EVU XXV 2016 – 02 Impulse-Momentum Analysis of Multibody Vehicle-Pedestrian Collision Simulations
Impulse-Momentum Analysis of Multibody
Vehicle-Pedestrian Collision Simulations
Raymond M. Brach
University of Notre Dame, USA
For purposes of vehicle-pedestrian crash simulation, vehicle speed, vehicle-pedestrian interaction and
pedestrian motion are currently related using one of three model types. These are models that relate
vehicle speed to: I) throw distance alone (through experimental data and/or mechanics), II) to throw
distance and vehicle and roadway parameters such as launch angle, pedestrian-ground drag coefficient
and travel distance, vehicle frontal geometry, etc. and III) the use of pedestrian multibody models and
vehicle finite element structural parameters. Type I models are simple to use but lack specificity and
ability to estimate simulation uncertainty. Multibody simulation models, Type III, are relatively complex, time consuming to carry out but are necessary and appropriate for use with vehicle design and for studying pedestrian safety and injury analysis and mitigation.
This paper presents a comparison of results from a Type II model to results from a multibody, Type III
model. The enhanced Han-Brach pedestrian throw model is a Type II model. It uses point-mass impact
mechanics to model the vehicle-pedestrian contact phase through the use of impact parameters, namely
the coefficient of restitution and impulse ratio (effective friction coefficient). Frontal vehicle geometry
such as the vehicle’s hood/bonnet slope and leading edge height is taken into account. Through the
use of least-square methods, the Han-Brach model is used to determine the impact parameters corresponding to the Type III MADYMO model simulations published in the 2012 IRCOBI proceedings by Hamacher, et al. These parameters provide an indication of how each MADYMO simulation satisfies
Newton’s laws in the form of impulse and momentum.
This is the first time Type II model results have been compared to Type III model output and the first time energy accountability of Type III simulations has been assessed. Using point mass impact equations and the proper values of impact parameters it is shown that the Han-Brach Type II model is capable of producing kinematic results identical or very close to MADYMO simulations. Comparable results include the pedestrian launch angle, launch speed and throw distance. The main finding from comparisons of simulations with impact equation solutions, is that the MADYMO simulations tend to display the counterintuitive trend that as vehicle speeds increase, the collisions become more elastic and display lower friction. That is, as vehicle speed increases, the percentage of kinetic energy lost during the vehicle-pedestrian contact phase decreases. Such trends are opposite to what is found in the literature for mechanical impacts.
La lettura di questo articolo è riservata ai soli Soci EVU Italia
|Raymond M. Brach University of Notre Dame, USA