ESyS-Particle

force in non-rot bonds

Asked by Dian

Hi all,

A couple questions about forces in non-rot bonds.

(1) When the initial pack of particles is set up and NRotBondPrms is applied, particle pairs could have space in between (i.e., D>R1+R2), be right in contact (D=R1+R2), or be slightly overlapped (D<R1+R2). D is distance of particle centers; R1 and R2 are radii of two paired particles. So, are there initial forces in the bonds of the particle pairs for any of the three situations? My guess is that force=0 for any initial particle pairs unless the D increases or decreases along with evolution of the model.

(2) How to give a value for "breakDistance" in NRotBondPrms, if I have a pack of particles with a range of sizes. Saying, I want the bond to break at D>=1.1*D0, where D is present distance of a particle pair and D0 is initial distance. So theoretically, I think the breakDistance should be 1.1*D0 for a given particle pair. However, D0 is not a single value for all particle pairs, particularly for a pack with particle size distribution, so how to give the value of breakDistance, practically.

(3) After the bonds break, can I use NRotElasticPrms and NRotFrictionPrms at the same time for un-bonded particles when they get to touch. My guess is NO, but I am not sure how the elastic rebound and/or friction work for a un-bonded and touched particle pair.

Just want to clarify some basic concerns. Thanks for answering.

Best,
Dian

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  • by Dian
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Dion Weatherley (d-weatherley) said : 		#1

Hi Dian,

Regarding question (1):
NRotBondPrms currently sets the equilibrium separation as the sum of the particle radii (R1+R2). Consequently there are small initial forces between particle pairs as the initial separation of the particles is not precised (R1+R2). The development team would like to change this so that the equilibrium separation is equal to the initial separation, however doing so caused problems when bonds break and are replaced with NRotFrictionPrms. We're working on a solution for this at the moment.

Regarding question (2):
The breakDistance provided as an argument to NRotBondPrms is a "relative" distance. The actual breaking distance for a given particle-pair is D_b = breakDistance * (R1+R2). Thus, simply set breakDistance=1.1 to achieve your desired results regardless of the particle radii.

Regarding question (3):
> After the bonds break, can I use NRotElasticPrms and NRotFrictionPrms at the same time for un-bonded particles
> when they get to touch.
 There is no need to do this. NRotFrictionPrms implements both elastic repulsion (as in NRotElasticPrms) as well as frictional forces in the shear direction. Hence, just use NRotFrictionPrms subsequent to bond breakage.

Cheers,

Dion

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Dian (hedian18) said : 		#2

Thanks Dion Weatherley, that solved my question.

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Dian (hedian18) said : 		#3

Hi Dion,

After many tests for a while, I found out that the software may not execute exactly what you said regarding question (2). When I gave the breakDistance=1.005, the bond is supposed to be easy to break up for just a little extension, but this is never the case from my tests. Could you help me check what's going on?

Thank you,
Dian

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Launchpad Janitor (janitor) said : 		#4

This question was expired because it remained in the 'Open' state without activity for the last 15 days.