US3174589A

US3174589A - Slender structure

Info

Publication number: US3174589A
Application number: US106772A
Authority: US
Inventors: Chen Yian-Nian
Original assignee: Sulzer AG
Current assignee: Sulzer AG
Priority date: 1960-05-06
Filing date: 1961-05-01
Publication date: 1965-03-23
Anticipated expiration: 1982-03-23
Also published as: CH380354A; GB950983A; ES259287A1; BE603473A

Description

March 23, 1965 YlAN-NIAN CHEN SLENDER STRUCTURE Filed May 1 1961 2 Sheets-Sheet l Jn-venfor: Y/n/v-N/A/v CHE/V March 23, 1965 YlAN-NIAN CHEN $474,539

SLENDER STRUCTURE 7 Filed May 1, 1961 2 Sheets-Sheet 2 Jnveniar:

United States Patent Ofilice 3,l?4,589 Patented Mar. 23, 1965 3,174,539 SLENDER STRUCTURE Yian-Nian Chen, Winterthur, Switzerland, assignor to Sulzer Freres, S.A., Winterthur, Switzerland, a corporation of Switzerland Filed May 1, 1961, Ser. No. 1%,772 Claims priority, application Switzerland, May 6, 1960, 5, 170/ 6d 9 Claims. (Cl. 18923) The invention relates to slender structures subjected to repeated bending, such as, for example, chimneys, towers, masts and the like, and relates more particularly to novel damping means for said structures.

Chimneys and other slender structures, in addition to withstanding the static loading caused by wind pressure in the plane of wind movement, also have to deal with those periodic forces which are produced by eddy cavitation, and are operative transversely of the wind direction thus causing the structure to oscillate. The oscillations produced become critical when the firequency of eddy cavitations reaches the natural frequency or" the structure. In masonry chimneys and riveted metal plate chimneys the internal damping is usually of sufiicient magnitude so that the oscillatory energy of relatively small oscillatory amplitudes is readily absorbed. However, this is generally not the case with Welded sheet metal chimneys. These structures require special measures to ensure that dangerous resonance cannot occur. The known means of achieving this object are to alter the natural frequency of the chimney and also to release the strain by bracing the chimney with wire ropes. The disadvantage of varying the natural frequency of the chimney is that chimney size and design often cannot be the most suitable for the particular purpose required and, for instance, uneconomically large thicknesses of sheet must be used just to alter the natural frequency. Where dangerous oscillations occur in existing chimneys, the method cannot be used at all. The second method -bracing by wire ropes-is expensive and is aesthetically unsatisfactory. Accordingly, it is an important object of this invention to provide means to reduce the oscillations of structures of the foregoing type without incurring the disadvantages inherent in the known expedients, said means comprising at least one dynamic oscillation damper. Other objects will appear from the following detailed description.

The invention will be described with reference to embodiments illustrated in the drawings wherein:

FIG. 1 illustrates a chimney according to the invention incorporating an oscillation damper of this invention.

FIG. 2 is a section through the damper shown in FIG. 1 on a somewhat enlarged scale.

FIG. 3 is a plan view of the damper mass shown in FIG. 2.

FIG. 4 is a side elevation showing the articulation of the several elements comprising the damper mass shown in FIG. 2.

FIG. 5 is a section through another embodiment of the oscillation damper of this invention.

FIG. 6 illustrates a detail of FIG. 5.

FIGS. 7-12 are sectional views of other embodiments of the oscillation dampers of this invention.

Referring to FIG. 1, the chimney 1 made of steel plate carries the oscillation damper structure 2 at its top end. FIG. 2 is a sectional view of the oscillation damper structure 2 and also includes the top end of the chimney. The chimney 1 comprises an outer generated surface 10 and a lining 11 with heat insulation 12 being therebetween. The surface It) bears brackets 13 to which an annular base plate 14 is secured. The damper structure is closed externally by an outer cylindrical cover 15. A ring 16 which constitutes the damping mass rests freely on the plate 14 and this ring includes buffer elements 17 and 18. The buffer elements 17 and 18 are disposed in bores 20 extending radially of the ring 16 and are normally pressed apart from one another by a spring 19. The bores 20 are closed by cover plates 21 and the whole damper assembly is protected against weathering by a cover plate 22. When the chimney starts to oscillate, for instance, because of eddy cavitation caused by wind, the damping mass 16 starts to slide on the base 14 once the oscillation exceeds a critical amplitude, the amount of energy being absorbed being equal to the product of the friction and the relative movement of the mass. The function of the buffer element pins 17 and i8 is to keep the damping mass at a distance from the closing walls as well as to intercept any impact of the damping mass against such walls. Conveniently, to ensure very uniform distribution of the friction forces over the periphery of the damping mass, the mass is articulated, as can be seen in FIGS. 3 and 4, by being formed from various sections 24 interconnected by means of pins 26 loosely fitting in apertures 25. The various sections 24 can move relatively to one another vertically and each section 24 engages and rests upon the base 14 by its own weight only. FIG. 3 illustrates an alternative method for the radial springing of the damping mass, using instead of the radial spring-loaded buffer elements 17 and 18, flat spring strips 27 which are secured by screws 28 to the associated sections 24. In the oscillation damper shown in FIG. 2, the base does not completely close the chamber surrounding the damping mass, gaps 29 being left through which abraded particles can drop.

