\(\renewcommand{\AA}{\text{Å}}\)

# pair_style smd/tri_surface command

## Syntax

    pair_style smd/tri_surface scale_factor

## Examples

    pair_style smd/tri_surface 1.0
    pair_coeff 1 1 <contact_stiffness>

## Description

The smd/tri_surface style calculates contact forces between SPH particles and a rigid wall boundary defined via the smd/wall_surface fix.

The contact forces are calculated using a Hertz potential, which evaluates the overlap between a particle (whose spatial extents are defined via its contact radius) and the triangle. The effect is that a particle cannot penetrate into the triangular surface. The parameter <contact_stiffness> has units of pressure and should equal roughly one half of the Young’s modulus (or bulk modulus in the case of fluids) of the material model associated with the SPH particle

The parameter scale_factor can be used to scale the particles’ contact radii. This can be useful to control how close particles can approach the triangulated surface. Usually, scale_factor =1.0.

## Mixing, shift, table, tail correction, restart, rRESPA info

No mixing is performed automatically. Currently, no part of MACHDYN supports restarting nor minimization. rRESPA does not apply to this pair style.

## Restrictions

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

## Related commands

pair_coeff

## Default

none