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Title:
PENDULUM TYPE LIQUID COLUMN DAMPER (PLCD) FOR CONTROLLING THE VIBRATION OF A BUILDING STRUCTURE
Document Type and Number:
WIPO Patent Application WO/2014/046549
Kind Code:
A1
Abstract:
The present invention provides a passive damping device (14) comprising an U- tube type like container (1) with to upwardly pointing arms (6) and one horizontal arm (5), partly filled with liquid and fixed to a holding structure (2) which is hingedly attached to a building structure (16), so that it can move like a pendulum relative to the building structure (16). The source of damping in this device is due to the sloshing motion of the liquid in the U-tube container (1) as it passes through an orifice (4) arranged within the bottom of the horizontal arm. (5)

Inventors:
SARKAR, Arunjyoti (Esterbakken 5, Tananger, NO-4056, NO)
GUDMESTAD, Ove Tobias (Søylandsvegen 61, Nærbø, NO-4365, NO)
Application Number:
NO2013/050159
Publication Date:
March 27, 2014
Filing Date:
September 23, 2013
Export Citation:
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Assignee:
UNIVERSITETET I STAVANGER (N Stavanger, O-4036, NO)
International Classes:
E04H9/02; B63B39/03; E04B1/98; F16F7/10; F16F15/023
Foreign References:
JPH06264647A1994-09-20
JPH06264646A1994-09-20
US0970368A1910-09-13
TWM272820U2005-08-11
EP1677003A22006-07-05
Attorney, Agent or Firm:
PROTECTOR IP CONSULTANTS AS (Oscarsgate 20, Oslo, NO-0352, NO)
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Claims:
Claims

1.

A damping device for dampening movements of a building structure, such as movements induced by earthquake, wind or waves, characterized in that it comprises a U-shaped tube (1 ) with the free ends (10) of the U-shaped tube (1 ) extending upwards, the U-shaped tube (1 ) being partially filled with liquid, and the U-shaped tube (1 ) is hingedly attached at a suspension point (0) to the building structure, so that it can move like a pendulum relative to the building structure. 2.

A damping device according to claim 1 , wherein the damping device is a compound pendulum whose natural frequency is a function of the rotational moment of inertia about the hinge at the suspension point (0) of the U-shaped tube (1 ) and the liquid used in the U-shaped tube (1 ) being selected to optimize the damping effect.

3.

A damping device according to claims 1 and 2, wherein the tube of the U-shaped tube (1 ) has varying diameter.

4.

A damping device according to claim 3, wherein the diameter is increasing towards the free ends (10).

5.

A damping device according to claim 1 and 2, wherein the free ends (10) of the U-shaped tube (1 ) are at the ends of upwardly pointing arms (6), the distance between which is increasing towards the free ends (10).

6.

A damping device according to claims 1 -5, wherein the liquid in the tube (1 ) being water. 7.

A damping device as described in some or all of the previous claims, wherein one or more orifices (4) are arranged within the tube (1 ) to restrict the flow of liquid during the pendulum motion. 8.

A damping device as described in some or all of the previous claims, wherein the damping device is a passive damping device.

9.

Method for dampening movements of a building structure, such as movements induced by earthquake, wind or waves, characterized in that a U-shaped tube (1 ) is suspended in a suspension point (0) within the building structure with the free ends (10) of the U-shaped tube (1 ) extending upwards, partially filling the U-shaped tube (1 ) with liquid, allowing the U-shaped tube (1 ) to oscillate like a pendulum relative to the building structure when motion is induced to the building structure, optimizing the flow of liquid back and forth within the tube so that the flow of liquid is in counter-phase with the pendulum motion.

10.

Method according to claim 9, wherein the flow of liquid is controlled by more orifices (4) within the U-shaped tube (1 ). Method according to claims 9 and 10, wherein the flow of liquid is controlled by the viscosity of the liquid. 12 .

