The Essence of Result Post- Processing

Transcription

1 APPENDIX E The Essence of Result Post- Processing Objectives: Manually create the geometry for the tension coupon using the given dimensions then apply finite elements. Manually define material and element properties. symmetric boundary constraints. edge pressure to model. Run the analysis and read the results back into MSC.Patran. Generate a fringe plot of X stress tensor and compare results. MSC.Nastran 120 Exercise Workbook E-1

2 E-2 MSC.Nastran 120 Exercise Workbook

3 APPENDIX E The Essence of Result Post-Processing Model Description: Figure E.1 is a schematic of a plate with a circular hole at the center. The dimensions and loads are indicated. The finite element model will be simplified by creating the 1/4 tension coupon model with two simple surfaces as shown in Figure E.2. The plate is inches thick; therefore it will be modeled with shell elements. The tension coupon will have the properties of Table E.1. The resulting finite element model will have X- and Y-symmetry constraints with an additional constraint for translation in the Z-direction. The uniform edge pressure load of 100 psi will be applied to the right edge. Since the Patran edge pressure convention is in terms of lb/in, 100 psi must be converted to a running load by multiplying the pressure by the thickness of the plate. Figure E.1 - Plate with Circular Hole psi psi Y Z X 10. Table E.1 - Tension Coupon Properties Elastic Modulus: 10E+06 psi Poisson Ratio 0.3 Plate Thickness: in Figure E.2 - Simplified Model with Dimensions Y Z X 5. MSC.Nastran 120 Exercise Workbook E-3

4 Suggested Exercise Steps: Create the necessary curves and surfaces of the tension coupon geometry and mesh the geometry to create a finite element model. Define symmetric boundary constraints and apply a uniform pressure to one edge (TENSION_LOAD). Define material (MAT_1) and element properties (PSHELL). Prepare the model for a Linear Static Analysis. Generate and submit an input file to MSC.Nastran. Generate a fringe plot of σ xx. Review the results. E-4 MSC.Nastran 120 Exercise Workbook

5 APPENDIX E The Essence of Result Post-Processing Exercise Procedure: 1. Open a new database called appendix_e.db. File/New... New Database Name appendix_e OK In the New Model Preference form set the following: Tolerance Analysis code: OK Default MSC/NASTRAN Create the necessary geometry for the plate model. NOTE: Whenever possible, toggle off the Auto Execute option by left clicking the check box. 2. Construct circular arcs to represent the outline of the model. Because the mapped surfaces in MSC.Patran can have up to 4 edges, the arc will be created in 2 steps. Geometry Object: Method: Radius 1.0 Start Angle 0.0 End Angle 45.0 Radius 1.0 Start Angle 45.0 End Angle 90.0 Create Curve 2D ArcAngles MSC.Nastran 120 Exercise Workbook E-5

6 3. Referring to the model dimensions (see Figure E.2), the outer edges of the geometry are created through the following steps: First the top right. Geometry Object: Method: To create the top edge: 4. Create two surfaces using the curves made in the previous steps. Figure E.3 - Surface and Curve Locations Create Curve XYZ Vector Coordinates List < 0, 2, 0 > Origin Coordinates List [5, 0, 0] Vector Coordinates List < -5, 0, 0 > Origin Coordinates List [5, 2, 0] Curve 4 Surface 2 Curve 3 Curve 2 Surface 1 Curve 1 E-6 MSC.Nastran 120 Exercise Workbook

7 APPENDIX E The Essence of Result Post-Processing Geometry Object: Method: Complete the surface model. 5. Create a Finite Element Model by meshing the surface. It is essential to know the direction of each of the curves and lines. The direction will determine the bias ratio (L2/L1) of the mesh seeds. In steps 2 to 4, the geometry of this model was created so that the direction of the lines, curves and surfaces coincide with Figure E.4. Simply following the next step will indicate the curves and lines directions. Figure E.4 Create Surface Curve Starting Curve List: Curve 1 Ending Curve List: Curve 3 Starting Curve List: Curve 2 Ending Curve List: Curve a) Curve and Line Directions b) Mesh Seeds and Bias Ratio 6 elem 1:4 3 elem 1:1 6 elem 4:1 MSC.Nastran 120 Exercise Workbook E-7

8 First the elements with mesh seed ratios. Finite Elements Object: Type: Create Mesh Seed One Way Bias Num Elems and L2/L1 Number= 6 L2/L1= 4 Curve List Surface 1.1 Change the bias ratio (L2/L1). Number= 6 L2/L1= 0.25 Curve List Curve 2 Finally, the uniform mesh seed. Finite Elements (Select the bottom edge) (Select the top half of arc) Object: Type: Create Mesh Seed Uniform Num Elems and L2/L1 Number= 3 Curve List Curve 1 (Select the bottom half of arc) E-8 MSC.Nastran 120 Exercise Workbook

