TECHNICAL FIELD OF THE INVENTION

The present invention relates to a device for wave energy conversion.

More in detail, the present invention relates to a high efficiency wave energy conversion device for seas having moderate wave climates, such as, but not limited to, the Mediterranean Sea.

BACKGROUND ART

In the renewable energy sector, devices for converting wave energy into electricity are going through a phase of intense development, even in seas with moderate wave climate content, such as, but not limited to, the Mediterranean Sea.

Various types of wave energy converting devices are currently known, which use the wave motion to produce electricity.

A very common type of such devices - which can be defined an oscillating water column - comprises a platform, usually installed on the shore, which supports a plurality of column elements, internally hollow and partially immersed in water, the respective lower ends of which are in direct fluid connection with sea water.

The platform, with the relevant column elements, is installed in such a way that the free water surface is - on average - at a given desired distance from the upper ends of the same column elements.

The column elements comprise, inside their respective cavities and at the aforesaid upper ends, members - typically turbines, or the like - which have the function of converting the cyclic displacement of the air contained within the column elements - and caused, in fact, by the water motion generated by the waves - into the rotary motion of an axis or shaft, which in turn is used to generate electric power.

An example of such a device is disclosed, for example, in the international patent application WO 2014/023401.

One such device, or others of similar configuration and/or operating according to the same principle, are able to achieve remarkable performances in application situations where there is a sufficiently intense and forceful wave motion throughout the year, such as the shores or oceanic coastal areas.

Equally interesting performances cannot be achieved in closed sea basins of relatively modest size, in which there are no winds or currents such as to generate wave motion of sufficient intensity.

In fact, to obtain the generation of electrical power that can be used for the desired purposes - for example to meet a part of the energy requirements of a given location - the only possible measure could be to significantly increase the number of column elements installed on one same platform, since the dimensions of each column element are, as a rule, already optimised in relation to the type of member (usually, a turbine) used to convert the motion of air into the rotation of an axis.

This solution, however, requires spaces along the coasts of the sea basin concerned, which are often not available to the extent required; or, for various reasons, it is not possible to carry out actions or modifications such as to obtain available spaces along the coasts, as this could unacceptably damage the landscape integrity in the areas concerned.

In addition to this, one should also take into account that, as the extent of the platforms increases, and consequently that of the relevant column elements immersed in water, the dimensions and extent of the plant components necessary for wave mechanical energy conversion into readily usable electricity also increase: these requirements can often also not be met due to territorial/landscape constraints, or the like.

OBJECTS OF THE INVENTION

The aim of the present invention is to improve the state of the art in the field of wave energy conversion devices.

Within such technical aim, it is an object of the present invention to develop a wave energy conversion device which allows the aforementioned drawbacks to be overcome.

Another object of the present invention is to provide a wave energy conversion device which allows satisfactory results to be obtained in case of use in sea basins that are either enclosed and/or of relatively limited extent, and in which, therefore, the wave motion is not as intense and/or forceful as in the case of larger oceans.

A further object of the present invention is to provide a wave energy conversion device that is more versatile than conventional devices, in particular independently of certain environmental and/or landscape constraints, possibly along the coasts of the area concerned.

Another object of the present invention is to provide a wave energy conversion device which is constructively simple and inexpensive.

Another object of the present invention is to develop a wave energy conversion device easy to install regardless of the conditions of the shores or coasts of the sea basin.

This aim and these objects are achieved by the device for wave energy conversion according to the attached claim 1.

The device for wave energy conversion comprises at least one tubular body, defining, in use, an upper end, a lower end and an axial through cavity.

The tubular body is suitable for being immersed, at least partially, in a liquid mass characterised by a wave motion, i.e. typically - but not exclusively - a sea basin.

The device further comprises energy conversion means, located inside the through cavity, which exploit the oscillatory motion of the liquid column, present inside the through cavity of the tubular body.

For example, the energy conversion means may comprise a rotating member having a rotation axis.

According to one aspect of the invention, the tubular body is floating when immersed in the liquid mass, and is configured to oscillate in phase opposition with respect to the aforementioned liquid column present in the through cavity, when it is hit by the wave motion.