Another embodiment of the oscillation damper of this invention is shown in FIG. 5. in this case the damping mass takes the form of a rigid ring 31 over which short ring segmental damping elements 32, which are of U- shaped cross-section, are loosely placed. The base over which the damping mass slides is in the form of an open grating 33. To prevent the damping mass from jamming, the damping elements 32 are formed with bevelled edges 35. In this embodiment the damping elements are prevented from striking the outer wall by the use of corrugated steel strips 34 (FIG. 6).

FIG. 7 illustrates an oscillation damper in which damping is provided by mechanical friction and by liquid friction. Disposed in a casing 40 secured to the chimney is an annular damping member 41; the inner chamber of the casing all is filled either Wholly or partly with a liquid, such as oil. When the damping mass 41 and the casing 4t move relatively to one another as the chimney oscillates, hydraulic forces are produced by the liquid filling, and not just mechanical friction as in the example hereinbefore described, the hydraulic forces thus created helping to dampen the oscillatory motion. Advantageously, the damping element 41 is formed at top and bottom with recesses 42 which reduce the contact surface of the casing, thus ensuring that, if the oil in the casing 49 becomes gummy, the adhesion between the element 41 and the casing remains low.

FIG. 8 illustrates an oscillation damper operating purely by liquid friction. An annular vessel 50 secured to the outer chimney surface 10 comprises radial perforate metal plates 51, and the sectors bounded by the plates 51 are filled with a porous loose fill, such as steel swarf. The vessel 50 is about half filled with a liquid forming the damping mass. As liquid there is used preferably an oil having a fiat viscosity-temperature pattern and a low coagulation point, such as silicone oil. The advantage of the embodiment shown in FIG. 8 is that damping is provided at very reduced oscillations. The liquid in the vessel can be loaded with suspended particles; if required, relatively coarse and non-suspendable particles, such as sand, stones, metal scrap and so on, can be added to the liquid and can move together therewith as the chimney oscillates. If such a filling is used in the vessel 50, the plates 51 and the porous loose fill can be omitted.

Referring to the embodiment shown in FIG. 9, the oscillation damper is devoid of any special damping mass; instead, some of the chimney is used as damping mass. As a rule, in chimneys consisting of an outer covering and a lining, the natural frequency of the outer covering is different from and usually higher than the natural frequency of the chimney lining which is loaded with the insulation layer. In the embodiment shown in FIG. 9, sheet metal rings 51 are welded into the outer chimney surface It), and the chimney lining bears against the rings 61, with reduced clearance, by way of sheet metal rings 62. As the chimney oscillates, there is friction between the

rings

61 and 62 so that oscillation damping is provided. The chimney lining 11 together with the insulation layer 12 is used as damping mass for the other part.

FIG. illustrates a variant of the damper shown in FIG. 9. Referring to FIG. 10, brackets 70 are secured to the lining 11, and a number of alternately arranged

rings

71, 72 rest on the brackets 70. The rings 71 have reduced clearance relatively to the lining 11 and considerable clearance relatively to the chimney outer surface 19. Conversely, the rings 72 have reduced clearance relatively to the surface 10 and considerable clearance relatively to the lining 11. When the chimney oscillates, the rings 71 move together with the lining 11, while the rings 72 move together with the surface 10. There is, therefore, friction between the rings '71 and 72 so that oscillation of the chimney is dampened.

Referring to FIG. ll, oscillation dampers 80 are secured to a chimney outer surface. The dampers take the form of cylinders 81 in which pistons 82 move freely. The cylinders 81 are wholly or partly filled with a liquid, for instance, an oil. The cylinders 81 comprise springs 83 which limit the movement of the pistons $2. When the chimney 10 oscillates, the pistons 82 move relatively to the cylinders 81 because of their inertia; liquid flows through the gap between the piston and the cylinder, leading to a friction which helps to dampen the oscillations. Of course, the piston 82 or the cylinder 81 can be formed with ducts interconnecting the two chambers of each cylinder, and such ducts can be provided, in manner known per se, with valves or flaps which inhibit or assist liquid flow in one or the other direction. The advantage of the dampers 80 shown in FIG. 11 is that they can be of unitary construction and retained on bearings and can be provided to any required number. Two dampers in which the damping mass in one damper moves perpendicularly to the damping mass in the other can be used, in the manner shown in FIG. 11, although more dampers can be used and can be, for instance, uniformly distributed around the chimney axis.

