diff --git a/doc/Section_howto.html b/doc/Section_howto.html index 694b55e99a..488eac796e 100644 --- a/doc/Section_howto.html +++ b/doc/Section_howto.html @@ -29,7 +29,8 @@ certain kinds of LAMMPS simulations. 4.13 NEMD simulations
4.14 Extended spherical and aspherical particles
4.15 Output from LAMMPS (thermo, dumps, computes, fixes, variables)
-4.16 Thermostatting, barostatting and computing temperature
+4.16 Thermostatting, barostatting and computing temperature
+4.17 Walls

The example input scripts included in the LAMMPS distribution and highlighted in this section also show how to @@ -1361,6 +1362,78 @@ thermodynamic output.

+

4.16 Walls +

+

Walls in an MD simulation are typically used to bound particle motion, +i.e. to serve as a boundary condition. +

+

Walls in LAMMPS can be of rough (made of particles) or idealized +surfaces. Ideal walls can be smooth, generating forces only in the +normal direction, or frictional, generating forces also in the +tangential direction. +

+

Rough walls, built of particles, can be created in various ways. The +particles themselves can be generated like any other particle, via the +lattice and create_atoms commands, +or read in via the read_data command. +

+

Their motion can be constrained by many different commands, so that +they do not move at all, move together as a group at constant velocity +or in response to a net force acting on them, move in a prescribed +fashion (e.g. rotate around a point), etc. Note that if a time +integration fix like fix nve or fix nvt +is not used with the group that contains wall particles, their +positions and velocities will not be updated. +

+ +

The fix move command offers the most generality, since +the motion of individual particles can be specified with +variable formula which depends on time and/or the +particle position. +

+

For rough walls, it may be useful to turn off pairwise interactions +between wall particles via the neigh_modify +exclude command. +

+

Rough walls can also be created by specifying frozen particles that do +not move and do not interact with mobile particles, and then tethering +other particles to the fixed particles, via a bond. +The bonded particles do interact with other mobile particles. +

+

Idealized walls can be specified via several fix commands. Fix +wall/gran creates frictional walls for use with +granular particles; all the other commands create smooth walls. +

+ +

The lj93, lj126, colloid, and harmonic styles all allow the +flat walls to move with a constant velocity, or oscillate in time. +The fix wall/region command offers the most +generality, since the region surface is treated as a wall, and the +geometry of the region can be a simple primitive volume (e.g. a +sphere, or cube, or plane), or a complex volume made from the union +and intersection of primitive volumes. Regions can also +be "dynamic" meaning they move with constant velocity, oscillate, or +rotate. +

+

The only frictional idealized walls currently in LAMMPS are flat or +curved surfaces specified by the fix wall/gran +command. At some point we plan to allow regoin surfaces to be used as +frictional walls, as well as triangulated surfaces. +

+
+
diff --git a/doc/Section_howto.txt b/doc/Section_howto.txt index 427e485a3a..bb01e026de 100644 --- a/doc/Section_howto.txt +++ b/doc/Section_howto.txt @@ -26,7 +26,8 @@ certain kinds of LAMMPS simulations. 4.13 "NEMD simulations"_#4_13 4.14 "Extended spherical and aspherical particles"_#4_14 4.15 "Output from LAMMPS (thermo, dumps, computes, fixes, variables)"_#4_15 -4.16 "Thermostatting, barostatting and computing temperature"_#4_16 :all(b) +4.16 "Thermostatting, barostatting and computing temperature"_#4_16 +4.17 "Walls"_#4_17 :all(b) The example input scripts included in the LAMMPS distribution and highlighted in "this section"_Section_example.html also show how to @@ -1348,6 +1349,78 @@ you can use the "thermo_modify"_thermo_modify.html command to re-define what temperature or pressure compute is used for default thermodynamic output. +:line + +4.16 Walls :link(4_17),h4 + +Walls in an MD simulation are typically used to bound particle motion, +i.e. to serve as a boundary condition. + +Walls in LAMMPS can be of rough (made of particles) or idealized +surfaces. Ideal walls can be smooth, generating forces only in the +normal direction, or frictional, generating forces also in the +tangential direction. + +Rough walls, built of particles, can be created in various ways. The +particles themselves can be generated like any other particle, via the +"lattice"_lattice.html and "create_atoms"_create_atoms.html commands, +or read in via the "read_data"_read_data.html command. + +Their motion can be constrained by many different commands, so that +they do not move at all, move together as a group at constant velocity +or in response to a net force acting on them, move in a prescribed +fashion (e.g. rotate around a point), etc. Note that if a time +integration fix like "fix nve"_fix_nve.html or "fix nvt"_fix_nvt.html +is not used with the group that contains wall particles, their +positions and velocities will not be updated. + +"fix aveforce"_fix_aveforce.html - set force on particles to average value, so they move together +"fix setforce"_fix_setforce.html - set force on particles to a value, e.g. 0.0 +"fix freeze"_fix_freeze.html - freeze particles for use as granular walls +"fix nve/noforce"_fix_nve_noforce.html - advect particles by their velocity, but without force +"fix move"_fix_move.html - prescribe motion of particles by a linear velocity, oscillation, rotation, variable :ul + +The "fix move"_fix_move.html command offers the most generality, since +the motion of individual particles can be specified with +"variable"_variable.html formula which depends on time and/or the +particle position. + +For rough walls, it may be useful to turn off pairwise interactions +between wall particles via the "neigh_modify +exclude"_neigh_modify.html command. + +Rough walls can also be created by specifying frozen particles that do +not move and do not interact with mobile particles, and then tethering +other particles to the fixed particles, via a "bond"_bond_style.html. +The bonded particles do interact with other mobile particles. + +Idealized walls can be specified via several fix commands. "Fix +wall/gran"_fix_wall_gran.html creates frictional walls for use with +granular particles; all the other commands create smooth walls. + +"fix wall/reflect"_fix_wall_reflect.html - reflective flat walls +"fix wall/lj93"_fix_wall.html - flat walls, with Lennard-Jones 9/3 potential +"fix wall/lj126"_fix_wall.html - flat walls, with Lennard-Jones 12/6 potential +"fix wall/colloid"_fix_wall.html - flat walls, with "pair_style colloid"_pair_colloid.html potential +"fix wall/harmonic"_fix_wall.html - flat walls, with repulsive harmonic spring potential +"fix wall/region"_fix_wall_region.html - use region surface as wall +"fix wall/gran"_fix_wall_gran.html - flat or curved walls with "pair_style granular"_pair_gran.html potential :ul + +The {lj93}, {lj126}, {colloid}, and {harmonic} styles all allow the +flat walls to move with a constant velocity, or oscillate in time. +The "fix wall/region"_fix_wall_region.html command offers the most +generality, since the region surface is treated as a wall, and the +geometry of the region can be a simple primitive volume (e.g. a +sphere, or cube, or plane), or a complex volume made from the union +and intersection of primitive volumes. "Regions"_region.html can also +be "dynamic" meaning they move with constant velocity, oscillate, or +rotate. + +The only frictional idealized walls currently in LAMMPS are flat or +curved surfaces specified by the "fix wall/gran"_fix_wall_gran.html +command. At some point we plan to allow regoin surfaces to be used as +frictional walls, as well as triangulated surfaces. + :line :line