4221946 Working Model Chapter3
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C H A P T E R
3
Working Model FEA: SolidWorks Exercises
This chapter presents simulation exercises designed to help you get started with Working Model FEA. The exercises are for the following products: • •
Working Model FEA: SolidWorks Working Model 4D
The exercises make use of the Simulation Wizards as well as the Working Model FEA standard menus to set up the problems, submit the simulation to analysis, solve the models, and evaluate results. • •
Exercise 3.1 uses the Stress Wizard to perform stress simulation on a bracket. Exercise 3.2 uses Working Model Shape Optimization to optimize a bracket design.
Exercise 3.1 Stress Simulation on a Bracket
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Exercise 3.1 Stress Simulation on a Bracket Figure 3-1 Choosing the Stress Wizard
This exercise introduces you to the Working Model FEA stress analysis feature. You will use the Stress Wizard to determine the failure stresses (von Mises stresses) generated in the object as a result of an applied pressure. You will then calculate the factor of safety based on von Mises stresses (minimum acceptable factor of safety=1). The Stress Wizard leads you through the entire simulation process.
Getting Started In this section you will open the bracket file in SolidWorks and launch the Stress wizard. From SolidWorks: 1.
Choose Open from the File menu.
This displays the File Open dialog.
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Chapter 3—Working Model FEA: SolidWorks Exercises
2.
Browse the Tutorial folder Chapter 3\Exercise 3.1 and open the Bracket.par file
This opens and displays the Bracket as shown in Figure 3-1.
Note: The default location for the Tutorials folder is Program Files\Working Model
3.
Choose Wizards from the Working Model FEA menu, then choose Stress Wizard from the Wizards submenu.
This launches the Stress Wizard as shown in Figure 3-2.
Figure 3-2 Stress Wizard
Defining the Problem and Units In this section you will define the problem for the Stress Wizard. 1.
Click Begin to initiate the simulation process.
2.
Click Define.
Exercise 3.1 Stress Simulation on a Bracket
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The Wizard creates a simulation model with a default name. The default is the name of your part with the word Model appended.
Figure 3-3 Simulation Model Name Window
3.
Click Next.
This displays the Units tab of the Stress Wizard. 4.
Click Units.
This displays the Desired Units window as shown in Figure 3-4. Since you already specified inches, the units default to the English system.
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Figure 3-4 Desired Units Window
5.
Click Finish and go to the next step.
Specifying Loads In this section you will specify a load for the stress simulation. In Working Model FEA, loads are grouped into named sets that can contain one or more loads. 1.
Click the Loads tab on the Stress Wizard window.
This displays a window that prompts you to accept a default name for the load set. 2.
Click Next.
This displays the How Loads are Applied window as shown in Figure 3-5.
Exercise 3.1 Stress Simulation on a Bracket
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Figure 3-5 How Loads Are Applied Window
3.
Select Face and click Next.
In this problem the load is pressure, which is applied on a face. 4.
Optionally click Change View.
If you need to zoom, rotate, or pan the view before you pick the face, click the “Change View” button. This allows you to access the Desktop View menu or toolbar commands and modify the view as needed. Click OK when you are finished with view modifications. 5.
Click Next.
This displays the Load Geometry window. 6.
Click on the top face of the base portion of the bracket. Be sure the correct face is selected. (You can right-mouse click to select faces.)
7.
Click Pressure (the load type) and then click Next.
This displays the Load Value dialog. 8.
Enter a load value of 50.
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Pressure has a single component perpendicular to the face. Pressure is positive if it is pointing at the face. 9.
Click Next in the Load Value dialog.
This displays the Symbol Data dialog. It lets you control the color and size of the load symbols. Force symbols will appear on the geometry, as shown in Figure 36. A dialog prompts you to create another load.
Figure 3-6 Force Symbols on Bracket Face
10. Click Finish and go to the next step.
Specifying Restraints In this section you will specify a restraint for the stress simulation. In Working Model FEA, restraints are grouped in named sets. 1.
Click the Restraints tab on the Stress Wizard window.
This displays a window that prompts you to accept a default name for the load set. The default load set name is Ex1_brkt_RS.
Exercise 3.1 Stress Simulation on a Bracket
2.
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Click Next.
This displays the Restraints window as shown in Figure 3-7.
Figure 3-7 How Restraints Are Applied Window
3.
Select Face and click Next.
In this problem the restraint is applied on the face. 4.
Click on the back vertical face of the bracket. Be sure the back vertical face is selected.
5.
Click Next.
This displays the Restraint Types window as shown in Figure 3-8.
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Figure 3-8 Restraints Types Window
6.
Select Fixed in the Restraint Type window and click Next.
This prevents the back of the bracket from moving or rotating in any direction. The Wizard displays the Symbol Data dialog, which lets you control the color and size of the Restraint symbols. 7.
Change the symbol size to 0.5 inches and click Next in the Symbol Data dialog.
Force symbols will appear on the geometry, as shown in Figure 39. A dialog prompts you to create another restraint.
Exercise 3.1 Stress Simulation on a Bracket
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Figure 3-9 Restraints and Loads on Bracket
8.
Click Finish and go to the next step.
Specifying Mesh and Getting Results In this section you will analyze your model to get results. You will first specify a mesh for the stress simulation. In Working Model FEA the material used for analyzing the model is actually assigned to the mesh. 1.
