Free and forced vibration Flashcards Preview

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Flashcards in Free and forced vibration Deck (12):

What is resonant frequency?

  • if you stretch and release a mass on a spring, it oscillates at its resonant frequency
  • freq at max amplitude




What happens if no energy is transferred to or from surroudnig


it will keep oscillating with the same amplitude forever



When do forced vibrations happen?

  • when there is an external driving force
  • system can be forced to vibrate by a periodic external force
  • the frequency of this is called the driving freuqency


When are the driving frequency in phase with the resonant frequency?

  • when driving frequency is less than the resonant frequency
    • the oscillator just follow the motion of the driver
  • if the driving freq is greater than the resonannt freq, the oscillator will not be able to keep up and will be oscillate




When does resonance happen?

  • driving freq = resibabt freq
  • 90 degress phase difference between oscillator and driver



What happens as the driving freq approaches resonant freq


  • system gains more and more energy from the driving force
  • and so vibrates with rapidly increase amplitude
  • when this happens the system in resonating


When does damping happen?

  • when energy is lost to the surroudning
  • in practice, any oscillating system loses energy to its surroundings



WHat causes damping?

  • damping forces
  • e.g. friction like air resistance




What is the effect of damping, and what does heavier damping mean?>

  • damping reducess the amplitude of the oscillation over time
  • the heavier the damping, the quick the amplitude is reduced to zero




What is critical damping?

  • reduces the amplitude in the shortest possible time


How does damping affect resonance

  • lightly
    • sharp resonance peak 
    • their amplitude only increases dramatically when the driving freq is very close to resonant freq
  • heavily damped system
    • flatter response
    • ampltude doesn't increase much near the resonant freq and they aren't as sensitive to the driving freq
  • lighter the damping
    • larger max ampltide at resonance
    • closer the resonant freq is to natural freq of system


What are the types of damping?