29.2 CONTROL

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Vibrations are the natural result of many engineered systems.

These vibrations can become significant when they shake carefully designed structures, or induce sounds in the air.

As an engineer attempts to suppress or negate vibrations and sound, one of the most powerful weapons is a good analytical understanding of the phenomena.

29.2.1 Vibration Control

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If this displacement is induced by a machine in the next room, and it travels through the floor, we want to isolate the noise source for the high frequency (2000Hz) that will be noticeable as a whine.

Your boss asks you to design a mounting for the machine that gets rid of the high frequency whine.

In this case the bode plot would reduce the noise by over 40dB for the high pitch sound. For the frequencies below 1000 Hz there would not be much reduction, but since this is 1/100th the frequency of the original sound, it should not be a problem.

We check the manuals and find the machine weighs 10000kg, and has 8 mounting points.

The result would look something like,

The force transmitted to the floor is,

To find gain,

We can develop a table of gains and phase angles for the isolator

Consider damping at various frequencies, but consider that with damping the isolation was reduced at the high frequency, but the resonance was also reduced.