Click the Analyze tab on the Stress Wizard window and select Analyze.
This displays the Materials for Mesh dialog. 2.
Select Choose an existing material and click Next.
This displays the Select Existing Material for Mesh window as shown in Figure 3-10.
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Figure 3-10 Select Existing Material or Mesh Window
3.
Scroll the material list to display Steel-ANSI 304. Select it and then click Next.
You are now ready to select the geometry to mesh. 4.
Click Next.
This displays the Analysis Execution window, which specifies the analysis start time. There is an abrupt geometric change where the top edge of the rib joins the vertical part of the bracket and this is likely to cause higher stress concentrations. To get a better picture of the stresses there, you need a fine mesh in that area. To save meshing and analysis time, it is better to specify larger elements in most of the body and apply mesh refinements in the critical areas than to use small elements overall. For this reason, we will use h-adaptivity. 5.
Select h-adaptivity.
Use default values for Map Iterations and Target Error. 6.
Accept Now and Click Finish to submit the model.
Exercise 3.1 Stress Simulation on a Bracket
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The program will first display a Working Model dialog that shows the progress of the Meshing process. Then the MSC.Nastran dialog (Figure 3-11) displays the progress of the analysis process.
Figure 3-11 MSC.Nastran Dialog
When the first iteration is complete, the program will refine the mesh where necessary to achieve the most accurate results. It will iterate several times until it reaches your desired accuracy setting. When the analysis is completed, the window displays: Analysis job completed successfully. Working Model FEA calculates an extensive range of analysis solutions. The Wizard, however, returns only those responses that can give you the quickest visual and numerical feedback about the success or failure of your part. For more comprehensive results you must use the dialogs activated by the Working Model FEA menu. These will be shown in other exercises.
Using the Design Doctor to Analyze Results The Design Doctor is an analysis expert designated to examine and interpret your analysis results. The Design Doctor checks aspects of your analysis results against various pre-established criteria and tells you what to correct should any of your results fail the test. Sometimes the Design Doctor can make the necessary repairs to your simulation data. 1.
Click Results in the Stress Wizard window.
This displays the Design Doctor window as shown in Figure 3-12.
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Figure 3-12 Design Doctor
2.
Click Next.
The Design Doctor displays the list of criteria against which your results will be tested (Figure 3-13).
Figure 3-13 Design Doctor Options
3.
Enter the minimum factor of safety value you consider acceptable for your design.
Exercise 3.1 Stress Simulation on a Bracket
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Working Model FEA will obtain the maximum yield stress of the material from the material library and get the von Mises stresses from the analysis results. 4.
Click Next.
The Design Doctor will proceed with the diagnostic tests for each criteria. If the results pass the test, the Design Doctor puts a check mark next to the criteria name. The dialog below (Figure 3-14) shows that all tests have completed successfully.
Figure 3-14 Design Doctor Results
To get more details from the Design Doctor: 5.
Highlight Design Intent/Animation and then click Diagnosis.
This displays the diagnosis for the Design Intent. 6.
Click Close, Finish, and Close to end the exercise.
You have completed this exercise.
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Exercise 3.2 Optimizing the Shape of a Bracket This exercise introduces you to shape optimization and Working Model Shape. The Optimization Wizard will lead you through the sequence of steps required to optimize the design of a bracket.
Using Working Model Shape Optimization Working Model Shape Optimization links finite element analysis and parametric geometric construction in a process called shape optimization. Shape optimization automates the search for an optimal design by varying dimensions to achieve a design objective, for example, minimum mass, while observing certain design criteria, such as maximum allowable stress limits. Working Model Shape Optimization must be used with Stress, Vibration, or Buckling Simulations. The following is a short outline of the optimization strategy. You will see each step in greater detail as you work your way through the exercise in this section. 7.
Start with your SolidWorks part geometry. Identify the dimensions that you will vary. Define the global design variables in SolidWorks. 8. Create a simulation model of the appropriate analysis type. Add loads (except in a Vibration Simulation), restraints, and mesh. Run the analysis of this model if you need to simulate the behavior of the part with its initial dimensions. 9. Define a shape optimization model and associate with it the following input criteria: •Design Objective—The goal of the optimization process. A common design objective is to minimize the mass of the part •Design Variables—Identified dimensional parameters that are permitted to change during the optimization process •Design constraints—Physical characteristics and responses that must be maintained (e.g., maximum allowable stress or displacement) 10. Run the shape optimization analysis. 11. Review the shape optimization results and observe the sensitivity of the overall design to each variable. 12. Update the SolidWorks part based on the new optimized dimensions.
Exercise 3.2 Optimizing the Shape of a Bracket
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Preparing the Part Open a Part
The part for this example is in Tutorials\Chapter 3\Exercise 3.2. The name of this part is Bracket_opt.par.
Define the Design Variable(s)
For this exercise, we have already defined the design variables. Design variables are defined in SolidWorks as Independent Global Design Variables. The equation field should contain the value with which the geometry was constructed.
Associate Design Variables and Dimensions
In this exercise, the design variables are already associated with the dimensions. Design variables and dimensions are associated through the SolidWorks Part menu. Choose Edit Feature to associate the variables with the dimensions.
