The Accumulator subnode is available from the context menu (right-click the Wall or Material Discontinuity parent node) or from the Physics toolbar, Attributes menu. Each Accumulator subnode defines a variable, called the accumulated variable, on each boundary element in the selection of the parent node. The accumulated variables are incremented when rays interact with the boundaries where they are defined.

Select an option from the Accumulator type list — Density (default) or Count.

Select an option from the Accumulate over list — Ray-wall interactions (the default) or Rays in boundary elements.

Enter the Accumulated variable name. The default is rpb. The accumulated variable is defined as <scope>.<name>, where <scope> includes the name of the physics interface node, parent boundary condition, and the Accumulator node, and <name> is the accumulated variable name.

For example, if the Accumulator subnode is added to a Wall node in an instance of the Geometrical Optics interface using the default variable name rpb, the accumulated variable name might be gop.wall1.bacc1.rpb.

Enter a Source R. The unit of the source term depends on the settings in the Units section. Whenever a ray collides with a boundary element in the selection of the parent node, the accumulated variable in that element is incremented by the source term. If the Accumulator type is set to Density, the source term is divided by the area of the boundary element (in 3D) or the length of the boundary element (in 2D).

For example, if the source is 1 and Count is selected from the Accumulator type list, a variable is created to store the number of times each boundary element is hit by a ray.

Select a Dependent variable quantity from the list; the default is Dimensionless [1]. To enter a unit, select None from the list and in the Unit field enter a value, for example, K, m/s, or mol/m^3.

The accumulated variables are computed using discontinuous shape functions. Select the Compute smoothed accumulated variable check box to compute a smoothed accumulated variable by computing the average value of the variable within a sphere of a user-defined radius. Then enter a Smoothing radius r (SI unit: m). The default is 0.1[m].