MV-1051: Understanding Sequential Simulation

In this tutorial, you will learn how to build a model with sensor elements to capture the state of a body, use the sensor signal to activate some joints and deactivate others, and carry out a sequential simulation.

Sequential Simulation allows you to write simulation instructions to change the model, modify the solver settings and submit analyses.

This tutorials covers the following topics:

Fixed joint definition between non-coinciding points using marker definitions.
Using a sensor to activate the joint when two markers coincide during simulation.
Using Templex statements to:
- Deactivate a fixed joint when markers are non-coincident.
- Activate a fixed joint when markers coincide.
- Simulate until t = 5.00 seconds.

Note: Copy the file located in the <installation_directory>\tutorials\hwdesktop\mv_hv_hg\mbd_modeling\interactive\sequential_simulation folder to your <working directory>.

Create Joints, Markers, and Sensors

Start a new MotionView session.
From the Standard toolbar, click Open Model .

OR

From the File menu, select Open > Model to open the model Sequential_simulation.mdl.

The model contains two bodies, namely a slider and a picker. You need to create markers, joints, and a sensor as well as use Templex statements to perform a sequential simulation.
Figure 1.
From the Project Browser, right-click on Model and select Add > Constraint > Joint (or right-click Joints from the toolbar).
Under Type, select Translational Joint. Label the joint slider trans.
Make the following selections:
1. For Body 1, select slider.
2. For Body 2, select Ground Body.
3. For Origin, select slider cg.
4. Define the Alignment axis using the point slide end.
  
  Figure 2.
Add another joint. For Type, select Fixed Joint and label the joint picker rest fix.
Make the following selections:
1. For Body 1, select picker.
2. For Body 2, select Ground Body.
3. For Origin, select part fix.
This joint will be deactivated when the slider body coincides with the picker body during simulation.
Figure 3.

When you create a fixed joint between the slider and the picker and they come in contact, you need to define two markers which are initially not coincident, but coincide during the course of simulation. Creating a joint based on markers must be done using Templex, as it is not possible to create it from the user interface.
From the Project Browser, right-click Model and select Add Reference Entity > Marker (or right-click Marker from the toolbar). Label it Marker Slider Track and set the properties as shown in the image below:

Figure 4.
Similarly, create another marker with the label Marker Picker Track and set the properties of the markers as shown in the image below:

Figure 5.
From the Project Browser, right-click Model and select Add Control Entity > Sensor (or right-click Sensor from the toolbar) to add a new sensor.
From the Signal field, select the type as Expression and enter the following expression:
```
`DX({m_slider_track.idstring},{m_picker_track.idstring})`
```
In the Compare To field, enter 0.0010 for the Value and 0.0010 for Error. Set Respond if to Signal is greater than VALUE - ERROR.
In the Response field, select Return to Command File.

This directs the solver to look into the template for further instruction on how to proceed once the signal is attained.
From the Project Browser, right-click on Model and select Add Constraint > Motion (or right-click Motion from the toolbar. Set the properties as shown in the figure below using the following expression:
```
`STEP(TIME, 0, 0, 5, 800)`
```

Create a Fixed Joint Between Two Non-coincident Markers Using Templex

To create a fixed joint between the slider and picker that is activated once the distance between the slider and picker is zero, from the Project Browser, right-click on Model and select Add General MDL Entity > Template (or right-click Template from the toolbar).
Label it Fixed Joint Defn. For Type, select Write text to solver input deck. Enter the following commands as they are listed below in the same order.
```
<Constraint_Joint
id                  = "5000"
type                = "FIXED"
i_marker_id         = "{the_model.m_slider_track.idstring}"
j_marker_id         = "{the_model.m_picker_track.idstring}"
/>
```
The panel should look like this:
Figure 8.

Create a Template to Define the Sequential Simulation

In this step, you will write a template to do the following:

Deactivate Joint between Slider and Picker for the initial simulation.
Perform a transient analysis for 3.5 seconds.
Activate Joint between Slider and Picker.
Deactivate Joint between Picker and Ground.
Deactivate the Sensor Element.
Run a transient analysis for 5 seconds.

From the Project Browser, right-click on Model and select Add General MDL Entity > Template (or right-click Template from the toolbar).
Set the Type as Write text to solver command file.

Type the following commands as listed below.

<Deactivate
element_type = "JOINT"
element_id   = "5000"
/>
<Simulate
analysis_type       = "Transient"
end_time            = "3.5"
print_interval      = "0.01"
/>
<Deactivate
element_type = "JOINT"
element_id   = "{the_model.j_picker_rest_fix.idstring}"
/>
<Deactivate
element_type = "SENSOR"
element_id   = "{the_model.sen_0.idstring}"
/>
<Activate
element_type = "JOINT"
element_id   = "5000"
/>
<Simulate
analysis_type       = "Transient"
end_time            = "5."
print_interval      = "0.01"
/>
<Stop/>

Run the Simulation and Animate the Results

Click Run Solver
Click the Save and run current model and enter a name for the solver run file.
Set End time as 5 and the Print interval as 0.01.
Click Run.
Once the solver procedure is complete, the Animate button on the Main tab is activated. Click Animate to animate the model. Click to start the animation and to stop the animation.

Figure 9.