acceleration excitation in harmonic response analysis and transient analysis (modal)?

SYS
SYS Altair Community Member
in Community Q&A

I've some problems and I need your help, I'm currently doing some dynamics analysis such as harmonic response, transient analysis (modal superposition). The structural system contains some rails and motors, and the source of excitation is the motor, so there are some rigid body modes the modal analysis.
The first challenge, when running the harmonic response analysis, I need to simulate the motor sweep, so I need to keep the magnitude of the acceleration value constant and the frequency varying instead of using a unit force for the input, how can I set it up to simulate this situation, I have tried the forced acceleration analysis of the SPCD card, but it will make the frequency and vibration pattern obtained from the modal analysis deviate. In addition to this, the large mass method is also not working and will also bias the modal analysis;
The second problem is that, in transient analysis (modal), it is also necessary to apply acceleration excitation, what setting method can be used to realize, in addition, I list several methods for discussion: 1, in the TLOAD1 card references to the ACCEL1 card, and the TYPE is set to LOAD, the calculation of the results can not be judged accurately or not; 2, the use of the SPCD card to apply the Acceleration excitation; 3, using DAREA card for force loading, acceleration input is realized by F=ma, but the size of m cannot be determined, it is the mass of the whole moving part, or the mass of the motor.
Thank you very much for your discussion and suggestions, thanks!

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Answers

  • Rajashri_Saha
    Rajashri_Saha
    Altair Employee

    Hi Sys,

    If you want to keep your acceleration value constant, then either give the required value in SPCD card, D1 field and keep the loading curve with Y-axis as constant or give unit value in D1 field of SPCD and in TABLED1 curve you can give the acceleration value constant throughout the loading frequency.

    For acceleration load , better use SPCD card.

    DAREA is used to apply force as load which is the value you need to apply for excitation.

    Thanks

    Rajashri

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