Frequency units

Altair Forum User
Altair Forum User
Altair Employee
edited October 2020 in Community Q&A

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

Tagged:

Answers

  • Altair Forum User
    Altair Forum User
    Altair Employee
    edited December 2015

    Have a look at this page: 

    https://en.wikipedia.org/wiki/Angular_frequency

     

  • Altair Forum User
    Altair Forum User
    Altair Employee
    edited December 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).

Categories