Anasys Full.ppt

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Chapter 2 - FEA and ANSYS
What is FEA?
• Finite Element Analysis is a way to simulate loading conditions on
a design and determine the design’s response to those
conditions.
• The design is modeled using discrete building blocks called
elements.
– Each element has exact equations
that describe how it responds to a
certain load.
– The “sum” of the response of all
elements in the model gives the
total response of the design.
– The elements have a finite number
of unknowns, hence the name
finite elements.
Historical Note
• The finite element method of
structural analysis was created
by academic and industrial
researchers during the 1950s
and 1960s.
• The underlying theory is over
100 years old, and was the basis
for pen-and-paper calculations in
the evaluation of suspension
bridges and steam boilers.

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...What is FEA?
• The finite element model, which has a finite number of unknowns,
can only approximate the response of the physical system, which
has infinite unknowns.
– So the question arises: How good is the approximation?
Physical System F.E. Model
– Unfortunately, there is no easy
answer to this question. It depends
entirely on what you are simulating
and the tools you use for the
simulation. We will, however,
attempt to give you guidelines
throughout this training course.

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...What is FEA?
Why is FEA needed?
• To reduce the amount of prototype testing
– Computer simulation allows multiple “what-if” scenarios to be tested
quickly and effectively.
• To simulate designs that are not suitable for prototype testing
– Example: Surgical implants, such as an artificial knee
• The bottom line:
– Cost savings
– Time savings… reduce time to market!
– Create more reliable, better-quality designs

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About ANSYS
• ANSYS is a complete FEA software package used by engineers
worldwide in virtually all fields of engineering:
– Structural
– Thermal
– Fluid, including CFD (Computational Fluid Dynamics)
– Electrical / Electrostatics
– Electromagnetics
• A partial list of industries in which ANSYS is used:
– Aerospace
– Automotive
– Biomedical
– Bridges & Buildings
– Electronics & Appliances
– Heavy Equipment & Machinery
– MEMS - Micro Electromechanical Systems
– Sporting Goods

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…About ANSYS
• ANSYS/Multiphysics is the flagship ANSYS product which
includes all capabilities in all engineering disciplines.
• There are three main component products derived from
ANSYS/Multiphysics:
– ANSYS/Mechanical - structural & thermal capabilities
– ANSYS/Emag - electromagnetics
– ANSYS/FLOTRAN - CFD capabilities
• Other product lines:
– ANSYS/LS-DYNA - for highly nonlinear structural problems
– DesignSpace - an easy-to-use design and analysis tool meant for
quick analysis within the CAD environment
– ANSYS/ProFEA - for ANSYS analysis & design optimization within
Pro/ENGINEER

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ANSYS/
Structural
ANSYS/
Professional
ANSYS/
ProFEA
DesignSpace
…About ANSYS
ANSYS/
ED
ANSYS/
University
ANSYS/
PrepPost
ANSYS/
Multiphysics
ANSYS/
FLOTRAN
ANSYS/
Emag
ANSYS/
LS-DYNA
ANSYS/
Mechanical

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…About ANSYS
• Other products:
– AI-EMAX – high frequency electromagnetic analysis product. Combines
the ICEM CFD preprocessor and postprocessor capabilities with the
ANSYS, Inc. HF Electromagnetic solver.
– ICEM CFD – preprocessing software used to create 3-D grids required by
CFD and structural analyses. This product is offered by ICEM CFD
(www.icemcfd.com), an ANSYS,Inc. subsidiary.
– AI-Workbench – is an open and flexible new generation CAE focused
application development platform from ANSYS Inc. The technology
components of this platform can be used to create market-specific vertical
applications or custom-design CAE solutions for large enterprise,
including the whole supply chain.
– DesignXplorer – a product that simplifies optimization studies of parts or
assemblies. Allowing bi-directional associativity with a number of CAD
packages, DesignXplorer coordinates the iterative design computations,
and automatically updates the CAD file to the optimized design.

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Compression of a Hyperelastic Seal
…About ANSYS
• Structural analysis is used to determine deformations, strains,
stresses, and reaction forces.
• Static analysis
–Used for static loading
conditions.
–Nonlinear behavior such
as large deflections, large
strain, contact, plasticity,
hyperelasticity, and creep
can be simulated.

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…About ANSYS
• Dynamic analysis
– Includes mass and damping effects.
– Modal analysis calculates natural frequencies and mode shapes.
– Harmonic analysis determines a structure’s response to sinusoidal
loads of known amplitude and frequency.
– Transient Dynamic analysis determines a structure’s response to
time-varying loads and can include nonlinear behavior.
• Other structural capabilities
– Spectrum analysis
– Random vibrations
– Eigenvalue buckling
– Substructuring, submodeling
Mode Shape Animation

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…About ANSYS
• Explicit Dynamics with ANSYS/LS-DYNA
– Intended for very large deformation simulations where inertia forces
are dominant.
– Used to simulate impact, crushing, rapid forming, etc.
Impact Analysis of a Vehicle Crash Test

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…About ANSYS
• Thermal analysis is used to determine the temperature
distribution in an object. Other quantities of interest include
amount of heat lost or gained, thermal gradients, and thermal flux.
• All three primary heat transfer modes can be simulated:
conduction, convection, radiation.
• Steady-State
– Time-dependent effects are
ignored.
• Transient
– To determine temperatures, etc.
as a function of time.
– Allows phase change (melting or
freezing) to be simulated.
Transient Temperature of a
Warming Clothes Iron

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…About ANSYS
• Electromagnetic analysis is used to calculate magnetic fields in
electromagnetic devices.
• Static and low-frequency electromagnetics
– To simulate devices operating with DC power sources, low-frequency
AC, or low-frequency transient signals.
– Example: solenoid actuators,
motors, transformers
– Quantities of interest include
magnetic flux density, field
intensity, magnetic forces and
torques, impedance, inductance,
eddy currents, power loss, and
flux leakage.

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…About ANSYS
• High-frequency electromagnetics
– To simulate devices with propagating electromagnetic waves.
– Example: microwave and RF passive components, waveguides,
coaxial connectors
– Quantities of interest include S-parameters, Q-factor, Return loss,
dielectric and conducting losses, and electric and magnetic fields.
Electric field (EFSUM) in a coaxial cable

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…About ANSYS
• Electrostatics
– To calculate the electric field from voltage or charge excitation.
– Example: High voltage devices, micro-electromechanical systems
(MEMS), transmission lines
– Typical quantities of interest are electric field strength and
capacitance.
• Current Conduction
– To calculate current in a conductor from an applied voltage
• Circuit Coupling
– To couple electric circuits with electromagnetic devices

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…About ANSYS
• Types of electromagnetic analysis:
– Static analysis calculates magnetic fields due to direct current (DC) or
permanent magnets.
– Harmonic analysis calculates magnetic fields due to alternating
current (AC).
– Transient analysis is used for time-varying magnetic fields.

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…About ANSYS
• Computational Fluid Dynamics (CFD)
– To determine the flow distributions and temperatures in a fluid.
– ANSYS/FLOTRAN can simulate laminar and turbulent flow,
compressible and incompressible flow, and multiple species.
– Applications: aerospace, electronic packaging, automotive design
– Typical quantities of interest are velocities, pressures, temperatures,
and film coefficients.
Velocity of Fluid in a Duct Pressure Distribution
on a Football

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…About ANSYS
• Acoustics
– To simulate the interaction between a fluid medium and the surrounding
solid.
– Example: speakers, automobile interiors, sonars
– Typical quantities of interest are pressure distribution, displacements,
and natural frequencies.
• Contained-Fluid Analysis
– To simulate the effects of a contained, non-flowing fluid and calculate
hydrostatic pressures due to sloshing.
– Example: oil tankers, other liquid containers
• Heat and Mass Transport
– A one-dimensional element is used to calculate the heat generated by
mass transport between two points, such as in a pipe.