Method according to claims 9-1 1 , wherein the oscillating frequency is tuned by varying the distance between upwardly pointing parts (6) of the U-shaped tube

(1 ).

Description:
Pendulum type liquid column damper (PLCD) for controlling the vibration of a building structure.

Field of the invention

The present invention relates to a damping device, more specifically a pendulum type liquid column damper (PLCD) intended to be attached to a primary structure e.g a building structure as a compound pendulum to control vibration in the structure. This is essentially a passive damping device whose configuration is derived as a hybrid of a pendulum type tuned mass damper (TMD) and tuned liquid column damper (TLCD).

Background of the invention and prior art

A damper is an active or a passive control device that helps to suppress the vibration of a structure excited by dynamic forces by dissipating energy from it. The role of such devices has gained considerable importance these days as structures in various applications are now becoming more flexible and lightly damped. An example of such a structure is an offshore wind turbine (OVVT) in shallow to intermediate water depth (~up to 50 m). The preliminary structural design of an OVVT is carried out in such a way that the natural frequency of the whole structure remains away from the peak frequency of the predominant environmental load and away from the frequency of the blades passing the tower. This general approach appears to result in large structural dimensions and it is expected that using a suitable damping device can help to optimize the design of such structures in the future.

Due to several practical advantages, the passive control devices are preferred over the active devices. Among the passive control devices, the tuned mass dampers (TMDs) and the tuned liquid dampers (TLDs) are commonly used.

In a tuned mass damper (TMD), a mass is attached to the structure with a spring, which tunes its motion with the natural frequency of the structure, and with a dashpot which dissipates energy from the system as the mass moves. The pendulum type TMDs are simple in form and have been used in many tall structures. Design of a suitable dashpot is essential for a TMD. Publication CN102864853 shows a tuned mass damper for performing vibration attenuation on a tall tower. The damper is arranged on the top of the upper part of a tower body, and comprises quality blocks, damping systems and spring systems wherein the quality blocks are respectively connected with the damping systems and the spring systems and can move by virtue of suspension or supporting.

TMDs have been used in many tall and slender structures, such as, buildings, chimneys etc. They provide excellent control performance. Commonly, an external source required for damping the motion of the mass needs periodic maintenance. The TMD is an excellent option for building structures, but if the location is inaccessible, this type of damper may not be a good choice.

In a tuned liquid damper (TLCD), a container partly filled with liquid is attached to the structure and the sloshing frequency of the liquid is tuned to the natural frequency of the structure. When the structure is excited, the liquid passes through an adjustable orifice which is located centrally in the tube, and thus dissipates energy from the system. Publication CN201843727 shows a Tuned Liquid Column Damper (TLCD)-based vibration control system for a wind power generation tower, which comprises a base, a tower frame, an engine room, a hub, paddle and a TLCD. The TLCD comprises a U-shaped container, a damping clapboard and viscous liquid. The damping clapboard is arranged in the center of the U-shaped container. The bottom surface of the U-shaped container is fixedly connected with the bottom surface of the engine room.

TLCDs have been used widely in tall building structures. Since the source of damping is the sloshing motion of the liquid, maintenance requirement is less demanding compared to the TMDs. It is reported in various research papers that such dampers can be as effective as the TMDs. But these are not suitable for stiff structures where the frequency is high which cannot excite the liquid sufficiently. A large number of papers have been published by various researchers on the effectiveness and the optimization of the TMDs and the TLCDs. The control performance of TMDs for instance is better than that of a liquid type damper. On a base isolated structure, a TMD can also achieve 15-25% reduction in the displacement demand.

On the other hand it is reported that a traditional TLCD can reduce the peak response of an offshore wind turbine by more than 50 % and also can improve its fatigue life. They are self-contained passive devices with little auxiliary equipment or power and have higher volumetric efficiency compared to the pendulum type TMDs.

