Aditya 0 Report post Posted December 16, 2015 Hello all, I was trying to perform modal analysis in OptiStruct and the corresponding modes that I get, I feel, are in radian/sec and I wanted to switch those to Hz. Can anyone assist me with the same? Thank you! Regards, Aditya Share this post Link to post Share on other sites

Guest Report post Posted December 16, 2015 Have a look at this page: https://en.wikipedia.org/wiki/Angular_frequency Share this post Link to post Share on other sites

Guest Report post Posted December 17, 2015 Hi Aditya, The output file (*.out) should have a table of modes with a column for "Frequency" and a column for "Eigenvalue". The "Eigenvalue" is the angular frequency SQUARED, with the angular frequency here expressed as radians/time. The "Frequency" is that same mode expressed as cycles/time. When interpreting the values be mindful of the units of time in your model. If you are using seconds for time then the "Frequency" will be in cycles/second, or Hertz (Hz). If your model uses milliseconds for the unit of time the "Frequency" is reported in cycles/milliseconds. Multiply by 1000 to get cycles/second (Hz). To convert from "Eigenvalue" to "Frequency" take the square root of "Eigenvalue", and then divide by (2*pi). Share this post Link to post Share on other sites