About NewtonIntegrator(damping) and utils.PWaveTimeStep()

Asked by jimtianxi on 2012-03-08

I'm researching the soil sampling process using yade. I want to know how to choose the damping parameter of the NewtonIntegrator(damping=) and how it influence the simulation speed. Additionally, I don't know how to choose the simulation step. Usually, O.dt=xxx*utils.PWaveTimeStep(),where xxx is sometimes less than 1, and sometimes more than 1, I want to know how to choose it, and is it related to the property of the soil. Thank you very much!!

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Last query:
2012-03-08
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2012-03-09

Hi,

1. The damping in NewtonIntegrator is an artificial parameter. If you want to use it you need to make sure that it does not influence your results to some level of approximation. You can employ it to accelerate the achievement of quasi-static equilibrium. If you run tests under dynamic conditions you should avoid to use it. I guess you can start using the default value and try to increase it but without much influence on the results (this is what you should check).

2. To prevent numerical instability you generally select a coefficient for the time step computed by PWaveTimeStep() less than 1, something like 0.2 or so. I would not choose a coefficient bigger than 1 as the solution might become unstable (but you should check that too). For the time step definition you can also use another engine in Yade, called https://yade-dem.org/doc/yade.wrapper.html?highlight=timeste#yade.wrapper.GlobalStiffnessTimeStepper, which updates the time step according to the current interactions (see documentation for more details). The time step definition is related to the properties (stiffness, mass and size) of your particles (the formula tells you how those properties are accounted for).
To answer your question, I guess you could run parametric studies for different values of xxx and identify the threshold per which the numerical solution converges.

Chiara

On 8 Mar 2012, at 15:35, jimtianxi wrote:

> New question #190075 on Yade:
> https://answers.launchpad.net/yade/+question/190075
>
> I'm researching the soil sampling process using yade. I want to know how to choose the damping parameter of the NewtonIntegrator(damping=) and how it influence the simulation speed. Additionally, I don't know how to choose the simulation step. Usually, O.dt=xxx*utils.PWaveTimeStep(),where xxx is sometimes less than 1, and sometimes more than 1, I want to know how to choose it, and is it related to the property of the soil. Thank you very much!!
>
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