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| | Spend money on a rechargeable battery for all your wireless gaming [http://Www.Adobe.com/cfusion/search/index.cfm?term=&controller&loc=en_us&siteSection=home controller]. You can buy standard rechargeable power supplies for your controller. If you want to play video games regularly, you will be eating through a small lots of money in the batteries used to run your controllers. A rechargeable battery could save you a lot of profit in the long run.<br><br> |
| [[File:Tuned mass damper.gif|200px|thumb|An animation showing the movement of a skyscraper versus the mass damper. Shown in green are the [[hydraulic cylinders]] used to damp the motion of the skyscraper.]]
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| A '''tuned mass damper''', also known as a '''harmonic absorber''', is a device mounted in structures to reduce the amplitude of mechanical [[vibration]]s. Their application can prevent discomfort, damage, or outright [[structural failure]]. They are frequently used in power transmission, automobiles, and buildings. | |
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| ==Principle==
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| {{Unreferenced section|date=October 2009}}
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| [[File:2dof sketch.svg|thumb|A schematic of a simple spring–mass–damper system used to demonstrate the tuned mass damper system.]]
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| Tuned mass dampers stabilize against violent motion caused by [[normal mode|harmonic vibration]]. A tuned damper reduces the vibration of a system with a comparatively lightweight component so that the worst-case vibrations are less intense. Roughly speaking, practical systems are tuned to either move the main mode away from a troubling excitation frequency, or to add damping to a resonance that is difficult or expensive to damp directly. An example of the latter is a crankshaft torsional damper. Mass dampers are frequently implemented with a frictional or hydraulic component that turns mechanical kinetic energy into heat, like an automotive [[shock absorber]]. An electrical analogue is an [[LCR circuit]].
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| Given a motor with mass <math>m_1</math> attached via motor mounts to the ground, the motor vibrates as it operates and the soft motor mounts act as a parallel spring and damper, <math>k_1</math> and <math>c_1</math>. The force on the motor mounts is <math>F_0</math>. In order to reduce the maximum force on the motor mounts as the motor operates over a range of speeds, a smaller mass, <math>m_2</math>, is connected to <math>m_1</math> by a spring and a damper, <math>k_2</math> and <math>c_2</math>. <math>F_1</math> is the effective force on the motor due to its operation.
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| [[File:Tuned mass damper.png|thumb|left|Response of the system excited by one unit of force, with (red) and without (blue) the 10% tuned mass. The peak response is reduced from 9 units down to 5.5 units. While the maximum response force is reduced, there are some operating frequencies for which the response force is increased.]]
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| The graph shows the effect of a tuned mass damper on a simple spring–mass–damper system, excited by vibrations with an amplitude of one unit of force applied to the main mass, <math>m_1</math>. An important measure of performance is the ratio of the force on the motor mounts to the force vibrating the motor, <math>F_0/F_1</math>. This assumes that the system is linear, so if the force on the motor were to double, so would the force on the motor mounts. The blue line represents the baseline system, with a maximum response of 9 units of force at around 9 units of frequency. The red line shows the effect of adding a tuned mass of 10% of the baseline mass. It has a maximum response of 5.5, at a frequency of 7. As a side effect, it also has a second normal mode and will vibrate somewhat more than the baseline system at frequencies below about 6 and above about 10. <!-- These really should have units. Does someone want to work the problem out? -->
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| The heights of the two peaks can be adjusted by changing the stiffness of the spring in the tuned mass damper. Changing the damping also changes the height of the peaks, in a complex fashion. The split between the two peaks can be changed by altering the mass of the damper (<math>m_2</math>).
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| [[File:2dof plots.png|thumb|A [[Bode plot]] of displacements in the system with (red) and without (blue) the 10% tuned mass.]]
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| The [[Bode plot]] is more complex, showing the phase and magnitude of the motion of each mass, for the two cases, relative to F1.
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| In the plots at right, the black line shows the baseline response (<math>m_2 = 0</math>). Now considering <math>m_2 = m_1/10</math>, the blue line shows the motion of the damping mass and the red line shows the motion of the primary mass. The amplitude plot shows that at low frequencies, the damping mass resonates much more than the primary mass. The phase plot shows that at low frequencies, the two masses are in phase. As the frequency increases <math>m_2</math> moves out of phase with <math>m_1</math> until at around 9.5 Hz it is 180° out of phase with <math>m_1</math>, maximizing the damping effect by maximizing the amplitude of <math>x_2-x_1</math>, this maximizes the energy dissipated into <math>c_2</math> and simultaneously pulls on the primary mass in the same direction as the motor mounts.
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| ==Mass dampers in automobiles==
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| ===Motorsport===
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| The tuned mass damper was introduced as part of the suspension system by Renault, on its 2005 F1 car (the [[Renault 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]].
