3 Replies Latest reply on Nov 20, 2013 12:12 AM by Jared Conway

    BEARING CONNECTORS

    Jung P

      I am having trouble with bearing connectors.The aim is to find the natural frequency of the system which has a shaft supported by a housing through a bearing.Shaft is free to rotate about its axis.The orginal angular contact (25 deg) bearing is having an axial stiffness of 250.6 N/micrometer and radial stiffness of 501.2 N/micrometer.For modelling sake i have put a skf bearing.Can anybody tell me how to carry out this analysis.Please help.model is attached below.

        • Re: BEARING CONNECTORS
          Jared Conway

          what is the problem that you're running into?

           

          have you reviewed other forum posts about the bearing connector/restraint and how it can cause instability in your model? ie at least one side should have a fixed restraint or similar?

            • Re: BEARING CONNECTORS
              Jung P

              Halo jared ...thank you for looking into this post.Yes i have reviewed other forum posts.The issue is iam not able to choose which is the real natural frequency of the system.I carried out an exercise exploring different options in bearing connectors and the results that it gave is having huge variations.I will decribe each exercise below with its results.

               

              1)Exercise I:  RIGID & Stabilise shaft rotation option checked.

                                  Frequency:143.66,2494.8,2519.9

              2)Exercise 2: Flexibile Cr:501.2 N/micrometer Ca:250.6 N/micrometer & Stabilise shaft rotation option checked.

                                  Frequency:85,85,87,2166,2494.9

              3)Exercise 3: RIGID & Stabilise shaft rotation option unchecked.

                                  Frequency:11.8,12.14,12.18,143.6,2494.9

              4)Exercise 4: Flexibile Cr:501.2 N/micrometer Ca:250.6 N/micrometer & Stabilise shaft rotation option unchecked.

                                  Frequency:11.838,12.148,12.18,2166,2494.9

              5)Exercise 5: Modeled a stainless steel ring of bearing size and gave bonded contacts.

                                  Frequency:2505.7,2533.4

               

              All these were performed with Allow self alignment option checked.When Unchecked simulation gave an error(?).

              Now which method out of these five describes correctly the natural frequency of my system as described in my first post.

                • Re: BEARING CONNECTORS
                  Jared Conway

                  jung, do you have an estimate for what the natural frequency should be?

                   

                  you probably looked at the mode shapes, did any of them look more reasonable than others?

                   

                  with these setups, have you looked at some loading conditions to see which one best matches how the system behaves? this is often easier than looking at frequency results. once you have a setup that works, you can move it to frequency.

                   

                  right off the bat, i'd question the ones with the stabilize option enabled. as you've seen in other posts, this can generate results that you don't expect. rigid and the bonded contact options seems like they would over restrain your system. i'd check how they move under static before keeping or rejecting them. i suspect that the ones without any rotation restraint will give questionable results, check with static. and you may want to check an example where instead of using bearing connectors you setup the spring connectors yourself.

                   

                  i know this isn't the answer you're looking for, but other than hand calc'ing or physically testing, it is impossible to say which one is the "right" one. however using the investigation method described above, you'll validate the setup that you're using through a static analysis and then once you're good with that you can use that setup in frequency with a high level of confidence.

                   

                  also regarding the error you got with self alignment unchecked. what was it? that may tell you more about the instability caused by some of these options you're trying. note that this option is selected based on the type of bearing that you're using. if you look at a static analysis with a gravity load, you'll see how it changes the shape of the deflection.