MPM Region and Hole Commands
In MPM, the most common way to discretize an object is to add material points to the background grid using Region commands and to designate regions of the grid has having no material points using Hole commands. Enclosed in these commands are various shape commands to define the object. An alternative and powerful option for discretizing an object is to create material points automatically from an image of the object.
Region Commands
Once the background grid is created, material points are added to the grid using a series of Region commands (or <Body> commands in XML files). In scripted files, the Region command defines material type, initial velocity, thickness (in 2D), and optionally an initial angle (for some anisotropic materials), temperature, and concentration. The command is
Region (matid),(velx),(vely),(velz) or (thick),<(property),(value)>... (any number of shape commands) EndRegion
In XML files, regions are defined using <Body> elements and optional one PointList element. All these element must be withinthe single MaterialPoints element in the input file:
<MaterialPoints>
<PointList>
(see help on creating individual material points)
</PointList>
<Body mat='(matid)' vx='(velx)' vy='(vely)' vz='(velz)' thick='(thick)'
angle='(angle)' temp='(temp)' conc='(conc)' wtconc='(wtconc)'>
(any number of shape commands)
</Body>
....
</MaterialPoints>
where
- (matid) is the material ID for a previously defined material.
- (velx), (vely), and (velz) are the components of the initial velocity for for all particles in the region (velx is only used for 3D simulations). The units or mm/sec
- (thick) is the thickness of each material point in mm. The thickness is only used for planar 2D calculations. In scripted files, the thickness parameter should still be provided for parameter alignment, although its value is ignored.
After the above required parameters, you can provide one to three optional parameters to set initial conditions for all particles in the region. In scripted files, the optional parameters appear in pairs. The first item in the pair, or (property), is the name of initial property to set and the second item, or (value), is the initial value for the property. In XML files, the optional parameters are three optional attributes:
- angle,(angle) to set the initial rotation angle for the material axes about the z axis. The units are degrees. This parameter is sufficient for 2D analysis with constant material angle. See help on setting material angles for methods to set variable angles or to set more than on rotation angle in 3D calculations.
- temp,(temp) to set the initial particle temperature. The units are degrees.
- conc,(conc) to set the initial particle concentration. The units concentration potential from 0 to 1.
- (wtconc)to set concentration use weight fraction concentration (0 to 1) instead of concentration potential. The result potential is (wtcon) divided my the material saturation concentration weight fracture. This option is only available in XML input files.
Between the Region command and the subsequent EndRegion command (or within the <Body> element), there can be any number of shape commands to define material point positions. The details on these shape command are given elsewhere:
Hole Commands
The Hole command is used to designate regions of the grid that should not have any material points. In scripted files, the Hole command is:
Hole (any number of shape commands) EndHole
In XML files, the <Hole> block is:
<Hole> (any number of shape commands) </Hole>
Between the Hole command and the subsequent EndHole command (or within the <Hole> block), there can be any number of shape commands to define hole locations. The details on these shape command are given elsewhere:
An object with holes is create by a sequence of Regions and Hole commands. Each Region command fills every location within its shapes with a material point unless that location was previous designated as a hole. Each Hole command designates every location within its shapes as not having a material point, but, if the a location already has a material point, that point is left intact. In other words, the order of these commands is crucial. By selecting the correctly order, you have greatly flexibility in creating objects with solid regions and void (or hole) regions.