Hi.
If i do a modal analysis for a structure. And, I use different damping models (such as: viscous damping model, structural damping, and so on.). So, How is effect of using different damping models in output of a modal analysis ? I mean what is meaning of output for these cases different?
Thank you so much.
Dear Mr. Dung,
the damping parameter in a dynamical system defines how the amplitudes of dynamic response decay with time. Based on the type of energy dissipation mechanism, the rate of decay varies (currently amplification of response is not touched upon - negative damping). Various types of damping mechanisms exist in different systems/ structures, which require specific mathematical modelling approach. Classically damped structures are considered to exhibit proportional damping to the way mass/ stiffness distributed in the structure; whereas, non-classically damped structure need not be proportional as such.
If example of concrete member/ structure is taken then depending on the extent of cracks induced in it, the magnitude of damping varies. Hence, frequency dependent damping (and/or for large deformations, amplitude dependent) may be considered such that corresponding to the modal (Eigen) frequencies the damping in each mode also vary. The viscous damping model probably is the most simple and widely used damping model, which is also many times used to model "equivalently" other types of damping mechanisms.
Hope this answers your query.
All the best.
With best regards,
Vasant Matsagar.
Hi I suggest you read second chapter of "Modal Testing: Theory, Practice and Application", 2nd Edition. by D.J. Ewins
It completely explains the difference.
Dear Vasant Matsagar.
First, i want to say: Thank you so much for your regard.
You said that "The viscous damping model probably is the most simple and widely used damping model, which is also many times used to model "equivalently" other types of damping mechanisms".
Actually, i begin only studying on modal analysis. And, i'm reading a book by Zhi Fang Fu and Jimin. He. And. in that, mathematically, when you use non-proportional viscous damping model to take into account damping into your model. It is more difficult to solve than structural damping model, and, you have to use "state-space approach" to solve it. And, they said when no have any evaluation on effect of using different damping models in output of a modal analysis, we can then use structural damping models because reason as i said.
So, in the paragraph above that i highlighted in "...". I have a question for you. What are fields where viscous damping model is used widely? and as i said above, mathematically, structural damping model (non-proportional) is more simple.
Of cause, may be i didn't understand their mean, fully.
Best Regard.
For more information the book i suggested analyse the systems below:
-Undamped systems
-Proportional viscous and proportional structural (hysteretic) damping
-General case (non-proportional) for both viscous and structural damping
hope it helps
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