ADAPTIVE PENDULUM DAMPER WITH VERTICAL SPRING DEVICE

Description

[0001] The invention relates to a pendulum damper for damping unwanted vibrations in vibration-sensitive systems, for example tall buildings and towers, in particular wind turbines.

[0002] The invention relates in particular to a pendulum damper whose vibration characteristics and thus damping capabilities, such as frequency and amplitude, are adjustable over a wide range. According to the invention, this is achieved by a spring device which acts predominantly in a vertical direction and exhibits a predominantly progressive or non-linear spring characteristic as a whole.

[0003] Wind turbines, in particular, are systems prone to vibration. To minimize the vibration amplitude of the wind turbine under resonance excitation, damping devices are typically integrated into the system. These damping absorbers must be tuned to the resonant frequency of the respective wind turbine. The stiffness of the wind turbine, its mass, and the stiffness of the foundation, which also depends on the soil conditions, primarily determine the natural frequency of the wind turbine.

[0004] A rigid foundation leads to a high resonant frequency of the wind turbine, and vice versa. A lower mass leads to a higher natural frequency of the wind turbine, and vice versa. This is precisely the situation during the installation of the turbine. There are temporary states in which only the tower, without the nacelle and rotor, can be excited into resonance by the wind. In this case, the natural frequency of the partially completed wind turbine is significantly higher than that of the later, fully installed turbine. A similar phenomenon can occur during the erection or construction of tall, slender structures (towers, skyscrapers, etc.).

[0005] In order to achieve optimal damping performance, the damper frequency must be adaptable and variable to the respective system frequency, especially the tower frequency, over a wide range.

[0006] For example, if a simple pendulum damper (variant 1; Fig. 1) is considered as a point mass, its frequency depends only on the pendulum length I1 (2). The physical relationship can be described as follows: f = 1 2 ∗ π ∗ g l 1 g→ Gravitational constant [m / s^2] I1→ Pendulum length [m]

[0007] The frequency can therefore only be influenced by the pendulum length. In practice, however, this can only be changed to a limited extent, especially in space-limited wind turbines.

[0008] To obtain further adjustment options for the damper frequency of a pendulum damper, variant 1 can usually be supplemented with horizontal springs. In variant 2.1, these horizontal springs (4) engage at the height of the damper mass (3). In variant 2.2, they are shifted towards the suspension point (1) ( Fig. 2 ).

[0009] This physical relationship between systems 2.1 and 2.2 can be described as follows: f = 1 2 ∗ π ∗ C ∗ l 2 ∧ 2 m ∗ l 1 ∧ 2 + g l 1 f = 1 2 ∗ π ∗ C m + g l 1 g→ Gravitational constant [m / s^2] I1→ Pendulum length [m] I2→ Length from pivot point to point of application of horizontal spring [m] C→ Spring stiffness of horizontal spring [N / m] m→ Damper mass [kg]

[0010] It is evident that the damper frequency can now be adjusted via several parameters.

[0011] Such solutions have been frequently described in the prior art. The horizontal springs (4) are subjected to tensile stress. Due to their installation position, in variant 2.1, the horizontal springs (4) follow the same path as the damping mass (3).

[0012] This results in very high dynamic loads, which makes a durable design very difficult or even impossible given the available installation space.

[0013] To minimize the travel of the horizontal springs (4), they can be moved further towards the suspension point of the damper (1) (variant 2.2). In this position, they travel less; however, in this configuration, the spring stiffness of these springs must increase to achieve the same performance compared to variant 2.1. Furthermore, this necessitates a rigid pendulum length (2), which effectively precludes the use of cables.

[0014] If the mass moves to the right, the left horizontal spring (4) is pulled further and the right horizontal spring (4) is relieved of tension. In this configuration, it must be ensured that the relief spring is not completely relieved of tension. This means that this horizontal spring (4) is pre-tensioned more in the neutral position than the oscillation path of the damper mass (3) can be. This fact makes assembly difficult.

[0015] As already mentioned, the damper frequency depends solely on the spring stiffness of the horizontal spring (4) and the pendulum length. If a different frequency is to be set, a horizontal spring (4) with a different spring stiffness must be installed, given a constant pendulum length (2), as is also frequently found in prior art. Increasing the spring preload, however, has no effect on the damper frequency.

