How to set damping ratio, driving frequency and driving damping? Answered

Hi Support:

I have done a resonance frequency test. Under the same structure, the analysis result of on scale is much lower than coventor or ANSYS. The attachment is the on scale configuration file.

<note>The natural resonance frequency of the designed cantilever is 6.5M Hz, but the resonance frequency of the on scale is 5.4M Hz; therefore, my understanding is that it may be due to the damping ratio, so I have two questions.

  1. How do I set the damping ratio in the on scale?
  2. How to set the driving frequency and driving damping in the on scale?

There are some files for you to verify, please download "OnScale question_202120911cc(in)-20210911-154532.zip" from shared folder here: To OnScale.

Thank you for your help.

3 comments

  • Official comment

    Hi Selena,

    Welcome to the forum.

    It looks like you have generated these files in Designer Mode so I will give you instructions for this. 

    Our project material database is where it looks like you have chosen your materials from, damping properties are not included for these materials in our database. To create your own material you can select Add Project Material in our Material Databse:

    From here you can create your material, specifying damping properties etc. 

    We have 4 options for material damping:

    You can learn more about these in this article. But basically you can do damping in Q or dB/distance. The Loss Frequency is the frequency at which the values dilatation and shear are specified. For even more information search matr vdmp, matr rdmp, matr sdmp and matr mdmp in the Command Reference (accessible through Help tab in Analyst mode).

    Frequency of interest and frequency of damping should be set in the Project Settings Properties in Designer.

    The frequency of interest is used as a parameter to control mesh resolution and should be set accordingly. We recommend 15 elements per wavelength to resolve discretize the waves sufficiently. This is typically set to the center of your operating frequency band. For example, if you interested in data up to 2 MHz, your drive frequency should be around 1 MHz assuming your time domain drive signal has enough energy to cover this frequency range. 

    For frequency of the damping, we set this to the center of the operational frequency band to ensure our damping models are accurate over this frequency range. If your drive signal is at the center of the operational band, then you set both to the same frequency value.

    Your driving frequency is set under Forcing Functions > Time in Designer.

    I hope this helps.

    Best Regards,

    Chloe

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  • Hi Chloe,

    Thank you for your prompt reply. Our user feedback as below:

    Please help me run this structure that you could download "202120911cc(in)-20210914-095243-1" and "202120911cc(in)-20210914-095243-2" here: To OnScale
    In addition, the picture shows the structure size, material and boundary conditions:

    Please help me what is the resonance frequency of the first mode?

    Best Regards,
    Selena

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  • Hi Chloe,

    May I know if there is any update for this case? Thank you.

    Best Regards,
    Selena

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