Results Postprocessing

1. Results Postprocessing Chapter Nine

2. April 22, 2004 Inventory #002071 9-2

3. April 22, 2004 Inventory #002071 9-3 A. Viewing Results When selecting a results branch, the Context toolbar displays ways of viewing results: All of these options except for �Convergence� will be discussed next. �Convergence� is covered in Section C.

4. April 22, 2004 Inventory #002071 9-4 � Displacement Scaling For structural analyses (static, modal, buckling), the deformed shape can be changed By default, the scaling is automatically exaggerated to visualize the structural response more clearly The user can change to undeformed or actual deformation

5. April 22, 2004 Inventory #002071 9-5 � Display Method The �Geometry� button controls the contourdisplay method. Four choices are possible:

6. April 22, 2004 Inventory #002071 9-6 � Contour Settings The �Contours� button controls the way inwhich contours are shown on the model

7. April 22, 2004 Inventory #002071 9-7 � Outline Display The �Edges� button allows the user show theundeformed geometry or mesh

8. April 22, 2004 Inventory #002071 9-8 � Slice Planes When in Slice Plane viewing mode, slice planescan be added and edited To add a slice plane, simply select the �Draw Slice Plane� icon, then click-drag with the left mouse across the Graphics window. The path created will define the slice plane. To edit a slice plane, select the �Edit Planes� icon. The defined planes will have a �handle� in the Graphics window. Drag the handle to move the slice plane Click on one side of the bar to show capped slice display Select the handle, then hit the �Delete� key to remove plane

9. April 22, 2004 Inventory #002071 9-9 � Min/Max and Probe Tool The min/max symbols can be removed by selectingthe �Maximum� and �Minimum� buttons Results can be queried on the model by selecting the �Probe� button Left-mouse click to add an annotation of the value being queried on the model. Use the �Label� button to select and delete unwanted annotations

10. April 22, 2004 Inventory #002071 9-10 � Animation Controls The animation toolbar allows user to play,pause, and stop animations The slider bar allows users to go through frame-by-frame The �Export Animation File� enables saving animation as AVI Animations will generally range from min to max value in a linear fashion. On the other hand, for free vibration and harmonic analysis, the full range will be correctly animated (+/- max value). Animation speed can becontrolled via �View >Animation Speed�

11. April 22, 2004 Inventory #002071 9-11 � Alerts Alerts are simple ways of check to see if a scalar result quantity satisfies a criterion Alerts can be used on most contour results except for vector results, Contact Tool results, and Shape Finder Simply select that result branch and add an Alert In the Details view, specify the criterion A minimum or maximum value of that result branch can be used Input the value which is used for the threshold In the Outline tree, a green checkmark indicates that the criterion is satisfied. A red exclamation mark indicates that the criterion was not satisfied.

12. April 22, 2004 Inventory #002071 9-12 � Manipulating the Legend For exterior contour plots, the legend can be manipulated to show result distributions more clearly. Select the legend with the left mouse Drag white bars to change overall min/max values Out-of-range values are purple (high) and brown (low) Drag yellow bars to rescale legend Drag grey bars to change intermediate ranges

13. April 22, 2004 Inventory #002071 9-13 � Manipulating the Legend For Capped IsoSurface plots, the legend has additional features to manipulate the display The middle long grey bar controls where the cutoffvalue is for capped plots The striped areas show what values will not be displayed. To toggle, simple click on the coloredareas on either side of the long grey bar

14. April 22, 2004 Inventory #002071 9-14 � Manipulating the Legend The legend may also be changed by selecting the values and directly inputting a numerical value Select the contour value, type in a new value, and [Enter] To rescale internal bands, select white bars and move them. Internal bands automatically get rescaled evenly For example, when comparing two results, one may want to change the legend to be the same for both

15. April 22, 2004 Inventory #002071 9-15 � Vector Plots Recall that vector plots are best viewed in wireframe mode Vector plots involve any vector result quantity with direction, such as deformation, principal stresses/strains, and heat flux

