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73 6 Bond Graphs 6.1 Bond Graph model In the previous sections you have learned how to enter equation models and block diagram models. You have also learned how to enter hierarchy into a model. In this lesson we will explain the basics of bond graph modeling in 20-sim. The lesson is meant for users interested in bond graph modeling. If you are not interested in bond graph modeling, we advise you to skip this section and continue with iconic diagrams. Bond Graph Model We consider the mechanical system of the figure below. A mass with spring and damper. This system can easily be transferred into the bond graph model shown below. Bond graph model of the mass-spring-damper system 1. Open 20-sim and select File, New and Graphical Model and make sure that 20-sim is in Debug Mode. The right part of the Editor will now allow you to enter graphical models. That is why we have named this part of the Editor the Graphical Editor.Getting Started with 20-sim 4.0 74 2. Put the mouse pointer in the middle of the Graphical Editor. 3. From the right mouse menu or from the Insert menu select Insert, Knot and OneJunction. This adds a 1-junction. 4. Go to the left of the Editor and click the Library tab. 5. Drag the following library models to the Graphical Editor: model library model Library\Bond Graph Library\Bond Graph Library\Bond Graph Library\Bond Graph C I R Se 6. Select the Se model. From the Model menu select the Properties command. This will open the Model Properties Editor. 7. Rename the model to Fg. Do so with all the submodels and use the names given in the bond graph at the top of this topic. 8. Select the C model and from the right mouse select the Show Name menu and the Right command. This will put the element name to the right of the element. 9. Do so with the other elements until your model looks like: The bond graph elements in the Editor.6 Bond Graphs 75 10. In the taskbar, choose the second left button (the mouse pointer with line). This is the connection mode button. 11. Select the model Fg (left mouse click on top of the element) and then the 1-junction (left mouse click on top of the element) This will create a connection between both elements: The red color of the bond indicates a conflict. In this case more bonds need to be inserted. The bond is drawn red, which means causality could not be assigned. Don't worry! This is because 20-sim has an on-line causality assignment and notices there is only one bond connected to the 1-junction. 12. Create a bond between the 1-junction and the submodel spring. Now your model should look like:Getting Started with 20-sim 4.0 76 The orange stroke indicates a non-preferred causality. The bond to the C model has an orange causal stroke. This means that the C model in this configuration has a non-preferred causality. 13. Enter the other connections until your model looks like: The complete bond graph model. 14. From the Model menu select the Check Complete Model command. Now the complete model will be checked. If the model is correct at the bottom of the Editor the Process tab should show a message indicating 0 errors and 0 warnings. If any errors are found, a6 Bond Graphs 77 message window pops up, showing the errors which 20-sim has found. You can click on the error in the Process tab to highlight the corresponding equation. 15. From the File menu click Save as. Store the model in a temporary directory (e.g. C:\temp) using the name BondGraphModel.emx. If you have problems creating the model, load the model Bond Graph Model from the Getting Started\Bond Graphs section of the library. Simulation 16. In the Editor toolbar from the Model menu select the Start Simulator command. This opens the Simulator window. We will proceed with this window. 17. In the Simulator toolbar from the Properties menu select the Parameters command and change the default parameter values to: friction\r Fg\effort Mass\i Spring\c 1 -9.8 1 0.5 18. From the Properties menu select the Run command and change the default values to: Start Finish Method Step Size 0 15 Euler 0.2 19. In the From the Properties menu select the Plot command. 20. Select the Plot Properties tab and change the following default values to: Plot Title Bond Graph Mainmodel 21. Select the Y-axis tab and click Choose to open the Variable Chooser 22. Select the variable spring\state from the list and click OK. 23. Change the label to x. 24. Set the following values: Tick Style Properties Tick Style Min. Distance (pixels) Color Diamond Closed 2 Red Scaling Scaling From To Manual -10 10Getting Started with 20-sim 4.0 78 24. Close the Plot Properties Editor by clicking the OK button. 25. From the Simulation menu select the Run command to start the simulation. The result should look like the figure below. 25. From the File menu click Save. If you have problems creating the model, load the model Bond Graph Model from the Getting Started\Bond Graphs section of the


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PACIFIC COMP 155 - Bond Graph model

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