BAJA/SAE engine support

AcostaAcosta Member Posts: 3
edited August 2020 in Student Competition

Hello,I'm simulating the engine support for my team's BAJA/SAE.

I have coupled static structural, modal and random vibration simulation. However, I had never used random vibration before and wanted to know if I am doing it wright.

We know that the engine will have a maximum vibration of 85 Hz, so in my PSD displacement tabular data I used frequency values between 1 and 85 Hz, for the displacement I used my stactic structural maximum deformation. Is this the wright way to do it ?

Ps: I tryed using my modal data in the psd, but those vibrations are between 200 and 650 Hz, driving to some bad results.

English is not my first language, please excuse any mistakes.

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Thanks. ?

Best Answers

  • peteroznewmanpeteroznewman Posts: 11,404Member
    edited August 2020 Accepted Answer

    Hello Acosta,

    How do you know the engine will have maximum vibration at 85 Hz?

    Using the displacement from your Static Structural model as a value in a PSD is wrong.

    The right way to get a PSD for input into a Random Vibration analysis is to measure it on an engine on that frame with an accelerometer.

    The accelerometer might have one axis or might have 3 axes. If the accelerometer has one axis, you will have to mount it in three orientations and record three times. The accelerometer should be fixed to the frame using wax or glue, very close to the bolt that fastens the engine to the frame. Repeat this measurement at the three or four places around the engine where it bolts to the frame. You should also take the measurement at a set of engine RPM values because the vibration may be greater at some particular RPM.

    The accelerometer is plugged into a data acquisition system. Some data acquisition systems only record a time history of acceleration. In that case, you need to analyze that data in matlab and compute the PSD from the acceleration-time data. I can help you with that. Other data acquisition systems can compute the PSD as it is measuring the vibration and will output PSD data directly.

    Someone at the University has accelerometers and data acquisition systems. Ask around, there should be a Vibrations lab that has that equipment. If not, there are places where you can rent that equipment for a week or two.

  • peteroznewmanpeteroznewman Posts: 11,404Member
    Accepted Answer

    You can do a Random Vibration analysis if someone has previously measured the PSD with an accelerometer on a similar frame.

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