CA1065738A - Device for deriving power from wave energy - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A device for extracting energy from wave energy and comprising a pluraliy of chambers adapted for pressurising a working gas, and a mechanical device such as an air turbine to which the collected pressurised working gas is conducted to extract energy therefrom and drive a device such as an electric generator.
The chambers are connected together in series relation-ship so that the pressurised working gas from one chamber is collected by an adjacent chamber as it progresses along the series to the mechanical device.

Description

1065~
Thi6 is a divisional of Canadian Application Serial No. 284,887 filed August 17, 1977.

BACKGROUND TO THE INVENIION
This invention relates to devices for extracting power from wave energ~ and more particularly, but not exclusively, wave energy from sea waves.
In one kno~n device for utilising wave energy invented by Yoshio Masuda and described in Briti6h Patent Specification No. 1~014,196, a working gas in a cha~ber is caused to flow through a turbine positioned above the chamber by the oscillation of a column of water in the chamber, the chamber being defined by a buoy device. Such devices have so far been used for applications requiring relatively low power output~ and the present invention is more particularly concerned with applications for deriving relativel~ larger amounts of power from wave energy.
SUMMARY OF THE INVENTION
Accordi~g to the present invention there is provided a device for extr-cting energg from uaves on a liquid upon which the device is adapted to float, comprising (a) a plurality of chambers, each chamber baving, (i) port means for flow of the liquid therethrough into and out of the chamber so as to cause a column of liquid to oscillate in the chamber fro~
the action of the waves;
~li) inlet port means for the flow of a working gas into the chamber; and (iii) outlet port means for the discharge fro~ the cha~ber of ~orking gas pressurised b~ the 06ciL-lations of said column of liquid, the chambers '' ".

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1065738 ;-being connected ln series relationship so that pressurised working gas tlscharged through the outlet port means of one chamber enters an ad~aceot chamber along the serles through the lnlet port ~eans thereof, and the lnlet port `~--means of the first chamber providing an lnlet -for the worklng gas into the series of chambers, ~ -and ~b) mechanlcal means for extractlng energy from the pressurised working gas and to which the pressurl~ed ` ~
working gas is dlscharget through the outlet port ~ans ~ ~-of the last chamber in the ~eries.
Some of the chambers ma~ be arran8ed in series relation-Jhip and so~e in parallel relationship, the Jeries and ;`
parallel arran8ements being adapted for connection together.
The device may be sdapted to operate as a generator uging alr as the working gas, and Jeawater as the liquid fro~ which wave energ~ is to be extracted, and the mechanical o ans may cooprise a turbine means adapted to drive an electric gen-rator _ n8. Alternativoly~ the device may be adapted to functlon a~ a breakwater, the mechanical means comprising an oriflce.
BRIEF EXPLANATION OF THE DRAWIJGS
The in~ention will now be particularl~ described by ;;
wa~ of ex y le only and with reference to the accompan~ing drawingJ, ln ~hichs-Flgure 1 shows in sectional elevation a diagra~atic repr-seDc-elon ol a d-~lce In ehe frr ol ,

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1065738 :
generstor structure having a parallel arran8ement of chambers allgnet perpendicular to the dlrection of the incoming waves;
Figure la shows a dlagrammatlc sectlonal representation on the line I-I in Pigure l; ~; ` i-Flgure 2 shows a generator structure similar to that of Figure l;
Figure 3 shows in sectlonal elevation a dlagra _ tlc representation of a generator structure having a serles arrangement of chambers perpendlcular to the inconing waves;
Figure 3a shows a dlagrammatlc sectional representatlon about the line III-III ln Figure 3; and Figure 4 shows a part-sectional vlew in the dlrectlon of arrow 'D' in Figure 3.
In the abo~e-mentloned Flgures, llke p-rts have l~ke ;~-numerals.
DETAILED DESCRlPTION OF THE INVENTION ;~
Referring now to Flgures 1 and la, the floating generator structure sho~n i8 lntended for derlvlng power from sea waves, ~ -nd comprlses a plurallty of chambers 1 for a working g-s (e.g.
lr) defined fore and aft with respect to the direction of the inco~lng waves a8 sho~n by the arrow ~A~ ln Flgure 1 by a generally trlangular-shaped buoyanc~ tank 2 and a generally rectangular-shaped buoyancy tank 3, both of whlch have a rounded lower edge and extend for the entire length of the generator structure to support the structure on the surface of the sea.
The top of the chamber 1 is deflned b~ a roof 5, and an _ 4 -outer casing 7 spaced from the roof S and the aft ;~-buoyancy tank 3 defines therebetween a common plenum duct ô whlch extends for the entire length of the generator structure. The lower ent 9 of the duct 8 extends below the sea level and is left open so as to provide an inlet for seawater which closes the lower end 9. -An outlet non-return valve 12 in the roof 5 allows ~-~
air to be discharged therethrough from the chamber 1 into the plenum duct 8. An inlet duct 13 of tubular form extends from the aft portion of the casing 7 to the roof 5 to provlde an lnle~ for alr from outside the caslng 7 into the chamber 1~ a non-return valve 14 in the inlet duct 13 ~-inhibiting the reverse flow of air from the chamber 1, and a hood 15 protecting the end of the inlet duct 13 at the caslng 7 fron sea spray.
The side~ of the chambers 1 are deflned by slde walls 16 and end walls 19 as shown ln Figure la. A mechanical means in the form of an air turbine 17 is coupled to an electric generator (not ~hown) and is posltioned in a duct 18 extending upwardly from an orifice 10 in the casing 7 80 as to be fed bg air contained in the plenum duct 8 to drive the electric 8enerator.
In operation, the level of seawater in each chamber 1 oscillates with the motion of the generator structure and that of the seawaves and is shown in Figure 1 st its mean , lowest level~ the mean upper level being shown by the broken line x-x. The oscillaeing seawater therefore acts in the manner of a piston member in the chamber 1~ causing an ,~ ,, ,, .. - . . . . - : .

