- 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 (MSUPkey = YES on the
MXPAND command) during the modal analysis.
- Enter SOLUTION.
Command(s):/SOLU
GUI: Main Menu> Solution
- Define the analysis type and analysis options. These are the same as described for the full method, except
for the following differences:
- Choose the mode-superposition method of solution (HROPT).
- Specify the modes you want to use for the solution (HROPT). This determines the accuracy of the
harmonic solution. Generally, the number of modes specified should cover about 50 percent more
than the frequency range of the harmonic loads.
- To include the contribution of higher frequency modes, add the residual vectors calculated in the
modal analysis (RESVEC,ON).
- Optionally, cluster the solutions about the structure's natural frequencies (HROUT) for a smoother and
more accurat e tracing of the response curve.
- Optionally, at each frequency, print a summary table that lists the contributions of each mode to the
response (HROUT). Note,OUTPR,NSOL must be specified to print mode contributions at each frequency.
- Apply loads on the model. Harmonic loading is the same as described for the full method, except for
the following restrictions:
- Only forces, accelerations, and the load vector created in the modal analysis are valid. Use the LVSCALE
command to apply the load vector from the modal solution. Use a zero scale factor on the LVSCALE
command to suppress a load vector at a particular load step. Note that ALL loads from the modal
analysis are scaled, including forces and accelerations. To avoid load duplication, delete any loads that
were applied in the modal analysis.
Note
You should apply accelerations in the modal analysis rather than in the harmonic
analysis in order to obtain consistent reaction forces.
- If the harmonic excitation is coming from support motion and you requested the pseudo-static modes
in the modal analysis (MODCONT command), you can use the DVAL command to specify the enforced
displacements and accelerations. Imposed nonzero displacements (D command) are ignored.
- Specify load step options.
- You can request any number of harmonic solutions to be calculated (NSUBST). The solutions (or sub-
steps) will be evenly spaced within the specified frequency range (HARFRQ). For example, if you specify
10 solutions in the range 30 to 40 Hz, the program will calculate the response at 31, 32, 33, ..., 39, and
40 Hz. No response is calculated at the lower end of the frequency range.
- For the cluster option, the NSUBST command specifies the number of solutions on each side of a
natural frequency if the clustering option (HROUT) is chosen.The default is to calculate four solutions,
Release 15.0 - © SAS IP, Inc. All rights reserved. - Contains proprietary and confidential information
Mode-Superposition Harmonic Analysis