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Deflection of a bi-metal
bar due to heating
…About ANSYS
• Coupled-Field Analysis considers the mutual interaction between
two or more fields. The fact that each field depends upon another
makes it impossible to solve each separately, therefore you need
a program that can solve both physics problems by combining
them.
• Examples:
– Thermal-stress analysis
– Piezoelectrics (electric & structural )
– Acoustics (fluid & structural)
– Thermal-electric analysis
– Induction heating (magnetic and thermal)
– Electrostatic-structural analysis

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About the Company
ANSYS, Inc.
• Developer of ANSYS family of products
• Headquartered in Canonsburg, PA - USA (south of Pittsburgh)

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…About the Company
ANSYS Support Distributors (ASDs)
• Sales and support network for ANSYS
• Over 75 offices worldwide
• Local expertise for ANSYS consulting and training

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…About the Company
ANSYS Support Coordinator (ASC)
• Contact for ANSYS at your company site
• Focal point for ANSYS correspondence; software updates, error
notices, newsletter and other mailings, etc.

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• Interactive mode allows you to interact “live” with ANSYS, reviewing
each operation as you go.
• Of the three main phases of an analysis — preprocessing, solution,
postprocessing — the preprocessing and postprocessing phases are
best suited for interactive mode.
• We will mainly cover interactive mode in this course.
Chapter 3 – Interactive Mode
Overview

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Chapter 3 - Interactive Mode
Starting ANSYS
Launcher –
• Allows you to start ANSYS and
other ANSYS utilities by pressing
buttons on a menu.
• On Windows systems, press:
Start > Programs > ANSYS 6.1
• On Unix systems, issue
tansys61 & to bring up the
launcher.

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• Pressing the Interactive button on the launcher brings up a dialog
box containing start-up options:
…Starting ANSYS
Windows systems UNIX systems
1
2
3
4
5
1
2
3
4
5
Select Edit >>Preferences > ANSYS
GUI Settings in main launcher

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Launcher (cont’d)
• After choosing the desired start-up options, press the Run button
to start ANSYS.
Command Line
• ANSYS is started by typing a command at the system level. For
example:
– ansys61
– ansys61 -g
– ansys61 -g -j plate
– ansys61 -g -p ANE3FL -d 3d -j proj1 -m 128
…Starting ANSYS

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Command Line (cont’d)
• Typical start-up options, commonly known as command line
options, are:
-g (to automatically bring up the GUI upon start-up)
-p product_code
-d graphics_device
-j jobname
-m memory
• The working directory is the directory in which the command is
issued.
• Refer to your ANSYS Installation and Configuration Guide for
details on the command line options.
…Starting ANSYS

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Chapter 3 – Memory
Overview
• ANSYS Executable memory is the memory required for the
ANSYS program.
• ANSYS Workspace is the memory ANSYS requires to run in
addition to the ANSYS Executable memory.
• Real memory is the amount of actual, physical memory (RAM)
available through memory chips on your machine.
• System virtual memory is simply a portion of the computer's hard
disk used by the system to supplement physical memory.

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Chapter 3 - Memory
Definitions
• Workspace space (i.e –m ) is the memory ANSYS needs to run.
Default is 64 MB on Windows machine and 128 on UNIX machines.
• Database space (i.e. –db) is used to work with the ANSYS
database. For example, model geometry, material properties,
loads, etc. Defaults to 32MB on Windows and 64MB on UNIX
machines.
• Scratch space is where all internal calculations are done. For
example, element matrix formulation, frontal solution, Boolean
calculations, and so on.
Scratch space = Workspace - Database

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• ANSYS Memory Guidelines:
– Use a workspace (i.e. –m) of 1 Gbyte per million DOFS
– Use a disk space of 10 Gbytes per million DOFS
Chapter 3 - Memory
Limits/Guidelines
• ANSYS Memory Limits

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Output
Window
Icon Toolbar Menu
Abbreviation Toolbar Menu
Utility Menu
Graphics Area
Main Menu
Input Line
Chapter 3 – The GUI
Layout
Raise/Hidden Icon
Current Settings
User Prompt Info

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Moving the top line also
resizes the Toolbar area
Moving the left line also
resizes the Main Menu area
Click and drag the top,
bottom, left and right lines
…Layout
•You can save your customized layout using
Utility Menu > MenuCtrls > Save Menu Layout.
• The layout can be customized:

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• System Fonts & Colors of the layout can be customized:
– Windows System
• Uses the system display properties
– Unix system:
• Common Desktop Environment (CDE) uses the system settings
• Otherwise (e.g. a telnet to a Unix Machine) uses the ~/.Xdefaults settings
– *EUIDL*Font: Times 12 normal
– *EUIDL*Background: purple
• The GUI has been modularized using the Tcl/Tk language which allows
for dialog boxes, ANSYS messages, etc. to be easily changed to a
country’s native language.
…Layout

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Graphics Window
Graphics Area
• Display location of model entities, postprocessing contours, and
postprocessing graphs.

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• Tree structure format.
• Contains the main functions required for an
analysis.
• Use scroll bar to gain access to long tree
structures.
Main Menu
scroll bar

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…Main Menu
Before collapsing Preprocessor Branch After expanding Preprocessor Branch
The tree structure is the same before
and after the Preprocessor branch of
Main Menu is collapsed
Select to collapse
Preprocessor Branch
• Tree structure behavior – sub branch preserved

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…Main Menu
The option to expand the
branch is displayed
Position mouse cursor on branch of Main
Menu – then select right mouse button
Selecting “Expand All” expands
the branch contents
• Expand all option

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Chapter 3 – Main Menu
UIDL Behavior
With UIDL behavior active …
Creating a Volume branch open
When Deleting branch is opened, the
Creating a Volume branch is closed

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Chapter 3 – Main Menu
Filtered Branches
Main Menu with structural and
thermal element type defined
Main Menu with only thermal
element type defined
Only “Apply” branches shown are those
for defined element types

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• Contains abbreviations -- short-cuts to commonly used
commands and functions.
• A few predefined abbreviations are available, but you can add
your own. Requires knowledge of ANSYS commands.
• A powerful feature which you can use to create your own “button
menu” system!
Abbreviation Toolbar Menu

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Pan-Zoom-Rotate
New Analysis
• Contains icons of commonly used functions.
• Can be customized by the user (i.e adding icons, additional
toolbars)
Open ANSYS File
Save Analysis
ANSYS Help
Image Capture
Report Generator
Icon Toolbar Menu

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• Jobname definition when using Open ANSYS File Icon:
– the ANSYS jobname will be changed to the prefix of the database file being resumed.
Open ANSYS File
When opening the “blades.db” database
(using the Open ANSYS File Icon), the
jobname will be changed to “blades”.
The Open ANSYS File Icon can be used to open either ANSYS
Database or ANSYS Command file types
….Icon Toolbar Menu

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Raise/Hidden Icon
Pan/Zoom/Rotate
Widget Hidden
Pan/Zoom/Rotate
Widget Shown
Select Raise/ Hidden Icon
• The Raise/Hidden Icon can be used to “bring to the front” any
hidden ANSYS created windows (except the output window).

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• Allows you to enter commands. (Most GUI functions actually
“send” commands to ANSYS. If you know these commands, you
can type them in the Input Window).
• Command format is dynamically displayed.
Input Window
As a command is typed, the format of the
command is dynamically displayed

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Select down arrow to see
list of issued commands
List of issued commands
Use scroll bar to gain access
to all commands issued
Commands can be reissued by double-
clicking on the listed command
The up and down arrows on the keyboard can be
used to select different listed commands
…Input Window
• Reissuing commands:

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• Contains utilities that are generally available throughout the
ANSYS session: graphics, on-line help, select logic, file controls,
etc.
• Conventions used in Utility Menu:
– “…” indicates a dialog box
– “ +” indicates graphical picking
– “ >” indicates a submenu
– “ ” (blank) indicates an action
Utility Menu

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Current Settings
• The current element attributes settings, and currently active
coordinate system are displayed at the bottom on the GUI.
Element Attributes Active Coordinate System

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User prompt info
• Instructions to the user are displayed in the lower left hand area of
the GUI. The user will be given user prompt info for operations
such as picking operations.
User Prompt Info

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Output Window
• The output window gives the user feedback on how ANSYS
interpreted the user’s input.
• The Output Window is independent of the ANSYS menus.
Caution: Closing the output window closes the entire ANSYS
session!
Able to verify the ANSYS version