~06S738 indraught of air through the inlet duct 13 into the chamber 1 as the level of seawater falls, and discharge of air through the outlet valve 12 into the common plenum duct 8, as the level rises, where the air is collectively conducted to the turbine 17. The pressurized air in the plenum duct 8 acts on the surface of the seawater at the -lower end 9 depressing the level of seaw~ter and thereby provides a restoring force from the seawater in the lower end 9 which pressurizes the air in the plenum duct 8 to ~mooth out and reduce pressure fluctuations in the air therein.
It will be appreciated that there is a greater volume . , -- . . .
of air available to operate the turbine 17 continuously than the possibly more intermittent use of the turbine in the device described in British Patent Specification -No. 1,014,196. Although the generator structure of Figures 1 ant la has been described in relation to the use of a ~`
single turbine 17~ everal turbines 17 may be installed and fod from a single plenum duct 8.
As n alternJtive to a generator structure having the air in the plenum duct 8 pressurized by seawater at the `~
lower end 9 of the plenum duct 8~ an alternati~e arran8enent may be used, for example, as shown in Figure 2 to which reference i8 now mate.
The gener-tor structure shown in section in Figure 2 is similar to that shown in Figure 1 and la except that the plenun duct 8 nc~ only extends above the roof and not behind the aft buoyanc~ tank 3. The air in the plenum duct 8 i5 1065738 ~::
;, - .
pressurlzed by a close-flttlng weighted cap 20 slidably ~ -disposed in a relatively large diameter duct 21 extenting -~
upwardly from the casing 7, an 'O~ ring seal 22 in an annular groove 23 extending around the cap 20 preventing the egress of air from the plenum duct 8. In operation ~-the cap 20 pro~ides a constant pressurizing force on the air in the plenum duct 8, so that the turbine 17 can be operated at a substantially constant head by the pressurised air in the plenum duct 8. If desired the pressure exerted by the cap 20 may be supplemented by resillent means (not shown)-As an alternative to the parallel arrangements ~hown in Figures 1, la and 2, the chambers 1 may be arranged in a linear series relationship as shown in Flgure 3 to which reference i- now made.
In Figure 3, a floating generator structure ha~ing a plurality of chambers 1 - ln 1- shown~ chamber la at one end of the structure ha~ing non-return inlet val~e 14 for the lndraught of air fro~ the at sphere~ and chamber ln at the other end having an upwardly extending duct 18 within which n air turblne 17 is disposed so as to drive an electric generator (noe shown). me chambers la - ln are separated from each other b~ slde walls 16 and plenum chJmbers 40a -40n whlch h ve non-return lnlet ~alves 42a-42n and non~
return outlet ~alves 43b - 43n to allow air to flow there-through the structure in serles rel~tionship from chamber la through to chamber ln. Each plenum chamber 40a - 40n connects rearwardly with a plenum duct 50 which itself extend~ rear-wardly to dip below the sea le~el so as to maintain a pressure on the air therein and also extend~ along the length of the structure to connect with the turbine duct 18 as shown ln Pigures 3a and 4 to which reference may be made. Shut-off valves 51 are disposet along the plenum duct 50 at the medlan position with respect to each chamber lb - ln. In other respects the structure shown in Figure 3 is similar to that shown in Figure 1 in that it is provided with fore and aft buoyancy tank~ 2 and 3.
In operation with shut-off -lves 51 closed and the lncomlng waves ln the dlrectlon of arrow "B" in Figure 3a, the level of seawater ln the chambers la - ln oscillates -with the motion of the generator structure ant that of the seawa-es, and is shown ln Pigure 3 at its mean le~el ln ~ -each chamber la - ln. As the seawater level falls, there ls an lndraught of air into chamber la through inlet valve 14. As the seawater level rlses, air is discharget unter pressure fro~ chamber la through inlet valve 42a into the plenum chamber 40a and that portion of plenum duct 50 between ;
closed shut-off valves 51 to whlch sald plenum chamber 40a is connected. ~hen the seawater level falls again, causing a fresh lndraught of air into chamber la, the pressurized ~ ;
alr in plenum duct 40a flows into chamber lb through outlet valve 43b, its pressurized state tepressing the mean seawater level in chamber lb below that in chamber la. The sequence ~ -of the collectively conducted flow of air from one chamber to another vi- a plenum tuct 40a - 40n continues along the series connectet chambers la _ ln with lncrease ln alr pressure ':

