WAVE ENERGY CONVERTER COMPRISING PRESSURE AND SUCTION PIPES

This invention concerns This invention concerns a wave energy converter (WEC) to utilization of the wave energy in the oceans. This WEC can be used both near shore and off shore on deep waters. This WEC will typically be used to change wave energy into electrical energy. The WEC is of the type where the waves put an air current in motion (OWC type). As power take off (PTO) a traditional air turbine can be used or another kind of PTO. The WEC consist of rows of pipes or chambers that sticks into the water and are typically tilted some degrees. Through these, hereafter just mentioned pipes, is both the suck energy and the pressure energy exploited, over up to several wavelengths. A set of valves by each pipe rectifies the airflow that hereafter is lead to a PTO e.g. an air turbine. Seen from above the WEC is typically formed like a boomerang and is typically anchored in the tip end or in each of the two arms.

Technical level of attainment

There has in several years been worked intensively to develop a device to exploit the wave energy in the oceans. These devices can be categorized in 4 main categories, which are over topping devices, point absorbers, line absorbers or Oscillating Water Column devices (OWC devices).

OWC devices are known both as devices that are build up at the coastline typically in concrete direct on the rocks, and as devices that are off shore based ether floating or anchored to the seabed on columns or similar. The known offshore based OWC devices has typical used a Wells turbine that rotates the same direction regardless of the direction of the airflow. It is also known to rectify the airflow in this way an ordinary air turbine can be used. The known OWC devices typically exploit the energy in one wave at the time and the devices that is not anchored to the seabed will move slightly in tact with the wave motion. hi the literature devices with open chambers downwards is described, but they can not be made very light as they are not using the suck forces to hold the WEC down. They do also have tight-fitting chambers and do not obtain the favourable effect that is obtained when the chambers is separated and also not the effect that is obtained when the pipes are tilted. These devices do also not use the boomerang form, which make the WEC both wide and at the same time makes the WEC stretch over up to several wavelengths. The structural and economical benefits that is achieved when the channels for airflow and structural design is an integrated part is not known from these devices. In the literature devices with a V-shape is described, but these devices is anchored several places on the WEC, and because of that they don't get the effect that is achieved when the WEC only is anchored in the tip, that makes that the WEC automatically adjust towards the wave front.

The particular that is achieved according to the technical level of attainment

By this invention there has been procured a wave energy converter off the off shore based OWC type. This device exploits the wave energy in up to several wavelengths at the same time, where by a very uniform airflow is achieved. The WEC will lay very still under the influence of the waves, and can be made in a very light material as the suck forces help to hold the WEC down. Because the airflow channels are an integrated part of the structural design, a WEC with a very low material consumption is achieved.

The shape of the device is designed in a way that secure that the WEC automatically adjusts towards the wave front. The shape is also designed to secure that the loads on the WEC is minimized by having a appropriate shape of the pipes or chambers that sticks into the sea.

The means that is used to achieve this inventions special effect

This is achieved according to this invention, by a WEC of the art mentioned in the introduction, that exploits the pressure force and suck force over up to several wave lengths. At the same time the boomerang shape makes that the WEC adjust towards the wave front. The shape of the pipes or chambers secures that the loads on the WEC is minimized, and that the energy in the waves is exploited effectively.

By placing the big channels for airflow immediately above the pipes and valves it is achieved that the channels and structural part of the WEC is an integrated part. At a structural point of view this is very favourable according to strength, stiffness and material consumption. Hereby a very light construction with a low material consumption is achieved. The big channels also secures that big amounts of air can be moved with a very little pressure loss. By placing pontoons on the WEC it is secured that the WEC doesn't tilt according to horizontal.

Mode and operation of the WEC Waves that rise inside a pipe will give an airflow with a given over pressure according to the surrounding atmosphere pressure. In the same manner waves that falls inside a pipe will give an airflow with a given under pressure according to the surrounding atmosphere pressure. Rectifier valves makes the over pressure airflow is lead into the pressure channel, and that the under pressure airflow is lead into the suck channel. By having many pipes that stretches over up to several wavelengths it is secured that a very uniform airflow with a constant air pressure is achieved in both the pressure channel and suck channel. Between the pressure channel and the suck channel the PTO is placed e.g. an air turbine. The PTO can also be placed above the main channels. Hereby the same PTO could be feed from all the main channels. By using many pipes that stretches over up to several wavelengths it is secured that the sum of the vertical forces on the WEC is constant, hereby the WEC lays very still in the sea when it is influenced by the wave impact.

