Note: Descriptions are shown in the official language in which they were submitted.
1 16476~
wave -ne~ ac~3r
This L.~n.~ion ~ s ~o ~ ~ev _~ 3 ~ ~ .Y _ ~ ~ C ~ ~ n
_rom waves on a li_uid.
.Ln e~ample o~ such a ~evice ia ~escrl~ed in 3ri-is~
Patent Speci ication ~o. 1,80805 (united Staces ?~ ~en,; ~To
4164383), and comprises a ~lurality of ?arZially in~la~d
bag-like enclosures formed f om flexible lmpe~ea~'e ~2~er a
and arranged along a s?ine aligned in t.ne di ection o
advance of waves. The enclosures are connec~d .o a s2s
circuit so as to pressurize a gas (e.g. ai ) in the circu
as the sea rises and falls about the enclosures, and ~
turbine installed in the circuit extracts ener~y from ~ae
pressurized gas, the device '~eing hereina-ter described as
the "Lancaster Flexible Bag device".
A modified form or the Lancaster Flexible 3ag device is
described in 3ritish Patent Specification No. 2060082.~, and
was featured in a paper presented by ?rofessor .~. J. ~-ench
at a First Symposium on Wave Energy Utilisation, Chalmers
Universitv of Technology, Gothenburg, Sweden, 30 Octobe~-!st
November 1979. In this modi'ied device, elongate ducts
positioned above the bag-li'ce enclosures cunction ~oth as
portions of the yas circuit, and as buoyancy ~hambers.
In another form of wave energy device, a plurality o~
movable panel members are aligned in the direction of advance
2S of the waves and are exposed to the waves so that movement o.
the panel members in response to the waves can be used to
pressurize a gas circuit similar to that described above,
examples of the latter wave energy device being described in
3ritish Patent Specifications Nos 2026621A and 2047353A.
One problem common to many wavs ener~y devices includin~
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1 164~6~
the aforedescribed wave energy devices, is tnat oE ?resenting
the devices to the waves in a manner such as to ~?.i~is~ t~.e
per~ormance of the device.
According to the present invention there is ~rovided a
device for extracting energy ~rom waves on a liquid and
comprising, a buoyant body, means incorporated in or
associated with the body for extracting energy from the
waves, at least one chamber in or attached to the body, the
chamber being open to the liquid and adapted to be ~artially
filled therewith so as to define a space above the liquid
therein, a closable port means for air flow into and out of
the air space in response to changes in level of the liquid
in the chamber, and means for sensing the ~otion of the body
in the liquid and for providing a signal related to said
motion to the port means so as to control the operation of
the port means in response to said signal in a manner such as
to influence the motion of the body in the liquid.
Advantageously, a said chamber is provided at the bows
and/or at the stern of the device, and the chamber(s) might
define a water plane area of about 10~ of the water plane
area of the device.
The port may be adapted such as to vary the rate of flow
of the air therethrough in response to said signal, and might
comprise a plurality of hinged louvres, with drive means for
controlling the position of the louvres in response to the
signal.
- Means might be provided for introduing pressurized air
into the space of a said chamber so as to change the level of
the liquid in the said chamber and thereby change the
buoyancy effect of the said chamber.
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1 16~768
Tl~e pressurized air means might com~ri~e ~ ?or~1on of thQ
energy extraction means, or air storage means, 3r l~clu~e air
displacement means such as a 'nigh ~ressure 'an.
Desirably, the distance from the chamber to the centre
of motion of the device is at least about half a wavelength
of the typical wave in the locality in which the device is to
be used.
The energy extraction means might comprise an ai
circuit arranged to be ?ressurized by the energy of the waves
and a tur~ine means through which the ai in the circuit is
to be discharged. The port means might also be connected to
an energy extraction means so as to maximise the energy
extracted from the waves.
The sensing means might comprise accelerometer means for
lS sensing a local heave component of the device motion,
gyro-stabilised inclinometer means for sensing the pitch of
the device, and wavegauge means for sensing the period, the
wavelength, and the wave height of the advancing waves.
The invention will now be further described by way of
example only with reference to the accompanying drawings, in
which:-
Figure 1 shows a diagrammatic cross-sectional
representration of a wave energy device;
Figure 2 shows to a reduced scale a diagrammatic view
on the line II-II of Figure li
Figure 3 shows to an enlarged scale a fragmentary
sectional view of one end of the device of
Figure 2;
Figure 4 shows a modification of the view of Figure 3;
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1 16~768
~igure ~ shows a view in the direction o. ar~ ow ' .~.' o.
