Wave energy converter with internal mass on spring oscillator

• US 20090085357A1
• Filed: 10/24/2008
• Published: 04/02/2009
• Est. Priority Date: 12/01/2005
• Status: Active Grant

• Current Assignee: Ocean Power Technologies, Inc.
• Original Assignee: Ocean Power Technologies, Inc.
• Inventors: Stewart, David B.
• Granted Patent: US 8,067,849 B2
• Time in Patent Office: Days
• US Class Current: 290/53
• CPC Class Codes: F03B 13/16 using the relative movement between a wave-operated member, i.e. a "wom" and another member, i.e. a reaction member or "rem"
• CPC Class Codes: F03B 13/20 wherein both members , i.e. wom and rem are movable relative to the sea bed or shore
• CPC Class Codes: F05B 2250/44 one element moving inside another one, e.g. wave-operated member (wom) moving inside another member (rem)
• CPC Class Codes: Y02E 10/30 Energy from the sea, e.g. using wave energy or salinity gradient

Abstract

A wave energy converter (WEC) system includes a shell containing an internal oscillator comprised of a reaction mass suspended from the shell by an elastic spring in parallel with a constant force spring. The constant force spring provides a relatively constant force (Fc) to counterbalance the static weight of the reaction mass and reduce the extension “static” length of the elastic spring while the elastic spring exerts a force (F_es) on the reaction mass that is proportional to the displacement, x, of the elastic spring. A power take-off (PTO) device, located within the shell, coupled between the shell and the internal oscillator converts their relative motion into electrical energy.

Claims

1. A wave energy converter (WEC) system comprising:

a shell responsive to wave motion in a body of water;

an internal oscillator including a reaction mass and a spring mechanism contained within the shell;

the spring mechanism including a constant force spring connected between the reaction mass and the shell and an elastic spring also connected between the reaction mass and the shell, said internal oscillator mounted within the shell for moving out of phase relative to the shell, when the shell and the internal oscillator are placed in a body of water subject to wave conditions; and

a power take-off (PTO) device, located within the shell, coupled between the shell and the internal oscillator for converting their relative motion into electrical energy.

2. A wave energy converter (WEC) system as claimed in claim 1 wherein the constant force spring is selected to exert a relatively constant force (Fc) which is a function of the mass (m) of the reaction mass multiplied by the gravitation constant (g).

3. A wave energy converter (WEC) system as claimed in claim 2 wherein the force, Fc, exerted by the constant force spring is selected to be less than (m)×

(g) to keep the elastic spring under tension during an upstroke.

4. A wave energy converter (WEC) system as claimed in claim 2 wherein the constant force spring counterbalances the weight of the reaction mass to control the static extension length of the elastic spring and maintain the static extension length of the elastic spring at a predetermined value.

5. A wave energy converter (WEC) system as claimed in claim 1 wherein the constant force spring exerts a relatively constant force to counterbalance a selected amount of the weight of the reaction mass to control the extension length of the elastic spring under static conditions.

6. A wave energy converter (WEC) system as claimed in claim 5 wherein the elastic spring has a first end and a second end, wherein the first end is connected to the shell and wherein the elastic spring has a length Xn when no weight is attached to its second end;

and wherein the elastic spring tends to have an extension length of Xo, for a total length of Xn+Xo, when a given reaction mass is attached to the second end of the elastic spring; and

wherein the constant force spring is connected between the shell and the reaction mass to counterbalance the weight of the reaction mass and reduce the extension length of Xo.

7. A wave energy converter (WEC) system as claimed in claim 6 wherein the constant force spring is selected to reduce the extension length Xo to zero.

8. A wave energy converter (WEC) system as claimed in claim 2 wherein the reaction mass is suspended from the top of the shell by the two springs

9. A wave energy converter (WEC) system as claimed in claim 6 wherein the reaction mass moves up and down about Xo+Xn in response to the waves.

10. A wave energy converter (WEC) system as claimed in claim 6, wherein the still water extension of the elastic spring would tend to be equal to Xo, where x₀=(T_n/2π

)²·

g; and

T is the period of a predominant wavelength of an ocean wave and g is the gravitational constant; and

wherein the constant force spring is connected in parallel with the elastic spring to make Xo a preselected constant value.

11. A wave energy converter (WEC) system comprising:

a float responsive to wave motion in a body of water;

an internal oscillator including a reaction mass and a spring system contained within the float;

the spring system including a constant force spring and an elastic spring;

means connecting the constant force spring between the float and the reaction mass for exerting a relatively constant force (Fc) counterbalancing the weight of the reaction mass; and

means connecting the elastic spring between the shell and the reaction mass for exerting a force (F_es) on the reaction mass that is proportional to the displacement, x, of the elastic spring.

12. A wave energy converter (WEC) system as claimed in claim 11 further including a power take-off (PTO) device, located within the shell, coupled between the shell and the internal oscillator for converting their relative motion into electrical energy.

13. A WEC as claimed in claim 11, wherein the reaction mass and spring oscillator system is tuned to the wavelength of the predominant waves of the body of water resulting in the still-water extension spring length (x₀) of an elastic spring tending to be x₀=(T_n/2π

)²·

g;

where T is the period of the predominant waves and g is the gravitational constant; and

wherein the constant force spring is selected to reduce Xo.