The shape of the pipes arid the tilt of the pipes makes that the impact of the waves is as minimal as possible and it also ensures that the wave energy is exploited effectively. This is among other things ensured in the way that the part of the wave that hit outside the pipes will slide off and continue to a possibly next row of pipes.

The WEC boomerang shape, where the WEC typically will be anchored in the tip, ensures that when the wave direction changes, then the one arm of the boomerang will be more parallel with the wave front than the other arm. The arm that is most parallel to the wave front will be exposed to a greater force than the arm that is more diagonally to the wave front. This heterogeneously force on the 2 arms will make that the WEC turns until both arms is exposed to the same force, which is when the WEC is laying parallel to the wave front. The WEC could also be made as one long arm that typically will be hold on in the mid of the arm. That what decide how deep the WEC sticks in the sea is the amount of air in the whole system, which in principle is a closed system. When there is a need to adjust how deep the WEC shall stick in the sea, there shall be taken some air out of the closed system, if there is a need for a increase in how deep the WEC sticks in the sea, or air shall be lead into the closed system, if there is a need to decrease how deep the WEC sticks in the sea. When air shall be lead out of the system a valve in the pressure channel is opened. When air shall be lead into the system a valve in the suck channel is opened. The air, that is lead in and out of the WEC, can be lead through a turbine to exploit the energy in this air. Pontoons are placed preferably on the lee side of the WEC where the waves is damped ensures that the WEC is laying horizontal and doesn't tilt. There will typically be placed one or more pontoons in both ends of the arms. By using more than one pontoon, placed in a certain mutual distance, in each end of the arms there will be compensated for the buoyancy difference there is at the wave crest and wave trough. It will also smoothen out the loads on the WEC from the pontoons.

Flow variations in the pressure flow and suck flow will equalize it selves because of the way the WEC is designed. An extra buffer function, e.g. an accumulating tank, could be made on the WEC if some extra equalizing of the flow variations is wanted. Differences in the flow on the pressure side or suck side can on the suck side can also be equalized by letting a in or out from the surrounding atmosphere. This could be done through a turbine to exploit the energy in this air

The design of the pipes and the way they are placed in the water does that during one wave period, when there is only looked at the forces in the horizontal plan, the pipes will in the first part of the wave period be exposed to forward forces and en the next part of the wave period be exposed to backwards forces. The sum of all these forces when there are many pipes will be a little backwards force. The total backwards force will be big enough to turn the WEC so that it is always parallel to the wave front.

Brief description of the drawings

This invention is explained further in the following referring to the drawings where: Fig. 1 shows a simple sketch of the principle of how the suck and pressure is used at the same time.

Fig. 2 shows how the WEC adjust it selves towards the wave front. Fig. 3 shows a main drawing of the WEC in perspective and the WEC seen in different sectional views.

Fig. 3b shows the WEC seen from above without the top and showing the valves and channels.

Fig. 3c shows the WEC in perspective seen from the side at a wave crest so that the pipes, valves and the placement of the channels can be seen

Fig. 3d shows the WEC in perspective seen from the side at a wave top so that the pipes, valves and the placement of the channels can be seen.

Fig. 4 shows how waves that doesn't rise inside the pipes glides off the first row of pipes. Fig. 5 shows an example on the suck and pressure works and an example on where the valves that regulates the depth adjustment is placed

Fig. 5b shows how there are suck forces and pressure forces across the whole length of the WEC.

Fig. 5c shows an example on how the PTO e.g. a turbine is placed.

Fig. 5d shows an example on how the valves that can reduce and increase the amount of air in the system are placed.

Fig. 6 shows an example on how the pontoons are placed.

Fig. 7 shows how the air pressure is boosted and how the energy in the wave that rises between the pipes is exploited.

Fig. 8 shows how the horizontal forces on the WEC, the forward forces and backward forces, almost neutralize each other.

Fig. 9 shows how the automatic build in gravity buffer equalizes the disharmony in the airflow that occurs, when the number of wave crests and wave troughs that the WEC is exposed to, are unequal.

