kan a écrit : > 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?
Exactly right. What you describe here is the centered second order finite diffence scheme (also called leap-frog), which is used in Yade. It is probably the most common (and most simple) scheme in DEM codes. Other schemes may be possible but are not implemented. Bruno > > > > Thanks again. > > Kan > > > > On 1/22/08, [EMAIL PROTECTED] > <mailto:[EMAIL PROTECTED]>* < > [EMAIL PROTECTED] > <mailto:[EMAIL PROTECTED]>> wrote: > > Send Yade-users mailing list submissions to > [email protected] > <mailto:[email protected]> > > To subscribe or unsubscribe via the World Wide Web, visit > https://lists.berlios.de/mailman/listinfo/yade-users > or, via email, send a message with subject or body 'help' to > [EMAIL PROTECTED] > <mailto:[EMAIL PROTECTED]> > > You can reach the person managing the list at > [EMAIL PROTECTED] > <mailto:[EMAIL PROTECTED]> > > When replying, please edit your Subject line so it is more specific > than "Re: Contents of Yade-users digest..." > > > Today's Topics: > > 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 <[EMAIL PROTECTED] <mailto:[EMAIL PROTECTED]>> > Subject: [Yade-users] How to get the micro-force from the > macro-stress > To: [email protected] <mailto:[email protected]> > Message-ID: > < > [EMAIL PROTECTED] > <mailto:[EMAIL PROTECTED]>> > 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 > -------------- next part -------------- > An HTML attachment was scrubbed... > URL: > > https://lists.berlios.de/pipermail/yade-users/attachments/20080121/93495eff/attachment-0001.html > > ------------------------------ > > Message: 2 > Date: Tue, 22 Jan 2008 09:20:53 +0100 > From: V?clav ?milauer < [EMAIL PROTECTED] <mailto:[EMAIL PROTECTED]>> > Subject: Re: [Yade-users] How to get the micro-force from the > macro-stress > To: [email protected] <mailto:[email protected]> > Message-ID: < [EMAIL PROTECTED] > <mailto:[EMAIL PROTECTED]>> > 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 > > > > ------------------------------ > > _______________________________________________ > Yade-users mailing list > [email protected] <mailto:[email protected]> > https://lists.berlios.de/mailman/listinfo/yade-users > <https://lists.berlios.de/mailman/listinfo/yade-users> > > > End of Yade-users Digest, Vol 19, Issue 14 > ****************************************** > > > ------------------------------------------------------------------------ > > _______________________________________________ > Yade-users mailing list > [email protected] > https://lists.berlios.de/mailman/listinfo/yade-users > -- _______________ Chareyre Bruno Maitre de conference Institut National Polytechnique de Grenoble Laboratoire 3S (Soils Solids Structures) - bureau E145 BP 53 - 38041, Grenoble cedex 9 - France Tél : 33 4 56 52 86 21 Fax : 33 4 76 82 70 43 ________________ _______________________________________________ Yade-users mailing list [email protected] https://lists.berlios.de/mailman/listinfo/yade-users
