"LIGGGHTS(R)-PUBLIC WWW Site"_liws - "LIGGGHTS(R)-PUBLIC Documentation"_ld - "LIGGGHTS(R)-PUBLIC Commands"_lc :c

:link(liws,http://www.cfdem.com)
:link(ld,Manual.html)
:link(lc,Section_commands.html#comm)

:line

fix sph/pressure command :h3

[Syntax:]

fix ID group-ID sph/pressure style args :pre

ID, group-ID are documented in "fix"_fix.html command
sph/pressure = style name of this fix command
style = {absolut} or {relativ} or {Tait}
args = list of arguments for a particular style :ul

  {absolut} args = B
    B = coefficient
  {relativ} args = B density0
    B = coefficient
    density0 = reference density
  {Tait} args = B density0 gamma
    B = coefficient
    density0 = reference density
    gamma = isentropic exponent :pre

[Examples:]

fix pressure all sph/pressure absolut
fix pressure all sph/pressure Tait 60000. 1000. 7. :pre

[Description:]

The equation of state (EOS) for the SPH calculation is the link between the density field and the pressure field. A lot of different equations can be found in the literature.

The {absolut} style was the first implemented EOS. The calculation rule is

:c,image(Eqs/fix_sph_pressure_abs.jpg)

where ρa is the density of particle a and B is the pressure prefactor.

The {relativ} style uses the rule

:c,image(Eqs/fix_sph_pressure_rel.jpg)

as EOS. B denotes the pressure prefactor and ρ0 is the reference density.

In case of {Tait} style the rule

:c,image(Eqs/fix_sph_pressure_tait_eq1.jpg)

is applied. B denotes the pressure prefactor which is calculated by

:c,image(Eqs/fix_sph_pressure_tait_eq2.jpg)

where c0 is the speed of sound of the material. ρ0 is the reference density and γ is the isentropic exponent defined as cp/cv.

NOTE: Monaghan has found that the speed of sound could be artificially reduced. (Monaghan, 1994) Therefore, we can choose a greater time step. He argues that the minimum sound speed should be about ten times greater than the maximum expected flow speed. (Δρ < 1%)

:line

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

No informatino about this fix is written to "binary restart files"_restart.html.

None of the "fix_modify"_fix_modify.html options are relevant to this fix.

No global scalar or vector or per_atom quantities are stored by this fix for access by various "output commands"_Section_howto.html#4_15.

No parameter of this fix can be used with the {start/stop} keywords of the "run"_run.html command.

This fix is not invoked during "energy minimization"_minimize.html.

:line

[Restrictions:]

One fix sph/density/summation (only dev-version) or sph/denstiy/continuity has to exist.

[Related commands:]

"pair_style sph/artVisc/tensCorr"_pair_sph_artvisc_tenscorr.html, "fix sph/density/continuity"_fix_sph_density_continuity.html

[Default:] none

:line

:link(LiuLiu2003)
[(Liu and Liu, 2003)] "Smoothed Particle Hydrodynamics: A Meshfree Particle Method", G. R. Liu and M. B. Liu, World Scientific, p. 449 (2003).

