8.7非线性瞬态分析步骤帮助学习

8.7. Performing a Nonlinear Transient AnalysisMany of the tasks that you need to perform in a nonlinear transient analysis are the same as (or similar to) those that you perform in nonlinear static analyses (described in Performing a Nonlinear Static Analysis) and linear full transient dynamic analyses (described in Structural Static Analysis). However, this section describes some additional considerations for performing a nonlinear transient analysis.Remember that the Solution Controls dialog box, which is the method described in Performing a Nonlinear Static Analysis, cannot be used to set solution controls for a thermal analysis. Instead, you must use the standard set of ANSYS solution commands and the standard corresponding menu paths.8.7.1. Build the ModelThis step is the same as for a nonlinear static analysis. However, if your analysis includes time-integration effects, be sure to include a value for mass density [MP,DENS]. If you want to, you can also definematerial-dependent structural damping [MP,DAMP].8.7.2. Apply Loads and Obtain the Solution1.Specify transient analysis type and define analysis options as youwould for a nonlinear static analysis:∙New Analysis or Restart [ANTYPE]∙Analysis Type: Transient [ANTYPE]∙Large Deformation Effects [NLGEOM]∙Large Displacement Transient (if using the Solution Controls dialog box to set analysis type)2.Apply loads and specify load step options in the same manner as youwould for a linear full transient dynamic analysis. A transient loadhistory usually requires multiple load steps, with the first loadstep typically used to establish initial conditions (see the BasicAnalysis Guide). The general, nonlinear, birth and death, andoutput control options available for a nonlinear static analysisare also available for a nonlinear transient analysis.In a nonlinear transient analysis, time must be greater than zero.See Transient Dynamic Analysis for procedures for defining nonzeroinitial conditions.For a nonlinear transient analysis, you must specify whether you want stepped or ramped loads [KBC]. See the Basic Analysis Guide for further discussion about ramped vs. stepped loads.You can also specify dynamics options: alpha and beta damping, time integration effects, and transient integration parameters.Command(s): ALPHAD, BETAD, TIMINT, TINTPGUI: Main Menu> Solution> Analysis Type> Sol'n Control ( : Transient Tab)Main Menu> Solution> Unabridged Menu> Load Step Opts> Time/Frequenc> DampingMain Menu> Solution> Unabridged Menu> Load Step Opts> Time/Frequenc> Time IntegrationAn explanation of the dynamics options follows.∙DampingRayleigh damping constants are defined using the constantmass [ALPHAD] and stiffness [BETAD] matrix multipliers. Ina nonlinear analysis the stiffness may change drastically -do not use BETAD, except with care. See Damping for detailsabout damping.∙Time Integration Effects [TIMINT]Time integration effects are ON by default in a transientanalysis. For creep, viscoelasticity, viscoplasticity, orswelling, you should turn the time integration effects off(that is, use a static analysis). These time-dependenteffects are usually not included in dynamic analyses becausethe transient dynamic time step sizes are often too short forany significant amount of long-term deformation to occur.Except in kinematic (rigid-body motion) analyses, you willrarely need to adjust the transient integration parameters[TINTP], which provide numerical damping to the Newmark andHHT methods. (See your Theory Reference for the MechanicalAPDL and Mechanical Applications for more information aboutthese parameters.)ANSYS' automatic solution control sets the defaults to a newtime integration scheme for use by first order transientequations. This is typically used for unsteady state thermalproblems where θ= 1.0 (set by SOLCONTROL, ON); this is thebackward Euler scheme. It is unconditionally stable and morerobust for highly nonlinear thermal problems such as phasechanges. The oscillation limit tolerance defaults to 0.0, sothat the response first order eigenvalues can be used to moreprecisely determine a new time step value.Note: If you are using the Solution Controls dialog box to set solution controls, you can access all of these options[ALPHAD, BETAD, KBC, TIMINT, TINTP, TRNOPT] on the Transienttab.3.Write load data for each load step to a load step file.Command(s):LSWRITEGUI: Main Menu> Solution> Load Step Opts> Write LS File4.Save a backup copy of the database to a named file.Command(s):SAVEGUI: Utility Menu> File> Save As5.Start solution calculations. Other methods for multiple load stepsare described in "Getting Started with ANSYS"in the Basic Analysis Guide.Command(s):LSSOLVEGUI: Main Menu> Solution> Solve> From LS Files6.After you have solved all load steps, leave SOLUTION.Command(s):FINISHGUI: Close the Solution menu.8.7.3. Review the ResultsAs in a nonlinear static analysis, you can use POST1 to postprocess results at a specific moment in time. Procedures are much the same as described previously for nonlinear static analyses. Again, you should verify that your solution has converged before you attempt to postprocess the results.Time-history postprocessing using POST26 is essentially the same for nonlinear as for linear transient analyses. See the postprocessing procedures outlined in Transient Dynamic Analysis.More details of postprocessing procedures can be found in the Basic Analysis Guide.。