Field of the Invention

The present invention relates to a multi-stage suspension damper for damping a structure such as a wind turbine generator.

Background of the Invention

Wind turbine towers are ever increasing in height and as a result the natural frequency of the wind turbine towers are also increasing, hence the suspension dampers must have ever increasing pendulum lengths to match.

The suspension damper should be placed at the maximum amplitude of the wind turbine tower . The tower has maximum amplitude at the tower top, however due to the increasing pendulum length then the pendulum mass is placed further away from the top of the wind turbine tower, which will reduce the damping efficiency.

Thus, there is a need for suspension dampers with better damping efficiency for wind turbine towers or other towers.

Object of the Invention

It is an object to provide a multi-stage suspension damper to solve the problems of the prior art.

Description of the Invention

An object of the invention is achieved by a multi-stage suspension damper for damping a structure. The multi-stage suspension damper comprises

- one or more frame structures including an innermost frame structure comprising an innermost frame top part and an innermost frame bottom part, wherein the innermost frame top part and the innermost frame bottom part are interconnected and define an innermost frame structure height, wherein the innermost frame structure is suspended by three innermost rods or three innermost cords connected to the innermost frame bottom part and extending from another frame structure of the one or more frame structures or the three innermost rods or the three innermost cords are adapted to be connected to an object;

- a pendulum suspended by a pendulum rod or a pendulum cord from the innermost frame top part, wherein the pendulum rod or pendulum cord is longer than the innermost frame structure height, wherein the pendulum comprises a pendulum mass.

The frequency of the multi-stage suspension damper is in the case of one frame structure defined by the lengths of a) the pendulum rod or pendulum cord; and b) the three innermost rods or the three innermost cords.

However, the height of the multi-stage suspension damper will be shorter than the sum of part a) and b), thereby the pendulum mass can be suspended closer to the top of a wind turbine tower. This will increase the dampening effect.

The frequency of the multi-stage suspension damper is in the case of more frame structures defined by a) and b) mentioned above and the length of the rods or the cords associated with the other frame structures not being the innermost frame structures. Thus, having more frame structures will enable that the total height of the multi-stage suspension damper can be reduced further and thus the pendulum mass can be closer to the top of a wind turbine tower, which will increase the dampening effect.

The multi-stage suspension damper is not limited to wind turbine towers and may be used in any other building that requires dampening such as offshore installations.

The innermost frame bottom part can take many shapes and should have an innermost frame bottom central aperture such that the pendulum cord or pendulum rod can extend past the innermost frame bottom part. The innermost frame bottom part may be an annulus.

The object can be part of the element to be damped i.e. part of the wind turbine tower. In other embodiments, the object may be a housing in which the multi-stage suspension damper is positioned. In these embodiments the housing may then be connected to the element to be damped. The innermost frame structure is a rigid structure.

There is an additional effect of using innermost rods instead of innermost cords. The innermost rods are rigid, which enables the multi-stage suspension damper to be transported in various positions not possible for the embodiments of the invention using cords. During transportation of a wind turbine tower, the wind turbine tower will often be placed in a horizontal position where the longitudinal axis of the wind turbine tower is horizontal. The multi-stage suspension damper is preferably installed in the wind turbine tower prior to the transportation as this is simpler. The embodiments of the multi-stage suspension damper with rods can be transported in the horizontal position without risk of damaging the multi-stage suspension damper.

The transportation in a horizontal state is not affected by how the pendulum is suspended. Thus, the pendulum can be suspended by a pendulum cord or a pendulum rod, or a combination of a pendulum cord and a pendulum rod, without affecting horizontal transportation of the multi-stage suspension damper.

The object may be a cylindrical housing partly or completely encompassing the multistage suspension damper.

In an aspect, the three innermost rods or the three innermost cords may be non-parallel relative to the pendulum rod or the pendulum cord, when the multi-stage suspension damper is at rest.

