Post-processing J.Cugnoni, LMAF/EPFL, 2009. Finite element « outputs » Essential variables: ...

Post-processing

J.Cugnoni, LMAF/EPFL, 2009

Finite element « outputs » Essential variables:

Displacement u, temperature T

find u such that : K u = f

Natural variables : Stress , heat flux q Directly related to (derivatives of) essential variables

by the constitutive relationship in linear problems

Derived variables : Like strain = u, strain energy density, enthalpy

FE results: type & localization

Data types: Scalars (T): 1 component Vectors (u): 3 components + magnitude 2nd order tensors (): 6 components if symm. + invariants (von

Mises, max. principal, hydrostatic)

Localization: Unique Nodal values Element Nodal values Gauss (integration) points values Element centroid

Displacement – Strain post processing

Nodal displacement u (unique nodal val., essential var.)

Shape functions & derivatives at integration pt of the element

=> B matrix

Strain tensor at integration pt = eB u

Unique Nodal value

Element Integration pt

Shape functions and derivatives are only evaluated at integ. pts

Stress calculation at integration pts (linear elasticity)

Constitutive relationship of element e=> eC matrix

Stress tensor at integration pt i of element e: ei = eC ei


Element-wise constitutive relation

Strain tensor at integration pt i of element e: ei = eB eu


From integration pts to unique nodal values

Stress tensor at nodal pt kof the global mesh: k

Shape functions or other extrapolation functions

Stress tensor at integration pt i of the element e: ei

Unique Nodal value


Stress tensor at nodal pt j of the element e: ej

Weighted (or conditionnal)averaging

Element Nodal value

FE results in Abaqus Field output:

A snapshot of the values at all points in the model for a given time

History output: A « time curve » for a single variable at a given point

over time In STEP module:

Specify which variables must be computed in field output & history outputs

Can specify a « frequency » to reduce the output size For history output, you need to define a « set » to

extract time evolution of given points / elements

Example: open thermoMecaExo1Correct.cae Select to Model-1-Transient In Step module:

Edit existing Field output: Add all Energy outputs, add Forces-> NFORC Add Thermal outputs NFLUX & HFLA (heat flux * area)

History outputs: Tool -> Set -> Create : create a set of points for history output Create a new history output Domain=Set, Output: Thermal->NT (nodal temperature)

Run the Job « thermoMecaTransient »

Video: PostProDemo1.swf

FE result visualization in Abaqus Field outputs:

Select in Results -> Field outputsSelect the desired output time (Step & Frame)Contour plot:

colormap + deformed shapeSymbol plot:

to display vectors or principal tensor componentsOther features:

Cutting planes, display groups A lot of options to customize display

Result localization in Abaqus Abaqus Standard solver stores only necessary results in

ODB files: Essential variables : unique nodal values Natural variables: only at integration points Derived variables: localized where in makes sense

Abaqus CAE / visualization module can « extrapolate » some results at other locations Example: evaluate unique nodal stresses from integration points You can control the extrapolation in Results -> Option.. View « discontinuities » to identify « strong gradient » (=low

accuracy) regions of your mesh

Example (open thermoMecaTransient.odb): Contour plots of stress field, select time = 2000 s:

Select Mises, S33, Max. Principal components Change Visualization options (deformation scale factor, colormap

range, edges) Cutting plane

Results Options (select Mises stress): Disable averaging, look at element nodal values, notice the

discontinuities. Enable averaging, change the averaging threshold (0% -> 100%) Display discontinuities, notice regions of large discontinuities: sharp

corners = stress singularities !! Symbol plot:

Use display group to isolate a region View principal stress tensor and displacements

Video PostProDemo2.swf

Extracting values at node / element Select Field output, activate Contour plot

Use Tools->Query->Probe Value Select Probe = Element or Probe = Node Select result localization (for elements only)

Integration pts, Centroid, Element nodal

Activate the desired results in the table Pick a node / element to add it to the list Can write the table values to a text file: write

Example: Extract different stress values (int. pt, elem. nodal,

averaged nodal) at a given point


Extracting curves in Abaqus Path = spatial curve to « cut the model »:

Use Tools -> Path -> Create to generate Generation method:

Node list: pick nodes to define a polyline Point list: enter coordinates of polyline vertices Edge list: select element edges = efficient !! Circular: select points to generate a circle

To plot / save the curve: Use Tools -> XY data -> Create

Select source = Path Choose the path choose configuration = « undeformed » activate include intersection Generate the curve & save it for later use

Example: Define a linear path based on 2 nodes Define a path along edges with « feature edge » or

« shortest distance » option Define a circular path by 3 points Extract curves of Mises Stress distribution along each

path, save XY data Plot all XY curves


Extracting curves in Abaqus Time evolution curves :

From Field outputs: Use Tools -> XY data -> Create Choose source = Field Output Select result localization (integ pt, nodal, …) Select result to extract Pick elements or nodes from 3D view Plot and save if necessary

From History outputs: Use Tools -> XY data -> Create Choose source = History output Select the desired history output, plot and save

Example: Extract time evolution curves of the temperature at

some nodes Extract time evolution curves of the Mises stress at

for different type of result localization Plot all XY curves


Exporting data from Abaqus

Exporting field outputs If needed, isolate a region of interest with

Display GroupUse Report -> Field OutputSelect the localization & type of the resultSelect output file & check append / overwriteSelect Data: all data, column totals, statistics?

Exporting data from Abaqus

Exporting XY curvesCreate XY data and save itUse Report -> XYSelect the XY curvesSelect output file & check append / overwriteSelect Data: all data, column totals, statistics?

Example: Use Report-> Field Output to extract the min, max

and average nodal temperature in a Text file Create a XY curve of the time evolution of the

temperature at one point and export it to another text file


Extracting images & movies Image capture / printing:

File -> Print Choose Destination = Printer or File If File, choose format (PNG for example) and file name

Movies: Enter an animation mode:

Animate -> Time History / Scale Factor / Harmonic Use Animate -> Save As to generate movie

Select destination file and format Set Options to choose the level of compression Choose display option (background ?) Set frame rate to ~5 image/s

Example: Extract an image of Mises stress field at

t=2000s showing the min & max valuesExtract a movie of the time evolution of the

temperature in the model


Advanced post-processing

Calculate new fields: If necessary, create a new coordinate system: Tools -> Coord.

System -> Create Run Tools -> Create Field outputs -> From fields

Pick a time: Step & Increment Enter an expression in the « calculator »:

Pick operators & operands (fields) in the list The new result will be « save » in memory only in a temporary

Step called « Session Step » You can use this tool to evaluate quantities in different

coordinate systems (for example stress in cylindrical coordinates)

Post-processing J.Cugnoni, LMAF/EPFL, 2009. Finite element « outputs » Essential variables: ...

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