Note: Descriptions are shown in the official language in which they were submitted.
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THIS INVENTION relates to the utilisation of wave
motion, particularly the motion of sea waves.
In the past attempts have been made to utilise
energy from the sea. There are three basic ways in which
these attempts have been made. Firstly, floats have been
used to follow the wave motion and to generate power.
Secondly, sea waves have been used, for example, by
generating power as sea water flows over or through a dam.
The third basic method, which has been considered for the
10 purpose of generating a minimal amount of power, is to use
sea water to blow air through an orifice in, for example,
- a floating buoy to cause a whistling sound.
These prior proposals have only met with limited
success and it is an aim of the present invention to
15 provide an improved method and unit for utilising power
from the sea.
According to the invention, there is provided a
power unit comprising a resonator having a mouth located
in the sea and containing a body of water and an air
20 cushion above the body of water; the air cushion being
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controlled to cause the water to resonate in response to
pressure fluctuations resulting from wave motions in the sea,
thereby developing fluctuations of increased pressure, said
controlling means comprising a sensor in the resonator and a
compressor for providing adjustment of air pressure in the
resonator in response to pressur~e sensed by the sensor; and
the unit being constructed so that the increased pressure
fluctuations create a fluid flow; and means for utilising the
fluid flow so created.
The resonator may be a Helmholtz resonator and have
a neck defining a relatively small flow area compared with the
surface area of the body of water immediately below the cushion.
The means for controlling the air cushion control the pressure
of the air forming the air cushion for tuning the resonator to
provide a suitable resonance in response to wave motion.
The means for controlling the fluid flow may include
an outlet above the neck of the resonator and through which
water can be forced, for example, into a pressure tank~ The
water from the pressure tank may be fed to a turbine for driving
an alternator or generator to generate power. Alternatively,
the mouth of the reson~tor may be provided with vanes for
directing water flowing from the mouth. This water flow can
be used, for example, to propel a boat or ship.
The invention also extends to a method of generating
power, which comprises providing a resonator having a mouth
located in the sea so that the resonator contains a body of
water and an air cushion; said mouth having a small flow area
compared with a surface area of said body of water immediately
below said air cushion; sensing the pressure in said air
cushion; controlling the pressure of the air cushion in response
to the pressure sensed in said air cushion; thereby causing
the water in the resonator to resonate in response to pressure
fluctuations resulting from wave motions in the sea so that
fluetuations of inereased pressure are developed; eausing the
increased pressure fluetuations to ereate a fluid flow; and
utilizing the fluid flow so created to generate power.
The invention further e~tends to an apparatus for
use in a power unit, the apparatus having a chamber for reeeiv-
ing an air eushion and a body of water below the air eushion
and having a mouth for loeating below sea level for plaeing a
body of water in the chamber in direct fluid eommunication with
the sea; a sensor for sensing pressure in the ~hamber; air
eontrol means for increasing or decreasing air pressure in the
chamber to create resonant conditions and means for utilising
fluid flow created as a result of said resonant conditions.
The apparatus can comprise a pair of resonators Or
different heights and arranged substantially side-by-side
with sensors in both of the resonators and means for controlling
the pressures of air cushions therein for normally maintaining
resonant conditions in said resonators.
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Embodiments of the invention will now be described,
by way of example, with reference to the accompanying
drawings, in which:
Figure la is a schematic diagram of a resonator
having a mouth located below sea level and Figure lb is an
- analogous electrical circuit;
Figure 2 is a schematic diagram showing a power
unit;
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Figure 3a is a schematic diagram showing a
1~ propulsion system;
Figure 3b shows an alternative position of part
of the system;
Figures 4a, 4b and 4c are provided to illustrate
tuning of a resonator;
Figure 5 shows diagrammatically one form of
generating station; and
Figure 6a and 6b show flow-directing vanes.
As shown in Figure l, an ocean-swell-tuned
Helmholtz resonator lO is substantially in the form of an
inverted cylinder having a closed upper end and an open
lower end providing a mouth 12. The mouth 12 of the
resonator is located below sea level and, as shown, the
resonator is filled with ater to a variable level 14. An
air cushion 16 is formed above the water level 14.
