On the stochastic nature of compact debris flight

The stochastic nature of debris flight is investigated through a series of Monte Carlo simulations based on the debris flight equations for compact debris presented by Holmes (2004). Any given debris flight situation presents a number of uncertainties such as the size of the piece of debris and the time-varying turbulent wind flow. Current debris flight models are largely deterministic and do not account for such uncertainty in input parameters. The simulations presented model the flight of a single spherical particle whose diameter is given by a probability distribution function, driven by a turbulent wind with velocity fluctuations appropriate to the atmospheric boundary layer. The model predicts the mean and standard deviation of the particle flight distance and impact kinetic energy. Results show that introducing uncertainty in particle diameter, horizontal turbulence intensity, or vertical turbulence intensity leads to larger mean values for flight distance and impact kinetic energy, compared to the condition where there is no variability in input parameters. Introducing input parameter variability also leads to variability in flight distance and impact kinetic energy that is quantified in this study. While the simulations presented do not realistically characterize the complex flow within an urban canopy, the results provide significant physical insight into the influence of particle size variability and turbulence on the mean and standard deviation of the flight distance and impact kinetic energy.

► Ignoring turbulence and particle size variability underestimates the mean flight.
► Turbulence has a greater impact on flight distance than impact kinetic energy.
► Vertical and horizontal turbulence correlation has no impact on mean outcome.
► Limited analytical approximations accounting for parameter uncertainty are given.