May be this article will help:
Zhang, D. & Whiten, W.
The calculation of contact forces between particles using spring and
damping models
Powder Technology, 1996, 88, 59-64
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Apparently, _forceData will not store vvector, but vvector*.
Because, if it will store vvector (as now) then _forceData[A].resize(N) can
affect _forceData[B]. Or no?
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I want to rewrite ensureSize() in order to the each thread do resize only the
"own" vector, not all.
So, no need locking at all. Vaclav, do you agree?
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revno: 2766
committer: Bruno Chareyre
branch nick: yade
timestamp: Fri 2011-02-25 21:42:33 +0100
message:
- remove save_vtk flag and add python wrapping
modified:
pkg/dem/FlowEngine.cpp
pkg/dem/FlowEngine.hpp
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XLatexIt! run report...
*** Found _expression_ $$dt_e,dt_v$$
Image was already generated
*** Found _expression_ $$dt_e$$
Image was already generated
*** Found _expression_ $$dt_v<2b/a$$
Image was already generated
*** Found _expression_ $$\dot{X} = (1 - dt.a/b)\dot{X}$$
*** Found
A lazy time-step determination :
I recall the problem we solve is:
$$a\ddot{X}+b\dot{X}+X=0$$
1/ If the viscous effects "b" are high compared to elastic effects, then
it means b>>1 and the "X" term can be neglected.
In that case a first order(*) explicit scheme will give
$$\dot{X}_{t+dt} = \dot{
> if the time step is ok without viscous damping, it will necessary be ok with
> the damping.
Actually not, or you are thinking of stiffness and viscosity in series?
If they are in parallel, dt will have to be smaller.
> Anyway it's million times better than the so called Cundall damping whic
revno: 2765
committer: Bruno Chareyre
branch nick: yade
timestamp: Fri 2011-02-25 20:11:02 +0100
message:
- per-point imposed pressure mechanism
- one fix in permeabilites along boundaries
modified:
lib/triangulation/FlowBoundingSp
revno: 2764
committer: Bruno Chareyre
branch nick: yade
timestamp: Fri 2011-02-25 20:07:36 +0100
message:
- per-point imposed pressure mechanism.
modified:
pkg/dem/FlowEngine.cpp
pkg/dem/FlowEngine.hpp
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Le 25 févr. 2011 à 11:38, Chiara Modenese a écrit :
> Yes, I agree. I think I was confused by Vincent's words such as: "let say
> that the critical time step determined for non-viscous contact will be
> smaller that the effectively minimum time step". Vincent, maybe you could
> clarify this po
revno: 2763
committer: Bruno Chareyre
branch nick: yade
timestamp: Fri 2011-02-25 19:19:15 +0100
message:
Small fix in unbalancedForce doc.
modified:
py/_utils.cpp
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Your te
On 25 February 2011 17:28, Bruno Chareyre wrote:
>
> > Well, I have to disagree here. I think we need first to clearly define
> > our equation, is it a linear or non linear one?
>
> It doesn't matter. If it is non-linear, you can linearize it by looking
> at tangent stiffness. So, in the end the s
> Well, I have to disagree here. I think we need first to clearly define
> our equation, is it a linear or non linear one?
It doesn't matter. If it is non-linear, you can linearize it by looking
at tangent stiffness. So, in the end the small oscillations that can
result in numerical instabilities
On 25 February 2011 14:51, Bruno Chareyre wrote:
> They are beside the scope as long as the question is "how to define in
> general a critical time-step for 2nd order explicit integration of
> acceleration-velocity-position=0?".
>
Well, I have to disagree here. I think we need first to clearly d
Yes, you're right, the locking logic in ForceContainer::resize is not
sufficient. What you propose does not solve the problem of adding bodies
inside the loop, though -- that is what a factory does, for instance.
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If the objective is to define the critical timestep, for the sake of
clarity I recommend to not speak about:
- equivalent mass (the paper sent by Vincent earlier),
- critical damping,
- over-damped / under-damped,
- restitution coefficient.
They are beside the scope as long as the question is "how
Ok, here I can imagine what you mean. Thanks.
Jerome
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But you speak about elastoplastic law with different stiffness for
loading/unloading.
I speak about viscoelastic law (with constant stiffness):
F = k x + c dx/dt
So, if dx/dt>0 (loading) then F > F_elastic=k x,
and if dx/dt<0 (unloading) then F
Ok for these inequalities ! Thanks for explanatio
Seems, cause is next:
After adding new particles, the first thread runs on the "old" particles, so
without resizing of _forceData in ensureSize() (ForceContainer.hpp:87)
And at time, when first thread adds new force to _forceData, second thread
starts to run on the "new" particles and do resize
Le 25/02/2011 14:32, Sergei D. a écrit :
But you speak about elastoplastic law with different stiffness for
loading/unloading.
I speak about viscoelastic law (with constant stiffness):
F = k x + c dx/dt
So, if dx/dt>0 (loading) then F > F_elastic=k x,
and if dx/dt<0 (unloading) then F
Ok for
But you speak about elastoplastic law with different stiffness for
loading/unloading.
I speak about viscoelastic law (with constant stiffness):
F = k x + c dx/dt
So, if dx/dt>0 (loading) then F > F_elastic=k x,
and if dx/dt<0 (unloading) then F
I think I do not have my mind in the viscous framewo
I think I do not have my mind in the viscous framework.
But, in a general case, some of your phrases do not correspond to my
current point of view:
If more stiffness then more force for given overlap.
In my former simulations, I used this "NormalInelasticityLaw" which
describes (Normal Force
25.02.2011 15:23, Jerome Duriez пишет:
Le 25/02/2011 11:20, Sergei D. a écrit :
So, viscoelastic loading force more then elastic force for given
overlap. So, need smaller time step for stability. No?
I would say (contrary to this) that critical time step is rather a
matter of stifnesses tha
Le 25/02/2011 11:20, Sergei D. a écrit :
So, viscoelastic loading force more then elastic force for given
overlap. So, need smaller time step for stability. No?
I would say (contrary to this) that critical time step is rather a
matter of stifnesses than a matter of forces ? No ?
And why c
On 25 February 2011 10:20, Sergei D. wrote:
>
>
>> Anyhow, according to the equations cited in PFC manual, the critical time
>> step would be smaller for viscous contacts even if the solution is
>> underdamped (at least for the linear dashpot model). Am I overlooking
>> something? Why would be th
Anyhow, according to the equations cited in PFC manual, the critical
time step would be smaller for viscous contacts even if the solution
is underdamped (at least for the linear dashpot model). Am I
overlooking something? Why would be the contrary to you? Sorry, I
admit I have no great expe
On 25 February 2011 08:06, Vincent Richefeu wrote:
>
> Le 23 févr. 2011 à 17:43, Bruno Chareyre a écrit :
>
> > p.s. Vincent, you defined viscosity in order to keep critical time-step
> below a given value IIRC. What was the reasoning behind?
>
> No. I (and other people like Sergei) defined the v
Le 23 févr. 2011 à 17:43, Bruno Chareyre a écrit :
> p.s. Vincent, you defined viscosity in order to keep critical time-step below
> a given value IIRC. What was the reasoning behind?
No. I (and other people like Sergei) defined the viscosity so that it is lower
than the critical viscosity. If
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