yade-users team mailing list archive

[kan <nicessgg@xxxxxxxxx>]

Thank you, Vaclav,

So the step for this is :
during each timestep, the position of each particle/element keeps the
same, so we can calculate the force brom the force-displacement
relationship(in this case, the order does not affect the calculation since
all the particle/elements do not move), after we get the forces, we use this
forces to calculate the acceleration, and then the velocity(average
velocity),  and then the movement/displacement in this timestep, and then
update the position of each particle/element to new positions by add
movement/displacement to current position. (until now, the calculation cycle
of this timestep is completed)
then go to next timestep by use the new positions of particles/elements as
the current position to do the next calculation cycle.

is my understanding right?



Thanks again.

Kan



On 1/22/08, yade-users-request@xxxxxxxxxxxxxxxx
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> Today's Topics:
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>   1. How to get the micro-force from the macro-stress (kan)
>   2. Re: How to get the micro-force from the macro-stress
>      (V?clav ?milauer)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Mon, 21 Jan 2008 13:29:54 -0600
> From: kan <nicessgg@xxxxxxxxx>
> Subject: [Yade-users] How to get the micro-force from the macro-stress
> To: yade-users@xxxxxxxxxxxxxxxx
> Message-ID:
>        <45213f870801211129l171d2a5cs69da2382202961f8@xxxxxxxxxxxxxx>
> Content-Type: text/plain; charset="utf-8"
>
> Hi, buddies,
>
> I have some questiones.
> 1. how to get the micro-force from the macro-stress?
> As we know,for most of current studies, the concept of stress is used to
> describe the stress status. but when we look into the micro level, we have
>
> to convert the macro-stress to descrete force that applied at each
> particle,
> then how to do this convert?
>
> 2. what is the calculation process in each time step?
> The problem is that, as see the relation ship below,
> ___\|/____\|/___\|/________
> 01---02---03---04---05---06...
> |   \   |  /  |      |       |      | ...
> 11---12---13---14---15---16...
> |      |      |   /  |   \  |      |...
> 21---22---23---24---25---26...
> ...
> ...
> x1---x2---x3---x4---x5---x6...
>
> in which, the number is the ID of a particle,
> and "--- " , "/" ,"\" and  "|" between the numbers mean there is a contact
> between the particles
> "\|/" means force.
> assume the 01-02-03-04...is the upper bounday layer, and the force is
> applied as shown "\|/".
> when the calculation begins, we need to detecte the contact and update the
>
> position of each particles,
> now my problem comes:
> what is the procedure to calculation and update the particles'
> information,
> you know the force is from up layer, so the first layer ("01-02-03-04...")
>
> should be calculated, then the second layer,and then the third layer....
> but
> in DEM, the particle is independent to move, so after some time, some
> particles in the first layer may move to the second layer and some
> particles
> in second layer may  move to the first layer(other other layer),then how
> should I do in order to know which particle should be calculated and
> updated
> first and which should be done later in the same timestep?
> For example,
> 01 has contacting neighbors 02 and 11, in a same timestep, after we have
> calculated 01's properties( velocity, position....), we should calculate
> 02
> first, then 03(the neighbor of 02), after the layer of 01-02-03...is done,
>
> then we can step to calculate the 11, which is to say, in a same timestep,
> though 02 and 11 are both contacting neighbors of 01, we should calculate
> 02, and 11 later though 02 and 11 are both affected because of teh
> movement
> of 01. so, how to indentify which particle should be calculated and update
> first , and which should be later?
> (because it is a dynamic process, so just use the order of  ID  is not  a
> way to solve this)
>
> Hope I have described the problem 2 clearly,
>
> Need your help, thanks so much.
>
> Kan
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> ------------------------------
>
> Message: 2
> Date: Tue, 22 Jan 2008 09:20:53 +0100
> From: V?clav ?milauer < eudoxos@xxxxxxxx>
> Subject: Re: [Yade-users] How to get the micro-force from the
>        macro-stress
> To: yade-users@xxxxxxxxxxxxxxxx
> Message-ID: <4795A765.9040403@xxxxxxxx>
> Content-Type: text/plain; charset=UTF-8
>
>
> > so, how to indentify which particle should be calculated and update
> > first , and which should be later?
> > (because it is a dynamic process, so just use the order of  ID  is
> > not  a way to solve this)
> The trick is that you have constant positions during the whole timestep,
> you calculate forces from all contacts (order doesn't matter, elements
> don't move during calculation) and then, before next timestep begins,
> there is LeapFrogPositionIntegrator, that calculates displacements based
> on velocity, inertia, applied forces, ... and moves elements to the new
> position. Obviously, your timestep must be small enough so that you get
> convergence.
>
> HTH, Vaclav
>
>
>
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> End of Yade-users Digest, Vol 19, Issue 14
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