Page 49 - Rotating Machinery Pratical Solutions to Unbalance and Misalignment
P. 49
Resonance and Beat Frequencies
est amplitude at its unsupported end. Simply marking the location
of the highest perceived amplitude on a component with a felt
marker can assist in determining the mode of the vibration.
If the frequency were to continue to increase above the natu-
ral or fundamental frequency, it would first decrease, and then
increase as it approaches the second harmonic of the component.
At the second harmonic, the component again vibrates freely
and the amplitude increases dramatically. The overall amplitude
of the second harmonic is not as great as the amplitude of the first
harmonic, but the frequency is twice as great.
Figure 3-5 depicts components undergoing second harmonic
vibration.
Figure 3-5. Second Harmonic Wave Forms
By examining Figure 3-5, it is easy to visualize what the third,
fourth, and fifth harmonic would look like.
Figure 3-6. Wave Length
Letting (λ) represent the length of the wave, a system in reso-
nance would have wavelengths of:
λ = 2L/n (3.3)
