Patent Application
20160123303
The present invention relates to wind turbine towers and in particular to such towers having a damper for use when erecting the tower and prior to installing a nacelle on the top of the tower, but which may also be used for otherwise damping the top or other part of the tower. The invention further relates to a method for damping wind turbine towers.
In particular tall and slender towers, when being erected or after completed erection, have a tendency to oscillate with high amplitude. The high amplitude is believed to be caused by vortexes from the wind passing around the tower. Apparently this is worsened for high towers, which have a higher portion of the tower being exposed to the wind.
A number of various tower dampers have earlier been proposed, but none which may be removed for reuse in a next tower.
One aspect of the invention involves a wind turbine tower with an upper tower structure and a damper comprising,
As no liquid is present in the damper housing, there is no need for pumping equipment to remove the liquid. Also, any accidental spilling of liquid is avoid, which could be detrimental to the environment. Also, the design of the damper is less complex than known dampers. However, a main technical progress is that the damper does not need detailed tuning to the tower eigenfrequency. As long as the damper mass is sufficient, it may be used for damping a range of tower sizes and heights. Generally speaking it is a rule of thumb that 6-8 percent of the mass of a structure to be dampened. It is to be notices, that it is not the entire mass of a tower that counts, as one end is fixed to the ground, so a 125 meter high tower only has an effective oscillating mass of 50 tons has been tested to be sufficiently dampened by a damper mass of only 500 kg, which is only 1 percent of the effective tower mass.
By sufficiently dampened is mean amplitude about 0.05 to 0.1 metres, which has been dampened from an undampened amplitude between 0.5 metres to 1, metres, i.e. a dampening factor of about 10. Hence, a very saving of mass is obtained, which makes the damping much less troublesome and time-consuming.
The damper mass may include a ball-shaped damper element. Hereby some friction is obtained as well a high inertia. The ball-shaped element may include several pieces, which when put together a fixated by e.g. screws form the ball-shape.
The damper mass may include a plurality of mass element, which makes handling easy and less hazardous.
The damper elements of the wind turbine tower damper may disc-shaped and comprise a central aperture. As the damper should be able to dampen oscillations in any direction, a disc-shape of the damper elements is beneficial as the disc-shape is rotational-wise symmetric. Hence, it is suited for impact in any horizontal direction. Furthermore, by splitting the damper mass into disc-shaped elements, these may easily be handled and moved up into the nacelle from where they may be lowered by crane, including several disc-shaped elements together.
A central pin may be centrally fixated to a lowermost damper element and a stack of disc-shaped damper elements be arranged on the central pin. This enables easy stacking of disc-shaped damper elements to obtain a desired total damper mass for the wind turbine tower as more elements may be added or some removed.
A shock absorbing structure may comprise a single damping element as well as a plurality of individual shock absorbers.
The damping element may also be disc-shaped and have a larger diameter than the damper elements. In this way the shock absorber may be mounted along with the disc-shaped damper elements on the central pin. As the diameter is larger of the shock absorber than the damper elements, it is ensured that during damping action, the shock absorber will impact with the damper housing to absorb the impact and provide damping action.
In another aspect of the invention, the damper mass may comprise a cylindrical container located inside the damper housing, where the cylindrical container is filled to a predetermined amount with one or more elements selected from a group comprising sand, metal granulate, metal pellets and metal balls. This also enables easy way of providing damper elements to obtain a desired total damper mass for the wind turbine tower as more elements may be added or some removed. Also, additional damping may be obtained from internal friction between the damper elements during impact with the damper housing.
Also, a shock absorbing structure may be arranged along the interior surface of the damper housing, such that a stack of disc-shaped damper elements or the cylindrical container may impact with the shock absorbing structure. Hence, the damper housing may be used both for the damper structure with the disc-shaped damper elements as well as for the version with the cylindrical container filled with a predetermined amount with one or more elements selected from a group comprising sand, metal granulate, metal pellets and metal balls.
Moreover, in another aspect the shock absorbing structure may be arranged along an outside of the cylindrical container of the damper mass. It is most often easier to arrange items like the shock absorbing structure on the outside, rather than the inside of a cylindrical surface, as a shock absorbing structure is often elastic and may hence be made with a slightly less diameter the cylindrical interior housing to allow an elastic circumferential stress fit.