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• The Preferences dialog (Main Menu >
Preferences) allows you to filter out
menu choices that are not applicable to
the current analysis.
• For example, if you are doing a thermal
analysis, you can choose to filter out
other disciplines, thereby reducing the
number of menu items available in the
GUI:
– Only thermal element types will be shown
in the element type selection dialog.
– Only thermal loads will be shown.
– Etc.
Preferences

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Other GUI Notes
• Some dialog boxes have both Apply and OK buttons.
– Apply applies the dialog settings, but retains (does not close) the
dialog box for repeated use.
– OK applies the dialog settings and closes the dialog box.
• Remember that you are not restricted to using the menus. If you
know the command, feel free to enter it in the Input Window!
• The output window is not affected by the Raise/Hidden Button.
For convenience, the user may want to resize the GUI, so part of
the output window is displayed to allow easy access.
…The GUI

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• Demo:
– Start ANSYS using the launcher
– Show the various parts of the GUI
– Bring up “Keypoints in Active CS” dialog box and show the difference
between OK and Apply
– Show the Preferences dialog
– Explain the Output window
– Show the use of the Raise/Hidden Icon
– Explain the Main Menu behavior
…The GUI

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• The most heavily used interactive
capabilities are graphics and graphical
picking.
– Graphics is used to visualize the model,
loading, results, and other input and output
data.
– Picking is used for model creation, meshing,
loading, etc.
• Use Plot in the Utility menu to produce
plots, or issue the commands shown.
Graphics and Picking
/replot
kplot
lplot
aplot
vplot
nplot
eplot
gplot

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• The PlotCtrls menu is used to control how
the plot is displayed:
– plot orientation
– zoom
– colors
– symbols
– annotation
– animation
– etc.
• Among these, changing the plot
orientation (/VIEW) and zooming are the
most commonly used functions.
…Graphics and Picking

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• The default view for a model is the front view:
looking down the +Z axis of the model.
• To change it, use dynamic mode — a way to
orient the plot dynamically using the Control
key and mouse buttons.
– Ctrl + Left mouse button pans the model.
– Ctrl + Middle mouse button:
zooms the model
spins the model (about screen Z)
– Ctrl + Right mouse button rotates the model:
about screen X
about screen Y
Note, the Shift-Right button on a two-button
mouse is equivalent to the Middle mouse
button on a three-button mouse.
P Z R
Ctrl





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• If you don’t want to hold down the
Control key, you can use the Dynamic
Mode setting in the Pan-Zoom-Rotate
dialog box.
– The same mouse button assignments
apply.
– On 3-D graphics devices, you can also
dynamically orient the light source.
Useful for different light source shading
effects.
When using 3-D driver

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• Other functions in the Pan-
Zoom-Rotate dialog box:
– Preset views
– Zoom-in on specific regions of
the model
– Pan, zoom, or rotate in
discrete increments (as
specified by the Rate slider)
• Rotation is about the
screen X, Y, Z coordinates.
– Fit the plot to the window
– Reset everything to default
Front +Z view, from (0,0,1)
Back -Z view (0,0,-1)
Top +Y view (0,1,0)
Bot -Y view (0,-1,0)
Right +X view (1,0,0)
Left -X view (-1,0,0)
Iso Isometric (1,1,1)
Obliq Oblique (1,2,3)
WP Working plane view
Zoom By picking center of a
square
Box Zoom By picking two corners
of a box
Win Zoom Same as Box Zoom,
but box is proportional
to window.
Back Up “Unzoom” to previous
zoom.

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Picking
• Picking allows you to identify model entities
or locations by clicking in the Graphics
Window.
• A picking operation typically involves the
use of the mouse and a picker menu. It is
indicated by a + sign on the menu.
• For example, you can create keypoints by
picking locations in the Graphics Window
and then pressing OK in the picker.

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Two types of picking:
• Retrieval picking
– Picking existing entities for a
subsequent operation.
– Allows you to enter entity numbers
in the Input Window.
– Use the Pick All button to indicate
all entities.
• Locational picking
– Locating coordinates of a point,
such as a keypoint or node.
– Allows you to enter coordinates in
the Input Window.
Example of
Locational Picker
Example of
Retrieval Picker

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Mouse button assignments for picking:
• Left mouse button picks (or unpicks) the entity
or location closest to the mouse pointer.
Pressing and dragging allows you to “preview”
the item being picked (or unpicked).
• Middle mouse button does an Apply. Saves the
time required to move the mouse over to the
Picker and press the Apply button. Use Shift-
Right button on a two-button mouse.
• Right mouse button toggles between pick and
unpick mode.
Note, the Shift-Right button on a two-button mouse is
equivalent to the Middle mouse button on a three-button
mouse.
Pick
Apply
Toggle
Pick / Unpick
Unpick
Pick
Cursor display:

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Type input followed by Enter, then [OK]
Cannot use the Command Input area
to enter the values
Prompt area indicates expected items

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Hotspot locations for picking:
• Areas and Volumes have one hotspot near the centroid of the
solid model entity.
• Lines have three hotspots - one in the middle and one near each
end.
• Why this is important: When you are required to “pick” an
entity, you must pick on the hotspot.

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• Demo:
– Show locational picking by creating a few keypoints. Also show the
use of middle and right mouse buttons.
– Show retrieval picking by creating a few lines
– Show “Loop” by creating an AL area
– Show “Pick All” by deleting area only
– Do KPLOT, LPLOT, etc. with and without numbering. Type in a few of
these commands.
– Show the use of pan-zoom-rotate

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• ANSYS uses an HTML-based documentation system to provide
extensive on-line help.
• You can get help on:
– ANSYS commands
– element types
– analysis procedures
– special GUI “widgets” such as Pan-Zoom-Rotate
• You can also access:
– Tutorials
– Verification models
– The ANSYS web site
On-Line Help

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• There are several ways to start the help system:
– Launcher > Help System
– Utility Menu > Help > Help Topics
– Any dialog box > Help
– Type HELP,name in the Input Window. Name is a command or
element name.
…On-Line Help

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• Pressing the Help System button on the launcher brings up a help browser
with:
– a navigational window containing Table of Contents, Index, and a Search Utility
– a document window containing the help information.
…On-Line Help

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• Use the Contents tab to browse
to the item of interest.
• Use the Index tab to quickly
locate specific commands,
terminology, concepts, etc.
• Use the Search tab to query the
entire help system for specific
words or phrases.
…On-Line Help

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• ANSYS also provides an
HTML-based on-line
tutorial.
• The tutorial consists of
detailed instructions for
a set of problems solved
in ANSYS.
• To access the tutorial,
click on Utility Menu >
Help > ANSYS Tutorials.
…On-Line Help

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• Demo:
– Launch the help system from the launcher
– Bring up an Analysis Guide
– Type “help,kplot” in the Input window
– Search for the string “harmonic response”
…On-Line Help

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• Suppose you wanted to do the following:
– Plot all areas located in the second quadrant
– Delete all arcs of radius 0.2 to 0.3 units
– Apply a convection load on all exterior lines
– Write out all nodes at Z=3.5 to a file
– View results only in elements made of steel
The common “theme” in these tasks is that they all operate on a
subset of the model.
• Select Logic allows you to select a subset of entities and operate
only on those entities.
Select Logic

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• Three steps:
– Select a subset
– Perform operations on the subset
– Reactivate the full set
Reactivate full set
Select subset
Operate on subset
…Select Logic

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Selecting Subsets
• Most selecting tools are
available in the Select Entities
dialog box: Utility Menu >
Select > Entities...
• Or you can use the xSEL
family of commands: KSEL,
LSEL, ASEL, VSEL, NSEL,
ESEL
Entity to select
Criterion by
which to select
Type of
selection
…Select Logic

