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Thread: How to properly place the CG in Flow Simulation for moment calculations

  1. #11
    Matt Gonitzke's Avatar
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    Context and precision of terms is important here when there are two similar but very different quantities being discussed here that contain the same word.

    Torque = force * distance, and "Moment" in the context of CG location and weight and balance is also force * distance. You have also probably seen this as "weight * arm = moment" on aircraft weight and balance calculations. In this context, torque and moment are functionally the same thing. Torque is not "dynamic"; it is not a function of time.

    In your screenshots, "[mass] Moment of Inertia" is is a quantity that relates the torque needed to generate a desired angular acceleration about a rotational axis.

  2. #12
    SOLIDWORKS Support Volunteer Jeffrey Meyer's Avatar
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    Wink

    This is somewhat off-topic, but I couldn't resist the temptation to make this post:
    IMHO torque and moment are 100% synonymous and interchangeable. The use of one or the other is entirely part of the beauty of the English language. Let's take the example of tightening a bolt with a torque-wrench. While the bolt is turning (read "in a dynamic state"), we are applying a torque. But when the bolt stops turning having reached the required torque, we have a static torque - a moment. So the tool should now be called a moment-wrench. In both cases we are applying a force on the handle at a fixed distance from the bolt. Nothing has changed except the name of the tool.
    At the moment I'm enjoying having this torque.

  3. #13

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    Torque vs. Moment

    With all due respect, here is a quick answer to this question (attachment 1). Please note the first comparison.

    The second attachment is from a RANS CFD tool I leased for a year. It is 'Stallion 3D.' It is primarily for analysis of models not within a closed flow environment. In other words, airplanes, sailing vessels, cars, etc.

    This attachment includes just a small portion of the data for my 207EF FWO model. Notice there is no mention of 'Torque.' Aero weenies want to know about moments, moment coefficients, moments about the X,Y, and Z axes, and the X, Y, and Z forces, along with the appropriate coefficients.

    I believe TORQUE is a vestige of the original purpose of the SolidWorks Flow Simulation software - internal flows. In that scenario, it is quite logical to want to know torques. Think about a flow passing through an impeller, vane, etc. The engineer would probably want to know the Torque that is acting on the impeller/vane.

    So, the REAL QUESTION is: Can I assume, in this software, that TORQUE can be substituted for moment?

    Regards,
    Joe T.
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  4. #14
    EAA StaffEAA Staff / Moderator
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    Joe T., Stephen Endersby from DS SolidWorks is developing a step-by-step guide. It may take a bit, but I will post a link out here when I have it. We may also turn this into a bit of a tutorial for others to post out here: http://eaa.org/swu

    Thanks!

    Cory

  5. #15
    EAA StaffEAA Staff / Moderator
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    Here are step-by-step instructions. Please let me know if we're missing something.

  6. #16
    EAA StaffEAA Staff / Moderator
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    That does seem to be a reasonable validation. I may be wrong, but I think the issue Joe was encountering was that SOLIDWORKS uses material weights to identify the CG. His model doesn't have material properties loaded and so he was trying to place the CG where he wanted it to be.

  7. #17
    Ok, Cory. I misunderstood his intention, so I deleted my post to avoid confusion.

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