Optimizing the Utility Scale Solar Megahelion Drive End-Cap (Imperial Units)

Transcription

1 Autodesk Inventor Tutorial Exercise Optimizing the Utility Scale Solar Megahelion Drive End-Cap

2 Contents OPTIMIZING THE USS SOLAR TRACKING END CAP... 3 OBJECTIVE... 3 DESCRIPTION... 3 DATASETS... 4 KEY TERMS... 4 TECHNICAL OVERVIEW... 6 EXERCISE... 7 DESIGN CRITERIA... 7 Create a New Simulation... 7 Review the Materials... 7 Add a Constraint... 8 Add a Load... 8 Run a Simulation... 9 CONCLUSION:...10 Modify the Wall Thickness...10 Run the Second Simulation...10 CONCLUSION:...11 Modify the End Cap Height...11 Run the Third Simulation...12 CONCLUSION:...12 Modify the Number of Ribs...12 Run the Fourth Simulation...13 CONCLUSION:...13 CHALLENGE

3 OPTIMIZING THE USS SOLAR TRACKING END CAP Datasets for this tutorial are the property of Utility Scale Solar, Inc. (USS) Copyright US & International Patents Pending. OBJECTIVE To create simulations of various end cap designs that are focused on reducing the mass of the current end cap design. The new designs include using a spherical profile, varying the number of support ribs, and modifying the depth and thickness of the spherical cap. DESCRIPTION The prototype and first generation design uses a cylindrical drum with a flat end cap. The current design is overbuilt and currently weighs 650 lbs. The new designs are focused on maintaining the design specifications of the current design, while reducing the mass of the assembly. The basic design change is to change the profile of the end cap from flat to spherical as shown. Using Autodesk Inventor, simulations will be run on four specific design modifications. They are: 1. The new design with the spherical end cap. 2. Modifying the end cap wall thickness. 3. Changing the depth of the end cap spherical shape. 4. Varying the number of support ribs that are welded to the end cap. The current design has 6 ribs as shown. A simulation will be run to check if 4 ribs meet the design criteria. 3

4 DATASETS End Cap.iam KEY TERMS KEY TERM assembly stress analysis simulation contact fixed constraint pressure von Mises Stress deformation DESCRIPTION Two or more components (parts or subassemblies) considered as a single model. An assembly typically includes multiple components positioned absolutely and relatively (as required) with constraints that define both size and position. Assembly components may include features defined in place in the assembly. Mass and material properties may be inherited from individual part files. The USS end-cap is part of a larger assembly that includes the drum of the drive, a pillar, and the solar or mirror array. We are optimizing the end-cap sub-assembly which consists of a cap with ribs positioned relative to it. An analysis showing that the model is statically and dynamically stable and free from divergence on application of external loads and frequencies. In this optimization, we are using stress analysis to ensure that the material and geometry of the end-cap can handle the internal pressure loads without deforming and failing. In the context of Autodesk Inventor, the term Simulation has grown to be an equivalent term to analysis. Defines how components in an assembly interact with one another during the simulation. In this example, the ribs make contact with the spherical end-cap. Fixed constraint prevents the face, edge, or vertex from moving or deforming. In the example of the end cap, a fixed constraint is added to the face of the end cap that is bolted to the drum. This constraint simulates how the end cap and drum are assembled. Pressure when applied on a face is the force measured per unit area. The design specifications for this design call for a 375 psi pressure load on the face of the end cap. Three-dimensional stresses and strains build up in many directions. A common way to express these multidirectional stresses is to summarize them into an Equivalent stress, also known as the von-mises stress. A three-dimensional solid has six stress components. Sometimes a uniaxial stress test finds material properties experimentally. In that case, the combination of the six stress components to a single equivalent stress relates the real stress system. Deformation is the amount of stretching that an object undergoes due to 4

