nx tutorial motion simulation including modal flexibility of … · 2018. 11. 20. · in nx, and it...

NX TUTORIAL

Motion Simulation Including Modal Flexibility of Components

NX 9

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ATA Engineering NX 9

Motion Simulation Including Modal Flexibility Tutorial in NX

Content subject to change without notice. © 2018 ATA Engineering, Inc. NX is a trademark of Siemens PLM Software, Inc.

Overview

This document walks through a motion simulation of a crank-slider mechanism using NX 9. RecurDyn is one of the motion solvers embedded in NX, and it will be used in this tutorial.

Software:NX 9

Difficulty Level:Intermediate

Preceding Tutorial:None

Input Files Required:crank_slider.x_t beam_sim1-flex.datbeam_sim1-flex.op2beam_sim1-flex_0.op2beam_sim1-flex_0.rfi

Output Files Created:crank_slider.prt

This tutorial is part of a series of free Siemens PLM Software training resources provided by ATA. For more tutorials, whitepapers, videos, and macros, visit ATA’s PLM Software website: http://www.ata-plmsoftware.com/resources.

http://www.ata-plmsoftware.com/resources



Content subject to change without notice. © 2018 ATA Engineering, Inc. NX is a trademark of Siemens PLM Software, Inc.

Concepts• Importing geometry

• Creating links

• Creating joints

• Creating flexible links

• Prescribed motions

• Analyzing and postprocessing the model

Figure 1: ▶ Example of NX motion model generated through this exercise.



1 Content subject to change without notice. © 2018 ATA Engineering, Inc. NX is a trademark of Siemens PLM Software, Inc.

ContentsTutorial 21. Introduction 2

1.1. Input Files Required 21.2. Output Files Created 2

2. Importing Geometry 32.1. Importing the Geometry into NX 3

3. Model Definition 53.1. Setting Up the Analysis 53.2. Creating the Links 63.3. Creating the Joints 103.4. Creating Flexible Links 163.5. Prescribing Relative Motions 19

4. Running the Simulation 204.1. Analyzing the Results 21




Tutorial

1. IntroductionThis document provides a description of a motion analysis for NX 9. The tutorial will take you step by step through the process of taking a model of a simple crank-slider mechanism from the part file to create a motion simulation of the model with parts moving together. It will also take a look at applying a flexible analysis to the motion simulation to see how part of the model will be reacting throughout the motion.

1.1. Input Files RequiredThe following files are provided:crank_slider.x_t beam_sim1-flex.datbeam_sim1-flex.op2beam_sim1-flex_0.op2beam_sim1-flex_0.rfi

1.2. Output Files CreatedThe following files will be created during this demonstration:crank_slider.prt

Figure 1-1: ▶ Example crank-slider model.




2. Importing GeometryThe Parasolid file geometry must be imported into NX.

2.1. Importing the Geometry into NX

1. File → New

2. Choose a new model and set the units to inches. Name the file “crank_slider.prt” and set the folder to your working folder

Figure 2-1: ▶New NX model.




3. File → Import → Parasolid and select the file crank_slider.x_t, which should be placed in your working folder. The imported geometry includes a 6″ crank, a 12″ connecting rod, and the slider.

Figure 2-2: ▶Imported geometry.




3. Model DefinitionNow, create the rigid bodies that will form the mechanism.

3.1. Setting Up the Analysis

1. File → Motion Simulation

2. Right-click on crank_slider (in the Motion Navigator), select Dynamics, check Flexible Body Dynamics, and set the simulation name to “simulation1”. Click OK.

The dynamics analysis type is used for a model with more than one degree of freedom. External loads can generate motion, and different contact effects are available. Using the flexible body analysis solution option enables the Flexible Link command and the Flexible Body solution type.

Figure 3-2: ▶Simulation Environment window.

Figure 3-1: ▶Motion Navigator window.




3. The simulation environment is now set up and ready to create the different motion components.

3.2. Creating the Links

1. Right-click on simulation1 and select New Link.

2. Highlight and then click on the crank link (the yellow body in the original geometry), and set the mass properties option to Automatic. Alternatively, the user can specify the mass properties manually by selecting User Defined in the Mass Properties option.

3. Name the link “crank”. Click OK.

Figure 3-4: ▶Link properties window and selection: crank.

Figure 3-3: ▶Motion Navigator window with new simulation.




4. To check the mass properties, right-click on the newly created crank link and select Information. Note that the assembly is made of steel, which was specified in the Parasolid file.

Figure 3-6: ▶Mass properties Information window.

Figure 3-5: ▶Link properties window: crank.




5. Repeat the process to define the connecting rod. Right-click on simulation1 and select New Link.

6. Highlight and then click on the connecting rod link (the green body in the original geometry), set the mass properties option to Automatic, and name the link “connecting_rod”. Click OK.

