# fix smd/wall_surface command

## Syntax

``` LAMMPS
fix ID group-ID smd/wall_surface arg type mol-ID
```

-   ID, group-ID are documented in [fix](fix) command

-   smd/wall_surface = style name of this fix command

-   arg = *file*

        *file* = file name of a triangular mesh in stl format

-   type = particle type to be given to the new particles created by
    this fix

-   mol-ID = molecule-ID to be given to the new particles created by
    this fix (must be \>= 65535)

## Examples

``` LAMMPS
fix stl_surf all smd/wall_surface tool.stl 2 65535
```

## Description

This fix creates reads a triangulated surface from a file in .STL
format. For each triangle, a new particle is created which stores the
barycenter of the triangle and the vertex positions. The radius of the
new particle is that of the minimum circle which encompasses the
triangle vertices.

The triangulated surface can be used as a complex rigid wall via the
[smd/tri_surface](pair_smd_triangulated_surface) pair style. It is
possible to move the triangulated surface via the
[smd/move_tri_surf](fix_smd_move_triangulated_surface) fix style.

Immediately after a .STL file has been read, the simulation needs to be
run for 0 timesteps in order to properly register the new particles in
the system. See the \"funnel_flow\" example in the MACHDYN examples
directory.

See [this PDF guide](PDF/MACHDYN_LAMMPS_userguide.pdf)\_ to use Smooth
Mach Dynamics in LAMMPS.

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

Currently, no part of MACHDYN supports restarting nor minimization. This
fix has no outputs.

## Restrictions

This fix is part of the MACHDYN package. It is only enabled if LAMMPS
was built with that package. See the [Build package](Build_package) page
for more info.

The molecule ID given to the particles created by this fix have to be
equal to or larger than 65535.

Within each .STL file, only a single triangulated object must be
present, even though the STL format allows for the possibility of
multiple objects in one file.

## Related commands

[smd/triangle_mesh_vertices](compute_smd_triangle_vertices),
[smd/move_tri_surf](fix_smd_move_triangulated_surface),
[smd/tri_surface](pair_smd_triangulated_surface)

## Default

none