Discrete particle elements

Discrete particle elements:

represent individual particles with a rigid, spherical shape;
are typically used in analyses with a large number of discrete particle elements interacting with each other and with other bodies;
can be used only in explicit dynamic analyses; and
must have only one node.

The following topics are discussed:

Typical Applications
Defining the elements section properties
Particle geometry, mass, and rotational inertia
Alpha damping

Typical Applications

Discrete particle elements (PD3D) are useful for simulations involving discontinuous media such as gravel. For a description of the discrete element method (DEM) and its typical applications, see Discrete element method.

Defining the elements section properties

You must associate a discrete section definition with a set of discrete particle elements. The section definition provides the density associated with the PD3D elements and particle radii.

Input File Usage

DISCRETE SECTION, ELSET=element_set_name

Particle geometry, mass, and rotational inertia

PD3D elements are spherical in shape, and each particle has uniform density. The particle radius and density are specified in a discrete section definition. Abaqus uses these quantities to compute the mass and rotational inertia of PD3D elements. Each discrete element is simple, but interactions of large systems of such particles and finite elements enable simulation of complex phenomena, as discussed in Discrete element method.

Particle sizes and densities will commonly be the same for all particles assigned to a single discrete section definition, but it is possible to specify variations in these quantities among particles associated with a single discrete section definition by assigning distribution names rather than scalar values to the radius and/or density. See Distribution definition for a discussion of distributions. If, for example, two particle sizes are to be considered, it may be most convenient to simply use two discrete section definitions with a single particle size in each.

Input File Usage

Use the following option to define the particle shape, density, and radius:

DISCRETE SECTION, SHAPE=SPHERE, DENSITY=particle density 
or a particle densities distribution table name
particle radius or particle radii distribution table name

Alpha damping

You can define mass and rotary inertia proportional damping for PD3D elements similar to that for point mass and rotary inertia elements (see Point masses and Rotary inertia). This damping acts on translational and rotational velocities of individual particles (with respect to “ground”) and is independent of contact damping (which acts on relative velocities for nearby particle pairings). Unlike other types of deformable finite elements in Abaqus/Explicit, there is no global viscous damping acting on PD3D elements. A small amount of mass proportional damping is beneficial in reducing the noise in the solution generated by numerous opening and closing contact conditions.

Input File Usage

Use the following option to specify mass and rotary inertia proportional damping:

DISCRETE SECTION, ALPHA=damping factor, α