16. April 22, 2004 Inventory #002071 9-16 � Multiple Viewports Using multiple viewports is especially useful forpostprocessing, where more than one resultcan be viewed at the same time Useful to compare multiple results, such as results from different environments or multiple mode shapes

17. April 22, 2004 Inventory #002071 9-17 � Default Settings Under �Tools > Options� > Simulation: Graphics,� the default graphics settings can be changed. This way, each user can make all results for new simulations be displayed to his/her preference

18. April 22, 2004 Inventory #002071 9-18 B. Scoping Results Sometimes, limiting the display of results is useful when postprocessing Although one can rescale the legend to get a better idea of the result distribution on a certain part or surface, results scoping automatically scales the legend and only shows the applicable surface(s) or part(s), making result viewing easier. Scoping results on edges produces a path plot, allowing users to see detailed results along selected edges Results scoping is very useful for convergence controls (discussed later in this chapter) When using Contact Tool, Simulation automatically scopes contact results to contact regions. Results scoping can be performed on any result item in the Solution branch for any type of geometric quantity.

19. April 22, 2004 Inventory #002071 9-19 � Scoping Surface/Part Results To scope contour results, simply do either of the following: Select part(s) or surface(s), then request the result of interest Select the result item, then click on �Geometry� in the Details view. Select the part(s) or surface(s), then click on Apply When this is performed, the Details view of the result item will indicate that results will be shown only for the selected items. The displayed values will show non-selected surfaces/parts as translucent.

20. April 22, 2004 Inventory #002071 9-20 � Scoping Surface/Part Results Some examples of scoping results on surfaces/parts:

21. April 22, 2004 Inventory #002071 9-21 � Scoping Edge & Vertex Results Results can be scoped to a single edge Select a single edge for results scoping A path plot of the result mapped on the edge will be displayed In a similar manner, results can also be scoped to a single vertex. No �contour� results will be displayed since only a vertex is present, but the value will reported in the Details view for the selected vertex

22. April 22, 2004 Inventory #002071 9-22 � Renaming Scoped Results For scoped results, it is often useful to automatically rename the result branch Right-click on the result branch and select �Rename Based on Definition.� The name will become more descriptive.

23. April 22, 2004 Inventory #002071 9-23 C. Exporting Results Tabular data from Simulation can be exported to Excel for further data manipulation To export Worksheet tab information, do the following: Select the branch and click on the Worksheet tab Right-click the same branch and select �Export� This can be used for Geometry, Contact, Environment, Frequency Finder, Buckling, and Harmonic Worksheets To export Contour Results Right-click on the result branch of interest and select �Export� This can be used for any result item of interest Node numbers and result quantities will be exported Exporting large amounts of data can take some CPU time

24. April 22, 2004 Inventory #002071 9-24 � Exporting Results Usually, for result items, the internal ANSYS node number and result quantity will be output as shown below. To include node locations, change this option under �Tools menu > Options� > Simulation: Export�

25. April 22, 2004 Inventory #002071 9-25 � Exporting Results For principal stresses and strains, additional information of the orientation needs to be included when export to .XLS: The generated Excel file will have 6 fields: The first three correspond to the maximum, middle and minimum principal quantities (stresses or strains). The last three correspond to the ANSYS Euler angle sequence (CLOCAL command in ANSYS) required to produce a coordinate system whose X, Y and Z-axis are the directions of maximum, middle and minimum principal quantities, respectively. This Euler angle sequence is ThetaXY, ThetaYZ and ThetaZX and orients the principal coordinate system relative to the global system.

26. April 22, 2004 Inventory #002071 9-26 D. Coordinate Systems If coordinate systems are defined, a new item will be displayed in the Details view of directional results: As shown below, one can select from defined coordinate systems. The selected coordinate system will define x-, y-, and z-axes Direction Deformation, Normal/Shear Stress/Strain, and Directional Heat Flux can use coordinate systems Principal stress/strain have their own angles associated with them Other result items are scalars, so there are no directions associated with it. Vector plots show the direction, so they cannot use coordinate systems.

