Damped forced vibration {[1-(u/un)2]2+[2u/wm2y2 c=01 =0.2 =0.5 0.5 15 2.5 /w,Damped Forced Vibration X = δst {[1 − (ω/ωn) 2] 2 + [2ζω/ωn] 2} 1/2 0 1 2 3 4 5 6 0 0.5 1 1.5 2 2.5 3 6