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• Criterion by which to select:
– By Num/Pick: to select based on entity numbers or by
picking
– Attached to: to select based on attached entities. For
example, select all lines attached to the current subset
of areas.
– By Location: to select based on X,Y,Z location. For
example, select all nodes at X=2.5. X,Y,Z are interpreted
in the active coordinate system.
– By Attributes: to select based on material number, real
constant set number, etc. Different attributes are
available for different entities.
– Exterior: to select entities lying on the exterior.
– By Results: to select entities by results data, e.g, nodal
displacements.
…Select Logic

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• Type of selection
– From Full: selects a subset from
the full set of entities.
– Reselect: selects (again) a subset
from the current subset.
– Also Select: adds another subset
to the current subset.
– Unselect: deactivates a portion of
the current subset.
– Invert: toggles the active and
inactive subsets.
– Select None: deactivates the full
set of entities.
– Select All: reactivates the full set
of entities.
…Select Logic
Select None
Reselect
Also Select
Unselect
Invert
From Full
Select All

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Operations on the Subset
• Typical operations are applying loads, listing
results for the subset, or simply plotting the
selected entities.
– The advantage of having a subset selected is that
you can use the [Pick All] button when the picker
prompts you pick desired entities. Or you can use
the ALL label when using commands.
– Note that most operations in ANSYS, including the
SOLVE command, act on the currently selected
subset.
• Another “operation” is to assign a name to the
selected subset by creating a component
(discussed in the next section).
…Select Logic

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Reactivating the Full Set
• After all desired operations are done on the selected subset, you
should reactivate the full set of entities.
– If all nodes and all elements are not active for solution, the solver will
issue a warning to that effect.
• The easiest way to reactivate the full set is to select “everything”:
– Utility Menu > Select > Everything
– Or issue the command ALLSEL
You can also use the [Sele All] button in the Select Entities dialog
box to reactivate each entity set separately. (Or issue KSEL,ALL;
LSEL,ALL; etc.)
…Select Logic

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• Components are named subsets. The name can then be used in
dialog boxes or commands in place of entity numbers or the label
ALL.
• A group of nodes, or elements, or keypoints, or lines, or areas, or
volumes can be defined as a component. Only one entity type is
associated with a component.
• Components can be selected or unselected. When you select a
component, you are actually selecting all of the entities in that
component.
…Select Logic

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• To create a component:
– First select the desired subset of entities.
– Then name the subset using the CM command or Utility Menu > Select >
Comp/Assembly > Create Component
• Up to 32 characters — letters, numbers, and _ (underscore) — are allowed
for the name.
• Beginning a component name with _ (underscore) will make it a “hidden
component” and it cannot be picked from a list. This is NOT recommended.
• Suggestion: Use the first letter of the name to indicate the entity type. For
example, N_HOLES for a node component, E_ALUMIN for an element
component, etc.
– Reactivate all entities.
…Select Logic

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Some useful options:
• Plot components
– Utility Menu > Plot > Components > Selected
Components
– Or CMPLOT
• Select, unselect, reselect, etc.
– Utility Menu > Select > Comp/Assembly >
Select Comp/Assembly
– Or CMSEL
• Listing components gives a list of currently defined and selected
components.
– Utility Menu > Select > Comp/Assembly > List Comp/Assembly
– Or CMLIST
…Select Logic

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• An assembly is a group of components. An assembly can also be
made up of one or more other assemblies and/or components.
• The groups that make up assemblies can consist of any
combination of entity types.
• To create an assembly:
– Utility Menu > Select > Comp/Assembly
– Or use CMGRP
• You can nest assemblies up to 5 levels deep.
…Select Logic

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MOTOR
ROTORASM
(Volumes & Lines)
AIRGAP
(Elements)
STATASM
(Volume & Elements)
STATOR
(Volume)
PERMMAG
(Elements)
ROTOR
(Volume)
WINDINGS
(Lines)
Components Assemblies Assembly
The assembly “MOTOR”
consists of Volumes,
Elements, and Lines.
…Select Logic
The MOTOR assembly is “built up” from other assemblies and
components to create a three-level deep assembly.

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• The term ANSYS database refers to the data ANSYS maintains in
memory as you build, solve, and postprocess your model.
• The database stores both your input data and ANSYS results data:
– Input data -- information you must enter, such as model dimensions,
material properties, and load data.
– Results data -- quantities that ANSYS calculates, such as
displacements, stresses, strains, and reaction forces.
The Database and Files

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Save and Resume
• Since the database is stored in the computer’s memory (RAM), it
is good practice to save it to disk frequently so that you can
restore the information in the event of a computer crash or power
failure.
• The SAVE operation copies the database from memory to a file
called the database file (or db file for short).
– The easiest way to do a save is to click on Toolbar > SAVE_DB
– Or use:
• Utility Menu > File > Save as Jobname.db
• Utility Menu > File > Save as…
• SAVE command
…The Database and Files

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• To restore the database from the db file back into memory, use the
RESUME operation.
– Toolbar > RESUME_DB
– Or use:
• Utility Menu > File > Resume Jobname.db
• Utility Menu > File > Resume from…
• RESUME command
• The default file name for SAVE and RESUME is jobname.db, but
you can choose a different name by using the “Save as” or
“Resume from” functions.

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• Notes on SAVE and RESUME:
– Choosing the “Save as” or “Resume from” function does NOT change
the current jobname.
– If you save to the default file name and a jobname.db already exists,
ANSYS will first copy the “old” file to jobname.dbb as a back-up.
– The db file is simply a “snapshot” of what is in memory at the time the
save is done.

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• Tips on SAVE and RESUME:
– Periodically save the database as you progress through an analysis.
ANSYS does NOT do automatic saves.
– You should definitely SAVE the database before attempting an
unfamiliar operation (such as a Boolean or meshing) or an operation
that may cause major changes (such as a delete).
• RESUME can then be used as an “undo” if you don’t like the
results of that operation.
– SAVE is also recommended before doing a solve.

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Clearing the Database
• The Clear Database operation allows
you to “zero out” the database and
start fresh. It is similar to exiting and
re-entering ANSYS.
– Utility Menu > File > Clear & Start New
– Or use the /CLEAR command.

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Files
• ANSYS writes and reads several files during an analysis. File names
are of the format jobname.ext.
• Jobname
– A name you choose while starting ANSYS, up to 32 characters. Defaults to
file.
– Can be changed within ANSYS with the /FILNAME command (Utility Menu >
File > Change Jobname).
• Extension
– Identifies the contents of the file, such as .db for database.
– Usually assigned by ANSYS but can be defined by user (/ASSIGN).

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• Typical files:
jobname.log: Log file, ASCII.
• Contains a log of every command issued during the session.
• If you start a second session with the same jobname in the same
working directory, ANSYS will append to the previous log file (with
a time stamp).
jobname.err: Error file, ASCII.
• Contains all errors and warnings encountered during the session.
ANSYS will also append to an existing error file.
jobname.db, .dbb: Database file, binary.
• Compatible across all supported platforms.
jobname.rst, .rth, .rmg, .rfl: Results files, binary.
• Contains results data calculated by ANSYS during solution.
• Compatible across all supported platforms.

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File Management Tips
• Run each analysis project in a separate working directory.
• Use different jobnames to differentiate various analysis runs.
• You should keep the following files after any ANSYS analysis:
– log file ( .log)
– database file ( .db)
– results files (.rst, .rth, …)
– load step files, if any (.s01, .s02, ...)
– physics files (.ph1, .ph2, ...)
• Use /FDELETE or Utility Menu > File > ANSYS File Options to
automatically delete files no longer needed by ANSYS during that
session.

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• Three ways to exit ANSYS:
– Toolbar > QUIT
– Utility Menu > File > Exit
– Use the /EXIT command in the Input Window
Exiting ANSYS

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• Refer to your Workshop Supplement for instructions on:
W3A Introductory Workshop
Chapter 3 – ANSYS Basics
Workshops

Creating the Solid Model
Chapter 5

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• The purpose of this chapter is to review some preliminary
modeling considerations, discuss how to import one’s geometry
into ANSYS, and finally discuss how to create one’s geometry
using ANSYS native commands.
Chapter 5 – Creating the Geometry
Overview

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• Many modeling decisions must be made before building an
analysis model:
– How much detail should be included?
– Does symmetry apply?
– Will the model contain stress singularities?
What to model?

