Aspen Touch Solutions ATM-123R Series Especificações Página 368

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A-32 Extensibility FAQ
A-32
A problem arises when the unit operation uses a “Balance”
call to calculate the compositions and flow of its streams.
The “Balance” performs all the logic to detect which values
are specified and which need to be calculated, combines
multiple feeds to produce a single product, etc., all without
the unit operation needing to be aware of the calculations.
Unfortunately, the results of these calculations will be
unavailable to the unit operation until after the streams have
had their Executes. If the unit operation wants to display,
e.g., the flow of a key component in each of its attached
streams, these values will be unavailable. However, the unit
operation will receive a third Execute, after the streams have
had theirs, during which the values “Balance” had calculated
will be available. Proper use of the third Execute for this
purpose is tricky, as the unit operation must avoid repeating
the work of the previous Execute.
Relatively few unit operations require the third Execute call.
If a unit operation can perform all of its calculations in the
first Execute, it should call “SolveComplete”, which will
prevent the third Execute call from being made by HYSYS.
21. Why is my Unit Operation’s PFD icon yellow?
Ans: HYSYS will outline a unit operation in yellow if it cannot
complete its calculations. Usually, the unit operation uses its
StatusQuery method to provide the user with a specific
reason why the solve can not be completed, but the “Not
Solved” warning is provided by default.
To prevent this warning from being added, the unit operation
must call “SolveComplete” when it has satisfactorily
completed its calculations. This unit operation’s Execute is
responsible for determining whether it has calculated all of
the variables it wants to calculate.
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