# 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 diameter, position and velocity values of the particles
    screen value = yes or no
    writeTime
      include this keyword to write the time to the out files
    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.

## 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 either by using the keyword vec_side or 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.

Warning

When using fix massflow/mesh with multispherical particles, the evaluation of the mass passing the mesh is done for each sphere within the multisphere particle. Each sphere counts as a fraction of a particle, i.e. floating point number might evolve for the number of particles passing the mesh if not all spheres belonging to one multisphere particle pass the mesh. The weight for each sphere is calculated taking into account the possible overlap between spheres in a multisphere particle.

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

none

## Related commands

compute nparticles/tracer/region

## Default

count = multiple, inside_out =false, delete_atoms = false