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Details
• Small details that are unimportant to the analysis should not be
included in the analysis model. You can suppress such features
before sending a model to ANSYS from a CAD system.
• For some structures, however, "small" details such as fillets or
holes can be locations of maximum stress and might be quite
important, depending on your analysis objectives.
…What to model?

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Symmetry
• Many structures are symmetric in some form and allow only a
representative portion or cross-section to be modeled.
• The main advantages of using a symmetric model are:
– It is generally easier to create the model.
– It allows you to make a finer, more detailed model and thereby obtain
better results than would have been possible with the full model.
…What to model?

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• To take advantage of symmetry, all of the following must be
symmetric:
– Geometry
– Material properties
– Loading conditions
• There are different types of symmetry:
– Axisymmetry
– Rotational
– Planar or reflective
– Repetitive or translational
…What to model?

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Axisymmetry
• Symmetry about a central axis, such as in light bulbs, straight
pipes, cones, circular plates, and domes.
• Plane of symmetry is the cross-section anywhere around the
structure. Thus you are using a single 2-D “slice” to represent
360° — a real savings in model size!
• Loading is also assumed to be
axisymmetric in most cases. However,
if it is not, and if the analysis is linear,
the loads can be separated into
harmonic components for independent
solutions that can be superimposed.
…What to model?

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Rotational symmetry
• Repeated segments arranged about a central axis, such as in
turbine rotors.
• Only one segment of the structure needs to be modeled.
• Loading is also assumed to be symmetric about the axis.
…What to model?

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This model illustrates
both reflective and
rotational symmetry
Planar or reflective symmetry
• One half of the structure is a mirror image of the other half. The
mirror is the plane of symmetry.
• Loading may be symmetric or anti-symmetric about the plane of
symmetry.
…What to model?

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This model illustrates both repetitive and reflective symmetry.
Repetitive or translational symmetry
• Repeated segments arranged along a straight line, such as a long
pipe with evenly spaced cooling fins.
• Loading is also assumed to be “repeated” along the length of the
model.
…What to model?

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• In some cases, only a few minor details will disrupt a structure's
symmetry. You may be able to ignore such details (or treat them
as being symmetric) in order to gain the benefits of using a
smaller model. How much accuracy is lost as the result of such a
compromise might be difficult to estimate.
…What to model?

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Stress singularities
• A stress singularity is a location in a finite element model where
the stress value is unbounded (infinite). Examples:
– A point load, such as an applied force or moment
– An isolated constraint point, where the reaction force behaves like a
point load
– A sharp re-entrant corner (with zero fillet radius)
• As the mesh density is refined at
a stress singularity, the stress value
increases and never converges.
P s = P/A
As A  0, s  
…What to model?

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• Real structures do not contain stress singularities. They are a
fiction created by the simplifying assumptions of the model.
• So how do you deal with stress singularities?
– If they are located far away from the region of interest, you can simply
ignore them by deactivating the affected zone while reviewing results.
– If they are located in the region of interest, you will need to take
corrective action, such as:
• adding a fillet at re-entrant corners and reruning the analysis.
• replacing a point force with an equivalent pressure load.
• “spreading out” displacement constraints over a set of nodes.
…What to model?

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• Importing an IGES file
– Utility Menu > File > Import > IGES…
– the two methods, No Defeaturing and Defeaturing
– the Merge, Solid, and Small options
Chapter 5 – Importing Geometry
IGES Imports

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• No Defeaturing Method — Imports and stores geometry in the
standard ANSYS database. [ioptn,iges,nodefeat]
+ Faster and more reliable than the Defeaturing method.
+ Allows the full set of solid model operations.
– No defeaturing tools are available.
+ This is the DEFAULT and recommended method.
…IGES Imports

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• Defeaturing Method — Imports and stores geometry in a
special database that allows you to repair and defeature
the model. [ioptn,iges,defeat]
+ Ability to defeature, i.e, to remove minor details such as
protrusions, cavities, and small holes.
– Because of the special database used to store geometry,
only a limited number of solid model operations are
available.
– Generally requires more memory and is somewhat slower
than the “No defeaturing” method.
+ This method is efficient for single solid models that will be
imported, loaded, meshed and solved.
– In general, it is NOT recommended when advanced
geometry capabilities are required.
…IGES Imports

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• Merge Option
– YES by default, to merge coincident entities so that adjacent areas
meet at a common line, and adjacent lines meet at a common
keypoint.
– Switch it to NO only if you are using the Defeaturing method and your
initial attempt runs out of memory.
– ioptn,merge,yes/no
merge
…IGES Imports

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• Solid Option
– YES default, to automatically create a volume (solid) after importing
and merging.
– Switch it to NO if you want to import surfaces only and create a shell
or 2-D plane model.
– ioptn,solid,yes/no
…IGES Imports

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• Small Option
– YES by default, to automatically delete small, sliver-like areas that
might be troublesome for meshing.
– Available only for the Defeature method.
– Switch it to NO if you find gaps or “holes” in the model.
– ioptn,small,yes/no
…IGES Imports

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• IGES importing works quite well, but because of the dual
translation process — CAD  IGES  ANSYS — there are many
cases when a 100% translation is not achieved.
• ANSYS Connection products help overcome this problem by
directly reading the “native” part files produced by the CAD
package:
– Connection for Pro/ENGINEER (“Pro/E” for short)
– Connection for Unigraphics (“UG” for short)
– Connection for SAT
– Connection for Parasolid
– Connection for CATIA
• To use a connection product, you need to purchase the
appropriate license.
Connection Products

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• Connection for Pro/E
– Reads .prt file produced by Pro/ENGINEER (from Parametric
Technology Corp.).
– Requires Pro/ENGINEER software.
– Can also read a Pro/Engineer assembly file (.asm)
– Utility Menu > File > Import > Pro/E...
– Or ~proein
Defeaturing option available
No Defeaturing is default
Command that launches your Pro/E
…Connection Products

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• Connection for UG
– Reads .prt file produced by Unigraphics (from Electronic Data
Systems Corp.).
– Requires Unigraphics software.
– Utility Menu > File > Import > UG...
– Or ~ugin
Option to read only
selected layers and
geometry types

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• Connection for SAT
– Reads .sat file produced by CAD packages that use the ACIS modeler.
– Does not require ACIS software.
– Utility Menu > File > Import > SAT...
– Or ~satin
Option to read only
selected geometry types

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• Connection for Parasolid
– Reads .x_t or .xmt_txt file produced by CAD packages that use the
Parasolid modeler.
– Does not require Parasolid software.
– Utility Menu > File > Import > PARA...
– Or ~parain
Option to read only
selected geometry types
Option to scale geometry

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• Connection for CATIA
– Reads .model or .dvl file produced by the CATIA
– Requires CATIA software.
– Utility Menu > File > Import > CATIA…
– Or ~catiain
Option to import blanked
bodies

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System Operation Level Pro/E UG SAT PARA CATIA
SGI-64bit IRIX64 6.5.10m 2001 18.0 ACIS70 13.0 v4.x
2001
(no R4000)
SUN-64bit Solaris 8 2001 18.0 ACIS70 13.0 v4.x
SUN-32bit Solaris 8 2001 18.0 ACIS70 13.0 v4.x
HP-64bit HP-UX B.11.0 2001 18.0 ACIS70 13.0 v4.x
HP-32bit HP-UX 10.20 A 2001 16.0 ACIS70 DROPPED v4.x
HPIA64 (itanium) HP-UX B.11.20 (11i) Not Supported Not Supported ACIS70 13.0 Not Supported
IBM-64bit AIX 4.3.3-09 2001 18.0 (new) Not Supported 13.0 v4.x
IBM-32bit AIX 4.3.3-09 2001 18.0 (new) Not Supported 13.0 v4.x
IBM RS64 AIX 5L 2001 Not Supported Not Supported 13.0 v4.x
17.0
(18.0 dropped)
LINUX-32bit RedHat 7.2 (Kernel 2.4..9-13) Not Supported Not Supported ACIS70 13.0 Not Supported
LINUX-64bit RedHat 7.1 (Kernel 2.4.3) Not Supported Not Supported ACIS70 13.0 Not Supported
Intel IA-32
Windows 2000 (Service pack
2)Version 5.00 (Build 2195)
2001 18.0 ACIS70 13.0 v4.x
Intel IA-32 Windows XP 2001 18.0 ACIS70 13.0 v4.x
Intel IA-32 Windows XP Professional 2001 18.0 ACIS70 13.0 v4.x
Intel IA-32
Windows NT 4.0 (Service Pack 5)
Build 1381
2001 18.0 ACIS70 13.0 v4.x
Intel IA-32 Windows XP Home 2001 18.0 ACIS70 13.0 v4.x
COMPAQ ALPHA ACIS70
ANSYS 6.1 Connection Product Support
SGI-32bit IRIX 6.5.10m 18.0 ACIS70 13.0 v4.x
13.0 Not Supported
2001
Tru64 UNIX v5.0A