5 safety factor the loading. All objects have a stress limit depending on the material used, which are presented as material yield or ultimate strengths. If steel has a yield limit of 40,000 psi, any stresses above this limit result in some form of permanent deformation. If a design is not supposed to deform permanently by going beyond yield (most cases), then the maximum allowable stress in this case is 40,000 psi. The safety factor is how much stronger the system is than it needs to be for a given load. You can calculate a factor of safety as the ratio of the maximum allowable stress to the equivalent stress (von-mises), when using Yield Strength. In the final design iteration of the end cap, the Yield Strength of the material is 40,000 psi and the von Mises value is 36,200 psi. This gives a minimum safety factor of 1.11 (40000 / = 1.11). 5

6 TECHNICAL OVERVIEW The following Autodesk Inventor features are used in this simulation. Icon Name Description Create Simulation Assign Materials Fixed Constraint Pressure Simulate Animate Results Displays the Simulation Properties dialog box where you define the type of simulation you want to run. The Assign Materials dialog box lists the assembly and components in hierarchical order. Each component can use either the originally assigned material, or you can override the material selection with another from the Material Library list provided. Material overrides are applied per simulation, thus one component can have several material assignments each in a different simulation within the same assembly document. Applies a fixed constraint on selected faces, edges, or vertices. The fixed constraint removes all degrees of freedom between the selected components. Applies a pressure of the specified magnitude to the selected faces. Pressure is uniform. Applied Normal to the selected face. Produces a set of FEA results for all the combinations of parameters you have defined. Animates the selected simulation results. 6

7 EXERCISE In this exercise, you review a design for the end cap on the solar tracker designed and built by Utility Scale Solar, Inc. of Palo Alto. Note that your exact simulation results may vary slightly. DESIGN CRITERIA The following table lists the maximum allowable stress and displacement values and the minimum allowable safety factor as provided by Utility Scale Solar, Inc. Note: For the purpose of this simulation, the bolt hole pattern is suppressed and the welds have been removed. Before making this change, it was verified that the holes and welds have minimum effect on the simulation results. 3. On the Environments tab, Begin panel, click Stress Analysis. 4. On the Manage panel, click Create Simulation. 5. For Name, enter End Cap Simulation 1. YIELD STRENGTH DISPLACEMENT 40 ksi 0.02 in 1.5 SAFETY FACTOR 6. Click OK. 7. On the Contacts panel, click Automatic. 8. In the browser, expand the Contacts > Bonded folder and review the contacts. The completed exercise Create a New Simulation In this section of the exercise, you open the first redesign of the end cap assembly. 1. Make End Cap.ipj the active project. 2. Open End Cap.iam. 9. Collapse the Contacts > Bonded folder. Review the Materials In this section of the exercise, you review the currently assigned materials. 1. On the Material panel, click Assign. 7

8 2. Review the Assign Materials dialog box. For this simulation the High Strength Low Alloy Steel is correct. 1. On the Constraints panel, click Fixed. 2. On the ViewCube, click the top-right corner. 3. Under the Component column, select End Cap, Hemispherical:1. Note that the part is highlighted in the graphics window. 3. Select the face of the end cap as shown. 4. Under the Safety Factor column, click on the down-arrow to ensure Yield Strength is selected for all parts. 4. Click OK. Add a Load In this section of the exercise, you add a pressure load to the inside face of the end cap. 1. On the Loads panel, click Pressure. Note: The Safety Factor is calculated on the Yield Strength or Ultimate Tensile Strength of the material. For example, if the Yield Strength of the material is 40, 000 psi and the von-mises equivalent stress is 20,000 the safety factor is 2.0 (40000/20000 = 2.0). 2. Select the inside face of the end cap as shown. 5. Click Cancel to close the Assign Materials dialog box. Add a Constraint In this section of the exercise, you add a fixed constraint to a face on the end plate because it is rigidly bolted to the drum. 8

