Documentation/UserGuide/Data Structure

The information for a single particle is stored in the structure named GrainS, which records the particle position, velocity, property, and identifier. The declaration of the GrainS structure is shown as below:

typedef struct Grain_s{
  Real x1,x2,x3;        /* coordinate in X,Y,Z */
  Real v1,v2,v3;        /* velocity in X,Y,Z */
  int property;         /* index of grain properties */
  short pos;            /* position: 0: ghost; 1: grid; >=10: cross out/in; */
  long my_id;           /* particle id */
#ifdef MPI_PARALLEL
  int init_id;          /* particle's initial host processor id */
#endif
}GrainS;

Particles are associated with the grid. An array of the above particle structure is contained in the structure GridS, which stores all the particles whose positions are within the grid. Particles are passed to other processors via MPI calls when they cross the grid boundaries.

Additional information about the particles are recorded in the structure Grain_Property defined as below:

typedef struct Grain_Property_s{
#ifdef FEEDBACK
  Real m;               /* mass of this type of particle */
#endif
  Real rad;             /* radius of this type of particle (cm) */
  Real rho;             /* solid density of this type of particle (g/cm^3) */
  long num;             /* number of particles with this property */
  short integrator;     /* integrator type: exp (1), semi (2) or full (3) */
}Grain_Property;

The properties include the quantities that are needed to compute the particle stopping time (rad and rho), particle mass for calculating the back reaction, as well as the index of particle integrator used to integrate this type of particles. See Particle Input Block and Particle Problem Generator for more details.

An arbitrary number particle types are allowed, with each type having different particle properties. The number of particle types is recorded in the global variable npartypes, and global array

Grain_Property *grproperty;

stores the information of each type of particles. The element property in the structure GrainS records the property type index that the particle belongs.

In numerical simulations, it is common practice that constant particle stopping time for each particle type is used. For this purpose, we further define a global array

Real *tstop0;

which records the stopping time of each particle types.