IV.A Free Targets

DELTAE reserves a place for a special input parameter to hold a target value in the segment types that have outputs commonly used in targets; these parameters are: heat exchanger temperatures and heat flows and complex impedances in HARD- and SOFTEnd segments (UNIONs, introduced in the next section, are a special case). The code knows, internally, to pair these input values with the appropriate output results of the segment for comparison. The experienced user, however, will soon hunger for more possibilities once a model is defined and converging to meet the basic targets. An application may call for work, pressure, or velocity (magnitude or phase) to be specified at a certain point, or some derived function of outputs may be desired for targeting or plotting. Free targets were introduced for these purposes. We can also use them to generate a new type of output based on other outputs in the model; in this case, the first `target' parameter is simply ignored. All free targets have one real input and one real output which DELTAE recognizes as a potential target/result pair. The other input parameters to these segments are one or more addresses.

There are 7 types of free targets: FREETarget, QUOTArget, COPRTarget, EFFRTarget, PRODTarget, DIFFTarget, and VOLMTarget. The latter six perform some basic math on the outputs they reference. For more complicated functions, free targets can be cascaded. However, it is not our intention to provide a complete (convoluted!) mathematical language using these modules. For more elaborate post processing of outputs, we encourage the use of spreadsheets or math-capable stream-edit tools such as awk or perl.

The ``target'' parameter of free targets, like that of any other targets, can be used as the independent variable in a plotting loop. All free targets should be placed after all the segments that they reference in the model so that, during processing (which is sequential), they will be updated with the most recent results. Free target specifications do not end with fluid and solid names like normal segments.

FREETarget.

The basic form of free target simply allows you to specify one additional input value that you wish to have the solver compare with an output value that it normally does not consider. It has two input parameters: the real target value, and an output address (e.g. 5F).

QUOTArget.

Almost the same as the FREETarget, the QUOTArget adds an additional output address; it generates its output value from the quotient of the first output (NumAdr) divided by the second output (DenomAdr). One obvious use for such a module is to generate an efficiency, W/Q, or a COP. The efficiency may be used as a target (which may or may not converge, depending on how greedy you are), or it can simply be inserted as a plot parameter, to save the trouble of doing the calculation later.

COPRTarget, EFFRTarget.

These two relative targets are quotient targets taken a step further: they also use the addresses of two temperatures, ThAdr and TcAdr, so that DELTAE can take the quotient and normalize it by Carnot's COP or efficiency. The COPRTarget has already been introduced in the previous chapter, in one of the Hofler refrigerator examples. COPRTarget computes

EFFRTarget computes

It is up to the user to ensure that the addresses given are truly what they are said to be. (Note: the COPRTarget and EFFRTarget can be set up to use gas temperatures, parameters G and H in the stack, instead of metal temperatures from the heat exchangers. The effect is to give system performance for ideal heat exchangers.)

PRODTarget.

Similar to the quotient target, a product target takes two output addresses but generates its output from their product. This module can be useful for generating some figure-of-merit that is to be maximized over a series of plot points. For example, COPR * COPR * Q_c can be generated from a COPRTarget and two PRODTargets by the following model fragment:

!------------------------------------------------------------------------
 COPRT	    COP/COP-Carnot         10
 0.13	    Target
 5G	    NumAdr
 1F	    DenomAdr
 3H	    ThAdr
 5H	    TcAdr
!------------------------------------------------------------------------
 PRODT	                           11
 0.0 	    Target
 10A	     M1Adr
 10A      M2Adr
!------------------------------------------------------------------------
 PRODT	                           12
 0.0 	    Target
 11A	     M1Adr
 5G       M2Adr

(This is about as extreme an example of `free target mathematics' as we would like to envision.)

DIFFTarget.

The difference target, which has been introduced in the final Hofler refrigerator example to maintain resonance at the speaker, is like quotient and product targets in that it takes two output addresses; it generates an output equal to their difference. These targets are often used for phases, so differences of 0 or +/- 90 will be common targets.

VOLMTarget.

The volume target has two address parameters, and it simply generates an output equal to the total volume contained in segments between those two addresses (inclusive). Only the segment number is used; the parameter letter is ignored. The first segment number must be less than or equal to the second. This target is intended to give an indication of the overall size and weight of a design (or a portion of it) for doing tradeoff analysis.