146 - understanding local sensitivity design studies

8/13/2019 146 - Understanding Local Sensitivity Design Studies

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DesignandSensitivityStudiesUnderstandingLocalSensitivityDesignStudiesLecture

UnderstandingLocalSensitivityDesignStudies.mp3Understanding Local Sensitivity Design Studies

Local Sensitivity Studies enable you to calculate how sensitive your

models quantities of interest are to slight changes in the design

variables.

Local Sensitivity Design Study

1% perturbation Helps determine most influential design variables

Design Variable edge_rad vs. Maximum von


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Local Sensitivity Design Study

Local Sensitivity Studies enable you to calculate how sensitive your models quantitiesof interest are to slight changes in the design variables.

In a Local Sensitivity Study, Mechanica perturbs a dimension parameter by 1% toestimate the sensitivity of your quantity of interest with respect to the design variable.Thus, for a given location in design variable space, a Local Sensitivity Design Studytakes a snapshot of the sensitivity of your model subjected to all design variables.Using these sensitivities, you can determine design variables that have the most

influence on the design.

The figures on the slide show three different design variables on which a Local

Sensitivity Study was performed. You can see from the graphs that the starting values

are perturbed plus 1% and minus 1% and that an analysis was run at each value. In

this case, the Local Sensitivity Study gives you an idea of how much impact a small

change in each of the studied design variables will have upon the maximum von Mises

stress in the model.

UnderstandingLocalSensitivityDesignStudiesDemonstrationUnderstandingLocalSensitivityDesignStudies_demo.mp4UnderstandingLocalSensitivityDesignStudiesProcedure

Procedure: Understanding Local Sensitivity DesignStudies

ScenarioIn this procedure, you will set up an analysis that can be used to investigate the effects ofchanging different design variables (2 dimensions) has upon the Von Mises stress and

max displacement measures. Based on this investigation, you can make informed

decisions about which design variables you might select for future Global Sensitivity

Studies.

Local_Sens_DS local_bracket_orig.prt

Task 1.Open the Mechanica application and define a Local Sensitivity Design Study.

1. Click Applications > Mechanica.

The simulation features (material, load, constraints, parameters, static

analysis) are already defined in this model.


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2. Click Mechanica Analyses/Studies from the main toolbar.

3. Click File > New Sensitivity Design Study....

4. In the Name field, type LOCAL_SENS_STUDY.

5. Select Local Sensitivityfrom the Typedrop-down menu.

6. In the Analysessection of the dialog box, select the BRACKET_STATIC (Static)analysis.

7. Click Select Dimension in the Sensitivity Study Definition dialog box (loads andconstraints removed from image for clarity).

8. Select the round feature under the mouse cursor in the figure. Select the R1.00dimension.

9. Select d4in the Variables area of the dialog box and type INNER_FILLET.


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10. Click Select Dimension in the Sensitivity Study Definition dialog box (loadsand constraints removed from image for clarity).

11. Select the Extrude feature as shown in the figure. Select the 7.00dimension.

12. Select d1in the Variables area of the dialog box and type FLANGE_LENGTH.

Note: Mechanica will automatically change these dimensions +/- 1% and run

analysis BRACKET_STATIC at each value to determine the local sensitivity

for each design variable.

13. Click OKto close the Sensitivity Study Definition dialog box and return to the

Standard Pro/ENGINEER mode by clicking Applications > Standard.

14. Click Save from the main toolbar and click OKto save the model.

15. Click File > Erase > Current > Yesto erase the model from memory.

This completes the procedure.

UnderstandingLocalSensitivityDesignStudiesExerciseExercise: Understanding Local Sensitivity Design Studies

Objectives

After successfully completing this exercise, you will be able to:

Prepare a Pro/ENGINEER model for Local Sensitivity Design Studies.


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Use judgment when approaching Local Sensitivity Design Studies. Interpret the results of a Local Sensitivity Design Study. Generate conclusions based on Mechanica findings.

ScenarioIn this exercise, you examine the structural stresses on the components of a jack that lifts

a car with a certain applied torque. When lifting a car, the brackets of the jack aresubjected to loads that transfer from one to another at the joints. The loads developed inthe model are mainly bearing loads and can be easily evaluated using the Mechanism

Design module within Pro/ENGINEER. Because the model is symmetrical (all the loads,constraints, and materials are as well) you can reproduce the structural behavior of the

entire model by simply examining one bracket part of the jack.

Also, it's important to investigate how sensitive the stresses are that developed in the

model due to certain design changes. In addition, you will examine the effects these

design changes have on the bracket's mass. The conclusions from this investigation will

provide important information for a Global Sensitivity and/or Optimization Study.

JackSens up_link.prt

Task 1.Open the Mechanica Structure Mode and Investigate the UP_LINK.PRT part.

1. Click Applications > Mechanica.

2. Investigate the model and note the existing material definition, bearing load, andconstraints. Additionally, there are midsurface shell idealizations because the model

is very thin and of uniform thickness.


