Boundary Condition Styles

Setting Styles

The possible boundary condition styles are defined below. In scripted files, the style can be set by name or number; in XML files, the style must be set by number. Unless otherwise specified, the units for (value) are the standard units for the current type of boundary condition (i.e., mm/s for velocity, degrees K for temperature, etc.) and the units for (time) are ms.

• constant (or 1) - the applied boundary conditions is set to the constant (value) and it is applied for times after (time).
• linear (or 2) - the applied boundary condition is
  
                       [math]\displaystyle{ BC = ({\rm value})*(t-({\rm time})) }[/math]
  
  where t is the current time (in ms). This condition is applied only for times after (time). The units for (value) should change to the standard units for the boundary condition per ms.
• sine (or 3) - the applied boundary condition is
  
                       [math]\displaystyle{ BC = ({\rm value})\sin\bigl[({\rm time})*t\bigr] }[/math]
  
  This condition is applied for all times. The units for (time) should change to 1/ms.
• cosine (or 4) - the applied boundary condition is
  
                       [math]\displaystyle{ BC = ({\rm value})\cos\bigl[({\rm time})*t\bigr] }[/math]
  
  This condition is applied for all times. The units for (time) should change to 1/ms.
• silent (or 5) - to apply an "absorbing" boundary conditions 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 ms), nodal point position , and/or of current clockwise particle rotation angle (2D only). 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) (in ms) 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 apply velocity conditions.

Silent Boundary 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 have 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)

apply an absorbing or silent boundary condition. This conditions can work for edges perpendicular to either the x or y directions. Parameter #1 should specify the normal vector direction for the edge. Parameters #3 and #4 are not needed. (See notes below).

Notes

1. When applying multiple velocity conditions on the same node, the combinations must either be in the same direction or in orthogonal directions. For example, you can apply any combination of velocities along analysis axes (x, y, or z).
2. When using skewed velocity conditions, the typical problem will use only a single skewed direction on a node. You can use any number of conditions in that single direction. You should not mix skewed velocity conditions with velocity conditions along one of the skew axes. For example, you should not apply some conditions in the x direction and others in the skewed x-y or x-z direction, because these two directions are not orthogonal. In principle orthogonal skewed directions could be used, but such problems can normally be recast to get the same fixed velocity by fixing the two axes in the skew plane instead.