ESyS-Particle

How to get the inertial(unbalanced) forces in the simulation

Asked by ceguo

Hello everyone,

To ensure the stability of the simulation, some DEM codes use unbalanced forces to control the time step increment and boundary strain ratio. Is it possible to get the unbalanced forces in ESyS?
Now I use the criteria that "dt < 0.1 sqrt(mass_min/k_max)" to control the time step increment and that
"loading ratio < 0.1 minParticleRadius / dt" to control the boundary strain ratio. Are these parameters small enough to ensure a quasi static simulation (set viscosity = 0.5)? Or is it more convincing to control the unbalanced forces as PFC does? I am running a triaxial compression test with unbonded particles assemblies.

Tks
Ning

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Dion Weatherley
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Best Dion Weatherley (d-weatherley) said : 		#1

Hi Ning,

I don't think it is currently possible to obtain the unbalanced forces in ESyS. I'll discuss with Steffen about this.

Regarding criteria for setting dt, I've found that as long as both of these are met, you should have no stability problems. The factor '0.1' is in fact quite a conservative factor-of-safety. In most of my scripts I've coded in these two criteria to ensure dt is always small enough.

Cheers,

Dion.

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ceguo (hhh-guo) said : 		#2

Thanks Dion Weatherley, that solved my question.