Detailed description of the drawings

Fig. 1, which is a principle sketch, shows how the suck and pressure effect is used at the same time. In the chambers where the waves are going upwards an air pressure is created. This is marked with an up going arrow. In the chambers where waves are going down an air suck is created. This is marked with a down going arrow. Rectifier valves ensure that the air pressure that is created from the up going waves is lead to the main air pressure channel. Other rectifier valves ensures that the air suck created from the down going movement from the waves is lead to the main air suck channel

Between the main channels the PTO unit is placed, on the drawing this is shown as an air turbine. hi the chambers with pressure there is an up going force on the WEC. In the chambers with suck there is a down going force on the WEC. The sum of these up going forces and down going forces is almost zero all the time when the WEC stretches over up to several wavelengths. The suck force is that what ensures that the WEC doesn't flow up on the crest of the waves. Fig. 2 shows how the WEC adjust it selves towards the wave front. Fig. 2a show a situation where the WEC is regulated in. This is when both arms are exposed to equal many meters of wave front. In this situation Fl and F2 is equal. Hereby the moment around the anchoring point is zero and the WEC stays in its position towards the wave front. Fig. 2b shows a situation where the direction of the wave front has changed. Arm 1 is now exposed to more meters of wave front than arm 2, which causes that Fl is bigger than F2. Hereby an anti clockwise moment (Mo) is created around the anchoring point. This causes that the WEC starts to turn around the anchoring point. This continues until both arms again are exposed to equal meters of wave front, and there again is an in-regulated situation as in fig. 2a. Fig. 2c shows an example where the WEC is anchored in two points, which is app. in the middle of both arms.

Fig. 3 shows a main drawing in perspective of the WEC equipped with four turbine units and with different details shown in sectional views. In the example in fig. 3b the WEC is shown with 2 rows of pipes where the pipes in row 2 is placed immediate behind the pipes in row 1. In this principle example there are 9 pipes in each row.

Fig. 3b shows the WEC seen from above without the top. Hereby it is possible to see the 4 main channels in each arm, two with pressure and two with suck. The WEC can be made with more or less main channels, hi the drawing the WEC stretches over two wavelengths.

Fig. 3 c shows a vertical sectional view it is seen how the pipes, valves and main channels are connected. The wave is moving towards the wave trough. Inside the pipe the wave is standing a little bit higher as the suck force holds it back. The suck valves are open and air is sucked from main channel 1 and 3 down into pipe 1 and 2.

Fig. 3d shows a vertical sectional view where it is shown how the pipes, valves and main channels are connected. The wave is on the way to the wave crest. Inside the pipe

the wave is standing a little bit lower because the air pressure is holding it down. The air pressure valves are open air is pushed into the main channel 2 and 4 from pipe 3 and 4. The airflow is lead through a PTO unit, typically an air turbine, from main channel 2 and 4, which are pressure channels to main channel 1 and 3 which are suck channels. The PTO unit converts the energy from the flow and pressure to typically mechanical energy, which hereafter typically is converted into electrical energy.

Fig. 4 shows, in this example where it is pipes that are used, the mutual distance between the pipes. The pipes in the two rows are here placed immediately after each other with a suitable mutual distance. When the pipes are placed in a suitable mutual distance has the part of the wave that rises up in front of the pipes a slide off and pass on to the next rows of pipes. The shape and tilt of the pipes helps to minimize the influence from the wave impact that the waves that rises outside the pipes, is putting to the pipes.

Fig 5 shows an example on how to adjust the depth of the WEC, and how the WEC is affected by down going forces and up going forces.

Fig. 5b shows how pipe 1,4 and 7 is sucking air out of main channel 1, and how pipe 2, 3, 5 and 6 are pressing air up into main channel 2. In this example an air turbine is placed between main channel 1 and main channel 2. When the WEC stretches over up to more than one wavelength a more or less constant pressure are created in the main channels. That what decide how deep the WEC sticks in the sea is the amount of air in the whole system, which in principle is a closed system. When there is a need to adjust the depth of the WEC in the sea there has to be lead air out of the closed system, if there is a need to increase the depth of the WEC. If there is a need to decrease the depth of the WEC, air has to be lead into the closed system. In this example the two suck channels are put together to one suck channel. When there is a need to lead air out of the system the valves in the pressure channels named 1 and 3 see fig. 5d, will be opened. When air has to be lead into the system, the valve in the suck channel named 2 will be opened. Turbines can be placed by the valves so that the energy in the air that is lead in and out of the system can be exploited.