Two effects are achieved from this; the frequency of the pendulum will change compared to the three innermost rods or the three innermost cords being parallel and the change will be larger at a larger angle. This will enable adjustment of the multi-stage suspension damper such that a mass-produced multi-stage suspension damper can cover a frequency range - thus the solution will provide frequency tolerance. This is especially important when producing multi-stage suspension dampers for a wind turbine farm as each wind turbine generator of the wind turbine farm will have slight variations in the frequency. The frequency of multi-stage suspension damper can then be controlled by increasing or decreasing the angle between the three innermost rods or the three innermost cords and the pendulum rod or the pendulum cord, when the multi-stage suspension damper is at rest. This can be adjusted during installation of the multi-stage suspension damper.

The other effect is that the innermost top part will be displaced more, which will cause a greater amplitude of the pendulum thereby causing a greater damping effect.

In an aspect, a diameter of the innermost frame bottom part is greater than the diameter of the innermost frame top part, thereby defining an overall truncated cone shape of the innermost frame structure.

This is particularly relevant when the multi-stage suspension damper comprises more frame structures as this enables that there is sufficient space for displacement of the frame structures, which is especially relevant when the cords or rods are parallel when the pendulum is at rest.

In an aspect, the one or more frame structures may include an outermost frame structure comprising an outermost frame top part and an outermost frame bottom part, wherein the outermost frame top part and the outermost frame bottom part are interconnected and define an outermost frame structure height, wherein the outermost frame structure is suspended by three outermost rods or three outermost cords connected to the outermost frame bottom part and being adapted to be connected to an object; wherein the three innermost rods or the three innermost cords being connected to the outermost frame top part; or wherein three intermediate rods or the three intermediate cords extend from the outermost frame top part to an intermediate frame structure of the one or more frame structures.

Thus, the multi-stage suspension damper comprises the innermost frame structure and the outermost frame structure, and optional one or more intermediate frame structures. The one or more intermediate frame structures are similar to the innermost frame structure or the outermost frame structure, however the one or more intermediate frame structures are just positioned between the innermost and the outermost frame structure.

The outermost frame structure and/or the one or more intermediate frame structures may have all the same technical features as the innermost frame structure except the pendulum rod or the pendulum cord.

In an aspect, the three outermost rods or the three outermost cords may be non-parallel relative to the pendulum rod or the pendulum cord, when the multi-stage suspension damper is at rest.

The effects are the same as the effect of the three innermost rods or the three innermost cords are non-parallel relative to the pendulum rod or the pendulum cord, when the multi-stage suspension damper is at rest. However, it will in most cases be easier to change the angle of the three outermost rods or the three outermost cords compared to the innermost rods or innermost cords when adjusting the frequency since the outermost rods or the outermost cords are more accessible.

In an aspect, the multi-stage suspension damper may comprise three frequency adjustment slides and each frequency adjustment slide comprises a displaceable connection member, wherein

- each of the three innermost rods or each of the three innermost cords is connected to one of the three displaceable connection members; or

- each of the three outermost rods or each of the three outermost cords is connected to one of the three displaceable connection members; wherein the frequency adjustment slides enable that said rods or said cords can change the angle relative to the pendulum rod or pendulum cord when the multi-stage suspension damper is at rest and thereby change the frequency of the multi-stage suspension damper.

Thereby, the frequency of the multi-stage suspension damper can be adjusted by displacing the displaceable connection member along the frequency adjustment slides. In an aspect, the innermost frame bottom part may comprise three bearing boxes and each of the three innermost rods extend to one of the three bearing boxes, and two bars extend from each bearing box to the innermost frame top part, wherein the two bars are positioned on each side of the innermost rod connected to the bearing box.

The two bars are positioned on each side of the innermost rod connected to the bearing box as this will cancel torque forces on the bearing box, thereby making the multistage suspension damper more mechanically stable. The two bars from each bearing box is connected to the innermost frame top part.

The innermost rod may comprise a bearing end inside a chamber of the bearing box, wherein the bearing end and the chamber are complementary to the bearing end for allowing for pivotal movement of the innermost rods. The innermost rod extent through a chamber opening. The innermost rods may have a rounded shape engaging the side of the chamber with the chamber opening, which side has a shape complementary to the rounded shape.

