# yade-users team mailing list archive

## Re: [Yade-dev] moment calculation and rotational speed problem

```Hi, Dear Bruno,

but for a real condition---assume a compression test,
just change the v from 20 m/s to 2 mm/s --this is a reasonable speed for
compression test
It will get a rotational speed will be 0.5rad/s (about 30 deg/sec) after a
1e-6 sec , well it is a very large value than I expected .
The rotated angle is delta_theta=0.5 rad/s * (1e-6 s) = 5e-7 rad = 1.5e-5
deg (rounded by assuming Pi=3)----well, this looks like reasonable .

one more question:
since in a rock, the particle is restrict by the cementing like material
between the particle, can we assume the particle can rotate freely as what
we calculated in here? Especially when the contacts on one particle are
many, the resistant force will be large and so the resistance to rotate is
also very large, it is not easy to lead to rotate with external moment
disturbance.

Thanks again.

Regards.

Kan

On Mon, Mar 2, 2009 at 11:26 AM, Bruno Chareyre
<bruno.chareyre@xxxxxxxxxxx>wrote:

>
>> , [...] particle radius is 1e-3 m, one particle is static, another one is
>> 20m/s [...]
>> rotational_speed= rotational_speed + rotational_acceleration * dt = 0 +
>> (5e9)*(1e-6)= 5e3 rad/sec !!!!!! WRONG!!!!
>>
>
> Why wrong? If I take the translational velocity divided by the radius, it
> gives 20/1e-3 = 2e4 rad/s, the same order of magnitude as 5e3 rad /s. So I'd
> say it is consistent (imagine the mobile particle has to roll on the other
> one with this initial velocity, a fraction of the initial momentum is
> converted into rotational momentum, that is why 5e3 is lower than 2e4).
>
> Bruno
>
>
>
>>    _______________
>>    Chareyre Bruno
>>    Maitre de conference
>>
>>    Grenoble INP
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>>    BP 53 - 38041, Grenoble cedex 9 - France
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>>    ________________
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>>
>>    _______________________________________________
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>
> --
>
> _______________
> Chareyre Bruno
> Maitre de conference
>
> Grenoble INP
> Laboratoire 3SR - bureau E145
> BP 53 - 38041, Grenoble cedex 9 - France
> Tél : 33 4 56 52 86 21
> Fax : 33 4 76 82 70 43
> ________________
>
>
> _______________________________________________