The still water level of the ocean is shown at 18
and a wave is shown at 20, the height of the wave peak being
illustrated at 22.
The column of water in the resonator is acted on
10 by the wave motion and, by suitably controlling the pressure
of the air cushion 16, it is possible to ensure that the
water in the resonator will resonate at the wave frequency.
Thus, it is possible to develop relatively intense pressure
fluc.uations in the air cushion and the water below.
In order to determine the characteristics of such
a resonator, it is possible to use an analogous electrical
circuit as shown in Figure lb. This circuit includes a
power generator 24 for generating a voltage which is analo-
gous to the ocean wave pressure fluctuations 20; and an
inductance L which is analogous to the mass of the water
column in the resonator. Capacitance C represents the air
cushion 16 above the mass of water and energy lost through
radiation of waves from the mouth of the resonator is
represented by the energy lost through resistance R. The
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energy extracted from the resonator for power generation
purposes, together wi-th coinciden-tal losses such as viscous
drag are represented by resistance Rl.
The power generation unit of Figure 2 is based on
the principles illustrated in connection with Figures la
and lb. The unit includes a Helmholtz resonator 26 having
a primary chamber 28 and a downwardly extending neck 30.
The lower end of the neck 30 defines a mouth 32. The
resonator is filled with a body of water up to a movable
water level 34 and an air cushion 36 is formed above the
body of water. A pressure control system 35 is provided for
controlling the pressure of the air defining the air cushion
36 for tuning the resonator. The system 35 has a sensor
35.l mounted in the air cushion 36 and this i9 connected
to a control device 35.2 for controlling the operation of
a reversible compressor 35.3. The reversible compressor
can increase or decrease the pressure in the cushion 36
until resonance is obtained. The resonator is mounted with
the neck extending below sea level.
The resonator lO is connected to a pressure tank
38 by an outlet 40 including a non-re-turn valve 42. The
valve is designed to allow substan-tially full-bore flow
through the outlet 40.
As shown in -the drawing, the tank 38 has an air
cushion 44 at its upper end and this is intermittently
compressed by flow of water through the outlet 40 into the
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tank and serves to stabilise the flow of water from the
pressure tank through an outlet 46 to a turbine 48. The
turbine may be any standard water turbine and is connected
to drive an alternator 50, another elec-trical generator
or any other suitable equipment.
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A plurality of resonators can be arranged to feed
the pressure tank if desired.
When the water in the resonator is subjected to
wave motion, the mass of water resonates with the compliance
10 of the air above the water. Intense pressure fluctuations
are developed above the neck of the resonator and water is
fGrced through the outlet 40 and valve 42 into the tank.
The water leaves the tank through the outlet 46 and then
drives the turbine 48.
As shown in Figure 5, a generating station com-
prises a floating hull 55 in which a plurality of resonators
26 like that of Figure 2 are mounted. Each of the resonators
is arranged with its mouth 32 opening through the bottom
of the hull at a location which is permanently below sea
20 level. The resonators are arranged in pairs with outlets
40 of the resonators of each pair communicating with a
single pressure tanks 38. The pressure tanks are again
arranged to supply water to drive -the turbine 48 and thus
the generator 50. The hull 50 can be moved at any suitable
25 location. Naturally, the generating station need not be a
floating one.
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Referring now to Figures 3a and 3b, a resonator
26 which is similar to the resonator of Figure 2 is mounted
in a ship or boat (not shown). The parts of this resonator
are indicated by the same reference numerals as those used
- 5 in Figure 2. The resonator is again provided with a pressure
control system for controlling the pressure of the air
cushion 36 and the mass of the water in the neck 30 again
resonates with the compliance of the air cushion.
A board or similar device 52 is pivotally mounted
10 on the inside wall of the neck at one side of the neck.
This board is connected to a set of streamlined vanes 54
by a coupling 57 so that water rushing into the resonator
pivots the board upwardly and serves to tilt the vanes.