The chamber may further comprise a biasing element positioned for pressing the bearing end towards the side of the chamber with the chamber opening. This will further reduce risk of damage during transportation of the multi-stage suspension damper in any orientation as the bearing end is prevented from moving freely in the chamber, which may result in damage during transportation.

The biasing element may be a spring.

The outermost frame bottom part and/or the outermost frame top part may comprise three bearing boxes as the innermost frame bottom part. If both the outermost frame bottom part and the outermost frame top part comprises three bearing boxes, then the two bars extend between two bearing boxes of the respective outermost frame bottom part and the outermost frame top part.

The one or more intermediate frame bottom parts and/or the one or more intermediate frame top parts may comprise three bearing boxes as the innermost frame bottom part. If both the intermediate frame bottom part and the intermediate frame top part comprises three bearing boxes, then the two bars extend between two bearing boxes of the respective intermediate frame bottom part and the intermediate frame top part.

In an aspect, the pendulum may comprise a pendulum bottom, a centre pylon extending from the pendulum bottom, and one or more slideable rondelles with increasing outer diameter being stacked on the pendulum bottom with the centre pylon as a common centre.

The one or more slidable rondelles will slide causing additional friction damping.

In an aspect, the multi-stage suspension damper comprises an impact wall surrounding at least the pendulum and being configured for impact with the pendulum.

Thereby, the pendulum becomes an impact pendulum designed to engage an impact wall surrounding the pendulum. The impact pendulum can have a higher dampening effect than a non-impact pendulum and as a result the mass of the pendulum can be reduced such that the weight of the multi-stage suspension can be lower. The slidable rondelle with the largest diameter will impact the impact wall first and be displaced and then the slidable rondelle with the second largest diameter will impact the impact wall next and so on and thereby the impact is divided into a series of larger and larger impacts which will slow the pendulum such that the final impact is smaller than in the case where the pendulum is one solid element. This gives additional friction damping and the impact wall and the pendulum will experience less wear.

An object of the invention is achieved with a wind turbine tower comprising a multistage suspension damper, wherein the multi-stage suspension damper is positioned at the top of the wind turbine tower.

Thereby a natural frequency of the wind turbine tower is dampened.

Description of the Drawing

Embodiments of the invention will be described in the figures, whereon: Fig. 1 illustrates cross-sections of three different embodiments of a multi-stage suspension damper comprising an innermost frame structure;

Fig. 2 illustrates cross-sections of three different embodiments of the multi-stage suspension damper comprising an innermost frame structure and an outermost frame structure;

Fig. 3 illustrates a cross-sections of embodiment of Fig. 1C having different frequencies;

Fig. 4 illustrates an embodiment of a multi-stage suspension damper;

Fig. 5 illustrates a bearing box; and Fig. 6 illustrates a bearing box with a spring.

Detailed Description of the Invention

Fig. 1 illustrates cross-sections of three different embodiments of a multi-stage suspension damper 1 comprising an innermost frame structure 121.

Fig. 1A discloses a cross-section of a multi-stage suspension damper 1 for damping a structure. The multi-stage suspension damper 1 comprises an innermost frame structure 101 comprising an innermost frame top part 121 and an innermost frame bottom part 141.

The innermost frame top part 121 and the innermost frame bottom part 141 are interconnected and define an innermost frame structure height 161. A solid cone or a series of bars extending may extend between the innermost frame top part 121 and the innermost frame bottom part 141 as long as the frame part 101 is rigid.

The innermost frame structure 101 is suspended by three innermost rods 181 or three innermost cords 181 connected to the innermost frame bottom part 141 extending to an object 90, which object 90 is a housing. The object is then to be installed in the structure to be damped.

The figure is a cross-section and therefore only two innermost rods 181 or two innermost cords is visible as they are equally spaced.

