4222174 working model chapter7

8/14/2019 4222174 Working Model Chapter7

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7-1

C H A P T E R 7

Analyzing

This exercise is for the following products:

Working Model Motion Working Model 4D

Exercise 7.1 demonstrates Working Model features that let you analyze

and test performance characteristics.


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7-2 Chapter 7Analyzing

Exercise 7.1 Analyzing a Piston ModelThis Exercise illustrates how you use Working Model to analyzeperformance characteristics (reaction forces, collision and partinterference) and test what-if scenarios on a model of a piston assembly.

The piston model that you analyze could have been created by:

Exporting a model from your favorite CAD software. For moreinformation on exporting CAD models, see Chapter 6 , ExploringCAD Integration and Associativity .

Building a model from scratch in Working Model. For moreinformation on building models, see Chapter 8 , Building aModel .

Opening a Model File First, you must open the file.

1. Open the file Piston.wm3 located in your Program Files\WorkingModel\Tutorials\Chapter 7\Exercise 7.1 directory.

The folder path may vary depending on where you installed Working Model.

The model of the piston assembly is displayed in the document window, as shown in Figure 7-1 .

Figure 7-1Model of a Piston Assembly
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Exercise 7.1 Analyzing a Piston Model 7-3

2. Click the Run button in the Tape Player Control.

This base model shows the piston mechanism in motion, driven bythe motor attached to the crankshaft.

Since this is the first time the simulation is being run, Working Model calculates the dynamics and stores the data.

3. Repeat the simulation by clicking the Stop button, then theReset button, and then the Run button again.

The animation is faster this time because the history has alreadybeen calculated.

Understanding Part Relationships You can see how the parts of the model are connected by selecting them

in the Object Manager that appears along the left edge of the documentwindow, as shown in Figure 7-2 .

When you select a body in the Object List or the Connections List,all of the constraints and Coords connected to that body aredisplayed in the Connections List.

When you select a constraint in the Object List or the ConnectionsList, all of the bodies and Coords connected to that constraint are

displayed in the Connections List. When you select a Coord in the Object List or the Connections List,

all of the bodies and constraints connected to that Coord aredisplayed in the Connections List.

Note: Objects that have been hidden in the drawing appear with dimmed icons in the Object List and Connections List. Although they are hidden,they are still active in the simulation, and you can select them in the lists .


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Figure 7-2 Object Manager

1. Select Piston Head-1 in the Object List.

The constraints and Coords connected to the piston head aredisplayed in the Connections List.

2. Select constraint[40] in the Connections List.

The Connections List now shows that constraint[40] connects the piston head, Piston Head-1, to the piston pin, Piston Head-1.

3. Double-click constraint[40] in the Connections List.

The Properties window displays the properties of constraint[40],as shown in Figure 7-3.

Selected

Bodies and Coords connected to the selected constraint

Move this bar up or down to resize the panels

Click to show Subassembly View

Object List

Connections

Constraint

Properties

List

List


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Figure 7-3 Properties Window for constraint[40]

4. Select other objects in the Object List.

As you select each object, it is highlighted in the modeling windowand its properties are displayed in the Properties window.

Setting the Initial Condition Working Model allows you to manipulate and configure parts withoutbreaking the assembly constraints that were created when the model wasbuilt in Working Model or in the CADsystem. In this step, you will movethe piston assemblys configuration so that the simulation starts halfwaythrough the combustion or compression cycle.

1. Click the Move tool in the Edit toolbar.

2. Move the mouse over the side surface of the crankshaftcounterweight.

As you move the mouse over objects in the modeling window, adashed box appears around them to show that they areframed (asshown in Figure 7-4 ).


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Note: The movement stopswhen the parts are dragged to the mechanicallimits imposed by the physical joints.


The simulation runs again, starting from its new initial position.

6. Click the Stop button, then reset the simulation by clicking theReset button.

The piston assembly returns to the new initial position, halfwaythrough the full stroke.

Using Simulation Controls

You can add input sliders to dynamically change the properties of aconstraint as the simulation is running. You can also use data from a tableto control a simulation. Unlike input sliders, the table data input is not aninteractive control. In the table, you specify values to be applied at listedtimes throughout the simulation.