Furthermore, according to another interesting aspect of the invention, the tubular body is configured so that said tubular body and liquid column, when hit by the wave motion, are caused to start an oscillatory motion in counterphase according to their respective resonance frequencies. This generates a relative oscillatory motion between the tubular body and the liquid column: this, with respect to a static tubular body situation as per known installations, determines an increase in the speed of the fluid that hits the energy conversion means, with a consequent increase in the power transmissible to an electric generator.

In other words, it is possible to make a more advantageous exploitation of the energy carried by the wave motion of the basin in which the device is installed. Dependent claims refer to preferred and advantageous embodiments of the invention.

BRIEF DESCRIPTION OF DRAWINGS.

The features of the invention will be better understood by any man skilled in the art from the following description and accompanying drawings, provided by way of non-limiting example, wherein:

Figure 1 is a schematic, partially sectioned, perspective view of the device according to the invention immersed in a liquid mass characterised by a wave motion;

Figure 2 is a partially sectioned top view of the device;

Figure 3 is a diameter cross-section of the device;

Figure 4 is a detailed side view of the device rotating member;

Figure 5 is a top view of the same rotating member;

Figure 6 is a schematic representation of the mooring system to the sea bed of the device, in one embodiment of the invention;

Figure 7 is a schematic representation of the mooring system of the device, in another embodiment of the invention;

Figure 8 is a schematic representation of the mooring system of the device, in yet another embodiment of the invention.

EMBODIMENTS OF THE INVENTION.

With reference to the accompanying figure 1, a wave energy conversion device, according to the present invention, is indicated as a whole with 1.

The device comprises at least one tubular body 2. The tubular body 2 comprises an upper end 2a, and a lower end 2b.

The terms upper and lower, referred to the ends of the tubular body, are conventional and refer to the position that the tubular body 2 assumes during use, i.e. during operation of the device 1.

In the embodiment illustrated in the figures, the tubular body 2 has a cylindrical or substantially cylindrical symmetry.

However, this is a preferred but not exclusive shape, and therefore, this feature is not to be considered limiting.

The tubular body 2 further comprises an axial through cavity 3.

The symmetry axis A of the through cavity 3 coincides with the symmetry axis of the tubular body 2.

In certain embodiments, however, the symmetry axis A of the through cavity 3 might not coincide with the symmetry axis of the tubular body 2.

The through cavity 3 ends in an upper opening 4 and a lower opening 5, at the upper end 2a and the lower end 2b of the tubular body 2 - respectively.

The through cavity 3 has a cylindrical or substantially cylindrical internal surface. Additionally, the inner surface of the through cavity 3 is smooth, or substantially smooth, i.e. without any roughness, or cross-section changes.

The tubular body 2 is suitable for being immersed, at least partially, in a liquid mass M, characterised by a given wave motion.

Preferably, but not exclusively, the tubular body 2 is suitable for being immersed in a sea basin.

By way of non-limiting example, the technical advantages deriving from the features of the present invention can be maximally exploited in a relatively small sea basin, such as for example the Mediterranean Sea basin.

When the tubular body 2 is immersed in the liquid mass M, the lower opening 5 allows the entry of part of this liquid mass M into the through cavity 3.

The upper opening 4 allows the liquid column 7, contained in the through cavity 3, to be kept instead under atmospheric pressure conditions (in any case the liquid may still overflow inside the through cavity 3). The device 1 further comprises energy conversion means 6.

The energy conversion means 6 are located inside the through cavity 3; said energy conversion means 6 exploit the reciprocating motion of the liquid column 7 present inside the aforementioned through cavity 3.

The energy conversion means 6 comprise, in an embodiment of the invention of high practical interest, at least one rotating member 6.

In other embodiments of the invention, the energy conversion means 6 could be of another type.

For example, the energy conversion means 6 could comprise an elastomeric element capable of generating energy thanks to changes of its surface.

Various other types of energy conversion means 6 may be employed, without any limitation to the objects of the present invention.

The rotating member 6 comprises at least one rotation axis B.

