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Car Suspension, sinusoidal road input

  1. Oct 10, 2009 #1
    1. The problem statement, all variables and given/known data
    The question extends more than this but this is where I have difficulty.

    An uneven road surface is modelled by a sinusoid with amplitude 25mm and the car is driven at 100km/hr. Use the bode plot calculate earlier to obtain and explain the steady state force response when the road period is:
    a. 10m
    b. 1m

    2. Relevant equations

    My problem is that i don't know what to use for angular frequency!

    The car suspension looks like this
    http://img27.imageshack.us/img27/2193/matlapassig2fig.jpg [Broken]

    The transfer function looks like this:

    [tex]
    Y(S)=F(S)\frac{sm_{u}ck+k_{t}}{s^{4}(m_{u}m_{s})+s^{3}(cm_{s}+cm_{u})+s^{3}(m_{s}k+m_{s}k_{t}+m_{u}k+s(ck_{t})+kk_{t}}
    [/tex]


    Bode diagram is below:
    http://img223.imageshack.us/img223/7718/bode.jpg [Broken]

    3. The attempt at a solution

    so if the road surface is 25mm in amplitude and the period of the sinusoidal is 10m. The car is traveling at 100kmph so this is 27.777m/s. This means the car completes one cycle of the road in 0.36 seconds.
    f = 0.36 Hz
    [tex] \omega = 2* \pi *f = 2.26 rad/sec [/tex]

    From here i just use the bode plot to find amplitude and phase. This, from what i believe, means the height the driver will move and the delay...


    \\OR



    being that the road period is 10m, do i just use this:
    [tex] \omega = \frac{2* \pi }{10} = 0.63 rad/sec [/tex]



    Can someone please verify that i am calculating the correct angular frequency. I think my first method is correct, but i just want to make sure.
     
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Oct 12, 2009 #2

    berkeman

    User Avatar

    Staff: Mentor

    One cycle in 0.36 seconds would be the period. How do you get the frequency in Hz from the period in seconds?
     
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