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# Post- processing - PowerPoint PPT Presentation

Post- processing. J.Cugnoni , LMAF/EPFL, 2012. Finite element « outputs ». Essential variables: Displacement u , temperature T find u such that : K u = f Natural variables : Stress s , heat flux q

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### Post-processing

J.Cugnoni, LMAF/EPFL, 2012

Finiteelement « outputs »

• Essential variables:

• Displacementu, temperature T

findu suchthat: Ku = f

• Natural variables :

• Stress s, heat flux q

• Directlyrelated to (derivatives of) essential variables by the constitutive relationship in linearproblems

• Derived variables :

• Likestrain = u, strainenergydensity, enthalpy

• Data types:

• Scalars (T): 1 component

• Vectors (u): 3 components + magnitude

• 2ndordertensors (s): 6 components if symm. + invariants (von Mises, max. principal, hydrostatic)

• Localization:

• Unique Nodal values

• Element Nodal values

• Gauss (integration) points values

• Elementcentroid

Nodal displacement u

(unique nodal val., essential var.)

Unique Nodal value

Shape functions and derivatives are only evaluated at integ. pts

Shape functions & derivatives at integration pt of the element

=> B matrix

Strain tensor at integration pt

e = eBu

Element Integration pt

Displacement – Strain post processing

Strain tensor at integration pt i of element e: eei = eBeu

Element Integration pt

Constitutive relationship of element e

=> eC matrix

Element-wise constitutive relation

Stress tensor at integration pt i of element e: esi = eCeei

Element Integration pt

Stress tensor at integration pt i

of the element e: esi

Element Integration pt

Shape functions or

other extrapolation functions

Stress tensor at nodal pt j

of the element e: esj

Element Nodal value

Weighted (or conditionnal)averaging

Stress tensor at nodal pt kof the global mesh: sk

Unique Nodal value

• Field output:

• A snapshot of the values at all points in the model for a giventime

• History output:

• A « time curve » for a single variable at a given point over time

• In STEP module:

• Specifywhich variables must becomputed in field output & history outputs

• Can specify a « frequency » to reduce the output size

• For history output, youneed to define a « set » to extract time evolution of given points / elements

How to: specify non-default field / history outputs

• Example:

• open thermoMecaExo1Correct.cae

• Select to Model-1-Transient

• In Step module:

• Edit existing Field output:

• 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

• Field outputs:

• Select in Results -> Field outputs

• Select the desired output time (Step & Frame)

• Contour plot:

• colormap + deformedshape

• Symbol plot:

• to display vectors or principal tensor components

• Otherfeatures:

• Cutting planes, display groups

• A lot of options to customize display

• Abaqus Standard solver stores onlynecessaryresults in ODB files:

• Essential variables : unique nodal values

• Natural variables: onlyatintegration points

• Derived variables: localizedwhere in makessense

• Abaqus CAE / visualization module can « extrapolate » someresultsatother locations

• Example: evaluate unique nodal stresses fromintegration points

• You can control the extrapolation in Results -> Option.

• Use view« discontinuities » to identify « strong gradient » (=lowaccuracy) regions of yourmesh

How to: visualize 3D fields

• 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 atnode / 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

How to: extract values atselected points

• Example:

• Extract different stress values (int. pt, elem. nodal, averaged nodal) at a given point

Video: PostProDemo3.swf

• 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

How to: extract a 2D curvealong a path

• 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

Video: PostProDemo4.swf

• 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

How to: extract a time-evolutioncurve

• 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

Video: PostProDemo5.swf

• Exporting field outputs

• If needed, isolate a region of interest with Display Group

• Use Report -> Field Output

• Select the localization & type of the result

• Select output file & check append / overwrite

• Select Data: all data, column totals, statistics?

• Exporting XY curves

• Create XY data and save it

• Use Report -> XY

• Select the XY curves

• Select output file & check append / overwrite

• Select Data: all data, column totals, statistics?

How to: export data to text files

• 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

Video: PostProDemo6.swf

• 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

How to: capture images and animations

• Example:

• Extract an image of Mises stress field at t=2000s showing the min & max values

• Extract a movie of the time evolution of the temperature in the model

Video: PostProDemo7.swf

• Changingcoordinate system:

• Create a coordinate system (for examplecylindrical)

• In Result -> Options:

• choose Transformation, User defined

• Pick the coordinate system to use for post processing

• Calculatenew fields:

• If necessary, create a new coordinate system: Tools -> Coord. System -> Create

• Run Tools -> Create Field outputs -> Fromfields

• Pick a time: Step & Increment

• Enter an expression in the « calculator »:

• Pickoperators & operands (fields) in the list

• The new resultwillbe « save » in memoryonly in a temporaryStepcalled « Session Step »

• You can use thistool to evaluatequantities in differentcoordinatesystems (for example stress in cylindricalcoordinates)