Generates Eureka format mesh file using Gmsh as meshing-tool. Gmsh is distributed under the terms of the GNU General Public License (GPL) which means that everyone is free to use Gmsh and to redistribute it on a free basis. MeshGen bundles Gmsh version 3.0.6 which is the latest version as of August 2018. It is recommended to have recent gnu modules loaded (at least gnu/4.8.5) along with OpenGL/Mesa libraries for Gmsh to run properly.
NOTE: MeshGen requires a C++11 capable compiler to build.
$ make clean
$ makeThis generates two programs: GeoGen and EurekaGen
GeoGen: Takes in input config file and outputs geometry script (.geo) fileEurekaGen: Takes in input Gmsh mesh (.msh) file and outputs Eureka format mesh (.dat) file
Change permission of the gen_mesh.sh script in order to make it an executable:
$ chmod 755 gen_mesh.shRun the mesh generation script as shown (the output is saved to a log file MeshGen.log):
$ ./gen_mesh.sh -c conf/BrakePad.conf -g mesh/BrakePad.geo -m mesh/BrakePad.msh -d mesh/BrakePad.dat 2>&1 | tee MeshGen.logThe script takes in the following command-line arguments:
| Argument | Description |
|---|---|
| -h | Help message |
| -c CONF | Input config file to both programs |
| -g GEO | Output geometry script file from GeoGen |
| -m MSH | Output mesh file from Gmsh |
| -d DAT | Output Eureka format mesh file from EurekaGen |
| -x | Do not delete intermediate material file (optional) |
The GeoGen program generates an intermediate material (GeoGen.mat) file which is used by the EurekaGen program to compute element groups for different materials. By default, the shell script removes this file after successful execution (i.e. after the .dat file is generated). One can choose to keep this material file for debugging purposes by including the command-line argument (-x) as shown below:
$ ./gen_mesh.sh -x -c conf/BrakePad.conf -g mesh/BrakePad.geo -m mesh/BrakePad.msh -d mesh/BrakePad.dat 2>&1 | tee MeshGen.logMeshGen comprises of a rigid directory structure which is as follows:
| Directory | Description |
|---|---|
| conf | Place all config files (.conf) here |
| EurekaGen | Contains the EurekaGen program executable and source files |
| GeoGen | Contains the GeoGen program executable and source files |
| mesh | Store all mesh-related output files (.dat, .geo, .msh) here |
Use mesh/ directory to store all output files, namely the (-g, -m, -d) options from the command-line arguments. The shell script will automatically create the mesh/ directory if it is missing. If you wish to use your own directory, make sure to create it first and use correct path to avoid dire consequences!
NOTE: All units are in microns (μm). Lines starting with # in .conf file are comments.
The input config file (for example, ./conf/BrakePad.conf) comprises of the following format:
Internally, we follow a cartesian coordinate system, where z points upward. Length (by default 10000.0) is measured in x-direction, width (by default 5000.0) in y-direction and height (including piston thickness; by default 5500.0) in z-direction.
# Box dimension
length=10000.0
width=5000.0
height=5500.0
One can specify the global matrix mesh-size (by default 200.0) for Gmsh to follow while meshing. This will propagate to the material particles if their individual mesh-sizes are not specified (see Material block below).
# Global mesh-size
global_mesh_size=200.0
Once can specify the tolerance-value between particles (by default 50.0), i.e. the minimum inter-particle distance while inserting each particle into the matrix.
# Tolerance between particles
tol_particles=50.0
Once can specify the tolerance-value between particles and the boundaries (by default 100.0) of the bounding box.
# Tolerance between particles and boundaries
tol_particles_boundaries=100.0
There is a steel piston on the top of the bounding box whose thickness (by default 500.0) needs to be specified.
# Piston thickness
piston_thicc=500.0
The output .geo file writes out the seed value used to initialize the randomizer on line 4.
