tuned mass damper - wikipedia, the free encyclopedia

10/17/2014 Tuned mass damper - Wikipedia, the free encyclopedia

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An animation showing themovement of a skyscraper versusthe mass damper. Shown in greenare the hydraulic cylinders used todamp the motion of theskyscraper.

Tuned mass damperFrom Wikipedia, the free encyclopedia

A tuned mass damper, also known as a harmonic absorber, is adevice mounted in structures to reduce the amplitude of mechanicalvibrations. Their application can prevent discomfort, damage, oroutright structural failure. They are frequently used in powertransmission, automobiles, and buildings.

Contents

1 Principle2 Mass dampers in automobiles

2.1 Motorsport2.2 Production cars

3 Mass dampers in spacecraft4 Dampers in power transmission lines5 Dampers in wind turbines6 Dampers in buildings and related structures

6.1 Sources of vibration and resonance6.1.1 Earthquakes6.1.2 Mechanical human sources6.1.3 Wind6.1.4 Examples of buildings and structures withtuned mass dampers

6.1.4.1 Canada6.1.4.2 China6.1.4.3 Germany6.1.4.4 Ireland6.1.4.5 Japan6.1.4.6 Russia6.1.4.7 Taiwan6.1.4.8 United Arab Emirates6.1.4.9 United States of America6.1.4.10 United Kingdom

7 See also8 References9 External links

Principle

Tuned mass dampers stabilize against violent motion caused by harmonic vibration. A tuned damperreduces the vibration of a system with a comparatively lightweight component so that the worst-casevibrations are less intense. Roughly speaking, practical systems are tuned to either move the main modeaway from a troubling excitation frequency, or to add damping to a resonance that is difficult or expensiveto damp directly. An example of the latter is a crankshaft torsional damper. Mass dampers are frequentlyimplemented with a frictional or hydraulic component that turns mechanical kinetic energy into heat, likean automotive shock absorber. An electrical analogue is an LCR circuit.



A schematic of a simple springmassdamper system used todemonstrate the tuned mass dampersystem.

Response of the system excited byone unit of force, with (red) andwithout (blue) the 10% tuned mass.The peak response is reduced from 9units down to 5.5 units. While themaximum response force is reduced,there are some operating frequenciesfor which the response force isincreased.

A Bode plot of displacements in thesystem with (red) and without (blue)the 10% tuned mass.

Given a motor with mass attached via motor mounts to the ground, the motor vibrates as it operates andthe soft motor mounts act as a parallel spring and damper, and . The force on the motor mounts is .In order to reduce the maximum force on the motor mounts as the motor operates over a range of speeds, asmaller mass, , is connected to by a spring and a damper, and . is the effective force on themotor due to its operation.

The graph shows the effect of a tuned mass damper on a simple springmassdamper system, excited byvibrations with an amplitude of one unit of force applied to the main mass, . An important measure of

performance is the ratio ofthe force on the motormounts to the force vibratingthe motor, . Thisassumes that the system islinear, so if the force on themotor were to double, sowould the force on the motormounts. The blue linerepresents the baselinesystem, with a maximumresponse of 9 units of forceat around 9 units offrequency. The red lineshows the effect of adding atuned mass of 10% of thebaseline mass. It has a maximum response of 5.5, at a frequency of7. As a side effect, it also has a second normal mode and will vibratesomewhat more than the baseline system at frequencies below about6 and above about 10.

The heights of the two peaks can be adjusted by changing the stiffness of the spring in the tuned massdamper. Changing the damping also changes the height of the peaks, in a complex fashion. The splitbetween the two peaks can be changed by altering the mass of the damper ( ).

The Bode plot is more complex, showing the phase and magnitudeof the motion of each mass, for the two cases, relative to F1.

In the plots at right, the black line shows the baseline response (). Now considering , the blue line shows

the motion of the damping mass and the red line shows the motionof the primary mass. The amplitude plot shows that at lowfrequencies, the damping mass resonates much more than theprimary mass. The phase plot shows that at low frequencies, the twomasses are in phase. As the frequency increases moves out ofphase with until at around 9.5 Hz it is 180 out of phase with

, maximizing the damping effect by maximizing the amplitudeof , this maximizes the energy dissipated into andsimultaneously pulls on the primary mass in the same direction asthe motor mounts.

Mass dampers in automobiles

Motorsport

The tuned mass damper was introduced as part of the suspension system by Renault, on its 2005 F1 car (theRenault R25), at the 2005 Brazilian Grand Prix. It was deemed to be legal at first, and it was in use up tothe 2006 German Grand Prix.