Figure 3-7: ▶Link properties window and selection: connecting rod.




7. Repeat the process with the slider. Right-click on simulation1 and select New Link.

8. Highlight and then click on the connecting rod link (the green body in the original geometry), set the mass properties option to Automatic, and name the link “slider”. Click OK.

Figure 3-9: ▶Link properties window and selection: slider.

Figure 3-8: ▶Link properties window: connecting rod.




9. Save the model.

The process of defining new links defines what bodies will be in motion. Each link can be a group of solids or sheets that will be moving together when motion is defined.

3.3. Creating the Joints

The links are ready to be connected.

1. Right-click on simulation1 and select New Joint → Revolute.

2. Click on Select Link and then click on the crank link shown in the Motion Navigator.

Figure 3-10: ▶Link properties window: slider.




3. Click on Specify Origin and then click on the Point dialog and set the X, Y, and Z coordinates to 0 in., 0 in., and 0 in., respectively. Click OK.

Figure 3-12: ▶Point dialog window: crank and ground joint.

Figure 3-11: ▶Joint properties window and selection: crank and ground.




4. On the Specify CSYS dialog, click on CSYS dialog. The CSYS dialog will open. Set the type to X-axis, Y-axis, Origin. Click on the Point dialog of the origin point and set the X, Y, and Z coordinates to 0 in., 0 in., and 0 in., respectively. Click OK.

5. Click on the Vector dialog of the X-axis. Set the type to XC-Axis. Click OK.

6. Click on the Vector dialog of the Y-axis. Set the type to YC-axis. Click OK. The joint coordinate will have its Z-axis parallel to the global Z-axis. Note that the local Z-axis is the revolute joint relative axis of rotation. Click OK.

7. Name the joint “crank-ground”. Click OK.

8. Highlighting the newly created joint on the Motion Navigator will give the user visual information regarding the joint orientation and connectivity.

Figure 3-14: ▶Vector dialog window: crank and ground joint.

Figure 3-13: ▶CSYS dialog window: crank and ground joint.




9. Repeat the process for the revolute joint connecting the crank and the connecting rod. Right-click on simulation1 and select New Joint → Revolute.

10. Under the Action header, click on Select Link and then click on the crank link shown in the Motion Navigator. Under the Base header, click on Select Link and then click on the connecting rod link shown in the Motion Navigator.


12. On the Specify CSYS dialog, click on CSYS dialog. The CSYS dialog will open. Set the type to X-axis, Y-axis, Origin. Click on the Point dialog of the origin point and set the X, Y, and Z coordinates to 6 in., 0 in., and 0 in., respectively.


14. Click on the Vector dialog of the Y-axis. Set the type to YC-axis. Click OK. The joint coordinate will have its Z-axis parallel to the global Z-axis. Click OK.

15. Name the joint “crank-rod”. Click OK.


Figure 3-15: ▶Graphical representation: crank and ground joint.




17. Repeat the process for the revolute joint connecting the crank and the connecting rod. Right-click on simulation1 and select New Joint → Revolute.

18. Under the Action header, click on Select Link and then click on the connecting rod link shown in the Motion Navigator. Under the Base header, click on Select Link and then click on the slider link shown in the Motion Navigator.




22. Click on the Vector dialog of the Y-axis. Set the type to YC-axis. Click OK. The joint coordinate will have its Z-axis parallel to the global Z-axis. Click OK.

23. Name the joint “rod-slider”. Click OK.


Figure 3-16: ▶Graphical representation: crank and connecting rod joint.




25. Repeat the process for the sliding joint that connects the slider to the ground. Right-click on simulation1 and select New Joint → Slider.

26. Under the Action header, click on Select Link and then click on the slider link shown in the Motion Navigator.



29. Click on the Vector dialog of the X-axis. Set the type to −ZC-Axis. Click OK.

30. Click on the Vector dialog of the Y-axis. Set the type to YC-Axis. Click OK. The joint local Z-axis will now be oriented along the global X-axis. The local Z-axis is the relative axis of motion between the ground and the slider.

31. Name the joint “slider-ground”. Click OK.

32. Highlight the newly created joint on the Motion Navigator to verify its connectivity and orientation.

Figure 3-17: ▶Graphical representation: crank and connecting rod joint.




33. Save the model.

These joints are what will connect the links of the model and define the types of motion that each link will have relative to each other. Overconstraining the motion of the model with joints will cause an error when solving but will not cause the solution to not run; the degree of freedom overconstrained will simply be released until constrained properly automatically. This may cause unanticipated results and motion and should be noted in the solution.

