6 Model file format

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6 Model file format

A model file has 12 procedures, which the user should fill out to specify the problem to be solved. The following figure shows the sequence in which the procedures are called from the simulation program:

1)Load Model

2)SetUpProblem

3)Start

4)PreCalc

	State Change	5) Stop	Yes	10) EndCalc
	Procedure
		No
	6)	ModelEquations		Sample Check
				Procedure
	Sample Check	7) StateShift
	Procedure
	Yes		No

	8) OnSolution						9) OnSolution

Figure 8. Calling sequence for the procedures in the model file.

The rounded rectangles in Figure 8 represent user-actions in the Simulation program.

Note that the boxes 6 and 7 in general are called several times at each time step. This is because the solver iterates to find a solution. The procedure OnQuit, which is not represented in figure 8, is called when the user closes the simulation program or selects another model. The procedures

OnUIValueChange, OnSaveSettings and OnLoadSettings all have to do with controlling the user-interface. They will be explained later.

WinDali

Morten Juel Skovrup

22 6 Model file format

The calling sequence with no state shift is straightforward (for now ignore the Sample Check Procedure regarding Sample time – it will be covered in chapter 6.8). But the calling sequence with a state shift needs some explanation.

The State Change Procedure looks like this:

	State Change Procedure
OnStateChange	ModelEquations	OnSolution

Figure 8a. State Change Procedure.

Lets say that we want to model a valve that is On when a temperature T is above 10°C, else it is Off. We want to record the temperature and the On-Off signal to the valve, and the initial temperature is 20°C. A plot of the temperature and the On-Off signal could look like this:

20°C
	T
10°C
On	2b
Off	2a
t1	t2

Figure 9. Temperature and On-Off signal.

When the solver reaches t2 where the valve goes On, it first calls OnSolution (block 8) to inform the model file that a solution has been found. But at t2 the equation system also shift state, which means that the solver has to start all over, and possibly with a new set of static equations.

The static equations have to be solved before the solver continues, and for this the solver needs guesses on the static variables.

In SetupProblem (as will be clear in chapter 6) default guesses on the static variables are given for each state, but if these guesses for some reason need to change, OnStateChange (see Figure 8a) is called. After OnStateChange, ModelEquations is called to solve the static equations in the new state, and before the solver continues, OnSolution is called to enable plotting of point 2b in Figure 9.

In the following the 12 procedures will be covered in detail.

WinDali

Morten Juel Skovrup