6 Replies Latest reply on May 24, 2013 3:41 PM by Jared Conway

    Force exerted by a spring arround a tube

    Carlos Garcia

      I would like to calculate the force that a extension spring makes to a tube when is wrapped on it. Imagine a circular tube where you wrap a extension spring so it remains tensed up, pressing the tube surface like a clamp.

      So I would like to calculate the force (knowing the K of the spring) that the spring makes on the tube walls.

      Actually the tube is not circular but has a obround (two flats joined by semicircles) secction, so in the "flat" zones of the obround the spring does not make any clampling (radial) force. So I would like to study different tube sections in order to optimize it.

       

      Could someone help me to simulate this?

       

      Thanks in advance!

        • Re: Force exerted by a spring arround a tube
          Jared Conway

          this is going to be a tough one

          if you cared about the tube, i'd say, figure out how to calculate the effect of the spring and then apply it as a boundary condition to the tube to see how the tube behaves.

          but it sounds like you're not sure how the spring behaves and are hoping to simulate it.

          you could certainly model the spring but to understand how it behaves, you're going to have to start in an unstretched position and then wrap it around your tube or push the tube through it to get it to do what you want it to do.

          we're talking about nonlinear for sure and a lot of work.

          before you go down that path, make sure there isn't a way to calculate by hand first

          • Re: Force exerted by a spring arround a tube
            Bill McEachern

            I am not sure that SWX sim can pull this off but I am pretty sure other codes could do it. I have had experience with a similar though idfferent problem. This one looks easier and the other one could be done in at least two other codes I know of. There are a few ways to approach it. The following is assuming an NL analysis is used. Step one, expand spring with a radial force, step 2 relax spring force and let the contacts settle on the tube. BC's on the spring get a bit tricky as you really only want the radial force acting on the spring and no other BC's. The behavoir of the spring when it hits the tube can get pretty wild. A square section spring might be a bit easier to handle than a round one of the same cross sectional area.

            • Re: Force exerted by a spring arround a tube
              Carlos Garcia

              So you are suggesting first to simulate the spring as a wrapped steel wire, expanded by a radial force. Isn't it? 

              Then knowing the shape of the tube I could apply that shape as displacementes bondary condition and to see how it behave, instead of relaxing the spring let it contact the tube.

               

              I am wondering now if a hand calculation could be done easier... of course neglecting friction, and maybe something else..

               

              What do you think?

                • Re: Force exerted by a spring arround a tube
                  Jared Conway

                  hi carlos, have you been able to model the "final" position for the purposes of your 3d model? that might help to understand what your spring looks like.

                   

                  i think we're both assuming your spring is a real spring that you're wrapping around. (like a slinky type spring)

                   

                  if you can simplify it down to acting like a steel band with the same elastic properties you'll have a lot more chance for success because of the simplified contact.

                   

                  you would expand it, move the tube in, then let the spring collapse on the tube to get the behavior you want.

                   

                  if you don't care about what is happening to the tube, or the tube is assumed to be stiff, you could just expand it to the size of the tube and find out how much force it pushes back with.

                    • Re: Force exerted by a spring arround a tube
                      Carlos Garcia

                      Hi,

                      Thank you,

                      Yes, it's a normal extension spring, so I wrap it on the tube and join the 2 ends of it, so it acts as a clamp. For now I dont have the model yet.

                       

                      I dont care about the tube, it's stiff enough but I want to know the force that the spring makes on that tube.

                        • Re: Force exerted by a spring arround a tube
                          Jared Conway

                          ok. just remember that your simulation will have to account for that whole process if you want to use the spring.

                           

                          start with the straight spring, bend it around, expand it, insert the tube, let it relax.

                           

                          if you model it already around the tube, you'll lose the force that is generated in that process.

                           

                          if you don't care about the tube, i would just start with straight, bend it around, expand it with a displacement on the 4 flat sides and read off the forces that it generates and translate that back to what it will do to the tube. what you'll lose is what happens at the corners and the exact "shape" that it will take.