Post-processing

J.Cugnoni, LMAF/EPFL, 2011

Essential variables:◦ Displacement u, temperature T

find u such that : K u = f Natural variables :

◦ Stress s, 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

Finite element « outputs »

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

invariants (von Mises, max. principal, hydrostatic)

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

FE results: type & localization

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 pte = 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: esi = eC eei

Element Integration pt

Element-wise constitutive relation

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

Element Integration pt

From integration pts to unique nodal values

Stress tensor at nodal pt kof the global mesh: sk

Shape functions or other extrapolation functions

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

Unique Nodal value

Element Integration pt

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

Weighted (or conditionnal)averaging

Element Nodal value

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

FE results in Abaqus

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

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

colormap + deformed shape◦ Symbol plot:

to display vectors or principal tensor components◦ Other features:

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

FE result visualization 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

Result localization in Abaqus

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

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

Extracting values at node / element

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

Extracting curves in Abaqus

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

Extracting curves in Abaqus

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 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?

Exporting data from Abaqus

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

Extracting images & movies

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

Changing coordinate system:◦ Create a coordinate system (for example cylindrical)◦ In Result -> Options:

choose Transformation, User defined Pick the coordinate system to use for 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)

Advanced post-processing