I'm running modal analysis of a structure using ANSYS APDL. If I give initial frequency very close to first natural frequency, the computing time is less (< 1 minute). Otherwise time is high more than 30 minutes. In the output window, Lancos solver takes very less time for first computing cycle, there on lot of time for successive cycles. How to reduce this computational time?
You have to check
1.) the number of modes you request to extract
2.) the number of modes you request to expand
3.) the frequency range you input
These three parameters significantly affect the performance of the eigensolver.
When you specify the frequency close to first natural frequency, it is faster because the solver extracts only the first mode. When you don't specify the frequency range, and when you don't specify any value for modes to extract/expand, then the solver extracts all the modes. (The default values include all the modes and the entire frequency range.) That's why it takes significantly more time.
I suggest going through the following article for more information on these options and then update your APDL script with the corresponding options.
http://www.ansys.stuba.sk/html/guide_55/g-str/GSTR3.htm
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