Development of Modelica-based one-dimensional thermodynamic cycle library and its application in simulation and multi-objective optimization of a He-Xe closed-Brayton-cycle system

System-level modeling offers a comprehensive perspective for understanding and analyzing the behaviors of complex systems, facilitating improved design and optimization. In this study, a one-dimensional thermodynamic cycle (ODTC) library was developed using the Modelica language, covering basic equipment components in the cycle, working fluids, and examples of energy system models. The library was then used to implement system-level simulation and multi-objective optimization of a helium-xenon (He-Xe) closed-Brayton-cycle (CBC) system. The simulation verification of the CBC system with He-Xe properties and the study of the system performance with key parameters were completed from the perspective of steady-state design. The results demonstrated that the ODTC library developed in this study is well suited for analyzing the He-Xe CBC system. Additionally, based on the coupling of Python and OpenModelica, the NSGA-II algorithm was used to optimize the established system model based on multiple objectives and obtain the optimal solution set for the system design. This study fully used the advantages of the Modelica language to model a multi-domain coupled visualization system and applied algorithms in Python to improve the design process. The ODTC library presented in this work serves as a valuable reference for future research on power system design and optimization based on the Modelica framework.