1. Modal Analysis of an Exhaust Manifold using NX CAE
WMCAE User Community Meeting
March 9, 2016
Sreedhar Chanda
Gary Webb

2. INTRODUCTION Modal analysis
Modal Analysis of an Exhaust Manifold using NX CAE
INTRODUCTION
Modal analysis
It involves calculation of natural frequencies and mode shapes of structure.
It can be done using physical testing, but it is much faster and cost effective to use CAE instead.
Natural frequency and its corresponding mode shape depend only on the distribution of stiffness and mass the assembly of parts. They help us quantify the flexibility of a structure.
In general, for a given structure, a very large number of natural frequencies can be calculated. But engineers usually calculate a few, depending on their field of interest.
The design goal is to keep the structure’s natural frequency away the frequency of excitation to avoid a resonance condition. The resonance condition will cause excessive vibration of the structure resulting in noise and eventually the structure’s failure.
Exhaust manifold and other components bolted to an automobile engine generally need to have a first natural frequency above 250 Hz.

3. 1.Load .prt file into NX. Set Load Options to “As Saved”.
Modal Analysis of an Exhaust Manifold using NX CAE
Model Preparation
1.Load .prt file into NX. Set Load Options to
“As Saved”.

4. Model Preparation (Cont’d)
Modal Analysis of an Exhaust Manifold using NX CAE
Model Preparation (Cont’d)
2.From Modeling, go to Gateway. Then File/Utilities/
Select Bundles…

5. Model Preparation (Cont’d)
Modal Analysis of an Exhaust Manifold using NX CAE
Model Preparation (Cont’d)
3. Add Advanced Simulation Bundle.
4.After Advanced Simulation Bundle has been
selected, go into Modeling/ Application/ Advanced.

6. 6.Select the Body, then click Automatically Create Face Pairs
Modal Analysis of an Exhaust Manifold using NX CAE
Mid-surface Creation
5.To create a Midsurface, in most instances, click on Midsurface by Face Pairs
6.Select the Body, then click Automatically Create Face Pairs

7. 7.Once Midsurfaces have been created go to New FEM and Simulation
Modal Analysis of an Exhaust Manifold using NX CAE
FEM Creation
7.Once Midsurfaces have been created go to New FEM and Simulation

8. Modal Analysis of an Exhaust Manifold using NX CAE
FEM Creation
8. In New FEM and Simulation, toggle on Create Idealized Part. Under Bodies, switch to All Visible.

9. Manage Materials
9. Within FEM, click on Manage Materials.
10. Select the from the NX Material Library. Once the material has been selected then click Load Library Material into File.

10. Physical Properties
11. Select the appropriate Property, then click Create
12.Fill in appropriate Name. Select the Material, and correct Thickness.

11. Mesh Collector
13.Select Element Family and the Shell Property.

12. MESHING
14. 2D Mesh Collectors created
15. Create 2D Elements. Set Meshing Method and Element Size. Select appropriate Collector

13. MESHING

14. Modal Analysis of an Exhaust Manifold using NX CAE
Solution-Step 1

15. Modal Analysis of an Exhaust Manifold using NX CAE
Solution-Step 2

16. Modal Analysis of an Exhaust Manifold using NX CAE
Solution-Step 3

17. Solution-Step 3 (detail settings)
Modal Analysis of an Exhaust Manifold using NX CAE
Solution-Step 3 (detail settings)

18. Modal Analysis of an Exhaust Manifold using NX CAE
Solution-Step 4

19. Modal Analysis of an Exhaust Manifold using NX CAE
Solution-Step 5

20. Solution-Step 6 This hole has 4 edges bringing total 11 objects.
Modal Analysis of an Exhaust Manifold using NX CAE
Solution-Step 6
This hole has 4 edges bringing total 11 objects.

21. .. Is being used in nat_freq
Modal Analysis of an Exhaust Manifold using NX CAE
Solution-Step 7
This constraint …
.. Is being used in nat_freq

22. Modal Analysis of an Exhaust Manifold using NX CAE
Solution-Step 8

23. Modal Analysis of an Exhaust Manifold using NX CAE
Solution-Step 9

24. Solution-Step 10 (intermediate screen shot)
Modal Analysis of an Exhaust Manifold using NX CAE
Solution-Step 10 (intermediate screen shot)

25. Solution-Step 10 (final screen shot)
Modal Analysis of an Exhaust Manifold using NX CAE
Solution-Step 10 (final screen shot)

26. Solution-Step 11 Double-click Results
Modal Analysis of an Exhaust Manifold using NX CAE
Solution-Step 11
Double-click Results

27. First natural frequency = 1025 Hz > 250 Hz
Modal Analysis of an Exhaust Manifold using NX CAE
Solution-Step 12
First natural frequency = 1025 Hz > 250 Hz
Target Achieved
Animation setup for mode shape is shown next
5 modes as per output request

28. 2 1 Solution-Step 13 Click play icon
Modal Analysis of an Exhaust Manifold using NX CAE
Solution-Step 13
Click play icon 2 1

29. Modal Analysis of an Exhaust Manifold using NX CAE
Solution-Step 14

30. Better look for presentation.
Modal Analysis of an Exhaust Manifold using NX CAE
Solution-Step 15
Better look for presentation.

31. Modal Analysis of an Exhaust Manifold using NX CAE
Solution-Step 16

32. Solution-Step 17 (two options)
Modal Analysis of an Exhaust Manifold using NX CAE
Solution-Step 17 (two options) OR

33. Modal Analysis of an Exhaust Manifold using NX CAE
MOST COMMON NEXT STEP
The next step commonly performed in CAE is the frequency response calculation. In this step, a vibration load is applied to the structure, usually at the mounting holes of the manifold inlet flange and the response of the structure is calculated.