Syntax¶

fix ID group-ID massflow/mesh mesh mesh-ID vec_side vx vy vz keywords values
fix ID group-ID massflow/mesh/universe mesh mesh-ID vec_side vx vy vz keywords values ukeywords uvalues

• ID, group-ID are documented in fix command

• massflow/mesh/face = style name of this fix command

• mesh = obligatory keyword

• mesh-ID = ID of a fix mesh/surface command

• zero or more keyword/value pairs may be appended to args

• keywords = check_property or count or point_at_outlet or append or file or screen or delete_atoms

  check_property property value
    property = name of atom property to check
    value = reference atom property value to check against
  count value = once or multiple
    once = count particles only once
    multiple = allow particles to be counted multiple times
  point_at_outlet  pointX pointY pointZ
    pointX pointY pointZ = coordinates of point on the outlet side of the surface
  inside_out
    use this in connection with point_at_outlet to flip direction particle counting
  file value = filename
  append value = filename
   filename = name of the file to print diameter, position and velocity values of the particles
  screen value = yes or no
  delete_atoms value = yes or no
    yes = to remove the particles that pass through the mesh surface
  cg value = cg
    cg = coarse grain ratio of measured particles (N/A to universe version)
  temperature value = yes or no
    yes = to measure the temperature of the particles
  chemistry value = yes or no
    yes = to measure the reduction state of the particles

• two ukeyword/uvalue pairs must be appended for the universe version of this command

• ukeywords = send_to_partition and couple_every

  send_to_partition value = partition
    partition = partition to send data to in multi-partition simulations
  couple_every value = interval
    interval = time interval for sending data

Examples¶

fix massflowcg2t all massflow/mesh/face mesh surfacet count once check_property i_cglevel 2 cg 2 inside_out

fix massflowcg2b all massflow/mesh/face mesh surfaceb count multiple check_property i_cglevel 2 cg 2 file post/massflowprop.txt

LIGGGHTS vs. LAMMPS Info:

This LIGGGHTS command is not available in LAMMPS.

Description¶

Fix massflow/mesh/face tracks how many particles penetrate through each face of a mesh surface, as defined by a fix mesh/surface command. It counts the total number of particles and the associated mass. It calculates the averaged velocity of the crossing particles and stores their size distribution as well as their atom types. Only particles part of group are eligible for counting. If check_property is specified, only particles with the given property value are considered. check_property may refer to a fix poperty/atom or a fix property/atom/lammps.

Particles are counted if they cross from the inner side of the mesh to the outer side of the mesh. The outer side can be defined by the winding order of the mesh vertices or by specifying a point at the outlet side of the mesh (keyword point_at_outlet).

The following restriction applies in case point_at_outlet is used: the count value has to be set to once.

The keyword point_at_outlet is especially useful in case a cylindrically-shaped surface is used. The point_at_outlet value should be on the cylinder axis in this case. If you like to track particles moving away from the cylinder axis, specify the point_at_outlet on the axis, and use the keyword inside_out to flip the direction.

If count = once, then each particle is only counted once, for count = multiple a particle contributes to the statistics each time it crosses the mesh face. This can happen e.g. in the case of periodic boundary conditions or in re-circulating flow conditions.

The timestep of the crossing, the ID of the crossed face, the atom ID, as well as the diameter, position and velocity of the particles can be written into a file using the file keyword and specifying a filename.

If the screen keyword is used, output by this fix to the screen and logfile can be turned on or off as desired.

If the delete_atoms keyword is used then the particles passing through the mesh surface are deleted at the next re-neighboring step.

If LIGGGHTS is invoked in multi-partition mode (cf. Command-line options), where each partition represents a separate coarse-graining level of the multi-level coarse-grain model, the universe version of this command needs to be used to provide input data for a fix of style insert/pack/face/universe on the coupled partition. The coupled partition must be specified via the send_to_partition option. Furthermore, in this mode the couple_every option specifies the sending interval.

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

Information about this fix is written to binary restart files .

This fix computes a per-atom vector (the marker) which can be accessed by various output commands. The per-atom vector (i.e., the marker) can be accessed by dumps by using “f_massflowface_ID”. This fix also computes a global vector of length 10. This vector can be accessed via “f_ID”, where ID is the fix id. The first vector component is equal to the total mass which has crossed the mesh surface, the second vector component indicates the (resolved) particle count. The third vector component is equal to the total mass which has crossed the mesh surface since the last output divided by the time since the last output (i.e., the mass flow rate), the fourth vector component indicates the (resolved) particle count since the last output divided by the time since the last output (i.e., the number rate of particles). The fifth and sixth vector components are the deleted mass and the number of deleted particles. The seventh component vector component indicates the (resolved) particle count since the last output. The last three vector components are the favre-averaged velocity components.

This vector can also be accessed by various output commands.

Restrictions¶

The mesh surface must provide the element property ‘face_id’, e.g. by loading it from a VTK file using the cell_data option of the fix mesh/surface command. All triangles with the same ID are considered to form a face.

Related commands¶

compute nparticles/tracer/region, fix massflow/mesh, partition

Default¶

count = multiple, inside_out = false, delete_atoms = false, cg = 1