At Hockenheim, the mass damper was deemed illegal by the FIA, because the mass was not rigidly attachedto the chassis and, due to the influence it had on the pitch attitude of the car, which in turn significantlyaffected the gap under the car and hence the ground effects of the car, to be a movable aerodynamic deviceand hence as a consequence, to be illegally influencing the performance of the aerodynamics.



Stockbridge dampers on a 400 KVpower line near Castle Combe,England

The Stewards of the meeting deemed it legal, but the FIA appealed against that decision. Two weeks later,the FIA International Court of Appeal deemed the mass damper illegal.[1][2]

Production cars

Tuned mass dampers are widely used in production cars, typically on the crankshaft pulley to controltorsional vibration and, more rarely, the bending modes of the crankshaft. They are also used on thedriveline for gearwhine, and elsewhere for other noises or vibrations on the exhaust, body, suspension oranywhere else. Almost all modern cars will have one mass damper, some may have 10 or more.

The usual design of damper on the crankshaft consists of a thin band of rubber between the hub of the pullyand the outer rim. This design is often called a harmonic damper. An alternative design is the centrifugalpendulum absorber which is used to reduce the internal combustion engine's torsional vibrations on a fewmodern cars.

All four wheels of the Citroen 2cv incorporated a tuned mass damper (referred to as a "Batteur" in theoriginal French) of very similar design to that used in the Renault F1 car, from the start of production in1949 on all four wheels, before being removed from the rear and eventually the front wheels in the mid1970s.

Mass dampers in spacecraft

One proposal to reduce vibration on NASA's Ares solid fuel booster is to use 16 tuned mass dampers as partof a design strategy to reduce peak loads from 6g to 0.25 g, the TMDs being responsible for the reductionfrom 1 g to 0.25 g, the rest being done by conventional vibration isolators between the upper stages and thebooster.[3][4]

Dampers in power transmission lines

High-tension lines often have small barbell-shaped Stockbridgedampers hanging from the wires to reduce the high-frequency, low-amplitude oscillation termed flutter.[5][6]

Dampers in wind turbines

A standard tuned mass damper for wind turbines consists of anauxiliary mass which is attached to the main structure by means ofsprings and dashpot elements. The natural frequency of the tunedmass damper is basically defined by its spring constant and thedamping ratio determined by the dashpot. The tuned parameter ofthe tuned mass damper enables the auxiliary mass to oscillate with aphase shift with respect to the motion of the structure. In a typicalconfiguration an auxiliary mass hung below the nacelle of a wind turbine supported by dampers or frictionplates.

Dampers in buildings and related structures

Typically, the dampers are huge concrete blocks or steel bodies mounted in skyscrapers or other structures,and moved in opposition to the resonance frequency oscillations of the structure by means of springs, fluidor pendulums.

Sources of vibration and resonance

Unwanted vibration may be caused by environmental forces acting on a structure, such as wind orearthquake, or by a seemingly innocuous vibration source causing resonance that may be destructive,unpleasant or simply inconvenient.

Earthquakes



Location of Taipei 101's largest tunedmass damper

Tuned mass damper atop Taipei 101.

Dampers on the Millennium Bridgein London. The white disk is not partof the damper.

The seismic waves caused by an earthquake will make buildingssway and oscillate in various ways depending on the frequency anddirection of ground motion, and the height and construction of thebuilding. Seismic activity can cause excessive oscillations of thebuilding which may lead to structural failure. To enhance thebuilding's seismic performance, a proper building design isperformed engaging various seismic vibration control technologies.As mentioned above, damping devices had been used in theaeronautics and automobile industries long before they werestandard in mitigating seismic damage to buildings. In fact, the firstspecialized damping devices for earthquakes were not developeduntil late in 1950.[7]

Mechanical human sources

Masses of people walking up and down stairs at once, or greatnumbers of people stomping in unison, can cause serious problemsin large structures like stadiums if those structures lack dampingmeasures. Vibration caused by heavy industrial machinery,generators and diesel engines can also pose problems to structuralintegrity, especially if mounted on a steel structure or floor. Largeocean going vessels may employ tuned mass dampers to isolate thevessel from its engine vibration.

Wind

The force of wind against tall buildings can cause the top ofskyscrapers to move more than a meter. This motion can be in theform of swaying or twisting, and can cause the upper floors of suchbuildings to move. Certain angles of wind and aerodynamicproperties of a building can accentuate the movement and causemotion sickness in people. A TMD is usually tuned to a certainbuilding's frequency to work efficiently. However, during theirlifetimes, high-rise and slender buildings may experience naturalfrequency changes under wind speed, ambient temperatures andrelative humidity variations, among other factors, which requires arobust TMD design.[8]

Examples of buildings and structures with tuned mass dampers

Canada

One Wall Centre in Vancouver It employs tuned liquid column dampers, at the time of itsinstallation, a unique form of tuned mass damper.

