Application of lumped RthCth and approximate steady-state methods for reducing transient analysis solution time

Three-dimensional, transient computational fluid-dynamic (CFD) models require finite-volume grids in the spatial as well as temporal domain. The grid can become extremely large, even for component-level problems. This initially results in long computation times during grid optimization, even with high-speed and parallel processing computers. It also results in extremely long computation times once the grid has been optimized. Solution times are further increased when the transient load is cyclic in nature. To reduce computation time, lumped resistance-capacitance (R_thC_th) methods developed by Larson and Li [2000] were benchmarked at the component level, then the system level. Next, the use of root-mean-squared current (I.) as a steady-state approximation was benchmarked at both the component and system level. Finally, both methods were applied to streamline the analysis of automotive electronic controls. Limitations of both the R_thC_th and steady-state methods are discussed. Cycle time reduction values for both component and system level are presented.