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How to set the damping coefficient of a crowd of powders

Asked by Yufan Zhao

Hello everyone,

I have a problem in setting the damping coefficient of powders. Could any one teach me how to determine this parameter.

My simulation is setting a cloud of metal powders which are settled down on a steel platform by gravity and then the powders is moved by a metallic rake from one side horizontally. That is the powder delivery process in powder bed additive manufacturing.

I have defined the powder, platform and rake with respective material properties. But I have no idea about the appropriate value of damping coefficient of powders.

I appreciate any helps.

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Bruno Chareyre
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Bruno Chareyre (bruno-chareyre) said : 		#1

Hi, I would suggest to make Newton's damping 0 in such case, since it is not a physical damping.
The question is if you need damping at all, I'm not sure of that. If you need some you could go for some sort of viscous contact damping.
As for which contact viscosity would be best I'm afraid I have no clue. A parametric analysis compared with measurements could help to decide.
Bruno

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Bruno Chareyre (bruno-chareyre) said : 		#2

I meant to make damping zero after the initial deposit is stable. If yo umake it zero from the beginning the gravitational deposition will take ages.

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Yufan Zhao (zhyf90215) said : 		#3

Bruno, thank you very much.
But I don't know your meaning that there is no physical damping clearly.

"kinetic energy of particles needs to be dissipated since the energy
dissipation through friction damping during sliding may not be enough to obtain
numerical stability within a reasonable convergence time to quasi-steady state .
Hence, a local non-viscous damping is added as a force term"----I saw similar states in some paper that conducted simulation under the case of powder bed additive manufacturing. And they set the damping coefficient as 0.75 but without further explaination.

Maybe I didn't understand its meaning. Can you give some tips for it?

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Best Bruno Chareyre (bruno-chareyre) said : 		#4

>"your meaning that there is no physical damping"

I meant that NewtonIntegrator::damping is a numerical trick to slow down the system. It does not correspond to any law of physics, so you better don't use that for realistic simulation of granular flow.

> "kinetic energy of particles needs to be dissipated since the energy
dissipation through friction damping during sliding may not be enough"

This is a very common fairy tail, leading to some bad practice. I actually do undamped simulations quite often, in many cases it is completely safe (not always though), and sometimes computationally more efficient (because the loading rate can be increased). So, I'll not try to justify the above claim. Instead, I would say: a problem that "may" occur should not be fixed by making the numerical model physically inconsistent.
I would start pushing the layer without damping. If you observe blatantly excessive bouncing of some elements then you can think of using viscous contacts, else you can just forget the issue I think.

Bruno

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Yufan Zhao (zhyf90215) said : 		#5

Thanks Bruno Chareyre, that solved my question.