General Mechanical

General Mechanical

Is it possible to analyze the precession of a spinning top?

    • sbjs7608
      Subscriber

       


      Hello, I am a college student who is attending a university in Korea. I want to design a spinnig top.


      What I want to know is the precession movement according to the change in the number of revolutions.


      I would also like to know the restoration moment of this precession.


      Is this possible in ansys?

    • peteroznewman
      Subscriber

      Yes, try to build a model in the Rigid Dynamics system.

    • sbjs7608
      Subscriber
       Thank thank you for the reply. 
      Are there any simple examples that are similar to these problems that I can practice?
      Or is there a related catalog or video lecture?
      I can't seem to figure out how to measure the restoring moment of the gyroscope due to the change in rotation speed.
    • peteroznewman
      Subscriber

      Please use the Attach button with the .wbpz Archive file after you post a reply saying what version of ANSYS you are using.

    • sbjs7608
      Subscriber

      Ansys workbench 2020 R1 student edition

    • peteroznewman
      Subscriber

      All other Rigid Dynamics programs allow you to specify an Initial Condition of Rotational Velocity. That is not provided in the ANSYS Workbench interface to the Transient Structural solver, which at least has an Initial Conditions folder. The Workbench interface to the Rigid Dynamics solver does not even have an Initial Conditions folder. You will have to figure out a way to achieve a system that is rotating on an axis but not introduce an additional constraint such as a revolute joint. That may require using some APDL code. I can't help with that.


      Another approach is to use the Static Structural analysis program which has a fully developed Rotodynamics capability. Open the ANSYS Help System, and click the Home button so you can select Mechanical APDL, then you will see the Rotodynamic Analysis Guide.  Read that whole guide. See if it can do what you want.


       

    • sbjs7608
      Subscriber

      Thank you


       


      I am trying to analyze the gyroscope with a harmonic response, but there is a problem.


      I am trying to apply a rotating force, but the message 'coriolis effect is vaild only in full harmonic' appears and it cannot be applied.


      What should I do?

    • peteroznewman
      Subscriber

      It means you can't have a Modal analysis upstream from the Harmonic Response.


      Drag a Harmonic Response from the toolbox and drop it on a Geometry cell.


      Open Mechanical on the new system and under Analysis Settings, change the Solution Method to Full.


      Then you can set the Coriolis Effect to On.

    • sbjs7608
      Subscriber

      It works, Thank you


      I am trying to apply a rotating force, but the message 'node not found at hit point location'


      First, I put remote displacement and then I'm trying to change mesh node to remote node but it doesn't work


      What should I do?


       

    • peteroznewman
      Subscriber

      I don't think a Harmonic Response is the analysis you want.


      It is either a Static Structural, with the CORIOLIS effect or it is a Transient Structural model without CORIOLIS, but applying a spinning motion using the IC command, or even better the ICROTATE command.


      Transient Structural is the more direct and understandable analysis because you know that the mass is actually spinning. Then you can support a horizontal axle at one end while gravity pulls down on the spinning disk and the whole system will exhibit precession motion.  You just have to figure out how to use the ICROTATE command using APDL snippets to define the rotational velocity, because as I said above, ANSYS has not put that into the Mechanical interface yet. The spinning mass could be a rigid body, which might simplify things.


      If the Remote Displacement holding one end of the axle in three translation directions at 0 also has a Rotation about Y constraint of 0 so the horizontal axle can't precess, then the moment to hold it in place can be measured using a Probe in the Results.

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