4.12. DRAW FEEEDBACK LOOPS WITH VENSIM
A simulation model with Vensim
We want to simulate the effects that will provoke a decrease in the number of maintenance workers in the number of damaged goods. We have a system with two elements: the number of maintenance workers and the number of damaged goods. We create a new file model - New Model with Initial period = 0 and final period = 24 months. We suppose that the number of workers drops from 10 to 5 in the 6th month.
We will define that the number of damaged pieces depends on the number of workers in that when there are 10 workers the damaged pieces are 0. If there are 8 workers we would have 100 pieces, if there are 6, we would have 200 pieces if there are 4 we would have 400 pieces, if there are 2 we would have 600 and if there are 0 we would have 800 pieces.
We will use an internal table for this, we will select Auxiliary Lookup as the type of variable number of pieces. The AsGraph button must be pushed and we will need to introduce the defined points as pairs of values of the independent variable (Input) and the dependant (Output). Once the information is entered, push OK.
A similar menu will appear from the table but in the input section we will put the months and in the Output, we will put the number of damaged pieces that we expect to see. In other words, we will draw the graph that we expect to have. In this case we expect to obtain 50 damaged parts in the 6th month, 200 in the 12 th, 500 in the 18th and 500 again in the 25th month.
It is always very convenient to draw the behaviour that we expect to observe in the variables in the model as the result of the model has to be used to validate our initial perception or it has to allow us to understand in what aspects our perceptions were not correct.
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