Tower vibration damper
The present invention relates to a tower damper adapted to be mounted in a wind turbine tower, the tower damper comprising a pendulum structure adapted to be suspended in the wind turbine tower; a plurality of springs arranged to dampen movements of the pendulum structure; a suspension arrangement for suspending the pendulum structure; and a chamber holding a damping liquid into which damping liquid the pendulum structure is at least partly immersed. The present invention further relates to a wind turbine comprising a tower damper.
1. A wind turbine tower having a tower damper, the tower damper comprising:
a pendulum structure suspended in the wind turbine tower, said pendulum structure comprising a cylindrically shaped pendulum body,
a plurality of springs arranged to dampen movements of the pendulum structure when suspended in the wind turbine tower,
a suspension arrangement for suspending the pendulum structure in the wind turbine tower such that the pendulum structure is allowed to displace from a neutral position for the pendulum structure, and
a chamber holding a damping liquid between an outer boundary, an inner boundary, and a bottom part that extends between the outer boundary and the inner boundary of the chamber, wherein the pendulum structure is at least partly immersed in the damping liquid.
2. The wind turbine tower according to claim 1 , wherein the number of springs are a multiple of three.
3. The wind turbine tower according claim 1 , wherein the outer boundary of the chamber forms part of the wind turbine tower wall.
4. The wind turbine tower according to claim 1 , wherein the springs are evenly distributed around a centre axis of the pendulum structure or around a centre axis of the wind turbine tower.
5. The wind turbine tower according to claim 1 , wherein the springs are arranged between the pendulum structure and the inner boundary of the chamber.
6. The wind turbine tower according to claim 1 , wherein the springs are arranged between the pendulum structure and the outer boundary of the chamber.
7. The wind turbine tower according to claim 1 , wherein the plurality of springs are arranged for urging the pendulum structure towards a neutral position for the pendulum structure.
8. The wind turbine tower according to claim 1 , wherein each of the plurality of springs comprises a leaf spring.
9. The wind turbine tower according to claim 8 , wherein each leaf spring at both of its two ends comprises leaf spring securing means for securing the leaf spring to the pendulum structure.
10. A wind turbine tower according to claim 9 , further comprising a contact arrangement for each of said plurality of leaf springs, wherein each of said contact arrangement is configured to provided operable contact between a leaf spring and an inner or outer boundary of the chamber at a position between the two ends of the leaf spring, wherein the contact arrangement comprises:
a contact member,
a guide configured for enabling vertical translation of the contact member, said vertical translation being induced by a displacement of the pendulum structure, and
a contact member spring arranged on each side of the contact member, said contact member spring being configured for, in concert, urging the contact member towards a neutral position for the contact member.
11. The wind turbine tower according to claim 10 , wherein each leaf spring securing means comprises:
a pair of rotatable rollers adapted to receive and clamp a leaf spring end, wherein the rollers are configured to flex in such a way that the leaf spring can move angularly in relation to the leaf spring securing means.
12. The wind turbine tower according to claim 10 , wherein the plurality of leaf springs form an end-to-end structure between the pendulum structure and the inner boundary of the chamber, and wherein a contact arrangement is attached to each leaf spring.
13. The wind turbine tower according to claim 1 , wherein each of the plurality of springs comprises a cantilever spring.
14. The wind turbine tower according to claim 13 , wherein each cantilever spring comprises a low-friction slide block arranged on a free end of the cantilever spring and wherein the slide block is configured for operable contact between the cantilever spring and the outer or inner boundary of the chamber.
15. The wind turbine tower according to claim 1 , wherein the suspension arrangement comprises tuning means configured for adjusting the natural frequency of the suspended pendulum structure.
16. The wind turbine tower according to claim 15 , wherein the suspension arrangement comprises a plurality of wires.
17. The wind turbine tower according to claim 15 , wherein the tuning means comprises, for each of said plurality of wires, a clamp secured to the tower at one end and to the wire at the other end, wherein the securing of the clamp is configured such that the clamp is movable along the longitudinal direction of the wire.
18. The wind turbine tower according to claim 1 , wherein the cylindrically shaped pendulum body of the pendulum structure is an annular ring.
19. The wind turbine tower according to claim 1 , wherein the outer boundary, inner boundary, and bottom part of the chamber form an annular trough.
20. The wind turbine tower according to claim 1 , wherein the tower damper further includes a plurality of buffer arrangements provided between the pendulum structure and each spring.