Figure 3-15 Bracket
The design variables and dimensions for the bracket shown in Figure 315 are as follows: • • • • • •
Unit system—English Load—2500 lbf total force pushing down on the top face of the base portion of the bracket. Restraint—The back face of the bracket is fully restrained. Material—Stainless Steel Design Objective—Minimize the mass of the part by changing the thickness of the base and of the rib. Initial mass= 26.5 lbm. Design Constraint—Allowable von Mises stress = 38000 psi.
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Chapter 3—Working Model FEA: SolidWorks Exercises
• • •
Design Variables—Two dimensions of the bracket will serve as design variables: Base thickness—Initial value = 1.0 in (Minimum value allowed = 0.1 in./Maximum value allowed = 1.1 in.) Rib thickness—Initial value=0.75 in (Minimum value allowed= 0.1 in./Maximum value allowed=1.0 in)
Getting Started In this section you will open the bracket file and define the simulation model required for optimization. If you need help with these steps, please refer to the first exercise in this chapter. From SolidWorks: 1.
Choose Open from the File menu.
This displays the File Open dialog. 2.
Browse the Tutorials\Chapter 3\Exercise 3.2 folder and open the bracket_opt.par file.
This opens and displays the Bracket as shown in Figure 3-15.
Note: The default location for the Tutorials folder is Program Files\Working Model
3.
Create a new simulation model, load set, and restraint set.
See Exercise 3.1 for help with these steps. The simulation type is Stress. Use the following parameters:
Loads
Total Force—2500 lbf in the Global Y direction on the top face of the base portion of the bracket.
Restraints
Fully restrain the back face of the bracket.
Exercise 3.2 Optimizing the Shape of a Bracket
Mesh
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Material—Steel Element Size— Accept the default
Figure 3-16 The Simulation Model
4.
Choose Wizards from the Working Model FEA menu and then choose Working Model Shape Wizard from the Wizards submenu.
5.
Click Begin, then Define.
6.
Accept Start a New Model and click Next.
The Model Name and Simulation Model page as shown in Figure 317 is displayed.
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Chapter 3—Working Model FEA: SolidWorks Exercises
Figure 3-17 Model Name and Simulation Model Page
7.
Accept the default Optimization Model Name and the Simulation Model Name.
8.
Click Finish and continue with the next section.
Specifying a Design Objective Before you can optimize a design’s performance or response, you must define what it is that you consider optimal. It may be a minimum mass, maximum first natural frequency, etc. Whatever you choose, this will be the design goal, or objective. For this project, the design objective is to minimize the mass of the part. 1.
Click the Objective tab in the Wizard window.
This displays the Design Objective page as shown in Figure 3-18.
Exercise 3.2 Optimizing the Shape of a Bracket
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Figure 3-18 Design Objective Page
2.
Accept the default design objective action as Minimize and the default design objective response as mass.
3.
Click Finish and continue with the next section.
Specifying Design Variables In this step you will identify the design variables. Working Model Shape enters the initial value of a predefined variable dimension and specifies default maximum and minimum allowable boundaries (+/- 10%). You can modify these boundary values to suit your optimization criteria. 1.
Click the Variables tab in the Wizard window.
This displays the Design Variable page as shown in Figure 3-19.
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Figure 3-19 Design Variable Page
2.
Select Thickness from the Name list.
3.
Accept the upper bound as 1.1 inches and set the lower bound to 0.1 in. in the Design Variable Bounds region.
4.
Click Next.
The Wizard prompts you to create another variable. 5.
Click Yes.
This redisplays the Design Variable window. 6.
Select RibThick
7.
Set the upper bound to 1.0 inch and the lower bound to 0.1 in.
8.
Click Next.
The Wizard prompts you to create another variable. 9.
Click Finish and continue with the next section.
Specifying Constraints A design constraint is a design response whose upper or lower limit value places certain restrictions on the magnitude of the design variable(s) changes. For example, by decreasing the thicknesses, this part can be
Exercise 3.2 Optimizing the Shape of a Bracket
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made lighter but the maximum allowable stress will limit how far you can reduce these dimensions. In this case, the maximum allowable stress is your design constraint. 1.
Click the Constraints tab in the Wizard window.
A dialog prompts you to accept a default constraint name. 2.
Accept the default constraint name and click Next.
This displays the Design Constraints Response page as shown in Figure 3-20.
Figure 3-20 Design Constraint Response Page
3.
Accept Response = stress and Component = von Mises and Click Next.
The design constraint is applied to All Solids. 4.
Click Next.
This displays the Design Constraint Limit page as shown in Figure 3-21.
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Chapter 3—Working Model FEA: SolidWorks Exercises
Figure 3-21 Design Constraint Limit Page
The Type of Constraint defaults to stress, and upper bound <= (less than or equal to). 5.
Change the stress limit to 10000 lbf/in**2.
On this page you also see a verbal summary of the design constraint information. 6.
Click Next to continue.
The Wizard prompts you to add another constraint 7.
Click Finish and continue with the next section.
Solving the Problem The solution process passes through a number of design cycles before it converges to an optimum value. Before submitting the problem you can specify the maximum number of design cycles the solver should perform. The selected number of iterations may or may not be sufficient to achieve convergence; the solver will issue a status report to notify you if further action is necessary. 1.
Click Solve.
