Yade

material damping

Asked by Ehsan Izadi

Hey,

I am simulating a number of gravels in a cylinder. And then make the cylinder to vibrate in a horizontal direction with frequency of 2~5 cps and amplitude of 10~25 mm. I am going to investigate compaction of the whole mass after vibration.

But the problem is that I don't know what value to put for damping to get realistic results?
I use linear elastic material for my particles.

Actually I found a range [1] for that, but I need to be more accurate.
Does anyone can help me?

Thank you in advance.
Regards,
Ehsan

[1] : http://books.google.be/books?id=wRxhiHf-ieIC&pg=PA191&lpg=PA191&dq=kokusho+1987+damping+ratio+soil&source=bl&ots=OKD1LyrMUb&sig=44MCwjFM01MgC4MplgjoqaTEUno&hl=en&sa=X&ei=Q-n4UpHELKWL0AXRqoCQDA&ved=0CCgQ6AEwAA#v=onepage&q=kokusho%201987%20damping%20ratio%20soil&f=false

Question information

Language:
English Edit question
Status:
Solved
For:
Yade Edit question
Assignee:
No assignee Edit question
Solved by:
Luc Sibille
Solved:
Last query:
Last reply:
Revision history for this message
Best Luc Sibille (luc-sibille) said : 		#1

Hi Ehsan,
Unfortunately, I think there is no way to determine a priori the value of the damping to use to make your simulations. In my opinion, when you aim to simulate the dynamic behaviour of granular media (I think it is your case), the damping should be calibrated from simple tests (for instance the bounce of one grain over a layer of other fixed grains, or the attenuation of elastic waves measured with bender elements ...), as the contacts stiffnesses and friction are calibrated.

Besides, note that different kinds of damping can be used. There is for instance a viscous damping introduced in the contact law, or the Cundall's non-viscous damping (which consists more or less to play with the inertia of grains). Cundall's damping may be more approriate to simulate quasi-static behaviour, viscous damping may be more realistic for dynamic simulation. I think you can find more details about that in dedicated papers.

Luc

Revision history for this message
Luc Sibille (luc-sibille) said : 		#2

Sorry, one of the sentences was incomplete:
the damping should be calibrated from basic tests, as contact stiffnesses and friction are calibrated from reference tests (triaxial compressions for instance).

Luc

Revision history for this message
Ehsan Izadi (ehsan-izadi) said : 		#3

Thanks Luc Sibille, that solved my question.

Revision history for this message
Alexander Eulitz [Eugen] (kubeu) said : 		#4

Hi Luc,
interesting topic you address. Could you please give some more examples for such basic tests for calibration of damping? I am interested in this topic, too.
Thanks,
Alex

Revision history for this message
Luc Sibille (luc-sibille) said : 		#5

Hi Alex,

Actually I know almost nothing about dynamic and impact behaviour of granular matter, I just know some colleagues in Grenoble who studied such questions. You can find some of their papers here:
http://link.springer.com/article/10.1007/s10035-008-0108-0
http://www.sciencedirect.com/science/article/pii/S0141029610003147
in which they explain how they chose the damping parameters.

Best,
Luc

Revision history for this message
Václav Šmilauer (eudoxos) said : 		#6

Hi Eshan, if you study dynamics, you should not use the nonviscous damping (which is the one to be used with the linear contact model) as that one is a purely numerical device to dissipate energy in simulations to achieve quasi-static state: the quasi-static state is "physical" but the dynamics involved not. You should use perhaps some of the contact mechanics models (such as the Hertz-Mindlin, JKR, ...) which can define coefficient of restitution. You could check http://woodem.eu/doc/theory/contact/hertzian.html and http://woodem.eu/doc/theory/contact/adhesive.html out for some theory behind that. HTH, Václav