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ANSYS Automatic Geometry Healing
• Based Upon ITI’s CADfix software
• Requires CADfix to be installed
• Simplified interface – one command ~heal,Filename,Ext,Dir,Method
• Works with existing ANSYS Connections (except for IGES)
• Optional CADfix-based imports also available with Healing Module
- IGES v5.3, STEP AP 203 and AP214, CATIA v4.x, VDAFS 2.0, STL, ACIS
6.3 and Parasolid 12.1
• If repair cannot be automated, user can manually repair model in
CADfix

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W5A. Importing Geometry – IGES Import
W5B. Importing Geometry – SAT Part Import
W5C. Importing Geometry – SAT Assembly Import
W5D. Importing Geometry – Parasolid Part Import
W5E. Importing Geometry – Parasolid Assembly Import
Workshops

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• Importing geometry is convenient, but sometimes you may need
to create it in ANSYS. Some possible reasons:
– You may need to build a parametric model — one defined in terms of
variables for later use in design optimization or sensitivity studies.
– The geometry may not be available in a format ANSYS can read.
– The Connection product you need may not be available on your
computer platform.
– You may need to modify or add geometry to an imported part or
assembly.
• ANSYS has an extensive set of geometry creation tools, which we
will discuss next.
Chapter 5 – ANSYS Native Commands
Overview

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• Solid Modeling can be defined as the process of
creating solid models.
• Definitions:
– A solid model is defined by volumes, areas, lines,
and keypoints.
– Volumes are bounded by areas, areas by lines, and
lines by keypoints.
– Hierarchy of entities from low to high:
keypoints < lines < areas < volumes
– You cannot delete an entity if a higher-order entity
is attached to it.
• Also, a model with just areas and below, such as
a shell or 2-D plane model, is still considered a
solid model in ANSYS terminology.
Volumes
Areas
Lines &
Keypoints
Keypoints
Lines
Areas
Volumes
Definitions

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• There are two approaches to creating a solid model:
– Top-down
– Bottom-up
• Top-down modeling starts with a definition of volumes (or areas),
which are then combined in some fashion to create the final
shape.
add
…Definitions

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• Bottom-up modeling starts with keypoints, from which you “build
up” lines, areas, etc.
• You may choose whichever approach best suits the shape of the
model, and also freely combine both methods.
• We will now discuss each modeling approach in detail.
…Definitions

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• Top-down modeling starts with a definition of volumes (or areas),
which are then combined in some fashion to create the final
shape.
– The volumes or areas that you initially define are called primitives.
– Primitives are located and oriented with the help of the working plane.
– The combinations used to produce the final shape are called Boolean
operations.
Top-Down Modeling

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• Primitives are predefined geometric shapes such as circles,
polygons, and spheres.
• 2-D primitives include rectangles, circles, triangles, and other
polygons.
…Top-Down Modeling

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• 3-D primitives include blocks, cylinders, prisms, spheres, and
cones.

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• When you create a 2-D primitive, ANSYS defines an area, along
with its underlying lines and keypoints.
• When you create a 3-D primitive, ANSYS defines a volume, along
with its underlying areas, lines and keypoints.

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• You can create primitives by specifying their dimensions or by
picking locations in the graphics window.
– For example, to create a solid circle:
• Main Menu > Preprocessor > Modeling > Create > Areas > Circle >
Instructions
Area Input:
1.) Pick the center and radius in
graphics window...
2.) Or enter in Picker Box
By picking

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– To create a block:
• Main Menu > Preprocessor > Modeling > Create > Volumes >Block >
Instructions
By picking
Volume Input:
1.) Pick the 2 diagonal corners and
Z-depth in graphics window...
2.) Or enter in Picker Box

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• The “WP” in the prompts and in the picker stands for Working
Plane — a movable, 2-D reference plane used to locate and orient
primitives.
– By default, the WP origin coincides with the global origin, but you can
move it and/or rotate it to any desired position.
– By displaying a grid, you can use the WP as a “drawing tablet.”
– WP is infinite despite the grid settings.
WX
WY
X2
X1
Y2
Y1
WX
WY
WP (X,Y)

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• All working plane controls are in
Utility Menu > WorkPlane.
• The WP Settings menu controls the
following:
– WP display - triad only (default), grid only, or
both.
– Snap - allows you to pick locations on the WP
easily by “snapping” the cursor to the nearest
grid point.
– Grid spacing - the distance between grid
lines.
– Grid size - how much of the (infinite) working
plane is displayed.

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• You can move the working plane
to any desired position using
the Offset and Align menus.
– Offset WP by Increments…
• Use the push buttons (with
increment set by slider).
• Or type in the desired
increments.
• Or use dynamic mode
(similar to pan-zoom-rotate).

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– Offset WP to >
This simply “translates” the WP,
maintaining its current orientation, to
the desired destination, which can be:
• Existing keypoint(s). Picking
multiple keypoints moves WP to
their average location.
• Existing node(s).
• Coordinate location(s).
• Global origin.
• Origin of the active coordinate
system (discussed later).

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– Align WP with >
This reorients the WP.
• For example, Align WP with Keypoints
prompts you to pick 3 keypoints -
one at the origin, one to define the
X-axis, and one to define the X-Y
plane.
• To return the WP to its default
position (at global origin, on global
X-Y plane), click on Align WP with >
Global Cartesian.

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• Demo:
– Clear the database
– Display WP and create a few keypoints by picking. Note the coordinates
displayed in the picker.
– Turn on the grid, change spacing, and activate snap.
– Create more keypoints. Note how the cursor snaps to grid points.
– Define 2 rectangles — one by picking corners and one by dimensions.
– Now offset WP to average of a few keypoints, then rotate in-plane by 30º.
– Define 2 more rectangles by picking and by dimensions. Note the change in
rectangle orientation.
– Align WP with global origin, then define some 3-D primitives. Use picking as well
as “By dimensions.”

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• Boolean operations are computations involving combinations of
geometric entities. ANSYS Boolean operations include add,
subtract, intersect, divide, glue, and overlap.
• The “input” to Boolean operations can be any geometric entity,
ranging from simple primitives to complicated volumes imported
from a CAD system.
add
Input entities Boolean operation Output entity(ies)

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• All Boolean operations are available in the GUI under Main Menu
Preprocessor > Modeling > Operate > Booleans
• By default, input entities of a Boolean operation are deleted after
the operation.
• Deleted entity numbers become “free” (i.e., they will be assigned
to a new entity created, starting with the lowest available number).

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• Add
– Combines two or more entities into one.

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• Glue
– Attaches two or more entities by creating a common boundary
between them.
– Useful when you want to maintain the distinction between entities
(such as for different materials).

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• Overlap
– Same as glue, except that the input entities overlap each other.

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• Subtract
– Removes the overlapping portion of one or more entities from a set of
“base” entities.
– Useful for creating holes or trimming off portions of an entity.

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• Divide
– Cuts an entity into two or more pieces that are still connected to each
other by common boundaries.
– The “cutting tool” may be the working plane, an area, a line, or even a
volume.
– Useful for “slicing and dicing” a complicated volume into simpler
volumes for brick meshing.

