to setup clear-all set adjust_inflow 0.011;; can change this initial number, currently set for steady-state system-dynamics-setup do-plots end to go system-dynamics-go do-plots end to do-plots ;;sets up two graphs, one of cooler volume, the other of inflow and outflow set-current-plot "water_volumes" set-current-plot-pen "cooler" plotxy ticks cooler set-current-plot "water_flows" set-current-plot-pen "outflow" plotxy ticks outflow set-current-plot-pen "inflow" plotxy ticks inflow end @#$#@#$#@ GRAPHICS-WINDOW 622 13 830 242 17 17 5.66 0 10 1 1 1 0 1 1 1 -17 17 -17 17 0 0 1 ticks CC-WINDOW 5 392 839 487 Command Center 0 PLOT 32 202 339 376 water_volumes time volume 0.0 3600.0 0.0 10.0 true true PENS "cooler" 1.0 0 -13345367 true SLIDER 196 54 493 87 adjust_inflow adjust_inflow 0 0.1 0.022 5.0E-5 1 L/sec HORIZONTAL BUTTON 59 41 122 74 NIL setup NIL 1 T OBSERVER NIL NIL NIL NIL BUTTON 61 107 124 140 NIL go T 1 T OBSERVER NIL NIL NIL NIL MONITOR 185 129 242 174 NIL inflow 3 1 11 MONITOR 284 132 342 177 NIL outflow 3 1 11 PLOT 423 126 765 378 water_flows time flow rate 0.0 3600.0 0.0 0.05 true false PENS "inflow" 1.0 0 -10899396 true "outflow" 1.0 0 -2674135 true @#$#@#$#@ WHAT IS IT? ----------- Dynamical systems models are powerful tools for studying many phenomena in Earth Science. These models (often rather sophisticated) are in increasingly wide use as research tools in hydrology, geochemistry, petrology, oceanography and climatology. This is a simple dynamical model used to develope insight into seemingly complex physical phenomena. HOW IT WORKS ------------ Computer models developed in combination with simple physical models allow students to better understand systems behavior. They gain confidence in computer modeling, and learn how theoretical models can be extended to study more complicated systems. HOW TO USE IT ------------- Each time you run the model, if you want to start with the intitial conditions, begin with "setup" each time. When you are ready to run the model with your parameter (either initial or modified), click "go" to watch the model run. When you want to stop the model, click "go" again. If you would like to change the "inflow" into the "cooler", you may use the "adjust_inflow" slider to change the rate of water flowing into the cooler system. But don't do this until you've observed the steady state system and are ready to make predictions. One plot, "water_volumes" will show the volume of water in the cooler. The second plot, "water_flows" will show how the "inflow" and "outflow" change and adjust to reach steady state. The black box does nothing, but I can't get it off the screen! THINGS TO NOTICE ---------------- One important point for the students to understand about the steady state system is that although water continually enters the reservoir and continually flows out, none of the parameters of the system change with time. This system is dynamically maintained, as opposed to one that is static. The input and output will not change and the volume of the system will remain at 8 liters indefinitely. THINGS TO TRY ------------- What if we were to change the parameters of the system? What would happen if we were to double the amount of water input to the reservoir? Before you begin adjusting the inflow, make a prediction about what you think will happen if you double the inflow rate. Write down your prediction. Then adjust the slider to double the original flow and click "go". Observe what happens and describe the response (shape of the curves). EXTENDING THE MODEL ------------------- What happens if the input is tripled rather than doubled? What is the new steady state volume? How long did the system take to adjust? Try these inputs to the System Dynamics Model rather than using the slider: Parameters input into the model for this perturbation are: Cooler = 8, Input = 0.011+STEP(0.011,600), Output = Cooler/720. Add some physics: If comparing to a physical model, you will find that, according to Bernoulli's equation for flow through a gravitationally fed pipe, the output rate should depend on the square root of the volume in a vertically walled container (e.g. Sears, Zemansky and Young, 1984, Ch.13). Our model may be easily modified to incorporate this relationship. The new output term is outflow = (8 / 720) * SQRT( cooler / 8). Now we have a model that not only accurately predicts the behavior of our particular cooler, but does so based on a fundamental understanding of the processes that control its behavior. You can add a seasonality to the water inflow by changing inflow = SIN(2 * PI) Add additional inflows and outflows, depending on the system you are now trying to model. Each time, try to make the system reach steady state. Good luck! NETLOGO FEATURES ---------------- NetLogo is not actually designed to best run this type of model, but it's free and available. Other models like this are more often created using STELLA. RELATED MODELS -------------- This section could give the names of models in the NetLogo Models Library or elsewhere which are of related interest. CREDITS AND REFERENCES ---------------------- The educational pedagogy and concepts as well as comparison to a physical model are from the following article published in the Journal of Geological Education, 1995, v.43, p. 153. 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