It is possible to release grains at user defined positions using the Release from Grid and Release from Data File features, or at arbitrary positions in the domains or on the boundaries using the Release and Inlet features, respectively.

When using the Release from Grid or Release from Data File features, the grains being released by a node must have the same material properties. These features are best suited for situations when the initial conditions of the grains to be released are predetermined.

The Release or Inlet features on the other hand allow for more flexibility both in terms of the initial positions and the material properties of the grains being released. The Release feature allows the initial positions to be either random or based on an analytic expression. The Inlet feature additionally supports a uniform distribution of the initial positions along the boundaries. Both the features support releasing multiple types of grains using a single node. The distribution of the grain types can be directly specified, or in terms of the number fraction, mass fraction, or volume fractions.

When grains are released using any of the four release features, the grains are released sequentially. If the grains are released using the Release or Inlet features, the species index of the grain is selected randomly according to the specified distribution. The grain is released at the release position only if the overlap with any grain or wall element is within acceptable limits. The contact search algorithm used to check for the overlap is described in Contact Search Theory. It is possible to override the contact search when using the Release from Grid or Release from Data File features.

Apart from the initial positions of the grains, other parameters such as the initial velocities and angular velocities also need to be specified using expressions. Additionally, if the Compute grain temperature checkbox is enabled, the initial temperature of the grains also need to be specified.