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Modal analysis of an automobile

  1. Jun 18, 2014 #1
    I need to locate a safe region in an automotive, where vibration level is very low.

    i have done modal analysis of that vehicle. In the result i got DMX valve. which is maximum deflection value. what does it actually represent?
    Does it means the amplitude of vibration.
    Can i conclude that the region with minimum displacement value as safe region (low vibration)

    thanks and regards
  2. jcsd
  3. Jun 22, 2014 #2


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    Science Advisor

    Welcome to PF.
    Yes, the peak displacement amplitude. Not the maximum acceleration, not the maximum velocity.

    My guess is that the most stable place will be low down on the mid-line of the vehicle, half way between the front and rear wheels. That is, next to where the driver's seat is usually mounted.
  4. Jun 23, 2014 #3
    Thank you for your reply and useful information.

    I have one more doubt.

    While doing modal analysis, I am asked to fix the tires (Boundary condition). That automotive is electric. So from specification sheet i got RPM(Rated revolution). from which i calculated frequency. I got mode shapes upto that frequency.

    Is the process I followed, right?

    Because, as tires are fixed vehicle can't move.
    and motor can't run at so much speed(rated revolution) when vehicle is stationary.

    If this process is wrong how can i proceed?
  5. Jun 23, 2014 #4
    It's not really that clear what you are doing. So it's hard to give any advice.

    There are many, many modes from a vehicle:
    Vehicle rigid body (translation and rotation modes)
    Vehicle bending modes
    Powertrain rigid modes (generally based on mounting bushes)
    Powertrain bending modes

    So a nodal point for one mode, might sit on a massive peak of another mode.
  6. Jun 23, 2014 #5
    To be clear:

    problem statement: I have one manually operated electric vehicle. I need to automate it. For which i need to add many sensitive on-board electronics to it. My work is to locate safe region for these electronics.

    What I have done: I created the model and run modal analysis in ANSYS. As it is electric vehicle and motor rated rpm is 3480, i calculated frequency as w=(N/60)=(3480/60)=58hz

    I gave frequency range between 0 to 58 and got around 13 natural frequencies and mode shapes.
    Finally I am concluding that in all these mode shapes, where ever DMX value is lower, will be the safe area for those electronics.

    My guide told me that there will be only translation modes are present but no rotational modes. he told me the reason but I dont remember as of now.
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