WO2009088311A2

WO2009088311A2 - Device for wave energy extraction

Info

Publication number: WO2009088311A2
Application number: PCT/PT2009/000003
Authority: WO
Inventors: Marc David Hadden; Paulo Alexandre Pelote Da Silva Justino; Nuno Miguel Freitas Ferreira; José Carlos DA COSTA AMADOR; Tiago António NUNES DA SILVA MORAIS
Original assignee: MARTIFER ENERGIA EQUIPAMENTOS PARA ENERGIA SA
Current assignee: MARTIFER ENERGIA EQUIPAMENTOS PARA ENERGIA SA
Priority date: 2008-01-10
Filing date: 2009-01-09
Publication date: 2009-07-16
Anticipated expiration: 2010-07-10
Also published as: PT103926A; PT103926B; WO2009088311A3

Abstract

This invention relates to a device intended for harnessing the offshore wave energy by means of the relative spinning motion of two articulated bodies (1) and (2). It is basically characterized by said bodies (1) and (2) being partially emersed, each of them being comprised of one arm (Ia, 2b) and of a partially emersed element (Ib, 2b). One of the articulated bodies (1, 2) also has a cylindrical central frame (3) around which the rotation of one of the articulated bodies (1, 2) in relation to the other allows the extraction of energy from the sea waves.

Description

DESCRIPTION

"DEVICE FOR WAVE ENERGY EXTRACTION"

Scope of the Invention

Fossil fuels are currently the most used energy source worldwide. Since they are a depletable energy source, it is imperative to discover new resources of energy.

The international financial crisis of 1970/73 led the countries of the OPEC (Organization of Petroleum Exporting Countries) to raise the posted prices of oil, thus causing inflation. The world financial crisis, in addition to the political crisis, gave origin to an increase up to unexpected levels in natural gas and oil prices. In 1979/1980, the world saw once more a major oil shock and the oil prices went up again in circumstances which were very similar to the ones of the year 1973.

Today, we are facing a new oil crisis and, as happened in all the previous ones and whenever we go through an oil crisis, the search for alternative energy sources gains a growing dimension and relevance. If we add this to the current environmental concerns, the renewable energy sources appear as a vital and inevitable alternative, with a strong demand for technical solutions of energy conversion mechanisms based on these sources of energy.

Previous art

One of the renewable energy sources that can be found in the planet Earth is the wave energy and the harnessing of this source has been studied for many years. Several ideas have been proposed and assessed, some of them having resulted in pilot systems. The systems with the most advanced stage of development and which have already been tested in offshore real life situations are the Pelamis (US6476511B1) , the AWS (Archimedes Wave Swing) (W099/11926) , the PowerBuoy from Ocean Power Technologies (WO2005/089379A3) , and the WaveDragon .

Pelamis technology is a semi -submerged structure composed of cylindrical horizontal sections linked by hinged joints and arranged depending on the direction of the incidence of waves. The wave-induced motion of these joints activates the hydraulic rams which will pump high- pressure oil into hydraulic motors. These hydraulic motors drive electrical generators, and the electricity produced by all joints is transported via a single umbilical cable to a connection point on the sea bed. (www. oceanpd. com) . AWS is a point absorber cylindrical device which is completely submerged, with a hollow upper body (float) vertically oscillating over a fixed base which is also hollow. Both bodies are filled with air under pressure in such a way that, in the absence of waves, the pressure of the inner air makes an ascending force to balance the float's weight and the strength resulting from the hydrostatic pressure produced by the outer water. During a wave's passage, the external pressure oscillates around the hydrostatic pressure, thus causing the vertical motion of the float over the base, in a process wherein the inner air operates as an air spring producing a vertical restitution force . (www. awsocean . com)

The PowerBuoy consists of a submerged buoy which is very close to the water surface, having a cylindrical structure designed to harness the wave-induced motion. Said buoy is fixed to the sea bed where the electrical generator is installed. (www, oceanpowertechnologies . com)

The WaveDragon is a floating device aimed at an offshore application. Its operating principle is based on the accumulation of water in a reservoir which is elevated in relation to the average level of the free surface of sea. The accumulated water is returned to the sea by low head Kaplan hydraulic turbines which will drive electrical generators of common manufacturing. The accumulation of water on the elevated reservoir takes place by the wave - A -

climbing a ramp. In order to increase this climbing angle, two parabolic reflectors are provided in the upstream of the ramp with the aim of concentrating the incident wave. (www. wavedragon . net)

The applicants have also deposited the Portuguese patent application No. 103394 whose object relates to articulated floating structures, having on their joint area a system for the conversion of the existing mechanical swinging rotational movement into electrical power.

