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### fix massflow/mesh command

Syntax:

    fix id group massflow/mesh mesh mesh-ID vec_side vx vy vz keyword value ...

- ID, group-ID are documented in fix command
- massflow/mesh = style name of this fix command
- mesh = obligatory keyword
- mesh-ID = ID of a fix mesh/surface command
- vec_side = obligatory keyword
- vx, vy, vz = vector components defining the "outside" of the mesh
- zero or more keyword/value pairs may be appended to args
- keywords = count or point_at_outlet or append or file or screen or delete_atoms

        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 radius, 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

Examples:

    fix mass all massflow/mesh mesh inface vec_side 0. 0. -1.

    fix mass all massflow/mesh mesh inface count once point_at_outlet 0. 0. 0.

LIGGGHTS vs. LAMMPS Info:

This LIGGGHTS command is not available in LAMMPS.

Description:

Fix massflow/mesh tracks how many particles penetrate through a mesh surface, as defined by a fix mesh/surface command. It counts the total number of particles and the associated mass. Only particles part of group are eligible for counting.

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 using the keyword vec_side, by specifying a point at the outlet side of the mesh (keyword point_at_outlet). Note that the vector defined by vec_side does not necessarily have to be perpendicular to the mesh face.

The following restrictions apply in case vec_side is specified: (i) the fix mesh/surface has to be planar, and (ii) the vector defined by vec_side may not lie inside the mesh plane.

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.

When count = once, then each particle is only counted once, for count = multiple a particle contributes to number and mass count 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 diameter, position and velocity of the particles can be written into a file using the file keyword, by 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.

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_massflow_ID", . This fix also computes a global vector of length 6. 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 particle count. The third vector component is equal to the total mass which has crossed the mesh surface since the last output divived by the time since the last output (i.e., the mass flow rate), the fourth vector component indicates the particle count since the last output divived 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. This vector can also be accessed by various output commands.

Restrictions:

Currently, this feature does not support multi-sphere particles.

Related commands:

compute nparticles/tracer/region

Default:

count = multiple, inside_out =false, delete_atoms = false