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How does damper work?

  1. Aug 18, 2015 #1
    Hi guys. It could be an easy question but I started at the deepest. I wonder how it works like a car suspension system. How does damper work with spring? What is the difference between forced-nonforced systems? Why do we calculate frequency of spring? What does it provide us? What is the point at writing motion equation? I need backup a little bit. I already thank you.
     
  2. jcsd
  3. Aug 18, 2015 #2

    DEvens

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  4. Aug 19, 2015 #3
    Thanks DEvens. I just wanted to some nonacademical info because I've already reviewed lots of site as yours. I wanted to talk fundamental concept. I have books :) I will consider your words. I will focus on just one topic.
     
  5. Aug 20, 2015 #4

    jack action

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    That would be a free system where only the gravity acts on it:

    Animated-mass-spring.gif
    A forced system would have an exterior force that would push and/or pull the mass (perhaps someone's hand or road disturbances on a moving vehicle).

    One fascinating thing about a forced system, is that if you set the force at a certain frequency (like pushing a kid on a swing), you can observe that the motion amplitude will increase under that force, sometime until the spring breaks. We call this frequency the resonance frequency of the system (not just the spring).

    Why do we care? Here is the typical example to demonstrate what can happen under this phenomena (the bridge's own weight represents the mass, its structure represents the spring stiffness plus some damping and a small wind creating turbulences under and over the bridge at the critical frequency is the force «gently» pushing the bridge):


    So now the questions are «Why?», «How do we identify this frequency?» and «How can we attenuate the phenomena?» The answer lies in the equations of motion, hence their importance.

    The damper provides the force that goes against the motion and can thus attenuate the amplification and slows down the motion until the mass goes to rest (without damping, the motion never stops, like in the previous animation).

    The damping is almost always provided by some form of friction to take energy from the system:
    • The surrounding air acting against the mass will eventually slow down the motion;
    • In the elastic hysteresis of rubber, energy will be dissipated due to material internal friction;
    • A shock absorber will force a fluid passing through a small valve;
    • etc.
     
    Last edited: Aug 21, 2015
  6. Aug 21, 2015 #5
    Thank you very much for your comment. It was very illuminative knowledge for me.
    P.S The video is the best :D
     
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