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lQ65738 along the series, untll at chamber ln the pressurlzet alr ls discharged lnto pleDum chamber 40n ant then lnto plenum tuct 50 and through the turblne 17 at a hlgher air pressure than can be achle~et by chambers connected in parallel.
The series arrangement shown ln Flgure 3 ls of partlcular -beneflt when the lnconing wa~e power falls to a level whlch . i .
would requlre the alr turbine 17 used in the parallel ~-arrangement shown in Figures 1 and and la to work outslte its efficient working range. The series arrangement may be co m ertet to a parallel arrangement similar to that described in relation to Figures 1 ant la by opening val~e~ 51 and closing val~es 43b - 43n using a switchlng means (not shoun).
With such a series/parallel arrangement, the parallel arrangement of chambers la - ln may be uset at hi8h inco~ing wavepower le els but switchet bg theswitching ~eans to a series arraDgement of chs~bers la - ln at low incoming wavepower ~ -levels. Combinations of part-series and part-parallel flo~
arrangements through the structure y also be arranged bg sult-ble selectlon of thoJe ~al~es 51 snd 43b to 43n to be op-Ded or closed by the switchlng means.
Although the in~ention has been described in relation ~-to the use of single air turbine, several turbines may be used depending on the quantity and pressure of the air discharged by the ~tructure. Alternati~e working gases may be u-ed~ for example~ ~here the g-s is to be cont-ined in closed circuit system, exhaust gas fro~ the turbine bein8 contucted to the inlet ducts to the chambers.
Alternative shapes for the buoyancy tanks 2 nd 3 may be .
used to suit particular applications.
The structures shown ln Figures 1 to 4 may be made~
for example, from metal or of a reinforced concrete construc-tlon, e.g. ferro-concrete or glass flbre relnforced concrete.
The forward buoyancy tank 2 shown ln Figures 1, 2, 3a ~-and 4, has been deslgned so that its forward face, upon - -which the incoming waves are incident, slopes downwardly and outwardly away from the freeboard of the floating generator structure in a direction towards the incoming waves, since it has been found that such an inclination of the forward face reduces the heave forces acting on the structure.
It will be appreciated that devices incorporating the -`
invention will usually be located with moorlng means (not shown). ~
Although the invention has been described as deriving ' --electrical ehergy from wave power~ the alr turblne 17 may be arranged to operate a mechanical device, for example a pump to derlve hydraulic or pneumatic power from wave power, or ~ ~;
nay be replaced by ~ome other alternatlve mechanical means such as a reciprocating air engine for deriving power from --the pressurized working gas. -~
Alternatively the device may be adapted to operate as a breakwater, by dispensing with the turbine 17 and ., .
eurbine duct 18 of Figures 1 to 4 and selecting the dimensions of the orifices 10 so as to maximise the energy lost b~ the gas ln flowing therethrough~ thereby dlsslpating some of the energy of the sea waves. For example, in a breakwater having parallel connected chambers 1~ a ratio of .; : - - . -. -: :
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'.'. . ' - ~ : - '"':', ." -, . . :' ' ~; ' , , area of orifice `1 sum of croSs-sectional of between 107 to 200 is tesirable.
areas of the chambers ; :

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Claims (6)

The embodiments 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 upon which the device is adapted to float, comprising a) a plurality of chambers, each chamber having (i) port means for flow of the liquid therethrough into and out of the chamber so as to cause a column of liquid to oscillate in the chamber from the action of the waves;
(ii) inlet port means for the flow of a working gas into the chamber, and (iii) outlet port means for the discharge from the chamber of working gas pressurised by the oscillations of said column of liquid, the chambers being connected in series relationship so that pressurised working gas is discharged through the outlet port means of one chamber enters an adjacent chamber along the series through the inlet port means thereof, and the inlet port means of the first chamber providing an inlet for the working gas into the series of chambers, and b) mechanical means for extracting energy from the pressurised working gas and to which the pressurised working gas is discharged through the outlet port means of the last chamber in the series.

2. A device as claimed in Claim 1 and having a forward face which is arranged to be incident to incoming waves, wherein the forward face slopes downwardly and out-wardly away from the freeboard of the device in a direction towards said incoming waves to reduce heave forces on the device.

3. A device as claimed in Claim 1, wherein a forward buoyancy tank defines one wall of each chamber, an aft bouyancy tank defines another wall of each chamber, and the for-ward and aft buoyancy tanks both have rounded lower edges.

4. A device as claimed in Claim 1 wherein the mechanical means comprises an air turbine.

5. A device as claimed in Claim 1 wherein the mechanical means comprises an orifice means selected so that the loss of energy of the pressurised working gas in flowing through the orifice means dissipates some of the energy of the waves, whereby the device may be operated as a breakwater.

6. A device as claimed in Claim 1 wherein the device is fabricated of ferro-concrete or glass fibre reinforced concrete.