Modal frequency response analysis

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

Hi sir,

I performed a modal analysis (with constraints) and a modal frequency response analysis on a motor. Modal analysis results shows the natural frequency starting from 322 Hz (1st NF) . while the Freq. response analysis results shows the Natural frequency starting from 30,712 Hz (1st NF). According to my knowledge both the analysis should produce same Natural frequencies as all the conditions are same. Both the '.out' files are attached below. Please help me figure out what has gone wrong.

Thank you

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Answers

  • Altair Forum User
    Altair Forum User
    Altair Employee
    edited January 2018

    Hi Mayur, 

     

    Frequency response analysis calculates response of strucure which undergo a periodic excitation. 

     

    When you say natural frequency the structure is not subjected to any external force.

  • Altair Forum User
    Altair Forum User
    Altair Employee
    edited January 2018

    Hi sir,

    so what does the FRA output frequencies signify? 

  • Altair Forum User
    Altair Forum User
    Altair Employee
    edited January 2018

    FRA outputs responses based on excitation. 

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