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Post- processing

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

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  1. Post-processing J.Cugnoni, LMAF/EPFL, 2012

  2. 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

  3. FE results: type & localization • 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

  4. 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

  5. Stress calculation at integration pts (linear elasticity) 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

  6. From integration pts to unique nodal values 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

  7. FE results in Abaqus • 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

  8. 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 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

  9. FE result visualization in Abaqus • 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

  10. Result localization in Abaqus • 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

  11. 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

  12. 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

  13. How to: extract values atselected points • Example: • Extract different stress values (int. pt, elem. nodal, averaged nodal) at a given point Video: PostProDemo3.swf

  14. 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

  15. 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

  16. 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

  17. 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

  18. Exporting data from Abaqus • 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?

  19. Exporting data from Abaqus • 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?

  20. 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

  21. 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

  22. 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

  23. Advanced post-processing • 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)

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