Tuned mass damper
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A tuned mass damper is a device mounted in structures to prevent discomfort, damage or outright structural failure by vibration. Typically, the dampers are huge concrete blocks mounted in skyscrapers or other structures, and moved in opposition to the resonant frequency oscillations of the structure by means of springs, fluid or pendulums. High-tension lines often have small barbell-shaped Stockbridge dampers hanging from the wires[citation needed]. See also damping.
Small devices working on the same priciples were used as shock absorbers to damp rear wheel bounce on the Citroën 2CV.
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[edit] Sources of vibration and resonance
Unwanted vibration may be caused by environmental forces acting on a structure, such as wind or earthquake, or by a seemingly innocuous vibration source causing resonance that may be destructive or unpleasant or simply inconvenient.
[edit] Earthquakes
The seismic waves caused by an earthquake will cause tall buildings to sway and oscillate in various ways depending on the frequency and direction of ground motion, as well as the height and construction of the building. When the seismic motion causes a harmonic oscillation in the frame of the building, where sections of the building are moving in opposing directions, it can result in structural failure.
[edit] Wind
The force of wind against tall buildings can cause the top of skyscrapers to move more than a metre. This motion can be in the form of swaying or twisting, and can cause the upper floors of such buildings to move. Certain angles of wind and aerodynamic properties of a building can accentuate the movement and cause motion sickness in people.
[edit] Mechanical human sources
Masses of people walking up and down stairs at once, or great numbers of people stomping in unison, can cause serious problems in large structures like stadiums if those structures lack dampening measures. Vibration caused by heavy industrial machinery, generators and diesel engines can also pose problems to structural integrity, especially if mounted on a steel structure or floor. Large ocean going vessels may employ tuned mass dampers to isolate the vessel from its engine vibration.
[edit] How they work
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Tuned mass dampers stabilize against violent motion caused by harmonic vibration. The presence of a tuned damper forces a comparatively lightweight structure to overcome the inertia of a great mass, such as a giant concrete block, placed in such a way that the mass only begins to move in one direction just as the structure begins to move in the other, thus damping the structure's oscillation. The counterweight may be mounted using massive spring coils and hydraulic dampers, and if the axis of the vibration is fundamentally horizontal or torsional, leaf springs and pendulum-mounted weights are employed. Tuned mass dampers are engineered, or "tuned" to specifically counter harmful frequencies of oscillation or vibration.
[edit] Examples of buildings and structures with tuned mass dampers
- Television Tower (Fernsehturm) in Berlin - tuned mass damper located in the spire.
- Burj al-Arab in Dubai - 11 tuned mass dampers.
- Dublin Spire in Dublin, Ireland. This narrow slender structure designed with a tuned mass damper to ensure aerodynamic stability during a wind storm.
- The Citigroup Center in New York City, designed by William LeMessurier and completed in 1977, was one of the first skyscrapers to use a tuned mass damper to reduce swaying.
- The John Hancock Tower in Boston had a tuned mass damper added to it after it was built.
- Taipei 101 skyscraper - contains the world's largest tuned mass damper.
- London Millennium Bridge - ('The Wobbly Bridge')
- Park Tower in Chicago is the first building in the United States to be designed with a tuned mass damper from the outset.
- The Trump World Tower in New York
- The One Wall Centre in Vancouver employs tuned liquid column dampers, which are a unique form of tuned mass dampers
- The Random House Tower in New York
- Bally’s-Bellagio, Bally’s-Caesar’s & Treasure Island-Venetian Pedestrian Bridges in Las Vegas
- Sakhalin-I - an offshore drilling platform
- Bloomberg Tower/731 Lexington in New York
- Yokohama Landmark Tower
- One Rincon Hill South Tower is the first building in the United States to have a liquid tuned mass damper.
[edit] Mass dampers in motorsport
The tuned mass damper was introduced as part of the suspension system by Renault, on its 2005 F1 car(the R25), at the 2005 Brazilian Grand Prix. It was deemed to be legal at first, and it was in use up to the 2006 German Grand Prix.
At Hockenheim, the mass damper was deemed by the FIA to be a moveable aerodynamic device due to the influence it had on the pitch attitude of the car, and hence, as a consequence, the performance of the aerodynamics. This conclusion was reached by the FIA despite the fact that the mass damper was fully enclosed within the car structure and hence not exposed to any airflow.
The Stewards of the meeting deemed it legal, but the FIA appealed against that decision. 2 weeks later, the FIA International Court of Appeal deemed the mass damper illegal. Despite the ban and the loss in pace it had caused, Renault still won both titles at the end of the 2006 season.
