Particle Screen¶

Particle Screen statistics are written to tab-separated ASCII .txt files that record time-evolving raw and reduced quantities associated with particle–screen intersection events. This output reduces the spatially resolved particle screen VTK visualization outputs to a simple set of descriptive statistics A unique output file is created for each screen, which reduces data from all particle families. The name of each output file is ParticleScreen{Axis}_{Intercept}.txt, where Axis and Intercept correspond to the Axis Direction and Intercept Value.

The data is written as a time series, where each row corresponds to a simulation time and each column corresponds to a statistic listed in the table below. Each row in the output file corresponds to a new statistics output time and is appended at the Statistics Output Write Interval.

Statistics Table¶

Statistics	Units	Details
Time	s	simulation time
Count	Dimensionless	number of particles not including number scale
Density COV	Dimensionless	spatial COV of particle density not including number scale
Density Mean	number/mm^2	spatial mean of particle density not including number scale
Density Std Dev	number/mm^2	spatial standard deviation of particle density not including number scale

Usage and Interpretation¶

The Particle Screen output is used to quantify how particles are distributed when they intersect a user-defined screen inside the simulation domain. Conceptually, the screen is treated as a two-dimensional sampling plane that is discretized into voxels consistent with the underlying simulation resolution. Each time a particle crosses the screen, its intersection contributes to a local landing-point density field defined on this plane. Rather than operating directly on the individual particle intersection events, all reported statistics are evaluated from this voxelized landing-point density field defined on the Output Plane (slice data). This field representation serves as the basis for all subsequent analysis.

If the screen is divided into \(N\) voxels with local landing densities \(ρ_i\), then the mean landing density across the screen is

\[\rho = \frac{1}{N} \sum_{i=1}^{N} \rho_i.\]

The spatial standard deviation of the landing density is

\[\sigma_{\rho} = \sqrt{\frac{1}{N} \sum_{i=1}^{N} (\rho_i - \rho)^2},\]

and the coefficient of variation is

\[\mathrm{COV}_{\rho} = \frac{\sigma_{\rho}}{\rho}.\]

A low density COV indicates that particle landings are distributed relatively uniformly across the screen, while a high density COV indicates a more heterogeneous distribution with localized clustering or channeling.