4.22. THE TANK We want to simulate the behaviour of a tank containing liquid, which contains only one entry and one exit that are always open. The tank has a capacity of 100 litres, and initially contains 50 litres of liquid. We want to know the dynamic of the tank's content before make changes in the entry and exit flows. In other words, we want to make sure that the tank will not get overfilled and that it won't get empty. The entry is regulated in a way that - to avoid overfilling - the flow increases when the tank is getting emptier, and the flow decreases when the tank gets filled up. Initially we equilibrate the entry in the tank in a way that enters a fraction of 1/10 of the volume in the tank. On the contrary, we regulate the exit in a way that - to avoid emptiness - we will increase the exit flow when the tank is almost filled, and it will decrease when the tank becomes empty. Initially, we regulate the exit in a way that exits a fraction of 1/10 of the volume in the tank. Questions: 1. What behavior would you expect, if initially - as we described earlier - the tank gets filled up at a rythm of 1/10 of it content, and gets empty at the same rythm ? 2. What would happen if initially, the tank contains 80 litres ? 3. What would happen if the entry is regulated at 1/20 of the volume of the tank, and the exit at 1/10 of the volume ? LINKS: Theory and Practical Exercises of System Dynamics System Dynamics Online Courses Building Models in Ecology Building models with Vensim Other resources in System Dynamics Boletín de Dinámica de Sistemas