MASS OPTIMIZED HOOD DESIGN FOR CONFLICTING PERFORMANCES
To be published on November 21, 2019 by SAE International in United States
Event: NuGen Summit
MASS OPTIMIZED HOOD DESIGN FOR CONFLICTING PERFORMANCES Santosh Swamy, Gulshan Noorsumar, Shivakumar Chidanandappa General Motors Technical Center, India Keywords Hood; Head Injury Criterion (HIC); Stiffness; Shape optimization; Multi-Disciplinary Optimization (MDO) Research and/or Engineering Questions/ Objective The objective of this work is to obtain a light weight hood which has least possible mass, and at the same time meets all contradicting performances of pedpro (pedestrian protection) and structural stiffness disciplines. Passenger vehicles have stringent safety norms from pedpro perspective to meet child and adult head injury criteria (HIC). These pedestrian safety requirements often conflict with structural stiffness performance criteria which pose a challenge for most automotive OEMs. Therefore, there is a growing need for mass optimization and performance balancing to meet both the requirements simultaneously. Methodology The outlined method uses a CAE based Multi-Disciplinary Optimization (MDO) approach involving shape variables to find an optimum design for stiffness and pedpro performances. Adding slots along the vertical beam walls of the hood inner panel helps soften the area around the head impact location, thereby improving pedpro performance locally. But in doing so, they also render the hood structurally weak and lead to reduced performance of stiffness requirements. As the requirements here are contradictory in nature, any attempt to independently resolve the performance for one discipline would deteriorate the performance of the other. Therefore it becomes imperative to address both disciplines simultaneously, thereby emphasizing the need for an MDO approach. Results Using this approach, a set of designs were found that were meeting the requirements of both pedpro and stiffness disciplines. The slots were found to be the most sensitive design variables for the current problem of interest. The unique shape morphing strategy employed on the CAE models ensured that these designs were feasible from both manufacturing and as well as packaging point of view. A GM in-house developed MDO tool was used for conducting shape optimization. Limitations of this Study The study was carried out for just a few handpicked locations in the front end of the hood where there was a HIC concern. This work provided a proof of concept as the intent here was mostly to develop a methodology for a holistic design. In future this approach can be scaled to account for all possible stiffness requirements along with all pedpro impact points. Although the current approach was found to be successful for problems involving shapes and thicknesses, it cannot be used for designing a clean sheet topology. What does the paper offer that is new in the field including in comparison to other work by the authors? The paper demonstrates successful application of shape optimization to design hood system using MDO approach. Treating slots as variables which are feasible to manufacture by using a unique morphing approach which can accommodate slots edges that have degrees of freedom to both expand as well as shrink in size independently. Additionally it gives provision for relative motion of the center of slot, thereby providing directions for an optimum slot location. This study also involves reduced content models which would reduce the computational time without compromising on the accuracy of results. Conclusions This new approach helps in meeting requirements of both pedpro and stiffness performances with least possible mass and thus reinforces the importance of shape optimization for such problems. It also results in reduced number of back and forth iterations between the stakeholders from structural stiffness and pedpro disciplines, thereby reducing the overall product development cycle turnaround time.