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Task 2.Compress and mesh the model using shell idealizations.

1. Click AutoGEM > Review Geometry...from the main menu. Click Applyfrom the

Simulation Geometry dialog box.

2. After you have examined the Shell surfaces, click Closein the Simulation Geometrydialog box.

3. Click Create from the main menu. Click Createfrom the AutoGEM dialog box.

4. Examine the resulting mesh and note the generation of about 80 shell elements.

5. Click Closefrom the AutoGEM Summary dialog box and Closeto close theAutoGEM dialog box. Click Noto close the AutoGEM information window.


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Task 3.Examine the maximum von Mises stress developed in the model due to theloads and constraints.

1. Click Mechanica Analyses/Studies from the main toolbar. SelectStatic_Analysis_3D_SHELLfrom the list in the Analyses and Design Studies

dialog box.

This analysis has been previously defined. It evaluates the structural

response to the bearing loads while fully constrained at the opposite end.

Also, the analysis evaluates the max von Mises stress using a multi-passadaptive convergence algorithm.

2. Click Start Run > Yesto start the analysis.


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3. Click Display Study Status once the analysis is started. When the analysis

completes, note the maximum Von Mises stress measure from the Run Status.

The max Von Mises value is listed as a default measure at the end of the

summary report. The max_stress_vm value is currently 472 MPa and

exceeds the allowable stress, 240 MPa. We can confidently say that the

bracket will fail due to structural stresses and we will look for model changes

in order to avoid this failure. These design changes will be covered in the

upcoming tasks.

4. Click Closefrom the Diagnostics and Run Status windows.

Task 4.Examine the buckling effects in the model due to the loads and constraints.

1. From the Analyses and Design Studies dialog box, select

Buckling_Analysis_3D_SHELLfrom the list of Analyses and Design Studies.


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The analysis has been previously defined. It evaluates the Buckling Load

Factor (BLF) from the bearing loads while fully constrained at the opposite

end.

2. Click Start Run > Yesto start the analysis.

3. Click Display Study Status once the analysis is started. When the analysiscompletes, note the BLF factor from the Run Status.

The BLF value is roughly 3. This means that you can apply about three times

the existing load without any buckling failures. From this, you can conclude

that you should concentrate on the maximum von Mises stress in the model

and limit it to 240 MPa or less.

4. Click Closefrom the Diagnostics and Run Status windows.

Task 5.Consider different design change scenarios and their anticipated effects onthe von Mises stress, and total mass measures.


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1. Our current task is centered on finding valid design changes in the model. This

translates to finding design variables (in this case, dimensions) that you can changeto limit the von Mises stress to 240 MPa or less.

There are more than 15 dimensions to select from the model, but you have to use yourbest judgment when determining which are important:

You cannot shorten the length of the bracket because the jack wont lift to theappropriate height.

Also, increasing the jack height would increase the likelihood that the jack bracketscould buckle.

You cannot modify the holes because they are designed for standard pins that fitthrough them in the assembly.

Thus, the model dimensions you can modify are the thickness of the bracket(adding more will reduce the stress) and the radial offset.

Additionally, you can add the curved edge radius (shaving off material will decreasethe total mass of the bracket).

2. Next, you investigate the effects of the mentioned design variables upon the max

Von Mises stress and total mass measures using a Local Sensitivity Design Study.Based on this study you can establish which one of these design variables

contribute dramatically to the measures of interest and which will be eliminatedfrom further investigation.

Task 6.Define a Local Sensitivity Study and Design Variables.

1. Click File > New Sensitivity Design Study...from the Analyses and Design

Studies dialog box. Type LINK_LSDSin the Name field.

2. From the Type drop-down menu, select Local Sensitivity.

3. Select STATIC_ANALYSIS_3D_SHELLfrom the Analyses list.


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4. Click Select Dimension from the Variables area of the dialog box.

5. Select Shell id 528from the model tree.

6. Select the resulting 3.81dimension from the display area.


8. Select Cut id 91from the model tree.



11. Select Cut id 91from the model tree.


13. The values in the Variables area of the dialog box should appear as shown in the

figure below. Click OKto complete the Sensitivity Study Definition and close the

dialog box.

Task 7.Run the Local Sensitivity Study.

1. Verify that LINK_LSDSis selected in the list of Analyses and Design Studies and

click Start Run > Yesto start the design study.

2. Click Display Study Status once the analysis is started.

The design study should complete in a few minutes. Once the analysis is

completed, you will create graphs for the measures of interest versus the

design variables.


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Task 8.Examine the design study results for von Mises stress.

1. Verify that LINK_LSDSis still selected in the Analyses and Design Studies dialogbox and click Results to start Results mode.

2. Type EDGE_RADin the Name field and von Mises vs. Edge Radiusin the Title

field.

