Unit System in Hyperworks - Material Properties and Results

Mark_21908
Mark_21908 New Altair Community Member
edited August 2023 in Community Q&A

Hello everyone,

 

I am currently using Hyperworks for my analyses and have encountered an issue related to the unit system. Initially, I specified the material properties in the unit system t-mm-s-N-MPa, following the standard specifications for steel. However, I later decided to switch to the SI unit system: kg m s N Pa. To do this, I set the SI system via DTI units at Cards and also in Model Verification-Check Units.

 

The problem is that when I specified the material properties in the SI unit system, I obtained completely different results compared to the default unit system. I have read in the online help that Hyperworks is unitless and it's the user's responsibility to adhere consistently to a unit system, but this general information didn't answer my specific questions.

 

Hence, I have the following questions:

 

  1. When defining the properties of a material, do I always have to specify them in the default unit system t-mm-s-N-MPa, even if I have changed the unit system under DTI-Cards?

 

  1. Is the output also in the units specified in the default system, or is there a way to display the unit system in which the results are output? Alternatively, is there any option in Hyperview to display the units if I specify them beforehand? In other words, is there a way to check the units once they are generated?

 

I appreciate any insights or suggestions to help resolve this issue. Thank you in advance for your assistance.

 

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Answers

  • Adriano_Koga
    Adriano_Koga
    Altair Employee
    edited August 2023

    DTI has another purpose which is not to change the units. It "informs" the units for interfacing with other softwares.

    https://help-staging.altair.mediag.com/2022/hwsolvers/os/topics/solvers/os/dti_units_bulk_r.htm?zoom_highlight=dti

     

    Generally speaking, a great number of FE codes work with consistent units, so that the units need to be defined by the user, and the same units used in the input is used for the results output.

    So if your input is N and mm, your stress is in N/mm2 (MPa).

    Entering your Young's modulus would be in MPa as well.

     

    Whatever the unit system you choose, stick to it from the beginning to the end.

    That's it.

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