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As the speeds of both passenger and freight trains increase, there is increasing concern that the unsteady gusts generated in train boundary layers and wakes will become more of for a risk to passengers waiting on platforms and for trackside workers. In addition, the demands of interoperability make this a problem of growing relevance to railway operators across Europe. A number of model scale and full-scale experiments have been carried out in recent years that have provided robust experimental data to quantify these flows. This paper considers all the available datasets for high-speed passenger trains and container freight trains, and in making a comparison between them, arrives at a number of conclusions concerning the characteristics of train slipstreams. It is concluded that the identification of a number of distinct flow regions in earlier work is generally valid and forms a useful framework for the consideration of the problem. The flow characteristics are different in each region, and, depending upon the train type, the measurement distance from the train and height above ground, the observed peak gusts for a train may occur at any time during the train passage or in its wake. It is also concluded that results obtained from measurements around small scale moving models are in good agreement with the full scale measurements and reproduce all the important flow features.

The lodging of cereal crops due to high wind and rain is of considerable significance in many parts of the world, leading to major economic losses and yield reductions. In earlier papers the authors have developed a model of the lodging of winter wheat that identified the major parameters of the problem and enabled the relationship between root and stem lodging to be examined. It has formed the basis of a methodology used in the UK for guidance to farmers and agronomists on ways of reducing lodging risk. However the authors would be the first to acknowledge that there are limitations to the model that make it difficult to apply for a wide range of crops--particularly in the specification of the wind field and the root/soil interaction, and in allowing for stem lodging elsewhere than at the base of the stem. This paper thus describes the development of a generalised model that overcomes these shortcomings. After a discussion of the lodging phenomenon in general and a description of the earlier work, the basis of the new model is set out, based upon a mechanical model of the wind/plant/soil interactions that capture most of the important physical processes. The manner in which this model can be applied to clarify the nature of the lodging process and calculate lodging risk through a simple graphical formulation is discussed. In particular simple formulae are defined for lodging risk that are functions of a small number of dimensionless variables with identified physical meanings. The model is then applied to the lodging of wheat, oat and oilseed rape crops and considers the sensitivity of the risk calculations to uncertainties in the model parameters. In general it is suggested that the risk of lodging can be determined from very simple functions of dimensionless stem and root lodging velocities.

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