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Using Finite Element

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Title: Using Finite Element


1
Using Finite Element
  • ANSYS Online Manuals
  • Operations Guide
  • Basic Analysis Procedures Guide
  • Getting Started w/ ANSYS

2
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.

3
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
4
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.

5
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.

7
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.

8
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

9
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

10
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.

11
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

12
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

13
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).

14
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.

15
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.

16
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.

17
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.

18
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.

19
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.

20
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.

21
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.

22
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

23
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.

24
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.)

25
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.

26
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.

27
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

28
DEMO
  • ANSYS 2D bracket tutor
  • ANSYS Structure Analysis Guide Structural Static
    Analysis
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