Transcript Post-processing

Post-processing
J.Cugnoni, LMAF/EPFL, 2009
Finite element « outputs »
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Essential variables:
 Displacement
u, temperature T
find u such that : K u = f
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Natural variables :
 Stress
s, heat flux q
 Directly
related to (derivatives of) essential variables
by the constitutive relationship in linear problems
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Derived variables :
 Like
strain = u, strain energy density, enthalpy
FE results: type & localization
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Data types:
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Scalars (T): 1 component
Vectors (u): 3 components + magnitude
2nd order tensors (s): 6 components if symm. + invariants (von
Mises, max. principal, hydrostatic)
Localization:
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Unique Nodal values
Element Nodal values
Gauss (integration) points values
Element centroid
Displacement – Strain post processing
Unique Nodal value
Shape functions and
derivatives are only
evaluated at integ. pts
Element Integration pt
Nodal displacement u
(unique nodal val., essential var.)
Shape functions & derivatives
at integration pt of the element
=> B matrix
Strain tensor at integration pt
e = eB u
Stress calculation at integration pts (linear elasticity)
Element Integration pt
Element-wise
constitutive relation
Element Integration pt
Strain tensor at integration pt i
of element e: eei = eB eu
Constitutive relationship
of element e
=> eC matrix
Stress tensor at integration pt i
of element e: esi = eC eei
From integration pts to unique nodal values
Element Integration pt
Stress tensor at integration pt i
of the element e: esi
Shape functions or
other extrapolation functions
Element Nodal value
Stress tensor at nodal pt j
of the element e: esj
Weighted (or conditionnal)
averaging
Unique Nodal value
Stress tensor at nodal pt k
of the global mesh: sk
FE results in Abaqus
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Field output:
 A snapshot
of the values at all points in the model for
a given time
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History output:
A«
time curve » for a single variable at a given point
over time
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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
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Example:
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open thermoMecaExo1Correct.cae
Select to Model-1-Transient
In Step module:
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Edit existing Field output:
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History outputs:
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Add all Energy outputs, add Forces-> NFORC
Add Thermal outputs NFLUX & HFLA (heat flux * area)
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
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Field outputs:
 Select
in Results -> Field outputs
 Select the desired output time (Step & Frame)
 Contour plot:
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colormap + deformed shape
 Symbol
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plot:
to display vectors or principal tensor components
 Other
features:
Cutting planes, display groups
 A lot of options to customize display
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Result localization in Abaqus
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Abaqus Standard solver stores only necessary results in
ODB files:
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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
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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
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Example (open thermoMecaTransient.odb):
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Contour plots of stress field, select time = 2000 s:
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Results Options (select Mises stress):
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Select Mises, S33, Max. Principal components
Change Visualization options (deformation scale factor, colormap
range, edges)
Cutting plane
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:
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Use display group to isolate a region
View principal stress tensor and displacements
Video PostProDemo2.swf
Extracting values at node / element
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Select Field output, activate Contour plot
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Use Tools->Query->Probe Value
 Select
Probe = Element or Probe = Node
 Select result localization (for elements only)
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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
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Example:
 Extract
different stress values (int. pt, elem. nodal,
averaged nodal) at a given point
Video: PostProDemo3.swf
Extracting curves in Abaqus
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Path = spatial curve to « cut the model »:
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Use Tools -> Path -> Create to generate
Generation method:
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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:
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Use Tools -> XY data -> Create
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Select source = Path
Choose the path
choose configuration = « undeformed »
activate include intersection
Generate the curve & save it for later use
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Example:
 Define
 Define
a linear path based on 2 nodes
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
Extracting curves in Abaqus
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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
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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 data from Abaqus
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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
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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?
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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
Extracting images & movies
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Image capture / printing:
 File -> Print
 Choose Destination = Printer or File
 If File, choose format (PNG for example) and file name
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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
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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
Advanced post-processing
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Calculate new fields:
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If necessary, create a new coordinate system: Tools -> Coord.
System -> Create
Run Tools -> Create Field outputs -> From fields
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Pick a time: Step & Increment
Enter an expression in the « calculator »:
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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)