Browsing by Author "Neades, Jon"

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    The determination of vehicle speeds from delta-V in two vehicle planar collisions
    (Institution of Mechanical Engineers, 2011) Neades, Jon; Smith, Roy
    The change of a vehicle’s velocity, delta-V (v), due to an impact is often calculated and used in the scientific investigation of road traffic collisions. In isolation however, this figure does not yield any information concerning the actual velocities of the vehicles and such information is often of prime concern to those investigating collisions. In this paper a method is developed which uses the change in velocity sustained by a vehicle in a planar collision to estimate the velocities of the vehicle before and after a collision. The key equations are derived from conservation of momentum, conservation of energy and restitution. As with the calculation of delta-V, the method requires an initial estimate of the principal directions of force. The pre and post impact angles of the vehicles’ velocities can be used to obtain better estimates of the principal directions of force and of the coefficient of restitution. In collisions where it is difficult to analyse the vehicles’ post-impact motion, this method provides a way to estimate the actual speeds of vehicles. To demonstrate the method, it is used to analyse one of the RICSAC collisions. The results of an analysis of other staged collisions illustrate the accuracy of the method
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    Equivalence of impact phase models in two vehicle planar collisions
    (Institution of Mechanical Engineers, 2013-07-03) Neades, Jon
    Determining the pre-impact velocities of vehicles are of prime importance when investigating road traffic collisions. Two types of impact-phase model are in common use to achieve this purpose, those based on the conservation of linear and angular momentum as exemplified by the models presented by Brach and Ishikawa and the CRASH model which explicitly includes the conservation of energy. A summary of the various models is provided to show how the models are related to each other together with a brief discussion of their strengths and weaknesses. Of particular significance is that although there are differences between these models it is shown that they are equivalent provided certain conditions are satisfied, namely that the crush or impact plane is orientated perpendicular to the impulse. In addition it is shown that they produce identical results from consistent input data. Explicit conversion factors between the models are provided together with a novel method to transform coefficients of restitution between various orientations of the crush plane. This facilitates comparison and movement between the models and it is shown that the choice of model utilised for an individual collision depends largely on the availability of particular data.