Figure 4i
Figure 6 shows a di2gr2mm2tic representation o- a
` sensing control circuit for ~e devi ce of
Figures 1 and 2;
Figures 7a to 7f show graphically variations of heave of
a rigid hull;
Figures 8a to 8r show graphically variations of ?it_h of
the rigid hull of ~igures 1a to 7f;
~igure 9 shows graphically the changes in pitch of the
rigid hull of ~igures 7a to 8f through a wave
period, and
Figure 10 shows graphically through a wave period the
pitch of a rigid hull similar to that of
Figure 9 but without incorporating the
invention.
In the above-noted drawings Fig. 6 appears on the same
sheet as Fig.2; Figs. 7a-7c appear with Figs. 8a-8c; Fig.7d appears
with Fig. 8d and Figs. 7e and 7f appear with Figs. 8e and 8f.
Referring now to Figures 1 and 2, there is shown a
device 10 for extracting energy from waves on a liquid 16
(e.g. the sea). The device 10 in most respects is similar to
the Lancaster Flexible Bag device of British Patent
Specification No. 2060082A, and comprises an elongate
structure 11 having a left-hand ballast tank means 12 and a
right hand ballast tank means 13 each being of triangular
cross-section and extending along the lower portion of the
device 10 in side adjacent relationship and provided by a
plurality of individual tanks 12a or 13a respectively each
filled with the liquid 16. Above the ballast tank means 12,
13, a plurality of left hand pumping chambers 14 and of right
hand pumping chambers 15 in side adjacent relationship extend
along the structure 11, each pumping chamber 14, 15 being air
filled and defined at least in part by a flexible wall 20 of a
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7 ~ ~
plastic coated cloth or similar r~lati~vely thic'c .lexi~le
impermeable material, and separated from each other by
respective relatively thin divisiorls 21 of Elexi~le
impermeable material similar to the material o~ the ~lexi~le
wall 20. A high pressure duct 25 and a low pressure duct 2
in side adjacent relationship extend along the device 10
above the pumping chambers 14, lS, each Qumping chamber 14,
15, having an outlet port 27 connected to the high ?ressure
duct 25 and an inlet port 28 connected to the low pressure
duct 26.
A housing 30 above the high pressure duct 25 and the low
pressure duct 26 contains a turbo-generator 31 having an
inlet duct 33 connected to the high pressure duct 25 and an
outlet duct 34 connected to the low pressure duct 26.
lS Each ballast tank 12a. 13a is capable of being eyacuated
in a conventional manne~, e.g. discharged by compressed air
through a port (not shown), to change the buoyancy and thus
the tri~ of the device 10 in the sea, the compressed air
being supplied from a maintenance vessel or from the device
10 itself. A buoyancy chamber 36 is located near each end of
the structure 11, and a stabilising chamber 40 provided at
each end of the structure 11. Each stabilising chamber 40 is
open to the liquid 16 at the bottom., and at the top thereof
has a closable port 41 with a plurality of adjustable louvres
42 (shown open) for controlling air flow into and out of the
chamber 40 through the port 41. The louvres 42 are
pivotable about respective centres 44 and are controlled by a
sensing and control circuit as shown in Figure 6 to which
reference is made, the control circuit comprising a sensing
and control unit 48 connected to respective electric drive
units 50 drivingly connected to the louvres 42 (not shown in
Figure 6) so as to open or close the louvres 42 in response
to a signal from the sensing unit 48. The sensing and
control unit 48 incorporates a gyro-stabilised inclinometer
(not shown) and an accelerometer (not shown) for sensing
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7 ~ ~
pitch and local heave components of the motion of tne devic~
10 res~ectively, and alsc recei~Jes dat~ -rom ~ wa~egauge ,2
at the bows of the device lO for sensing the ?eriod, the
wavelength, and the waveheight of the ~dvancing waves.
Referring again to Figure 2, the liquid 16 in the stabilising
chambers 40 deEines an air space ~6 ~elow the louvres 42, and
by appropriate phasing of the o~ening of the louvres 42 ~see
Figures 2 and 3) or the closing of the louvres 42 (see
Figures 4 and S), the motion of the device lO in the liquid
16 can be influenced in a desired manner.
The device 10 in use is aligned ?arallel to the mean
direc~ion of the advancing waves so that waves pass along the
device as shown by the line 38 of Figure 2. Thus the
flexible wall 20 of each pumping chamber 14, 15 is subjected
to compression as a wave crest rises about it so that air is
discharged from the respective pumping chamber 14 or 15
through the respective outlet port 27 into the high pressure
duct 25 as the flexible wall 20 progressively collapses under
the compressive load applied by the wave crests as shown by
the broken lines 20a .... 20c. Air in the high pressure duct
25 flows through the inlet duct 33 to the turbo-generator 31
to perform useful work and from the turbo-generator 31 flows
through the outlet duct 34 to the low pressure duct 26. As
the wave crest passes so that the level of the liquid 16
falls about each flexible wall 20, air from the low pressur
duct 26 discharges through the respective inlet port 28 into
the respective pumping chamber 14 or 15 and thus expands the
pumping chamber 14 or 15 and moves its flexible wall 20
outwardly.