[0016] SU 1076662 discloses a vibration damper for a tall, slender structure, comprising essentially a pendulum with a damping mass and a spring device in the form of a coil spring, wherein the cylindrical coil spring is installed below the damping mass and is arranged such that the entire spring force of the spring device acts essentially in the vertical direction. The damping mass is connected via the coil spring to an attachment point on the structure or building. In this solution, the spring stiffness of the spring device remains essentially constant, and the damping frequency cannot be changed without other measures.

[0017] The task was therefore to provide a pendulum damper through which the damper frequency could be easily and variably adjusted while keeping the pendulum length unchanged.

[0018] It has now been found that the problem can be solved by pendulum dampers equipped with relatively short vertical springs as damping units, which have areas with different spring stiffnesses and a progressive or non-linear overall spring characteristic.

[0019] The subject of the invention is therefore a vibration damper for tall, slender structures and installations, which essentially comprises a pendulum with an absorber mass and a spring device, wherein the spring device comprises one or more vertical springs and is mounted below the absorber mass in such a way that its total spring force acts essentially in the vertical direction, and the absorber mass is connected via the spring device, directly or indirectly, to a fastening point in the installation or in the structure below the vibration damper.According to the invention, the spring device comprises either (i) a vertical spring which has at least two spring sections with different spring stiffnesses distributed along its length with a non-linear or progressive overall spring characteristic, or (ii) two vertical springs which are connected in series or in parallel and have different spring stiffnesses with a non-linear or progressive overall spring characteristic.

[0020] In a preferred embodiment of the invention, the spring device has a first spring section with a first defined spring stiffness and a second spring section with a second defined spring stiffness that differs from the first spring stiffness. According to the invention, the first spring stiffness is in a range < 200 N / mm, preferably < 150 N / mm or < 100 N / mm, for example between 3 and 200 N / mm, preferably between 30 and 150 N / mm, while the second spring stiffness is in a range > 200 N / mm, preferably > 500 N / mm or > 1000 N / mm, for example between 200 and 3000 N / mm, preferably between 500 and 1500 N / mm.

[0021] The spring device according to the invention comprises one or more substantially vertical or vertically acting springs, which can be used as compression and / or tension springs. According to the invention, "substantially vertical" means the vertical orientation or action of the spring, including a deviation of a maximum of 30°. Accordingly, a "vertical spring" is understood to be a spring which is "substantially vertical".

[0022] If the spring device of the pendulum damper according to the invention comprises only a vertical spring, the different spring stiffnesses are perceived by different regions along the spring (7), so that the spring as a whole has a progressive spring characteristic curve. This makes it possible for a soft spring to act during normal operation and for a stiff spring to prevent the damper mass (3) from deflecting during extreme events. This can be achieved, for example, by different windings (density, diameter) or by different materials or different thicknesses of the spring wire. By appropriately designing the spring, it is also possible for the spring regions within the spring to block one after the other, which causes the spring stiffness to increase above the damper amplitude.

[0023] In another embodiment of the invention, the spring device comprises two or more, for example, two, three, four, five, or six vertical springs, whereby these two, three, four, five, six, or more vertical springs can be connected in series or in parallel. Combinations of series and parallel connections are also possible in principle. Here, too, the progression of the spring characteristic can be influenced by influencing certain springs, which can also be designed as tension or compression springs.

[0024] In another embodiment of the invention, several vertical springs can act in parallel. The frequency can be further / also changed by removing / adding vertical springs. A combination of horizontal and vertical springs is also conceivable, as is the replacement of individual springs in such a configuration with corresponding weights, which ultimately increases the frequency, or decreases it when the weight is removed.

[0025] As a rule, these different vertical springs or groups of vertical springs have a defined spring stiffness that differs from the other vertical springs or groups of vertical springs, so that a desired larger or smaller spring stiffness range adapted to the conditions of the system to be damped can be covered, thereby enabling a variable progressive spring characteristic of the overall spring device to be set.

[0026] The invention relates in particular to a corresponding vibration damper having at least two vertical springs of different spring stiffness, wherein the first vertical spring has a spring stiffness of > 3N / mm to < 200N / mm, preferably 50 to 150N / mm and the second vertical spring has a spring stiffness of > 200N / mm to < 3,000N / mm, preferably 300 to 1500 N / mm.

