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Torsional Pendulum, Logarithmic Decrement

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tone999
#1
Jul21-09, 06:24 PM
P: 18
The amplitude of a torsional vibration decreases so that the amplitude on the 100th cycle is 13% of the the amplitude of the first cycle. Determine the level of damping in terms of the logarithmic decrement.

Is this simply ln(100/13)= 2.04

or ln(13/100)= -2.04?
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rl.bhat
#2
Jul22-09, 06:18 AM
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P: 4,433
Quote Quote by tone999 View Post
The amplitude of a torsional vibration decreases so that the amplitude on the 100th cycle is 13% of the the amplitude of the first cycle. Determine the level of damping in terms of the logarithmic decrement.

Is this simply ln(100/13)= 2.04

or ln(13/100)= -2.04?
Level of damping δ = 1/n*ln(xo/xn)
where n is the number of cycles, xo is the initial amplitude and xn is the amplitude after n cycles.


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