Using an Input Slider as a Simulation Control In this step, you will add an input slider that controls the angular velocityof the motor that turns the pistons crank.

1. Select the revolute motor, constraint[10] in the Object List.

The revolute motor is selected (even though it may not be visible in

the modeling window).

2. Choose Control in the Insert menu, then choose RotationalVelocity in the Control submenu.

This displays the Choose Input Type dialog.


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Figure 7-6 Choose Input Type Dialog

3. Choose Slider and click OK.

An input slider window appears above the modeling window withthe title Rot. Velocity of constraint [10], as shown in Figure 7-7 .

Figure 7-7 New Input Slider for Rotational Velocity of Motor

4. Select the input slider, then choose Properties in the Edit menu.

The input sliders properties appear in the Properties window.

5. Click the Appearance tab in the Properties window, then enterMotor Rotational Velocity as the name for this input slider, asshown in Figure 7-8.

The new name appears as the title of the input slider window.


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Figure 7-8 Properties Window (Appearance Page) for Input Slider

6. Click the Input tab in the Properties window, then enter 0 asthe minimum value for the input range and 3600 as themaximum value, as shown in Figure 7-9 .

The numbers are interpreted in degrees per second.

Figure 7-9 Properties Window (Input Page) for Input Slider


8. As the simulation runs, try dragging the input slider to higherand lower values.

As you drag the slider to the right, the angular velocity of

the motor increases and the crank rotates more quickly. Conversely,as you drag the slider to the left, the crank rotates more slowly.


The piston assembly returns to the initial position, halfway throughthe full stroke.


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10. Click the close box in the input slider window.

The input slider is still available in the Object List, but it istemporarily hidden from view. You can re-display the input slider bydouble-clicking it in the Object List.

Using a Table as a Simulation Control You can also use data from tables to control a simulation. You candirectly enter data in a table in Working Model, or you can import thetable data from a file. For more on this, see the chapter on SimulationControls in the Working Model Users Manual .

In this step, you will create a table that provides torque inputs to therevolute motor.

Note: The default table configuration is to index value parameters totime. However, you can index value parameters to any other variable. Todo so, you use Formulas as shown below. For more on using formulas,see the Working Model Users Manual.

To create an input control for table data:

1. Select constraint[10], a revolute motor, in the Object list.

2. Choose Control in the Insert menu, then choose Torque in theControl submenu.

This displays the Choose Input Type dialog.

3. Select Table.

4. Click OK.

This displays the Insert Table window.


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Figure 7-10 Insert Table Window

5. Enter Lookup entries of the dependent variable (i.e., the valueor 2ndcolumn) Values in the table. Use the data shown in Figure7-10 . You can also click the Browse button to select a file

containing table data.

6. Click OK.

7. Run the Simulation.

Working Model applies the torque values at the time intervalsspecified in the table during the simulation.

Measuring Reaction Forces You can add meters to the model to measure the reaction forces in thepiston assembly. For example, in this step, you will create a meter tomeasure the constraint force experienced by the revolute joint connectingthe connecting rod and piston pin.

1. Select Piston Pin-1 in the Object List.

The list of constraints and Coords connected to the piston pinappears in the Connections List.

2. Select constraint[34], the revolute joint that connects theconnecting rod to the piston pin, in the Connections List.

The Lookup column refers to the independent variable to be used when looking up the correspondi dependent variable (Value).


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Note that coord[32] on Piston_Pin_par_1 and coord[33] onConnecting_Rod_par_1 are listed as the Coords attached toconstraint[34] in the Connections List.

3. Choose Meter in the Insert menu, then choose ConstraintForce... in the Meter submenu.

The Constraint Force Settings dialog appears as shown in Figure 7-11 .

Figure 7-11Constraint Force Settings Dialog

The Tiling Options dialog appears.

4. Click OK.

5. Select coord[33] on Connecting_Rod_par_1 in the Expressedin section of the Constraint Force Settings dialog and click OK.