Exercise 3.2 Optimizing the Shape of a Bracket
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The Simulation Parameters tree-diagram displays the simulation components. A default result set is created, displaying the load set and restraint set that will be applied in the analysis. 2.
Click Next.
The General Job Information page (Figure 3-22) displays the parameters of the optimization job.
Figure 3-22 General Job Information Page
3.
Accept the default Optimization Result Set name, set the maximum number of design cycles to 10 and accept the default optimization type - Optimization plus sensitivity.
4.
Click Next to continue.
This displays the execution option dialog. 5.
Accept the default execution option Immediate automatic execution and Click Finish.
This sends the optimization job to the solver. The message in the MSC.Nastran window will inform you that the job has completed. 6.
Click OK and continue with the next section.
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Chapter 3—Working Model FEA: SolidWorks Exercises
Processing Optimization Results When the solver completes the job, the Results Wizard (Figure 3-23) displays. The Results Wizard contains all information about your optimization results.
Figure 3-23 Results Wizard
The Results Wizard includes the following: • •
•
1.
Optimization result set—Accept the default current set. Optimization exit status—Provides information about how the optimization completed. For example, Optimization converged to an optimal solution indicates that the optimization converged to a set of design variables and all constraints are satisfied. Information at final design cycle—Displays the optimized value of the objective and the value(s) of the design variables.
Click Next and proceed to the next section.
Exercise 3.2 Optimizing the Shape of a Bracket
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Interpreting Optimization Results A number of graphs and bar charts are used to illustrate the outcome of shape optimization. The Optimization Results window (Figure 3-24) lists the three major categories of results that can be displayed in a graphical form. The last option on this page updates the model geometry to the dimensions calculated for any one of the design cycles.
Figure 3-24 Optimization Results Window
The following sections describe each of these results categories.
Design Cycle History Graphs Design cycle history graphs show how a specific optimization component changes from its initial value to its final value through the optimization process. 1.
Select Design Cycle History Graph and click Next.
This displays the Design Cycle History Data window as shown in Figure 3-25.
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Chapter 3—Working Model FEA: SolidWorks Exercises
Figure 3-25 Design Cycle History Data
A design cycle history graph can be created for any of the following result data: • • • •
2.
Objective Function— Shows how the design objective changed with each design cycle. Design Variable(s)—Shows how one or more design variables changed with each design cycle. Design Constraint(s)—Shows how one or more design constraints changed with each design cycle. Maximum Constraint Violation—Shows how the maximum constraint violation changed with each design cycle (expressed as a percentage of constraint violation).
Select Design Variable(s).
The checklist box window shows the design variables Thickness and RibThick. You can select either one of them, but for this display accept both. 3.
Click Next and continue with the next section.
Exercise 3.2 Optimizing the Shape of a Bracket
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Design Cycle History Scaling You use the Design Cycle History Scaling window (Figure 3-26) to create and display a results graph.
Figure 3-26 Design Cycle History Scaling Window
.
1.
Select No Scaling (true value) and click Next.
This displays a window that prompts you to create a graph. The selections are as follows: 2.
Select Create a Graph and click Next.
This creates and displays the graph.
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Figure 3-27 Design Variable History Graph
Note: In the following steps, a number of graphs will be displayed. You can close the graphs after viewing or keep them open to compare results between graphs.
3.
Click Yes to display more optimization results and continue with the next section.
This displays a window with more results graph selections.
Updating the Model To see how the geometric model changes is shape in each design cycle, open the Explorer or click on the Working Model FEA tab of your Desktop Browser. Look for the Ex1_brkt_opt_Model and double click on one of the model shape design cycle listings. Before updating the model you can view stress results as described in this exercise. You can also update the geometric model and the mesh to match any of the design
Exercise 3.2 Optimizing the Shape of a Bracket
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cycles. The purpose of updating the mesh is to be able to run a simulation analysis of the updated model and get new stress, deformation, vibration, or buckling results. In the Optimization Wizard Results window: 1.
Select Update the Model.
This displays the Model Update window as shown in Figure 3-28.
Figure 3-28 Model Update Window
2.
Select the last design cycle from the list in the Select Design Cycle region.
The Select Design Cycle list shows all design cycles that the optimizer evaluated. Your selection is used to update the model. 3.
Accept the default to update the mesh with the model.
The Information at selected design cycle provides the following information: •Objective—The value of the objective function at the end of the selected design cycle. •Design variables—The value of the design variables at the end of the selected design cycle.
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Note: The values found for the last design cycle and the next-to-last design cycle are generally identical, indicating that the results have converged.
4.
Click Next.
The update will be based on the design variables found for the selected design cycle. A dialog prompts you to update the model. 5.
Click Yes to update.
This procedure will update the mesh and delete any results associated with the original model. 6.
Click on Finish to close the Results.
7.
Click Close to exit the Wizard.
The bracket is updated as shown in Figure 3-29.
Figure 3-29 Updated Bracket
Exercise 3.2 Optimizing the Shape of a Bracket
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Viewing Stress Simulation Results In this section you will display the stress simulation results of the optimized model to verify stress constraints and see deflection values. 1.
Choose Explorer from the Working Model FEA menu expand Ex1_brkt_opt_Model_OptResults1.
2.
Double Click on StressResultSet.
3.
Close the Explorer.
