PRACTICAL EXPERIENCES
IN VIBRATION
By
S. Ziaei Rad
FAMOUS EXAMPLES OF VIBRATION
Perhaps the most infamous example in the engineering community
of ‘bad’ vibrations occurred during the two days preceding the
Catastrophic failure of the Tacoma Narrows Bridge in Tacoma,
WA in 1940
Tacoma bridge
Bad Vibration
After a day of large amplitude oscillations back-and-forth,
the bridge material eventual gave way due to fatigue similar
to how a paper clip fails when it is opened and closed repeatedly.
On November 7, 1940, at approximately 11:00 AM,
the first Tacoma Narrows suspension bridge collapsed due
to wind-induced vibrations.
Situated on the Tacoma Narrows in Puget Sound, near the
city of Tacoma, Washington, the bridge had only been
open for traffic a few months.
Tacoma bridge
A footpath bridge in London
Dampers used in Bridge
Tuned mass damper
Damper to ground
Dampers used in Bridge
Viscous Damper
Pier- Viscous Damper
A footpath bridge in London
sideways force
A footpath bridge in London
Modification
There are two fundamental ways to limit dynamic excitation:
Stiffen the structure, so the frequency of the bridge and
our footsteps no longer match
Add damping to absorb the energy.
galloping
Galloping
) Interphase spacers(
Pendulum detuners.
These anti-galloping devices are based on the fact that
the torsional movement of the bundle interacts
dynamically with the vertical motion. Wind energy is injected
to the vertical motion through torsional movement.
The control of torsion can control the vertical movement.
This occurs only when the torsional movement is close to
the frequency of the vertical motion, which is valid
for bundle conductor lines
‫جاذب ارتعاشی غیر فعال‬
The torsional damper detuner
(TDD).
The TDD is a new device, which
combines the properties of
torsional damping with those of
detuning. It has some dynamic
action able to avoid energy transfer
from torsion to vertical
motion, the basic mechanism of
flutter.
The torsional damper detuner
(TDD).
Fatigue
Fatigue of the structure could potentially cause an aircraft,
for example, to crash resulting in serious injuries and/or fatalities.
The devastating results of a corrosion Vibrations fatigue failure
in Aloha Airlines flight #243 are shown in the below Figure.
Fatigue
This failure occurred because corrosion in the overlapping
aluminum fuselage panels near the rivet locations on the skin of
the aircraft introduced cracking.
As multiple cracks near the rivets joined together to
produce a catastrophic failure of the fuselage, the front panel of the
fuselage tore away nearly completely and one stewardess was killed.
Luckily, the pilots were able to land the plane in spite of the damage to
the fuselage.
Fatigue failure can often be devastating and is the most common type of
failure in mechanical systems. This type of failure is caused partially by
vibrations of the structural components.
Good vibrations
These spiders can actually be
observed using vibration
to their advantage to locate
and restrain prey like
the Japanese beatle shown in
the figure.
The routine that this type of
spider follows in order to
capture and restrain prey is
based entirely on vibration.
Ultrasound
Expectant mothers are usually examined at least once during the
term of their pregnancy using ultrasound to determine if any risks
are anticipated for them or their fetus during pregnancy and/or delivery.
During the ultrasound procedure, high frequency sound waves
(>20 kHz) are sent through a wetting gel into the mother’s womb.
These waves are then reflected by different parts of the fetus in slightly
different ways. By processing the reflected waves, a two and sometimes
even a three-dimensional sonogram image of the fetus can be rendered.
Ultrasound
Three dimensional ultrasound image of a fetus using
propagating high frequency compressional sound/vibration waves
Condition Monitoring
(Left) ‘Black box’ for monitoring the vibrations of a machine
tool lathe in a manufacturing facility; (Right) Unusual vibrations
Indicate that a tool needs to be replaced or that a misalignment exists
between the tool and the part during the cutting operation.
component feeders
ultrasonic cleaning baths
concrete
compactors
pile drivers
Vibration Strength Training
 Invention of the first vibrations training device at the
end of the 1970‘s
Work principle:
 Increased recruitment and activation of motor-units
 Producing a cyclic muscle-stretching-reflex
 Overlapping and continuous contraction of the
muscles  TVR (tonic-vibration-reflex)
Vibration Strength Training vs.