9 3. In the Pressure dialog box, for Magnitude, enter 375 psi. 4. Click OK. The pressure load is added and is displayed as glyphs on the face of the part. 3. In the browser, review the Results folder. By default, Von Mises Stress is active. 5. On the ViewCube, click Home. Run a Simulation In this section of the exercise, you run a simulation. 4. Review the Maximum and Minimum values (your results may vary slightly).the values are ksi and 0 ksi respectively. Comparing these values to the supplied design criteria shows that the design is compliant. 5. In the browser, double-click Displacement. 1. On the Solve panel, click Simulate. 2. Click Run. Depending on the speed of your computer, this can take a few minutes. 6. Review the Maximum and Minimum values. The values are in and 0 in respectively. Comparing these values to the supplied design criteria shows that the design is compliant. 7. In the browser, double-click Safety Factor. 8. Review the Minimum value. The value is Comparing this value to the supplied design criteria shows that the design is compliant. 9. On the Exit menu, click Finish Stress Analysis. 10. In the browser, right-click End_Cap.iam. Click iproperties. 11. On the Physical tab, click Update. The mass of the end cap assembly is 565 lb. By comparison, the mass of the original 9

10 design is 650 lb. This is a reduction of 95 pounds. 12. Click Close. 13. On the Environments tab, Begin panel, click Stress Analysis. 14. In the browser, under Results, doubleclick Von Mises Stress. 15. On the Result panel, click Animate. 16. On the Animate Results dialog box, click Play. 17. Close the Animate Results dialog box. 18. Repeat the animation for Displacement and Safety Factor. 19. Close the Animate Results dialog box. CONCLUSION: The design results indicate that further modifications can be made to optimize the design. The first modification is to reduce the wall thickness of the end cap. Modify the Wall Thickness In this section of the exercise, you modify the wall thickness of the end cap and run another simulation. 1. In the browser, if required, expand End Cap.iam > Weldment, End Cap:1. 2. In the browser, right-click End Cap, Hemispherical:1. Click Open. 3. Right-click End Cap, Skeleton.ipt. Click Open Base Component. 4. On the Manage tab, Parameters panel, click Parameters. 5. Under User Parameters, Thickness row, change the Equation value to 0.5 to change the thickness of the flange. Press ENTER. 6. Click Done. 7. Save and close the file. 8. On the Quick Access Toolbar, click Local Update to propagate these changes to the simulation environment. 9. On the Manage tab, Parameters panel, click Parameters. 10. Under User Parameters, Thickness row, change the Equation value to 0.5. This changes the thickness of the hemisphere. Press ENTER. 11. Click Done. 12. Save End Cap, Hemispherical: Close the file. 14. On the Quick Access Toolbar, click Local Update. Run the Second Simulation In this section of the exercise, you run the second simulation by carrying over the 10

11 constraints, loads, and contacts that you ve already defined. 1. On the Solve panel, click Simulate. 2. Click Run. Depending on the speed of your computer, this can take a few minutes. of 139 pounds and we are still within our design requirements 10. Click Close. 11. On the Environments tab, Begin panel, click Stress Analysis. CONCLUSION: The design results indicate that further modifications can be made to optimize the design. We could try even thinner walls, but the next modification is to reduce the height of the end cap. Modify the End Cap Height In this section of the exercise, you modify the height of the end cap. 3. Review the Maximum and Minimum values. The values are ksi and 0 ksi respectively. Comparing these values to the supplied design criteria shows that the design is compliant. 4. In the browser, double-click Displacement. 5. Review the Maximum and Minimum values. The values are in and 0 in respectively. Comparing these values to the supplied design criteria shows that the design is compliant. 6. In the browser, double-click Safety Factor. 7. Review the Minimum value. The value is Comparing this value to the supplied design criteria shows that the design is compliant. 8. On the Exit menu, click Finish Stress Analysis. 9. In the browser, right-click End_Cap.iam. Click iproperties. 20. On the Physical tab, click Update. The mass of the end cap assembly is 511 lb. By comparison, the mass of the original design is 650 lb. This is a total reduction 1. In the browser, if required, expand End Cap.iam > Weldment, End Cap:1. 2. In the browser, right-click End Cap, Hemispherical:1. Click Open. 3. Right-click End Cap, Skeleton.ipt. Click Open Base Component. 4. Double-click the vertical dimension. Change the value to On the Quick Access Toolbar, click Local Update. 6. Save and Close the file. 7. In End Cap, Hemispherical.ipt, click Local Update. 8. Save and Close the file. 9. In End Cap.iam, click Local Update. 11

