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THE SCIENCE AND APPLICATIONS OF ACOUSTICS - H. H. Arnold ...

THE SCIENCE AND APPLICATIONS OF ACOUSTICS - H. H. Arnold ...

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588 20. Vibration and Vibration ControlCase 3: ξ = 1(Critically damped system)The roots are s 1 , s 2 =−ω n and system response is given byx(t) = Ate −ω nt + Be −ω ntCase 4: ξ = 0(Undamped system)The roots are s 1 , s 2 =±iω n and the system response is given byx(t) = A cos (ω n t + θ)Figure 20.2(b) shows the domains of the roots in the s plane as a function of thedamping ratio ξ for a constant value of ω n .In order for us to appreciate the influence of system damping, consider the systemof Figure 20.1 which is subjected to an initial displacement x 0 and whichhas no external forcing function acting on it. The dependency of the response ofthe system on the root locations is shown in Figure 20.3 for ω n held constant. InFigure 20.3. System responses showing the influence of root location in a second-orderdynamic system.

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