# fix smd/integrate_ulsph command

## Syntax

``` LAMMPS
fix ID group-ID smd/integrate_ulsph keyword
```

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

``` LAMMPS
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](PDF/MACHDYN_LAMMPS_userguide.pdf)\_ 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](Build_package) page
for more info.

## Related commands

none

## Default

none