Improved NSGA-II and its application in BIW structure optimization

Based on the crowding distance algorithm of Non-Dominated Sorting Genetic Algorithm-II (NSGA-II), three improved algorithms are proposed: side length optimization strategy, diagonal optimization strategy, center optimization strategy. Zero-Ductility Transition (ZDT) series functions and Diode-Transistor Logic with Zener diode (DTLZ) series functions are used to calculate and compare the convergence and diversity of three improved algorithms and NSGA-II. The center optimization strategy based NSGA-II is confirmed to be the optimal algorithm. The body-in-white (BIW) optimization functions are established and optimized by center optimization strategy based NSGA-II, and the most appropriate BIW structure is calculated and verified by mode tests. The result shows: after the optimization, the BIW total mass increment is less than 3%, the first torsional mode frequency increment is more than 15%, and the torsion stiffness increment is more than 10%.