# yade-users team mailing list archive

## Re: hello? -help with a spinning bucket!

```might I ask how you know if your timestep is too large?  do you compare your results with experiment?  or are there funky results that you have learned to associate with time steps that are too big?

Subject: Re: [Yade-users] hello? -help with a spinning bucket!
Received: Thursday, July 8, 2010, 2:10 PM

Hi,
this is a more-less normal time step for simulations.
Sometimes I have to do:
O.dt = 0.1*pWavetimestep

2010/7/8 Michael Jensen <jenmichael2000@xxxxxxxx>

one thing that I would be particularly interested in is how the formula on this page:

for spherepwavetimestep is computed.

2.8284271247461903e-07 is a very small number, meaning a huge
number of iterations are required (almost 10 million) before a=20
single second goes by in the simulation.  that's a hell of a lot

of iterations!  for one second!  is it really necessary?

-mike..

--- On Thu, 7/8/10, Bruno Chareyre <bruno.chareyre@xxxxxxxxxxx> wrote:

From: Bruno Chareyre <bruno.chareyre@xxxxxxxxxxx>

Subject: Re: [Yade-users] hello? -help with a spinning bucket!
To:
Received: Thursday, July 8, 2010, 10:13 AM

It seems to me that if I put some beads into a container,
then tip the container, the angle at which they start flowing is the
angle of internal friction..  I am not at all sure of this, it seems
far to simple.

Not really. Angle of repose corresponds to "internal packing friction",
which "depends on" contact friction but is not equal.

Most materials have contact friction around 30°. Put this value at
contact in a loose sphere packing and you will get an internal friction
around 18°.

Anyway, you should get realistic results as soon as you define a decent
friction (say between 10 and 40), this is not a crucial parameter yet.

Bruno

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