The Accumulator (for Velocity Reinitialization) feature transfers information from particles to the domain they occupy. Each
Accumulator defines a variable, called the accumulated variable, on the domains in the selection of the parent
Velocity Reinitialization node. The accumulated variable is discretized using constant shape functions, so its value is uniform over every mesh element and may be discontinuous between adjacent mesh elements.
The name of the accumulated variable is specified in the Accumulated variable name text field in the
Accumulator Settings section of the settings window. The default variable name is
rpv.
The options in the Accumulator type list are
Density and
Count. If
Count is selected, then whenever the parent feature’s velocity reinitialization condition is satisfied, the accumulated variable in the element occupied by the particle is incremented by the value of the source term,
If instead Density is selected, the source term is first divided by the volume (in 3D) or area (in 2D) of the mesh element the particle is in,
A simple demonstration of the Accumulator subnode for the
Velocity Reinitialization node is illustrated in
Figure 3-9 below. A single particle is released into a square domain with initial velocity
(1,0.5) m/s. From left to right, the particle trajectory is shown at solution times
t =
0.25 s,
t =
0.50 s,
t =
0.75 s, and
t =
1.00 s. The accumulated variable is shown as a surface plot and the mesh element boundaries are also shown. The reinitialization criterion is
qx>0.6&&pt.vx>0. It is clear that the accumulation is applied uniformly over the mesh element the particle occupies at the time step when the reinitialization condition is met, at about
t =
0.60 s.