Using Finite Element

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Using Finite Element

• ANSYS Online Manuals
• Operations Guide
• Basic Analysis Procedures Guide
• Getting Started w/ ANSYS

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Organization of ANSYS Program

• The ANSYS program is organized into two basic
  levels
• Begin level
• Processor (or Routine) level
• The Begin level acts as a gateway into and out of
  the ANSYS program. It is also used for certain
  global program controls such as changing the
  jobname.
• At the Processor level , several processors are
  available. Each processor is a set of functions
  that perform a specific analysis task. For
  example, the general preprocessor (PREP7) is
  where you build the model, the solution processor
  (SOLUTION) is where you apply loads and obtain
  the solution, and the general postprocessor
  (POST1) is where you evaluate the results of a
  solution.

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ANSYS File Types
File Type File Name File Format
Log file Jobname.LOG ASCII
Error file Jobname.ERR ASCII
Output file Jobname.OUT ASCII
Database file Jobname.DB Binary
Results file structural or coupled Jobname.RST Binary
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Communicating Via GUI

• The easiest way to communicate with the ANSYS
  program is by using the ANSYS menu system, called
  the Graphical User Interface (GUI).
• The GUI consists of windows, menus, dialog boxes,
  and other components that allow you to enter
  input data and execute ANSYS functions simply by
  picking buttons with a mouse or typing in
  responses to prompts.

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Communicating Via Commands

• Commands are the instructions that direct the
  ANSYS program. ANSYS has more than 1200 commands,
  each designed for a specific function. Most
  commands are associated with specific (one or
  more) processors, and work only with that
  processor or those processors.
• The ANSYS Commands Reference describes all ANSYS
  commands in detail, and also tells you whether
  each command has an equivalent GUI path. (A few
  commands do not.)

6
ANSYS Procedures

• A typical ANSYS analysis has three distinct
  steps
• Build the model.
• Apply loads and obtain the solution.
• Review the results.

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Build the Model

• Building a finite element model requires more of
  an ANSYS user's time than any other part of the
  analysis. First (optionally), you specify a
  jobname and analysis title. Then, you use the
  PREP7 preprocessor to define the element types,
  element real constants, material properties, and
  the model geometry.

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Defining the Jobname

• The jobname is a name that identifies an ANSYS
  job. When you define a jobname for an analysis,
  the jobname becomes the first part of the name of
  all files the analysis creates. (The extension or
  suffix for these files' names is a file
  identifier such as .db)
• Command /FILNAME
• GUI Utility MenugtFilegtChange Jobname

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Defining the Title

• The /TITLE command defines a title for the
  analysis. ANSYS includes the title on all
  graphics displays and on the solution output.
• Command /TITLE
• Utility MenugtFilegtChange Title

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Defining Units

• The ANSYS program does not assume a system of
  units for your analysis. You can use any system
  of units (except in magnetic field analyses) so
  long as you make sure that you use that system
  for all the data you enter. (Units must be
  consistent for all input data.)
• Using the /UNITS command, you can set a marker in
  the ANSYS database indicating the system of units
  that you are using. This command does not convert
  data from one system of units to another it
  simply serves as a record for subsequent reviews
  of the analysis.

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Defining Element Types (I)

• The ANSYS element library contains more than 150
  different element types. Each element type has a
  unique number and a prefix that identifies the
  element categoryBEAM4, PLANE77, SOLID96, etc.
• The element type determines, among other things
• The degree-of-freedom set (which in turn implies
  the discipline-structural, thermal, magnetic,
  electric, quadrilateral, brick, etc.)
• Whether the element lies in two-dimensional or
  three-dimensional space.
• The degree of the interpolation function within
  each element

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Defining Element Types (II)

• BEAM4, for example, has six structural degrees of
  freedom (UX, UY, UZ, ROTX, ROTY, ROTZ), is a line
  element, and can be modeled in 3-D space. PLANE77
  has a thermal degree of freedom (TEMP), is an
  eight-node quadrilateral element, and can be
  modeled only in 2-D space.
• Many element types have additional options (e.g.
  integration method), known as KEYOPTs, and are
  referred to as KEYOPT(1), KEYOPT(2)
• Command ET
• GUIMain Menu gtPreprocessor gtElement Type
  gtAdd/Edit/Delete

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Defining Element Types (III)

• You define the element type by name and give the
  element a type reference number. For example, the
  commands shown below define two element types,
  BEAM4 and SHELL63, and assign them type reference
  numbers 1 and 2 respectively.
• ET,1,BEAM4
• ET,2,SHELL63
• While defining the actual elements, you point to
  the appropriate type reference number using the
  TYPE command (Main Menugt Preprocessorgt Creategt
  Elementsgt Elem Attributes).

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Defining Element Real Constants

• Element real constants are properties that depend
  on the element type, such as cross-sectional
  properties of a beam element. For example, real
  constants for BEAM3, the 2-D beam element, are
  area (AREA), and moment of inertia (IZZ), height
  (HEIGHT). Not all element types require real
  constants, and different elements of the same
  type may have different real constant values.
• Cmd R GUI Main Menu gtPreprocessor gtReal
  Constants
• As with element types, each set of real constants
  has a reference number. While defining the
  elements, you point to the appropriate real
  constant reference number using the REAL command.