27. April 22, 2004 Inventory #002071 9-27 � Coordinate Systems For the model shown below, one localcylindrical coordinate system is defined Note that displaying Deformation in the x-direction in the global and local coordinatesystems will show different results. If the user wants to see what is the radialdisplacement at the larger hole, a local cylindrical coordinate system allows to visualize this type of displacement.

28. April 22, 2004 Inventory #002071 9-28 E. Solution Combinations For ANSYS Professional licenses and above, the Solution Combination branch can be added to the Model branch to provide combinations of existing Environment branches Solution combinations are only valid for linear static structural analyses. Linear combinations are only valid if the analyses are linear (Chapter 4). Nonlinear results should not be added together in a linear fashion, although Contact Tool results can be added. Thermal-stress and other types of analyses are not supported The supports must be the same between Environments for the results to be valid. Only the loading can change to allow for solution combinations. Solution combination calculations are very quick and does not require a re-solve.

29. April 22, 2004 Inventory #002071 9-29 � Solution Combinations To perform solution combinations, do the following: Add a Solution Combination branch. The Worksheet view will appear In the Worksheet view, add Environments and a coefficient (multiplier). The solution combination will be the sum of the multiples of the various Environments selected. Request results from the Context toolbar. These results will reflect the sum of the products of the selected Environments

30. April 22, 2004 Inventory #002071 9-30 � Solution Combinations For example, consider the case below of a sample model with two environments

31. April 22, 2004 Inventory #002071 9-31 � Solution Combinations Use of solution combinations allows the user to solve different environments, thereby considering the effect of different loads separately. By using the Solution Combination branch, a linear combination of solutions can be solved for very quickly without having to perform another separate solution. Multiple Solution Combination branches may be added, as needed.

32. April 22, 2004 Inventory #002071 9-32 F. Stress Singularities In any finite-element analysis, one seeks to balance accuracy and computational cost. As the mesh is refined, one expects to get mathematically more precise results. Quantities directly solved for (degrees of freedom) such as displacements and temperatures, converge without problems Derived quantities, such as stresses, strains, and heat flux, should also converge as the mesh is refined, but not as fast or smooth as DOF since these are derived from the DOF solution In some cases, however, derived quantities such as stresses and heat flux will not converge as the mesh is refined. These are situations where these values are artificially high. This section will discuss situations where derived solution quantities are artificially high. In thermal analyses, since temperature is the main quantity of interest, the discussion in this section will focus on stresses instead, not heat flux.

33. April 22, 2004 Inventory #002071 9-33 � Stress Singularities In a linear static structural analysis, there are several sources which may cause artificially high stresses, two common ones which are listed below: Stress singularities Geometry discontinuities, such as reentrant corners (shown on right) Point/edge loads and constraints Overconstraints Fixed supports and other constraints which prevent Poisson�s effect Fixed supports and other constraints which prevent thermal expansion In the above situations, refining the mesh at the artificially high stress area will keep increasing the stresses

34. April 22, 2004 Inventory #002071 9-34 � Stress Singularities If the area of artificially high stresses is not an area of interest, one can usually scope results only on part(s) or surface(s) of interest instead If the area of artificially high stresses is of interest, there are several ways to obtain more accurate stress results: Stress singularities Model geometry with fillets or other details which do not cause geometric discontinuities since some form of these (albeit small) would exist in the actual system Point loads and constraints should only be used on line bodies. For solid bodies, every load/constraint has a finite area on which it is applied, so these should be applied on areas rather than vertices Overconstraints A Fixed Support is an idealization, and modeling the constraint properly may be required (possibly including the geometry on which the part is connected) Although the above are some suggestions, these usually involve additional effort or more nodes/elements, so it is up to the user to review the results and understand if and why stresses may be artificially high.

