# fix smd/wall_surface command

## Syntax

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

• ID, group-ID are documented in 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

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 style. It is possible to move the triangulated surface via the smd/move_tri_surf 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 USER-SMD examples directory.

See this PDF guide to use Smooth Mach Dynamics in LAMMPS.

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

Currently, no part of USER-SMD supports restarting nor minimization. This fix has no outputs.

## Restrictions

This fix is part of the USER-SMD package. It is only enabled if LAMMPS was built with that package. See the Build package doc 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.