The multi-stage suspension damper 1 further comprises a pendulum 50 suspended by a pendulum rod 52 or a pendulum cord 52 from the innermost frame top part 121, wherein the pendulum rod 52 or pendulum cord 52 is longer than the innermost frame structure height 161, wherein the pendulum 50 comprises a pendulum mass. The pendulum 50 further comprises a pendulum bottom 54, a centre pylon 56 extending from the pendulum bottom 54, and one or more slidable rondelles 58 with increasing outer diameter being stacked on the pendulum bottom 54 with the centre pylon 56 as a common centre.

In this embodiment, the pendulum rod 52 or a pendulum cord 52 and the three innermost rods 181 or the three innermost cords 181 are parallel when the multi-stage suspension damper 1 is at rest.

Fig. IB discloses a cross-section of a multi-stage suspension damper 1 for damping a structure. The multi-stage suspension damper 1 comprises an innermost frame structure 101 comprising an innermost frame top part 121 and an innermost frame bottom part 141.

The innermost frame top part 121 and the innermost frame bottom part 141 are interconnected and define an innermost frame structure height 161. A solid cone or a series of bars may extend between the innermost frame top part 121 and the innermost frame bottom part 141 as long as the frame part 101 is rigid.

The innermost frame structure 101 is suspended by three innermost rods 181 or three innermost cords 181 connected to the innermost frame bottom part 141 extending to an object 90, which object 90 is a housing. The object is then to be installed in the structure to be damped.

The figure is a cross-section and therefore only two innermost rods 181 or two innermost cords is visible as they are equally spaced.

The multi-stage suspension damper 1 further comprises a pendulum 50 suspended by a pendulum rod 52 or a pendulum cord 52 from the innermost frame top part 121, wherein the pendulum rod 52 or pendulum cord 52 is longer than the innermost frame structure height 161, wherein the pendulum 50 comprises a pendulum mass.

The pendulum 50 further comprises a pendulum bottom 54, a centre pylon 56 extending from the pendulum bottom 54, and one or more slidable rondelles 58 with increasing outer diameter being stacked on the pendulum bottom 54 with the centre pylon 56 as a common centre.

In this embodiment, the pendulum rod 52 or a pendulum cord 52 and the three innermost rods 181 or the three innermost cords 181 are non-parallel when the multi-stage suspension damper 1 is at rest. Thus, assuming that embodiments of Fig 1A and fig. IB have the same dimensions, the two embodiments will have different frequencies.

Fig. 1C discloses a multi-stage suspension damper 1 similar to the embodiments of figure 1A and figure IB. However, the multi-stage suspension damper 1 further comprises three frequency adjustment slides 30 adapted to be connected to an object and each frequency adjustment slide 30 comprises a displaceable connection member 32, wherein each of the three innermost rods 181 or each of the three innermost cords 181 is connected to one of the three displaceable connection members 32. The third frequency adjustment slide 30 is not shown since figure 1C is a cross-section.

The frequency adjustment slides 32 enable that said innermost rods 181 or said innermost cords 181 can change the angle relative to the pendulum rod 52 or pendulum cord 52, when the multi-stage suspension damper 1 is at rest and thereby change the frequency of the multi-stage suspension damper 1. This is further discussed for figure 3.

Fig. 2 illustrates cross-sections of three different embodiments of the multi-stage suspension damper 1 comprising an innermost frame structure 121 and an outermost frame structure 120. The embodiments are similar to the embodiments of figure 1 but these embodiments include the outermost frame structure 12N.

Fig. 2A discloses a cross-section of a multi-stage suspension damper 1 for damping a structure.

The multi-stage suspension damper 1 comprises an innermost frame structure 101 comprising an innermost frame top part 121 and an innermost frame bottom part 141. The innermost frame top part 121 and the innermost frame bottom part 141 are interconnected and define an innermost frame structure height 161. The innermost frame structure 101 is suspended by three innermost rods 181 or three innermost cords 181 connected to the innermost frame bottom part 141 and extending from an outermost frame structure 10.

