ws08-1 vnd101, workshop 08 msc.visualnastran 4d exercise workbook analyzing the piston model

WS08-1VND101, Workshop 08

MSC.visualNastran 4D

Exercise Workbook

Analyzing the Piston Model


Analyzing

Objectives This exercise is for the following products:

• visualNastran Motion

• visualNastran 4D

This exercise demonstrates visualNastran features that let you analyze and test performance characteristics.

Exercise Overview Open native .wm3 file Understand part relationships. Set initial condition. Create Slider control. Measuring Reaction forces. Insert Vectors. Use Formula language to simulate a realistic throttle. Verify result.


I - Open Model

First, you must open the file.

1) Open the file “Analyzing Piston Model.wm3”. (Figure 1)

The model of the piston assembly is displayed in the document window. (Figure 2)

2) Click the “Run” button in the Tape Player Control.

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

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

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

The animation may be faster this time because the history has already been calculated.

Figure 2 Model of a Piston Assembly

Figure 1 Open File


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 document window, as shown in Figure 3.

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

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

II - Understanding Part Relationships


4) Select “Piston Head-1” in the Object Manager List.

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

5) Select “Concentric6” in the Connections List.

The Connections List now shows that Concentric6 connects the piston head, “Piston Head-1”, to the piston pin, “Piston Pin-1”.

6) Select other objects in the Object List.

As you select each object, it is highlighted in the modeling window and its properties can be found its Properties dialog box.

II - Understanding Part Relationships

Figure 3 Object Manager

Properties List

Connection List

Object Manager


Setting the Initial Condition

MSC.visualNastran allows you to manipulate and configure parts without breaking the assembly constraints that were created when the model was built in visualNastran or in the CAD system. In this step, you will move the piston assembly’s configuration so that the simulation starts halfway through the combustion compression cycle.

7) Click the Move tool in the Edit toolbar.

8) Move the mouse over the side surface of the crankshaft counterweight.

As you move the mouse over objects in the modeling window, a dashed box appears around them to show that they are framed. (Figure 4)

III - Initial Conditions

Figure 4 Bounding Box


9) Hold the mouse button down, and drag the mouse to rotate the crankshaft.

As you drag the mouse, the crank rotates around the crank pin.

10) Position the crankshaft so that the piston is halfway through the down stroke. (Figure 5)

You can change the configuration by using the Move tool to drag any of the moving parts in the model. Try dragging the piston head or the connecting rod.

Note: The movement stops when the parts are dragged to the mechanical limits imposed by the physical joints.


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

12) Click the “Stop” button, then reset the simulation by clicking the “Reset” button.

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

Figure 5 Piston Rotated Halfway through the Full Stroke

III - Initial Conditions


You can add input sliders to dynamically change the properties of a constraint as the simulation is running. You can also use data from a table to control a simulation. Unlike input sliders, the table data input is not an interactive control. In the table, you specify values to be applied at listed times throughout the simulation.

Using an Input Slider as a Simulation Control

In this step, you will add an input slider that controls the angular velocity of the motor that turns the piston’s crank.

13) Select the revolute motor, “Concentric1” in the Object List. (Figure 6)

The revolute motor is selected (even though it may not be visible in the modeling window).

14) In the Insert menu, choose Control>Rotational Velocity.

This displays the Choose Input Type dialog box. (Figure 7)

15) Choose Slider and click OK.

An input slider window appears above the modeling window with the title “Rot. Velocity of Concentric1”. (Figure 8)

Figure 7 Choose Input Type Dialog

IV - Using Simulation Controls

Figure 6 Select Motor

Figure 8 New Input Slider for Rotational Velocity of Motor


16) Select the input slider, then go to the Edit menu and pick Properties.

The input slider’s properties appear in the Properties window.

17) Click the Appearance tab in the Properties window, then enter “Motor Rotational Velocity” as the name for this input slider. (Figure 9)

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

18) Close the “Properties” dialog box.


20) As the simulation runs, try dragging the input slider right and left.

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 through the down stroke. Because the motion history is recorded, you can replay the simulation by hitting the play button. When replaying the simulation, you cannot move the slider and erase the previously recorded motion history. To erase it, go to the World pull-down menu and select Erase Motion History.

22) Click the “x” box in the right upper corner to closethe input slider window.

The input slider is still available in the Object List, but it is temporarily hidden from view. You can re-display the input slider by double-clicking it in the Meter tab of the Object List.

Figure 9 Properties Window (Appearance Page )

IV - Using Simulation Controls

Figure 10 Motor Rotation Velocity


You can also use data from tables to control a simulation. You can directly enter data in a table in visualNastran, or you can import the table data from a file.

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

Note: The default table configuration is to index value parameters to time. However, you can index value parameters to any other variable. To do so, you use Formulas as shown below.

