yade-users team mailing list archive

[chiara modenese <c.modenese@xxxxxxxxx>]

Bruno, I still have some doubts ;( I will try to explain myself. What I see
regarding the shear force is simply the need of a tangent unit vector
exactly for the same reason we define a normal one. The direction of the
normal force is not dependent upon which id is which because we define the
normal vector, but in the shear direction we are not defining any vector of
reference... I can see what you mean in the normal direction but not in the
shear one. Can you see my point? Am I completely wrong?

Thanks for your help, Chiara


On 18 March 2010 19:13, chiara modenese <c.modenese@xxxxxxxxx> wrote:

>
>
> On 18 March 2010 18:38, Bruno Chareyre <bruno.chareyre@xxxxxxxxxxx> wrote:
>
>>
>>   what about the shear velocity? Do you agree that the way we define it is
>>> related to a local system? This is simple to see, just try to invert the ids
>>> and you will see what I mean.
>>>
>>
>> No! It is not related to any local system!
>> Let grainA with id=1, grainB with id=2.
>>
>> Compute relVel, then force=f is applied by grainA on grainB.
>>
>> Now let grainA with id=2, grainB with id=1.
>>
>> the force is now -f, but it represents the one applied by grainB on
>> grainA. What's wrong? This holds whatever the convention.
>>
>> Now, going from one convention to the other just results in 2 sign
>> inversions, you get force=-f instead of force=f, but you apply "force" on
>> body1 instead of body2. Same result.
>>
>> Ops, I was not considering the last sign conversion... Now I see! Thanks a
> lot ;)
> Chiara
>
>
>>  B.
>>
>>
>>
>>
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>