The rotating member 6 is suitable for converting the reciprocating motion of the liquid column 7, present inside the through cavity 3, into the rotary motion of the aforesaid rotation axis B.

Such rotary motion of the rotation axis B - with given torque and speed characteristics - can then, in turn, be used to operate an electric generator.

In the embodiment of the invention illustrated in the figures, the rotation axis B of the rotating member 6 coincides with the symmetry axis A of the through cavity 3. In other embodiments of the invention, the rotation axis B of the rotating member 6 might not coincide with the symmetry axis A of the through cavity 3, and therefore could be parallel, or substantially parallel, to the latter.

At the portion of the through cavity 3 in which the energy conversion means 6 are installed, a reduction of the section such as to determine an increase in the speed of the fluid may be provided, according to the continuity principle.

According to one aspect of the invention, the tubular body 2 is floating when immersed in the liquid mass M.

Constructively, therefore - from the shape and materials point of view - the tubular body 2 is made to be floating in the liquid mass M, so as to identify a given waterline G: this waterline G is located at the upper end 2a of the tubular body 2.

In this way, the tubular body 2 is free to oscillate, along a vertical or substantially vertical direction, when it is hit by the wave motion of the liquid mass M.

More in detail, the tubular body 2 is free to oscillate in phase opposition with respect to the liquid column 7 contained in the through cavity 3.

This interesting aspect of the invention will be further explored hereinafter in the description.

According to another aspect of the invention, the rotating member 6 is fixed to the tubular body 2 substantially at the centre of gravity of the tubular body 2 itself, as shown in Figure 3.

Moreover - with reference to Figure 1 - the tubular body 2 is implemented and dimensioned in such a way that, in its use configuration, the rotating member 6 is always at a lower level with respect to the waterline G of the tubular body 2: in this way, the rotating member 6 is constantly immersed in the liquid column 7 contained in the through cavity 3.

The fixing of the rotating member 6 to the inner surface of the through cavity 3 can be carried out with means of different types.

Figure 3 shows, in an entirely schematic manner, the fixing means 8 of the rotating member 6 to the inner surface of the through cavity 3.

These fixing means 8 can be selected and sized in different ways, without any particular limitations.

According to a further aspect of the invention, the rotating member 6 of the device 1 comprises - or consists of - at least one self-rectifying type turbine.

In other words, the rotating member 6 comprises - or consists of - at least one turbine able to rotate always in the same direction, notwithstanding the direction of the fluid flow passing through it.

More in detail, as mentioned, the rotating member 6 is constantly immersed in the liquid column 7 contained in the through cavity 3.

In view of this, and according to an aspect of the invention which is not self- evident, the rotating member 6 comprises at least one Wells turbine. The rotating member 6 (i.e. the Wells turbine) is shown in detail in Figures 4,5, wherein (and in particular in Figure 4) it is possible to see the typical profile of the blade 6a of this type of turbine.

It should be noted, in this respect, that the Wells turbine was designed for use in air, or in any case in a gaseous fluid.

In a not self-evident way, the applicant provides instead for its use with a fluid in the liquid state (i.e. inside the liquid column 7 contained inside the through cavity 3).

As was mentioned, the liquid column 7 oscillates, with a certain frequency, inside the through cavity 3 of the tubular body, and therefore the rotating member 6 is hit by a water flow which periodically reverses its own direction of movement.

The rotating member 6, therefore, being self-rectifying, is able to always rotate in the same direction, notwithstanding the direction of movement of the liquid column 7.

In other embodiments of the invention, the rotating member 6 could comprise at least one self-rectifying type turbine different from the Wells turbine, chosen for example according to certain application or design requirements.

As was said, the rotating member 6 has its own rotation axis B which coincides with the symmetry axis A of the through cavity 3 of the tubular body 2.

In an embodiment of the invention not illustrated in the accompanying figures, the device 1 could comprise a plurality of rotating members 6, located inside the through cavity 3 of the tubular body 2.

For example, the various rotating members 6 could be coaxial with each other, and therefore be arranged, so to speak, in series with each other.

