Patent Application
20210246879
The present invention relates to an impact damper assembly comprising one or more impact dampers each having adjustable damping characteristics.
Vortex shedding is a phenomenon that occurs due to instability of the flow around an object, such as a wind turbine tower. Low-pressure vortices are created on the downstream side of the tower and intermittently detach from either side of the tower. The tower will tend to move towards the low pressure, i.e. an alternating force is applied to the tower. The frequency by which the force alternates from side to side depends on the diameter of the tower and the wind speed. At a certain wind speed, the frequency of the alternating forces coincides with the natural frequency of the wind turbine tower. This wind speed is known as the critical wind speed. At this wind speed the tower will start to oscillate.
The amplitudes of the oscillations at the critical wind speeds depend on the structural damping of the wind turbine tower. If no additional damping is added to the wind turbine tower the oscillations can result in severe deflections of the wind turbine tower. This may lead to structural damage and/or damage to equipment or personnel in the wind turbine tower.
It may be seen as an object of embodiments of the present invention to provide a tower damper for damping oscillations a wind turbine tower or wind turbine tower section.
It may be seen as a further object of embodiments of the present invention to provide a simple and robust impact damper assembly for damping in particular oscillations originating from the second natural frequency of a wind turbine tower or wind turbine tower section.
The above-mentioned objects are complied with by providing, in a first aspect, an impact damper assembly for damping oscillations of an associated tower structure, the impact damper assembly comprising one or more impact dampers each comprising
Thus, according to the first aspect of the present invention an impact damper assembly comprising one or more impact dampers having adjustable damping characteristics is provided. The adjustable damping characteristics of the one or more impact dampers may be provided by adjusting the tension applied to the suspension arrangement. By adjusting the tension applied to the suspension arrangement the damping characteristics of the one or more impact dampers may be adjusted to dampen a selected natural frequency of the tower structure, such as the second natural frequency of the tower structure. This is a major advantage as the natural frequency of the tower structure may change dependent on the stage of completion of the wind turbine tower as weight and height changes.
The tensioner may be implemented in various ways, such as an in-line tensioner forming part of the suspension arrangement. The tensioner may be controlled manually, i.e. the tension applied to the suspension arrangement may be set manually. Alternatively, the tensioner may be controlled in real time, i.e. automatically, in response to measured Vortex-induced oscillations of the tower structure. Automatic and real time control of the tensioner may be performed via an electric motor or a linear actuator in combination with a suitable control loop involving a control unit.
The impact damper assembly may be attached to the tower structure which may involve a completely assembled wind turbine tower or a wind turbine tower section. The impact damper assembly may be attached to either the inside or outside of the wind turbine tower or wind turbine tower section.
The impact damper assembly may further comprise a sensor adapted to measure movements of the tower structure, and a control unit for adjusting the defined tension to the suspension arrangement in response to measured movements of the tower structure. The adjustment of the defined tension to the suspension arrangement in response to measured movements of the tower structure may be performed in real time in order to facilitate that for example the second natural frequency of the tower structure, at any time, may be properly damped.
In terms of attaching the impact damper assembly to the tower structure each impact damper may further comprise fastening elements, such as brackets, wherein a fastening element may be located at each suspension position for suspending the suspension arrangement of each impact damper. The fastening elements of each impact damper may be adapted to be attached to two vertically distanced tower flanges of the tower structure. In this way the tower flanges may become the vertically distanced suspension positions. One or both of the fastening elements may be adapted to be attached to brackets connected to the tower wall and/or a platform arranged in the tower.
The suspension arrangement may comprise a wire. This wire may be adapted to be suspended between the vertically distanced suspension positions of the tower structure. By adjusting the tension applied to the wire (optionally in real time) the damping characteristics of a given impact damper may be constantly adjusted to dampen a selected natural frequency of the tower structure in a desired and/or an optimal manner.
The impact damper assembly may comprise at least three impact dampers, i.e. 3, 4, 5, 6 etc. impact dampers. To ensure proper damping of the tower structure the impact dampers may be evenly distributed along a periphery of the tower structure. Thus, if for example the impact damper assembly comprises three impact dampers an angular separation of approximately 120 degrees is preferably provided between the impact dampers. In case of 6 impact dampers an angular separation of approximately 60 degrees is preferably provided.
The impact damper assembly may be adapted to dampen tower structure oscillations having a natural frequency below 11 Hz, such as below 5 Hz, such as below 2 Hz, such as below 1.5 Hz, such as below 1 Hz. The natural frequency of the tower structure may be higher than 0.2 Hz, such as higher than 0.5 Hz, preferably within the range of 0.8 to 1.0 Hz. As mentioned above the impact damper assembly of the present invention may in particular be intended to dampen tower oscillations at or near the second natural frequency of the tower structure, which was estimated to be the range below 2 Hz and higher than 0.5 Hz. In a further embodiment, the impact damper assembly is particularly intended to dampen tower oscillations at or near the third natural frequency of the tower structure, which was estimated to be the range below 11 Hz and higher than 0.8 Hz.