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Defining Material Properties

• Most element types require material properties.
  Depending on the application, material properties
  may be
• Linear or nonlinear
• Isotropic, orthotropic, or anisotropic
• Constant temperature or temperature-dependent
  .
• As with element types and real constants, each
  set of material properties has a material
  reference number. Within one analysis, you may
  have multiple material property sets (to
  correspond with multiple materials used in the
  model). ANSYS identifies each set with a unique
  reference number.

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Linear Material Properties

• Linear material properties can be constant or
  temperature-dependent, and isotropic or
  orthotropic. To define constant material
  properties (either isotropic or orthotropic), use
  one of the following
• Command(s) MP
• GUI Main MenugtPreprocessorgtMaterial
  PropsgtMaterial Models
• the appropriate property label for example EX,
  EY, EZ for Young's modulus, KXX, KYY, KZZ for
  thermal conductivity.
• For isotropic material define only the
  X-direction property the other directions
  default to the X-direction value. Other material
  property defaults are built-in to reduce the
  amount of input. For example, Poisson's ratio
  (NUXY) defaults to 0.3 (?), shear modulus (GXY)
  defaults to EX/2(1NUXY)), and emissivity (EMIS)
  defaults to 1.0. See the ANSYS Elements Reference
  for details.

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Creating the Model Geometry

• Once you have defined material properties, the
  next step in an analysis is generating a finite
  element model, nodes and elements, that
  adequately describes the model geometry.

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Creating the Model Geometry

• There are two methods to create the finite
  element model solid modeling and direct
  generation.
• With solid modeling, you describe the geometric
  shape of your model, then instruct the ANSYS
  program to automatically mesh the geometry with
  nodes and elements. You can control the size and
  shape of the elements that the program creates.
• With direct generation, you "manually" define the
  location of each node and the connectivity of
  each element. Several convenience operations,
  such as copying patterns of existing nodes and
  elements, symmetry reflection, etc. are
  available.
• Details of the two methods are described in the
  ANSYS Modeling and Meshing Guide.

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Apply Loads and Obtain the Solution

• In this step, you use the SOLUTION processor to
  define the analysis type and analysis options,
  apply loads, specify load step options, and
  initiate the finite element solution.
• You also can apply loads using the PREP7
  preprocessor.

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Defining the Analysis Type

• choose the analysis type based on the loading
  conditions and the response you wish to
  calculate. For example, if natural frequencies
  and mode shapes are to be calculated, you would
  choose a modal analysis.
• analysis types in the ANSYS program static (or
  steady-state), transient, harmonic, modal,
  spectrum, buckling, and substructuring.
• not all analysis types are valid for all
  disciplines. Modal analysis, for example, is not
  valid for a thermal model.

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Defining the Analysis Options

• Analysis options allow you to customize the
  analysis type. Typical analysis options are the
  method of solution, stress stiffening on or off,
  and Newton-Raphson options.
• If you are performing a static or full transient
  analysis, you can take advantage of the Solution
  Controls dialog box to define many options for
  the analysis.
• You can specify either a new analysis or a
  restart, but a new analysis is the choice in most
  cases. See Restarting an Analysis for complete
  information on performing restarts.
• You cannot change the analysis type and analysis
  options after the first solution.

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Applying Loads

• The word loads as used in this manual includes
  boundary conditions (constraints, supports, or
  boundary field specifications) as well as other
  externally and internally applied loads. Loads in
  the ANSYS program are divided into six
  categories
• DOF Constraints
• Forces
• Surface Loads
• Body Loads
• Inertia Loads
• Coupled-field Loads

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Applying Loads

• You can apply most of these loads either on the
  solid model (keypoints, lines, and areas) or the
  finite element model (nodes and elements).
• However, the loads assigned on the solid model
  will be transferred to the mesh model before
  solution.

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Load Step Substep

• Two important load-related terms you need to know
  are load step and substep. A load step is simply
  a configuration of loads for which you obtain a
  solution. In a structural analysis, for example,
  you may apply wind loads in one load step and
  gravity in a second load step. Load steps are
  also useful in dividing a transient load history
  curve into several segments.
• Substeps are incremental steps taken within a
  load step. You use them mainly for accuracy and
  convergence purposes in transient and nonlinear
  analyses. Substeps are also known as time
  steps-steps taken over a period of time. (The
  word time in here is not always the same as the
  time in physical.)

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Initiating the Solution

• To initiate solution calculations, use either of
  the following
• Command(s) SOLVE
• GUI Main MenugtSolutiongtCurrent LS
• Results are written to the results file
  (Jobname.RST, Jobname.RTH, Jobname.RMG, or
  Jobname.RFL) and also to the database.
• The only difference is that only one set of
  results can reside in the database at one time,
  while you can write all sets of results (for all
  substeps) to the results file.

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Review the Results

• Once the solution has been calculated, you can
  use the ANSYS postprocessors to review the
  results. Two postprocessors are available POST1
  and POST26.
• You use POST1, the general postprocessor, to
  review results at one substep (time step) over
  the entire model or selected portion of the
  model.
• You use POST26, the time history postprocessor,
  to review results at specific points in the model
  over all time steps.

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Other Manuals

• Modeling and Meshing Guide
• Structural Analysis Guide
• Advanced Analysis Techniques Guide
• APDL Programmer's Guide
• ANSYS Verification Manual
• ANSYS Commands Reference
• ANSYS Element Reference

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DEMO

• ANSYS 2D bracket tutor
• ANSYS Structure Analysis Guide Structural Static
  Analysis