Modal Analysis of a Steel Frame

Transcription

1 Modal Analysis of a Steel Frame Name: Sushanth Kumareshwar Panchaxrimath Department: Mechanical Engineering Course: Powertrain NVH of Electrified Vehicles Date: 11/26/2016

2 SUMMARY A dynamic modal analysis of a steel frame is conducted using two CAE tools from Altair HyperWorks, namely Optistruct and solidthinking Inspire. The geometry of the steel frame from the given engineering drawing is constructed using the CAD sketcher tool that comes pre-built with the Inspire software or using HyperMesh. Modal analysis of the steel frame using free-free condition is performed in both, Optistruct and solidthinking Inspire. Results obtained using Optistruct and Inspire are compared with the given experimental modal analysis results.

3 CONTENTS SL.NO Topics Pg. No 1 CAD Creation 1 2 Model Set-up 6 3 Analysis & Results 11 4 Results Comparison 25 5 Conclusion 31

4 1. CAD Creation Engineering Drawing: The given engineering drawing of the CAD geometry (steel frame) is as shown below: 1 P a g e

5 Geometry Creation using solidthinking Inspire: The above CAD geometry of a steel frame can be designed using the CAD sketcher tool that comes prebuilt with the solidthinking Inspire, an Altair HyperWorks product. The sketching ability of the software is commendable and makes it really simple to build the geometry. The geometry can be then either imported into HyperMesh for preprocessing and analyzed using OptiStruct, or analysis can be performed by using the Inspire software alone. Steps followed: The solidthinking Inspire software is started and the geometry option is selected form the menu. 2 P a g e

6 Rectangles option is selected and the 2D geometry of the steel frame is built as per the given engineering drawing. After the 2D design is completed, the geometry is extruded for a given thickness (1 Inch). The final geometry of the steel frame is shown below. 3 P a g e

7 CAD Creation in HyperMesh The CAD geometry can either be built from scratch or imported into HyperMesh software in many ways. One of the methods is explained below: Nodes and lines are created at intervals as per the given dimensions on the X-Y plane. Next, the 2D elements are created within the boundary of the lines, using the spline option. 4 P a g e

8 The 2D elements are then offset by 1inch, with 4 layers of 3D elements. Later, the 2D surface elements are deleted. This completes the creation of geometry and meshing in HyperMesh. 5 P a g e

9 2. Model Set-up Model Set-up in HyperMesh: Once the geometry and meshing is done, the material properties need to be assigned to the model. Please note, if the geometry is in different units say, inches and has to be converted to millimeters, the entire model must be scaled by a factor of 25.4, before meshing. Right click on the model browser, create material. Material properties: Young s Modulus, E=2.06 E11; Poison s Ratio, NU=0.29; Density, RHO = 7.80E P a g e

10 Next step is to create properties. Right click on the model browser and select create properties. Select the card image as PSOLID. Assign the steel material to this property. 7 P a g e

11 Next, create a load collector. Right click on the model browser and select create load collector. In the load collector, select EIGRL as the card image to request the number of modes. V1 and V2 are the initial and final frequencies. So, enter the value for V1 as 0 and V2 as Next, assign the material property and the property created to the solid elements that are generated. Next step is to define the load step to perform the normal mode analysis. Right click on the model browser and select Create Load Step. Click on the drop-down menu for Analysis type and select Normal modes. 8 P a g e

12 For METHOD (STRUCT), click Unspecified Loadcol. In the Loadcol dialog, select EIGRL and click OK. 9 P a g e

13 Model Set-up in solidthinking Inspire: Once the CAD geometry is created in the built in sketcher of Inspire software, material has to be assigned to the model. Click on structure menu, and select material. A default material or a new material with the properties of the user s choice can be created and assigned to the model. In our case, we can define a new material named, New Steel with the given properties. 10 P a g e

14 3. Analysis & Results Analysis & Results in OptiStruct: Click on the Analysis page and select OptiStruct. Click the OptiStruct button on the right side of the panel. 11 P a g e

