12 Replies Latest reply on May 1, 2015 9:50 AM by Bill McEachern

    initial mesh level

    C. Bryant

      hello

       

      To ensure accuracy of my thermal analysis

       

      I'm trying to do grid convergence test to figure out which mesh level I should choose

       

      I change the initial mesh level from 2 to 7

       

      my understanding is the higher level I choose, the higher cells number is

       

      level 2level 3level 4level 5level 6level 7
      cells4525572290916660687267296726982262698223

       

      however, it seems so strange the cell count of level4 is the lowest.

       

      and I want to know why the cell count does not increase when I changed the initial mesh level from 5 to 7

        • Re: initial mesh level
          Amit Katz

          I don't know why your level 4 mesh is lower, however I can provide you with some insight for the other levels.

           

          The mesh level from 1-5 (in my experience at least) is inversely proportional to the size of your basic mesh. That is to say: the higher your mesh level, the smaller your cells will be. Once you go to levels 6-8, the software does not shrink the cells automatically. Rather what happens is that the level of refinement and automatic mesh adaptation increases, so that your final mesh size (once the simulation is complete) may be larger (in some cases MUCH larger) than your initial mesh size.

            • Re: initial mesh level
              C. Bryant

              thank you for quick reply, Amit

               

              I do not really understand the part of level 6-8

              If the level of refinement increases, I think the cell count should also increase

              however in my case, the cell counts of level 5-7 are almost the same

                • Re: initial mesh level
                  Chris Michalski

                  6-8 refine the mesh DURING the calculation.  After it solves it looks for large gradients and refines those areas for the next iteration.  You are only comparing the initial mesh so it has not been able to determine if it needs to refine it locally yet.

                  • Re: initial mesh level
                    Amit Katz

                    Chris is correct.

                    Bryant, I recommend going over the meshing chapter in the online help, it will give you a lot of good information.

                     

                    In addition to controlling the solution adaptive meshing, the higher level initial mesh levels also adjust convergence accuracy variables such as interval length, parameter delta, etc. Basically this means your simulation will run for more iterations and hopefully will give you more accurate results.

                    • Re: initial mesh level
                      Jared Conway

                      there is wayyyy too much going on behind the scenes to think that things are that linear. like amit says, go through the mesh optimization tutorial and read through the technical documentation about meshing and you'll see why this isn't as linear as you think. just one example, there is a rule about how cells can be split and how big/small they can be in relationship to the cells next to them, this can cause cells to not be split the way you're expecting.

                       

                      something you can also do is just change the slider, then take a look at the settings that are changing in the manual settings, that might help you understand what is going on.

                       

                      you'll most likely need to use a better basic mesh and mesh controls to increase the number of cells or use manual controls or solution adaptive.

                    • Re: initial mesh level
                      C. Bryant

                      thanks for all your replies and helps

                      I think i have understood what is  going on

                       

                      now I have another question about "optimize thin wall resolution" option after reading online user's guide

                      I did a test to figure out the function of this option

                       

                      It reduced the cell count and the goal value is almost the same (compare to the model not select this option)

                      it looks really good , but I think I miss something should be noticed  , like disadvantage of this option or something

                        • Re: initial mesh level
                          Jared Conway

                          that would tell me that in the regions of your thin walls, there isn't a lot going on and therefore the additional mesh is not necessary.

                           

                          generally though, the developers do not recommend turning that option off because it helps more often than it hurts

                            • Re: initial mesh level
                              C. Bryant

                              so "optimize thin wall resolution" option is always recommended to be used in most cases ?

                               

                              this option reduced the cells considerably

                               

                              if it helps more often than it hurts as you said, I would like to use it in most of my analysis

                                • Re: initial mesh level
                                  Jared Conway

                                  i would recommend reading through the tech reference and also the solidworks kb to get deeper insight but it should definitely be used. if you don't have thin walls, its not as relevant but if you do and you have it turned off, either you'll lose fidelity of your results or will need more cells to capture the same geometry

                                    • Re: initial mesh level
                                      Amit Katz

                                      The thin walls option is only relevant for thermal analysis, correct? I can't imagine the thickness of your walls has much to do with the flow momentum, as long as you're accurately capturing the surfaces with your mesh.

                                        • Re: initial mesh level
                                          Bill McEachern

                                          flow is an immersed boundary cart code - all the cells are aligned with the global CS so walls at angles need the stair step idea with cells about the thickness of the wall without the thin wall option due to the fact that  cells can only have 2 volumes - one fluid and one solid. So you need a really fine mesh to get a wall that does not have any holes in it. The thin wall option partitions the cell regardless of the walls thickness - via a different approach and it took a while for this to show up in the code so I don't think it was the easiest thing to pull off. I can't imagine a scenario where you don't want it on but I am sure there is one which is why the switch is left available.