
increasing and decreasing their buoyancy, usually by means of pumping fluids.
The Water Electrolytic Transformation buoyancy engine exploits an
electrochemical reaction to achieve buoyancy changes. This approach is very
efficient, especially in depths associated with littoral waters, and is also
silent. It uses
no moving parts, and is consequently extremely reliable. It is also very
inexpensive to
construct and uses no toxic materials. Furthermore, it lends itself well to
scaling,
which indicates that much smaller devices could be deployed.
Because of their simplicity, WET buoyancy engines are an attractive
replacement for the engines that currently drive stealth buoys and underwater
gliders.
The scope of the claims should not be limited by the preferred embodiments
set forth in the examples, but should be given the broadest interpretation
consistent
with the description as a whole.
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REFERENCES
1. Rudnick, D.L., Davis, R.E., Eriksen, C.C., Fratantoni, D.M., and Perry,
M.J. (2004).
Underwater gliders for ocean research. Marine Technology Society
Journal, 38, 73-84.
3. Cameron, C.G. and Freund, M.S. (2002). Electrolytic actuators: Alternative,
high-performance, material-based devices. Proc. Natl. Acad. ScL U.S.A., 99,
7827-7831.
=
4. Cameron, C.G. and Freund, M.S. (2003). Reversible and efficient
materials-based actuation by electrolytic phase transformation. Chem. Eng.
Technol, 26,1007-1011.
5. Cameron, Colin G. and Freund, Michael S. (2003). Electrolytic phase
transformation actuators. Proc. SPIE, 4878, 14-20.
6. Bard, Allen J. and Faulkner, Larry R. (2001). Electrochemical Methods, 2
ed.
Wiley.
7. Eriksen, C.C., Osse, T.J., Light, R.D., Wen, T., Lehman, T.W., Sabin, P.L.,
Ballard, J.W., and Chiodi, A.M. (2001). Seaglider: A long-range autonomous
underwater vehicle for oceanographic research. IEEE J. Ocean. Eng., 26, 424-
436.
8. Sherman, J., Davis, R.E., Owens, W.B., and Valdes, J. (2001). The
autonomous underwater glider "spray". IEEE J. Ocean. Eng., 26, 437-446.
9. Webb, D.C., Simonetti, P.J., and Jones, C.P. (2001). SLOCUM: An underwater
glider propelled by environmental energy. IEEE J. Ocean. Eng., 26, 447-452.
