workshop 4.1 – linear structural analysis

Linear Structural Analysis

Workshop 4.1

August 26, 2005Inventory

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Workshop 4.1 - Goals• Workshop 4 consists of a 5 part assembly representing an

impeller type pump. Our primary goals are to analyze the assembly with a preload on the belt of 100N to test:– That the impeller will not deflect more than 0.075mm with the

applied load.– That the use of a plastic pump housing will not exceed the

material’s elastic limits around the shaft bore.


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Workshop 4.1 - Assumptions• We’ll assume the pump housing is rigidly mounted to the

rest of the pump assembly. To simulate this, a frictionless support is applied to the mounting face.

• Similarly, frictionless surfaces on the mounting hole counter bores will be used to simulate the mounting bolt contacts. (Note if accurate stresses were desired at the mounting holes, a “compression only” support would be a better choice).

• Finally, a bolt load (X = 100 N) is used on the pulley to simulate the load from the drive belt. The bolt load will distribute the force over the face of the pulley only where the belt contact occurs (compression only).


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Workshop 4.1 – Contact Assumptions• For the workshop we will use the 2 forms of linear contact

available in DS, bonded and no separation. It’s important to review and understand all assumptions related to contact behavior when including it in an analysis.


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Workshop 4.1 - Start Page• From the launcher start Simulation.

• Choose “Geometry > From File . . . “ and browse to the file “Pump_assy3.x_t”.

• When DS starts, close the Template menu by clicking the ‘X’ in the corner of the window.


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Workshop 4.1 – Preprocessing1. Set the working unit system to the metric mm system.

– “Units > Metric (mm, Kg, N, C, s)”.

2. Highlight the pump housing (part 1) in the tree.– “Model > Geometry > Part 1”.

3. From details import the material “polyethylene”.

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. . . Workshop 4.1 – Preprocessing• Change the first 4 contact regions

(shown below) to “No Separation”.

4. Hold the shift key and highlight the first 4 contact branches.

5. From the detail window change the contact type to “no separation”.

• The remainder of the contacts will be left as “bonded”.

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Workshop 4.1 - Environment• Apply the bolt load:

6. Highlight the Environment branch.

7. Highlight the pulley surface shown.

8. Insert a bolt load.– “RMB > Insert > Bearing Load”

9. From the detail window change to “Components” and “X = 100 N”.

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. . . Workshop 4.1 - Environment10. Highlight the mating face on the pump housing (part 1).

11. Insert a frictionless support.– “RMB > Insert > Frictionless Support”.

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. . . Workshop 4.1 - Environment• Now we will add the frictionless

supports to the 8 countersink portions of the mounting holes (shown here).

• Each of the required surfaces could be selected individually while holding the CTRL key however we will use a macro (select by size) provided with the DS installation. After selecting the initial surface, running the macro finds and selects all surfaces of the same size (area). Note, this macro also works with edges or bodies.


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. . . Workshop 4.1 - Environment12. Highlight 1 of the countersink surfaces

(arbitrary).

• Run the select by size macro:

13. Choose “Tools > Run Macro . . . “

14. In the browser choose “selectBySize.js”– Note: typical path shown below.

15. “Open”

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C:\Program Files\ANSYS Inc\v100\AISOL\DesignSpace\DSPages\macros


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. . . Workshop 4.1 - Environment• With all surfaces selected apply a frictionless surface

support.

16. “RMB > Insert > Frictionless Support”

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Workshop 4.1 – Macro Notes• The result of running the selectBySize macro is that all

similarly sized surfaces are automatically added to the selection set as shown on the previous page.

• While the selections here (8 surfaces) would be trivial to select individually, this technique can be a valuable time saver when a large selection set is needed.

• Care should be taken when using select by size. All entities of the same size will be selected. Make sure “extra” selections do not occur.

• Other macros are also available in the same directory. Macros are written in Jscript and can be opened and viewed using typical text editors such as Notepad.


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Workshop 4.1 - Solution• Add results to solution:

17. Highlight the solution branch:– “RMB > Insert > Stress > Equivalent (von-Mises)”

18. Repeat to add “Total Deformation”

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. . . Workshop 4.1 - Solution• Because of the presence of frictionless supports non

bonded contact, DS will trigger the use of weak springs during the solution. If we know the model is fully constrained we can turn off this function. Before turning off weak springs make SURE that rigid body motion is prevented. Failing to do so can result in an unconverged solution.

19. Highlight the Solution branch and from the details window change “Weak Springs” from “Program Chosen” to “Off”.

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20. Solve

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Workshop 4.1 – Postprocessing• When the solution is complete highlight the results to plot

each. – While the overall plots can be used as a reality check to verify

our loads, the plots are less than ideal since much of the model is only slightly effected by them.

• To improve the quality of results available we will “scope” results to individual parts”.


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. . . Workshop 4.1 – Postprocessing21. Highlight the “Solution” branch and

switch the selection filter to “Body” select mode.

22. Select the impeller (part 2).

• Insert equivalent stress.– “RMB > Insert > Stress > equivalent (von

Mises)”

• Notice the detail for the new result indicates a scope of 1 Body.

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. . . Workshop 4.1 – Postprocessing• Repeat the procedure on the previous page to insert “Total

Deformation” results for the impeller part.

• Repeat the procedure to add individually scoped stress and total deformation results to the pump housing (part 1).

• Rename the new results as shown here to simplify postprocessing.

• Solve again. – Note: adding new results and resolving the model will not cause

a complete solution to take place. Results are stored in the database and new quantities requires only an update.


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. . . Workshop 4.1 – Postprocessing• By checking the impeller deformation we can verify that

one of our goals is met. The maximum deformation is approximately 0.024mm (goal < 0.075mm).


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. . . Workshop 4.1 – Postprocessing• Inspection of the housing stress shows that, overall, the

stress levels are below the material’s elastic limit (tensile yield = 25 MPa). We can again using the scoping technique to isolate the result in the area of interest.

Maximum stresses

Area of interest


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. . . Workshop 4.1 – Postprocessing• To simplify scoping first hide the pulley and impeller parts.

23. Select the pulley then “RMB > Hide Body” (note: although we are hiding the entire body this also works while in face or edge select mode).

• Repeat for the impeller part.

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. . . Workshop 4.1 – Postprocessing24. Highlight the “Solution” branch and

switch the selection filter to “Face” select mode.

25. Select the 5 surfaces shown on the pump housing (part 2).

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. . . Workshop 4.1 – Postprocessing• Insert equivalent stress.

– “RMB > Insert > Stress > equivalent (von Mises)”

• Notice the detail for the new result indicates a scope of 1 Body.

• Select the back face (shown here) and repeat the process.


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. . . Workshop 4.1 – Postprocessing• Inspect the new results to determine if our goal has been

met.

• Finish the workshop by inserting any figures that you feel are required and generating a Report.

workshop 4.1 – linear structural analysis

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