FIG. 12 illustrates a variant of the damper shown in FIG. 11, the piston 82 being replaced by a ball 83. This step helps to reduce very considerably the possible disturbing mechanical friction between the cylinder 81 and the damping mass.

I claim:

1. In a relatively elongated vertical structure fixed at the lower end and free to oscillate at the upper end on being subjected to a bending stress, the combination with the free upper end of said structure of oscillation damping means, said damping means comprising a mass supported on and in mechanical and dry frictional engagement with the free end of said structure, said mass being free to move relative to said structure when the latter oscillates from the vertical thereby to convert at least part of the energy of said oscillation to dry mechanical friction and effect the desired damping.

2. In a relatively elongated vertical structure fixed at the lower end and free to oscillate at the upper end on being subjected to a bending stress, the combination with the free upper end of said structure of oscillation damping means, said damping means comprising an annular mass supported on and in mechanical and dry frictional engagement with a bracket integral with the free end of said structure, said annular mass being free to move relative to said bracket and said structure when the latter oscillates from the vertical thereby to convert at least part of the energy of said oscillation to dry mechanical friction and effect the desired damping.

3. In a damped structure in accordance with claim 2, the combination of spring-loaded impact means cooperating with said annular mass, said impact means being adapted to absorb the radially directed impact energy of said freely movable annular mass when coming in contact with the elongated structure on which it is supported as said structure oscillates.

4. A damped structure in accordance with claim 2 wherein the annular mass comprises a plurality of articu lated segments joined together.

5. In a relatively elongated structure comprising an inner shell and an outer shell which are fixed at one end and free to oscillate at the other end on being subjected to a bending stress, the combination with the free end of said structure of oscillation damping means, said damping means comprising a first mass supported on the inside of the outer shell and another mass supported by said first mass, said mass es being in frictional engagement with but free to move relative to each other when said structure oscillates thereby to convert at least part of the energy of said oscillation to friction and effect the desired damping.

6. In an oblong structure comprising an inner shell and an outer shell and a space therebetween, said shells being fixed at one end and free to oscillate at the other end on being subjected to a bending stress, the combination with the free end of said structure of oscillation damp ing means, said damping means being placed in said space and comprising:

a first mass supported by one of said shells,

a second mass resting on said first mass,

said means being in frictional engagement with but free to move relative to each other when said structure oscillates thereby to convert at least part of the energy of said oscillation to friction and effect the desired damping.

7. In an oblong structure as defined in claim 6 and wherein said first mass is supported on the outside of the inner shell.

8. In an oblong structure as defined in claim 6 and wherein said masses are annular.

9. In anoblong structure comprising an inner shell and an outer shell and a space therebetween, said shells being fixed at one end and free to oscillate at the other end on being subjected to a bending stress, the combination with the free end of said structure of oscillation damping means, said damping means being placed in said space and comprising in alternating sequence the combination of at least one annular mass supported on the outto side of the inner shell and in peripheral contact with the 5 6 inside of the outer shell and a second annular mass rest- References Cited in the file of this patent ing thereon whose inside is in peripheral contact with UNITED STATES PATENTS the outside of the inner shell, said masses being in frictional engagement with each other but free to move rela- 2,514,140 Connor I 3 1950 tive to each other when said structure oscillates from the 5 2,635,398 sllverman P 21, 1953 vertical thereby to convert at least part of the energy of said oscillation to friction and to effect the desired damp- FOREIGN PATENTS i 446,532 Canada Feb. 3, 1948

Claims

1. IN A RELATIVELY ELONGATED VERTICAL STRUCTURE FIXED AT THE LOWER END AND FREE TO OSCILLATE AT THE UPPER END ON BEING SUBJECTED TO A BENDING STRESS, THE COMBINATION WITH THE FREE UPPPER END OF SAID STRUCTURE OF OSCILLATION DAMPING MEANS,SAID DAMPING MEANS COMPRISING A MASS SUPPORTED ON AND IN MECHANICAL AND DRY FRICTIONAL ENGAGEMENT WITH THE FREE END OF SAID STRUCTURE, SAID MASS BEING FREE TO MOVE RELATIVE TO SAID STRUCTURE WHEN THE LATTER OSCILLATES FROM THE VERTICAL THEREBY TO CONVERT AT LEAST PART OF THE ENERGY OF SAID OSCILLATION TO DRY MECHANICAL FRICTION AND EFFECT THE DESIRED DAMPING.