12 Replies Latest reply on May 16, 2008 8:39 PM by Bill McEachern

    Expert in Floworks required-Rotating drum with picks:

    David O'Lone
      I am trying to get a pressure/flow pattern around a patch planer/cold planer. The planer consists of a drum with a number of picks on it.
      I have done a rotational analysis on the assembly with the drum rotating at 35 rad/s, and the housing (box section) is fixed as a Real Wall.

      I am trying a water fluid for the moment to get some results and it enters the channel at a velocity of 0.8 m/s. The outlet boundary is set to environmental pressure.

      I have attached pictures to clarify my description.

      The problem I am having is that when I view the results as a flow trajectory, for example, the flow pattern does not seem to be influenced by the picks on the drum. It has been suggested to me to try a different resolution so I am trying this at the moment.

      Does anyone else have any suggestions, or see any faults in my analysing conditions or worked on a similar assembly?

      Thanks in advance.
        • Expert in Floworks required-Rotating drum with picks:
          Basil Gello
          David,
          if you have used the rotating regions, have you specified the housing or something immovable as stator?
          Regards, Basil
          • Expert in Floworks required-Rotating drum with picks:
            Hello David,
            Are we having fun yet? First, I don't see a rotational domain. If you are spinning the drum and the picks, the rotational domain must include the whole volume including the picks. Second, I don't know what mesh call out, you are using but I have found that using a local initial mesh that is defined by the rotational domain body works well. Make sure to click the minimum wall thickness call out and reduce it to less than half of the smallest items. For the last job that I did I had to tighten all of the setting up to get it to work and then reduce things till I saw a significant change in the value. Another thing that helped me is hiding the drum and picks. Do a cut plot and adjust the depth. You should see the picks outline as seen by Floworks. If they are just nubs, then your mesh is too low. I hope this helps. I am no expert, I just use rotating domains from time to time.

            Bill



              • Expert in Floworks required-Rotating drum with picks:
                David O'Lone
                Hello Bill,

                Well I've got it to work, not quiet sure what the results mean but using the results is not the main priority just yet.
                The mistake I made was inserting the drum assembly as a part. By doing this FloWorks does not seem to recognise the drum/picks.
                So I've replaced with the original assembly, calculation time has increased quiet alot though but at least the results are looking respectable. Have attached a video of the results with the drum rotating at 35 rad/s.

                When you say rotational domain, does this mean selecting the rotation option in the wizard and then selecting global rotating, reference axis and angular velocity, because I have done this previous to running the analysis.

                The mesh I have used was simply set at the wizard and I accepted the defaults. Is there a way that using a confined mesh could reduce my calculation times, you mention about using a "local initial mesh"???

                Thank you for your suggestions, very much appreciated.

                David
                  • Expert in Floworks required-Rotating drum with picks:
                    David,
                    I really don't see it turning in that model. When I say rotational domain, I am checking the box in the wizard, but not Global, click Local Region. You must draw a cylinder that is large enough to encompass all of the items that are rotating together. The center line of this cylinder must be on the center of rotation. The cylinder can be larger than the items that are rotating but should not include any stationary items like items hanging from the walls. This is the rotational domain area. This way Solidworks will know what is spinning. After you are done with the wizard you will have under Input data, a new line "Rotating Regions". Before you go there right click on "Input Data". Under that you will see something like component control. Click on that, find the cylinder that you are going to use and DISABLE IT. Now go to Rotational Domain, right click, insert new. Put in your rad/s and select the cylinder. Now you have the section rotating. You can now go back to the FlowWorks header, the top of the FloWorks analysis tree and right click on the line above Input Data. Click on custom tree, "local Initial Mesh". Now it will show under Input. Right click, insert, select the cylinder, adjust your settings and your in business.

                    Have fun, its all up hill from here.

                    Bill


                      • Expert in Floworks required-Rotating drum with picks:
                        David O'Lone
                        Bill,

                        Four questions on your method...

                        Firstly does the cylinder need to be capped at the sides or is a hollow extruded circle good enough.
                        Secondly, when inserting the rotational region and rotational speed is it only necessary to select the cylinder or should I be selecting the drum and picks also?
                        Also, with your method is it always necessary to use a local initial mesh or is using the mesh from the wizard good enough?
                        Finally, I presume I set my inlet and outlet boundaries the same, is it necessary to set the non-rotating parts of the model as stators?

                        Thanks again for your help Bill.

                        David
                          • Expert in Floworks required-Rotating drum with picks:
                            Good Morning
                            David,
                            First question, it must be a solid extruded round.
                            This defines the volume that is rotating. It encompasses and occupies the same area as all rotating components.
                            By selecting this, you select everything with in it as rotating.
                            No, you do not need to uses a local initial mesh. With that said, for the program to see the tips of the picks, you need a tight mesh. Do the thing I mentioned earlier about a cut plot. If the picks are clean, go with that setting. My problem is that I don't need a tight mesh everywhere, only around the rotational domain. With out the local mesh I end up with a very high cell count and a very long run time if it doesn't run out of resources and crashes.
                            For the stators, using a rotational domain, I don't believe that you need to state that except if it is a part inside of the rotational region that is non-rotating. I have never had a problem with that. If you are using global, yes, you do.

                            Good Luck

                            Bill


                              • Expert in Floworks required-Rotating drum with picks:
                                David O'Lone
                                Hello Bill,

                                What actually is the difference between your method of rotating the drum (locally) and a global rotation?
                                Because there is an obvious difference in the results.

                                And also is there anyway that the rotating parts can be animated during the animation of the Flo results?

                                Thanks,
                                David
                                  • Expert in Floworks required-Rotating drum with picks:
                                    David,
                                    The first thing that is different is that the global rotation is around the origin. For the rest of it, it depends on the model. I can make guess beyond that but that is all it would be. For the animation, I don't know of any way. If anyone know of a way please let us know.

                                    Bill


                                    David, did you get a chance to do that cut plot?
                                      • Expert in Floworks required-Rotating drum with picks:
                                        David O'Lone
                                        Thank you for your reply Bill,

                                        I've attached a picture of the cut plot adjusted to beside the pick tip. It's obvious there is some interaction but the accuracy is probably low.
                                        I am restricted to using a coarse mesh for each analysis due to processing power so there's nothing I can really do to improve the results. My main concern is to get the method to work, which I have achieved fairly well.

                                        I also meant to ask you, have you found anyway of changing the direction of rotation when using global or local rotation analysis, rather than readjusting the assembly or the boundary conditions?
                                          • Expert in Floworks required-Rotating drum with picks:
                                            David,
                                            If you get a chance, redo the cut plot from the side looking right at the center of the drum. Hide the drum and all of the other parts that are rotating. This way, what you see is the flow plot instead of the model. I still don't see the drum rotating. Its hard to tell from a plot. Any chance you can send me the model so I can see what you are doing. Are you getting any torque readings from the drum? For the direction of rotation, you can input a negative value. It will not change the direction of the arrow for rotational domain but it does change the direction of rotation.

                                            I hope this helps.

                                            Bill
                            • Expert in Floworks required-Rotating drum with picks:
                              Bill McEachern
                              This type of flow is really amenable to the a rotating frame sort of approximation. You need a moving mesh capability to do it justice and it is probably a non-trivial sort of adventure even with the capability. This is a rotating region in a cross flow - not floworks best game. Be skeptical of whatever you get.