View the stress simulation result contour as shown in Figure 3-30.
Figure 3-30 Stress Simulation Result Contour
You have completed this exercise.
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Chapter 3—Working Model FEA: SolidWorks Exercises
C H A P T E R
3
Working Model FEA: SolidWorks Exercises
This chapter presents simulation exercises designed to help you get started with Working Model FEA. The exercises are for the following products: • •
Working Model FEA: SolidWorks Working Model 4D
The exercises make use of the Simulation Wizards as well as the Working Model FEA standard menus to set up the problems, submit the simulation to analysis, solve the models, and evaluate results. • •
Exercise 3.1 uses the Stress Wizard to perform stress simulation on a bracket. Exercise 3.2 uses Working Model Shape Optimization to optimize a bracket design.
Exercise 3.1 Stress Simulation on a Bracket
3-2
Exercise 3.1 Stress Simulation on a Bracket Figure 3-1 Choosing the Stress Wizard
This exercise introduces you to the Working Model FEA stress analysis feature. You will use the Stress Wizard to determine the failure stresses (von Mises stresses) generated in the object as a result of an applied pressure. You will then calculate the factor of safety based on von Mises stresses (minimum acceptable factor of safety=1). The Stress Wizard leads you through the entire simulation process.
Getting Started In this section you will open the bracket file in SolidWorks and launch the Stress wizard. From SolidWorks: 1.
Choose Open from the File menu.
This displays the File Open dialog.
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Chapter 3—Working Model FEA: SolidWorks Exercises
2.
Browse the Tutorial folder Chapter 3\Exercise 3.1 and open the Bracket.par file
This opens and displays the Bracket as shown in Figure 3-1.
Note: The default location for the Tutorials folder is Program Files\Working Model
3.
Choose Wizards from the Working Model FEA menu, then choose Stress Wizard from the Wizards submenu.
This launches the Stress Wizard as shown in Figure 3-2.
Figure 3-2 Stress Wizard
Defining the Problem and Units In this section you will define the problem for the Stress Wizard. 1.
Click Begin to initiate the simulation process.
2.
Click Define.
Exercise 3.1 Stress Simulation on a Bracket
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The Wizard creates a simulation model with a default name. The default is the name of your part with the word Model appended.
Figure 3-3 Simulation Model Name Window
3.
Click Next.
This displays the Units tab of the Stress Wizard. 4.
Click Units.
This displays the Desired Units window as shown in Figure 3-4. Since you already specified inches, the units default to the English system.
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Figure 3-4 Desired Units Window
5.
Click Finish and go to the next step.
Specifying Loads In this section you will specify a load for the stress simulation. In Working Model FEA, loads are grouped into named sets that can contain one or more loads. 1.
Click the Loads tab on the Stress Wizard window.
This displays a window that prompts you to accept a default name for the load set. 2.
Click Next.
This displays the How Loads are Applied window as shown in Figure 3-5.
Exercise 3.1 Stress Simulation on a Bracket
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Figure 3-5 How Loads Are Applied Window
3.
Select Face and click Next.
In this problem the load is pressure, which is applied on a face. 4.
Optionally click Change View.
If you need to zoom, rotate, or pan the view before you pick the face, click the “Change View” button. This allows you to access the Desktop View menu or toolbar commands and modify the view as needed. Click OK when you are finished with view modifications. 5.
Click Next.
This displays the Load Geometry window. 6.
Click on the top face of the base portion of the bracket. Be sure the correct face is selected. (You can right-mouse click to select faces.)
7.
Click Pressure (the load type) and then click Next.
This displays the Load Value dialog. 8.
Enter a load value of 50.
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Pressure has a single component perpendicular to the face. Pressure is positive if it is pointing at the face. 9.
Click Next in the Load Value dialog.
This displays the Symbol Data dialog. It lets you control the color and size of the load symbols. Force symbols will appear on the geometry, as shown in Figure 36. A dialog prompts you to create another load.
Figure 3-6 Force Symbols on Bracket Face
10. Click Finish and go to the next step.
Specifying Restraints In this section you will specify a restraint for the stress simulation. In Working Model FEA, restraints are grouped in named sets. 1.
Click the Restraints tab on the Stress Wizard window.
This displays a window that prompts you to accept a default name for the load set. The default load set name is Ex1_brkt_RS.
Exercise 3.1 Stress Simulation on a Bracket
2.
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Click Next.
This displays the Restraints window as shown in Figure 3-7.
Figure 3-7 How Restraints Are Applied Window
3.
Select Face and click Next.
In this problem the restraint is applied on the face. 4.
Click on the back vertical face of the bracket. Be sure the back vertical face is selected.
5.
Click Next.
This displays the Restraint Types window as shown in Figure 3-8.
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Figure 3-8 Restraints Types Window
6.
Select Fixed in the Restraint Type window and click Next.
This prevents the back of the bracket from moving or rotating in any direction. The Wizard displays the Symbol Data dialog, which lets you control the color and size of the Restraint symbols. 7.
Change the symbol size to 0.5 inches and click Next in the Symbol Data dialog.
Force symbols will appear on the geometry, as shown in Figure 39. A dialog prompts you to create another restraint.
Exercise 3.1 Stress Simulation on a Bracket
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Figure 3-9 Restraints and Loads on Bracket
8.
Click Finish and go to the next step.
