General Mechanical

General Mechanical

Balloon with frame

    • F. Semih Y
      Subscriber

      I want to simulate a special silicon rubber balloon (red) blowing up in a frame (grey). Air inlet from underneath.



      Right now  I computed a structural analysis with just constant pressure from the inside of the balloon and frame. I selected faces of the frame and balloon that are bounded (auxiliary: bounded inside and bounded outside). Also selected faces that are initially in touch but not bounded (auxiliary: free inside and free outside). I want to analyse the deformation, stresses and fatigue of both frame and balloon. The inlet cilinder is fixed


      I want to have a more realistic model and I think I should try the fluid-solid interaction but I already get solver errors at the static analysis (without fatigue). If I run the simulation with automatic contact interface conditions, it works.



      But the problem is that not every contact surface is bonded. The concentric surface inside needs to be free from te frame in order to inflate upwards. only te edges should be bounded. So I need my own selection of interface surfaces given above. I used frictionless contact. Recommend something else? Should I leave a GAP in my CAD drawing rather than trusting Ansys manual interface selection?


      Also I am not sure if i need to apply pressure to both inside and outside surfaces. The air pushes the balloon but also the frame. I think that only in a fluid simulation Ansys will compute the reaction forces of the air for the whole chamber. 


      Also, in my geometry I have 2 symmetry planes (x-y and y-z planes). Is it possible to take this into account and decrease the simulation time?


      The site does not let me attach files? any other way to share my files ?

    • peteroznewman
      Subscriber

      You can attach your Workbench Project Archive .wbpz file using the Attach button that appears after you post.


      I don't think you need a fluid to inflate the balloon, but I will be interested to read other comments. If I understand the images you included, the silicon rubber is molded in the shape of the cylindrical frame.


      Yes, you can apply symmetry on 2 planes and reduce the model to a quarter symmetry model, however, I can imagine that due to small deviations in a physical prototype, non-symmetric inflation may occur.


      It sounds like you are able to change a Bonded Contact to a Frictional Contact (I would not use Frictionless).


      Regards,
      Peter

    • F. Semih Y
      Subscriber

      I changed the contact conditions to Frictional Contact. The rubber is indeed molded in shape.


      I have looked for ways to apply symmetry but i cant find a guide for Ansys Discovery AIM 19.0. Should I change my CAD model to a quarter (already have one ready)? Or can I select symmetry planes. Is one of them easier to implement?


       

    • peteroznewman
      Subscriber

      If you have quartered the CAD model, you can apply displacements to the cut faces to create the Symmetry BC that you need. If the model is entirely solids, then on a cut face whose normal is parallel to the Z axis, assign a displacement of Z=0 while leaving X and Y free. Similarly, on a cut face whose normal is parallel to the X axis, assign a displacement of X=0 while leaving Y and Z free.


      If you have midsurfaces, then you also have to constrain two rotations on the cut edges of a midsurface; the two axes that are not the zero displacement axis.


      Regards,
      Peter

    • F. Semih Y
      Subscriber

      I did the above for the quarter model but in both cases (full and quarter) the solution is only partially solved.

    • Sandeep Medikonda
      Ansys Employee

      Are you seeing an error? If so, can you elaborate with pictures?


      Regards,
      Sandeep

    • F. Semih Y
      Subscriber

      I attached files above, maybe it is possible to run them? Meanwhile I will prepare a proper problem description anyway. Since I have no (physics solver) problems when I use the interface generator, I think I wrongfully describe my interfaces. The concentric part only is free (frictional contact) and te other touching surfaces are bonded. 

    • F. Semih Y
      Subscriber

      The warning I get:


      Physics 1: Contact status has experienced an abrupt change for Contact 2. Check results carefully for possible contact separation and review the Contact Best Practices documentation for more information on avoiding such an abrupt change.


      attached: transcript file txt

    • F. Semih Y
      Subscriber

      The solution is to not select the contact faces that are initially in contact but are not bonded to the frame. Just select the bonded faces.


       

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