PRACTICAL EXPERIENCES IN VIBRATION

1. PRACTICAL EXPERIENCES IN VIBRATION By S. Ziaei Rad

2. 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

3. Tacoma bridge

4. 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.

5. Tacoma bridge

6. A footpath bridge in London

7. Dampers used in Bridge Tuned mass damper Damper to ground

8. Dampers used in Bridge Pier- Viscous Damper Viscous Damper

9. A footpath bridge in London sideways force

10. A footpath bridge in London

11. 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.

12. galloping

13. Galloping )Interphase spacers(

14. 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

15. جاذب ارتعاشی غیر فعال

16. 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.

17. The torsional damper detuner (TDD).

18. 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.

19. 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.

20. 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.

21. 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.

22. Ultrasound Three dimensional ultrasound image of a fetus using propagating high frequency compressional sound/vibration waves

23. 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.

24. component feeders ultrasonic cleaning baths concrete compactors pile drivers

25. 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)

26. Vibration Training Conventional Power Increase [%] Maximal Force/Power Vibration Strength Training vs. Conventional Strength Training Increase of Maximum Force/Power

27. Use of Vibration Strength Training in Space Vibration Strength Training Equipment will be used besides other Training Devices on the Mars Mission

28. Electro-Stimulation [EMS] Electro-Stimulation [EMS]

29. 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).

30. Simple Mass-Spring Absorber

31. 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.

32. 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.

33. 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

34. Earthquake (Left) A friction pendulum bearing and (Right) an elastomeric bearing for isolating civil infrastructure from earthquake

35. 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.

36. انواع کنترل سيستمها کنترل غيرفعال کنترل فعال کنترل نيمه­فعال

37. ميراگرها و جداسازهای غير فعال لزج اصطکاکی

38. ميراگرتسليم فلزي به کاررفته دربرج دهانه ورودي يک سد

39. کاربردميرايي تسليم فلزي درساختمانها

40. ميراگرهاي جرمي ميزانشده يکدرجهآزادیMulti-degree-of freedom tuned mass dampers (MDOF-TMD)

41. نمايي شماتيک ازيکTMDکاربردي وکم حجم، مورداستفاده درساختمانها

42. مدل هاي جديدوکم حجم TMD ها،مورداستفاده در برج«تن بوش» درناکازاکي ژاپن

43. ميراگرهاي جرمي ميزانشده يکدرجهآزادي فعال(ATMD)Active tuned mass dampers يک ATMD همان TMD معمولي است، با اين تفاوت که به آن يک عملگر فعالبهصورت موازي با المان فنري و المان ميرايي داخلي جزء ميراگر، اضافه شدهاست.اين عملگر، نيروي فعال را در مواقع لازم، اضافه بر نيروهاي ناشي از فنر و دمپر بين دو جرم و وارد ميکند.

44. کاربرد ATMD در ساختمان «کيوباشي سيوا» در توکيوي ژاپن

45. نماي ATMDبکاررفته در برج «آپلائوس» در شهر «اوساکا»،استفاده از فرودگاه هليکوپتر بهعنوان المان جرم ميراگر

46. ميراگرهاي جرمي ميزان شده يک درجه آزادي نيمه فعال (SATMD) TMDهاي نيمهفعال ميراييمتغير(SAIVD-TMD). TMDهاي نيمه فعال سختيمتغير(SAIVS-TMD). TMDهاي نيمهفعال اينرسيمتغير(SAIVI-TMD). 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)

47. نماي شماتيک از يک SAIVD-TMD در جهت افقي

48. ميراگرهاي جرمي نيمهفعال با سختي داخلي متغير نخستين سازوکارهاي سختيمتغير مورداستفاده در SAIVS-TMDها، توسط«کوبوري»، «پتن»، و «يانگ» ارائه شدهاند که همگي بهصورت دو وضعيتي(on-off) ميباشند. ولي نخستين بار، «ناگاراجايا»در سال 1998 طرحي ابتکاري ارائه کرد که يک المان سختيمتغير پيوسته را تأمين ميکند.اين طرح که در شکل نشان داده شدهاست، در سال 2000 در يک SAIVS-TMD نصبشده در برج اداري 76طبقه و 306متريشهرملبورن استراليا، مورد استفاده واقع گرديد.

49. ميراگرهاي جرمي نيمهفعال با سختي داخلي متغير

50. ميراگرهاي جرمي ميزانشده مرکب فعال-غيرفعال از کنار هم قرار گرفتن يک ميراگر جرمي ميزانشده فعال(ATMD) و يک ميراگر جرمي ميزانشده غيرفعال(TMD) بهطور مجزا، ايجاد ميشوند. اين نوع از HMDها، نخستين بار در سال 1994 توسط «اوروي»ارائه گرديد.