This sequence of the progressive collapse and subsequent
outward movement of the flexible walls 20 with the associated
discharge and expansion of the pumping chambers l4 and 15
continues as wave crests move a~ong the device lO, and the
electrical output produced by the turbo-generator 31
1 16~7~
\
re2resents ene~gy extracted ~rom the waves.
The motion of the device 10 in the liquid 16 is
influenced by the effect of the stabilising chambers ~0 so ~s
. to optimise the energy extracted from the waves. For
example, if the louv~es 42 are held closed as the liquid lo
rises about the device 10 adjacent to the particular
stabilising chamber 40, an upward force is exerted by the ai
pressure in the air space 46 on the device 10 at this
stabilising chamber 40 as the liquid 16 in the stabilising
chamber 40 rises. aY appropriate phasing of the sequence of
opening and closing the louvres 42 of both.stabilising
chambers 40, this upward force can be used to minimise the
pitch behaviour of the device lO in response to waves, and in
a similar manner can control the heave motion of the device
lS 10. For example, the heave and the pitch amplitudes of a
hypothetical model of a rigid hull (not shown) fitted with
stablising chambers 40 operating at twice the wave frequency
were calculated, and are shown graphically in Figures 7a to
7f and Figures 8a to 8f at different wave periods (T seconds)
for a device 5.5 metres long in waves having a wavelength of
4 metres. Figures ia to 7f show the effect on heave, and
Figures 8a to 8f show the effect on pitch, using either a
stabilising chamber 40 at the bows or at the stern of the
hull, of an opening and closing sequence of the louvres 42 at
a frequency of twice the wave frequency, the louvres ~2 being
opened initialiy at a time ('t' seconds) after a datum
represented by the instant that the local wave about each
stabilising chamber 40 starts to rise from the trough of the
wave. In each Figure 7a to 7f and Figure 8a to 8f there is a
lowest point of the curve ~herein which represents the time
(t) from which the opening of the louvres 42 should be phased
to provide minimum heave or pitch components of the motion of
the hull. Referring to Figure 9, the effect on the pitch of
a hull 60 from the opening of the louvres 42 of the
stabilising chamber 40 in the bows of the hull 60 is shown
for a wave period of l.6 seconds and a time
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7 6 ~
't' seconds after the aforesaid datum of the local wave abou.
the stabilising chamber 40. The angle of inclination o~ th~
hull 60 in Figure 9 represents the instantaneous ?i.ch ang1-
of the hull 60, and this pitch angle sho~ld be contrasted as
S shown in Figure lO, with the 2itch angle Ot a huLl 60a
similar to the hull 60 of Figure 9 but without ha~ing a
stabilising chamber 40 and in the same wave conditions.
Although the stabilising chambers 40 have oeen shown at
each end of the device lO, the chambers 40 may be provided
solely at one or other of the ends of the device lO and
elsewhere on the device lO, for example at the middle of the
device 10, and may be used to minimise roll of the device
10 .
~ne advantage of the use of the invention for a
Lancaster Flexible Bag devic.e is that such a device with its
elongate structure is bistable in pitch in still water,
whereas for optimum energy extraction the device should be
approximately horizontal. In the still water condition,
pressurized air might be introduced into the air space with
the port means closed so as to level the device from the
change in the ~uoyancy effect of the chamber. This
pressurized air could be supplied ~rom the high pressure duct
25, or from storage cylinders (not shown), or from a high
pressure fan (not shown). ~owever, the invention may be
incorporated in other wave energy devices to modify the
motion and/or to optimise wave energy extraction thereof.
For most purposes stabilising chambers having a total
waterplane area of approximately 10% of the total waterplane
area of the wave energy device are satisfactory.
It will be understood that although the invention has
been described in relation to a port means in the form of a
two-state louvre device, the port means might be arranged so
as to be capable of varying the opening thereof to introduce
1 1~4768
a variable resistance on the rate of air flow ~hrousn ~e
oort means. If desire~ t~e air flow through the ?or~ means
might be used as a supplementary source of energy ex~racted
from the waves. Alternative forms of ?or. ~eans may be used,
S not necessarily in the form of pivotable louvres.
It is usually convenient for the stabilising chamber(s)
to be integral with the device, but for some applications a
stabilising chamber attached to the device may be used.
The electric drive means SO for operating the louvres
42 might comprise an electric motor, although alternative
drive means might be used, for example electro-hydraulic
means.
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