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Tower: Breaking wind ring of tower anti-vibration measures

Release time:

2022-08-01

Towers: Tall buildings resonate under the influence of wind. Once the vibration damage is serious, the flange will leak, the anchor bolts will be loose, and the heavy ones will be fatigued and damaged, causing accidents. So to prevent resonance.

Towers: Tall buildings resonate under the influence of wind. Once the vibration damage is serious, the flange will leak, the anchor bolts will be loose, and the heavy ones will be fatigued and damaged, causing accidents. So to prevent resonance.

One of the anti-vibration measures is to use a spoiler, such as a windshield

Axial-fin or helical-fin spoilers are installed in the upper 1/3 of the tower height.

The length l of the axial fins is 0.75 -0.9 times the diameter D of the column, and the width b of the fins is 0.069 times D. The number of fins on the same circumference is 4, The angle between them is 90°. The fins on adjacent circumferences are staggered by 30°, and for column equipment with axial fins, the resonance amplitude will be reduced by about 1/2.

When the fin is spiral, the number of its heads is 3, staggered by 120. The pitch t is 5 times the diameter d, and the fin width w is 0.1 times the diameter d, where the diameter refers to the outer diameter of the column, including insulation. Spiral sheets are better than axial fins.

Let's take a look at the anti-vibration structure and windproof ring on the chimney

The windshield is a part on the chimney, in order to avoid or reduce the resonance of the chimney caused by the Karman vortex caused by the airflow, the spiral wound belt or fins are welded on the upper section of the chimney. There are also axial arrangements.

When the fluid flows laterally through the cylinder, vortices are generated alternately on both sides of the back of the cylinder, which form a vortex tail after separation, also known as “Kaman Vortex".

The vortex is generated by the mutual conversion of kinetic energy and pressure energy after the fluid is blocked, and the pressure changes along the circumference of the cylinder and the thickness of the boundary layer. The larger pressure of the fluid outside the boundary layer forces the particles with lower pressure inside the boundary layer to flow in the opposite direction, thereby thickening the boundary layer, forming a vortex, which then separates from the cylinder. As the flow velocity increases, the vortex lengthens and disappears. When the vortex on one side grows and separates, the vortex on the other side is forming and growing, thereby alternately forming two rows of vortex wakes, similar to a "vortex street". The vortices of the Karman vortex street are generated, separated and dissipated at a certain frequency, and the pressure on both sides of the cylinder changes periodically at the same frequency. When the vortex shedding frequency is equal to the natural frequency of a certain mode of the cylinder, the cylinder will vibrate violently, which is an induced vibration. Experiments show that the vortex shedding frequency is related to the outer diameter of the cylinder and the fluid velocity. Under the action of wind load, when the above conditions are met, the tower equipment will also have periodic eddy currents and induce vibration, which may lead to equipment failure and damage in severe cases.

The chimney design should avoid resonance caused by eddy currents. Increasing the stiffness of the chimney or adding a concrete lining can improve the chimney's resistance to vibration. But a more effective method is to weld a helical outer "windshield" to the top of the chimney.

The setting of the windshield should meet the following requirements:

I. Setting conditions:

When the critical wind speed of the chimney is less than 6~7m/s, a windshield should be installed.

When the critical wind speed of the chimney is 7 ~ 13.4 m/s, which is lower than the design wind speed, and it is not economical to change the height, diameter and thickness of the chimney, the windshield ring can also be installed.

b. The chimney shape factor within the windshield circle shall be selected according to the rough surface.

c. Setting position: When the windshield ring needs to be set, it should be set within the range of not less than 1/3 of the height of the chimney from the upper end of the chimney.

d. Type and size of windshield:

a) Staggered vertical plates: the thickness of the vertical plates is not less than 6mm, the length is not more than 1.5m, and the width is 1/10 of the outer diameter of the chimney; the number of vertical plates in each circle is 4, which are evenly distributed along the circumference of the chimney, adjacent circles The risers are staggered by 45°.

b) Spiral plate type: The thickness of the spiral plate is not less than 6mm, and the plate width is 1/10 of the outer diameter of the chimney. There are three spiral plates evenly distributed along the circumference, and the spiral pitch can be 5 times the outer diameter of the chimney.

Jiangsu Kaitong Boiler and Pressure Vessel Co., Ltd. is a professional manufacturer of boilers, pressure vessels and non-standard vessels. The main products are steam boilers, electric boilers, hot water boilers, heat exchangers, gas storage tanks, storage tanks, reactors, towers, chemical equipment, condensers, low nitrogen boilers, etc. The company was established on February 10, 2012. Its predecessor was Yangzhou Boiler Chemical Equipment Installation Company established in 1994. The company adheres to the corporate philosophy of "creating green energy equipment for human beings and creating technological products for the industry". With the business philosophy of "market-oriented, innovation-driven, quality-based survival, and development-oriented growth", we will produce high-quality, high-performance boiler and pressure vessel products with continuous innovation in science and technology and modern management concepts. .