Description: The particle generator can introduce a mixture of several particle species during a simulation via an arbitrarily shaped inlet surface. The inlet surface can be meshed using triangular and quad elements allowing the meshing of complex inlet shapes. The inlet surface can translate, rotate, expand, skew, or collapse during a simulation. Each particle species in the mixture can have a different particle size distribution defined by a probability density function, which allows simultaneous generation of particulate media of large and small sizes (such as a mixture of sand, cement, and aggregates). In addition, separate mass flow rates can be specified for each species, which allows for ramping up or down the generation rate of individual species during the analysis. The entry velocity of particles into the problem domain can also be varied during the course of the analysis.