ANSYS LS-DYNA in Mechanical APDL - ... 2012 ANSYS, Inc. February 5, ... Solution and Simulation...

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Transcript of ANSYS LS-DYNA in Mechanical APDL - ... 2012 ANSYS, Inc. February 5, ... Solution and Simulation...

  • 2012 ANSYS, Inc. February 5, 2013 1 Release 14.5

    14.5 Release

    Lecture 7 Solution and Simulation Controls

    ANSYS LS-DYNA in Mechanical APDL

  • 2012 ANSYS, Inc. February 5, 2013 2 Release 14.5

    Objectives

    This lecture concerns Solution and Simulation Controls. The tools used to optimize and control explicit analyses are discussed.

    Topics:

    A. Basic ANSYS LS-DYNA Solution Controls

    B. Controlling LS-DYNA Binary Output Files

    C. Controlling LS-DYNA ASCII Output Files

    D. Visualization of Small Time Steps

    E. Mass Scaling

    F. Additional Time Controls

    G. Adaptive Meshing

    H. Simulation Control

    I. Editing the LS-DYNA Input File

    J. LS-DYNA Batch Launcher

    K. LS-DYNA Solver Precision

    L. Solution and Simulation Controls Workshop

  • 2012 ANSYS, Inc. February 5, 2013 3 Release 14.5

    Many of the solution control parameters specified in an explicit analysis are similar to those encountered during an implicit run:

    Termination Time

    Integration Point Output

    Results Output and Restart Frequency

    Termination Time : TIME

    The termination time is the actual time for which the physical process is being simulated. In an explicit dynamic analysis, this time is usually of very short duration often in milliseconds.

    Solution > Time Controls > Solution Time

    A. Basic ANSYS LS-DYNA Solution Controls

  • 2012 ANSYS, Inc. February 5, 2013 4 Release 14.5

    ... Basic ANSYS LS-DYNA Solution Controls

    Integration Point Output : EDINT

    The EDINT command is used to specify the number of shell and beam integration points for which results data will be written for. The actual number of integration points used in the calculations is controlled by the NIP real constant associated with the element.

    Solution > Output Controls > Integ Pt Storage

    To adequately capture plastic effects in shells, the NIP real constant

    needs to be at least 3, but 5 is recommended if a Gauss distribution

    is used. For the trapezoidal formulation, NIP > 20 is recommended.

    For beam elements, POST1 requires that integration point data be

    saved in order to plot the elements (EDINT > 0). Resultant beams lack

    integration point data, and are, therefore, not plotted in POST1.

    Default values shown

  • 2012 ANSYS, Inc. February 5, 2013 5 Release 14.5

    ... Basic ANSYS LS-DYNA Solution Controls

    Results Output and Restart Frequency : EDRST, EDHTIME, and EDDUMP

    The EDRST command specifies how often results for the entire model are written to the binary Jobname.RST file. Typically, only 10 to 100 result sets are saved to this POST1 file, due to the large volume of data. The Jobname.RST file can be post-processed in POST26, but the Jobname.HIS file (see below) is generally used in POST26 instead.

    The EDHTIME command specifies how often results for a subset of the model are written to the binary Jobname.HIS file. Typically, 1,000 to 100,000 results sets are saved to this POST26 time history file.

    If more than 1,000 sets are requested, the /CONFIG,NRES command must be issued to allocate the necessary model space.

    The output data is restricted to those nodal and element components specified via the EDHIST command. Reissue EDHIST, as needed

    The EDHTIME command also controls the frequency for which the LS-DYNA ASCII output files are written (discussed later).

  • 2012 ANSYS, Inc. February 5, 2013 6 Release 14.5

    ... Basic ANSYS LS-DYNA Solution Controls

    Results Output and Restart Frequency (continued):

    Similarly, the EDDUMP command specifies how often the binary restart files are written (d3dump01, d3dump02, d3dump03, etc.). The EDSTART command (discussed later) is used to restart an analysis from one of these files.

    The frequency for which results and restart files are written is based on the number of desired data sets or the actual time interval desired:

    Solution > Output Controls > File Output Freq > Number of Steps

    Solution > Output Controls > File Output Freq > Time Step Size

    Default values shown

    for the Number of Steps

    input format.

  • 2012 ANSYS, Inc. February 5, 2013 7 Release 14.5

    B. Controlling LS-DYNA Binary Output Files

    Since LS-PREPOST, the LS-DYNA postprocessor, is provided for free with ANSYS LS-DYNA, the user can create and review the LS-DYNA binary results files d3plot and d3thdt in addition to the ANSYS LS-DYNA binary results files, Jobname.RST and Jobname.HIS. Please note that the LS-PREPOST postprocessor is not supported by ANSYS, Inc.