15 The OptiStruct solver performs the analysis and provides the results. The analysis is completed once you see the window as shown below. The window can now be closed. 12 P a g e

16 In order to view the results (post processing), click on the HyperView tab in the OptiStruct panel. HyperView is the post processor for all the Altair HyperWorks products. It provides the results and animation for the modal analysis of the steel frame. 13 P a g e

17 In the HyperView window, click on contour plot, and click apply. All the animation results along with the respective values for each mode is displayed upto 1000 HZ (79 modes), as per the given data. 14 P a g e

18 Analysis Results (Mode v/s Frequency) The results are available in the output file created by the solver deck. Another key aspect to note is that, in OptiStruct, the first six modes are the rigid body modes, hence they are filtered, i.e., the first mode in experimental analysis is the same as the 11 th mode in OptiStruct. 15 P a g e

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20 Frequency (Hz) 1.20E E E E+02 Frequency 4.00E E E Modes Analysis Results from OptiStruct (Modes v/s Frequency) 17 P a g e

21 Analysis & Results in solidthinking Inspire: Click on the play button present in the Analyze menu. Select the number of modes for the normal mode analysis. Select the more accurate option, to perform the second order meshing to obtain more accurate results and click on the run icon. 18 P a g e

22 Now the job gets submitted to the built-in solver. 19 P a g e

23 Once the analysis is complete, a green flag appears on the analyze icon. Click the green flag to view the animation results for the various modes. The main advantage in using this software is that, once the geometry is constructed and the material is assigned, it performs automatic meshing and provides the analysis results which saves a lot of time thus, making it a very efficient product. 20 P a g e

24 Animation results: 21 P a g e

25 Result Values: The first mode in experimental analysis is the same as the 5 th mode in Inspire. 22 P a g e

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27 Frequency (Hz) 1.20E E E E+02 Frequency 4.00E E E Modes Analysis Results from Inspire (Modes v/s Frequency) 24 P a g e

28 4. Results Comparison OptiStruct and Inspire analysis results, are compared with the experimental analysis results, for the purpose of validation. This includes two sub sections, namely, comparison of the numerical results and the comparison of the animation results (mode shapes comparison). Comparison of Numerical results: Modal Mode Frequency (Hz) OptiStruct Mode Frequency (Hz) Inspire Mode Frequency (Hz) P a g e

29 Comparison of Mode Shape Animation Results: 1. Modal Mode 1 v/s OptiStruct Mode 11 v/s Inspire Mode 5 Experimental (given) OptiStruct Inspire 26 P a g e

30 2. Modal Mode 2 v/s OptiStruct Mode 14 v/s Inspire Mode 8 Experimental (given) OptiStruct Inspire 27 P a g e

31 3. Modal Mode 3 v/s OptiStruct Mode 18 v/s Inspire Mode 12 Experimental (given) OptiStruct Inspire 28 P a g e

32 4. Modal Mode 4 v/s OptiStruct Mode 20 v/s Inspire Mode 14 Experimental (given) OptiStruct Inspire 29 P a g e

33 5. Modal Mode 5 v/s OptiStruct Mode 24 v/s Inspire Mode 18 Experimental (given) OptiStruct Inspire Modal Mode OptiStruct Mode Shape Inspire Mode Shape 1 Checked Checked 2 Checked Checked 3 Checked Checked 4 Slightly off Slightly off 5 Slightly off Slightly off 30 P a g e

34 5. Conclusion The modal analysis of a steel frame was performed and the results were compared. From the analysis, it is observed that the results obtained from OptiStruct and Inspire CAE tools, match the given experimental results for the first three modes. When the experimental results are compared to the CAE results, a mismatch occurs in the mode shape animation of the 4 th and 5 th mode, Hence, it can be observed that as the mode number and frequency increases, it is difficult to obtain matching results between the CAE tools and experimental analysis. Finally, when the pre-processing, analysis setup, simplicity and post processing is taken into consideration, Altair s solidthinking Inspire tool proved to be the most efficient. 31 P a g e