Steven Hoffenson

A multi-objective optimization framework for assessing military ground vehicle design for safety

In recent years, the greatest safety threat to military personnel has been from underbody vehicle blast events, but other major threats exist against fuel convoys and due to rollover events. Ground vehicle designers make choices that affect one or more of these risk areas, including the weight and structural design of the vehicle underbody, as well as the design of seating systems that cushion the occupants from the rapid accelerations caused by blast loading. This study uses mathematical and computational tools to evaluate underbody blast, fuel convoy, and rollover safety criteria, and the models are combined into a multi-objective design optimization formulation that minimizes personnel casualties. The models and framework are highlighted and described in detail, and preliminary optimization results are presented under various conditions. The multi-objective behavior of the design problem is explored through weighted-objective Pareto frontiers, and the utility of the model in real-world situations is discussed.

A market systems analysis of the U.S. sport utility vehicle market considering frontal crash safety technology and policy

Active safety features and adjustments to the New Car Assessment Program (NCAP) consumer-information crash tests have the potential to decrease the number of serious traffic injuries each year, according to previous studies. However, literature suggests that risk reductions, particularly in the automotive market, are often accompanied by adjusted consumer risk tolerance, and so these potential safety benefits may not be fully realized due to changes in consumer purchasing or driving behavior. This article approaches safety in the new vehicle market, particularly in the Sport Utility Vehicle and Crossover Utility Vehicle segments, from a market systems perspective. Crash statistics and simulations are used to predict the effects of design and policy changes on occupant crash safety, and discrete choice experiments are conducted to estimate the values consumers place on vehicle attributes. These models are combined in a market simulation that forecasts how consumers respond to the available vehicle alternatives, resulting in predictions of the market share of each vehicle and how the change in fleet mixture influences societal outcomes including injuries, fuel consumption, and firm profits. The model is tested for a scenario where active safety features are implemented across the new vehicle fleet and a scenario where the U.S. frontal NCAP test speed is modified. While results exhibit evidence of consumer risk adjustment, they support adding active safety features and lowering the NCAP frontal test speed, as these changes are predicted to improve the welfare of both firms and society.

On the impact of the regulatory frontal crash test speed on optimal vehicle design and road traffic injuries

Many countries have instituted New Car Assessment Programs (NCAPs) to help consumers compare the crashworthiness of automobiles on the market. These typically involve four or fi ve standardised tests, for which each new vehicle is rated on a 5-star scale. The ratings are available to customers and so, automakers strive for high scores by optimising their vehicle designs to the scenarios represented by the tests. The United States NCAP rates vehicles for frontal crashworthiness with a 56-kilometreper- hour (35-mile-per-hour) full-engagement barrier collision, which is a relatively severe test, considering that over 98% of crashes on US roadways occur at slower speeds. This paper presents a methodology for understanding the impact of the NCAP crash test speed on vehicle design and the consequent on-road safety outcomes, using physics-based simulations and optimisation tools. The results suggest that lowering the test speed from the current level to 48 kilometres per hour (30 miles per hour) may decrease the rates of serious injuries to vehicle occupants in the US by up to 21%.

Quantification of the design relationship between ground vehicle weight and occupant safety under blast loading

Military ground vehicle design must consider the threat posed by underbody blasts to new vehicles and their occupants, while also accounting for weight reduction goals for improving fuel economy and mobility. A two-stage process is presented to model the blast event, using LS-DYNA for simulating vehicle response and MADYMO for the occupants response. Issues including computational expense, objective function formulation and multi-objective seating system design optimisation are addressed in detail, and three different blastworthiness optimisation formulations are presented and evaluated.