| New Program for Modeling and Simulation by Tom Abel At the last emergy conference I had a poster on a simulation environment that I had developed with the assistance of two student programmers at my university. A few people took copies of it (although it was missing the final version of the Help file). I now have it available on my website here: http://www.tabel.tcu.edu.tw/SystemsModeling-V1.rar You can read the abstract and features that I copied from my poster below. Hopefully it will be useful. I’m interested in any feedback from people. Don’t forget to read the ReadMe file. This brings up a general question-do people still use systems modeling in their teaching (yes)? In their research (no)? My apologies to Mac users, it only runs on PCs. The history is that I originally intended to make this a web-based application, executed from your browser and therefore platform free. For that reason the programmers used a language called C#. Unfortunately we encountered a few difficulties in addition to time limits. It runs well now as a stand-alone C# application, but it can only run on PCs. Also, on your PC you will need to install the Microsoft .NET Framework (an environment that runs in the background and allows the execution of stand-alone C#, J#, VB. NET and others). Sorry for the inconvenience - heck, it’s free! ABSTRACT: A number of simulation environments have been utilized for systems modeling (Odum and Odum 2000). These include Extend, Stella, Excel Spreadsheets, and Basic. There are advantages and disadvantages of each. Extend and Stella are object oriented simulation environments that permit the user to apply predefined objects representing storages, sources, etc., and link them with flows. The simulation produces graphs of flow and storage values as selected by the user. Shortcomings of these environments include (in the case of Extend) poor graphics for representing systems models, and modeling that is limited to the objects previously defined by others (or requiring difficult programming of new objects), or (in the case of Stella) no recognizable systems model, and complicated procedures for ‘adapting’ systems modeling to the Stella language. The greatest shortcoming, however, is the loss of pedagogical value in the systems modeling exercise. By using predefined objects! For example, the student is not required to write the relatively simple difference equations that are the heart of the systems modeling exercise. Excel and Basic systems modeling environments do not suffer this shortcoming. In both cases, it is necessary to manually write the difference equations, and in addition to calculate flow coefficients. These two exercises create a deeper understanding of the simulation process. However, both environments require tedious coding for much of the overhead needed to generate simulation graphs, and calculate coefficients. Further, in the Excel case, the difference equations are buried in cells and review and modification are difficult. In the Basic case, finding a desirable Basic programming environment is nearly a lost cause. For these reasons, a new simulation environment has been produced. The program is written in C#, and will be available free as a compiled runtime application that can run on any PC (it requires the .NET environment! It includes an extensive HELP. The application was written by two student programmers under the guidance of Thomas Abel, all of Tzu Chi University. Features The user will program every flow equation and difference equation; the software assists the user with some automated inputs The environment allows the user to initialize all flows, storages, R’ s, and sources; with that data and the flow equations the user calculates coefficients via an automated function. The environment uses a powerful graphing module called NEVRON Chart, which can produce publication quality jpg files from simulation runs Graphic displays can be the customary 2D curves, or alternately 3D with multiple starting values for sensitivity testing and simulation exploration. Systems diagrams are easily linked and stored with each model Thomas Abel Tzu Chi University Hualien, Taiwan Phone: 857-2677 Ext. 2416 http://www.tabel.tcu.edu.tw/ |
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