Particle-Based Boundary Conditions

Introduction

Particle-based boundary conditions are used to apply conditions directly to particles for loads, tractions, heat fluxes, and concentration fluxes. Particle-based boundary conditions are typically applied to particles on the boundary of the object. Besides particle conditions, simulations can set Grid-Based Boundary Conditions.

Particle-Based Boundary Condition in Scripted Files

In scripted files, all particle-based boundary conditions are created by a series of ParticleBC command blocks that select particles:

ParticleBC
  (one 2D or 3D shape command, which can be nested)
  (one or more load, traction, heat flux, or concentration flux condition)
    ...
EndParticleBC

In XML files, particle-based boundary conditions are created with a <BCShape> block

<BCShape>
  (one 2D or 3D shape command, which can be nested)
  (one or more load, traction, heat flux, or concentration flux condition)
    ...
</BCShape>

which must be within the main <ParticleBC> block.

The particles that will get boundary conditions are selected by defining one 2D shape (for 2D simulations) or one 3D shape (for 3D simulations). The shape can be a nested shape.

All particles within the one shape will be set to all provided load, traction, heat flux, and/or concentration flux conditions.

Deprecated Commands

Prior to the particle-based boundary condition commands in the previous section, the boundary conditions used to be set with boundary condition shape commands. The deprecated commands are:

• LoadLine and <BCLine>
• LoadArc and <BCArc>
• LoadRect and <LdRect>
• LoadBox and <BCBox>

See documentation for conversion of old commands to the new method.

Explicit Grid-Based Boundary Condition in XML Files

An option in XML files is to explicitly set boundary conditions on particles without using shape functions. The format is

<GridBCs>
   (one or more <BCShape> blocks)
   ...
   <LoadBCs>
      (one or more explicit boundary conditions)
   </LoadBCs>
</GridBCs>

The <BCShape> blocks set boundary conditions as explained above. The <DisplacementBCs> blocks lets you explicitly list each grid point. The explicit method is limited to velocity conditions, and is usually generated with other software. You can use both <BCShape> commands and a <DisplacementBCs> block in the same input file.

Particle-Based Boundary Condition in XML Files

All particle-based boundary conditions must be set up within a single <ParticleBCs> element. The format is

<ParticleBCs>
   (one or more particle BC shape commands)
     ...
   <LoadBCs>
      (one or more explicit boundary conditions)
   </LoadBCs >
</ParticleBCs>

There are two ways to specify particle boundary conditions. The most common approach is to generate boundary conditions using one or more shape commands to select particles and assign specified load, traction, heat flux, and or concentration flux conditions to those particles. The other way is to explicitly list each particle condition. The explicit method is shown in the <LoadBCs> section above; it is limited to load conditions, and is usually generated with other software. You can use both shape commands and a <LoadBCs> section in the same input file.