[0027] As already explained above, it is desirable to keep the swing of the pendulum as small as possible across the entire range when vibrations occur in the system. This is particularly sensible due to space constraints in the usually very narrow towers of a wind turbine or other tall structure. This means that the distance between the pendulum mass, to which the spring device is attached on one side, either directly or via a piece of rope, rod, or pole, and the attachment point, which is located in the system below the pendulum damper and below the spring device and which in turn is connected to the other end of the spring device, either directly or via a piece of rope, rod, or pole, should not be greater than 5 or 6 m for medium to large systems, preferably < 3 m, in particular < 2 m, for example 0.5 m to 5.0 m, preferably 1.0 to 3.0 m.

[0028] According to the invention, the use of vertical springs instead of horizontal springs influences the damper frequency. In variant 3 ( Fig. 3 ) these horizontal springs (4) are replaced by one or more vertical springs (7).

[0029] The physical relationship for a point mass can be described as follows: f = 1 2 ∗ π ∗ m ∗ g + F F ∗ 1 + l 1 l 3 m ∗ l 1 g→ Gravitational constant [m / s^2] I1→ Pendulum length (2) [m] I3→ Length of attachment point rope (5) and damper mass (3) [m] FF → Preload force vertical spring (7) [N / m] m→ Damper mass (3) [kg]

[0030] It is evident that the damper frequency can now be adjusted via several parameters. In this configuration, the damper frequency can be influenced by the vertical preload force and not by the spring stiffness of the vertical spring (7). This has the advantage that an entire frequency range can be covered with one vertical spring (7), and unlike the prior art, the spring does not need to be replaced with one of a different spring stiffness. This phenomenon is familiar from everyday use with a guitar string. If the preload force is increased, the pitch / frequency is higher. The spring stiffness of the string remains constant.

[0031] Furthermore, the dynamic displacement of the vertical spring (7) is smaller compared to variant 2, given the same displacement of the damper mass (3). This allows for a more durable design of the spring. The longer the dimension I3, the smaller the dynamic change in length of the vertical spring (7) relative to the movement of the damper mass (3). The longer the dimension I3, the less influence the vertical spring (7) has on the damper frequency. This effect can be used to advantage by shortening the dimension I3 to the dimension I3*, similar to a guitar string (variant 4). Fig. 4 ). This significantly increases the damper frequency while maintaining the same preload force of the vertical spring. This reduction can be achieved by a stop ring (6), which can be moved vertically or is fixed in a fixed position. In the latter case, this stop ring (6) represents the fixed stop point of the spring.

[0032] In a further embodiment of the invention, the damper according to the invention has a movable or permanently mountable stop or fastening device between the lower end of the spring device and the fastening point on the system, whereby the distance between the fastening point and the spring device can be shortened or lengthened, so that the frequency of the damper can be varied due to the resulting expansion or compression of the spring device. As already described above, a significantly higher damper frequency is required during the installation phase of the wind turbine. This can be achieved according to variant 4 by shortening to dimension I3*. Once the system has been completely erected, a significantly lower damper frequency is required. To meet this requirement, the stop ring (6) is removed or moved downwards. The damper frequency drops because dimension I3 and not I3* now determines the damper frequency.The damper frequency can now be fine-tuned by increasing or decreasing the preload of the vertical spring (7). It is important to ensure that the vertical spring (7) is positioned above the stop ring (6). If the damper mass (3) moves in this configuration, relative movement between the cable (8) and the stop ring (6) is prevented. Conversely, the damper frequency can be increased by pushing the stop ring upwards or lowering it.

[0033] If such or a similar damper is installed in a wind turbine, external influences (e.g., emergency shutdown, gusts, shutdown procedures) can result in large amplitudes of the damper mass (3). To keep the oscillation path of the damper mass (3) short in these situations (which may be necessary to prevent the pendulum from striking the tower wall), the dimension I3* should be chosen to be short (e.g., between 0.3 m and 6 m). This results in variant 5 ( Fig. 5) as follows: If, in combination with the short length of I3*, a vertical spring (7) with a high spring stiffness is installed, this results in significantly smaller deflection paths (Y) of the absorber mass (3) compared to variant 3 (deflected) with lower spring stiffness and larger I3. The smaller the dimension I3* is selected, the greater the deflection angle (A2) of the vertical spring (7) becomes, with the same deflection path (Y) of the absorber mass (3). This results in a greater diagonal pull of the spring, which counteracts the movement of the absorber mass (3) and limits the absorber mass in its amplitudes during operation and extreme events.

