Syntax:
fix ID group gravity style args
chute args = angle angle = angle in +x away from -z axis (in degrees) spherical args = phi theta phi = azimuthal angle from +x axis (in degrees) theta = angle from +z axis (in degrees) gradient args = phi theta phi_grad theta_grad phi = azimuthal angle from +x axis (in degrees) theta = angle from +z axis (in degrees) phi_grad = rate of change of angle phi (full rotations per time unit) theta_grad = rate of change of angle theta (full rotations per time unit)
Examples:
fix 1 all gravity chute 24.0 fix 1 all gravity spherical 0.0 -180.0 fix 1 all gravity gradient 0.0 -180.0 0.0 0.1
Description:
Impose an additional force on each granular particle in the group due to gravity. The direction in which gravity operates is specified.
Style chute is typically used for simulations of chute flow where the specified angle is the chute angle, with flow occurring in the +x direction. Style spherical allows an arbitrary 3d direction to be specified for the gravity vector. Style gradient allows the direction of the gravity vector to be time dependent. The units of the gradient arguments are in full rotations per time unit. E.g. a timestep of 0.001 and a gradient of 0.1 means the gravity vector would rotate thru 360 degrees every 10,000 timesteps. For the time-dependent case, the initial direction of the gravity vector is phi,theta at the time the fix is specified.
The strength of the acceleration due to gravity is 1.0 in LJ units, which are the only allowed units for granular systems.
Restrictions:
Can only be used with atom_style granular.
Related commands:
Default: none