WO1987003045A1

WO1987003045A1 - Apparatus for converting the energy in ocean waves into useful energy

Info

Publication number: WO1987003045A1
Application number: PCT/NO1986/000075
Authority: WO
Inventors: Knut BÖNKE
Original assignee: Boenke Knut
Priority date: 1985-11-14
Filing date: 1986-11-14
Publication date: 1987-05-21
Also published as: AU6624986A

Abstract

An apparatus for converting the mechanical energy in ocean waves into effective mechanical, thermal, chemical or electrical energy based on the use of an oscillating water column, the apparatus including an oscillatory chamber (4) for receiving the water mass of the water column, and the oscillatory chamber (4) having a longitudinal axis forming an angle (O/) with the vertical. This angle is chosen such that it satisfies the relation, formula O/ = Arc Cos AD((2pifr,O/)2.$(1,3)$O/)/g BD, wherein fr,O/ is the desired resonant frequency of the water column (5), $(1,3)$O/ is the length of the water column, and g is the acceleration of gravity.

Description

Apparatus for converting the energy in ocean waves into useful energy

¹ ₅ Then invention relates to an apparatus for con¬ verting the mechanical energy in ocean waves into effective mechanical, thermal, chemical or electrical energy based on the use of an oscillating water column, the apparatus including an oscillatory chamber for receiving the water

10 mass of the water column, the oscillatory chamber having a longitudinal axis forming an angle with the vertical.

Wave power plants based on the principle of an oscillating water column are currently being tested in Norway. Experimental works are taking place also in Canada,

15 Japan, China, Portugal and Great Britain.

In order to be able to extract energy from ocean waves by means of an oscillating water column, the natural frequency(ies) (resonant frequency(ies)) of the water column must be located close to the frequency of the waves from which energy is wanted to be extracted.

An oscillating water column in principle is half a U tube. The resonant frequency f of a U tube leg is determined from the length -& of the leg by the formula

1_ g

2T I

wherein g is the acceleration of gravity.

In other words, when a definite resonant frequency is wanted, the length of the U tube leg is given by

30

-*> I =

Dependent on the wave surroundings at the site

35 where a wave power plant is to be built, it may be topical to choose f between approximately 1/14 and 1/7 Hz. This in¬ volves lengths between 47 and 12 meters.

The power which it is possible to produce with an oscillating water column, is directly proportional to the so-called "wetting volume". This volume is equal to the water surface area in the U tube multiplied by the amplitude of oscillation of the water level. Since large parts of the ⁵ pure building costs (initial expenses) of wave power plants are directly proportional to the volume of the U tube leg, * the costs in conventional wave power plants will be very large when large power quantities are to be produced.

The object of the invention is to provide an ιo apparatus of the introductorily stated type which results in a substantial reduction of the building costs of wave power plants.

According to the invention, the above-mentioned object is achieved in that the angle of inclination φ of

¹5 the oscillatory chamber in relation to the vertical is chosen such that it satisfies the relation

(21Tf , ) ² ' l ψ - Arc cos ,

^*_o

wherein f J is the desired resonant frequency of the water column, JL is the length of the water column, and g is the acceleration of gravity. 25 The invention will be further described below with reference to the drawing, wherein

Fig. 1 shows a water column in a vertically positioned oscillatory chamber, and

Fig. 2 shows a water column in an oscillatory 30 chamber which is inclined in accordance with the invention.

In Fig. 1 there is shown an oscillatory-chamber forming U tube leg 1 which is vertically disposed in a body of water 2 and includes an oscillating water column 3.

Fig. 2 schematically shows an embodiment illu- 35 strating the solution according to the invention, and wherein the oscillatory-chamber forming U tube leg 4 which contains an oscillating water column 5, is inclined and forms an angle φ to the vertical. By means of known theory it may be shown that the resonant frequency now becomes

This emplies that, in order to achieve a desired resonant frequency, one may choose the length ± of the U tube leg 4 equal to

The tilting of the oscillatory chamber 5 also gives a larger horizontal water surface area A^ = A_n/cos φ , wherein A_n is the area perpendicularly to the axis of the U tube leg 4.

Thus, in order to achieve a desired horizontal

15 water surface area A, one may choose

^A0 ^{= A}φ ^{' cos} '

Thus, the total volume of the U tube leg, A_n ^• , can be

__ 2. reduced proportionally to cos φ , whereas the resonant fre¬ quency and the horizontal water surface area are maintained constant. This means that the energy production per unit

_2 of space of the U tube leg increases proportionally to cos φ

Since large parts of the pure building costs of wave power plants, as mentioned, are directly proportional to the volume of the U tube leg, it is seen that the costs can be reduced substantially when choosing the angle φ > 0.

In the illustrated fundamental embodiment, the U tube leg forms an oscillatory chamber having a recti-

30 linear center line forming said angle φ with the vertical. However, it may also be advantageous with embodiments wherein the center line of the oscillatory chamber is curved or forms a helix.

Claims

P a t e n t c l a i m s

1. An apparatus for converting the mechanical energy in ocean waves into effective mechanical, thermal, chemical or electrical energy based on the use of an oscilla¬ ting water column, the apparatus including an oscillatory chamber (4) for receiving the water mass of the water column (5), the oscillatory chamber (4) having a longitudinal axis forming an angle ( φ ) with the vertical, CHARACTERIZED IN that said angle ( φ ) is chosen such that it satisfies, the relation

ψ = Arc cos ^(2,rf_ , ^* * ,

wherein f , is the desired resonant frequency of the water column (5), _<, is the length of the water column, and g is the acceleration of gravity.

2. An apparatus according to claim 1, CHARACTERIZED IN that the center line of the oscillatory chamber (4) is a straight line forming said angle ( φ ) with the vertical.

3. An apparatus according to claim 1, CHARACTERIZED IN that the center line of the oscillatory chamber is curved.

4. An apparatus according to claim 1, CHARACTERIZED IN that the center line of the oscillatory chamber is a helix.