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[Jan Stránský <question404284@xxxxxxxxxxxxxxxxxxxxx>]

Question #404284 on Yade changed:
https://answers.launchpad.net/yade/+question/404284

    Status: Open => Answered

Jan Stránský proposed the following answer:
Hi Liu,

what you wrote is correct.

But PBC can be used also if the "macro" geometry is arbitrary, e.g. in the
case you expect the deformation is uniform in certain area, then you
simulate only a small volume.

It also (as averything) depends on the purpose of simulation. For example
for evaluating macroscopic stiffness, PBC are considered as a very good
choice. On the other hand, in simulation of cracking phenomena, in might
not be a good choice as the cracks are usually not periodic (but PBC force
them to be).

Jan

PS: I **personally** prefer the term Periodic contact detection, as it is
not really a boundary condition in the sense I use it..


2016-11-22 10:04 GMT+01:00 liukeqi <question404284@xxxxxxxxxxxxxxxxxxxxx>:

> New question #404284 on Yade:
> https://answers.launchpad.net/yade/+question/404284
>
> Hi, everyone
>
>    I want to know the purpose that using periodic boundary in the
> simulation.
>
>    I search the meaning of "periodic boundary condition" and get the
> definition as following in Wikipedia[1].
> “Periodic boundary conditions (PBCs) are a set of boundary conditions
> which are often chosen for approximating a large (infinite) system by using
> a small part called a unit cell. The large systems approximated by PBCs
> consist of an infinite number of unit cells. In computer simulations, one
> of these is the original simulation box, and others are copies called
> images. During the simulation, only the properties of the original
> simulation box need to be recorded and propagated. The minimum-image
> convention is a common form of PBC particle bookkeeping in which each
> individual particle in the simulation interacts with the closest image of
> the remaining particles in the system."
>
>   I do not really understand its meaning. As far as I understand, if a
> simulation sample has cube or rectangular prism boundary and its loading
> manner is homogeneous in the boundary, but it has too many particles to
> compute, then in order to improve efficiency in computation, we can use the
> periodic boundary which size  is proportional small to the original
> simulation sample and loading manner is similar to original simulation
> boundary. Because through using periodic boundary, we can using a small
> number of particles to get almost the same result as the original
> simulation do.
>
> Do I have some misunderstandings about it?
>
> [1]https://en.wikipedia.org/wiki/Periodic_boundary_conditions
>
> Thank you.
>
> Liu
>
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