35. April 22, 2004 Inventory #002071 9-35 G. Convergence As noted earlier, as the mesh is refined, the mathematical model becomes more accurate. However, there is computational cost associated with a finer mesh. Obtaining an optimal mesh requires the following: Having criteria to determine if a mesh is adequate Investing more elements only where needed Performing these tasks manually is cumbersome and inexact The user would have to manually refine the mesh, resolve, and compare results with previous solutions. Simulation has convergence controls to automate adaptive mesh refinement to a user-specified level of accuracy

36. April 22, 2004 Inventory #002071 9-36 � Convergence To use this feature, simply select a result branchand select the �Convergence� button on theContext toolbar A Convergence branch will appear below the result branch In the Details view of the Convergence branch, select whether the max or min value will be converged upon and input the allowable change (as a percentage) For �Type,� �Minimum� is available since some result quantities (e.g., directional deformation or minimum principal stress) may have negative values For allowable change, default is 20%. However, 5% fordisplacement and temperatures and 10% for other quantities is a good starting point. In the Details view of the Solution branch, input the max number of refinement loops per solve Input a reasonable value, such as 1 to 4, so that Simulation will not try to refine the mesh indefinitely.

37. April 22, 2004 Inventory #002071 9-37 � Convergence After this is completed, when solving, Simulation will automatically refine the mesh and resolve At least two iterations are required (initial solution and first refinement loop) The �Max Refinement Loops� in the Solution branch details allows the user to set the max number of loops per solve to prevent Simulation from excessive refinement. Usually, 2 to 4 max loops should be more than enough. Default is 1 loop per solve. The mesh will automatically be refined only in areas deemed necessary, based on error approximation techniques The convergence results will be stored for review in the �Convergence� branch If not converged within the specified percentage, a redexclamation mark will appear. If converged within the limits, a green checkmark will be shown The result branches will display only the last solution

38. April 22, 2004 Inventory #002071 9-38 � Convergence After the solution is complete, one can view the results and the last mesh Note that the mesh is refined only where needed, as shown in the example below The Convergence branch shows the trend for each refinement loop as well as the values and number of nodes and elements in the mesh

39. April 22, 2004 Inventory #002071 9-39 � Convergence & Stress Singularities As noted in the previous chapter, there are some causes for artificially high stresses Stress singularities are theoretically infinite stress, so Simulation�s adaptive mesh refinement will indicate this By specifying a reasonable value for the �Max Refinement Loops,� this will allow the user to know quickly whether a stress singularity or other type of artificially high stress source is present

40. April 22, 2004 Inventory #002071 9-40 � Convergence & Scoping Besides adding details to get rid of stress singularities, one can also converge on scoped results. If the artificially high stress region is not of interest, one can scope results on selected part(s) or surface(s) and add convergence controls to those results only. This provides the user with control on where to perform mesh refinement This also allows the user to ignore areas of artificially high stresses which are not of interest

41. April 22, 2004 Inventory #002071 9-41 � Convergence & Scoping Example For example, consider the simple part below. The part below has some geometric discontinuities, where smoothers were not modeled to reduce model complexity For a given set of loading conditions, if the user knew that the bottom of the part was failing, this may be a region of interest the user would focus on.

42. April 22, 2004 Inventory #002071 9-42 � Convergence & Scoping Example

43. April 22, 2004 Inventory #002071 9-43 � Results Not Used with Convergence Convergence cannot be used on the following result quantities: Any type of vector result Contact Tool results Frequency Finder stress/strain results Buckling stress/strain results Harmonic analysis results Shape Finder results Fatigue Tool graph results

44. April 22, 2004 Inventory #002071 9-44 � Convergence Summary Using convergence controls helps to achieve a given level of accuracy. Note that the �percent change� is related to the previous solution. This is not �percent error� since Simulation does not know beforehand what the �actual answer� is. Convergence controls provides a way to get an accurate answer based on the mathematical model. It does not compensate for inaccurate assumptions, however! Hence, if loads, supports, material properties, etc. are wrong, the solution will still be inaccurate. Because use of convergence controls results in adaptive mesh refinement, each new iteration will take longer than the previous solution Although adaptive meshing will put more nodes and elements only where needed, the mesh density will still increase Scoping results helps to minimize mesh density by explicitly indicating to Simulation the areas of interest

45. April 22, 2004 Inventory #002071 9-45