This aspect opens a possibility to optimize the support structure of an offshore wind turbine which will also be beneficial from an installation point of view. The PLCD is a compound pendulum type mass damper where the source of damping is the motion of the liquid as it passes through an orifice placed at the center of the tube.

The main objective of the present invention is therefore to provide a new damping device which is a U-tube with an adjustable orifice placed at the center of the tube, partly filled with liquid, and attached to a holding structure which can be hinged to a primary structure so that it can oscillate as a compound pendulum. The primary structure is hereinafter called building structure and can for example be structures of wind turbines, tall and slender structures, chimney or other structures where the damping device is suitable.

Summary of the invention

The invention provides a damping device for dampening movements of a building structure, such as movements induced by earthquake, wind or waves, distinctive in that it comprises a U-shaped tube with the free ends of the U- shaped tube extending upwards, the U-shaped tube being partially filled with liquid, and the U-shaped tube is hingedly attached at a suspension point to the building structure, so that it can move like a pendulum relative to the building structure.

The damping device preferably comprises additional features, as defined in dependent claims 2-8.

The invention also provides a method for dampening movements of a building structure, such as movements induced by earthquake, wind or waves, distinctive in that a U-shaped tube is suspended in a suspension point within the building structure with the free ends of the U-shaped tube extending upwards, partially filling the U-shaped tube with liquid, allowing the U-shaped tube to oscillate like a pendulum relative to the building structure when motion is induced to the building structure, optimizing the flow of liquid back and forth within the tube so that the flow of liquid is in counter-phase with the pendulum motion.

The invention preferably provides additional methods, as defined in dependent claims 10-12.

The pendulum type liquid column, subsequently called PLCD, typically consists of a U-tube type container with orifice in the middle of the horizontal arm, partly filled with liquid, and a holding structure supporting the U-tube. The holding structure can be attached to a building structure by a hinge which allows the U- tube to vibrate as a compound pendulum. Since the natural frequency of a compound pendulum is a function of the polar moment of inertia about the point of suspension (hinge), it gives some freedom to the designer to use it at places where available space is limited. The inertia can for instance be adjusted by selecting the length of the horizontal or the upwardly pointing arms of the U-tube, the diameter of the U-tube, the diameter of the upwardly pointing arms and the amount of water. The adjusting of arms is also referred to as to tune the natural frequency.

The source of damping in this device is due to the sloshing motion of the liquid in the U-tube as it passes through the orifice; hence the maintenance demand lies primarily on the hinge. Since the hinge can be accessible from the primary structure this device will be particularly useful for applications where accessibility is a problem.

The damper is of the passive type is beneficial because no active power source is required.

As described above, the PLCD damper can be used to control the vibration of a flexible structure which might be excited at its natural frequency. The source of damping is the sloshing motion of the liquid as it passes through the orifice, i.e., the maintenance requirement will be small. Only the hinge and the height of the liquid column need proper maintenance. The damper acts as a compound pendulum, hence, it can be suited for applications where available space is somewhat limited. The designer may have freedom to adjust the arms to tune the natural frequency.

Figures

Fig. 1 is illustrating a schematic description of the damper of the invention where the building structure is moving in the direction X-i .

Fig. 2 is illustrating a schematic description of the damper of the invention where the building structure is moving in opposite direction X 2 .

Fig. 3 is illustrating a schematic description of the damping device attached to a building structure.

Fig. 4 is illustrating a schematic diagram of the two circular arcs of the U-tube. Detailed description

