AdvancedTopic 78 of 106Engineering Mechanics
Vibration isolation
Soft mounts reduce transmitted force when driving frequency is well above natural frequency.
In depth
Isolation reduces transmitted force or motion if excitation frequency exceeds √2·ωₙ; transmissibility TR=√((1+(2ζr)²)/((1-r²)²+(2ζr)²)). Soft mounts lower ωₙ, but too little damping amplifies resonance during run-up.
Key points
- Isolate machine from floor or sensor from floor
- Rubber, springs, air mounts
- Damping trade-off
ExampleEngine mounts isolate cabin from engine vibrations.
What is Vibration isolation?
Soft mounts reduce transmitted force when driving frequency is well above natural frequency.
Why is it important to understand vibration isolation?
Vibration isolators protect sensitive equipment and people from machine vibration, and their design depends on the frequency ratio.
When does isolation work?
Isolation works when the forcing frequency is well above the natural frequency of the mount, because transmissibility then falls below one.
Why can a stiffer mount make vibration worse?
A stiffer mount raises the natural frequency, which may move it closer to the operating frequency and cause more transmission.
How is Vibration isolation used in practice?
Typical applications include mounting a compressor on rubber pads to reduce floor vibration, isolating a precision instrument from building vibration and choosing mounts for a vehicle engine to reduce cabin noise.
What should I learn before Vibration isolation?
Study "Resonance" first (topic 77 of 106 in Engineering Mechanics). It covers the groundwork this topic builds on.
What are the key points of Vibration isolation?
Isolate machine from floor or sensor from floor. Rubber, springs, air mounts. Damping trade-off.
Can you give an example of Vibration isolation?
Engine mounts isolate cabin from engine vibrations.
What comes after Vibration isolation?
The next topic is "Multi-degree-of-freedom systems", which builds directly on this one.
How difficult is Vibration isolation?
It is classed as Advanced in Engineering Mechanics (topic 78 of 106). It is an advanced topic. It assumes you are comfortable with the intermediate topics in Engineering Mechanics.