/** Gmsh geometry script generated by GeoGen (author: Rajdeep Konwar)
* Copyright (c) 2018, Robert Bosch LLC
* Timestamp: Mon Jul 30 10:34:56 2018
* Rand seed: 1532972096
**/
One can use that seed value for a different run by placing it in the config file (as shown below) to achieve the same placement and orientation of all the particles.
# Random seed
rand_seed=1532972096
If left blank, the randomizer will use the current system time as seed (default behavior).
The following table describe all aspects of a material block and the possible options and combinations:
| key-phrase | Description |
|---|---|
| material | Name of the material, used for element group names |
| vol_frac | Volume fraction in percentage (wrt the total volume) of the material |
| count | Instead of volume fraction, one can specify the exact count of particles for a material. Either one of these values are required |
| mesh_size | Individual mesh-size for the material. If left blank, will use the global_mesh_size value |
| morph | Morphology of the material particles. Available options are cylinder/cyl and sphere/sph |
| rad_distrib | Probability distribution for radius (base-radius for cylinder whereas actual radius for sphere). Available options are gaussian/gauss and uniform/flat |
| rad_mean | Mean-value of radius. Only applicable for Gaussian distribution. GeoGen will output error if tried to use with Uniform distribution |
| rad_min rad_max | Minimum and maximum value of radius. Used only if rad_mean isn't specified (i.e. rad_mean has higher priority). Applicable for both types of distribution. For Gaussian distribution, the rad_min and rad_max correspond to -3σ and 3σ respectively, where σ is the standard deviation (rad_std_dev), i.e. 99.7% of the data are within 3 standard deviations of the mean |
| rad_std_dev | Standard deviation for radius. Must be specified when using rad_mean (otherwise GeoGen will output error) whereas automatically computed from rad_min & rad_max |
| len_distrib | Probability distribution for length of cylinder. The following key-phrases are only applicable for cylinder morphology. Available options are gaussian/gauss and uniform/flat |
| len_mean | Mean-value of cylinder length. Only applicable for Gaussian distribution. GeoGen will output error if tried to use with Uniform distribution |
| len_min len_max | Minimum and maximum value of cylinder length. Used only if len_mean isn't specified (i.e. len_mean has higher priority). Applicable for both types of distribution. For Gaussian distribution, the len_min and len_max correspond to -3σ and 3σ respectively, where σ is the standard deviation (len_std_dev), i.e. 99.7% of the data are within 3 standard deviations of the mean |
| len_std_dev | Standard deviation for cylinder length. Must be specified when using len_mean (otherwise GeoGen will output error) whereas automatically computed from len_min & len_max |
One can add as many materials according to their use-case by placing each material in its own block as described by the above table (for reference, see ./conf/BrakePad.conf). For example:
# Material 3
material=Friction Dust
#vol_frac=0.16
count=5
mesh_size=
morph=sphere
rad_distrib=gaussian
rad_mean=600.0
rad_std_dev=50.0
As described above, the GeoGen program outputs an intermediate material file (GeoGen.mat) in MeshGen's root directory which is used later by EurekaGen to help identify the material element groups. For debugging purposes, the material file format is as follows:
Name of the material
Morphology
Number of particles
Available options for Morphology are cyl (for cylinder) and sph (for sphere).
The following lines (corresponding to the number of particles) for cylinder morphology:
base-radius center1.x center1.y center1.z center2.x center2.y center2.z
where center1 is the center of the left face and center2 is the center of the right face of the cylinder.
Whereas for sphere morphology, we have:
radius center.x center.y center.z
where center is the center of the sphere. x, y, z are the cartesian coordinate values of a point.
The code uses certain constants and typedefs which can be changed (although not recommended) according to the need of the user. The file ./GeoGen/GeoConstants.h contains the iteration limit (by default 1 million) for the part where it tries to insert cylinder and sphere into the matrix while trying to avoid placing it out of the bounding box and avoid all types of collision detection. If the code fails to do so in the specified number of iterations, it will quit the program by throwing an error message like:
Reached limit for iterative cylinder insertion! Exiting..