R/get_lac_factor.R

In HiDef-Aerial-Surveying/stochLAB: Stochastic Collision Risk Model

#' Large array correction factor
#'
#' A correction factor for large windfarms with a large array of turbines, to
#' take into account the depletion of bird density in later rows of the site.
#'
#' @param n_turbines Integer, the number of turbines on the wind farm
#'   (\eqn{T}).
#' @param rotor_radius Numeric value, the radius of the rotor (\eqn{R}), in
#'   metres.
#' @param avoidance_rate Numeric value within the interval \eqn{[0, 1]}. The species
#'   avoidance rate, expressing the probability that a bird flying on a
#'   collision course with a turbine will take evading action to avoid
#'   collision. (\eqn{A}).
#' @param avg_prob_coll Numeric value, the average probability of collision
#'   for a single bird transit through a rotor, assuming no avoidance action
#'   (\eqn{p_average}).
#' @param avg_prop_operational Numeric value, the average proportion of time
#'   turbines are operational through the year.
#' @param wf_width Numeric value, the approximate longitudinal width of the
#'   wind farm, in kilometres (\eqn{w}).
#'
#' @return The large array correction factor to be applied
#'
#' @examples
#'   get_lac_factor(
#'      n_turbines = 100,
#'      rotor_radius = 120,
#'      avoidance_rate = 0.989,
#'      avg_prob_coll = 0.1494609,
#'      avg_prop_operational = 0.6388292,
#'      wf_width = 52
#'      )
#'
#' @export
get_lac_factor <- function(n_turbines,
                           rotor_radius,
                           avoidance_rate,
                           avg_prob_coll,
                           avg_prop_operational,
                           wf_width){

  NTurbRows <- n_turbines^0.5

  if(NTurbRows == 0){stop("Error: There are no turbines in your WFArea, please check your input data")}


  # the collision risk for a single bird due to any one turbine (i.e. disregarding risks by other turbines)
  CollRiskSinglePassage <- n_turbines * (pi * rotor_radius^2)/(2 * rotor_radius * wf_width * 1000) *
    avg_prob_coll * avg_prop_operational * (1-avoidance_rate)

  L_ArrayCF <- 1 - (NTurbRows - 1) / (2*NTurbRows) * CollRiskSinglePassage +
    (NTurbRows - 1) * (NTurbRows - 2)/(6 * NTurbRows^2) * (CollRiskSinglePassage ^2)


  # BC --> OK!! Found an error in Masden's code. The 2 terms after the '+' sign should
  # be (n-1)*(n-2), *NOT* (n-1)*(2n). Causes a negligible difference (order of 1e-6),
  # but enough to fail the consistency test with Band's spreadsheet
  # L_ArrayCF = 1 - (NTurbRows - 1) / (2*NTurbRows) * CollRiskSinglePassage +
  #   (NTurbRows - 1) * (2*NTurbRows)/(6 * NTurbRows^2) * (CollRiskSinglePassage ^2)

  return(L_ArrayCF)
}