Читать книгу Engineering Acoustics - Malcolm J. Crocker - Страница 49
Solution
ОглавлениеThe excitation frequency is f = 1000/60 = 16.7 Hz, or ω = 1000 × (2π/60) = 104.7 rad/s. For 80% isolation the maximum force transmissibility is 0.2.
Using Eq. (2.21) with δ = 0 and noting that isolation only occurs when we get that 0.2 ≥ [(ω/ωn)2 − 1]−1 which is solved giving ω/ωn ≥ 2.45. This result can be also obtained from Figure 2.10. Therefore, the system's maximum allowable natural frequency is fn = 6.8 Hz, or ωn = ω/2.45 = 104.7/2.45 = 42.7 rad/s. Consequently, the maximum isolator stiffness is K = Mωn2 = (300) × (42.7)2 = 5.47 × 105 N/m.
