A computer package MEDIEM (Multi-Energy Domain Interactive Element Modelling) has been developed and mounted on a minicomputer for the purpose of interactive modelling of multi-energy domain engineering systems. The basis of the package is a graphical language called “structure graphs” which allows the user to model the “structure” or essential features of a lumped parameter engineering system in close correspondence to a schematic. It is shown that structure graphs arise naturally when modelling is considered within an interactive computer-aided environment. The approach has certain advantages over those based on current techniques such as bond graphs, linear graphs, and signal flow graphs; the main ones being the ease of model construction and the ease of effecting model changes (both structural and parameter changes). The package will handle both linear and nonlinear systems. Some illustrative examples of the use of structure graphs are provided together with a detailed example of the use of MEDIEM for modelling a complex differential pressure transducer. Lastly some special causal problems reported in the bond graph literature are examined and shown not to exist when MEDIEM is used.

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