Conventional Strength Training
Increase of Maximum Force/Power
Power Increase [%]
Vibration Training
Conventional
Maximal Force/Power
Use of Vibration Strength
Training in Space
Vibration Strength Training Equipment will
be used besides other Training Devices on
the Mars Mission
Electro-Stimulation [EMS]
Electro-Stimulation [EMS]
Hand-Arm Vibration
Syndrome
Prolonged exposure to high level of vibration can cause a series of
disorders. Specifically, vibration exposure of Hand-Arm System can
cause diseases so-called; Hand-Arm Vibration Syndrome (HAVS).
Simple Mass-Spring Absorber
Earthquake
Earthquakes produce another form of ‘bad’ vibration, which can have
devastating effects.
It has been said that ‘earthquakes don’t kill people, structures do’
because it is rare that an earthquake will harm someone directly.
In most earthquakes, the vibrations of large surrounding structures
(e.g., buildings, highway overpasses and houses) are responsible for
the majority of injuries and deaths.
Earthquake
Figure shows representative pictures of the severe type of damage
that was sustained by a highway overpass (left) and bridge support
member (right) when they oscillated excessively during the
Northridge, CA earthquake of 1994.
Earthquake
Engineers of so-called ‘smart structures’ have been working for
decades, and continue to work, to design and build structures that
have enough intelligence and power to not only withstand but to
respond to earthquakes and other forms of environmental excitations
in order to suppress as much of the resulting vibration as possible.
In fact, it has been shown that this type of damage due to earthquakes
can be largely mitigated by implementing the kinds of design
modifications for vibration suppression
Earthquake
(Left) A friction pendulum bearing and (Right) an elastomeric bearing
for isolating civil infrastructure from earthquake
Earthquake
In that sense, these two isolation system can be thought of as
Mechanical ‘filters’, which bypass mechanical energy that would
otherwise destroy the isolated structure.
In effect, the bearings pictured in Figure, block much of the energy
From the seismic oscillations thereby protecting the isolated
infrastructure.
There are also many examples of passive and active isolation systems
for civil infrastructure and smaller scale mechanical systems like
rotating machinery.
‫انواع کنترل سيستمها‬
‫کنترل غيرفعال‬
‫کنترل فعال‬
‫کنترل نيمهفعال‬
‫ميراگرها و جداسازهای غيرفعال‬
‫لزج‬
‫اصطکاکی‬
‫ميراگرتسليم فلزي به کاررفته دربرج دهانه ورودي يک‬
‫سد‬
‫کاربردميرايي تسليم فلزي درساختمانها‬
‫ميراگرهاي جرمي ميزان شده يک درجه آزادی‬
Multi-degree-of freedom tuned mass dampers (MDOF-TMD)