China

Shanghai World Financial Center in Shanghai, China

Germany

Berlin Television Tower (Fernsehturm) tuned mass damper located in the spire.

Ireland

Dublin Spire in Dublin, Ireland This narrow slender structure was designed with a tuned massdamper to ensure aerodynamic stability during a wind storm.

Japan



Akashi-Kaiky Bridge, between Honshu and Shikoku in Japan, currently the world's longestsuspension bridge, uses pendulums within its suspension towers as tuned mass dampers.Tokyo Skytree, vertically placed two units (total 100 tons) in the housing as atop.Yokohama Landmark Tower

Russia

Sakhalin-I An offshore drilling platform

Taiwan

Taipei 101 skyscraper Contains the world's largest and heaviest tuned mass dampers, at 660 metric

tons.[9]

United Arab Emirates

Burj al-Arab in Dubai 11 tuned mass dampers.

United States of America

Bally's to Bellagio, Bally's toCaesars Palace, and Treasure Island to The Venetian Pedestrian Bridgesin Las Vegas, NVBloomberg Tower/731 Lexington in New York City, NYCitigroup Center in New York City, NY Designed by William LeMessurier and completed in

1977, it was one of the first skyscrapers to use a tuned mass damper to reduce sway. [10] Uses aconcrete version.Comcast Center in Philadelphia, PA Contains the largest Tuned Liquid Column Damper (TLCD)

in the world at 1,300 tons.[11]

Grand Canyon Skywalk, AZJohn Hancock Tower in Boston, MA A tuned mass damper was added to it after it was builtmaking it the 1st building to use a tuned mass damper.One Rincon Hill South Tower, San Francisco, CA First building in California to have a liquidtuned mass damperPark Tower in Chicago, IL The first building in the United States to be designed with a tunedmass damper from the outset.Random House Tower Uses two liquid filled dampers in New York City, NYTheme Building at Los Angeles International Airport Los Angeles, CATrump World Tower in New York City, NY

United Kingdom

London Millennium Bridge 'The Wobbly Bridge'

See also

Antiresonance

References

1. ^ Bishop, Matt (2006). "The Long Interview: Flavio Briatore". F1 Racing (October): 6676.2. ^ "FIA bans controversial damper system" (http://www.pitpass.com/fes_php/pitpass_news_item.php?



Wikimedia Commons hasmedia related to Tunedmass dampers.

fes_art_id=28765). Pitpass.com. Retrieved 2010-02-07.3. ^ "Ares I Thrust Oscillation meetings conclude with encouraging data, changes"

(http://www.nasaspaceflight.com/2008/12/ares-i-thrust-oscillation-meetings-encouraging-allowance-for-changes/). NASASpaceFlight.com. 2008-12-09. Retrieved 2010-02-07.

4. ^ "Shock Absorber Plan Set for NASA's New Rocket" (http://www.space.com/news/080819-nasa-ares1-vibration-update.html). SPACE.com. 2008-08-19. Retrieved 2010-02-07.

5. ^ "On the hysteresis of wire cables in Stockbridge dampers" (http://cat.inist.fr/?aModele=afficheN&cpsidt=13772262). Cat.inist.fr. Retrieved 2010-02-07.

6. ^ "Cable clingers - 27 October 2007" (http://www.newscientist.com/backpage.ns?id=mg19626273.000). NewScientist. Retrieved 2010-02-07.

7. ^ Reitherman, Robert (2012). Earthquakes and Engineers: An International History(http://www.asce.org/Product.aspx?id=2147487208&productid=154097877). Reston, VA: ASCE Press.ISBN 9780784410714.

8. ^ ALY, Aly Mousaad (2012). "Proposed robust tuned mass damper for response mitigation in buildings exposedto multidirectional wind" (http://onlinelibrary.wiley.com/doi/10.1002/tal.1068/abstract). The Structural Designof Tall and Special Buildings. doi:10.1002/tal.1068 (http://dx.doi.org/10.1002%2Ftal.1068).

9. ^ taipei-101.com.tw (http://www.taipei-101.com.tw/en/Tower/buildind_13-1.html)10. ^ Petroski, Henry (1996). Invention by Design: How Engineers Get from Thought to Thing. Harvard University

Press. pp. 205208.11. ^ "Comcast Center" (http://www.rwdi.com/cms/publications/84/pp_comcast_center.pdf). Retrieved 2010-02-07.

External links

Further information about tuned mass dampers(http://www.esm-gmbh.de/EN/Products/Tuned_mass_dampers)

Retrieved from "http://en.wikipedia.org/w/index.php?title=Tuned_mass_damper&oldid=629684823"

Categories: Mechanical engineering Mass Earthquake engineering

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