SIMPLE PROCESS EQUATIONS, FIXED-POINT METHODS, AND CHAOS

The chaotic behavior of fixed‐point methods for steady‐state process simulation is studied. It is shown that direct substitution and Newton's method exhibit all of the rich structure of chaos (period doubling, aperiodicity, fractal basin boundaries, and related properties) on simple process examples. These examples include finding roots to the Soave‐Redlich‐Kwong and Underwood equations, dew point and flash calculations for heterogeneous mixtures, and a simple process flowsheet. For single variable problems, it is shown that direct substitution follows a classical period‐doubling route to chaos. On the other hand, the chaotic behavior of direct substitution and Newton's method on multivariable problems is considerably more complex, and can give the appearance that no organized route to chaos is followed. For example, for the dew point problems, truncated period doubling, odd periodic cycles, and chaotic behavior can be observed, within which are embedded narrow regions of global convergence. Many numerical results and geometric illustrations are presented. Copyright © 1990 American Institute of Chemical Engineers