General Mechanical

General Mechanical

Checking hourglass energy in transient thermal module

    • Aashranth
      Subscriber

      Hello all,


       


      I am doing a transient thermal analysis using ANSYS R3 WB, where a single body loses heat through convection and radiation. I meshed the body using default options, and the element created is Hex20. I would like to check if there is any hourglassing due to the heat transfer.


      Visibly I can't see any distortion, but I would like to quantify it using the energy plots that have been discussed on this forum, such as https://studentcommunity.ansys.com/thread/hourglass-control/?order=all#comment-46c2dc67-ba1b-4e7a-8f84-aa0e0022aeb4


       


      Thank you!

    • Keyur Kanade
      Ansys Employee

      Please post the questions in appropriate category. Moving this question to other category to get better response. 


      Moving to structural mechanics. 

    • Wenlong
      Ansys Employee

      Hi,


      Hourglass mode can happen when a solid element only has one integration point. When it happens, the element deforms without producing any stress. In other words, an element has deformation but no strain energy. So I don't believe hourglass mode is an issue in a thermal analysis because there is no deformation.


      Others can correct me if I am wrong. 


      Regards,


      Wenlong


       


       

    • Aashranth
      Subscriber

      Dear Wenlong,


       


      Thank you for your response! In my case, the solid is cooled very fast, leading to possible distortion because of rapid, inhomogeneous contraction.


      Could the stress due to this cause the hourglass mode? Or is there a need to additionally add something from a structural module to simulate this?


       


      Thank you!

    • Wenlong
      Ansys Employee

      Hi,


      What type of analysis are you doing? Is it a transient thermal analysis? If yes, then there will be no stress involved no matter how fast the temperature changes. You can verify that by checking the material property.  if there is no "coefficient of thermal expansion", then it means temperature change won't cause any deformation. 


      Regards,


      Wenlong


       

    • Aashranth
      Subscriber

      Dear Wenlong,


      Thanks for your response. Yes, it is a transient thermal analysis. The material property does have the (secant) coefficient of thermal expansion (marked below).


      Do I need to add some specific analysis to incorporate the contraction/residual stress effects?


       


      Thanks!


      Thermal expansion


       


       


       

    • Wenlong
      Ansys Employee

      Hi,


      Sorry I was not making myself clear. I meant in the “Engineering Data" in a "Transient Thermal Analysis" in Workbench, there is no thermal expansion coefficient defined. It means the thermal expansion coefficient is not needed for this analysis. 


      In the materials overview in Mechanical (shown in your image), it will show all the material properties of that material, whether or not it can be used in this simulation. 


      To bring more peace to your mind, you can refer to the equations in the theory manual of a transient thermal analysis (for some reason I cannot insert an image, but please refer to this website: https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v194/ans_thry/thy_heat1.html.


      If you want to incorporate contraction/residual stress effect, you can do a static structural analysis. You can pass the result of a steady state thermal analysis or transient thermal to a static structural analysis. 


      Please let me know if you have more questions. 


      Regards,


      Wenlong


       



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    • Aashranth
      Subscriber

      Thank you Wenlong, for your patience and clear explanation!

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