Conversely, water rushing out of the resonator pivots the
15 board downwardly and tilts the vanes to an opposite angle.
In this way, water can be caused to enter the resonator in
the direction of arrows 56 and is driven from the resonator
in the direction of arrows 58 (Figure 3b). The water
rushing in and out of the resonator between the vanes thus
20 exerts a fluctuating force on the ship carrying the vanes
and this force can be used to propel the ship. Of course,
any suitable number of resonators of different shapes and
sizes can be used in this manner.
Instead of using the board 52 and coupling 57, it
25 is possible to use self-orientating vanes 60 as shown in
Figures 6a and 6b. ~hese vanes are symmetrical vanes each
pivotally moun-ted towards one side on pivots 62 fixed to
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the mouth of the resonator 26. As the water flows into
the resonator mouth 32 in the direction of arrows 64, the
vanes 60 automatically rotate in a clockwise direction
until further movement is limited by stops, shown
diagrammatically at 66. The inclination of the vanes to
the horizontal is then 45. On the other hand, as water
flows out of the mouth, the vanes 60 rotate in an anti-
clockwise direction until they strike schematically
illustrated stops 68. The direction of flow of the water
10 longitudinally of the ship is thus reversed automatically
by the vanes.
A resonator arrangement similar to that of
Figure 2 can also be used to drive a ship or boat, in which
case the flow through outlet 40 is guided to a nozzle for
15 driving the ship.
As ocean waves have a fairly wide frequency
spectrum but normally have one predominant frequency at
which a maximum amount of energy can be extracted, the
resonator should suitably be tuned to this predominent
20 frequency. Tuning can be effected by ad~usting the air
pressure of the air cushion 36 in the resonators of Figures
2 and 3a. Correct tuning is indicated by a maximum
pressure fluctuation above the water level, which can be
measured by means of sensors 35.l.
In practice, an automatic hill climbing mechanism
is desirable in order to keep the resonator tuned to the
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correct frequency. For this purpose, two resonators 70 of
different heights are arranged side by side as shown in
Figure 4a. The same air pressure initially exists in both
air spaces above the water and the resonant frequencies
of both resonators increase with an increase in pressure.
However, there is a difference in resonant frequency as
shown in Figure 4b, the lower resonator responding to the
higher frequency.
A relatively flat-topped resonance curve, as
10 shown in Figure 4c, can be obtained if the power in the
two resonators is added. A maximum amount of power is
obtained from the combined system when the peaks for the
two resonators in Figure 4b are substantially the same.
The resonators are both connected to an arrange-
15 men-t 72 including a reversible compressor 74 for pumping
air pressure up or down so that, when the air pressure
fluctuations in the air cushion marked A are smaller than
those in the air cushion marked B, the compressor is
automatically switched by control device-76 to raise the
20 pressure in the cushions A and B until the pressure
fluctuations in the two resonators are substantially
the same. When the air pressure fluctuations in cushion
s are smaller than those in cushion A, the compressor is
automatically switched to reduce the pressure in the
25 cushions A and B until the pressure fluctuations in the
two resonators become approximately the same. The pressure
fluctuations are measured by sensors 78. Thus, the system
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is automatically set to absorb the maximum amount of wave
energy.
The tuning of the resonators can be taken off the
resonant frequency by means of a pressure increase or
reduction when reduced power is required. This is particu-
larly important when a resonator is used to propel a ship,
as described with reference to Figure 3. Of course, a ship
being driven by the r:esonator system can be put into reverse
by changing the connection 57 between the board 52 and vanes
10 54 to reverse their operation. An auxiliary engine will
normally be required for a resonator driven ship.
The resonators described can be used in floating
break water units consisting of at least two resonators per
unit and a similar hill climbing mechanism to that described
15 with reference to Figure 4a can be used for tuning the
resonators. Energy can be dissipated by providing suitable
leaks above the throats of the resonators at a connection
between the resonators and a pressure tank similar to that
of Figure 2.
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