puff (version 0.1.0)

simulate_grid_mode: Simulate Atmospheric Concentration on a Grid

Description

Simulates methane concentrations at each grid point over time using the Gaussian puff forward model. Supports one or more emission sources. Each puff retains constant wind speed and direction throughout its lifetime, and corresponding dispersion parameters are determined at the time of emission.

Usage

simulate_grid_mode(start_time, end_time, source_coords, emission_rate, wind_data,
  grid_coords, sim_dt, puff_dt, output_dt, puff_duration, ws, wd)

Value

A matrix of concentrations (ppm) with rows representing output time steps and columns representing grid points. Columns correspond to the flattened grid defined by expand.grid(grid_coords).

Arguments

start_time

POSIXct. Start time of the simulation.

end_time

POSIXct. End time of the simulation.

source_coords

Numeric vector or matrix. Coordinates of the emission source(s) in meters (x, y, z). If simulating multiple sources, provide a matrix with one row per source. E.g., matrix(c(0, 0, 2.5, 10, 10, 2.5), ncol = 3, byrow = TRUE).

emission_rate

Numeric. Emission rate in kg/hr per source. If multiple sources are provided, this value will be assumed the same for each. (Note: source-specific rates are not yet supported.)

wind_data

Data frame. Must contain either columns `wind_u` and `wind_v` (wind vector components in x/y directions) or columns representing wind speed and direction, declared as `ws` and `wd`.

grid_coords

List. A list with three numeric vectors specifying the grid points for x, y, and z coordinates, e.g., list(x = seq(-50, 50, by = 5), y = seq(-50, 50, by = 5), z = c(2.5)).

sim_dt

Integer. Simulation time step in seconds (default = 1). Determines how frequently puff positions are updated.

puff_dt

Integer. Puff emission interval in seconds (default = 1). New puffs are emitted from each source at this frequency.

output_dt

Integer. Desired time resolution (in seconds) for final output concentrations.

puff_duration

Numeric. Maximum puff lifetime in seconds (default = 1200). Puffs beyond this age are discarded.

ws

Optional. String. Name of the column in `wind_data` containing wind speeds (m/s). Required if `wind_data` contains polar wind components instead of Cartesian (`wind_u`, `wind_v`).

wd

Optional. String. Name of the column in `wind_data` containing wind directions (degrees from).

Details

- Each source (from one to many) emits puffs at intervals of puff_dt. - Each puff maintains a fixed wind vector and dispersion parameters. - Puffs are advected over time based on their individual wind vectors. - Concentration contributions from all active puffs are computed at each grid point and summed. - Concentrations are aggregated and returned at a coarser time resolution defined by output_dt.

References

Jia, M., Fish, R., Daniels, W., Sprinkle, B. and Hammerling, D. (2024) <doi:10.26434/chemrxiv-2023-hc95q-v3>

Examples

# \donttest{
set.seed(123)

sim_dt <- 7
puff_dt <- 7
output_dt <- 60
start_time <- "2024-01-01 12:00:00"
end_time <- "2024-01-01 13:00:00"
source_coords <- c(0, 0, 2.5)
emission_rate <- 3.5
wind_data <- data.frame(
  wind_u = runif(3601, min = -3, max = 0.7),
  wind_v = runif(3601, min = -3, max = 1.5)
)

grid_coords <- list(
  x = seq(-2, 2, by = 1),
  y = seq(-2, 2, by = 1),
  z = c(2.5)
)
  out <- simulate_grid_mode(
    start_time = start_time,
    end_time = end_time,
    source_coords = source_coords,
    emission_rate = emission_rate,
    wind_data = wind_data,
    grid_coords = grid_coords,
    sim_dt = sim_dt,
    puff_dt = puff_dt,
    output_dt = output_dt,
    puff_duration = 1200
  )
# }