Accumulator (Domain)
Use the Accumulator node to define additional degrees of freedom on a domain. Each Accumulator defines a variable, called the accumulated variable, on each domain element in the set of selected domains. The values of the accumulated variables are determined by the properties of particles in each domain element.
Accumulator Settings
Select an option from the Accumulator type list: Density (default) or Count.
•
For Density the accumulated variable is divided by the volume of the mesh element where it is defined.
•
For Count the accumulated variable is unaffected by the element size.
Select an option from the Accumulate over list: Elements (default) or Elements and time.
•
For Elements the value of the accumulated variable in an element is the sum of the source terms of all particles in that element. If the Accumulator type is set to Density, this sum is divided by the mesh element volume. At a later time, a particle has no effect on the value of the accumulated variable in an element it passed through previously.
•
For Elements and time the time derivative of the accumulated variable in an element is the sum of the source terms of all particles in that element. If the Accumulator type is set to Density, this sum is divided by the mesh element volume. As each particle moves through a series of mesh elements, it leaves behind a contribution to the accumulated variable that remains even after the particle has moved on.
Enter the Accumulated variable name. The default name is rpd. The accumulated variable is defined as <name>.<varname>, where <name> is the physics interface name and <varname> is the accumulated variable name. For example, in an instance of the Mathematical Particle Tracing interface with default name pt and default accumulated variable name rpd, the variable would be named pt.rpd.
Enter a Source R. The unit of the source depends on the settings in the Units section. The source term is used to calculate the accumulated variable in a manner specified by the Accumulate over and Accumulator type settings.
If Elements and time is selected from the Accumulate over list, select an option from the Source interpolation list: Constant, Linear (the default), Quadratic, or Exponential. The Source interpolation determines what functional form the Source is assumed to follow during each time step taken by the solver. This information is used to compute the accumulated variable in mesh elements that the particles pass through during each time step.
Units
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.
Accumulator Theory: Domains