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Equivalent stiffness and damping

  1. May 11, 2013 #1
    1. The problem statement, all variables and given/known data
    A scheme of springs and dampers is given. What is equivalent stiffness and damping?

    vibrations.png

    2. Relevant equations
    For stiffness in series: keq=ka*kb/(ka+kb)
    For stiffness in parallel: keq=ka+kb
    For dampers similarly.

    3. The attempt at a solution

    To me it looks like k1 and k2 are in parallel. After summation I'd say that k3 is in series and calculate for that. Dampers c1 and c2 seem to be in series so I'd calculate them similarly.

    I'm puzzled because textbook says that k3 is parallel to k1 and k2 and simply sums it up (keq=k1+k2+k3). I doubt it's like that, could you also explain about c1 and c2?
     
  2. jcsd
  3. May 11, 2013 #2

    rude man

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    Best thing to do is go back to Newton: mx'' = ƩFx.

    Call x = 0 when the mass is in its equilibrium position. If m goes up (x > 0) what are the forces acting on m?

    You will see that your textbook is right ...
     
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