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Re: [Question #699589]: i.geom.normal is not normalized (unit) vector from the branch vector (for the case of sphere-sphere contact)

To: yade-users@xxxxxxxxxxxxxxxxxxx
From: Jan Stránský <question699589@xxxxxxxxxxxxxxxxxxxxx>
Date: Mon, 22 Nov 2021 13:50:45 -0000
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Question #699589 on Yade changed:
https://answers.launchpad.net/yade/+question/699589

    Status: Open => Answered

Jan Stránský proposed the following answer:
Hello,

there might be several reasons, difficult to tell without actual data
[1]. For a general case:

A) contact normal vector  vs.  contact normal force:
> ... contact normal force vector ...
> print("force",i.phys.normalForce + i.phys.shearForce)

you are printing TOTAL force, not normal force.
If i.geom.shearForce is non-zero, then you naturally get non-parallel vector

O.forces.f(i.id1) result is "independent" of constituent interactions

B) branch vector  vs.  contact normal vector:

i.geom.normal is computed in InteractionLoop.
Body positions are THEN updated by NewtonIntegrator.
So b2.state.pos - b1.state.pos and i.geom.normal (in general) are not parallel.

Cheers
Jan

[1] https://www.yade-dem.org/wiki/Howtoask

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