Instead of the tower just oscillating relatively the damper mass, which in effect may be regarded as the damper mass from side to side in the damper housing, the damper mass may be supported by at least three fixated roller ball wheels allowing the damper mass to move in any horizontal direction with low friction. The lower friction may cause the damper to act more quickly and hence dampen only minor tower oscillations. On the other hand, letting the damper mass slide from side to side adds to the damping function due to the friction between the damper mass and an interior bottom of damper housing.
Other aspects of the invention will be apparent from and elucidated with reference to the variations described hereinafter, where features may be added to the core of the invention and/or replaced by alternative features.
A wind turbine having a wind tower with a wind tower damper according to the invention will now be described in more detail with regard to the accompanying figures. The figures show one way of implementing the present invention and is not to be construed as being limiting to other possible embodiments falling within the scope of the attached claim set.
Inside the lower housing 7 and the upper housing 8 there is room for a mass element 23, which may be configured in various alternative ways as well as a damping element 11 made from a rubber or rubber-like material. In the shown configuration, the mass 23 comprises a number of discs 15 having a central aperture, such that the discs 15 may be arranged and fixed by a central shaft 12 and be secured by a lock 15. The shaft 12 may be welded or bolted to a lowermost disc 15. The discs 15 are preferably made with a mass, where one or two humans may handle the discs for assembling and disassembling the tower damper 5. Also, the damping element 11 may be arranged on the shaft 12 between the discs 15. In another configuration some of the discs may have a smaller diameter, so that the damping element 11 may have a ring-shaped form, where the discs 15 with the smaller diameter may provide a recess for receiving a ring-shaped damping element.
Although not shown, the damping element 11 may be fixated in a ring-like shape to the bottom housing 7 instead.
The lowermost disc 15 is shown in a configuration having roller ball wheels 16, so that the mass element 23 may move freely in any horizontal direction inside the housings 7, 8, when the tower is oscillating along with the housings. In an alternative configuration the wheels 16 may be dispensed with, so that the mass element 23 slides instead of rolling on the wheels.
When initially the tower 2, in a first oscillation, moves westward, the damping mass 23, initially placed centrally in the damper housing, will collide with the damper housing at the eastside. When the tower 23 later starts moving eastward, the damper housing will move with the tower 2 to the east. However, by then the mass element with and the damping element 11 will collide with the damper housing to the west and the inertial energy of the mass element 23 will restrict the towers 2 movement to the east and vice versa. Also some of the towers 2 oscillation energy will be absorbed be the deformation of the damping element 11. The damper 5 will continue working and provides a certain minimum amplitude of the tower 2 oscillation. A dampening factor about 10 may be obtained by such a tower damper.
In
In
In both
A tower having a tower damper according to
The weight of each section is, starting from the bottom and going upwards:
It is believed that a similar tower damper will have a similar technical effect, as long the lowest natural frequency is 1 Hz or lower. This will of course rely on further tests, but a damping mass between 200 and 600 kg should cover steel wind turbine tower in lengths from 60 metres and above.
The tower damper described herein, may preferably be used in a location near or at the top of the tower. However, one or more further dampers of a similar type may be used at lower locations, such as midway between the tower top and bottom to dampen higher order natural frequencies.
Although the present invention has been described in connection with the specified embodiments, it should not be construed as being in any way limited to the presented examples. The scope of the present invention is set out by the accompanying claim set. In the context of the claims, the terms “comprising” or “comprises” do not exclude other possible elements or steps. Also, the mentioning of references such as “a” or “an” etc. should not be construed as excluding a plurality. The use of reference signs in the claims with respect to elements indicated in the figures shall also not be construed as limiting the scope of the invention. Furthermore, individual features mentioned in different claims, may possibly be advantageously combined, and the mentioning of these features in different claims does not exclude that a combination of features is not possible and advantageous.
| Number | Date | Country | Kind |
|---|---|---|---|
| PA 2013 70314 | Jun 2013 | DK | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/DK2014/050164 | 6/11/2014 | WO | 00 |