The impact mass of the one or more impact dampers may be at least partly encapsulated in a resilient or elastic material, such as rubber, in order to reduce load on the tower structure during collision. The mass of the impact mass of the one or more impact dampers may be around 2-3% of the tower turbine generalized mass even thou the mass may be lower such as for example 1-3% or 0.5-3% of the tower turbine generalized mass.
The impact mass of the one or more impact dampers may be positioned at or near a centre point of the suspension arrangement.
The impact damper assembly according to the present invention is also effective against oscillations originating from third or higher natural frequency of a wind turbine tower when tuned to such frequencies. By use of an automatic and real time control of the tensioner, the impact damper assembly may hence be effective against oscillations of several (natural) frequencies of a wind turbine tower. It should be noted that oscillations of higher than second mode is not typically observed in the presently used wind turbine designs, but the impact damper assembly according to the invention will be effective to these higher modes should future designs of wind turbine towers lead to higher modes of oscillation.
In a second aspect the present invention relates to a wind turbine tower having an impact damper assembly according to the first aspect secured thereto. The impact damper assembly may be intended to dampen Vortex induced oscillations of the wind turbine tower, such as Vortex induced oscillations of the wind turbine tower at or near the second natural frequency of the wind turbine tower.
The term wind turbine tower is here to be understood as a partly or completely assembled wind turbine tower with or without the nacelle and optionally the rotor. In other words, the invention concerns both a completed wind turbine generator as well as a partly assembled wind turbine generator or wind turbine tower during assembly, transportation and at energy production position.
The impact damper assembly may be attached to the wind turbine tower in a manner so that the vertical position of the impact mass of an impact damper is between 40% to 80%, preferably between 45% to 70%, more preferably between 50% to 66%, such as about 66% of the height of the wind turbine tower. Here, the height of the wind turbine tower is defined as the distance from the attachment of the tower to the foundation and to the attachment to the nacelle, i.e. from the bottom flange of the lowermost tower section to the top flange of the uppermost tower section.
For conical towers and towers with conical sections is it preferred to place the impact mass above or above the middle of the tower, such as 50% to 66% or about 66% of the height of the wind turbine tower.
For the second mode tower oscillations the tower deflection will reach its extremum at approximately this location. Therefore, the effect of the damper will be highest towards reducing second mode tower oscillations when located at this position in relation to the tower as opposed to first mode tower oscillations, where the deflections are most pronounced at the top to the tower. Dampers for reducing first mode tower oscillations using an impact mass are therefore placed as high as possible in the tower, such as at 90% to 100% or 95% to 100% of the height of the wind turbine tower. The damper of the present invention is especially suitable for locations lower than the high positions of dampers for first mode tower oscillations as the damper of the present invention requires space above and below the impact mass (see above for paragraphs for identified advantageous positioning of the impact mass of the damper of the present invention).
Moreover, the suspension arrangement of an impact damper may be configured with a distance between the suspension positions between 5 to 20% of the height of the wind turbine tower. In meters, the distance between the suspension positions may be between 5 to 25 m. The larger distances are typically realized when the suspension positions are flanges of tower sections, whereas the shorter distances typically are realized when the suspension positions are a combination of one or more flanges, brackets on the tower wall and platforms in the tower.
The wind turbine tower may further comprise load spreading devices attached to the wind turbine tower in order to reduce loads on the wind turbine tower during the repeated collision with the impact mass. The load spreading device may include a resilient material attached to the wind turbine tower at the point of collision.
The impact damper assembly attached to the wind turbine tower may comprise three impact dampers being angularly spaces preferably by approximately 120 degrees around the periphery of the wind turbine tower. It should be noted that the impact damper assembly may comprise a different number of impact dampers, such as 6, 9, 12 etc. impact dampers preferably being evenly distributed around the periphery of the wind turbine tower. Each of the three impact dampers are secured to vertically neighbouring tower flanges via brackets or otherwise vertically distanced suspension positions like brackets on the tower wall or platforms in the tower.
As addressed above the impact damper assembly may be adjusted to dampen the second natural frequency of the wind turbine tower.