[0034] Variant 5 results in a greater change in length (delta X2) of the vertical spring (7) compared to variant 3 (displaced), for the same displacement (Y). The resulting increase in spring force is calculated as follows: Federkraftzunahme = C ∗ delta X C→ Spring stiffness of spring (7) delta X→ Change in length of spring (7) during deflection of the damper mass (3)

[0035] The formula shows that in variant 5 the increase in spring force is greater than in variant 3 (displaced).

[0036] If a vertical spring (7) with high spring stiffness is installed in a corresponding pendulum damper, the spring force increases significantly above the target level even at small damper amplitudes. According to equation 3, it is clear that this will also significantly increase the damper frequency, which in turn has a negative impact on the damper's effectiveness.

[0037] This problem can be solved by calculating a spring force curve of the vertical spring (7) over the damper amplitude according to Fig. 6should be aimed for. This can be achieved according to the invention by a vertical spring device that can have a progressive or non-linear spring characteristic curve over the damper deflection.

[0038] A distinction is made between "resonance excitation" and "operation / extreme event" conditions. A passive damper (as described here) can only be effective under harmonic force excitation. This harmonic force excitation only occurs during "resonance excitation." During operation or extreme events, however, stochastic force excitation with large damper amplitudes is present. A damping effect is generally not achieved under these system conditions with the passive damper described here. The requirement is rather to keep the damper amplitudes small during operation / extreme events and to ensure a damping effect only during resonance excitation (small damper amplitudes).

[0039] The spring stiffness C1 of the vertical spring (7) is low in the resonance range. If the damper amplitudes increase during operation or extreme events, the damper enters the range of high spring stiffness C2. The restoring forces of the vertical spring (7) thus increase significantly, which considerably reduces the damper amplitudes in these system conditions. This is also seen in combination with the short vertical spring (7) from variant 5, which further increases the restoring component.

[0040] By combining a relatively short (0.3 m - 3 m) vertical spring device with a progressive spring characteristic, a frequency- and amplitude-variable pendulum damper can be provided according to the invention. This damper can be used in extreme conditions, normal conditions, and conditions such as those encountered during the construction, modification, or dismantling of a vibration-sensitive system or structure. This allows the pendulum damper to be built larger within the tower without the risk of collisions with the tower or building walls or the fixtures located therein. Furthermore, an additional stop can be omitted, as the damper amplitudes are generally smaller.

[0041] In a further embodiment, the vibration damper according to the invention additionally has a mechanical or hydraulic, mobile or fixedly mounted device for changing and adjusting the preload of the spring device by subjecting the spring device or parts thereof to compressive or tensile loads.

[0042] The invention therefore also relates to a corresponding vibration damper in which the distance between the mounting point and the spring assembly can be shortened and lengthened again by means of a movable or fixedly mounted stop or mounting device, so that the frequency of the damper can be varied or adapted by the resulting extension or compression of the spring assembly. The invention further relates to a vibration damper that additionally comprises a mechanical or hydraulic, mobile or fixedly mounted device for changing and adjusting the preload of the spring assembly.

[0043] According to the prior art, the pendulum length (2) in a pendulum damper is realized by cables. This allows the damper to twist torsionally in the cables. The vertical spring (7) and also the dampers would have to follow this twist, which would technically lead to malfunctions. In an alternative embodiment according to the invention, the pendulum length (2) can be replaced by a torsionally rigid element (tube). At the same time, the upper suspension point of the damper (1) must be implemented by a variable joint, for example a cardan joint. This prevents torsional twisting in the event of a possible movement of the damper mass (3) by 360° ( Fig. 7). The subject of the invention is therefore a corresponding vibration damper in which the pendulum consists of a rod or tube, at the lower end of which the damper mass is attached, which has a fastening point for the spring device, and at the upper end of which a joint is attached that ensures the free movement of the pendulum through 360°, so that torsional twisting is impossible.

