calculate center of mass command

Purpose

This command calculates the center of mass of the bulk material (examples).

Warning

GPU support for this command has not been tested and may not work as expected.

Syntax

calculate center_of_mass keyword/value pairs

Keywords

Description

id
user-assigned name for the command call
default: center_of_mass_[number of calculate]

particle_group
particle group for which the center of mass is evaluated
default: all

write_every_time
time step width for data output
default: same value as write_to_terminal_timestep; range: (0,∞); units: [time]

file

filename for data output

final_update
Recomputes at the last step of a simulate command.
available options: yes or no
default: yes

Examples

calculate center_of_mass
calculate center_of_mass particle_group blueParticles id comBlue
calculate center_of_mass write_every_time 1e-3 file com_output.txt

Description

This command calculates the center of mass of the particles in the simulation or, if the particle_group keyword is used, of a subset (definition see define_group command).

Per default, the command is evaluated at every write_to_terminal_timestep, the write_every_time keyword can be used to modify the interval.

The final_update keyword will force a recomputation of the value at the last integration step of a simulate command. This is useful if the value is required in the input script between two simulate commands, e.g. for setting a variable.

Output information

The calculate center_of_mass command produces a global 3D-vector with the x, y and z position of the center of mass in distance units. The components of the generated vector for a command with ID COMID can be accessed by id_COMID[1], id_COMID[2] and COMID[3] or id_COMID.x, id_COMID.y and id_COMID.z.

When using the output_settings command, the results are automatically written to the simulation_data_aspherix.csv / result_monitor.txt file.

If the file keyword is used to explicitly define an output file name, the result is additionally written to the defined file. The file contains of an array with four columns, the first column contains the time, followed by the values for the x, y and z component of the position.

Alternatively, also the write_to_file command can be used to output the data to a specified file.

Example for saving the center of mass to a separate file

calculate center_of_mass write_every_time 1e-3 id com
write_to_file file center_of_mass.txt string "id_time id_com[1] id_com[2] id_com[3]" &
    title "# time x y z" write_every_time 1e-3

Restrictions

For multispheres, bonded and fibers the center of mass specified by the center_of_mass keyword of the particle_template command is ignored by the calculate center_of_mass command.