In a third aspect the present invention relates to a method for damping preselected oscillations of a tower structure using an impact damper, the method comprising the steps of
The implementation of the impact damper may be as discussed in relation to the first aspect of the present invention. Thus, the impact damper may form part of an impact damper assembly comprising one or more impact dampers. Thus, the impact damper assembly may comprise three impact dampers which are suspended between vertically shifted tower flanges. Moreover, the three impact dampers may be angularly spaces by approximately 120 degrees around the periphery of the tower structure.
As addressed above, the impact damper assembly may comprise a sensor adapted to measure movements of the tower structure, and a control unit for adjusting the defined tension to the suspension arrangement in response to measured movements of the tower structure. The method according to the third aspect of the present invention may thus comprise the step of adjusting the defined tension to the suspension arrangement in response to measured movements of the tower structure in real time. This step facilitates that for example the second natural frequency of the tower structure, at any time, may be properly damped.
The present invention will now be explained in further details with reference to the accompanying figures, wherein
While the invention is susceptible to various modifications and alternative forms specific embodiments have been shown by way of examples in the drawings and will be described in details herein. It should be understood, however, that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.
In a general aspect the present invention relates to an impact damper assembly for damping oscillations of an associated tower structure, such as a wind turbine tower, to which the impact damper assembly is attached. The impact damper assembly comprises one or more impact dampers. Each impact damper comprises a tensioner adapted to apply a defined tension to a suspension arrangement suspending an impact mass in order to adjust the damping characteristics of the impact damper. The damping characteristics of each impact damper may thus be adjusted (preferably in real time) in response to measured movements of the tower structure to which tower structure the impact damper assembly is attached.
Referring now to
When assembling wind turbine generators of the type depicted in
Uncontrolled swaying or deflections of wind turbine towers due to Vortex-induced oscillations can be effectively counteracted by the impact damper assembly 200 according to the present invention as depicted in
As the wind turbine tower deflects due to Vortex-induced oscillations the impact mass 201 will move as illustrated by the horizontal arrow. At some stage the impact mass 201 will collide with the tower wall 203, cf. the dashed part in
The natural frequency of the impact damper as well as the collision force between the tower wall and the impact mass may be adjusted by an in-line tensioner 211 adapted to apply a defined tension to the wire 202. Thus, by adjusting the tension applied to the wire 202 the damping characteristics of the impact damper may be adjusted.
The in-line tensioner 211 may be controlled manually, i.e. the tension applied to the wire 202 may for example be set manually. Alternatively, the in-line tensioner 211 may be controlled in real time, i.e. automatically, in response to measured Vortex-induced oscillations of the wind turbine tower. Automatic control of the in-line tensioner 211 may be performed via an electric motor or a linear actuator in combination with a suitable control loop involving a control unit. The impact damper assembly according to the present invention may thus comprise a sensor adapted to measure Vortex-induced oscillations of the wind turbine tower, and a control unit for adjusting, in real time, the tension applied to the wire 202 in response to measured movements of the wind turbine tower in order to reduce Vortex-induced oscillations of the wind turbine tower, in particular at or near the second natural frequency of the wind turbine tower. Even thou the natural frequency of the impact damper could be changed by adjusting any one of the parameters mentioned above (e.g. mass and length of wire), and despite change in mass is much more simple to carry out, it was found to be highly advantageous to adjust the natural frequency by changing the tension applied to the wire as this allows for fast adjustment, which may be carried out automated and from a distance. Particularly for offshore wind turbines being able to change the tension applied to the wire to adjust the natural frequency of the impact damper turned out to be highly advantageous. Also, the use of a change in tension applied to the wire to adjust the natural frequency of the impact damper was found to be advantageous and particularly for offshore wind turbines.
The impact damper according to the present invention comprises at least three impact dampers evenly distributed along a periphery of the wind turbine tower. In case the impact damper assembly comprises three impact dampers these impact dampers are preferably separated by approximately 120 degrees, cf.
In order to reduce load on the wind turbine tower structure during collision the impact mass 201 of the impact damper is preferably at least partly encapsulated in a resilient or elastic material, such as rubber. The shape of the impact mass may be various, including cylindrical and spherical shapes. The impact mass of the impact damper may be positioned at or near a centre point of the suspension arrangement, i.e. at or near the centre between the brackets 206, 207. The mass of the impact mass typically amounts 2-3% of the generalized mass of the tower turbine but may be lower such as for example 1-3% or (particularly in cases with fast and exact automatic changing of tension applied to the suspension arrangement) 0.5-3% of the generalized mass of the tower turbine.
As addressed above the present invention also relates to a method for damping preselected oscillations of a tower structure using an impact damper assembly comprising one or more impact dampers as depicted in
| Number | Date | Country | Kind |
|---|---|---|---|
| 18180750.4 | Jun 2018 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2019/066937 | 6/26/2019 | WO | 00 |
