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transient analysis by Fourier transformation

User: "cjc_21934"
cjc_21934
Altair Community Member
Updated by cjc_21934

Hi all,

 

I am attempting to run a transient response analysis which applies a sinusoidal 1g acceleration peak to peak over a sweep of 15 Hz to 50 Hz to 15 Hz. The total cycle is 1 minute.

Is there an example with transient by Fourier transform method somewhere in the documentation?

I can't find a way to define the load as above; especially the up and down the frequency range part. 

 

Thank you

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    User: "Xiaolei"
    Xiaolei
    Altair Employee
    Updated by Xiaolei

    Hi, others may have better ideas, but for now I would suggest using Compose chirp function. https://2022.help.altair.com/2022.2/compose/business/en_us/topics/reference/oml_language/SignalProcessing/chirp.htm?hl=chirp

    The below is the scripts I wrote. It outputs the chirp signal to chirp.csv file. 

    dt = 0.001;
    t = 0:dt:60;
    c1 = chirp(0:dt:30,15,30,60,'linear');
    c3 = chirp(0:dt:60,105,60,15,'linear');
    c4 = c3(30/dt+2:end);
    c = [c1,c4];
    semilogx(t,c);
    m = [t;c]';
    csvwrite('chirp.csv', m,'precision', '%0.6f');

     

    I also attached the script wrote by Roberta Varela & Lorenzo Moretti in ebook Altair_Ebook_SignalProcessing_1201_Final.pdf, which can be used to create spectrogram of the chirp signal. 

    The entire script is attached to this reply.

    Hope this is helpful. 

     

    Thanks. 

    Xiaolei

    chirp_test.oml
    User: "cjc_21934"
    cjc_21934
    Altair Community Member
    OP
    Updated by cjc_21934

    Hi Xiaolei, 

    Thank you for the suggestion. If I understand correctly this addresses the part of defining the load, though I am confused as to how to fold the script into the TLOAD1 definition.

    At the moment I'm struggling getting a simplified Fourier direct transient going; as soon as I tick the FREQ box in loadcase definition, the solver fatals out with:

     

    *** INTERNAL PROGRAMMING ERROR # 252 ***

    Point force vector file not open. 

     

    Is there anything in the documentation regarding Fourier transform dynamic  loadcases, perhaps a tutorial or an example?

     

    Regards,

    Cristian

    User: "Xiaolei"
    Xiaolei
    Altair Employee
    Updated by Xiaolei

    Hi Xiaolei, 

    Thank you for the suggestion. If I understand correctly this addresses the part of defining the load, though I am confused as to how to fold the script into the TLOAD1 definition.

    At the moment I'm struggling getting a simplified Fourier direct transient going; as soon as I tick the FREQ box in loadcase definition, the solver fatals out with:

     

    *** INTERNAL PROGRAMMING ERROR # 252 ***

    Point force vector file not open. 

     

    Is there anything in the documentation regarding Fourier transform dynamic  loadcases, perhaps a tutorial or an example?

     

    Regards,

    Cristian

    Hi Cristian, 

    When the csv file is created, you can copy or import into HyperWorks to create a tabled1 curve. This tabled1 curve can be used to define TLOAD1. 

    I will find an example file and share with you later. 

     

    Thanks. 

    Xiaolei

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