LIGGGHTS WWW Site - LAMMPS WWW Site - LIGGGHTS Documentation - LIGGGHTS Commands

fix seaice/wind command

Syntax:

fix ID group-ID seaice/wind U10x U10y Cds Cdf keyword value ... 

Examples:

fix NW all seaice/wind 5.0 -5.0 0.002 0.001
fix storm all seaice/wind v_ux v_uy 0.002 0.002 region regID 

Description:

This fix is part of the USER-SEAICE package; it is only enabled if LIGGGHTS was built with that package.

It adds wind-generated force to the x and y components of force for each disk-shaped atom in the group.

It is assumed that the wind is horizontal, i.e., it does not contribute to the force along the z-axis. It is also assumed that the wind does not contribute to the torque acting on the disks.

This fix requires two global variables, defining the values of water density and air density, that can be set with the fix property/global commands:

fix m2 all property/global rhoWater scalar 1025.0 
fix m3 all property/global rhoAir scalar 1.27 

No default values for these constants are predefined and the lack of the above definitions in the input script will produce an error.

The skin drag acting on a given disk is proportional to its upper surface area. The form drag is proportional to the disk diameter times its freeboard, calculated from its relative density and thickness.

Any of the 4 quantities defining the wind speed components and drag coefficients can be specified as an equal-style or atom-style variable. If the value is a variable, it should be specified as v_name, where name is the variable name. In this case, the variable will be evaluated each timestep, and its value(s) used to determine the instantaneous wind speed/drag coefficient. For more details concerning specifying variable forcing, see the documentation of the fix addforce command.

If the region keyword is used, the atom must also be in the specified geometric region in order to have force added to it.


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

See the documentation of the fix addforce command.

Restrictions: none

Related commands:

fix addforce, fix seaice/coriolis, fix seaice/current, fix seaice/waves

Default: none

(Herman) Agnieszka Herman, Geosci. Model Devel., submitted (2015).