Or, the various rotating members 6 could be arranged, so to speak, in parallel, that is, side by side and with their respective rotation axes B parallel to one another.

The latter solution could be chosen in the case in which a tubular body 2 of relatively large dimensions (and therefore, also a large through cavity 3 of same) were available.

According to a further aspect of the invention, the tubular body 2 comprises, at its lower end 2b, a disc-shaped base 9.

The base 9 has a diameter greater than the outside diameter of the tubular body 2; the lower opening 5 of the through cavity 3 opens at the base 9.

The base 9 has the function of damping the oscillations of the tubular body 2 when it is hit by the wave motion, since the device 1 is dimensioned and optimised so as to operate with defined amplitude oscillations, which must not exceed a predetermined limit.

Moreover, the base 9 also has the task of offsetting the motion induced by the waves with respect to that of the tubular body 2, in order to obtain the amplification of the corresponding motion.

The tubular body 2 further comprises, at the upper end 2a, an enlarged top portion

10.

The enlarged top portion 10 has a substantially conical, or substantially frustoconical shape.

This conical or frustoconical shape has the function of facilitating the overflow from the device, so as to let in the fluid M during the down-stroke of the tubular body 2, increasing the pressure gradient and therefore, the relative speed.

More in detail (see for example figure 3) the enlarged top portion 10 may comprise two frustoconical portions 11, 12 with inverse taper, i.e. with their respective larger bases lying on the same plane P.

Approximately, this plane P also coincides, in use, with the free surface of the liquid mass M (i.e. it substantially defines the aforementioned waterline G of the tubular body 2).

According to another aspect of the invention, the device 1 comprises at least one mooring system, indicated globally with 13, of the tubular body 2 to the floor F of the liquid mass M (for example a seabed).

This mooring system 13 is preferably, but not exclusively, of the CALM (Catenary Anchor Leg Mooring) type.

The mooring system 13 is made using one or more spiral cables 14, much lighter than chains, which could be chosen as an alternative. The mooring system 13 has the function of limiting the horizontal shifting of the tubular body 2, but at the same time it must not constitute a too rigid constraint for the vertical shifting (oscillation) of the tubular body 2 itself, so as not to cause the unwanted damping of the tubular body 2 oscillations.

A CALM type system was therefore deemed suitable for these purposes.

Figures 6, 7, 8 show various possible embodiments of the device 1 according to the invention, which differ one from the other for the configuration of the mooring system 13 of the CALM type used.

More specifically, in the embodiment of Figure 6 a mooring system 13 is used, comprising at least two cables 14 (one on each side, i.e. fixed at connection points l5a, 15b diametrically opposed to the tubular body 2).

In this embodiment, the connection points l5a, 15b are provided at the base 9 of the tubular body, and are located at a certain connecting height C with respect to the seabed F.

In the embodiment of Figure 7, the mooring system 13 comprises at least four cables 14 (two on each side, i.e. fixed at respective connection points l5a, 15b diametrically opposed to the tubular body 2).

In this embodiment, the connection points l5a, 15b are provided at the base 9 and at the enlarged top portion 10 of the tubular body 2, and are located at respective connecting heights Cl,C2 with respect to the seabed F.

In the embodiment of Figure 8, the mooring system 13 comprises at least two cables 14 (one on each side, i.e. fixed at connection points l5a, 15b diametrically opposed to the tubular body 2).

In this other embodiment, the connection points l 5a, 15b are provided at the centre of gravity of the tubular body 2, respectively, at yet another different connecting height C3 to the seabed.

During practical operation, mooring systems 13 with different characteristics allow different oscillatory responses to be obtained from the tubular body 2, when hit by the wave motion.

For example, different mooring systems 13 allow more or less stable responses of the tubular body 2, more or less damped oscillations of same, etc., to be obtained. Suitable choices can therefore be made between:

the floating level K of the tubular body 2 with respect to the seabed F;

the distance D between the projection (on the seabed F) of the tubular body 2 and the mooring point J to the same seabed F;

the connecting height C, Cl, C2, C3 of the cables 14 to the tubular body 2, again with respect to the seabed F;

all this in order to obtain the desired dynamic behaviour of the tubular body 2 of the device 1.