The air moves from the pressure pipes fig. 5c up into the pressure channels named 1 and 3. The air is hereafter lead through the turbines (PTO) and over into the suck channel named 2. The same suck channel named 2 is seen in fig. 5d where the air continues down into the suck pipe, which downwards are bounded by the surface of the water. When the wave in fig. 5d reach the wave trough and starts to rise again this what was a sucking pipe now becomes a pressure pipe and the whole process repeats it selves.

In fig. 5c it is seen how the wave between the two pipes rises to a higher level than it would have done if the pipes haven't affected it. This gives a greater difference in the height between the wave inside the pipe and the wave outside the pipe. This gives an increased pressure and increased energy absorption.

In fig. 5d it is seen how the wave between the two pipes falls to a lower level than it would have fallen to if the pipes haven't affected it. This gives an increased difference in height between the wave inside the pipe and the wave outside. This gives an increased under pressure and increased energy absorption.

Fig. 6 shows an example on how pontoons can be placed on the WEC, here placed on the lee side of the WEC. The pontoons can also be placed in the centre of the WEC, this will give some other advantages such as a lower tendency to unequal twist. These pontoons give a little buoyancy and secure that the WEC doesn't tilt but stay in horizontal position. The purpose of the pontoons is not to make the WEC floating as the WEC floats because of the buoyancy from the pipes. Without these pontoons the WEC would be as stable as a seesaw.

Fig. 7 shows the pressure boosting effect that occurs when the pipes are placed in a certain mutual distance. The pressure boosting makes that the valves opens earlier than they would have done if this pressure boosting hasn't been there, and it also makes that the energy in the waves that rises between the pipes can be exploited.

The principle is that when the wave rises under the pipes the air pressure inside the pipes makes that it rises slower inside the pipe. The water that doesn't rise inside the pipe will rise outside the pipe. This will increase the pressure in the pipe as the height difference between the waves inside the pipe and outside is increased. This increased pressure is what makes that the energy in the wave between the pipes is exploited and it also makes that the valve opens earlier that it would have done without this increased pressure.

On the drawing the dotted line shows the contour of the wave if the two pipes hadn't affected it. But as the pipes has affected the wave and it can't rise, as much inside the pipes, it has to raise more outside the pipes. Fig. 7a shows a the pressure boosting effect with a rising wave and fig. 7b shows suck boosting effect with a falling wave.

Fig. 8 shows how the horizontal forces on the WEC, the forward forces and backward forces, almost neutralize each other, hi the drawing the WEC stretches over two wavelengths. In fig. 8a it is seen how sections of the WEC is exposed to forward forces and how other sections is exposed to backward forces. The total sum of all these forces is close to zero. The backward forces is a little bigger than the forward forces which make it possible for the WEC to adjust towards the wave front as described in fig. 2. hi fig. 8b it is seen how a wave gives a forward force on the WEC.

In fig. 8c it is seen how a falling wave gives a backward force on the WEC

Fig. 9 shows how the automatic build in gravity buffer equalizes disharmony in the airflow. As the air in this WEC flows in a closed system the airflow from rising waves

and the airflow from falling waves has to be equal. In practice the number of rising waves is not always equal to the number of falling waves. This WEC compensate for that by changing how high the WEC is laying in the sea according to the standard water line (SWL). When the WEC is exposed to more wave crests than wave troughs the WEC rises, where by some potential energy is build up. This potential energy is released again when the WEC is exposed to more wave troughs than wave crests.

In fig. 9a, which is a principle drawing with only 3 pipes to illustrate the principle, is seen a situation where the WEC is exposed to only one wave crest and because of that is laying very low in the sea. When the wave situation changes from a situation as in fig. 9a with few wave crests to a situation as in fig. 9b with more wave crests the WEC rises to a higher level. The level change is here named H. By this level change the airflow from the pressure pipes and the suck pipes has been equalized. The volume in fig. 9a, which is the sum of Vl, V2 and V3, is the same as the volume in fig. 9b, which is the sum ofV4, V5 and V6.

The air volume in the pipes in a normal working situation will always be constant as it is a closed system. It is only when it has to be adjusted how deep the WEC shall lay in the sea air is lead in or out of the system.

In a sewer storm situation where the WEC will be operated in surviving mode it can happen that wave troughs goes beneath some of the pipes. The flow of air will be stopped and the WEC will float high on the wave crests.