Main Help → All Commands → MPM Boundary Conditions → Boundary Conditions Styles
The possible boundary condition styles are defined below. The style can be set by name or number. Unless otherwise specified, the units for (value)
are the standard units for the current type of boundary condition and the units for (time)
are alt time units.
"constant"
(or 1) - the applied boundary conditions is set to constant (value)
and is applied for times after (time)
."linear"
(or 2) - he applied boundary condition isBC = (value) * (t - (time))where
t
is the current time. This condition is applied only for times after (time)
. The units for (value)
should change to the standard units for the boundary condition per alt time unit."sine"
(or 3) - the applied boundary condition is
BC (value) * sin((time)*t)where
t
is the current time. This condition is applied for all times. The units for (time)
should change to 1/alt time units."cosine"
(or 4) - the applied boundary condition is
BC (value) * cos((time)*t)where
t
is the current time. This condition is applied for all times. The units for (time)
should change to 1/alt time units."silent"
(or 5) - to apply an "absorbing" boundary condition as explained below. These are only allowed for load, heat flux, and concentration flux conditions."function"
(or 6) - the applied boundary condition is determined by a user-defined function of time (t
in alt time units), nodal point position, and/or of current clockwise particle rotation angle (2D only), entered as quoted text in (value)
. The function should evaluate to the desired value in the standard units for the type of boundary condition. If (time)
is supplied, the condition starts at time (time)
and the function is evaluated at [t-(time)]
(instead of at t
)To get any time-dependence for a boundary condition, you can combine more than one conditions in the same direction and the resulting condition will be a superposition of the applied conditions. See below for some special considerations when applying velocity conditions.
The object of silent boundary conditions is to apply an absorbing edge. The goal is to simulate a small portion of a large object by having stress waves, heat fluxes, and concentration fluxes absorbed by the edges rather the reflect back into the object. Their development in MPM is in a paper by Shen and Chen (2005). These conditions can be shown to work well in small, idealized simulations. They have been less useful on other simulations.
Some considerations about using silent boundary conditions are:
(k grad T).n
extrapolated from particles along the edge with the boundary condition. It should enable simulation of heat flow through materials, but its use is relatively unexplored. Here
k is thermal conductivity tensor, T
is temperature, and n
is normal vector; this condition works for isotropic and anisotropic materials.(D grad c).n
extrapolated from particles along the edge with the boundary condition. It should enable simulation of solvent flow through materials, but its use is relatively unexplored. Here D
is diffusion tensor, c
is concenration, and n
is normal vector; this condition works for isotropic and anisotropic materials.