To create an input control for table data:

23) Select “Concentric1”, a revolute motor, in the Object list.

24) In the Insert menu, choose Control>Torque.

Choose “Table” when the Input Type dialog box appears. (Figure 11)

25) Click “OK”.

The Table window is shown in Figure 12.Figure 12 Properties Window for Table Input

V - Using Table as Simulation Controls

Figure 11 Table Input Type


26) You can either open up the Data Table located on the CD and Copy and Paste the information directly to the cells or use the Browse Button to find the file containing table data.

The Lookup entries of the dependent variable (i.e., the “value” or 2nd column). (Figure 13)

27) Click OK.

28) Run the Simulation.

visualNastran applies the torque values at the time intervals specified in the table during the simulation.

Figure 13 Table Values

V - Using Table as Simulation Controls


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

29) Select “Piston Pin-1” in the Object List.

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

30) Select “Concentric5”, the revolute joint that connects the connecting rod to the piston pin, in the Connections List. (Figure 14)

Note that “coord[39] on Piston Pin-1” and “coord[38] on Connecting Rod-1” are listed as the Coords attached to “Concentric5” in the Connections List.

31) Choose Meter in the Insert menu, then choose “Constraint Force...” in the Meter submenu.

The Constraint Force Settings dialog appears as shown in Figure 15.

32) Measure Concentric5 Force on “Connecting Rod-1” expressed in “coord[38] on Connecting Rod-1” and click “OK”. (Figure 15)

The Tiling Options dialog appears.

VI - Measuring Reaction Forces

Figure 15 Constraint Force settings Dialog

Figure 14 Concentric5


33) Select Tile Horizontally and click OK.

A new meter window opens, titled “Concentric5 Force on Connecting Rod-1 in coord[38] on Connecting Rod-1”, as shown in Figure 16. The new meter will display the x, y, and z components and the total constraint force exerted by “Concentric5” on the “Connecting Rod-1” as separate plots.

34) Click the Run button in the Tape Player Control.

As the simulation runs, the values of the x, y, and z components and the total constraint force between the piston pin and the connecting rod is plotted in the meter window. Notice how Fx and Fy oscillate as the crank rotates through a full stroke. (Figure 17)

Note: Your results may not match Figure 17. The appearance of the plots depends upon the initial position of the Crankshaft and the Torque values inside the table driving the motor.

35) Click the “Stop” button, then reset the simulation by clicking the Reset button.

The piston assembly returns to the initial position.

36) Click the close box in the meter window.

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

Figure 16 Simulation Window and Meter.

VI - Measuring Reaction Forces

Figure 17 Constant Force Meter Window


visualNastran allows you to visualize vectors in 3D space as the simulation runs. Although the animated simulation itself serves as a powerful visualization tool, hard-to-see qualitative data such as vectors reveal even more information that can’t be seen in a physical prototype.

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

37) Double-click “Connecting Rod-1” in the Object List. (Figure 18)

The connecting rod’s properties appear in the “Properties” dialog box. Since the “Vectors” tab is unavailable, we must pick it from the Properties List.

38) Click the “Vectors” checkbox in the Properties List. (Figure 19)

The “Connecting Rod-1” dialog box appears opened to the Vectors tab.

39) With the Vectors tab on top, click the “Angular Acceleration” vector box to put a check mark in it, and then close the “Properties” dialog box. (Figure 20)

40) Click the arrow next to the sphere in the toolbar and pick the wireframed sphere. (Refer to toolbar above)

Make sure the modeling window is highlighted before clicking the Wireframe. The modeling window changes to a wireframe rendering, which will make it easier for you to see the acceleration vector (which is often hidden by the sides of the crank) as the simulation runs.

Figure 20 Inserting Vectors

VII - Inserting Vectors

Figure 18 Connecting Rod

Figure 19 Properties List



As the simulation runs, the acceleration vector is displayed, but can be difficult to see because it is size. In the next step, you will resize the acceleration vector to make it easier to see.



VII - Inserting Vectors

Figure 21 Run Simulation


Figure 23 Color Palette

VIII - Scaling Vectors

You can Change the size and color of the vectors displayed to make it more visible as the simulation runs.

43) Choose Display Settings in the World menu and click the Vectors Tab.

The Vector Setting Dialog appears. (Figure 22)

44) Enter “0.07” for the scaling factor for the length of the “Angular Acceleration” vector and press “Enter” or click “Apply”.

The default value is 0.0175. If you quadruple the scaling factor, the angular acceleration vectors will now be four times as long.

45) Click the green color button next to the “Angular Acceleration” vector field.

A color palette will appear. (Figure 23) Figure 22 Vector’s Tab


46) Click the “Other” button to select a different color for the vector.

The Color Dialog appears. (Figure 24)

47) Choose a bright red color and click “OK” to close the Color dialog box.

The Angular Acceleration vector will now be displayed in red.



