AWS90 Ch08 Results

Results Postprocessing

Chapter Eight

March 29, 2005Inventory

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Chapter Overview• In this chapter, aspects of reviewing results will be covered:

– Viewing Results– Scoping Results– Exporting Results– Coordinate Systems & Directional Results– Solution Combinations– Stress Singularities– Error Estimation– Convergence

• The capabilities described in this section are applicable to all ANSYS licenses, except when noted otherwise


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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.

Displacement Scaling Display Method Contour Settings Outline Display Slice Planes

Min/Max Probe Tool Animation Controls Export AVI Convergence Alerts


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… 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

Model shown is from a sample Pro/ENGINEER assembly.

No Displacement Scaling Automatic Displacement Scaling


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… Display Method• The “Geometry” button controls the contour

display method. Four choices are possible:Exterior IsoSurfaces

Capped IsoSurfaces Slice Planes

“Exterior” is the default display option and is most commonly used.

“IsoSurfaces” is useful to display regions with the same contour value.

“Capped IsoSurfaces” will remove regions of the model where the contour values are above (or below) a specified value.

“Slice Planes” allow a user to ‘cut’ through the model visually. A capped slice plane is also available, as shown on the left.

Model shown is from a sample Inventor assembly.


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… Contour Settings• The “Contours” button controls the way in

which contours are shown on the modelSmooth Contours Contour Bands

Solid FillIsolines


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… Outline Display• The “Edges” button allows the user show the

undeformed geometry or mesh

No Wireframe Show Undeformed Wireframe

Show Undeformed Model Show Elements


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… Slice Planes• When in Slice Plane viewing mode, slice planes

can 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

Move a slice plane by dragging handleHandles of 3 defined slice planes Click on one side of bar to cap view


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… Min/Max and Probe Tool• The min/max symbols can be removed by selecting

the “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


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… 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”


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… 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.


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… 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

Original Contour Legend Modified Contour Legend


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… Manipulating the Legend• For Capped IsoSurface plots, the legend has additional

features to manipulate the display– The middle long grey bar controls where the cutoff

value 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

Default Capped IsoSurface Modified Capped IsoSurface


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… 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

Same legend values used for both results make comparison easier


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… Vector Plots• Vector plots involve any vector result quantity with

direction, such as deformation, principal stresses/strains, and heat flux– Activate vectors for appropriate quantities using the vector

graphics icon

– Once the vectors are visible their appearance can be modified using the vector display controls (see next slide for examples)

Proportional Vectors Equal Length Vectors

Vector Length Control

Element AlignedGrid Aligned Line Form Solid Form

Vector Length Control


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… Vector Plots• Examples

Solid Form, Grid Aligned Line Form, Grid Aligned

Proportional Length Equal Length


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… Multiple Viewports• Using multiple viewports is especially useful for

postprocessing, 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


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… 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


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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.


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… 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.


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… Scoping Surface/Part Results• Some examples of scoping results on surfaces/parts:

Scoping results on a single part Stress results on selected surfaces

Vector Principal Stresses on single part


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… 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


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… 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.

The result branch name is now more descriptive, indicating it is a scoped result on a given edge.Renaming result branches is also useful for directional results, as it will change the name to the direction of the stress or deformation or heat flux.


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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


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… 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”


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… 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.


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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.


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… Coordinate Systems• For the model shown below, one local

cylindrical 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.

Deformation in Global X-Direction Deformation in Local Cylindrical X-Direction


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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.

ANSYS License AvailabilityDesignSpace EntraDesignSpaceProfessional xStructural xMechanical/Multiphysics x


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… 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



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… Solution Combinations• For example, consider the case below of a sample model

with two environments


“Environment” “Environment 3”

Solution Combination Results


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… 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.



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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.


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… 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

Model shown is from a sample Mechanical Desktop assembly.


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… 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.


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G. Error Estimation• You can insert an Error result based on stresses

(structural), or heat flux (thermal) to help identify regions of high error (see example next page).

• These regions show where the model would benefit from a more refined mesh in order to get a more accurate answer.

• Regions of high error also indicate where refinement will take place if convergence is used.

• More information on error estimation is available in section 19.7 of the ANSYS Theory Reference.


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. . . Error Estimation• Error plot shows region where element mesh refinement

may be necessary.

• Error is plotted in terms of energy.


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H. 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


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… Convergence• To use this feature, simply select a result branch

and 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.


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… 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


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… 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


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… 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

In this case, it is clear that the stresses will increase without bound.

By examining the model, it was clear that a stress singularity existed, which explains why the stresses do not converge as it normally would.


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… 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


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… 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.

Model shown is from a sample Mechanical Desktop assembly.

Possible stress singularity

Region of interest


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… Convergence & Scoping Example

On the other hand, convergence controls on scoped results allows for adaptive refinement only in user-specified locations, providing the user with more control over the mesh and the adaptive solution.

In this way, the user can get accurate stresses on the bottom surface of the part.

If convergence controls were simply added to the entire model, the geometric discontinuity would cause a stress singularity which increases without bounds.

The solution becomes very costly by including the stress singularity.


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… 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


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… 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


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• Workshop 8 – Advanced Results Processing

• Goal:– Analyze the high pressure vent assembly shown below and

then use some of the advanced postprocessing features to review the stress and deflection results.

I. Workshop 8

Documents

AWS90 Ch08 Results