General Mechanical

General Mechanical

Modeling cables for a flexible actuator

    • donabbel
      Subscriber

      Hi,


      I'm trying to simulate a segment of a flexible actuator made with silicone rubber. The real segment has 3 SMA springs that go through the silicone cylinder and are attached at the top and bottom to a rigid plastic glued to the rubber. To make the segment move, 2 of those 3 springs get contracted making a curve (the top of the segment is fixed so only the bottom moves).


      To simplify the simulation I substituted the springs with cables attached to the bottom rigid plastic and pulled at the top, similar to this previous discussion my actual objective is to displace this cables 25 mm in the Y axis and observe the resulting curve in the silicone cylinder. 


      Screenshot1


      The material for the cables is unimportant as long as it's flexible and behaves like a cable, I chose nylon. At first I used beam elements for the cables and obtained the best results so far (in static structural) but the program wont converge beyond a 12 mm displacement (using more than 3 steps, auto time stepping on defined by substeps and kept incrementing initial, minimum and max substeps without luck). The error just showed "Solution not converge at X time. Run terminated" and warnings about too much penetration.


      Then I tried using link180 elements but I'm inexperienced and do not know how to achieve a cable without bending stiffness even after looking at past discussions and their files. I'm not sure about the value of the initial stress necessary, I've been reducing it until I see no displacement at step 0 but this is basically a shot in the dark. Of course, I've been getting high pivoting warnings, elements have become highly distorted, etc. Once I set the displacement at 10mm, it becomes incredibly distorted. 

      The commands for the link180 are:


      et, matid, 180


      *get, area, secp, matid, prop, area


      sectype, matid, link


      secdata, area


      seccontrol,, 1 


      INISTATE,SET,CSYS,-2 


      inistate,set,mat,matid 


      INISTATE,SET,DTYP,STRE 


      INISTATE,DEFINE,,,,,0.00001


       


      I would be very grateful if anyone can give me suggestions about changes or point out the problems in my model. 

    • Montassar
      Subscriber
      HI @donabbelnI want to know if there is any update concern your inquiry. Did you try to use Cable280 element?nnn
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