The outermost frame structure ION comprises an outermost frame top part 12N and an outermost frame bottom part 14N, wherein the outermost frame top part 12N and the outermost frame bottom part 14N are interconnected and define an outermost frame structure height 16N. The outermost frame structure 10 is suspended by three outermost rods 18N or three outermost cords 18N connected to the outermost frame bottom part 14N and are connected to an object 90. This object 90 is in this embodiment a housing which can be installed in the structure to be damped. The three innermost rods 181 or the three innermost cords 181 are connected to the outermost frame top part 12N.

The pendulum 50 is suspended by a pendulum rod 52 or a pendulum cord 52 from the innermost frame top part 121, wherein the pendulum rod 52 or pendulum cord 52 is longer than the innermost frame structure height 161 and the outermost frame structure height 161, wherein the pendulum 50 comprises a pendulum mass.

The pendulum 50 further comprises a pendulum bottom 54, a centre pylon 56 extending from the pendulum bottom 54, and one or more slidable rondelles 58 with increasing outer diameter being stacked on the pendulum bottom 54 with the centre pylon 56 as a common centre.

In this embodiment the rods 181, 180 or cords 181, 180 are parallel with the pendulum rod 52 or pendulum cord 52, when the pendulum 50 is at rest.

Figure 2B discloses a cross-section of a multi-stage suspension damper 1. The multistage suspension damper 1 has the same features as figure 2A. However, the three innermost rods 181 or the three innermost cords 181 are non-parallel relative to the pendulum rod 52 or the pendulum cord 52, when the multi-stage suspension damper 1 is at rest. Assuming, that the embodiments of figure 2A and 2B have the same dimensions then the frequency will be different for the embodiments.

Figure 2C discloses a cross-section of a multi-stage suspension damper 1. The multistage suspension damper 1 has the same features as figure 2A. However, the multistage suspension damper 1 further comprises three frequency adjustment slides 30 adapted to be connected to the object 90 and each frequency adjustment slide 30 comprises a displaceable connection member 32. Each of the three outermost rods 18N or each of the three outermost cords 18N is connected to one of the three displaceable connection members 32.

The frequency adjustment slides 32 enable that said outermost rods 18N or said outermost cords 18N can change the angle relative to the pendulum rod 52 or pendulum cord 52. when the multi-stage suspension damper 1 is at rest and thereby change the frequency of the multi-stage suspension damper 1.

Fig. 3 illustrates cross-sections of the embodiment shown Fig. 1C having different frequencies due to different angles. The frequency is defined by the length of the pendulum rod or pendulum cord 52 and the innermost rods 181 or innermost cords 181 and the mutual angle when the pendulum 50 is at rest. The references is shown in figure 1C.

In figure 3 A, the pendulum rod or pendulum cord 52 and the innermost rods 181 or innermost cords 181 are parallel i.e. the angle is zero. The following frequencies examples are made assuming that the frequency of the multi-stage suspension damper 1 in configuration figure 3A is 0.24 Hz.

In figure 3B, the angle is 3 degrees and 0.22 Hz.

In figure 3C, the angle is 7 degrees and 0.20 Hz.

In figure 3D, the angle is 12 degrees and 0.18 Hz.

Thus, by displacing the displaceable connection member 32 the multi-stage suspension damper 1 can be adapted to different structure having variations of the frequency to be damped. This is particularly relevant for some offshore wind turbine farms where each wind turbine tower will have slight variations due to different water depths.

Fig. 4 illustrates an embodiment of a multi-stage suspension damper 1 comprising an innermost frame structure 101 and an outermost frame structure ION.

The multi-stage suspension damper 1 comprises three frequency adjustment slides 30 equipped with three multi-stage suspension dampers 32 which can be displaced to adjust a frequency of the multi-stage suspension damper 1. Three outermost rods 18N (not all a visible in the figure) extend from the multi-stage suspension damper 32 to three bearing boxes 60 forming part of the outermost frame bottom part 14N.

The outermost frame bottom part 14N is substantially an annulus with the bearing boxes 60 positioned at equal distances i.e. there is substantially 120 degrees between neighbouring bearing box. Two bars 62 positioned on each side of the outermost rods 18N extend from each of the bearing boxes 60 to three bearing boxes 60 forming part of an outermost frame top part 12N. The outermost frame top part 14 is substantially an annulus with the bearing boxes 60 positioned at equal distances i.e. there is substantially 120 degrees between neighbouring bearing box.

