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Dynamics cheat sheet

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5.4 impulse F 0 δ (t) loading<br />

⎧<br />

⎨ −iω<br />

roots<br />

ζ = 0<br />

⎩<br />

+iω<br />

u ′′ + ω 2 u = 0<br />

ζ < 1<br />

ζ = 1<br />

ζ > 1<br />

transient<br />

{ }} {<br />

u (t) = u(0) cos ωt + u′ (0)<br />

⎧<br />

ω<br />

⎨ −ξω + iω √ 1 − ξ 2<br />

roots<br />

⎩<br />

−ξω − iω √ 1 − ξ 2<br />

steady state<br />

{ }} {<br />

sin ωt + F 0<br />

sin ωt<br />

mω<br />

transient<br />

steady state<br />

{ (<br />

}} ){<br />

{ ( }} ){<br />

u (t) = e −ξωt u(0) cos ω d t + u′ (0) + u(0)ξω<br />

sin ω d t + e −ξωt F0<br />

sin ω d t<br />

⎧<br />

ω d<br />

mω d<br />

⎨ −ω<br />

roots<br />

⎩<br />

−ω<br />

u (t) = (u (0) (1 + ωt) + u ′ (0) t) e −ωt + F 0t<br />

⎧<br />

⎨ λ 1 = −ωξ + ω √ ξ 2 − 1<br />

roots<br />

⎩<br />

λ 2 = −ωξ − ω √ ξ 2 − 1<br />

⎧<br />

u (t) = Ae<br />

⎪⎨<br />

λ1ωt + Be λ2ωt +<br />

⎪⎩<br />

A = u′ (0)−u(0)λ 2<br />

2ω √ ξ 2 −1<br />

B = −u′ (0)+u(0)λ 1<br />

2ω √ ξ 2 −1<br />

m e−ωt<br />

F 0<br />

m<br />

2ω √ ξ 2 −1 eλ 1ωt −<br />

The impulse response can be implemented in Mathematica as<br />

parms = {m -> 10, c -> 1.2, k -> 4.3, a -> 1};<br />

tf = TransferFunctionModel[a/(m s^2 + c s + k) /. parms, s]<br />

sol = OutputResponse[tf, DiracDelta[t], t];<br />

F 0<br />

m<br />

2ω √ ξ 2 −1 eλ 2ωt<br />

Plot[sol, {t, 0, 60}, PlotRange -> All, Frame -> True,<br />

FrameLabel -> {{z[t], None}, {Row[{t, " (sec)"}], eq}},GridLines -> Automatic]<br />

26

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