As was said, the rotating member 6 must naturally be coupled to a generator.

For example, a permanent magnet generator can be used, although this choice is not restrictive.

The implementation of a supervision system is also provided which, based on the detected speed of the liquid column oscillation 7, is able to change some operating parameters so as to operate in the ideal working conditions for the rotating member 6.

In light of the above description, the operation of the device 1 is completely intuitive.

The wave motion that hits the tubular body 2 causes the liquid column 7 contained in the through cavity 3 to oscillate; the same wave motion also causes the tubular body 2 to oscillate, thanks to the fact that, according to the invention, it is floating. Moreover, this solution allows - with a wave motion having certain characteristics - simultaneous oscillations of both the liquid column 7 and the tubular body 2 to be obtained, according to the respective resonance frequencies.

In addition, and according to an important aspect of the present invention, the oscillations of the liquid column 7 and of the tubular body 2 - respectively, also take place in counterphase with each other.

This last aspect, in particular, allows a relative oscillatory motion to be obtained between the two dynamic components of the device - the tubular body 2 and the liquid column 7 - which then increases the speed of the fluid that hits the blades 6a of the rotating member 6, compared with a static condition typical of known devices, in which normally only the liquid column 7 oscillates.

Again with respect to known devices, the increase in the speed of the fluid - consequently to the onset of the aforesaid relative motion - determines an increase in power which - obviously after deducting the efficiency of the various components - can be transmitted to the electric power generator.

It should also be noted that another important difference with respect to known devices is that the self-rectifying rotating member 6 (i.e. in particular the Wells turbine) is constantly immersed in a liquid, and not in air, as is the case in devices of known types: this fact, obviously, positively influences the power that can be transmitted to the electric generator.

By way of non-limiting example only - numerical simulations of the dynamic behaviour of the device 1 have been carried out by assuming the wave motion conditions typical of a relatively small sea basin (for example the Mediterranean basin).

For example, a wave height between 0.25 and 4.5 metres, and a period between 3 seconds and 16 seconds, have been assumed.

In such simulations, the tubular body 2 has an outside diameter, for example, between 3 m and 10 m; preferably, the tubular body 2 can have an outside diameter of 5 m, or 6 m.

Moreover, the inside diameter of the tubular body 2 is comprised, for example, between 1.5 m and 3 m; preferably, the tubular body 2 can have an inside diameter of 2.2 m.

Finally, the overall length of the tubular body 2 is, for example, between 6 m and 12 m; preferably, the tubular body 2 can have a total length of 10 m, wherein the normally immersed portion is 9 m.

The tubular body 2 can be made - not exclusively - in a material chosen among steel, GRP (Glass Reinforced Plastic), or reinforced concrete, or in a combination/association/composition of two or more of the aforesaid materials. With regard to the construction parameters of the rotating member 6, in consideration of the relatively small dimensions of the device 1, numerical evaluations and simulations have been carried out assuming the use of Wells turbines comprising three, or four, or five blades.

The optimal choice, in particular from the point of view of maximizing the obtainable power, as well as from the point of view of system stability, turned out to be a Wells turbine with five blades.

Again by way of example, a clear resonance oscillatory behaviour was determined for a 6-second wave period.

It has thus been seen how the invention achieves the intended purposes.

The device according to the invention makes it possible to obtain from the wave motion an interesting energy efficiency result even in small basins of limited size, such as for example sea basins like the Mediterranean Sea.

The innovative characteristics of the device described above actually allow a dynamic behaviour to be obtained from the system - in particular the oscillation in resonance and counter-phase conditions of the two main components of same - highly advantageous in terms of mechanical power transferable to the rotating member, compared with other known installations.

The proposed solution is constructively simple and low cost, if compared to other known installations.

Again, when compared with known installations, the solution that is the object of the present invention - which includes a floating tubular body associated with a mooring system - is minimally invasive for the coastline and landscapes of the basin in which it is intended to be installed.

The present invention has been described according to preferred embodiments, but equivalent variants are still possible without departing from the scope of the appended claims.