Heuristic Process Model Simplification in Frequency Response Domain

Frequency response diagrams of a system include detailed and recognizable information about the structural and parameter effects of the transfer function model of the system. The information are qualitatively and quantitatively obtainable from simultaneous consideration of amplitude ratio and phase information. In this paper, some rules and relationships are presented for making use of frequency response information in order to identify the structure of rational and irrational models in a heuristic manner. Estimation of the values of the parameters are also accomplished in a graphical trial and error procedure. As an example, the heuristic method was applied for identifying the simplified model of a rotary cement kiln from the frequency response information of the analytically derived model of the system. The analytical model of the kiln, used in this paper, was obtained elsewere in a detailed procedure with some assumptions and by using initial and boundary conditions. Results obtained from identification of the simplified model for rotary cement kiln not only reveal the application of the heuristic method for model identification, but also demonstrate the appearance of unstable poles and zeros in the model of the system.