Aspen Touch Solutions ATM-123R Series Especificações descarregar pdf (Página 139)

Extensibility 3-55

3-55

condition occurs. When this happens, the Solver stops and

switches in to Hold Mode. To allow different objects to calculate

different values because of changes in the flowsheet, it is

necessary that values that depend on another changing value be

forgotten. This forgetting occurs during the Forget Pass.

Forget Pass

When the value of a variable changes, the Solver first does one

Solve Pass on the flowsheet with the value marked as unknown.

Each object that is linked to the object with the changed variable

has its Execute method called, and the object must perform as

many calculations as it can with the remaining known

information.

Any calculations that were performed based on the value of the

newly forgotten variable in the last pass are not able to be

calculated during this pass. After the object has finished its

Execute call, the Solver then determines which variables the

object calculated last time that have not been touched this time.

These variables are then marked as unknown, and the Solver

propagates this information to other linked objects in the

flowsheet.

Normally, an object need not behave any differently during the

Forget Pass than during the Calculate Pass. In order to prevent

unnecessary propagation of forgotten information (and

therefore the unnecessary recalculation of this information in

the Calculate Pass), the object must still calculate all that it can

to ensure that the variables it calculated last time are touched.

Calculate Pass

After all information based on the previous value of a variable

has been forgotten, the new value is set in to the variable and

the second Solver pass (the Calculate Pass) is started. In this

pass, each object affected by the change in the variable has its

Execute method called. Any changes these objects make are

propagated through the flowsheet as the variables in other

objects are touched.

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Aspen Touch Solutions ATM-123R Series Especificações Página 139