First Steps. Creating a simple model
Engee allows you to first model a system and then simulate its dynamic behaviour. The basic techniques discussed in this example for creating a simple model are also applicable to more complex models.
As an example, consider a simplified model of an equally accelerated car. The input will be a signal corresponding to the position of the accelerator pedal, and the output will be a graph of the car movement, representing the dependence of the distance travelled on time.
Let us assume the following assumptions:
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if the accelerator pedal is depressed, the car accelerates;
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if the accelerator pedal is released, the car moves inertially.
Equally accelerated motion of the car in this case can be described by the formula:
,
where:
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- vehicle position at time ;
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- car position at the initial time ;
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- vehicle speed at the initial time ;
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- vehicle acceleration when the accelerator pedal is depressed.
Selecting and setting the units
To create a new model, click 
in the Navigation bar. The first time you start the system, a new model is created automatically.
Let’s design a model with given conditions using blocks. Block Engee is an element of the model that realises the mathematical relationship between its input and output.
The finished model is shown in the figure.
Let’s consider selection and setting of model blocks in details.
In the example we use blocks from the library subsections Basic:
| Subsection name and block name | Block icon | Block task | Modelling object |
|---|---|---|---|
Sources: Pulse Generator |
|
Generates rectangular pulses. |
Accelerator pedal position. |
Maths: Gain |
|
Multiplies the input signal by a constant value. |
Vehicle acceleration value , when the accelerator pedal is depressed. |
Continuous: Second-Order Integrator |
|
Integrates the input signal twice. |
Calculates the position of depending on the accelerator pedal position and the set acceleration. |
Receivers: Terminator |
|
Service block. |
Closes the outputs of the blocks. |
To add blocks to the model:
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Drag them from the Block Library onto the canvas using the left mouse button.
-
Or double left-click on the canvas to bring up the block search bar.
| Searching by block name works even if the keyboard layout is set incorrectly. |
To learn more about working with blocks on canvas, see the article Model building.
| You can run models with unconnected blocks and lines on the canvas. This is convenient for debugging models and conducting virtual tests, and also reduces the routine when developing multi-variant models. |
After adding a block, its parameters are set by default. To view and change parameters of a block, double left-click on the required block, or right-click on the block and select Parameters.
For our example, set the Gain parameters in the Gain block to 2, this value will correspond to the value of car acceleration when the accelerator pedal is pressed. The settings for parameters of other blocks will be left by default.
The output signal from the block Pulse Generator simulates the position of the accelerator pedal. By default parameters of the block correspond to the following mode of operation: the signal period is 10 seconds, the output signal has a value of 1 during the first 0.5 seconds of the period (the accelerator pedal is pressed and the car is travelling with acceleration), the rest of the period the output signal has a value of 0 (the accelerator pedal is released, the car is moving with inertia, gradually decelerating). The output signal is shown in the figure.
To output the simulation results on the graph, click on the output signal x of the block Second-Order Integrator and select the item Write from the context menu. This signal will output the value of linear movement of the car. For a better understanding of the model, you can also record the signal at the output of Pulse Generator block, which will correspond to the position of the accelerator pedal, and the output signal dx of Second-Order Integrator block, which will correspond to the speed of the car.
|
Engee allows you to change some parameters during simulation. To find out which parameters can be changed, open the help for the block in question. If a block parameter has a *Tunable attribute, its value can be changed directly during the simulation.
|
Running the model
In the Head menu of the workspace, in the field for setting the simulation time, specify the required simulation time in seconds, e.g. 30. You can then start the simulation.
To run the simulation, click Start 
. The current status of the simulation can be seen in the Status bar:
You can read more about setting up and running the model at Setting up and running the model.
The graph window opens automatically. The graph will show the set state of the accelerator pedal and the calculated speed and linear movement of the vehicle during the simulation time.
For clarity, we will plot the signal values on different graphs.
You can read more about working with charts at link.
After analysing the results, you can go back to the original model and change the parameters of the blocks (e.g. accelerator position settings) and run simulations with other parameters of the model.
More information about Model-Based Design in Engee can be found at the links:
Saving and opening a saved model
To save a model, right-click on the model and then click:
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Save as for a new (not saved in the file browser) model.
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Save or Save as for a previously created model.
Next, you can change the name of the model in the file browser. To rename a model, right-click on the desired model, then click Rename. Enter the new model name and press Enter.
To open an existing model, click File Browser 
. A file browser window will open, find the desired model and double click on it with the left mouse button. The model will appear in the Navigation Pane.
