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Dynamics cheat sheet

my dynamics notes - 12000.org

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where<br />

A =<br />

B =<br />

F 0<br />

m<br />

2ω √ ξ 2 − 1<br />

− F 0<br />

m<br />

2ω √ ξ 2 − 1<br />

Hence<br />

u impulse (t) =<br />

F 0<br />

(<br />

m<br />

2ω √ ξ 2 − 1 e −ξ+ √ )<br />

ξ 2 F 0<br />

(<br />

−1 ωt −<br />

m<br />

2ω √ ξ 2 − 1 e −ξ− √ )<br />

ξ 2 −1 ωt<br />

If the initial conditions were not zero, then the solution for these are added to the above. From earlier, it<br />

was found that the solution is u (t) = Ae p 1t + Be p 2t , therefore, the full solution is<br />

u (t) = Ae λ 1ωt + Be λ 2ωt +<br />

F 0<br />

F 0<br />

m<br />

2ω √ ξ 2 − 1 eλ 1ωt m<br />

−<br />

2ω √ ξ 2 − 1 eλ 2ωt<br />

8.4.2 sin impulse input<br />

Now assume the input is as follows<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 />

given by F (t) = F 0 sin (ϖt) where ϖ = 2π<br />

2t 1<br />

= π t 1<br />

undamped system with sin impulse<br />

⎧<br />

⎨ F 0 sin (ϖt) 0 ≤ t ≤ t 1<br />

mü + ku =<br />

⎩<br />

0 t > t 1<br />

with u (0) = u 0 and ˙u (0) = v 0 . For 0 ≤ t ≤ t 1 the solution is<br />

( )<br />

( )<br />

v0<br />

u (t) = u 0 cos ωt +<br />

ω − u r<br />

1 π<br />

st<br />

1 − r 2 sin ωt + u st<br />

1 − r 2 sin t<br />

t 1<br />

43

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