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The following Miles equation calculates a quas-static acceleration which
simulates the 3σ
acceleration at a given frequency:
where:
g = the equivalent quasi-static acceleration
3 = 3σ Raleigh
distribution
PSD = the power spectral density at the resonant frequency
Q = the transmissibility at resonance (typically square root natural
frequency)
F = the resonant frequency
TRANSMISSIBILITY, Q
The transmissibility, Q, of a component can be conservatively
estimated to be the square root of its natural frequency. Typical values range
from 15 to 25 depending on the application. Real values can only be obtained
through vibe testing.
APPLYING G LOADING TO FEA (BASED ON METHOD I)
From the Mile's equation, the resulting quasi-static
acceleration is applied as a static body load in a finite element model (FEM) of
the component. In the FEMAP preprocessor, the 3s g loading should be multiplied
by gravity, 386.4 (in/sec2), to convert it into an acceleration loading.
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