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Homework Help: Spring, Mass , Dumper system. Dumper Value.

  1. May 17, 2010 #1
    Spring, Mass , Damper system. Damper Value.

    1. The problem statement, all variables and given/known data


    I have a problem with first question from site below:

    3. The attempt at a solution

    I was trying to solve it using transmissibility equation but there is no mass so I cant find a natural frequency.

    Transmissibility is in this case 0.01% because the isolation required is 99.9%.

    T= sqrt {[1+4*d^2*(f/f0)^2]/[(1-(f/f0)^2)^2 + 4*d^2*(f/f0)^2]}

    d- damper value
    f- frequency which is 100Hz
    f0- natural frequency

    The other way is to use dynamic equation and then find transfer function:

    dynamic equation: cx' + kx = M x''

    but the Mass is unknown and it's the problem.

    Please help
    Last edited: May 17, 2010
  2. jcsd
  3. May 18, 2010 #2


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    Staff Emeritus
    Science Advisor
    Gold Member

    I believe you are correct - you need the mass, and there is no way to absorb it into the value of the damping coefficient. I guess you could proceed by assuming some convenient value for the mass.
  4. May 19, 2010 #3
    Thanks for answer,

    The other way that i was trying to assume that system is in resonance because of low damper value, but 100Hz of forcing frequency doesn't need to be natural frequency.:(

    First question when I have started to practice and I found without enough data.

    Ehhh I'm lucky :cool:
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