Granular

Granular is a sphere or circle mesher included as an optional plugin.

It try to pack spheres with tangency. Spheres could cross a little the volume boundary.
It allow to specify particle radius based on statistical distributions.

The algorithm is based in this paper:
"Procedure of packing generic particles for the discrete element method"
Irvin Pérez Morales, Roberto Roselló Valera, Yordanis Pérez Brito, Harold Díaz-Guzmán Casañas y Carlos A. Recareu Morfa
Revista Internacional de Métodos Numéricos para Cálculo y Diseño en Ingeniería

options:

Sphere and circle main options

Boundary tolerance factor: This parameter is a relative factor of the maximum element size, it is used to set the maximum distance to find a particle considered as belonging to the boundary. Value 1.0 (default) means that it will be considered as boundary all particles with distance to boundary less or equal to the maximum diameter defined.

Distribution Type: Allow select the kind of statistical distribution of the particle sizes to be obtained.

Gauss: Normal distribution
Exponential: Exponential distribution
Cauchy: Cauchy distribution
Flat: Uniform distribution (linear)
Constant: Uniform distribution with constant particle size

Some parameters are enabled only depending on the selected distribution

Standard deviation: Standard deviation of a gaussian distribution, relative to mean element's radius
Scale: Scale parameter for the Exponential, Cauchy and Rayleigh distributions
Minimum radius factor: Defines a factor related with the mean element's radius that is used to calculate its minimum radius to be generated.
Maximum radius factor: Defines a factor related with the mean element's radius that is used to calculate its maximum radius to be generated.

Advanced options

Random mesh: This option allows to define if we want to obtain the same mesh on each meshing. In case of select it each meshing will provide a different result because elements size will be obtained in a random way.
Prioritize: Allow to weight more for the meshing process to preserve more the boundary shape or the particles size.

Boundary fitting: Prioritize adjust better the particles to the geometry boundary

Size distribution: Prioritize adjust better the particle sizes to the selected statistical distribution

High porosity: Selecting it allows to mesh with high porosity values, then the slide widget sets the porosity value to be achieved.