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| At Hockenheim, the mass damper was deemed illegal by the [[Fédération Internationale de l'Automobile|FIA]], because the mass was not rigidly attached to the chassis and, due to the influence it had on the pitch attitude of the car, which in turn significantly affected the gap under the car and hence the [[ground effect (cars)|ground effect]]s of the car, to be a movable aerodynamic device and hence as a consequence, to be illegally influencing the performance of the [[aerodynamics]].
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| 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.<ref>{{cite journal | last = Bishop | first = Matt | year = 2006 | title = The Long Interview: Flavio Briatore | journal = F1 Racing | volume = | issue = October | pages = 66–76 | accessdate = 2006-10-30}}</ref><ref>{{cite web|url=http://www.pitpass.com/fes_php/pitpass_news_item.php?fes_art_id=28765 |title=FIA bans controversial damper system |publisher=Pitpass.com |date= |accessdate=2010-02-07}}</ref>
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| ===Production cars===
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| Tuned mass dampers are widely used in production cars, typically on the crankshaft pulley to control [[torsional vibration]] and, more rarely, the bending modes of the crankshaft. They are also used on the driveline for gearwhine, and elsewhere for other noises or vibrations on the exhaust, body, suspension or anywhere else. Almost all modern cars will have one mass damper, some may have 10 or more.
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| The usual design of damper on the crankshaft consists of a thin band of rubber between the hub of the pully and the outer rim. This design is often called a harmonic damper. An alternative design is the [[centrifugal pendulum absorber]] which is used to reduce the [[internal combustion engine|internal combustion engine's]] torsional vibrations on a few modern cars.
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| ==Mass dampers in spacecraft==
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| One proposal to reduce vibration on NASA's [[Ares I|Ares]] solid fuel booster is to use 16 tuned mass dampers as part of a design strategy to reduce peak loads from 6g to 0.25 g, the TMDs being responsible for the reduction from 1 g to 0.25 g, the rest being done by conventional [[vibration isolation|vibration isolators]] between the upper stages and the booster.<ref>{{cite web|url=http://www.nasaspaceflight.com/2008/12/ares-i-thrust-oscillation-meetings-encouraging-allowance-for-changes/ |title=Ares I Thrust Oscillation meetings conclude with encouraging data, changes |publisher=NASASpaceFlight.com |date=2008-12-09 |accessdate=2010-02-07}}</ref><ref>{{cite web|url=http://www.space.com/news/080819-nasa-ares1-vibration-update.html |title=Shock Absorber Plan Set for NASA's New Rocket |publisher=SPACE.com |date=2008-08-19 |accessdate=2010-02-07}}</ref>
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| ==Dampers in power transmission lines==
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| [[File:Stockbridge Damper.jpg|thumb|180px|[[Stockbridge damper]]s on power lines.]]
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| [[High tension line|High-tension lines]] often have small [[barbell]]-shaped [[Stockbridge damper]]s hanging from the [[Electric power transmission|wires]] to reduce the high-frequency, low-amplitude oscillation termed [[Conductor gallop#Flutter|flutter]].<ref>{{cite web|url=http://cat.inist.fr/?aModele=afficheN&cpsidt=13772262 |title=On the hysteresis of wire cables in Stockbridge dampers |publisher=Cat.inist.fr |date= |accessdate=2010-02-07}}</ref><ref>{{cite web|url=http://www.newscientist.com/backpage.ns?id=mg19626273.000 |title=Cable clingers - 27 October 2007 |publisher=New Scientist |date= |accessdate=2010-02-07}}</ref>
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| ==Dampers in buildings and related structures==
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| [[File:Taipei 101 Tuned Mass Damper.png|thumb|Location of Taipei 101's largest tuned mass damper.]]
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| [[File:Tuned mass damper - Taipei 101 - Wikimania 2007 0224.jpg|thumb|Tuned mass damper atop [[Taipei 101]].]]
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| Typically, the [[damping|dampers]] are huge concrete blocks or steel bodies mounted in [[skyscraper]]s or other structures, and moved in opposition to the [[resonance|resonance frequency]] oscillations of the structure by means of [[spring (device)|springs]], fluid or pendulums.
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| ===Sources of vibration and resonance===
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| 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, unpleasant or simply inconvenient.
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| ====Earthquakes====
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| The [[seismic wave]]s caused by an [[earthquake]] will make buildings sway and [[oscillate]] in various ways depending on the frequency and direction of ground motion, and the height and construction of the building. Seismic activity can cause excessive oscillations of the building which may lead to [[structural failure]]. To enhance the building's [[seismic performance]], a proper building design is performed engaging various seismic [[vibration control]] technologies.
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| As mentioned above, damping devices had been used in the aeronautics and automobile industries long before they were standard in mitigating seismic damage to buildings. In fact, the first specialized damping devices for earthquakes were not developed until late in 1950.<ref name=Reitherman>{{cite book|last=Reitherman|first=Robert|title=Earthquakes and Engineers: An International History|year=2012|publisher=ASCE Press|location=Reston, VA|isbn=9780784410714|url=http://www.asce.org/Product.aspx?id=2147487208&productid=154097877}}</ref>
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| ====Mechanical human sources====
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| [[File:London Millennium Bridge - Damper beneath deck, north side - 240404.jpg|thumb|180px|Dampers on the [[Millennium Bridge (London)|Millennium Bridge]] in London. The white disk is not part of the damper.]]
