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FORD : iSIGHT Each year, car manufacturers spend millions of dollars to improve vehicle crashworthiness. The use of computer simulation to predict the performance of alternate vehicle designs in a crash scenario has revolutionized the field of automotive design. Simulation helps engineers improve vehicle crashworthiness by allowing them to evaluate alternative design scenarios more quickly and at a lower-cost than full vehicle crash tests that cost nearly $250,000 per crash. While traditionally, crash simulation was initiated as a design verification step at the end of a structural design cycle, nonlinear dynamic crash and safety simulation packages are now increasingly applied by the automotive industry during the early design phases of the car body structure and occupant restraint systems. In an effort to reduce crash test costs and improve vehicle safety, engineers at the Ford Motor Company (Dearborn, MI) are using iSIGHT design optimization and automation software from Engineous Software, Inc. (Morrisville, NC). Like many OEMs, Ford knows that instead of building and testing expensive prototypes, carmakers are increasingly relying on computer-based crash simulation to provide an alternate, cost-effective method of obtaining feedback on the performance of a proposed design. Bumper bashing For one of its initial crash simulations, Ford engineers selected a front rail attached to a bumper. The bumper was modeled using a commercial FEA package that is part of Ford's product development suite of tools. The goal of the optimization was to maximize the energy absorbency of the rail without increasing its weight. Energy absorbency is a critical property in the front rail because the more energy the rail absorbs, the less absorbed by the passengers of the vehicle. Seven design variables, five thicknesses and two yield stresses for mild steel and high strength steel, were selected as the design parameters to be controlled by the optimization. This rather limited assortment of variables was selected because of the large amount of time needed to run each crash simulation iteration. In the future, Ford engineers plan to greatly increase the scope of the problem by allowing the optimization software to control the shape of the component design by using iSIGHT. "This software package offers a wide range of optimization algorithms and approximation methods as well as DOE techniques that would be time prohibitive to try and match in our own internal code," said Dr. Ren-Jye Yang, Sr. Staff Technical Specialist for Ford. Yang interfaced iSIGHT and the FEA software and was able to identify critical output parameters such as finite element mesh volume, which correlates to weight, and energy absorbency. Yang used iSIGHT's design of experiment techniques to reduce the number of design points that needed to be computed in order to determine an optimum value. A single factorial experiment was performed for the seven design variables. DOE provides a mechanism for determining a near-optimum value from a discrete set of allowable values while studying far less than all combinations of these values. Other calculations were used to identify the main factors and interdependencies of the experiments and to select an initial design. A filtering scheme was used to rank the DOE design data points for the optimization problem. After five design iterations, total internal energy was increased by 3.5% without any increase in mass. If the design problem is to increase the total internal energy by 20%, the rail mass must increase by 13%. "This example demonstrates the enormous potential of design optimization for improving the crash performance of passenger vehicles," Yang said. "Additional studies will consider other crash modes such as rear impact, side impact, and head impact and will also consider system aspects that are required to achieve robustness for crash optimization." For more information, please contact Engineous Software, 1800 Perimeter Park West, Suite 275, Morrisville, NC, 27560. Phone: 919-319-7666 Internet: www.engineous.com. Editor: Laura Carrabine |