Specifying Mesh and Getting Results In this section you will analyze your model to get results. You will first specify a mesh for the stress simulation. In Working Model FEA the material used for analyzing the model is actually assigned to the mesh. 1.
Click the Analyze tab on the Stress Wizard window and select Analyze.
This displays the Materials for Mesh dialog. 2.
Select Choose an existing material and click Next.
This displays the Select Existing Material for Mesh window as shown in Figure 3-10.
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Chapter 3—Working Model FEA: SolidWorks Exercises
Figure 3-10 Select Existing Material or Mesh Window
3.
Scroll the material list to display Steel-ANSI 304. Select it and then click Next.
You are now ready to select the geometry to mesh. 4.
Click Next.
This displays the Analysis Execution window, which specifies the analysis start time. There is an abrupt geometric change where the top edge of the rib joins the vertical part of the bracket and this is likely to cause higher stress concentrations. To get a better picture of the stresses there, you need a fine mesh in that area. To save meshing and analysis time, it is better to specify larger elements in most of the body and apply mesh refinements in the critical areas than to use small elements overall. For this reason, we will use h-adaptivity. 5.
Select h-adaptivity.
Use default values for Map Iterations and Target Error. 6.
Accept Now and Click Finish to submit the model.
Exercise 3.1 Stress Simulation on a Bracket
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The program will first display a Working Model dialog that shows the progress of the Meshing process. Then the MSC.Nastran dialog (Figure 3-11) displays the progress of the analysis process.
Figure 3-11 MSC.Nastran Dialog
When the first iteration is complete, the program will refine the mesh where necessary to achieve the most accurate results. It will iterate several times until it reaches your desired accuracy setting. When the analysis is completed, the window displays: Analysis job completed successfully. Working Model FEA calculates an extensive range of analysis solutions. The Wizard, however, returns only those responses that can give you the quickest visual and numerical feedback about the success or failure of your part. For more comprehensive results you must use the dialogs activated by the Working Model FEA menu. These will be shown in other exercises.
Using the Design Doctor to Analyze Results The Design Doctor is an analysis expert designated to examine and interpret your analysis results. The Design Doctor checks aspects of your analysis results against various pre-established criteria and tells you what to correct should any of your results fail the test. Sometimes the Design Doctor can make the necessary repairs to your simulation data. 1.
Click Results in the Stress Wizard window.
This displays the Design Doctor window as shown in Figure 3-12.
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Figure 3-12 Design Doctor
2.
Click Next.
The Design Doctor displays the list of criteria against which your results will be tested (Figure 3-13).
Figure 3-13 Design Doctor Options
3.
Enter the minimum factor of safety value you consider acceptable for your design.
Exercise 3.1 Stress Simulation on a Bracket
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Working Model FEA will obtain the maximum yield stress of the material from the material library and get the von Mises stresses from the analysis results. 4.
Click Next.
The Design Doctor will proceed with the diagnostic tests for each criteria. If the results pass the test, the Design Doctor puts a check mark next to the criteria name. The dialog below (Figure 3-14) shows that all tests have completed successfully.
Figure 3-14 Design Doctor Results
To get more details from the Design Doctor: 5.
Highlight Design Intent/Animation and then click Diagnosis.
This displays the diagnosis for the Design Intent. 6.
Click Close, Finish, and Close to end the exercise.
You have completed this exercise.
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Exercise 3.2 Optimizing the Shape of a Bracket This exercise introduces you to shape optimization and Working Model Shape. The Optimization Wizard will lead you through the sequence of steps required to optimize the design of a bracket.
Using Working Model Shape Optimization Working Model Shape Optimization links finite element analysis and parametric geometric construction in a process called shape optimization. Shape optimization automates the search for an optimal design by varying dimensions to achieve a design objective, for example, minimum mass, while observing certain design criteria, such as maximum allowable stress limits. Working Model Shape Optimization must be used with Stress, Vibration, or Buckling Simulations. The following is a short outline of the optimization strategy. You will see each step in greater detail as you work your way through the exercise in this section. 7.
Start with your SolidWorks part geometry. Identify the dimensions that you will vary. Define the global design variables in SolidWorks. 8. Create a simulation model of the appropriate analysis type. Add loads (except in a Vibration Simulation), restraints, and mesh. Run the analysis of this model if you need to simulate the behavior of the part with its initial dimensions. 9. Define a shape optimization model and associate with it the following input criteria: •Design Objective—The goal of the optimization process. A common design objective is to minimize the mass of the part •Design Variables—Identified dimensional parameters that are permitted to change during the optimization process •Design constraints—Physical characteristics and responses that must be maintained (e.g., maximum allowable stress or displacement) 10. Run the shape optimization analysis. 11. Review the shape optimization results and observe the sensitivity of the overall design to each variable. 12. Update the SolidWorks part based on the new optimized dimensions.
Exercise 3.2 Optimizing the Shape of a Bracket
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Preparing the Part Open a Part
The part for this example is in Tutorials\Chapter 3\Exercise 3.2. The name of this part is Bracket_opt.par.
Define the Design Variable(s)
For this exercise, we have already defined the design variables. Design variables are defined in SolidWorks as Independent Global Design Variables. The equation field should contain the value with which the geometry was constructed.
