Mechanical APDL Structural Analysis Guide

5.4.3. Obtain the Mode-Superposition Transient Solution

In this step, the program uses mode shapes extracted by the modal solution to calculate the transient
response. The following requirements apply:

• The mode shape file (Jobname.MODE) must be available.


• The full file (Jobname.FULL) must be available if linear acceleration (ACEL) is present in the mode
  superposition analysis.


• The database must contain the same model for which the modal solution was obtained.


• The element modal load file (Jobname.MLV) must be available if load vectors were created (MOD-
  CONT,ON) and the element results were written on the Jobname.MODE file (MSUPkey = YES on the
  MXPAND command) during the modal analysis.

5.4.3.1. Obtaining the Solution

The procedure to obtain the mode-superposition transient solution is described below:

1. Enter SOLUTION.
   Command(s):/SOLU
   GUI: Main Menu> Solution


2. Define the analysis type and analysis options. These are the same as the analysis options described
   for the full method (in Set Solution Controls (p. 113) and Set Additional Solution Options (p. 115)),
   except for the following differences:
   
   
   • You cannot use the Solution Controls dialog box to define analysis type and analysis options for
     a mode-superposition transient analysis. Instead, you must set them using the standard set of
     solution commands (which are listed in Set Solution Controls (p. 113) and Set Additional Solution
     Options (p. 115)) and the standard corresponding menu paths.
   
   
   • Restarts are available (ANTYPE).
     
     
     • Choose the mode-superposition method of solution (TRNOPT).
     
     
     • When you specify a mode-superposition transient analysis, a Solution menu appropriate for the
       specified analysis type appears. The Solution menu will be either “abridged” or “unabridged,”
       depending on the actions you took prior to this step in your session.The abridged menu contains
       only those solution options that are valid and/or recommended for mode-superposition transient
       analyses. If you are on the abridged Solution menu and you want to access other solution options
       (that is, solution options that are valid for you to use, but their use may not be encouraged for
       this type of analysis), select the Unabridged Menu option from the Solution menu. For details,
       see Using Abridged Solution Menus in the Basic Analysis Guide.
     
     
     • Specify the number of modes you want to use for the solution (TRNOPT). This determines the
       accuracy of the transient solution. At a minimum, you should use all modes that you think will
       contribute to the dynamic response. If you expect higher frequencies to be excited, for example,
       the number of modes specified should include the higher modes. The default is to use all modes
       calculated in the modal solution.
     
     
     
     
   
   
   • To include the contribution of higher frequency modes, add the residual vectors calculated in the
     modal analysis (RESVEC,ON).
   
   
   
   

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Transient Dynamic Analysis