A synthesized windfield model for tornado missile transport

Abstract

A tornado windfield model has been developed for use in a probabilistic assessment of the tornado missile hazard to nuclear power plants. Tornado flow characteristics have been identified which are significant in terms of missile transport phenomena. In order to account for both modeling uncertainty and the natural variability observed among tornadoes, serveral random variables are specified in the model, including: tornado intensity, path width, translational speed, radius to maximum tangential velocity, ratic of radial-to-tangential wind speeds, vertical variation of core size, and boundary layer thickness. Considering the lack of agreement regarding detailed tornado dynamics as well as the difficulty in establishing a priori conservative flow characteristics for missile transport, the windfield model was synthesized from theoretical, observational, and probabilistic considerations. A significant aspect of the model is that the parameters can be adjusted to make the intensity, size and velocity variables consistent with the tornado path width boundary specification. The modelling considerations are discussed, the windfield model and calculational procedure presented, sample windfield component velocity profiles illustrated, and missile velocity statistics given for a simulation case study involving several thousand missile histories.