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• Intersect
– Keeps only the overlapping portion of two or more entities.
– If there are more than two input entities, you have two choices:
common intersection and pairwise intersection
• Common intersection finds the common overlapping region
among all input entities.
• Pairwise intersection finds the overlapping region for each pair of
entities and may produce more than one output entity.
Common
Intersection
Pairwise
Intersection

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• Partition
– Cuts two or more intersecting entities into multiple pieces that are still
connected to each other by common boundaries.
– Useful, for example, to find the intersection point of two lines and still
retain all four line segments, as shown below. (An intersection
operation would return the common keypoint and delete both lines.)
L1
L2
L3
L6
L5
L4
Partition

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• Demo:
– “Drill” a hole by subtracting a circle from a rectangle (or a cylinder
from a block)
– Create two overlapping entities, save db, and do the overlap
operation. Now resume db and add the entities. Note the difference
between the two operations. (Glue is similar to overlap.)
– Interesting model:
• block,-2,2, 0,2, -2,2
• sphere,2.5,2.7
• vinv,all ! intersection

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W5F. Pillow Block

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• Bottom-up modeling begins with a definition of keypoints, from
which other entities are “built up.”
• To build an L-shaped object, for example, you could start by
defining the corner keypoints as shown below. You can then
create the area by simply “connecting the dots” or by first
defining lines and then defining the area by lines.
Bottom-Up Modeling

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• To define keypoints:
– Main Menu > Preprocessor > Modeling > Create >
Keypoints
– Or use the K family of commands: K, KFILL,
KNODE, etc.
• The only data needed to create a keypoint is the keypoint number
and the coordinate location.
– Keypoint number defaults to the next available number.
– The coordinate location may be provided by simply picking locations
on the working plane or by entering the X,Y,Z values.
How are the X,Y,Z values interpreted? It depends on the active
coordinate system.
…Bottom-Up Modeling

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Active Coordinate System
• Defaults to global Cartesian.
• Use CSYS command (or Utility Menu
> WorkPlane > Change Active CS to) to
change it to
– global Cartesian [csys,0]
– global cylindrical [csys,1]
– global spherical [csys,2]
– working plane [csys,4]
– or a user-defined local coordinate
system [csys, n]
Each of these systems is explained
next.

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Global Coordinate System
• The global reference system for the model.
• May be Cartesian (system 0), cylindrical (1), or spherical (2).
– For example, location (0,10,0) in global Cartesian is the same as
(10,90,0) in global Cylindrical.

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Local Coordinate System
• A user-defined system at a desired location, with ID
number 11 or greater. The location may be:
– At WP origin [CSWP]
– At specified coordinates [LOCAL]
– At existing keypoints [CSKP] or nodes [CS]
• May be Cartesian, cylindrical, or spherical.
• May be rotated about X, Y, Z axes.
X
Y
X11
Y11
X12
Y12

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Working Plane Coordinate System
• Attached to the working plane.
• Used mainly to locate and orient solid model primitives.
• You can also use the working plane to define keypoints by
picking.

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• You can define any number of
coordinate systems, but only one
may be active at any given time.
• Several geometry items are affected
by the coordinate system [CSYS] that
is active at the time they are defined:
– Keypoint and node locations
– Line curvature
– Area curvature
– Generation and “filling” of keypoints
and nodes
– Etc.
• The graphics window title shows the
active system.
Areas created between keypoints at
(1,0,0), (0,1,0), & (0,0,1)

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• There are many ways to create lines, as shown here.
• If you define areas or volumes, ANSYS will automatically generate
any undefined lines, with the curvature determined by the active
CS.
• Keypoints must be available in order to create lines.
Create > Lines >
Arcs
Create > Lines >
Lines
Create > Lines >
Splines
Operate >
Extrude

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• Creating areas using bottom-up method requires keypoints or
lines to be already defined.
• If you define volumes, ANSYS will automatically generate any
undefined areas and lines, with the curvature determined by the
active CS.
Create > Areas >
Arbitrary
Operate > Extrude

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• Creating volumes using bottom-up method requires keypoints or
areas to be already defined.
Create > Volumes >
Arbitrary
Operate > Extrude

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• Demo:
– Clear the database
– Create 5 keypoints at (1,2), (3,2), (4,0), (1,1.5), (2.5,0)
– Switch to CSYS,1 and create a line “in active CS” between KP4 & KP5
– Switch back to CSYS,0 and create an area “through KP’s.” Notice that
the remaining lines were automatically generated lines, all of them
straight.
– Define two circles:
• 0.3R, centered at (2.25,1.5)
• 0.35R, centered at (3.0,0.6)
– Subtract the two circles from base area. (We have used a combination
of bottom-up and top-down modeling.)
– Save as r.db

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• Boolean operations are available for entities created by both top-
down and bottom-up modeling approaches.
• Besides Booleans, many other operations are available:
– Extrude
– Scale
– Move
– Copy
– Reflect
– Merge
– Fillet

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Extrude
• To quickly create volumes from existing areas (or areas
from lines, and lines from keypoints).
• If the area is meshed, you can extrude the elements
along with the areas.
• Four ways to extrude areas:
– Along normal — creates volume by normal offset of areas
[VOFFST] .
– By XYZ offset — creates volume by a general x-y-z offset
[VEXT]. Allows tapered extrusion.
– About axis — creates volume by revolving areas about an
axis (specified by two keypoints) [VROTAT].
– Along lines — creates volume by “dragging” areas along a
line or a set of contiguous lines [VDRAG].

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• Scaling is typically needed when you want to convert the geometry to a
different set of units, say from inches to millimeters.
• To scale a model in ANSYS:
– First save the database -- Toolbar >
SAVE_DB or SAVE command.
– Then Main Menu > Preprocessor > Operate >
Scale > Volumes (choose the highest-level
entity available in the model)
• [Pick All] to pick all volumes
• Then enter desired scale factors for
RX, RY, RZ and set IMOVE to “Moved”
instead of “Copied”
– Or use the VLSCALE command:
• vlscale,all,,,25.4,25.4,25.4,,,1

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Move
• To translate or rotate an entity by
specifying DX,DY,DZ offsets.
– DX,DY,DZ are interpreted in the active CS.
– To translate an entity, make the active CS
Cartesian.
– To rotate an entity, make the active CS
cylindrical or spherical.
– Or use the commands
• VGEN, AGEN, LGEN, KGEN
• Another option is to transfer coordinates
to a different system.
– Transfer occurs from the active CS to a
specified CS.
– This operation is useful when you need to
move and rotate an entity at the same time.
– Or use the commands
• VTRAN, ATRAN, LTRAN, KTRAN
Transfer
from csys,0
to csys,11
Rotate
-30°

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Copy
• To generate multiple copies of an
entity.
• Specify the number of copies (2 or
greater) and the DX,DY,DZ offset for
each copy. DX,DY,DZ are interpreted
in the active CS.
• Useful to create multiple holes, ribs,
protrusions, etc.
Copy in
local
cylindrical
CS
Create outer
areas by
skinning

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Reflect
• To reflect entities about a plane.
• Specify the direction of reflection:
– X for reflection about the YZ plane
– Y for XZ plane
– Z for XY plane
All directions are interpreted in the
active CS, which must be a Cartesian
system.
What is the direction of
reflection in this case?

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Merge
• To attach two entities together by removing coincident keypoints.
– Merging keypoints will automatically merge coincident higher-order entities, if
any.
• Usually required after a reflect, copy, or other operation that causes
coincident entities.
Merge or glue
required
Reflect

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Subtract from
base area
Fillet
• Line fillet requires two intersecting lines with a
common keypoint at the intersection.
– If the common keypoint does not exist, do a
partition operation first.
– ANSYS does not update the underlying area (if any),
so you need to either add or subtract the fillet
region.
• Area filleting is similar. Create
fillet
Create
area

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• Demo:
– Resume r.db (if necessary)
– Create two keypoints for the axis, at (0,0) and (0,1), then extrude the area by
revolving about the axis 60º
– Resume r.db
– Make copies of the rib tangentially about the Y-axis:
• Create a local cylindrical CS at global origin, with THYZ = -90
• Generate 7 total copies (6 new ones) with DY=15
– Create the three outer “skin” areas using ASKIN,P
– Resume r.db
– Create a 0.5R fillet between the top and right lines. (Notice that the lines
attached to the area have been modified. This is allowed in some cases.)
– Create the triangular fillet area by lines (AL,P), then subtract it from the main
area.

