CA1164768A

CA1164768A - Wave energy extractor

Info

Publication number: CA1164768A
Application number: CA000384150A
Authority: CA
Inventors: Robert V. Chaplin
Original assignee: UK Secretary of State for Energy
Current assignee: UK Secretary of State for Energy
Priority date: 1980-08-27
Filing date: 1981-08-19
Publication date: 1984-04-03
Also published as: NO812789L; JPS57116171A; FR2496180A1

Abstract

ABSTRACT OF THE DISCLOSURE

A wave energy extractor A wave energy device 10 incorporates at least one stabilising chamber 40 for influencing the motion of the device 10 in response to waves. The stabilising chamber 40 is open at the bottom to the sea, and has a closable port 41 at the top of the stabilising chamber 40 for controlling air flow into and out of the stabilising chamber 40 resulting from changes in level of the seawater inside the stabilising chamber 40. Appropriate timing of an opening and closing sequence of the port 41 is used to produce air pressure forces in the stabilising chamber 40 acting on the device 10 in a manner to control the heave and pitch components of the motion of the device 10.

Description

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~

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.

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;

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 '~:
~. ..

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 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 .

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.

Claims

The embodiment of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A device for extracting energy from waves on a liquid, comprising a bouyant body and means at the bouyant body for extracting energy from the waves, wherein the improvement comprises:

a) at least one chamber associated with the body, the chamber being open to the liquid and adapted to be partially filled therewith so as to define a space above the liquid therein;

b) a closable port means of the chamber for air flow into and out of the space in response to changes in the level of the liquid in the chamber; and c) means for sensing the motion 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 a manner such as to influence the level of the liquid in the chamber by controlling the air flow through the port means thereby influencing the motion of the body in the liquid from the effect of the bouyancy provided by the chamber, the sensing means comprising, means for sensing a local heave motion of the device, means for sensing the pitch of the device, and means for sensing the period, the wavelength, and the wave-height of the advancing waves.

2. A device as claimed in Claim 1, wherein the distance from a said 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.

3. A device as claimed in Claim 2, wherein a said chamber is provided near an end of the device.

4. A device as claimed in Claim 1, wherein the water plane area of the chamber, or the total water plane area of the chambers, is about 10% of the water plane area of the device.

5. A device as claimed in claim 1 or claim 2, wherein the port means are adapted to vary the rate of flow of air therethrough in response to the signals provided by the sensing means.

6. A device as claimed in claim 3 or claim 4, wherein the port means are adapted to vary the rate of flow of air therethrough in response to the signals provided by the sensing means.

7. A device as claimed in claim 1 or claim 2, wherein the port means are adapted to vary the rate of flow of air therethrough in response to the signals provided by the sensing means, and wherein the port means comprises a plurality of hinged louvres disposed across a port at said chamber, and means drivably connected to the louvres for pivoting the louvres in response to said signal from the sensing means.

8. A device as claimed in claim 3 or claim 4, wherein the port means are adapted to vary the rate of flow of air therethrough in response to the signals provided by the sensing means and wherein the port means comprises a plurality of hinged louvres disposed across a port at said chamber, and means drivably connected to the louvres for pivoting the louvres in response to said signal from the sensing means.