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Functional Specification

Functional Specification

Document Version: 1.0 | Date: October 30, 2025

This page provides an overview. View the full Functional Specification on GitHub.

Purpose

The Functional Specification describes how the CDM system implements the user requirements defined in the URS. It provides detailed specifications of the system's behavior, interfaces, and algorithms.

System Architecture

The CDM system consists of the following major components:

Component Description
Input Parser Reads and validates JSON configuration
Atmospheric Module Calculates derived atmospheric properties
Wind Profile Module Characterizes the wind velocity profile
Droplet Size Module Processes droplet size distributions
Transport Module Integrates droplet transport ODEs using CVODE
Deposition Module Calculates ground deposition profiles
Output Module Generates JSON output and console reports

Input Specification

The model accepts JSON-formatted input containing:

  • Droplet Size Distribution — Tabular diameter/cumulative volume data
  • Atmospheric Properties — Temperature, pressure, humidity
  • Wind Velocity Profile — Elevation/velocity measurement pairs
  • Application Parameters — Nozzle configuration and application rate
  • Field Geometry — Field dimensions and nozzle spacing
  • Solution Properties — Spray solution physical properties

Processing Specification

Atmospheric Property Calculations

Derived properties calculated from input conditions:

  • Wet air density (ρ_A)
  • Dynamic viscosity of wet air (μ_A)
  • Dew point temperature
  • Wet bulb temperature (iterative calculation)

Droplet Transport ODE System

The model solves a 6-component ODE system for each droplet size class:

Component Symbol Description
Vertical position Z Height above ground (m)
Horizontal position X Downwind distance (m)
Vertical velocity V_z Vertical speed (m/s)
Horizontal velocity V_x Horizontal speed (m/s)
Water mass M_w Droplet water mass (kg)
Wind velocity V_vwx Local wind speed (m/s)

Integration uses CVODE (BDF method) with specified error tolerances.

Deposition Calculation

Deposition is computed by:

  1. Integrating transport for each size class and streamline
  2. Tracking ground-level crossings
  3. Accumulating mass at downwind distance intervals
  4. Expressing results as percentage of intended application rate (%IAR)

Output Specification

JSON Output

Structured JSON containing:

  • Input echo (all configuration parameters)
  • Derived properties (atmospheric, wind profile)
  • Deposition results (distance–%IAR pairs)
  • Summary statistics (mass balance, on/off-field totals)

Console Report

Human-readable summary including:

  • Atmospheric properties
  • Wind profile characteristics
  • Integration statistics
  • Deposition summary

API Specification

See the API Reference for the complete C API documentation.

Integration Interfaces

Command-Line Interface

cdmcli <input.json> [-o output.json] [-q]
Option Description
<input.json> Path to JSON configuration file
-o output.json Write JSON results to file
-q Quiet mode (suppress console output)

R Package

The R package provides a wrapper around the C API. See Getting Started for installation instructions.