Setting Forces and Fluxes

These commands are used within shape commands for grid-based boundary conditions to set loads, tractions, heat fluxes, and concentration fluxes on particles

Load Conditions

The scripted Load command applies a force directly to each particle within the shape command that encloses it:

Load (dir),(style),(value),<(time)>

In XML files, the command is:

<LoadBC dir='(dir)' style='(style)' load='(value)' time='(time)'
                function='(function)'/>

where

• (dir) is 1, 2, or 3 to specify the loading direction as in the x, y, or z direction (In scripted files, (dir) can be x, y, or z or can be R or Z if axisymmetric).
• (style) specifies the style of the applied load. Each load depends on two parameters specified by arguments (value) and (time). The (value) is required because there is no point in applying zero laod. If (time) is not supplied, it is set to zero. The styles are described here. The standard units are N for (value) and ms for (time) (but the units may change depending on the (style) setting). The final magnitude of the load depends on the LoadType setting.
• (function) - if the (style) is function (or 6), this attribute in XML files specifies a user defined function. In scripted files, the user defined function should replace the (value) argument and must be entered as quoted text. The function should evaluate to the desired force in N.

LoadType Options

By default, the (value) argument or the result returned by a function gives the load on each particle with that boundary condition (with standard units of N). Alternatively, a load or function can evaluate to the total Newtons applied to all particles in the current shape. To chose to load style in scripted files, include the command:

LoadType (loadType)

within the current shape. If (loadType) is "net", the boundary conditions specifies to the total load spread out over all particles in the current shape. Alternative, if (loadType) is "perParticle" (or omitted), the load for the boundary condition is applied to each particle. You can switch back and forth between net load and per-particle load in a single shape by using mutliple LoadType commands. Each load boundary condition uses the loading option specified by the most recent LoadType command (or uses "perParticle" is no LoadType command was used).

In XML files, the loading option is set by using the following commands within the current shape:

<net/>
<perParticle/>

As expected, the "net" option is specified with a <net/> command and the "perParticle" option is specified with a <perParticle/> command. These commands can be intersperse to apply different loading options to various load boundary conditions.

These loading-option commands only apply to particle load boundary conditions and have no effect on other traction, heat flux, and concentration flux conditions that happen to be within the same shape command.

Traction Conditions

The scripted Traction command sets traction load on the edge of each particle within the shape command that encloses it:

Traction (dir),(face),(style),<(value)>,<(time)>

In XML files, the command is:

<Traction dir='(dir)' face='(fact)' style='(style)' stress='(value)' time='(time)'
                function='(function)'/>

where

• (dir) is 1, 2, or 3 to specify the loading direction as in the x, y, or z direction (In scripted files, (dir) can be x, y, or z or can be R or Z if axisymmetric). For TractionBC, dir can be 11 or 12 to mean normal or shear traction relative to the selected face, respectively. A normal traction is positive if pointing out of the particle domain and a shear traction is positive when oriented in the counter-clockwise direction. Shear tractions (option 12) are not yet allowed in 3D calculations.
• (face) defines which face of the original particle domain is loaded by the traction. In 2D, the faces are the edges numbered 1 through 4 in the counter-clockwise direction with the bottom edge (with normal (0,-1)) being number 1. In 3D, 1 to 4 are the same faces (i.e., faces with normals (0,-1,0), (1,0,0), (0,1,0), and (-1,0,0) on the original particle domain, respectively), 5 is the bottom (with normal (0,0,-1)), and 6 is the top (with normal (0,0,1)).
• (style) specifies the style of the applied traction. Each velocity depends on two parameters specified by arguments (value) and (time). The (value) is required because there is no point in applying zero traction. If (time) is not supplied, it is set to zero.The styles are described here. The standard units are MPa for (value) and ms for (time) (but the units may change depending on the (style) setting).
• (function) - if the (style) is function (or 6), this attribute in XML files specifies a user defined function. In scripted files, the user defined function should replace the (value) argument and must be entered as quoted text. The function should evaluate to the desired traction in MPa.

Not that valid calculation of grid forces resulting from specified traction during 2D simulations requires that you have correctly specified the grid thickness and that the grid thickness matches the particle thickness. Furthermore, the use of traction boundary conditions is only allowed when using uGIMP or lCPDI anlaysis methods.