Learning Forum

[murali]

How do I give a value for damping ratio in Transient analysis? The damping controls show only Stifnness coefficient and Mass coefficient. If there is no option to define the damping ratio directly where can I find the alpha and beta values for my problem?

[Akshay Maniyar]

Hi Murali,

Please check the below AIC course for more details on damping.

Damping | Ansys Innovation Courses

Thanks,

Akshay maniyar

[murali]

Hi, I had watched the video. While doing MSUP analysis there is an option to give damping ratio directly in the damping control. But while doing full transient analysis, that option is not there. There is a dropdown with damping vs frequency. Will it be enough to enter the value there?

[murali]

In the damping vs frequency option, what frequency should i enter??

[Rahul Kumbhar]

You need to input the structural damping coefficient for stiffness matrix or mass matrix or both. Whereas Damping ratio is ratio of system damping to the critical damping. Generally Structural Damping Coefficient = 2 x Damping Ratio.

[murali]

Hi, all I have for the problem is the damping ratio 0.01. I need to do transient analysis on a beam. My doubt is how do I find out the stiffness and mass coefficient from the damping ratio value that I have. On the other hand, in the option damping vs Freq, I am supposed to enter frequency along with the damping ratio. What frequency should I enter?? Is it the natural frequency??

[murali]

Any help would be appreciated.

 

[Erik Kostson]

Hi

This is a very good discussion:

/forum/forums/topic/material-damping-and-modal-analysis/

All the best

Erik

[murali]

 

Hi Erik,

I had seen this discussion as well. I have a confusion as to what value of frequency we need to give with the damping ratio. 

What I am trying to do here is to find the transient response of a cantilever beam to an intitial displacement. I need to find out the reponse of the beam to different damping scenarios. I have a set of damping ratios (coulomb damping) obtained experimentally. I am tryuing to simulate the condition. So need to conduct thze anlysis for different damping values. 

 

[Erik Kostson]

 

See that discussion Peteroznewman explains what Ansys does when you give a frequency of interest (say the freq. of your dominant mode of interest that will be excited – frequency_given) and a damping ratio (damp_ratio_given).

As he says, it calculates 
beta = (2*damp_ratio_given)/(2*PI*frequency_given).

You can check that in Ansys yourself, by giving freq. = 20 Hz, damping ratio = 0.01, then Ansys will give a beta as =

0.000159

All the best, and perhaps some other forum members can give some more feedback, but the post and this should explain (also see some more material on the internet about Rayleigh damping.

Erik

 

[murali]

So this frequency is the undamped natural frequency of the beam, right??

 

 

[Erik Kostson]

See that discussion Peteroznewman explains what Ansys does when you give a frequency of interest (say the freq. of your dominant mode of interest that will be excited – frequency_given) and a damping ratio (damp_ratio_given).

As he says, it calculates 
beta = (2*damp_ratio_given)/(2*PI*frequency_given).

So if you want a damping ratio of 0.01 at your frequency of interest (say 20 Hz) that are the values you put in. So beta will give you then 0.01 damping at 20 Hz that all the equation says.

[murali]

Clear. Thanks a lot.

[Erik Kostson]

Glad we could help.

Erik