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# pair_style smd/ulsph command

## Syntax

    pair_style smd/ulsph args

- these keywords must be given

    keyword = *DENSITY_SUMMATION or *DENSITY_CONTINUITY and *VELOCITY_GRADIENT or *NO_VELOCITY_GRADIENT and *GRADIENT_CORRECTION or *NO_GRADIENT_CORRECTION

## Examples

    pair_style smd/ulsph *DENSITY_CONTINUITY *VELOCITY_GRADIENT *NO_GRADIENT_CORRECTION

## Description

The smd/ulsph style computes particle interactions according to continuum mechanics constitutive laws and an updated Lagrangian Smooth-Particle Hydrodynamics algorithm.

This pair style is invoked similar to the following command:

    pair_style smd/ulsph *DENSITY_CONTINUITY *VELOCITY_GRADIENT *NO_GRADIENT_CORRECTION
    pair_coeff i j *COMMON rho0 c0 Q1 Cp hg &
                   *END

Here, i and j denote the LAMMPS particle types for which this pair style is defined. Note that i and j can be different, i.e., ulsph cross interactions between different particle types are allowed. However, i–i respectively j–j pair_coeff lines have to precede a cross interaction. In contrast to the usual LAMMPS pair coeff definitions, which are given solely a number of floats and integers, the ulsph pair coeff definition is organized using keywords. These keywords mark the beginning of different sets of parameters for particle properties, material constitutive models, and damage models. The pair coeff line must be terminated with the *END keyword. The use the line continuation operator & is recommended. A typical invocation of the ulsph for a solid body would consist of an equation of state for computing the pressure (the diagonal components of the stress tensor), and a material model to compute shear stresses (the off-diagonal components of the stress tensor).

Note that the use of *GRADIENT_CORRECTION can lead to severe numerical instabilities. For a general fluid simulation, *NO_GRADIENT_CORRECTION is recommended.

Please see the SMD user guide for a complete listing of the possible keywords and material models.

## 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