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

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  1. #1

    Join Date
    Apr 2020
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    How to properly place the CG in Flow Simulation for moment calculations

    All,

    I want to be able to determine moments about my design's CG. How do I do that?

    When I have SW create a CG, it is not where I need it. Alternatively, how do I move the 'Local Coordinate Axis?'

    Regards,
    Joe T.

  2. #2

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    Jan 2014
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    From Stephen Endersby (DS SolidWorks - Dir. Product Portfolio Mgmt.):
    The easiest way is to can create a custom coordinate system in the SOLIDWORKS assembly (aircraft) at the location of the CofG.
    Then assemble this SOLIDWORKS assembly into a new assembly (call if flow_aircraft) and mate the CofG coord system of the aircraft to the new assembled default coordinate system. That way your flow moments are calculated around the aircraft CofG.

  3. #3

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    Cori/Steve,

    I'll try that. I was doing something similar, but I could not get the CG to move to the new local coordinate axis. I'll try again.


    Also, Cori, I'll have you the parameters that would be very useful for Flow Simulation.

    Joe T.
    Last edited by JoeT; 08-10-2020 at 03:30 PM.

  4. #4

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    I can't get the CG to 'Mate' to the re-located coordinate system. I get the following message:

    "Mating to the Center of Mass of the top level assembly is not allowed because it would create a circular reference."

    Any suggestions?

    Regards,
    Joe T.

  5. #5

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    Joe, was this after watching the video I shared with you from Stephen?

    For those of you curious about this video, it was a quick screen recording without sound of the process of creating a custom coordinate system relative to the CG stored here.
    Last edited by Cory Puuri; 08-14-2020 at 07:30 AM.

  6. #6

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    Cori,

    I've watched it several times. As stated in your post above, there is no audio. That's a real problem.

    Also, the video is very poor quality. I am not sure what menus. etc., were clicked.

    I plan to watch it again shortly with my SW Flow Sim up and running and will try to follow and understand the logic better.

    I will have you the 'wish list' of functions that are needed to properly analyze aircraft performance today. I will also send you, separately, how I am trying to move the CG to the desired location. Included in that will be some questions for Stephen that may be useful for other folks following this thread.

    Regards,
    Joe T.

  7. #7
    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.

  8. #8

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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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  9. #9

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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

  10. #10

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    Here are step-by-step instructions. Please let me know if we're missing something.

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