Object of the invention

One of the main problems encountered in the extraction of this renewable energy is the type of geometry to be adopted for the devices, their efficiency, yield, strength and economic feasibility. The object of this innovative invention is to eliminate these difficulties with the floating devices so as to recover the waves energy for offshore application.

The proposed device has been conceived to present a wideband of frequencies for which it has a high yield, to be economically feasible, and to be susceptible of optimization as appropriate in view of the characteristics of the site where it will be implemented. Brief description of the drawings

The following description is based on the enclosed drawings which, without representing a limitation, illustrate a preferred embodiment of the invention. In the drawings :

Figure 1 is a perspective view of the invention, which is comprised of the two bodies (1) and (2) articulated between them.

Figure 2 is a plan view of one of the components, the articulated body (1) of the proposed device, which is comprised of one arm (Ia) , a partially emersed element (Ib) and a cylindrical central frame (3) .

Figure 3 is a raised view of one of the components, the articulated body (1) of the proposed device, which is comprised of one arm (Ia) , a partially emersed element (Ib) and a cylindrical central frame (3) .

Figure 4 is a plan view of one of the components, the articulated body (2) of the proposed device, which is comprised of one arm (2a) and a partially emersed element (2b) .

Figure 5 is a raised view of one of the components, the articulated body (2) of the proposed device, which is comprised of one arm (2a) and a partially emersed element (2b) .

Figure 6 is a plan view of the integration mechanism of both components, the articulated bodies (1) and (2) of the proposed device. Figure 7 is a raised view of the integration mechanism of both components, the articulated bodies (1) and (2) of the proposed device.

Detailed description of the invention

One of the main problems encountered in the extraction of this renewable energy is the type of geometry to be adopted for the devices, their efficiency, yield, strength and economic feasibility.

Therefore, the teams committed to the development of systems aimed at extracting energy from the waves have to find an appropriate geometry for the device, so that it can present a high yield when converting the wave energy into mechanical energy without, however, sacrifying its strength and economic feasibility.

As observed in the figures, the device which is the object of the invention comprises two articulated bodies (1) and (2) having one same axis of rotation. Each part of the device has a geometry which is intended to maximize its yield in the process of converting the wave energy into mechanical energy, as well as to keep the device's structural integrity considering the sea conditions on the system's implementation site.

Both articulated bodies (1) and (2) are partially emersed. Each body is comprised of one arm (Ia) and (2a) and of a partially submerged element (Ib) and (2b) . The size of the arms (Ia) and (2a) , and well as of the partially submerged elements (Ib) and (2b) , is defined in such a way that it causes the device to present one or more resonance periods, i.e., wherein the system has for these periods the highest possible efficiency in terms of wave energy extraction. The choice of sizes as regards the arms (Ia) and (2a) and the elements (Ib) and (2b) will allow the resonance periods to be adjusted to the range of periods according to the wave climate on the implementation site.

The partially submerged elements (Ib) and (2b) exhibit a significant submerged volume so that the device's resonance periods are within the range of periods which is observed with reference to the incidence of waves on the system at the offshore implementation site. This means that the selected geometry for the submerged elements is designed to make the device to have different resonance periods within the considered range of periods of interest .

Since both articulated bodies have distinct characteristics in terms of inertia and hydrodynamic behaviour, their action in response to the sea agitation is also different.