Associate Design Variables and Dimensions
In this exercise, the design variables are already associated with the dimensions. Design variables and dimensions are associated through the SolidWorks Part menu. Choose Edit Feature to associate the variables with the dimensions.
Figure 3-15 Bracket
The design variables and dimensions for the bracket shown in Figure 315 are as follows: • • • • • •
Unit system—English Load—2500 lbf total force pushing down on the top face of the base portion of the bracket. Restraint—The back face of the bracket is fully restrained. Material—Stainless Steel Design Objective—Minimize the mass of the part by changing the thickness of the base and of the rib. Initial mass= 26.5 lbm. Design Constraint—Allowable von Mises stress = 38000 psi.
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• • •
Design Variables—Two dimensions of the bracket will serve as design variables: Base thickness—Initial value = 1.0 in (Minimum value allowed = 0.1 in./Maximum value allowed = 1.1 in.) Rib thickness—Initial value=0.75 in (Minimum value allowed= 0.1 in./Maximum value allowed=1.0 in)
Getting Started In this section you will open the bracket file and define the simulation model required for optimization. If you need help with these steps, please refer to the first exercise in this chapter. From SolidWorks: 1.
Choose Open from the File menu.
This displays the File Open dialog. 2.
Browse the Tutorials\Chapter 3\Exercise 3.2 folder and open the bracket_opt.par file.
This opens and displays the Bracket as shown in Figure 3-15.
Note: The default location for the Tutorials folder is Program Files\Working Model
3.
Create a new simulation model, load set, and restraint set.
See Exercise 3.1 for help with these steps. The simulation type is Stress. Use the following parameters:
Loads
Total Force—2500 lbf in the Global Y direction on the top face of the base portion of the bracket.
Restraints
Fully restrain the back face of the bracket.
Exercise 3.2 Optimizing the Shape of a Bracket
Mesh
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Material—Steel Element Size— Accept the default
Figure 3-16 The Simulation Model
4.
Choose Wizards from the Working Model FEA menu and then choose Working Model Shape Wizard from the Wizards submenu.
5.
Click Begin, then Define.
6.
Accept Start a New Model and click Next.
The Model Name and Simulation Model page as shown in Figure 317 is displayed.
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Figure 3-17 Model Name and Simulation Model Page
7.
Accept the default Optimization Model Name and the Simulation Model Name.
8.
Click Finish and continue with the next section.
Specifying a Design Objective Before you can optimize a design’s performance or response, you must define what it is that you consider optimal. It may be a minimum mass, maximum first natural frequency, etc. Whatever you choose, this will be the design goal, or objective. For this project, the design objective is to minimize the mass of the part. 1.
Click the Objective tab in the Wizard window.
This displays the Design Objective page as shown in Figure 3-18.
Exercise 3.2 Optimizing the Shape of a Bracket
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Figure 3-18 Design Objective Page
2.
Accept the default design objective action as Minimize and the default design objective response as mass.
3.
Click Finish and continue with the next section.
Specifying Design Variables In this step you will identify the design variables. Working Model Shape enters the initial value of a predefined variable dimension and specifies default maximum and minimum allowable boundaries (+/- 10%). You can modify these boundary values to suit your optimization criteria. 1.
Click the Variables tab in the Wizard window.
This displays the Design Variable page as shown in Figure 3-19.
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Figure 3-19 Design Variable Page
2.
Select Thickness from the Name list.
3.
Accept the upper bound as 1.1 inches and set the lower bound to 0.1 in. in the Design Variable Bounds region.
4.
Click Next.
The Wizard prompts you to create another variable. 5.
Click Yes.
This redisplays the Design Variable window. 6.
Select RibThick
7.
Set the upper bound to 1.0 inch and the lower bound to 0.1 in.
8.
Click Next.
The Wizard prompts you to create another variable. 9.
Click Finish and continue with the next section.
Specifying Constraints A design constraint is a design response whose upper or lower limit value places certain restrictions on the magnitude of the design variable(s) changes. For example, by decreasing the thicknesses, this part can be
Exercise 3.2 Optimizing the Shape of a Bracket
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made lighter but the maximum allowable stress will limit how far you can reduce these dimensions. In this case, the maximum allowable stress is your design constraint. 1.
Click the Constraints tab in the Wizard window.
A dialog prompts you to accept a default constraint name. 2.
Accept the default constraint name and click Next.
This displays the Design Constraints Response page as shown in Figure 3-20.
Figure 3-20 Design Constraint Response Page
3.
Accept Response = stress and Component = von Mises and Click Next.
The design constraint is applied to All Solids. 4.
Click Next.
This displays the Design Constraint Limit page as shown in Figure 3-21.
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Figure 3-21 Design Constraint Limit Page
The Type of Constraint defaults to stress, and upper bound <= (less than or equal to). 5.
Change the stress limit to 10000 lbf/in**2.
On this page you also see a verbal summary of the design constraint information. 6.
Click Next to continue.
The Wizard prompts you to add another constraint 7.
Click Finish and continue with the next section.
Solving the Problem The solution process passes through a number of design cycles before it converges to an optimum value. Before submitting the problem you can specify the maximum number of design cycles the solver should perform. The selected number of iterations may or may not be sufficient to achieve convergence; the solver will issue a status report to notify you if further action is necessary. 1.
Click Solve.
