UCLA

Simulation-based design and design-by-analysis methods are important tools in the development of modern complex systems due to their impact on attaining shorter manufacturing and construction cycles and lower testing cost. The research in this thesis is devoted to the development of a multiphysics-multiscale FEM framework to provide precise analysis of complex energy conversion structural components with relatively high computational efficiency. The main focus is on applications where the incident heat flux on component surfaces is extreme. This motivation leads to four major contributions. Firstly, various widely-used multiphysics simulation strategies and algorithms are assessed, and recommendations on how to select a suitable multiphysics modeling strategy are made. Fully-coupled 3D CFD and heat transfer simulations are found to be necessary in forced-convection cooling in channels under single-sided heat load. Secondly, two multiscale methods for coupling heterogeneous constitutive models in coupled global-local domains are proposed for self-consistent structural analysis. The first is based on the Hu-Washizu variational principle that leads to accurate matching of all stress components across a global-local interface. This matching cannot be achieved by conventional sub-modeling methods. The second method couples the crystal plasticity framework with conventional continuum plasticity by matching the plastic slip at the coupling interface. These two methods have been shown to be accurate and numerically convergent. The superiority of the proposed approaches is demonstrated by comparison to three conventional sub-modeling methods from the literature. Thirdly, an advanced dislocation-based crystal plasticity model has been developed. The model is sensitive to the material microstructure, and can be readily incorporated into the multiscale framework. The model is validated by micro-indentation experiments, where the force-displacement curve, lattice rotations, and dislocation patterns obtained from experiment are quantitatively reproduced. The developed comprehensive multiphysics-multiscale modeling framework has been successfully implemented in the design of three real-life critical components for energy conversion in fusion energy power plants, demonstrating the practical feasibility of the framework.