EFFECT OF STEADY STATE ASSUMPTION ON THE STRUCTURAL SOLVABILITY OF DYNAMIC PROCESS MODELS

Abstract

The variable structure of dynamic process models is represented by a directed graph termed the representation graph for the purpose of solvability analysis in this paper. Structural solvability analysis, the determination of the structural differential index and the structural decomposition of the DAE model set can be performed using the representation graph. It is shown that the effect of steady state assumption for a state variable x can be handled on the representation graph by modifying the assignment of the derivative variable vertex x'. The method enables us to select a suitable modification of the original specification such that the structural solvability and the differential index of index 1 process models remains unchanged. In the case of index 2 models, a steady state assumption may decrease the differential index of the modified model to 1 if the derivative variable is on the underspecified subgraph. The notions and methods are illustrated on simple process examples.