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[Bruno Chareyre <bruno.chareyre@xxxxxxxxxxx>]

V
>>> Bruno, how does this value compare to critical timestep calculated from
>>> elastic wave propagation speed along the particle calculated for
>>> cotinuum, i.e. , which is 2*particle diameter / sqrt(Young's modulus /
>>> density)?
>>>       
I see how it compares now, with global stiffness approach we have :

- The stiffness of one contact is proportional to D*E  (D : particle 
diameter, E elastic modulus)
- The mass of one particle is proportional to density*pow(D,3)

So, if a particle has only one contact, its critical timestep (with 
global stiffness approach) will be :
sqrt(mass/stiffness) = D*sqrt(density/E) = your equation.

Advantage :
The underlying physics is the same but your equation is faster.

Potential problems :
-As soon as a particle has two contacts it will explode.
-If shear stiffness is high compared to normal stiffness (unusual 
situation in fact), it will explode.

Conclusion : you need to find a reasonable value for a security 
coefficient to include in your expression.

Bruno










>>>     
O



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Chareyre Bruno
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Institut National Polytechnique de Grenoble
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