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Mechanical Vibrations

Mechanical Vibrations. Jeff Rhoads and Terry Ballinger. MST @ MSU 2006. What is Vibration?. What is Vibration?. Scientific Definition. Any motion that repeats itself after an interval of time. What is Vibration?. Scientific Definition.

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Mechanical Vibrations

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  1. Mechanical Vibrations Jeff Rhoads and Terry Ballinger MST @ MSU 2006

  2. What is Vibration?

  3. What is Vibration? • Scientific Definition Any motion that repeats itself after an interval of time

  4. What is Vibration? • Scientific Definition Any motion that repeats itself after an interval of time • Engineering Definition Deals with the relationship between forces and oscillatory motion of mechanical systems

  5. Why is Vibration Important? The Tacoma Narrows Bridge Disaster November 7, 1940

  6. Why is Vibration Important? Amplitude of oscillation reached 14 feet!

  7. What was the cause?

  8. Vortex Shedding …Caused Wind-Induced Vibration (?)

  9. Why is Vibration Important?

  10. Why is Vibration Important?

  11. Why is Vibration Important?

  12. Wing Flutter Failures

  13. Basic Concepts Every object has: • Frequencies at which it “likes” to vibrate • Characteristic geometries of vibration

  14. Basic Concepts Every object has: • Frequencies at which it “likes” to vibrateç • Characteristic geometries of vibration

  15. Modeling Vibration The Ingredients: • Inertia(stores kinetic energy) • Elasticity(stores potential energy) 1 Realistic Addition: • Energy Dissipation

  16. Modeling Vibration The Ingredients: • Inertia(stores kinetic energy) • Elasticity(stores potential energy) 1 2 Realistic Addition: • Energy Dissipation

  17. Modeling Vibration The Ingredients: • Inertia(stores kinetic energy) • Elasticity(stores potential energy) 1 2 Realistic Addition: • Energy Dissipation 3

  18. Modeling Vibration The Ingredients: • Inertia(stores kinetic energy) • Elasticity(stores potential energy) 1 2 3 Realistic Addition: • Energy Dissipation

  19. Modeling Vibration The Ingredients: • Mass, m • Stiffness, k m k c Realistic Addition: • Damping, c

  20. How is this model useful? m k c

  21. Basic Concepts • Resonance

  22. Basic Concepts • Resonance • A vibration of large amplitude • Occurs when an object is forced near its natural frequency

  23. Resonance • A vibration of large amplitude • Occurs when an object is forced near its natural frequency Object

  24. Resonance • A vibration of large amplitude • Occurs when an object is forced near its natural frequency Object Model

  25. Vibration Absorbers • Used to eliminate vibration of an object Object (that vibrates too much)

  26. Vibration Absorbers • Used to eliminate vibration of an object Vibration Absorber (‘absorbs’ vibration) Object (that vibrates too much)

  27. Vibration Absorbers • Used to eliminate vibration of an object Vibration Absorber Choose these to eliminate motion of object. Object (that vibrates too much)

  28. Vibration Absorbers

  29. Mode Shapes “Characteristic Geometry” of Vibration • Mode Shapes • Resonance • Natural Frequencies

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