A new meter window opens, titled constraint[34] Force onConnecting Rod-1 in coord[33] on Connecting Rod-1, as shown inFigure 7-12 . The new meter will display the x, y, and z componentsand the total constraint force exerted by constraint[34] on thecoord on Connecting Rod-1 as separate plots.


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Figure 7-12 Constraint Force Meter Window


As the simulation runs, the values of the x, y, and z components and the total constraint force between the piston pin and the connectingrod is plotted in the meter window. Notice how Fx and Fy oscillateas the crank rotates through a full stroke, as shown in Figure 7-13 .

Figure 7-13 Constraint Force Meter Window


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Note : Your results may not match Figure 7-13 . The appearance of the plots depends upon the Motor Rotational Velocity that you select with theinput slider.


The piston assembly returns to the initial position.

8. Click the close box in the meter window.

The meter is still available in the Object List, but it is temporarilyhidden from view. You can redisplay the meter by double-clicking it in the Object List.

Display the Acceleration of the Connecting Rod Working Model allows you to visualize vectors in 3D space as thesimulation runs. Although the animated simulation itself serves as apowerful visualization tool, hard-to-see qualitative data such as vectorsreveal even more information that cant be seen in a physical prototype.

In this step, you will display vectors that show the acceleration of theconnecting rod.

1. Double-click Connecting Rod-1 in the Object List.

The connecting rods properties appear in the Properties window.

2. Click the right arrow in the Properties window to scroll the tabsuntil the Vectors tab is displayed, then click the Vectors tab.

The Vectors page is displayed, as shown in Figure 7-14.


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Figure 7-14 Properties Window (Vectors Page) for the Connecting Rod

3. Click the Acceleration Vector box to put a checkmark in it, thenclose the Properties window.

4. Click the Toggle Wireframe button in the View toolbar.

The modeling window changes to a wireframe rendering, which will

make it easier for you to see the acceleration vector (which is oftenhidden by the sides of the crank) as the simulation runs.


As the simulation runs, the acceleration vector is displayed, but it isdifficult to see because it is small. In the next step, you will resize theacceleration vector to make it easier to see.



Make the Acceleration Vector More Visible You can change the size and color of the vectors displayed to make themmore visible as the simulation runs.

1. Choose Wireframe from the View menu.

2. Choose Display in the World menu and click the Vectors tab inthe Display Settings window.


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The Vector Settings dialog appears, as shown in Figure 7-15 .

Figure 7-15 Vector Settings Dialog

3. Enter 0.09 as the scaling factor for the length of the Accelerationvector.

The default value is 0.03. Because you are tripling the scaling factor, the acceleration vectors will now be three times as long.

4. Click the Color button next to the Acceleration vector in theVector Settings dialog.

The Color dialog appears, as shown in Figure 7-16 .

Figure 7-16 Color Dialog

5. Choose a bright red color and click OK to close the Color dialog.

The acceleration vector will now be displayed in red.



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As the simulation runs, note that the acceleration vector attached tothe connecting rod switches sides (because the acceleration

switches direction halfway through the full cycle), as shown inFigure 7-17 .

Figure 7-17 Acceleration Vector on Connecting Rod



Seeing Through Bodies Working Model provides an alternative to selecting a shaded orwireframe view of your drawing. The alternative is variabletranslucency, a feature that allows you to quickly render one or severalbodies translucent. This is helpful when you want to view internalconstraints and coords or obstructed bodies before or during asimulation.

1. Choose Shaded from the View menu.

2. Double-click the Piston head.

The Properties window appears.

3. Click the Color tab in the Properties window, scrolling all theway to the right.

Acceleration Vector


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The Color dialog appears as shown in Figure 7-18 . (If there is noColor tab, enable it by clicking in the Color checkbox in the

Properties List.)

Figure 7-18 Properties Window Color Page

4. Enter 0.4 in the Translucency text region and press Return.

The piston head is rendered translucent as shown in Figure 7-19 .

Figure 7-19 Translucent Piston Head

Try entering different translucency values ranging from 0 (least translucent) to 1 (most translucent).

Specify Translucency

Scroll here


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The modeling window changes to a shaded rendering, which willmake it easier to complete the next steps.

