Abstract
Two kinds of modeling approaches, namely the functional model and the bond graph, are introduced and compared each other. Both of them can explain flow and transform of energy among different physical fields, for example mechanic, electric, fluidic and thermal areas, by the common method over engineering disciplines. Functional model proposed by the authors is used as the core approach of virtual testing system for product development of machines. First, outlines of functional model and bond graph are introduced. Second, single degree of freedom mechanical and electrical systems are modeled by these two approaches as simple examples. Third, difference points between these two approaches are stated.