As the simulation runs, note that the acceleration vector attached to the connecting rod switches sides (because the acceleration switches direction halfway through the full cycle). (Figure 25)



Figure 24 Color Dialog

Figure 25 Angular Acceleration Vector on Connecting Rod

VIII - Scaling Vectors


IX - Seeing Through Bodies

MSC.visualNastran provides an alternative to selecting a shaded or wireframe view of your drawing. The alternative is variable translucency, a feature that allows you to quickly render one or several bodies translucent. This is helpful when you want to view internal constraints and coords or obstructed bodies before or during a simulation.

51) Choose Shaded from the View menu.

The piston becomes a solid gray color again.

52) Double-click the piston head.

The “Properties” dialog box appears.

53) Place a check in the “Color” checkbox by clicking inside the square next to the “Color” field in the Properties list. (Figure 26)

The Color dialog box appears as shown in Figure 27.

54) Enter “0.4” in the “Translucency” text region and click “Apply”.

The piston head is rendered translucent as shown in Figure 28.

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


Figure 27 Properties Window Color Page

Figure 28 Piston Head with Translucency of 0.4

Figure 26 Properties List


Up to this point, the piston mechanism has been driven by a motor constraint attached to the crankshaft. In a more realistic simulation of an internal combustion engine, a throttle force generated by a gas explosion in a cylinder chamber would push the piston down to torque the crankshaft. In this last step, you will fine-tune the model to simulate this more realistic scenario.

Convert the Motor

First, you will convert the motor to a revolute joint.

56) Double-click the revolute motor, “Concentric1” in the Object List.

The constraint’s properties are displayed in the Properties window.

57) Click the Constraint tab.

58) Select “Revolute Joint” from the list of available constraints and close the “Properties” dialog box. (Figure 29)

The motor is replaced by a revolute joint.

X - Fine-Tuning the Simulation

Figure 29 Constraint Settings Dialog


Next, you will attach a force load to the top of the piston to simulate the force generated by a gas explosion in a cylinder chamber.

59) Click on the background to de-select everything.

60) Press “T” on the keyboard, so that you can see the top of the piston head.

61) Click the Rotate Around tool in the View toolbar and use the mouse to rotate the piston.

Position your view to look similar to Figure 30. The Piston Head has been shaded with zero translucency for demonstration purposes.

62) Click the Force tool in the Sketch toolbar.

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

The precise location of the attachment is not important for this exercise.

XI - Attaching Force Load

Figure 30 Top View


Figure 31 Properties Window (Force Page)

64) Double-click the force icon in the modeling window or in the Object List.

The force’s properties appear in the Properties window.

65) Click the Structural Load tab, then enter “–10” in the y-field to apply a 10 Newton force downward. (Figure 31)

The force’s Coord attachment dictates this orientation setting.


67) 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 because the force is applied constantly, which isn’t a realistic scenario.



XI - Attaching Force Load


Figure 32 Formula Editor Dialog (Active Page) for Force

XII - Modify the Force to Simulate Realistic Throttle

As a final step, you will modify the force to simulate realistic throttle by using a formula to control when the force is applied.

70) Double-click the force icon in the modeling window or in the Object List.

The force’s properties appear in the Properties window.

71) Click the Active tab.

This displays the Active Page of the Properties window.

72) Click the “Active while:” radio button, then click on the ‘…’ button.

This displays the Formula Editor dialog as shown in Figure 32.

73) Delete the current Formula.

74) Enter the following formula, and click “OK”:

and(body[12].v.z<=0, mag(body[4].w)<600 rpm)

The expression returns angular velocity in radians per second. The formula applies the explosive force only when the piston is coming down, and cuts off the push to limit the motor to approximately 600 rpm.

75) Close the “Properties” dialog box and run the simulation.

The piston behaves as expected under the realistic throttle force.

Figure 33 Properties Window (Active Page) for Force


Figure 34 Units Page

XIII - Verify the Result

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

76) Select “Crank-1”, the left half of the crank, in the Object List.

77) In the Insert menu, Choose Meter>Angular Velocity.

78) In the pop-up dialog box, accept the default tiling option.

A new meter window appears.

79) In the World menu, choose Display Settings.

80) Click on the Units tab of the Display Settings window. (Figure 34)

81) Choose “rpm” in the “Rot. Vel.” pull-down list. (Figure 34)

82) Close the “Settings” dialog.

83) Run the simulation.

As the simulation runs, the angular velocity, |W|, grows to approximately 600 rpm, then levels off. (Figure 35)


Figure 35 Angular Velocity Meter

XIII - Verify the Result

ws08-1 vnd101, workshop 08 msc.visualnastran 4d exercise workbook analyzing the piston model

Documents

object list

connections list

object manager list

piston model slide

piston head

piston assembly figure

piston pin

piston mechanism