**Rball**

Rball is a sphere or circle mesher included internally in GiD.

It has several algorithms in order to try to pack spheres with tangency.

Spheres are tried to be packed without cross the volume boundary.

The different options to choose are:

**Algorithm**

·Optimization radius: iterative, optimizes distances and positions for minimum porosity.

(ref:Carlos Labra, Eugenio Oñate. High-density sphere packing for discrete element method simulations, Communications in Numerical Methods in Engineering 2009)

·Porosity predefined : iterative with fixed radius .Experimental.

·Explicit: iterative, radius defined with porosity and optimizes positions. (Experimental)

·Radius expansion : iterative, corrects positions and increases radius.

·Optimization radius fast: it's 'Optimization radius' with less precision. (Experimental)

·Position correction and inflate

·Optimization radius corrected

- Delta radius factor: Randomness of initial radius. Minimum radius = (1-DeltaRadius)*UserRadius; Maximum radius = (1+DeltaRadius)*UserRadius.

- Min. radius factor: Minimum radius Factor. Minimum radius = MinRadius*UserRadius(size of element/2).

- Max. radius factor: Maximum radius Factor. Maximum radius = MaxRadius*UserRadius(size of element/2).

**Options**

- Max. iterations: Maximum number of iterations for the choosed algorithm.

- Max. local iterations: Number of iterations for filters.

- Tolerance: Tolerance of distance function to terminate the process.

- Delta position factor: Perturbation of initial position factor. Maximum perturbation = DeltaPosition*UserSize.

- Preprocess with porosity: Initial generation of spheres with porosity.

·Porosity: Value of porosity for preprocess.

·Postprocess: correction of final positions. (Experimental)

·Overlaps: Checked permits overlaping between spheres. If not checked corrects radius of the sphere.

Note:Delta postition and Delta radius: define randomness of generations: if both of them equals 0, the generation will be structured.

Note:Maximum values recomended for Delta position and Delta radius:

2D: delta position: 0.6; delta radius:0.6

3D: delta position: 0.4; delta radius:0.4

**Filters**

- Filter iterations: Number of global iterations before activate sphere size filter.

- Search iterations: Number of global iterations before activate the search of new overlapings between spheres.

- Search type: Type of search: Spatial search (Tree-based); Delauny remeshing.

- Factor contact: Sphere Neighborhood factor distance. Neighbor if Distance(sphere1,sphere2)<ContactFactor*(sphere1.Radius+sphere2.Radius)

- Factor neighbor: Penalty factor between overlaped spheres (in optimization algorithm must be 1.0)

- Factor facet : Penalty factor between overlaped sphere with a surface (in optimization algorithm must be 1.0).

- Factor overlap: Factor to eliminate sphere with overlaps. Delete sphere if maximum Overlap>OverlapFactor*Sphere radius