12 Run the Third Simulation In this section of the exercise, you run the third simulation. 1. On the Solve panel, click Simulate. 2. Click Run. Depending on the speed of your computer, this can take a few minutes. 3. Review the Maximum and Minimum stress values. The values are ksi and 0 ksi respectively. Comparing these values to the supplied design criteria shows that the design is compliant. 4. In the browser, double-click Displacement. 5. Review the Maximum and Minimum values. The values are in and 0 in respectively. Comparing these values to the supplied design criteria shows that the design is compliant. 6. In the browser, double-click Safety Factor. 7. Review the Minimum value. The value is Comparing this value to the supplied design criteria shows that the design is still compliant, but is very close to the minimum safety factor. 8. On the Exit menu, click Finish Stress Analysis. 9. In the browser, right-click End_Cap.iam. Click iproperties. 10. On the Physical tab, click Update. The mass of the end cap assembly is 481 lb. By comparison, the mass of the original design is 650 lb. This is a reduction of 169 pounds and we are still within our design requirements. 11. Click Close. 12. On the Environments tab, Begin panel, click Stress Analysis. CONCLUSION: The design results indicate that this design is close the maximum and minimum values set by Utility Scale Solar, Inc. Further modifications can be made to optimize the design, but may exceed the design specifications. The next modification is to modify the number of ribs. Modify the Number of Ribs In this section of the exercise, you modify the number of support ribs. 1. In the browser, if required, expand End Cap.iam. 2. Right-click Weldment, End Cap:1. Click Open. 3. Right-click Component Pattern 1:1. Click Edit. 4. For Count, enter For Angle, enter 360/4. 12

13 6. Click OK. 7. Save and Close the file. 8. On the Quick Access Toolbar, click Local Update. Run the Fourth Simulation In this section of the exercise, you run the fourth simulation. 1. On the Solve panel, click Simulate. 2. Click Run. Depending on the speed of your computer, this can take a few minutes. 5. Review the Maximum and Minimum values. The values are in and 0 in respectively. Comparing these values to the supplied design criteria shows that the design is compliant for displacement. 6. In the browser, double-click Safety Factor. 7. Review the Minimum value. The value is Comparing this value to the supplied design criteria shows that the design is not compliant since the maximum allowable Safety Factor is On the Exit menu, click Finish Stress Analysis. 9. In the browser, right-click End Cap.iam. Click iproperties. 13. On the Physical tab, click Update. The mass of the end cap assembly is 467 lb. By comparison, the mass of the original design is 650 lb. This is a reduction of 183 pounds, but we have exceeded the acceptable design requirements for stress and safety factor. 10. Click Close. 11. Save the file. 12. Close the file. CONCLUSION: The design results from this fourth simulation are no longer within the design criteria provided by Utility Scale Solar, Inc. 3. Review the Maximum and Minimum stress values. The values are ksi and 0 ksi respectively. Comparing this value to the supplied design criteria shows that the design is not compliant since the maximum allowable stress is 27 ksi (as determined by the Yield Strength and Safety Factor). 4. In the browser, double-click Displacement. Based on these results of the four simulations, the third simulation with a wall thickness of 0.5 inches, an end cap height of 6 inches and 6 ribs is the recommended design. YIELD STRENGTH DISPLACEMENT 40 ksi 0.02 in 1.5 SAFETY FACTOR ksi in

14 The mass of the end cap assembly with these parameters is 481 lb. By comparison, the mass of the original design is 650 lb. This is a reduction of 169 pounds. CHALLENGE Is it possible to refine the design further, and still meet the design criteria? Possible modifications include, Reducing the end cap wall thickness. Using 5 ribs instead of 6. Reducing the end cap height from 6 inches to 5 inches. Try these modifications, and others that you may have thought of, and then check the design results for compliance with the Utility Scale Solar, Inc. criteria. Autodesk and Autodesk Inventor are registered trademarks or trademarks of Autodesk, Inc., and/or its subsidiaries and/or affiliates in the USA and/or other countries. All other brand names, product names, or trademarks belong to their respective holders. Autodesk reserves the right to alter product and services offerings, and specifications and pricing at any time without notice, and is not responsible for typographical or graphical errors that may appear in this document Autodesk, Inc. All rights reserved. 14