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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