Three outermost rods 18N (not all a visible in the figure) extend from the multi-stage suspension damper 32 to three bearing boxes 60 forming part of the innermost frame bottom part 141. The innermost frame bottom part 141 is substantially an annulus with the bearing boxes 60 positioned at equal distances i.e. there is substantially 120 degrees between neighbouring bearing box. Two bars 62 positioned on each side of the innermost rods 18N extend from each of the bearing boxes 60 to the innermost frame top part 121. The innermost frame top part 121 has a central bearing box from which a pendulum rod 52 extends partly towards a pendulum 50, however a pendulum cord 52 is connected to the pendulum rod 52 which extend to the pendulum 50. The pendulum cord 52 is further equipped with means enabling the pendulum length to be increased such that the pendulum can be lowered to a rest surface shown as the large circular element at the bottom of the figure. This will allow service of the multi-stage suspension damper 1. The pendulum 50 comprises a pendulum bottom 54, a centre pylon 56 (not visible) extending from the pendulum bottom 54, and one or more slidable rondelles 58 with increasing outer diameter being stacked on the pendulum bottom 54 with the centre pylon 56 as a common centre. The pendulum 50 further comprises a pendulum top such that the slidable rondelles 58 are trapped between the pendulum top and the pendulum bottom 54, hence why the centre pylon 56 is not visible.

The large circular element is not part of the pendulum 50 nor is it part of the multistage suspension damper 1 as such. The large circular element may form part of the object 90 (not shown) to which the multi-stage suspension damper 1 can be connected, or the large circular element can represent a floor forming part of the structure to be damped.

Although not shown, the multi-stage suspension damper 1 may comprise an impact wall surrounding at least the pendulum 50and being configured for impact with the pendulum 50 as this will increase the damping effect.

The bearing boxes 60 may be according to the bearing boxes 60 shown in figure 5 or 6.

Fig. 5 illustrates a bearing box 60. The shown bearing box 60 may be used in any of the shown embodiments in figure 1-4 even if not explicitly disclosed. The figure is a cross-section.

The bearing box 60 comprises a chamber 64 into which a bearing end 19 of a rod 18 extends. The bearing end 19 extends through a chamber opening 66 and a side of the chamber 64 with the chamber opening 66 being complementary to the bearing end 19 such that the bearing end 19 can function as a bearing. The bearing box 60 further comprises two bars 62 (only one is shown) extending towards either a frame top part 12 or a frame bottom part 14. The two bars 62 are positioned on each side of the rod 18 such that torque forces are cancelled. In the present embodiment the bearing end 19 also has a rounded shape opposite to the side of the chamber 64 with the chamber opening 66 and the chamber is made as compact as possible such that the bearing end 19 has limited movement and the rounded shape will minimise damages and allow for transportation wherein the multi-stage suspension damper 1 is substantially oriented horizontally.

The bearing box 60 is further connected to a frame top part 12 or a frame bottom part 14.

Fig. 6 illustrates a bearing box with a spring. The shown bearing box 60 may be used in any of the shown embodiments in figure 1-4 even if not explicitly disclosed.

The bearing box 60 comprises a chamber 64 into which a bearing end 19 of a rod 18 extends. The bearing end 19 extends through a chamber opening 66 and a side of the chamber 64 with the chamber opening 66 being complementary to the bearing end 19 such that the baring end 19 can function as a bearing. The bearing box 60 further comprises two bars 62 (only one is shown) extending towards either a frame top part 12 or a frame bottom part 14. The two bars 62 are positioned on each side of the rod 18 such that torque forces are cancelled.

The bearing box 60 is further equipped with a biasing element 68 in the form of a spring such that the bearing end 19 is forced towards the complementary side having the chamber opening 66. This will enable transportation wherein the multi-stage suspension damper 1 is substantially oriented horizontally.

The bearing box 60 is further connected to a frame top part 12 or a frame bottom part 14.