# Frequency units

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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,

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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).