\(\renewcommand{\AA}{\text{Å}}\)

# fix smd/integrate_ulsph command

## Syntax

    fix ID group-ID smd/integrate_ulsph keyword

- ID, group-ID are documented in fix command

- smd/integrate_ulsph = style name of this fix command

- zero or more keyword/value pairs may be appended

- keyword = adjust_radius or limit_velocity

adjust_radius values = adjust_radius_factor min_nn max_nn

  adjust_radius_factor = factor which scale the smooth/kernel radius min_nn = minimum number of neighbors max_nn = maximum number of neighbors

limit_velocity values = max_velocity

  max_velocity = maximum allowed velocity.

## Examples

    fix 1 all smd/integrate_ulsph adjust_radius 1.02 25 50
    fix 1 all smd/integrate_ulsph limit_velocity 1000

## Description

The fix performs explicit time integration for particles which interact with the updated Lagrangian SPH pair style.

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

The adjust_radius keyword activates dynamic adjustment of the per-particle SPH smoothing kernel radius such that the number of neighbors per particles remains within the interval min_nn to max_nn. The parameter adjust_radius_factor determines the amount of adjustment per timestep. Typical values are adjust_radius_factor =1.02, min_nn =15, and max_nn =20.

The limit_velocity keyword will control the velocity, scaling the norm of the velocity vector to max_vel in case it exceeds this velocity limit.

## 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 page for more info.

Changed in version 29Aug2024.

This fix is incompatible with deformation controls that remap velocity, for instance the remap v option of fix deform.

## Related commands

none

## Default

none