The calculation of train stability in tornado winds

This paper presents a novel methodology for calculating the risk of a train overturning accident due to tornadoes. It applies a recently developed model of tornado wind fields to the complex case of a moving vehicle passing at different distances from the centre of a moving tornado. The wind speed and direction relative to the vehicle can thus be calculated. Through the use of quasi-steady force coefficients and an allowance for dynamic effects, this allows aerodynamic forces and moment time histories on the vehicle to be calculated. A parametric investigation of the effects of tornado size, strength and translational speed, and vehicle speed is then presented. A stochastic analysis methodology is then set out that allows the probability of a train overturning accident to be determined for specified statistical distributions of tornado parameters and vehicle operational parameters. It is shown that the reduction of train speed at times when tornadoes are expected would lead to a very significant reduction in accident risk. Finally the requirements for further work to refine the methodology are set out - specifically the need for statistical distributions of tornado parameters and for force and moment coefficients obtained from proper physical or numerical simulations of tornado characteristics.