The Accumulator subnode is available from the context menu (right-click the Wall, Outlet, Periodic Condition, Axial Symmetry or Thermal Reemission 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. Whenever a particle hits a boundary element, the value of the accumulated variable in that element is incremented based on the value of the user-defined Source term R for the incident particle. The accumulated variable may be influenced by all particles or may be restricted to particles corresponding to a specific release feature or a Particle Properties node.

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

Select an option from the Accumulate over list: Particle-wall interactions (default) or Particles 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 Mathematical Particle Tracing interface using the default variable name rpb, the accumulated variable name might be pt.wall1.bacc1.rpb.

Enter a Source R. The unit of the source term depends on the settings in the Units section. Whenever a particle 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).

Select an option from the Particle selection list to specify whether the accumulated variable collects information from the particles based on a Release feature (the default) or a Particle properties node.

If Release feature is selected, select an option from the Release feature list. If All (the default) is selected, the accumulated variable collects information about all particles in the selected domains or boundaries, regardless of how they were released. Alternatively, select a particle release feature from the list, and then only the particles produced by that release feature are included.

If Particle properties is selected from the Particle selection list, select an option from the Released particle properties list. If All (the default) is selected, the accumulated variable collects information about all particles in the selected domains or boundaries, regardless of their particle properties. Alternatively, select a particle properties feature from the list, and then only the particles associated with the selected Particle Properties node are included.

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 checkbox 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.