Mechanical Engineering - Theory of machines - Discussion

3. 

In a vibrating system, if the actual damping coefficient is 40 N/m/s and critical damping coefficient is 420 N/m/s, then logarithmic decrement is equal to

[A]. 0.2
[B]. 0.4
[C]. 0.6
[D]. 0.8

Answer: Option C

Explanation:

No answer description available for this question.

Bheemesh said: (Aug 5, 2013)  
Logarithmic Decrement = 2*(Pi)*Zeta/sqrt(1-zeta^2).

Where zeta = Actual damping coefficient/Critical damping coefficient.

Yas said: (Apr 26, 2014)  
2*pi*(40/440)/sqrt(1-(40/440)^2.

The Sark said: (Oct 5, 2014)  
2*pi*(40/420)*(1-(40/420)^2) = 0.59.

Gaurav said: (Mar 7, 2015)  
Solution without calculator.

Zeta = 40/420 = 0.1 (approx.).

Log decrements = 2*pie*0.1/(1-0.1^2) = 2*pie*0.1 = 0.63 (approx..).

Sarvesh Jaiswal said: (Mar 12, 2015)  
Ld = 2*3.14*0.1/(1-0.1^2).

Murtadha Abass said: (Jun 25, 2015)  
2*pi*Zeta = 2*3.14*0.09 = 0.565.

Ankit said: (Sep 6, 2015)  
2xpixZeta/sqrt(1-Zeta^2).

Swagat said: (May 28, 2016)  
Thanks for all you explanation.

Pradeep said: (Jul 18, 2016)  
What is zeta?

Peviks said: (Jul 20, 2016)  
Thank you all, it great to understand the solution.

Rohit said: (Jul 22, 2016)  
May be Zeta is the damping coefficient.

Ramu said: (Aug 5, 2016)  
Zeta is damping factor or damping ratio.

Vicky Pooraneeswar said: (Nov 7, 2016)  
Can anyone please explain in a simple way?

Jithin said: (Dec 8, 2016)  
@Vicky.

Just find logarithmic decrement using following equation.

Logarithmic Decrement = 2 * (Pi) * Zeta/sqrt(1-zeta^2).

Where zeta is ratio of Actual damping coefficient/Critical damping coefficient.

Kareena Shah said: (Dec 17, 2016)  
Perfect answer @Jithin.

Mohan said: (Feb 8, 2017)  
Good explanation. Thank you all.

Nagamalleswarao said: (Feb 16, 2017)  
Could you please confirm the zeta. Is this zeta is a damping factor or damping coefficient, or both are same?

Mech Hod said: (Apr 14, 2017)  
LD = 2 x π x 40 / sqrt(420^2-40^2) = 0.601.

Pranay Mishra said: (May 11, 2017)  
I am not getting this, Explain it simple way, please.

Leela said: (Jun 13, 2017)  
Cc=2π40/420 = 0.61.

Prince Kumar said: (Jan 13, 2018)  
@Pranay Mishra.

Logarithmic decrement is the rate through which amplitude of free damped vibration is decreases.

It is only for under damped vibration system.

Mithun Kumar said: (Dec 22, 2018)  
Since ln(x0/x1)= 2 * π*zeta/√ (1-zeta^2).

Where zeta=actual damping coefficient/critical damping coefficient.

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