Simulation of windborne debris trajectories
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Windborne debris is possibly the major cause of building damage and destruction in strong wind events such as hurricanes and tornadoes. It has been long recognized that fast-flying debris can penetrate building envelopes, inducing internal pressurization and doubling the net loading on roofs, side walls, and leeward walls. Consequently, failed roofing structures, damaged wall cladding panels, and broken glass become debris sources, threatening downwind areas. Knowledge of debris aerodynamics is necessary for proper estimation of debris trajectory and for establishment of rational debris impact criteria. This research aims to investigate the aerodynamics of flying debris through simulating debris trajectories. Extensive wind-tunnel tests on 3D (compact-like), 2D (plate-like), and 1D (rod-like) debris are carried out in the Texas Tech University wind tunnel. The simulation procedure is introduced. Full-scale simulation is explored, employing a C-130 Hercules aircraft to generate strong winds. Three categories of parameters affecting debris trajectories are investigated: wind field, debris properties, and debris initial support. It is determined that although many parameters influence debris trajectory in the vertical direction, the Tachikawa parameter (1983) governs the horizontal trajectory of debris. Aerodynamic functions for debris horizontal trajectory are established based on both experimental data and theoretical equations of debris motion. These functions can be used to predict debris horizontal speed (at a given flight distance) and flight distance (for a given flight time). The application of these functions in debris impact criteria is discussed. The incorporation of these functions into debris risk analysis is recommended for the further research.