Reference is made to Figure 1 , illustrating an embodiment of a passive damping device according to the invention. The damping device 14 comprising a U- tube liquid container 1 i.e. two upwardly pointing arms 6 and a horizontal arm 5 are connected by two circular arcs 9. The arcs are added for practical reasons to fabricate a model and this inclusions, may be useful from an architectural point of view. The upwardly pointing arms 6 are preferably parallel to each other and extending upwards with a free end 10, but can the distance between can also be increasing towards the free ends 10. An orifice 4 is located at the middle of the horizontal arm 5 of the tube, at the inside of the horizontal arm 5. The U- shaped tube 1 is fitted with the holding structure 2 by means of a frame 8 supporting the lower section of the tube 1 . A hinge 3 connects the holding structure 2 to the building structure 16 (fig 3) and allows the damping device 14 to vibrate as a compound pendulum with an angle a between a vertical line 1 1 through the hinge 3 and a central axis 13 from the hinge through the damping device 14. The rotational centre of the damping device 14 is the suspension point 0 (fig 4) which is congruent with the hinge 3. It is possible to use other fixed joints suitable for the purpose instead of a hinge 3.

The U-shaped tube 1 is partially filled with liquid. The peak point of the water in each of the upwardly pointing arms 6 are marked as liquid column 7. The heights of these columns are adjustable according to the embodiment of the invention and will be further described below. The liquid column altitude above the liquid equilibrium line 15 is named ω.

Fig. 2 shows the damping device where the building structure is moving in opposite direction than in figure 1 . In this position the building structure is moving a distance X 2, the damping device rotates an angle a 2 and the altitude of the liquid column is ω 2 .

Fig 3 shows the damping device 14 connected to the building structure 16. The building structure 16 is e.g. comprised of a cantilever beam 17 and a mass M, The figure shows a simple approach to model tower type structures like a chimney, an offshore wind turbine (OTW) etc. The damping device is hinged by a low friction hinge at the suspension point 0 at the bottom of the building structure.

Fig 4 shows the direction of liquid flow in the two circular arcs 9 when the building structure 16 is displaced a distance X from the static position of the structure. In another embodiment of the invention, the U-shaped tube 1 is designed with an increasing distance between the two upwardly pointing arms 6a, 6b of the tube 1 towards the free ends 10. The angle between the vertical arms and the horizontal arm is greater than 90°.

In yet another embodiment of the invention, the upwardly pointing arms 6a, 6b of the U-shaped tube 1 have a conical shape where each of the upwardly pointing arms 6a, 6b has an increasing diameter within the upwardly pointing arms 6a, 6b towards the free end 10.

Since the natural frequency of such a system will be related to the mass moment of inertia of the pendulum, it may provide more freedom to the designer to tune it to the structure ' s targeted natural frequency compared to a conventional pendulum type, TMD. The Damping device can be tuned i.e. by means of different liquid amounts in the tube, different length of the horizontal arm or different lengths of the vertical arms. Other methods for tuning the damper can also be applied.

The damper can be described with three degrees of freedom, which are X, α, ω where X is the translational degree of freedom of the building structure on which the damper is intended to work, a is the angular displacement of the damper and ω is the displacement of the water column from the static position as described above. The building structure 16 can vibrate in a two-dimensional plane at distances and X 2 from the static position. When the structure 16 and the suspension point 0 are moving a distance Xi the damping device 14 beneath the structure is rotating to an angle a-i . At the inside of the U-tube 1 the liquid will flow in the direction of right upwardly pointing arm 6a towards an altitude ω-ι of the liquid column. The orifice 4 at the bottom of the U-shaped tube 1 increases the speed of the liquid due to its narrowed opening. As a result of the Bernoulli equation, the pressure of the liquid will decrease and reduce the altitude oui compared to a situation with no orifice. The orifice 4 can have different openings, the damping ratio increases with increase in the opening. (An orifice opening at 0% means no orifice in the tube i.e. there is none orifice damping).

In the opposite direction the building structure 16 and the suspension point 0 moves a distance X 2 . The damping device rotates around the hinge 3 to and angle a 2 and the liquid moves towards the left upwardly pointing arm 6b to an altitude ω 2 .

The U-shaped tube 1 will oscillate like a pendulum relative to the building structure 16, optimizing the flow of liquid back and forth within the tube 1 so that the flow of liquid is in counter-phase with the pendulum motion.