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Figure 4.4
Specifying tear streams.
has an unconverged trial solution, each variable is in turn perturbed by a small amount;
thus,
n
t
(
2
n
+
1
)
passes through the flowsheet are made. Convergence is quadratic.
The Broyden (1965) method is a variant of Newton's which estimates the values of
the partial derivatives from the current values and may require fewer passes through
the flowsheet. Convergence is linear.
4.2 HEURISTICS
1. Prior to attacking a material and energy balance problem, attempt a solution with
simple blocks without energy balances.
2. Solve easy variations of a problem prior to attempting the actual problem (i.e.,
do not use tight specifications).
3. If errors are found in the solution and corrected, for the next run be sure to
reinitialize the flowsheet; otherwise, Aspen Plus will continue the solution using
the current, incorrect, values when it executes, which may prevent convergence.
4. For a large flowsheet or one with a complex configuration in which the tear
streams are dependent on each other:
a. If it fails to converge try solving with Aspen Plus's defaults.
b. Break the flowsheet into smaller segments and converge them separately prior
to integrating them into the complete configuration.