‫نمايي شماتيک ازيک‪ TMD‬کاربردي وکم حجم‪،‬‬
‫مورداستفاده درساختمانها‬
‫مدل هاي جديدوکم حجم ‪ TMD‬ها‪،‬‬
‫مورداستفاده در برج«تن بوش» درناکازاکي ژاپن‬
‫ميراگرهاي جرمي ميزان شده يک درجه آزادي فعال‬
‫(‪Active tuned mass dampers)ATMD‬‬
‫يک ‪ ATMD‬همان ‪ TMD‬معمولي است‪ ،‬با اين تفاوت که به آن يک عملگرفعال به‬
‫صورت موازي با املان فنري و املان ميرايي داخلي جزء ميراگر‪ ،‬اضافه شده است‪ .‬اين‬
‫عملگر‪ ،‬نيروي فعال را در مواقع الزم‪ ،‬اضافه برنيروهاي ناش ي از فنرو دمپربين دو جرم‬
‫و وارد ميکند‪.‬‬
‫کاربرد ‪ ATMD‬در ساختمان «کيوباش ي سيوا» در‬
‫توکيوي ژاپن‬
‫نماي ‪ ATMD‬بکاررفته در برج «آپالئوس» در شهر «اوساکا»‪،‬‬
‫استفاده از فرودگاه هليکوپتر به عنوان املان جرم ميراگر‬
‫ميراگرهاي جرمي ميزان شده يک درجه آزادي نيمه‬
)SATMD( ‫فعال‬
.)SAIVD-TMD(‫هاي نيمه فعال ميرايي متغير‬TMD 
.)SAIVS-TMD(‫هاي نيمه فعال سختي متغير‬TMD 
.)SAIVI-TMD(‫هاي نيمه فعال اينرس ي متغير‬TMD 
Semi-active variable damper tuned mass dampers (SAIVD-TMD)
Semi-active variable stiffness tuned mass dampers (SAIVS-TMD)
Semi-active variable inertia tuned mass dampers (SAIVI-TMD)
‫نماي شماتيک از يک ‪ SAIVD-TMD‬در جهت‬
‫افقي‬
‫ميراگرهاي جرمي نيمه فعال با سختي داخلي متغير‬
‫نخستين سازوکارهاي سختي متغير مورداستفاده در‪SAIVS-TMD‬ها‪،‬‬
‫توسط «کوبوري»‪« ،‬پتن»‪ ،‬و «يانگ» ارائه شده اند که همگي به صورت دو‬
‫وضعيتي(‪ )on-off‬مي باشند‪.‬‬
‫ولي نخستين بار‪« ،‬ناگاراجايا» درسال ‪ 1998‬طرحي ابتکاري ارائه کرد‬
‫که يک املان سختي متغير پيوسته را تأمين مي کند‪ .‬اين طرح که در‬
‫شکل نشان داده شده است‪ ،‬درسال ‪ 2000‬دريک ‪SAIVS-TMD‬‬
‫نصب شده دربرج اداري ‪76‬طبقه و ‪306‬متري شهرملبورن استراليا‪ ،‬مورد‬
‫استفاده واقع گرديد ‪.‬‬
‫ميراگرهاي جرمي نيمه فعال با سختي داخلي متغير‬
‫ميراگرهاي جرمي ميزان شده مرکب‬
‫فعال‪-‬غيرفعال‬
‫ازکنارهم قرارگرفتن يک ميراگرجرمي ميزان شده فعال(‪ )ATMD‬و يک ميراگر‬
‫جرمي ميزان شده غيرفعال(‪ )TMD‬به طور مجزا‪ ،‬ايجاد مي شوند‪.‬‬
‫اين نوع از‪HMD‬ها‪ ،‬نخستين باردرسال ‪ 1994‬توسط «اوروي» ارائه گرديد‪.‬‬
‫ميراگرهاي جرمي پاندولي‬
‫ً‬
‫ميراگرهاي جرمي پاندولي‪ ،‬اساسا با تبديل و پراکنده سازي انرژي نوساني‬
‫سيستم به صورت انرژي جنبش ي و انرژي پتانسيل گرانش ي کار ميکنند‪.‬‬
‫درعين حال‪ ،‬املانهاي فنري را هم ميتوان در تعامل با آنها استفاده‬
‫نمود و از اين طريق باعث افزايش فرکانس طبيعي سيستم ميراگر گرديد‪.‬‬
‫نمونه اي از يک ميراگر جرمي پاندولي‬
‫با قابليت داشتن فرکانس پايين‬
‫ميراگرجرمي پاندولي چندگانه‪ ،‬مورداستفاده دربرج‬
‫اختصاص ي شهريوکوهاما‬
‫ميراگرهاي ضربهاي‬
‫ً‬
‫دراين نوع ميرايي معموال‪ ،‬براي مهارسازي نوسانات با دامنه زياد و به ويژه درمورد‬
‫تحريکات پرآشوب و داراي هرج ومرج استفاده ميشود‪ .‬هزينه کم‪ ،‬ساختمان‬
‫ساده‪ ،‬و ميزان سازي آسان‪ ،‬ازمهمترين مزيتهاي اين نوع ميراگرها ميباشد‪.‬‬