Exercise 3.2 Optimizing the Shape of a Bracket
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The Simulation Parameters tree-diagram displays the simulation components. A default result set is created, displaying the load set and restraint set that will be applied in the analysis. 2.
Click Next.
The General Job Information page (Figure 3-22) displays the parameters of the optimization job.
Figure 3-22 General Job Information Page
3.
Accept the default Optimization Result Set name, set the maximum number of design cycles to 10 and accept the default optimization type - Optimization plus sensitivity.
4.
Click Next to continue.
This displays the execution option dialog. 5.
Accept the default execution option Immediate automatic execution and Click Finish.
This sends the optimization job to the solver. The message in the MSC.Nastran window will inform you that the job has completed. 6.
Click OK and continue with the next section.
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Processing Optimization Results When the solver completes the job, the Results Wizard (Figure 3-23) displays. The Results Wizard contains all information about your optimization results.
Figure 3-23 Results Wizard
The Results Wizard includes the following: • •
•
1.
Optimization result set—Accept the default current set. Optimization exit status—Provides information about how the optimization completed. For example, Optimization converged to an optimal solution indicates that the optimization converged to a set of design variables and all constraints are satisfied. Information at final design cycle—Displays the optimized value of the objective and the value(s) of the design variables.
Click Next and proceed to the next section.
Exercise 3.2 Optimizing the Shape of a Bracket
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Interpreting Optimization Results A number of graphs and bar charts are used to illustrate the outcome of shape optimization. The Optimization Results window (Figure 3-24) lists the three major categories of results that can be displayed in a graphical form. The last option on this page updates the model geometry to the dimensions calculated for any one of the design cycles.
Figure 3-24 Optimization Results Window
The following sections describe each of these results categories.
Design Cycle History Graphs Design cycle history graphs show how a specific optimization component changes from its initial value to its final value through the optimization process. 1.
Select Design Cycle History Graph and click Next.
This displays the Design Cycle History Data window as shown in Figure 3-25.
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Figure 3-25 Design Cycle History Data
A design cycle history graph can be created for any of the following result data: • • • •
2.
Objective Function— Shows how the design objective changed with each design cycle. Design Variable(s)—Shows how one or more design variables changed with each design cycle. Design Constraint(s)—Shows how one or more design constraints changed with each design cycle. Maximum Constraint Violation—Shows how the maximum constraint violation changed with each design cycle (expressed as a percentage of constraint violation).
Select Design Variable(s).
The checklist box window shows the design variables Thickness and RibThick. You can select either one of them, but for this display accept both. 3.
Click Next and continue with the next section.
Exercise 3.2 Optimizing the Shape of a Bracket
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Design Cycle History Scaling You use the Design Cycle History Scaling window (Figure 3-26) to create and display a results graph.
Figure 3-26 Design Cycle History Scaling Window
.
1.
Select No Scaling (true value) and click Next.
This displays a window that prompts you to create a graph. The selections are as follows: 2.
Select Create a Graph and click Next.
This creates and displays the graph.
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Figure 3-27 Design Variable History Graph
Note: In the following steps, a number of graphs will be displayed. You can close the graphs after viewing or keep them open to compare results between graphs.
3.
Click Yes to display more optimization results and continue with the next section.
This displays a window with more results graph selections.
Updating the Model To see how the geometric model changes is shape in each design cycle, open the Explorer or click on the Working Model FEA tab of your Desktop Browser. Look for the Ex1_brkt_opt_Model and double click on one of the model shape design cycle listings. Before updating the model you can view stress results as described in this exercise. You can also update the geometric model and the mesh to match any of the design
Exercise 3.2 Optimizing the Shape of a Bracket
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cycles. The purpose of updating the mesh is to be able to run a simulation analysis of the updated model and get new stress, deformation, vibration, or buckling results. In the Optimization Wizard Results window: 1.
Select Update the Model.
This displays the Model Update window as shown in Figure 3-28.
Figure 3-28 Model Update Window
2.
Select the last design cycle from the list in the Select Design Cycle region.
The Select Design Cycle list shows all design cycles that the optimizer evaluated. Your selection is used to update the model. 3.
Accept the default to update the mesh with the model.
The Information at selected design cycle provides the following information: •Objective—The value of the objective function at the end of the selected design cycle. •Design variables—The value of the design variables at the end of the selected design cycle.
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Note: The values found for the last design cycle and the next-to-last design cycle are generally identical, indicating that the results have converged.
4.
Click Next.
The update will be based on the design variables found for the selected design cycle. A dialog prompts you to update the model. 5.
Click Yes to update.
This procedure will update the mesh and delete any results associated with the original model. 6.
Click on Finish to close the Results.
7.
Click Close to exit the Wizard.
The bracket is updated as shown in Figure 3-29.
Figure 3-29 Updated Bracket
Exercise 3.2 Optimizing the Shape of a Bracket
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Viewing Stress Simulation Results In this section you will display the stress simulation results of the optimized model to verify stress constraints and see deflection values. 1.
Choose Explorer from the Working Model FEA menu expand Ex1_brkt_opt_Model_OptResults1.
2.
Double Click on StressResultSet.
3.
Close the Explorer.
View the stress simulation result contour as shown in Figure 3-30.
Figure 3-30 Stress Simulation Result Contour
You have completed this exercise.
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