2. Click on the background to de-select everything and then pressT on the keyboard, so that you can see the top of the pistonhead. Click the Rotate Around tool in the View toolbar and usethe mouse to rotate the piston.

Your view should be similar to Figure 7-21 .

Figure 7-21Top of the Piston Head

3. Click the Force tool in the Sketch toolbar.

4. Click the mouse pointer at the top of the Piston, near the center.

The precise location of the attachment is not important for thisexercise.

5. Double-click the force icon in the modeling window or in theObject List.

The forces properties appear in the Properties window.

6. If necessary, click the Force tab, then enter 10 in the z-fieldto apply a 10 Newton force downward, as shown in Figure 7-22 ,and change the Fy field from -1 to 0.

The forces Coord attachment dictates this orientation setting.


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Figure 7-22 Properties Window

(Force Page)

7. Choose Go Home in the View menu.

Your original view of the piston assembly (which provides a better view of the motion) is restored.


As the simulation runs, the piston behaves like a pendulum becausethe force is applied constantly, which isnt a realistic scenario.



Modify the Force to Simulate Realistic Throttle As a final step, you will modify the force to simulate realistic throttle byusing a formula to control when the force is applied.

1. Double-click the force icon in the modeling window or in theObject List.

The forces properties appear in the Properties window.

2. Click the Active tab.

This displays the Active Page of the Properties window.

3. Click the Active while: radio button, then click on the Formulabutton.


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This displays the Formula Editor dialog as shown in Figure 7-23 .

Figure 7-23 Formula Editor Dialog (Active Page) for Force

4. Enter the following formula, and click OK.

and(body[7].v.z


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Verify the Result

You can verify that your model is accurate by creating a meter tomeasure angular velocity of the crankshaft, and setting the angularvelocity unit system to RPM. The angular velocity of the crankshaftshould settle at around 600 rpm.

1. Select Crank-1, the left half of the crank, in the Object List.

2. Choose Meter in the Insert menu and then choose AngularVelocity in the submenu.

A new meter window appears.

3. Choose Display in the World menu and click on the Units tab ofthe Display Settings window.

The Units page in the Display Settings window appears as shown inFigure 7-25 .

Figure 7-25 Units Page

4. Choose rpm in the Rot. Vel. pull-down list.

5. Click OK to close the Settings Window.

6. Run the simulation.

As the simulation runs, the angular velocity, |W|, grows toapproximately 600 rpm, then levels off, as shown in Figure 7-26.

Choose rpm


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Figure 7-26 Angular Velocity Meter

Prescribing a Harmonic Function You can use an advanced feature of Working Model to create and applya variety of functions. This exercise shows how to build an oscillatingfunction.

1. Double-click the Piston Head-1 in the Object List or on thePiston Head in the modeling window.

The Properties Window appears showing the Position page.

2. On the Position page, click the Prescribed Motion button.

The Prescribed Motion window appears as shown in Figure 7-27 .

E i 7 1 A l i Pi t M d l 7 25


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Figure 7-27 Prescribed Motion Window

3. Click on the Z setting in the Position and Velocity region of thePrescribed Motion window.

4. Click on the Formula button next to the Z setting.

This displays the Formula Editor dialog.

5. Choose Harmonic in the Function menu.

The Harmonic Function Settings window appears as shown inFigure 7-28 .

Figure 7-28 Harmonic Function Window

Select the Formula button

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6. Enter the following values and then click OK.

Period: 0.5 sec Amplitude: 68 mm Offset: 164 mm Phase: 90 deg

The function appears in the Formula Editor dialog.

7. Click OK in the Formula Editor dialog.

The function appears in the Z setting of the Prescribed Motionwindow.

8. Close the Properties window and click OK in the PrescribedMotion window.

9. Delete the force acting on the Piston Head in the Object List.

10. Run the simulation.The piston will move based on the prescribed motion. The force is nolonger needed to drive the piston.

The first few frames of the simulation will be inconsistent with theharmonic prescribed motion. This is because the harmonic functionhas been set up to start the piston at the top of its stroke. Working Model uses the first few frames to rapidly move the piston head to its prescribed location. The results of this can be seen as a large initialspike in the Angular Velocity meter.

4222174 working model chapter7

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