[0044] Depending on the nature of the system, tower, or structure, the upper suspension point of the damper can be located at the respective upper end of the tower, system, or structure, or at any position in the upper half or upper third. It is also possible for the damper mass (3) to be suspended from one or more damper (1) suspension points. It is also conceivable to install a universal joint directly on the damper mass (3) and the damper (1) connection point, with a torsionally rigid element installed between them.

[0045] As already explained several times, the dampers according to the invention are particularly suitable for installation in wind turbines. The invention therefore also relates to a wind turbine which incorporates a vibration damper according to the invention.

[0046] The subject matter of the invention is in particular the use of the damper according to the invention for preventing and reducing vibration events during the construction and operation of such a wind turbine or other vibration-sensitive structures, but also for reducing and avoiding large damper amplitudes in the event of vibration-related extreme events and resonance-related vibrations of the system or structure in the normal state or normal operation.

[0047] The following items are referenced in the description, illustrations, and claims: 1 Suspension point absorber 2 Pendulum length 3 absorber mass 4 horizontal spring 5 Rope attachment point 6 stop ring 7 vertical spring 8 Rope

Claims

1. Vibration damper for tall, slender structures and installations, the damper substantially comprising a pendulum having a damper mass, and a spring device, wherein (i) the spring device comprises one or more vertical springs and is mounted below the damper mass such that its total spring force acts substantially in the vertical direction, and (ii) the damper mass is connected via the spring device, directly or indirectly, to an attachment point in the installation or in the structure below the vibration damper, characterized in that the spring device comprises a vertical spring which, distributed over its length, has at least two spring regions having a different spring stiffness for a non-linear or progressive overall spring characteristic.

2. Vibration damper according to claim 1, characterized in that the vertical spring has a first spring region having a spring stiffness of < 200 N / mm and a second spring region having a spring stiffness of > 200 N / mm.

3. Vibration damper for tall, slender structures and installations, the damper substantially comprising a pendulum having a damper mass, and a spring device, wherein (i) the spring device comprises one or more vertical springs and is mounted below the damper mass such that its total spring force acts substantially in the vertical direction, and (ii) the damper mass is connected via the spring device, directly or indirectly, to an attachment point in the installation or in the structure below the vibration damper, characterized in that the spring device comprises at least two vertical springs which are connected to one another in series or in parallel and have different spring stiffnesses for a non-linear or progressive overall spring characteristic.

4. Vibration damper according to claim 3, characterized in that the first vertical spring has a spring stiffness of < 200 N / mm, and the second vertical spring has a spring stiffness of > 200 N / mm.

5. Vibration damper according to claim 4, characterized in that the first vertical spring has a spring stiffness of > 3 N / mm to < 200 N / mm and the second vertical spring has a spring stiffness of > 200 N / mm to < 3,000 N / mm.

6. Vibration damper according to one of claims 1 - 5, characterized in that the different spring stiffness of the at least one vertical spring is caused by different windings of the spring.

7. Vibration damper according to one of claims 1 - 6, characterized in that the distance between the damper mass and the attachment point is 0.5 m to 5.0 m.

8. Vibration damper according to one of claims 1 - 7, characterized in that the distance between the attachment point and the spring device can be shortened and lengthened again by means of a movable or fixed stop or attachment device, so that the frequency of the damper can be varied by the resulting stretching or compression of the spring device.

9. Vibration damper according to one of claims 1 - 8, characterized in that it additionally comprises a mechanical or hydraulic, movable or fixed device for changing and adjusting the preloading of the spring device.

10. Vibration damper according to one of claims 1 - 9, characterized in that the pendulum consists of a rod or tube, at the lower end of which the damper mass is mounted, the damper mass having an attachment point for the spring device, and at the upper end of which a joint is mounted, the joint ensuring free movement of the pendulum without torsional twisting being possible.

11. Wind turbine, characterized in that it has a vibration damper according to one of claims 1 - 10.

12. Use of a vibration damper according to one of claims 1 - 10 for preventing and reducing vibration events during the construction and operation of a wind turbine.

13. Use of a vibration damper according to one of claims 1 - 10 for reducing and avoiding large damper amplitudes in the case of extreme vibration-related events and resonance-related vibrations of the installation or the structure in the normal state or in normal operation.