3. Verify that the drop-down menu in the Display type area of the dialog box is set to

Graphand that the Graph Ordinate (vertical) Axis field is set to Measure.4. Click Define Measure to open the Measures dialog box.

5. Select max_stress_vmfrom the list of Measures and click OKto close the

Measures dialog box.

6. From the second drop-down menu in the Graph Location area of the dialog box,select edge_rad:UP_LINK, if required.

7. The dialog box should now appear as shown in the figure. Click OK and Showto

complete the Result Window Definition and show the resulting graph.


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8. Click Copy from the main toolbar in the Results window.

9. Type RAD_OFFSETin the Name field and von Mises vs. Radial Offsetin the Title

field.

10. From the second drop-down menu in the Graph Location area of the dialog box,

select radial_offset:UP_LINK.




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13. Type THICKin the Name field and von Mises vs. Thicknessin the Title field.

14. From the second drop-down menu in the Graph Location area of the dialog box,select thick:UP_LINK.

15. The dialog box should now appear as shown in the figure. Click OK and Showtocomplete the Result Window Definition and show the resulting graph.


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16. Examine the resulting graphs.

The software varies each of the design variables, one at a time, 1% of the

current settings to estimate the derivative of the max_stress_vm measure.

Thus, for a given location in design variable space, the design study takes a


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snapshot of the sensitivity of the max_stress_vm measure to changes in

each design variable.

You now need to quantify this in the graph format: a sharper slope indicates

that the design variable dramatically affects the defined measure whereas a

flat slope does not. For the purposes of comparison, you should set the Y-

axis for all of the design measures to the same scale. You will not modify the

X-axis range.The minimum of all the Y-axes is 462 and maximum is 481 (MPa), so you

will adjust all the graphs to these new Y-axis values in order easily compare

the slopes of each graph.


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17. Select the von Mises vs. Radial Offsetgraph. Click Utilities > Tie > GraphQuantityfrom the main menu and select the von Mises vs. Thicknessgraph.

Note how the Y axis values in the von Mises vs. Thicknessis now tied to

the same values that are in the von Mises vs. Radial Offsetgraph.

You could also get the same effect by selecting a graph, clicking Format >Graphand manually setting the Maximum and Minimum values.

18. Select the von Mises vs. Thicknessgraph. Click Utilities > Tie > Graph

Quantityfrom the main menu and select the von Mises vs. Edge Radusgraph.

With all of the Y-axes set to the same scale, it is much easier to compare the

slopes of each parameter.

From these three graphs you can conclude that the Von Mises stress is

sensitive to changes in the radial_offset design variable, less sensitive to

changes in the thick design variable, and relatively insensitive to changes in

the edge_rad design variables.

Based on this information, you should consider the radial_offset and thick

design variables in future Global Sensitivity and Optimization Studies.


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Task 9.Examine the design study results for total mass.

1. Click Show Definitions from the main toolbar.

2. De-select all of the items in the list except EDGE_RADand click OK.

3. Click Edit Selected Definition from the main toolbar.

4. Type Mass vs. Edge Radiusin the Title field.

5. Click Define Measure to open the Measures dialog box.

6. Select total_massfrom the list of Measures and click OKto close the Measuresdialog box.




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9. Type THICK_MASSin the Name field and Mass vs. Thicknessin the Title field.


select thick:UP_LINK.




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12. Click Copy from the main toolbar in the Results Window.

13. Type RAD_OFFin the Name field and Mass vs. Radial Offsetin the Title field.


select radial_offset:UP_LINK.

15. The dialog box should now appear as shown in the figure. Click OK and Showtocomplete the Result Window Definition and show the resulting graph.


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The minimum in all the Y-axes is 171 and maximum is 175 (grams). As

before, you will adjust all the graphs to the new Y-axis values in order to

more easily compare the slopes.

16. Select the Mass vs. Thicknessgraph. Click Utilities > Tie > Graph Quantityfrom the main menu and select the Mass vs. Radial Offsetgraph.

17. Select the Mass vs. Radial Offsetgraph. Click Utilities > Tie > Graph

Quantityfrom the main menu and select the Mass vs. Edge Radiusgraph.


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18. Examine the resulting graphs and make conclusions about the design variableeffects on the total_mass measure.

From these three graphs you can conclude that the mass of the bracket is

sensitive to all of the design variables changes, especially the thickdesign

variable. This is a rather obvious engineering observation (increasing or

decreasing the thickness changes the mass of the bracket).

The edge_radand radial_offsetdesign variables sensitivities are similar.

As such, you should consider all these design variables for future Global

Sensitivity and Optimization Studies where you are concerned about

affecting the total mass measure.

19. Click File > Exit Results > Noto exit the Result Window without saving anyresults.

20. If necessary, return to the Standard Pro/ENGINEER mode by clicking Applications

> Standard.

21. Click Save from the main toolbar and click OKto save the model.22. Click File > Erase > Current > Yesto erase the model from memory.

This completes the exercise.

146 - understanding local sensitivity design studies

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