An analytical downburst model and its application to a moving train wind loading

For the first time, a simple analytical model of a downburst has been developed which correctly reproduces the shape of the radial velocity close to the ground, i.e., in a region applicable to trains and low-rise buildings. The proposed model satisfies the continuum and Euler momentum equations, has been used to obtain an expression for the pressure field and also includes an intensity decay function to represent the time varying life cycle of a downburst. The model is used to obtain an insight into the wind-induced forces on a train arising from a downburst. A novel outcome of this research is the finding that, whilst higher train speeds increase the risk of train overturning, taking dynamic effects arising from the flow acceleration related to the train movement into consideration reduces the values of train overturning moments. A parametric study is performed to examine the influence of train speed, downburst translation velocity and relative distance and angle between the train and downburst paths on the resulting overturning moment coefficients. This methodology has been included in a stochastic analysis for specified distributions of downburst parameters and operational train data to undertake a risk analysis. The research shows that the reduction of train speed has a very significant effect on decreasing accident risk.