One of the articulated bodies (1) or (2) has also a cylindrical central frame (3) wherein the electromechanical equipment is installed for the production of energy. The axis of rotation of the articulated bodies (1) and (2) is coincident with the longitudinal axis of the cylinder (3) . Each part of the device has a geometry which satisfies, so effectively as possible, the different technical specifications of the considered application.

In the embodiment of the invention described herein and shown in the drawings, the partially submerged elements (Ib) and (2b) existing at the ends of the device exhibit a length (the horizontally measured highest dimension) which is greater than the cross-dimension (the horizontally measured lowest dimension) of the arms (Ia) and (2a) . However, said elements (Ib) and (2b) can have the same or different lengths.

Accordingly, the two arms (Ia) and (2a) of the articulated bodies can also have the same or different lengths .

The operating principle is based upon the fact that the articulated bodies (1) and (2) have different rotations in terms of amplitudes and phases for the several periods of incident waves. It is the relative rotation of the articulated body (1) in relation to the articulated body (2) that will allow the energy to be extracted. By selecting the sizes and inertias of the articulated bodies (1) and (2) , it is possible to acknowledge that they present a rotation with distinct and phase-shifted amplitudes for a wideband of frequencies which should fit the sea conditions on the implementation site of the device .

Either one of the articulated bodies (1) or (2) can be the first to be approached by the incident waves.

One of the advantages brought by this device is that it is not an axisymmetrical system, thus existing some preferred directions for the incident waves in what concerns the device's orientation. It has been noted that, as regards the optimization of the electrical power generation, the incidence of the waves crest should preferably be parallel to the longitudinal axis (the greatest horizontal axis) of the partially submerged elements (Ib) and (2b) . As a result, the hydrodynamic behaviour of the device will also be optimized. The mooring system should allow the device to be oriented in such a manner that it will naturally take the above mentioned position .

The system for energy extraction - referred to as "Power Take Off" - located on the cylinder (3) uses the relative rotation of two articulated bodies (1) and (2) between them for the production of energy. The Power Take Off equipment to be adopted can be hydraulic, electrical, of the linear or rotary generator type, or other.

Claims

1. A device intended for harnessing the offshore wave energy by means of the relative spinning motion of two articulated bodies (1) and (2) , characterized in that said bodies (1) and (2) are partially emersed, each of them being comprised of one arm (Ia) and (2a) and of a partially emersed element (Ib) and (2b) , one of the articulated bodies (1) or (2) having also a cylindrical central frame (3) around which the rotation of one of the articulated bodies (1) or (2) in relation to the other allows the extraction of energy from the sea waves.

2. A device according to claim 1, characterized in that the cross-sectional shape of the two partially submerged elements (Ib) and (2b) located at the ends of the device, their length, as well as the length and the cross- dimension of the arms (Ia) and (2a) , are chosen in order to provide a device having one or more resonance periods within a range of periods which is adjustable to the selected site for offshore implementation.

3. A device according to claims 1 and 2, characterized in that the two articulated bodies (1) and (2) have phase-shifted rotations for the range of periods which is adjustable to the selected site for offshore implementation, i.e., the rotation phase of the articulated body (1) is different from the rotation phase of the articulated body (2), which allows the wave energy extraction to occur.

4. A device according to claims 1, 2 and 3, characterized in that the partially submerged elements (Ib) and (2b) existing at the ends of the device exhibit a length (the horizontally measured highest dimension) which is greater than the cross-dimension (the horizontally measured lowest dimension) of the arms (Ia) and (2a) .

5. A device according to the preceding claims, characterized in that the two arms (Ia) and (2a) of the articulated bodies (1) and (2) can have the same or different lengths.

6. A device according to the preceding claims, characterized in that the two partially submerged elements (Ib) and (2b) existing at the ends of the device can have the same or different lengths.

7. A device according to the preceding claims, characterized in that the cylindrical central frame (3) accommodates the electromechanical equipment aimed at generating the electrical power.

8. A device according to the preceding claims, characterized in that either one of the articulated bodies (1) and (2) can be the first to be approached by the incident waves, and in that the incidence of the waves crest should preferably be parallel to the longitudinal axis (the greatest horizontal axis) of the elements (Ib) and (2b) .