9 APPENDIX E The Essence of Result Post-Processing Mesh the surface. Finite Elements Create Object: Mesh Type: Surface Isomesh Surface List Surface 1, 2 Before continuing, equivalence the entire model to delete any duplicate nodes created when meshing. Finite Elements Object: Type: Equivalence All Tolerance Cube The model should appear as below. Figure E.5 - Completed Model with Finite Element Mesh. MSC.Nastran 120 Exercise Workbook E-9

10 6. Create material properties for the plate. Materials Create Object: Isotropic Method: Manual Input Material Name mat_1 Input Properties... Elastic Modulus= 10E6 Poisson Ratio= 0.3 OK 7. Define element properties. Properties Create Dimension: 2D Type: Shell Property Set Name plate Input Properties... Material Name m:mat_1 Thickness OK Select Members Surface 1, 2 Add 8. the boundary conditions to the model using Loads/BCs. This model will have three different contraints sets. E-10 MSC.Nastran 120 Exercise Workbook

11 APPENDIX E The Essence of Result Post-Processing Figure E.6 - Boundary Condition Placement X-symmetry (constraint along edge) Tension-load (pressure along edge) Rigid_body (Point 1) Y-symmetry (constraint along edge) First, create the X-symmetry contraints placed on the left side of the model. Selecting geometry may be done by typing in entity id s or clicking them as shown in Figure E.6. Loads/BCs Object: Type: New Set Name Input Data... Create Displacement Nodal x_symmetry Translations <T1 T2 T3> < 0,, > Rotations <R1 R2 R3> <, 0, 0 > OK Select Application Region... Geometry Filter Geometry MSC.Nastran 120 Exercise Workbook E-11

12 The surface edge may be typed into the input box or by clicking on the edge itself. This is done by first choosing the Curve or Edge icon from the Select Menu. Curve or Edge Select Geometry Entities Surface 2.3 Add OK Next, create the Y-symmetry constraints. (see Figure E.6) New Set Name y_symmetry Input Data... Translations <T1 T2 T3> <, 0, > Rotations <R1 R2 R3> < 0,, 0 > OK Select Application Region... Geometry Filter Geometry Select Geometry Entities Surface 1.1 Add OK (see Fig. E.6) Finally, assign one extra constraint set to remove rigid body motion in Z-direction. New Set Name rigid_body Input Data... Translations <T1 T2 T3> <,, 0 > Rotations <R1 R2 R3> <,, > E-12 MSC.Nastran 120 Exercise Workbook

13 APPENDIX E The Essence of Result Post-Processing OK Select Application Region... Geometry Filter Geometry The point may be typed into the input box or by clicking on the edge itself. This is done by first choosing the Point or Vertex icon from the Select Menu. Point or Vertex Select Geometry Entities Point 1 (see Figure E.6) Add OK Now the pressure load may be added to the model. Loads/BCs Object: Type: New Set Name Target Element Type: Create Pressure Element Uniform tension_load 2D Input Data... Edge Pressure OK Select Application Region... Geometry Filter Geometry MSC.Nastran 120 Exercise Workbook E-13

14 Type in the selected edge in the input box or click on the right edge of the model. Use the Edge icon from the Select Menu. Edge Select 2D Elements or Edge Surface 1.2 Add OK (see Figure E.6) NOTE: Positive pressure is always going into the surface/edge according to MSC.Patran convention. Therefore, the tensile load must be applied as The finished model should resemble Figure E.7. Figure E.7: Finished Model and Critical Elements Element 24 Element 23 Element 22 Element Use the Reset Graphics and Refresh Graphics icons to clean up the display. Reset Graphics Refresh Graphics E-14 MSC.Nastran 120 Exercise Workbook

15 APPENDIX E The Essence of Result Post-Processing 9. Submit the model for analysis. Analysis Analyze Object: Entire Model Method: Analysis Deck Job Name Solution Type... Solution Type: OK appendix_e LINEAR STATIC An MSC.Nastran input file called appendix_e.bdf will be generated. This process of translating the model into an input file is called the Forward Translation. The Forward Translation is complete when the Heartbeat turns green. MSC.Nastran 120 Exercise Workbook E-15

16 Submitting the Input File for Analysis: 10. Submit the input file to MSC.Nastran for analysis. 10a. To submit the MSC.Patran.bdf file for analysis, find an available UNIX shell window. At the command prompt enter: nastran appendix_e.bdf scr=yes. Monitor the run using the UNIX ps command. 11. When the run is completed, edit the appendix_e.f06 file and search for the word FATAL. If no matches exist, search for the word WARNING. Determine whether existing WARNING messages indicate modeling errors. E-16 MSC.Nastran 120 Exercise Workbook

17 APPENDIX E The Essence of Result Post-Processing Comparison of Results: 12. Compare the results obtained in the.f06 file with the results on the following pages. MSC.Nastran 120 Exercise Workbook E-17

