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# Ch4-5(correction) - mounting rubber pad So it is expected...

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11 Modal eqs & guessing of damping (wrong) 1 1 2 2 3 3 ( ) 29.0 ( ) 20.6 ( ) ( ) 114 ( ) 5.1 ( ) ( ) 907 ( ) 45.3 ( ) r t r t t r t r t t r t r t t δ δ δ + = - + = - + = - && && && - - = - - = = 011 . 0 424 . 0 906 . 0 , 967 . 0 194 . 0 102 . 0 , 219 . 0 885 . 0 412 . 0 3 2 1 v v v Mode 1 is dominated by x 2 , mode 2 by x 3 and mode 3 by x 1 . Thus the damping in mode 1 will come largely from the platform mounting rubber pad. So, it is expected to be large. Hence choose ζ 1 = 0.1. Likewise ζ 2 = 0.01, ζ 3 = 0.05. This observation is not correct!!!

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Consideration of Mode Shape (correct  approach) 22 Mode 1 is dominated by x 2 –x 3 ; mode 2 by x 2 – x 3 & x 3 ; mode 3 by x 1 x 2 . Thus the damping in mode 1 will come largely from the platform mounting rubber pad.
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Unformatted text preview: mounting rubber pad. So, it is expected to be large. Hence choose Î¶ 1 = 0.1. Likewise Î¶ 2 = 0.01, Î¶ 3 = 0.05. 1 2 3 0.0206 0.0051 0.0453 0.0198 , 0.0043 , 0.0095 0.0025 0.0108 0.0001--= = -=-u u u 33 Damped Modal Equations & Solution Obj104 1 1 1 2 2 2 3 3 3 ( ) 1.08 ( ) 29 ( ) 20.6 ( ) ( ) 0.214 ( ) 114 ( ) 5.1 ( ) ( ) 3.01 ( ) 29 ( ) 45.3 ( ) r t r t r t t r t r t r t t r t r t r t t Î´ + + = -+ + = -+ + = -&& & && & && & Obj106 Dies off slowly, but of small amplitude Dominant terms...
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Ch4-5(correction) - mounting rubber pad So it is expected...

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