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fix wall/gran command

Syntax:

fix ID group-ID wall/gran wallstyle args keyword values ... 

Examples:

fix 1 all wall/gran xplane -10.0 10.0 50.0 0.5
fix 2 all wall/gran zcylinder 15.0 50.0 0.5 wiggle z 3.0 2.0
fix 1 all wall/gran zplane 0.0 NULL 100.0 0.5 

Description:

Bound the simulation domain of a granular system with a frictional wall. All particles in the group interact with the wall when they are close enough to touch it.

The wallstyle can be planar or cylindrical. The 3 planar options specify a pair of walls in a dimension. Wall positions are given by lo and hi. Either of the values can be specified as NULL if a single wall is desired. For a zcylinder wallstyle, the cylinder's axis is at x = y = 0.0, and the radius of the cylinder is specified. For all wallstyles, a damping and friction coefficient for particle-wall interactions are also specified.

Optionally, a wall can be oscillated, similar to the oscillations of frozen particles specified by the fix_wiggle command. This is useful in packing simulations of granular particles. If the keyword wiggle is appended to the argument list, then a dimension for the motion, as well as it's amplitude and period is specified. Each timestep, the position of the wall in the appropriate dim is set according to this equation:

position = pos0 + A - A cos (omega * delta) 

where pos0 is the position at the time the fix was specified, A is the amplitude, omega is 2 PI / period, and delta is the elapsed time since the fix was specified. The velocity of the wall is also set to the derivative of this expression.

Restrictions:

A zcylinder wall can only be oscillated in the z dimension. This fix can only be used with atom_style granular.

Related commands:

fix_wiggle

Default: none