‫اما‪ ،‬عيب عمده آنها اين است که بيشتردرسازه ها و سيستمهاي کوچک کارايي‬
‫دارند‪.‬‬
‫کاربرد ميراگرضربهاي درپره هاي يک توربين‬
‫ميراگرهاي ذره اي‬
‫تعداد زيادي ازذرات با ابعاد کوچک(بين ‪ 0.05 mm‬تا ‪ )5 mm‬درون يک‬
‫محفظه ويژه قرارگرفته‪ ،‬و درنتيجه برهم کنشهاي بين آنها(ازجمله‪ ،‬برهم کنش‬
‫ضربهاي) يک اثرميرايي ايجاد ميشود‪.‬‬
‫ميراگرهاي مايع‬
‫عامل اصلي ميرايي دراين نوع ميراگرها برعهده يک مايع(سيال) ميباشد‪،‬‬
‫ً‬
‫که اين مايع هم عمدتا آب است‪.‬‬
‫دراينجا‪ ،‬ميراگرهاي مايعي درقالب دو گروه اصلي زيرتقسيم بندي و‬
‫بررس ي ميشوند‪.‬‬
‫‪ -1‬ميراگرهاي مايعي ميزانشده )‪Tuned liquid dampers (TLD‬‬
‫‪ -2‬ميراگرهاي ستون مايعي ميزانشده‬
‫)‪Tuned liquid column dampers (TLCD‬‬
‫ميراگرهاي مايعي ميزانشده‬
‫يک عيب عمده ‪TLD‬ها‪ ،‬اين است که کارايي آنها در مقايسه با جرم شان پايين است‪.‬‬
‫اين بدان خاطر است که‪ ،‬بخش قابل توجهي از حجم مايع ميراگر که در محفظه قرار گرفته‪،‬‬
‫به دليل عدم تالطم اثر ميراکننده اي به دنبال ندارد‪ .‬يک راه حلي که براي اين مشکل ارائه‬
‫گرديده‪ ،‬اضافه کردن يک سري تورهاي سيمي فوالدي درون حجم مايع ميباشد‪.‬‬
‫اين کار درحقيقت‪ ،‬باعث پراکنده شدن حرکات و تالطمات مايع در سرتاسر حجم آن‬
‫خواهد شد‪.‬‬
‫عيب ديگر ‪TLD‬ها‪ ،‬اين است که در هنگام قطع تحريک سيستم اوليه‪ ،‬تالطم باقيمانده‬
‫درون حجم مايع ميتواند انرژي جذب شده از سيستم اوليه را دوباره به آن بازگرداند و‬
‫موجب تحريک مجدد آن شود(خودتحريکي)‪ .‬تاکنون‪ ،‬طرح هاي چندي براي رفع نسبي‬
‫اين مشکل ارائه شدهاست‪ .‬ازجمله‪« ،‬گاردارسون» طرحي ارائه کرده که در آن‪ ،‬کف محفظه‬
‫يا تانک حاوي مايع ميراگر‪ ،‬در جهت موازي با راستاي تحريک سيستم شيبدار ميباشد‬
‫(شيب ‪.)30°‬‬
‫ميراگرهاي مايعي ميزانشده‬
‫الف) سيستم بدون ميراگر‬
‫ب) سيستم با ‪ TLD‬معمولي‬
‫ج) سيستم با ‪ TLD‬داراي ذرات غوطه ور اضافي‬
‫نمونههاي کاربردي ‪TLD‬ها درساختمانها‬
‫نمايي ازميراگرهاي مايعي بهکاررفته دربرج طاليي شهرکاگاوا‬
‫نمونههاي کاربردي ‪TLD‬ها درساختمانها‬
‫نمايي ازهتل سلطنتي يوکوهاما‪ ،‬و ميراگرهاي مايعي نه اليه مورداستفاده درآن‬
‫نمونههاي کاربردي ‪TLD‬ها درساختمانها‬
‫نمايي ازميراگرهاي مايعي بهکاررفته درفرودگاه بين املللي «هاندا» درشهرتوکيو‪،‬‬
‫سمت راست‪ :‬نماي يکي ازاجزاي ميراگر سمت چپ‪ :‬سايراجزا درحالت سوارشده‬
‫ميراگرهاي ستون مايعي ميزانشده (‪)TLCD‬‬
‫ايده آن براي نخستين بارتوسط «ساکايي» و «سامالي»ارائه گرديد‪.‬‬
‫دراين ميراگرها‪ ،‬مايع ميراگردرون يک لوله ‪U‬شکل قرارميگيرد‪،‬‬
‫که البته لوله مذکور ميتواند داراي خمهاي با زاويه دلخواه و گوناگون‬
‫ً‬
‫(معموال بين ‪ 30°‬تا ‪ )90°‬درگوشههاي خود‪ ،‬باشد‪.‬‬
‫)‪Sakai (1989) & Samali (1990‬‬
‫ميراگرهاي ستون مايعي ميزانشده (‪)TLCD‬‬
‫کاربرد ‪TLCD‬ها درساختمانها و سازه هاي عمراني‬
‫کاربرد ‪TLCD‬ها درساختمانها و سازه هاي عمراني‬
‫کاربرد ‪TLCD‬ها درساختمانها و سازه هاي عمراني‬
‫کاربرد ‪TLCD‬ها درساختمانها و سازه هاي عمراني‬
‫کاربرد ‪TLCD‬ها درساختمانها و سازه هاي عمراني‬