Janek Kozicki said: (by the date of Sun, 4 Jul 2010 20:47:40 +0200)
> I'm not sure if I worded myself clearly.... I hope that you can
> understand what I mean?
to rephrase in even different words: in plastic regime the Fs remains
constant at the limiting value. While the sphere slipping distance
sᵢ-sᵢ₋₁ can be actually bigger, that what has been contributed into
the value of Fs, and is 's'.
hmm, I see that ElasticContactLaw.cpp lines 96-104 are actually
implementing a simlar thing to what I'm saying, by actually
calculating the difference between s and sᵢ-sᵢ₋₁.
So apparently there is just a bug inside here. Is maxFs correct? is
trialForce the right value? Is the formula really similar?
Let's rewrite this:
plasticDissipation +=
((1/currentContactPhysics->ks)*(trialForce-shearForce))//plastic disp.
.dot(shearForce);//active force
into:
Ep += (Fs-Fsmax)⋅Fsmax/ks
And compare this with:
Es+=(Fs²⁄ks)⁄2
hmmm is there a "⁄2" missing?
I mean:
Ep += ((Fs-Fsmax)⋅Fsmax/ks)⁄2
I'm not sure in fact :)
Next I am trying to check this again:
Es+=(Fs²⁄ks)⁄2
where in fact: Fs²⁄ks = (ks*s)²/ks = ks*s²
And compare again with this:
Ep += ((Fs-Fsmax)⋅Fsmax/ks)⁄2
and try to rewrite it:
(Fs-Fsmax)⋅Fsmax/ks = Fs⋅Fsmax/ks-Fsmax²/ks =
= (ks*s)*(ks*∑(sᵢ-sᵢ₋₁))/ks - (ks*∑(sᵢ-sᵢ₋₁)²/ks =
= s*ks*∑(sᵢ-sᵢ₋₁) - ks*∑(sᵢ-sᵢ₋₁)²
but I must leave now. You could start derivation from this place
where I stopped, and try to continue verifying if Ep is correct or
not.
Also I wanted to check how Ep could be expressed if using the same
terms as in (or in terms of)
Ws =∑ (Fsᵢ+Fsᵢ₋₁)*(sᵢ-sᵢ₋₁)⁄2
but unfortunately not today, I must go. But maybe you will be able to
figure this out?
best regards
--
Janek Kozicki http://janek.kozicki.pl/ |
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