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| 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 damping 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.
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| ====Wind====
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| The force of wind against tall buildings can cause the top of skyscrapers to move more than a meter. 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. A TMD is usually tuned to a certain building's frequency to work efficiently. However, during their lifetimes, high-rise and slender buildings may experience natural frequency changes under wind speed, ambient temperatures and relative humidity variations, among other factors, which requires a robust TMD design.<ref>{{cite journal|last=ALY|first=Aly Mousaad|title=Proposed robust tuned mass damper for response mitigation in buildings exposed to multidirectional wind|journal=The Structural Design of Tall and Special Buildings|year=2012|url=http://onlinelibrary.wiley.com/doi/10.1002/tal.1068/abstract|doi=10.1002/tal.1068}}</ref>
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| ====Examples of buildings and structures with tuned mass dampers====
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| {{Unreferenced section|date=April 2012}}
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| =====Canada=====
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| * [[One Wall Centre]] in [[Vancouver]] — It employs tuned liquid column dampers, at the time of its installation, a unique form of tuned mass damper.
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| =====China=====
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| * [[Shanghai World Financial Center]] in [[Shanghai, China]]
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| =====Germany=====
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| * [[Berlin]] Television Tower ([[Fernsehturm Berlin|Fernsehturm]]) — tuned mass damper located in the spire.
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| =====Ireland=====
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| * [[Dublin Spire]] in [[Dublin, Ireland]] — This narrow slender structure was designed with a tuned mass damper to ensure aerodynamic stability during a wind storm.
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| =====Japan=====
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| * [[Akashi-Kaikyō Bridge]], between [[Honshu]] and [[Shikoku]] in Japan, currently the world's longest suspension bridge, uses pendulums within its suspension towers as tuned mass dampers.
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| * [[Tokyo Skytree]], vertically placed two units (total 100 tons) in the housing as atop{{vague|date=November 2013}}.
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| * [[Yokohama Landmark Tower]]
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| =====Russia=====
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| * [[Sakhalin-I]] — An [[oil platform|offshore drilling platform]]
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| =====Taiwan=====
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| * [[Taipei 101]] skyscraper — Contains the world's largest and heaviest tuned mass dampers, at 660 metric tons.<ref>'''http://www.taipei-101.com.tw/en/Tower/buildind_13-1.html''' 2.9.3013</ref>
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| =====United Arab Emirates=====
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| * [[Burj al-Arab]] in [[Dubai]] — 11 tuned mass dampers.
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| =====United States of America=====
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| * [[Bally's Las Vegas|Bally's]] to{{vague|date=November 2013}} [[Bellagio (resort and casino)|Bellagio]], Bally's to{{vague|date=November 2013}} [[Caesars Palace]], and [[Treasure Island Hotel and Casino|Treasure Island]] to [[The Venetian (Las Vegas)|The Venetian]] Pedestrian Bridges in [[Las Vegas Valley|Las Vegas]], NV
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| * [[Bloomberg Tower|Bloomberg Tower/731 Lexington]] in [[New York City]], NY
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| * [[Citigroup 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. Uses a concrete version.
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| * [[Comcast Center (office building)|Comcast Center]] in [[Philadelphia]], PA — Contains the largest Tuned Liquid Column Damper (TLCD) in the world at 1,300 tons.<ref>{{cite web|url=http://www.rwdi.com/cms/publications/84/pp_comcast_center.pdf |title=Comcast Center |publisher= |date= |accessdate=2010-02-07}}</ref>
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| * [[Grand Canyon Skywalk]], AZ
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| * [[John Hancock Tower]] in [[Boston]], MA — A tuned mass damper was added to it after it was built making it the 1st building to use a tuned mass damper.
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| * [[One Rincon Hill|One Rincon Hill South Tower]], [[San Francisco]], CA— First building in California to have a liquid tuned mass damper
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| * [[Park Tower (Chicago)|Park Tower]] in [[Chicago]], IL — The first building in the United States to be designed with a tuned mass damper from the outset.
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| * [[Random House Tower]] — Uses two liquid filled dampers in [[New York City]], NY
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| * [[Theme Building]] at [[Los Angeles International Airport]] [[Los Angeles]], CA
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| * [[Trump World Tower]] in [[New York City]], NY
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| =====United Kingdom=====
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| * [[London Millennium Bridge]] — 'The Wobbly Bridge'
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| ==References==
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| {{reflist}}
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| ==External links==
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| {{Commons category|Tuned mass dampers}}
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| *[http://www.esm-gmbh.de/EN/Products/Tuned_mass_dampers Further information about tuned mass dampers]
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| [[Category:Mechanical engineering]]
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| [[Category:Mass]]
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| [[Category:Earthquake engineering]]
| |
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