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fix mesh/gran command

Syntax:

fix ID group-ID mesh/gran filename walltype scalefactor xoff yoff zoff phix phiy phiz (conveyor conveyor-values)

• ID, group-ID are documented in fix command

• mesh/gran = style name of this fix command

• filename = name of STL file containing the STL data

• walltype = atom type of the wall imported from the STL file

• scalefactor = scaling factor applied to the geometry (dimensionless)

• xoff, yoff,zoff = x-, y-, and z-offsets applied to the imported geometry (length units)

• phix, phiy, phiz = Angle of geometry rotation around x-, y-, and z-axis (in grad)

• conveyor, rotation, temperature, curvature = optional keywords for conveyor belt / heat transfer model
  conveyor values = vx vy vz

    vx = x-velocity of conveyor belt (velocity units) 
    vy = y-velocity of conveyor belt (velocity units) 
    vz = z-velocity of conveyor belt (velocity units) 
rotation values = px py pz rx ry rz omega
    px py pz = origin for rotation axis (distance units) 
    rx ry rz = axis vector for rotation (distance units) 
    omega = rotational velocity (rad/time units) 
curvature value = c
    c = maximum angle between mesh faces belonging to the same surface (in °) 
temperature value = T0
    T0 = Temperature of the wall (temperature units)  

Examples:

fix cad all mesh/gran indenter.stl 1 1.0 0. 0. 0. 0. 0. 0.

LIGGGHTS vs. LAMMPS Info:

This command is not available in LAMMPS.

Description:

This fix allows the import of complex wall geometry for granular simulations from CAD by means of ASCII STL files or legacy ASCII VTK files. You can apply offset, scaling and rotation to the imported mesh.

If applying more then one of these operations, the offset is applied first and then the geometry is scaled. Then the geometry is rotated around the x-axis first, then around the y-axis, then around the z-axis.

One fix represents one wall with a specific material, where the material is identified with the walltype. If multiple walls with different materials are desired, the respective walls must be imported with different fix mesh/gran commands.

IMPORTANT NOTE: For periodic boundaries, the mesh is NOT mapped. Instead, a warning is generated if a vertex lies outside the simulation box.

With the optional conveyor model, you can specify the imported mesh as conveyor belt. The velocity direction for each mesh face is given by the projection of the conveyor belt velocity parallel to the mesh face, the velocity magnitude for each mesh face is equal to the conveyor belt velocity. This ensures the model makes sense also in case the mesh is curved. Likewise, the optional rotation model mimics rotational motion of the mesh (e.g. for modeling a shear cell)

With the temperature keyword, you can define a constant temperature for a mesh in conjunction with heat conduction via fix heat/gran. Note that the actual calculation of the heat transfer happens only if you use the mesh in conjunction with a granular wall, see fix wall/gran.

The curvature keyword lets you specify up to which angle between two triangles the triangles should be treated as belonging to the same surface (e.g. useful for bends). This angle is used to decide if (a) contact history is copied from one triangle to the other as the contact point proceeds and (b) if edge and corner interaction is calculated.

Restart, fix_modify, output, run start/stop, minimize info:

This fix writes the STL data to binary restart files to be able to correctly resume the simulation in case the mesh is moved. None of the fix_modify options are relevant to this fix. No global scalar or vector or per-atom quantities are stored by this fix for access by various output commands. No parameter of this fix can be used with the start/stop keywords of the run command. This fix is not invoked during energy minimization.

Restrictions:

To date, only ASCII STL files can be read (binary is not supported). In the current implementation, each processor allocates memory for the whole geometry, which may lead to memory issues for very large geometries . It is not supported to use both the moving mesh and the conveyor belt feature.

Related commands:

fix wall/gran, fix mesh/gran/stressanalysis, fix mesh/gran/6dof

Default: c = 0°