    The EDOPT command determines which binary results files are output:

    Solution > Output Controls > Output File Types

    The corresponding LS-DYNA Keyword is *DATABASE_FORMAT

    File options include ADD,

    DELETE, and LIST a file.

    Output can be produced

    for ANSYS only (.RST

    and .HIS), LS-PREPOST

    only (d3plot and d3thdt),

    or both postprocessors.

  • 2012 ANSYS, Inc. February 5, 2013 8 Release 14.5

    C. Controlling LS-DYNA ASCII Output Files

    In addition to LS-DYNA binary results files, the user can output a series of LS-DYNA ASCII output files that contain specialized information about an analysis:

    GLSTAT - Global statistics data (contents controlled by EDENERGY) BNDOUT - Boundary condition forces and energy RWFORC - Rigid wall forces DEFORC - Discrete element forces MATSUM - Material energies summary (on a Part ID basis) NCFORC - Nodal interface forces RCFORC - Resultant interface forces DEFGEO - Deformed geometry data SPCFORC - Single point constraint reaction forces SWFORC - Nodal constraint reaction forces (spotwelds & rivets) RBDOUT - Rigid body data GCEOUT - Geometry contact entities SLEOUT - Sliding interface energies data JNTFORC - Joint force data NODOUT - Node data ELOUT - Element data

  • 2012 ANSYS, Inc. February 5, 2013 9 Release 14.5

    ... Controlling LS-DYNA ASCII Output Files

    The EDOUT command controls which ASCII files are written: Solution > Output Controls > ASCII Output

    Select individual ASCII files desired (multiple selections permitted).

    Additional options include: Write ALL ASCII output files

    LIST output files selected

    DELETE all specifications

    For some of the ASCII output files, data is written only for a subset of the model. The EDHIST command specifies which nodal and element components data will be written for: Solution > Output Controls > Select Component

    Output frequency controlled by EDHTIME command.

    Multiple selections allowed.

  • 2012 ANSYS, Inc. February 5, 2013 10 Release 14.5

    D. Visualization of Small Time Steps

    The LS-DYNA solver automatically calculates the minimum time step for each element based on its characteristic length, density, etc.

    The smallest of these element time steps is called the critical time step.

    The actual time step used during solution is the product of the current critical time step and a stability factor (usually 0.90). As elements distort during the analysis, their time steps are recalculated, and the subsequent actual time step is written to the glstat file.

    At the beginning of the run, the initial 100 smallest time steps (and their corresponding element numbers) are written to the d3hsp file.

    The EDTP command is used to visualize elements with the smallest time steps before the LS-DYNA solver is invoked.

    Elements with smallest time steps are plotted in red.

    Elements with intermediate time steps are plotted in yellow.

    A translucency option is available along with a time step listing option.

    Re-meshing and mass scaling decisions can be made before the solution is initiated, but the EDTP macro is rather slow for large models.

  • 2012 ANSYS, Inc. February 5, 2013 11 Release 14.5

    ... Visualization of Small Time Steps

    EDTP, OPTION, VALUE1, VALUE2 OPTION = 1, 2, or 3:

    1 = element plot of VALUE1 smallest element time steps

    2 = #1 above + element listing of these time step values

    3 = #2 above + VALUE2 translucency of remaining elements

    VALUE1 = plot/list limit for smallest designation (red elements decide size)

    VALUE2 = translucency ( 0 = no translucency, 1 = maximum, 0.9 = default level)

    Solution > Time Controls > Time Step Prediction

  • 2012 ANSYS, Inc. February 5, 2013 12 Release 14.5

    E. Mass Scaling

    An elements time step is calculated based on its material properties (EX, NUXY, and DENS) and characteristic length:

    element 1 2 3

    l1 l2 l3

    tl

    c

    l

    c

    cE

    min

    min

    ( )

    2

    21

    t

    l E

    t E

    lfor element i

    specified

    i

    i

    i

    specified

    i

    2 2

    2

    2 2

    1

    1

    ( )

    ( )

    The equation can be rearranged to find the required density of each

    element for a desired time step size. By adding the corresponding

    mass to these elements, the solution time will be reduced.

    This procedure is known as mass

    scaling. However, care must be

    taken as to not add so much mass

    as to invalidate the results

  • 2012 ANSYS, Inc. February 5, 2013 13 Release 14.5

    ... Mass Scaling

    EDCTS, DTMS, TSSFAC

    If DTMS is a POSITIVE