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[Jan Stránský <question701385@xxxxxxxxxxxxxxxxxxxxx>]

Question #701385 on Yade changed:
https://answers.launchpad.net/yade/+question/701385

    Status: Needs information => Answered

Jan Stránský proposed the following answer:
Hello,

> (1) the curve is not smooth, why?

DEM, discrete/distinct element method, is **discrete**.
You are dealing with discrete points in space and discrete instances of time.
The results are values at discrete time steps.
The resulting "curve" is not smooth by definition..

If you mean non-linear, non-monothonic or something similar, there are a few reasons.
- triaxial engines for prescribed stress does not directly prescribe stress, but rather "guess" strain (rate) such that stress matches the desired value. This "guessing" may cause some fluctuation.
- inertial and dynamic effects cause fluctuations naturally 

> (2) It seems that different results can be got when run the same
simulations for several times. which factors cause this uncertainty?

There are a few main factors:
- uncertainty by design, e.g. using python random package, for some stochastic analysis
- multi-core running [1]
- using PyRunner with realPeriod, which can be executed at different simulation times each run
- nondeterminism in 3rd party software

Cheers
Jan

[1] https://yade-dem.org/doc/formulation.html#result-indeterminism

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