3.4. Creating Flexible Links

1. Right-click on simulation1 and select New Flexible Link.

2. In the flexible link dialog, select as Link the connecting rod rigid link defined earlier.

3. Under Flexible Model, browse and select the beam_sim1-flex_0.rfi file. This file contains the finite element information of the connecting rod link, which was modeled as a beam of rectangular cross-section (1.2 in. x 0.5 in.) with 21 nodes (126 DOF) reduced to a flexible component with 20 modes: 6 rigid and 14 elastic modes.

4. Set the placement method to Three Point Method. The flexible link will be positioned along the centerline of the connecting rod.

5. Under Positioning Pair, click on Select Node and then select the beam origin node by clicking on it in the Flexible Link Preview window.

6. Click on Specify Point and then click on the Point dialog and set the X, Y, and Z coordinates to 6 in., 0 in., and 0.465 in., respectively. The beam origin will be located here.

7. Under 1st Orientation Pair, click on Select Node and then select the beam origin node by clicking on it in the Flexible Link Preview window.

Figure 3-18: ▶Graphical representation: slider and ground joint.




8. Click on Specify Point and then click on the Point dialog and set the X, Y, and Z coordinates to 6 in., 0 in., and 0.465 in., respectively.

9. Under 2nd Orientation Pair, click on Select Node and then select the beam tip node by clicking on it in the Flexible Link Preview window.

10. Click on Specify Point and then click on the Point dialog and set the X, Y, and Z coordinates to 18 in., 0 in., and 0.465 in., respectively. The beam orientation will be based on the first and second orientation points. In this case, its orientation will be parallel to the global system.

11. Name the link “connecting_rod_flex”. Click OK.

Figure 3-19: ▶Flexible Link dialog window.




12. Right-click on the newly created flexible link and select Information to verify the flexible link mass properties, orientation, and position.

13. Save the model.

The flexible link will show data at each step of the motion when viewing the solution as contours, similar to NX Advanced Simulation.

Figure 3-21: ▶Flexible link information.

Figure 3-20: ▶Flexible Link Preview window.




3.5. Prescribing Relative Motions

1. Click on the Driver tab. Select Constant on the Rotation header and set a speed of 100 rev/min. Click OK.

2. Save the model.

This will prescribe motion for this specific joint. Another possibility is to use the separate driver button and then select the joint of choice to prescribe motion.

Figure 3-22: ▶Prescribed rotation: crank and ground joint.




4. Running the Simulation

The modeling phase is now complete. We can now run the simulation.

1. Right-click on simulation1 and click on New Solution.

2. Set the time to 6 s.

3. On the Gravity header, click on Specify Direction, then on the Vector dialog, and then set the type to −YC-Axis. Click OK.

4. Set the name to “solution1”.

Figure 4-1: ▶Solution dialog window.




5. Click OK.

6. Right-click on the newly created solution 1. Click on Solve. After a few seconds of computations, the Motion Navigator should look like the following screenshot.

4.1. Analyzing the Results

1. Click on the Results tab.

2. Click on Play to visually inspect the mechanism behavior.

3. The crank should rotate counterclockwise (about the positive global Z-axis), and the slider should move along the global X-axis.

Figure 4-3: ▶Animation dialog.

Figure 4-2: ▶Motion Navigator window: finished solution.




4. In the Motion Navigator, expand Results and then right-click on XY-Graphing. Click on New to create a new graph.

5. In the Objects tab, select the crank-ground revolute joint. Set the request to Force and the component to TZ. Click on the + icon (located under the Axis Definition header) to add the plot. Click OK.

Figure 4-4: ▶Crank-slider mechanism: animation with flexible connecting rod.




6. The Viewport window will appear. Click on Create New Window.

Figure 4-6: ▶Viewport window.

Figure 4-5: ▶Graph window: crank and ground joint torque.




7. A time plot of the torque required to drive the system will appear.

8. Create a new graph. In the Objects tab, select the slider[Mass Center]. Set the request to Displacement and the component to X. Click on the + icon (located under the Axis Definition header) to add the plot. Click OK.

Figure 4-7: ▶Torque required to drive the flexible crank-slider mechanism.




9. The Viewport window will appear. Click on Create New Window.

10. A time plot of the slider position will appear.

Figure 4-8: ▶Graph window: slider displacement.




11. To inspect the stresses at different time steps, click on the Post Processing Navigator. The imported results should appear.

12. Expand Increment 11, then expand Stress-Element-Nodal, right-click on Von-Mises, and select Plot. A plot of the von Mises stress at time t = 0.06 s on the connecting rod will appear.

Figure 4-10: ▶Post Processing Navigator: Von Mises stress.

Figure 4-9: ▶Slider position.




13. Save the model.

14. Close the model.

Figure 4-11: ▶Von Mises stress along the connecting rod at t = 0.06 s.

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nx tutorial motion simulation including modal flexibility of … · 2018. 11. 20. · in nx, and it...

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