6 Replies Latest reply on Jan 30, 2015 7:54 PM by Jared Conway

    Pipe fitting simulation

    Nick Yavorsky

      I am attempting to conduct a force simulation on a pipe connection. One pipe slip fits into another and they extend in opposite directions. i need to place a point force on one pipe and fixture the other so that it remains still. I believe I have covered all the proper steps, but I receive an inadequate fixture error. I guess my question is how to fixture one component and apply a force to another? (this simulation is being done in a larger assembly with the other part suppressed

        • Re: Pipe fitting simulation
          Shaun Densberger

          I guess my question is how to fixture one component and apply a force to another?

           

          It's somewhat tricky. All finite element models (minus non-linear dynamics) require that all components in your model are constrained against rigid body motion, which can be somewhat confusing to people. In short, you need to make sure that you have enough constraints defined such that your parts can't freely move as a rigid body in space. My guess is that the top pipe in your model is under-constrained; how you properly constrain it depends on system and how it function, so I'd need to know more to be able to tell you. However, the solution will most likely involve soft-springs to stabilize the model.

           

          Out of curiosity, is your entire goal to calculate the force required to insert one pipe into the other? Do you expect the lower pipe's outer surface to not expand in the radial direction (I ask because it looks like you have a constraint that prevents radial expansion of the outer surface of the lower pipe)? Do you need any information (displacement, stress, etc.) on the lower plate? If so, how exactly is the lower plate constrained?

           

          I ask all of these questions because, based on what I can see, the information you've provided, and the assumptions I'm making, I think you can do this simulation with a 2D axisymmetric idealization. If this is the case, the the simulation time required for this model can easily be dropped by an order of magnitude or more.

          • Re: Pipe fitting simulation
            Nick Yavorsky

            Hi Shaun,

             

            Thanks for your input. The pipes are designed to fit into each other easily, what I am trying to examine is the stress in the bottom pipe/flange weldment as a force is applied perpendicular to the upper pipe. the flange will be bolted to a piece of sheet metal, which I would like to treat as "fixed".  

              • Re: Pipe fitting simulation
                Shaun Densberger

                Ahhh, I understand now. In that case, there's two ways you can do this:

                1. A contact analysis with soft-springs to restraint the top pipe.
                2. Use a remote load and excluded the top pipe (since it seems like you're not interested in the stress in it) and approximate the contact region between the top and bottom pipe.

                The second option will require less work on the computer side (it's purely a linear analysis, whereas the contact analysis is non-linear), but will require a little more setup work.

                 

                Can you provide some additional explanation behind the constraints shown in image you provided? What is the purpose of the one circled in red and the one circled in blue? Could you post your model?

                 

                Pipe.png

                  • Re: Pipe fitting simulation
                    Jared Conway

                    option 2 definitely sounds the best

                     

                    for option 1, may not need soft springs, just some kind of restraint to hold it in space and then bend it/push it

                      • Re: Pipe fitting simulation
                        Nikhil Phatak

                        Yeah,

                         

                        Now i find it after searching for long. I am having somewhat similar or at least comparable condition but in my case top pipe is having some pressure in it and instead of force i need to apply imposed displacement in perpendicular direction.(Even i can get force as an input but that depends on another department which provides me an input). These two pipes are having some gap initially .And i need to check stresses on both connecting pipes.I agree that if  we add no penetration contact and restrain it properly then i may get results in static solver.Even we can add soft springs to stabilize it.(i don't like this option though )and run it with static.

                         

                        But how to guess when we need non-linear or when we need static. When we can consider this problem as a rigid body motion ?. In fact what Nick said sounds like rigid body motion but it is do-able by static solver. So how will i decide if it is dependent on mesh size w.r.t. gap size or model size(In this case pipe length) w.r.t gap size. or what?? @ i mean i am confused deciding the way i should solve it.Should we solve it with large displacement? but when i treat pipe as a shell i can not use large displacement in static. Also agreed that non-linear may give me accurate results but never tried as i use static.

                         

                        Regards,

                        Nikhil Phatak

                          • Re: Pipe fitting simulation
                            Jared Conway

                            woah, a lot going on there. are you making a statement or are you asking a question? what question or questions? can you list them out?

                             

                            if your question is when to use linear static vs nonlinear static, the world is nonlinear, linear static is an assumption. it is good for most cases but nonlinear is required in some cases.