particle_template fiber command

Purpose

Command for defining flexible fibers (examples).

Warning

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

Syntax

particle_template [general_keywords] shape fiber keyword value

General particle_template keywords are documented here. This document only describes the specific keywords for the definition of flexible fibers.

Return to the particle_template documentation.

Keyword

Description

file
obligatory; name of the file containing the center coordinates and the radius
of the spheres forming the fiber (*.csv or *.txt)

scale
factor for scaling up or down the sphere positions and radii
default: 1; range: (0,∞); units: [-]

check_template
yes or no; yes: during the particle template creation checks are performed
(if particles overlap) are performed; no: skip all checks (it is expected that
particles are non-overlapping!), which will speed up particle template creation
default: yes

bounding_sphere
radius value position vector; value = radius of the bounding sphere
vector = position of the center of the bounding sphere
units: [length]

center_of_mass
position vector of the center of mass; if not specified, it is calculated
using the analytical expression
units: [length]

Examples

particle_template id myFibers material grass shape fiber file grass_blade.csv

particle_template id pts1 material material1 shape fiber file fiber.txt scale 0.1 &
     center_of_mass (1.0,0.0,0.0)

particle_template id pts1 material grass shape fiber file fiber.csv &
     bounding_sphere radius 0.01 position (0.01,0,0)

Description

_images/fiber.png

Fibers are made of spherical particles that are bonded together in a row. The particle parameters (i.e., positions and radii) are defined via a text file, whose name is set by the obligatory keyword file. The format of this text file is:

x1 y1 z1 r1
x2 y2 z2 r2
...
xn yn zn rn

where n is the total number of spheres, x, y and z is the position of the respective sphere and r its radius. Comments can be made in this file via the ‘#’ character.

Optionally, the keyword scale can be used to define a factor for scaling up or down the particle positions and radii.

After the spheres are read, a Monte Carlo procedure is used to assess everything that is needed for the motion integration: mass, center of mass, and the inertia tensor including its eigensystem. The values calculated are written to the logfile.

Per default, also the bounding sphere of the fiber is determined with a Monte Carlo approach. By using the keyword bounding_sphere followed by radius and position this can be done explicitly. This is of particular interest if the create_particles command is used for particle insertion and the exact particle position is required for positioning.

The simulation of fibers requires the usage of the cohesion model fiber model or an advanced fiber model (see advanced fiber models) and the satisfaction of the cohesion model’s distance criterion. Then, the spheres are connected by bonds and the particle behaves like a fiber.