Vibration Theory
Vibration Isolation reduces the level of vibration transmitted to or from a machine, building or structure from another source.
The degree of isolation achieved depends on the ratio:2: The level of isolator damping C/Cc.
Referring to the diagram 3.07, the degree of isolation is given as Transmissibility (i.e. amount of vibration transmitted at a specific frequency ƒe as a fraction of the disturbing vibration at the same frequency ƒe).
Transmissibility
> 1 = Increased transmitted vibration
= 1 = No vibration isolation
< 1 = Vibration isolationTransmissibility T can be read from diagram 3.2 or calculated as follows:
If no damping present in isolators i.e. C/Cc = 0
Damping Factorfrequency ratio R fe/fn
| C/Cc | 1.5 | 2.0 | 2.5 | 3.0 | 3.5 | 4.0 | 4.5 | 5.0 |
|---|---|---|---|---|---|---|---|---|
| 0.05 | 20 | 66 | 80 | 87 | 91 | 93 | 94 | 95 |
| 0.10 | 19 | 64 | 79 | 85 | 89 | 91 | 93 | 94 |
| 0.15 | 17 | 62 | 76 | 83 | 87 | 90 | 91 | 93 |
| 0.20 | 16 | 59 | 74 | 81 | 85 | 87 | 89 | 91 |
| 0.30 | 12 | 52 | 67 | 75 | 80 | 83 | 85 | 87 |
| Percentage Isolation Efficiency | ||||||||
Ktd = Sum of Isolator Dynamic Spring Constants
(K1+K2+K3…) N/m
M = Supported system mass kg.
For natural rubber and coil spring isolators static and dynamic spring constants are the same.