Development of novel approaches to design of vehicle components with reliability-based optimization techniques

In the deterministic design optimization of the engineering structures, the uncertainties of the design variables are neglected and excluded. However, elements such as geometric dimensions, material properties, external loads, tolerances in the manufacturing process, and operating conditions contain a number of uncertainties. Reliability-based design optimization (RBDO), is a methodology used to find the best balance between safety and production costs by taking into account these uncertainties of the design variables. An RBDO problem is usually solved by methods consisting of two nested loops. While the inner loop evaluates the performance function for reliability analysis, the outer loop performs the deterministic optimization by invoking the inner loop in each iteration. Reliability index approach (RIA) and performance measure approach (PMA) are the two most commonly used approaches to evaluate the performance function for reliability analysis. Many methods have been developed to evaluate probabilistic constraint functions in the reliability analyzes performed with the more effective approach PMA. However, these methods cannot reach the correct results for each problem or they may be computationally inefficient. In this thesis, three different novel methods were developed for reliability analysis with PMA, called as hybrid gradient analysis (HGA), hybrid conjugate gradient analysis (HCGA), and improved hybrid gradient analysis (EHGA). The accuracy, stability, and efficiency of these methods to obtaining optimum results, were compared with commonly used methods in the literature such as advanced mean value (AMV), conjugate mean value (CMV), hybrid mean value (HMV), chaos control (CC), modified chaos control (MCC), and conjugate gradient analysis (CGA) methods. For this purpose, the algorithms of both the developed methods and the existing methods used for comparison were created and their MATLAB codes were written. Reliability analyzes were performed by evaluating the different types of performance functions. In RBDO comparisons, some general engineering problems and design problems of vehicle structural components were discussed. The reliability analysis and RBDO results demonstrated that the developed novel methods are more efficient than the current methods and converge to the optimum result more quickly.