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W5G. Connecting Rod – Bottom-Up Approach
W5H. Connecting Rod – Importation/Clean-up

Create Finite Element Model
Chapter 6

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Chapter 6 – Creating the Finite Element Model
Overview
• The purpose of this chapter is to discuss the meshing element
attributes, various means to create a mesh in ANSYS, and finally
how to import one’s finite element model directly into ANSYS.
Recall, ANSYS does not use the solid model in the solution of the
model, rather it needs to finite elements.

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• Meshing is the process used to “fill” the solid model with nodes
and elements, i.e, to create the FEA model.
– Remember, you need nodes and elements for the finite element
solution, not just the solid model. The solid model does NOT
participate in the finite element solution.
Solid model FEA model
meshing
…Overview

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• There are three steps to meshing:
– Define element attributes
– Specify mesh controls
– Generate the mesh
• Element attributes are characteristics of the finite element model
that you must establish prior to meshing. They include:
– Element types
– Real constants
– Material properties
Element Attributes

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Element Type
• The element type is an important choice that determines the
following element characteristics:
– Degree of Freedom (DOF) set. A thermal element type, for example,
has one dof: TEMP, whereas a structural element type may have up to
six dof: UX, UY, UZ, ROTX, ROTY, ROTZ.
– Element shape -- brick, tetrahedron, quadrilateral, triangle, etc.
– Dimensionality -- 2-D (X-Y plane only), or 3-D.
– Assumed displacement shape -- linear vs. quadratic.
• ANSYS has a “library” of over 150 element types from which you
can choose. Details on how to choose the “correct” element type
will be presented later. For now, let’s see how to define an
element type.
…Element Attributes

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Element category
• ANSYS offers many different categories of elements. Some of the
commonly used ones are:
– Line elements
– Shells
– 2-D solids
– 3-D solids

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• Line elements:
– Beam elements are used to model bolts, tubular members, C-sections,
angle irons, or any long, slender members where only membrane and
bending stresses are needed.
– Spar elements are used to model springs, bolts, preloaded bolts, and
truss members.
– Spring elements are used to model springs, bolts, or long slender
parts, or to replace complex parts by an equivalent stiffness.

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• Shell elements:
– Used to model thin panels or curved surfaces.
– The definition of “thin” depends on the application, but as a general
guideline, the major dimensions of the shell structure (panel) should
be at least 10 times its thickness.

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• 2-D Solid elements:
– Used to model a cross-section of solid objects.
– Must be modeled in the global Cartesian X-Y plane.
– All loads are in the X-Y plane, and the response (displacements) are
also in the X-Y plane.
– Element behavior may be one of the following:
• plane stress
• plane strain
• axisymmetric
• axisymmetric harmonic
Y
X
Z

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• Plane stress assumes zero stress in
the Z direction.
– Valid for components in which the Z
dimension is smaller than the X and Y
dimensions.
– Z-strain is non-zero.
– Optional thickness (Z direction)
allowed.
– Used for structures such as flat plates
subjected to in-plane loading, or thin
disks under pressure or centrifugal
loading.
Y
X
Z

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• Plane strain assumes zero strain in the Z
direction.
– Valid for components in which the Z dimension is
much larger than the X and Y dimensions.
– Z-stress is non-zero.
– Used for long, constant cross-section structures
such as structural beams.
Y
X
Z

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• Axisymmetry assumes that the 3-D model and its
loading can be generated by revolving a 2-D
section 360° about the Y axis.
– Axis of symmetry must coincide with the global Y
axis.
– Negative X coordinates are not permitted.
– Y direction is axial, X direction is radial, and Z
direction is circumferential (hoop) direction.
– Hoop displacement is zero; hoop strains and
stresses are usually very significant.
– Used for pressure vessels, straight pipes, shafts,
etc.

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• Axisymmetric harmonic is a special case of axisymmetry where
the loads can be non-axisymmetric.
– The non-axisymmetric loading is decomposed into Fourier series
components, applied and solved separately, and then combined later.
No approximation is introduced by this simplification!
– Used for non-axisymmetric loads such as torque on a shaft.

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• 3-D Solid elements:
– Used for structures which, because of geometry, materials, loading, or
detail of required results, cannot be modeled with simpler elements.
– Also used when the model geometry is transferred from a 3-D CAD
system, and a large amount of time and effort is required to convert it
to a 2-D or shell form.

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Element Order
• Element order refers to the polynomial order of the element’s
shape functions.
• What is a shape function?
– It is a mathematical function that gives the “shape” of the results
within the element. Since FEA solves for DOF values only at nodes,
we need the shape function to map the nodal DOF values to points
within the element.
– The shape function represents assumed behavior for a given element.
– How well each assumed element shape function matches the true
behavior directly affects the accuracy of the solution, as shown on the
next slide.

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Quadratic distribution of
DOF values
Actual quadratic
curve
Linear approximation
(Poor Results)
Quadratic approximation
(Best Results)
Linear approximation
with multiple elements
(Better Results)

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• When you choose an element type, you are implicitly choosing
and accepting the element shape function assumed for that
element type. Therefore, check the shape function information
before you choose an element type.
• Typically, a linear element has only corner nodes, whereas a
quadratic element also has midside nodes.

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Linear elements
• Can support only a linear variation of
displacement and therefore (mostly)
only a constant state of stress within a
single element.
• Highly sensitive to element distortion.
• Acceptable if you are only interested
in nominal stress results.
• Need to use a large number of
elements to resolve high stress
gradients.
Quadratic elements
• Can support a quadratic variation of
displacement and therefore a linear
variation of stress within a single
element.
• Can represent curved edges and
surfaces more accurately than linear
elements. Not as sensitive to element
distortion.
• Recommended if you are interested in
highly accurate stresses.
• Give better results than linear
elements, in many cases with fewer
number of elements and total DOF.

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• Notes:
– For shell models, the difference between linear and quadratic
elements is not as dramatic as for solid models. Linear shells are
therefore usually preferred.
– Besides linear and quadratic elements, a third kind is available, known
as p-elements. P-elements can support anywhere from a quadratic to
an 8th-order variation of displacement within a single element and
include automatic solution convergence controls.

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Mesh Density
• The fundamental premise of FEA is that as the number of
elements (mesh density) is increased, the solution gets closer and
closer to the true solution.
• However, solution time and computer resources required also
increase dramatically as you increase the number of elements.
• The objectives of the analysis usually decide which way the slider
bar below should be moved.

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• If you are interested in highly accurate stresses:
– A fine mesh will be needed, omitting no geometric details at any
location in the structure where such accuracy is needed.
– Stress convergence should be demonstrated.
– Any simplification anywhere in the model might introduce significant
error.
• If you are interested in deflections or nominal stresses:
– A relatively coarse mesh is sufficient.
– Small geometry details may be omitted.

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• If you are interested in mode shapes (modal analysis):
– Small details can usually be omitted.
– Simple mode shapes can be captured using a relatively coarse mesh.
– Complex mode shapes may require a uniform, moderately fine mesh.
• Thermal Analyses:
– Small details can usually be omitted, but since many thermal analyses
are followed by a stress analysis, stress considerations generally
dictate the detail of the model.
– Mesh density is usually determined by expected thermal gradients. A
fine mesh is required for high thermal gradients, whereas a coarse
mesh may be sufficient for low gradients.

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• To define an element type:
– Main Menu > Preprocessor >
Element Type > Add/Edit/Delete
• [Add] to add new element type
• Choose the desired type
(such as SOLID92) and press
OK
• [Options] to specify additional
element options
– Or use the ET command:
• et,1,solid92

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• Notes:
– Setting preferences to the desired discipline (Main Menu > Preferences)
will show only the element types valid for that discipline.
– You should define the element type early in the preprocessing phase
because many of the menu choices in the GUI are filtered out based
on the current DOF set. For example, if you choose a structural
element type, thermal load choices will not be not shown at all.

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