Optimization of Vehicle Structures under Uncertainties

Abstract: New emission targets, increased safety requirements and competition in the global market have led the automotive industry to focus more on developing efficient, optimised vehicle structures. Consequently, the use of simulation-based design in vehicle engineering has increased significantly in recent years. Advancements in computational power and efficient algorithms have made the simulation-based design process faster and more efficient and also made it possible to include structural optimisation. However, optimised design using classical (deterministic) optimisation techniques might not achieve the desired performance in real life due to uncertainties in input parameters such as variation in material properties, geometrical parameters, loading conditions, etc. Consequently it is necessary to consider these variations in the optimisation process in order to create a robust and reliable design. However, the incorporation of uncertainties into the design optimisation of a full-scale vehicle model tends to be computationally expensive so approximation models have often been utilised to minimise  computational effort.In this thesis, different approaches to evaluate robustness and to perform non-deterministic optimisation have been studied. Primary focus was on robust design and reliability-based optimisation methods. These methods were verified using a complex vehicle engineering application. The first part of the study involves evaluation of robustness analysis methods and a comparative study has been performed between FE-based robustness analysis and metamodel-based robustness analysis. Furthermore, different metamodelling techniques were also compared with respect to performance. An approach to handle the fracture risk factors using metamodels is also presented. In the second part of the study, an approach to perform multiobjective reliability-based optimisation and robust design optimisation is presented and verified using a vehicle side impact crashworthiness application. The importance of a non-deterministic optimisation approach as compared to a deterministic approach is illustrated by comparing the results from non-deterministic optimisation with those from deterministic optimisation. The approaches presented in the study were found to be suitable for applications related to vehicle structures.