18 Table E.2 - Stress Values of Critical Elements in Tension Coupon S T R E S S E S I N Q U A D R I L A T E R A L E L E M E N T S ( Q U A D 4 ) OPTION = BILIN ELEMENT FIBRE STRESSES IN ELEMENT COORD SYSTEM PRINCIPAL STRESSES (ZERO SHEAR) ID GRID-ID DISTANCE NORMAL-X NORMAL-Y SHEAR-XY ANGLE MAJOR MINOR VON MISES 21 CEN/ E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E CEN/ E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E CEN/ E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E CEN/ E E E E E E E E E E E E E E E E E E E E E+02 ELEMENT FIBRE STRESSES IN ELEMENT COORD SYSTEM PRINCIPAL STRESSES (ZERO SHEAR) ID GRID-ID DISTANCE NORMAL-X NORMAL-Y SHEAR-XY ANGLE MAJOR MINOR VON MISES E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E+02 E-18 MSC.Nastran 120 Exercise Workbook

19 APPENDIX E The Essence of Result Post-Processing 13. MSC.Nastran Users have finished this exercise. MSC.Patran Users should proceed to the next step. 14. Proceed with the Reverse Translation process, that is attaching the appendix_e.xdb results file into MSC.Patran. To do this, return to the Analysis form and proceed as follows: Analysis Object: Method: Select Results File... Select Results File Attach XDB Result Entities Local appendix_e.xdb When the translation is complete bring up the Results form. 15. Post process the results. Generate the fringe plot of the X stress tensor. Results Object: Create Fringe Choose the Select Results icon. Select Results Select Result Case(s) Select Fringe Result Position...(At Z1) Close Quantity: Default, Static Subcase Stress Tensor X Component MSC.Nastran 120 Exercise Workbook E-19

20 Click on the Target Entities icon. Target Entities Target Entity: Current Viewport NOTE: This feature allows controls which elements the stresses will be plotted on. Click on the Display Attributes icon. Display Attributes Style: Display: Title: Discrete/Smooth Free Edges Tension Coupon, Stress Tensor, - X Component, At Z1 Go to the Plot Options menu. Plot Options Coordinate Transformation: None Filter Values: Domain: Method: Extrapolation: None All Entities Derive/Average Shape Fn. The display should resemble Figure E.8. E-20 MSC.Nastran 120 Exercise Workbook

21 APPENDIX E The Essence of Result Post-Processing Figure E Examine the results. Question 1: What coordinate is the XX in reference to? Is it referring to global, element, material,...? Question 2: Does the plot match the Nastran results listed in Table E.2? 17. Create a different fringe plot and review the results. Click on the Plot Options icon. Plot Options Define the XX axis in the global coordinate system. Coordinate Transformation: Global Filter Values: None Turn off nodal averaging since Nastran results are reported at each element. Domain: Method: Extrapolation: None Derive/Average Shape Fn. MSC.Nastran 120 Exercise Workbook E-21

22 The plot should resemble Figure E.9. Figure E.9 The new results are significantly different from the previous plot. However, this plot correctly illustrates the individual element stresses in global X-axis. Question: Does this plot match the results listed in Table E.2? Why not? 18. Create another fringe plot and review the results. Click on the Plot Options icon. Plot Options This time define the XX axis by changing the previous global coordinate system to none. Coordinate Transformation: None Filter Values: None E-22 MSC.Nastran 120 Exercise Workbook

23 APPENDIX E The Essence of Result Post-Processing Turn off the averaging domain since Nastran results are reported at each element. Domain: Method: Extrapolation: None Derive/Average Shape Fn. The plot should resemble Figure E.10. Figure E.10 Cross reference this plot with the previous results table. Be certain that they are the same. In the interest of further study, the following is a continuation of this exercise in order to examine differences in analysis result values. 19. Create a new coordinate system. Geometry Object: Method: Create Coord 3Point Origin [0, 0, 0] MSC.Nastran 120 Exercise Workbook E-23

24 Point on Axis 3 [0, 0, 1] Point on Plane 1-3 [1, 1, 0] Generate the X stress plot again, but use CID option. Results Object: Create Fringe Click on the Select Results icon. Select Results Select Result Case(s) Select Fringe Result Position...(At Z1) Close Quantity: Default, Static Subcase Stress Tensor X Component The previous form selections are still valid and will not be changed, therefore, skip the Target Entities and Display Attributes icons and continue on to the Plot Options form. Click on the Plot Options icon. Plot Options Coordinate Transformation: CID Select Coordinate Frame Coord 1 Filter Values: None Domain: None Method: Derive/Average Extrapolation: Shape Fn. E-24 MSC.Nastran 120 Exercise Workbook

25 APPENDIX E The Essence of Result Post-Processing See Fig. E.11 and review results. Figure E.11 Quit MSC.Patran after finishing this exercise. MSC.Nastran 120 Exercise Workbook E-25

26 E-26 MSC.Nastran 120 Exercise Workbook