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Entry  Mon Jan 22 21:13:25 2018, aaron, Mechanics, PonderSqueeze, tips from Shoaib 
    Reply  Mon Jan 29 23:02:13 2018, aaron, Mechanics, PonderSqueeze, tips from Shoaib 
Message ID: 126     Entry time: Mon Jan 29 23:02:13 2018     In reply to: 125
Author: aaron 
Type: Mechanics 
Category: PonderSqueeze 
Subject: tips from Shoaib 

I started implemented some of these changes:

  • Started the mesh with a boundary free quad mesh on the interface between the upper tapers and the main part of the fiber. I used the following size setting
    • Maximum element size is fiber_taper_length, which I felt was a good characteristic maximum because it wouldn't make sense to have radial elements larger than the length of the taper itself. This setting does not limit the mesh (elements are much smaller than the maximum)
    • Minimum element size: skin_depth/10, where I use the thickness of the surface layer as the characteristic length, and allow a mesh with elements substantially smaller than this characteristic length.
    • Maximum element growth rate I set at 8, which from some trial and error isn't strongly affecting the mesh as long as it isn't brought much lower than this (so the mesh is allowed to get coarse relatively quickly, though other settings limit this)
    • Curvature factor is 0.7, and actually does affect the mesh strongly; for now value seems to give a 'pretty' (symmetric to the eye) mesh.
    • The resolution of narrow regions is set to 5, where this value again strongly affects the mesh and this value was chosen because it looks 'pretty'
    • Note that in contrast to the previous way I had defined the mesh, I now am defining the surface and bulk of the mesh in the same step, which seems to help these two regions match up. Shoaib had mentioned using a nonconformal mesh, which I may end up implementing in a later update.
  • Instead of doing a free mesh in each non-cylindrical region, I continued with a swept mesh along the length of the fiber (still sweeping in sections, though I'm not sure this is necessary)
  • I also slightly increased the number of mesh elements along the length of the fibers (ie, used more elements in each section of the mesh sweeping).
  • In this model, I still have a free tet mesh on the horn and test mass, since those seemed a bit more involved to move over to a hex mesh (there is no free hex mesh in COMSOL that I could see right away, and I'm not sure that the horn can be meshed with a swept mesh due to its irregularity. I'll look in to this further, but I had no immediate solution for making a hex mesh in the horn) and anyway they are much coarser than the fibers so I don't expect them to cause much trouble.

These changes were fine with a 10um mesh, but ended up with much too fine a mesh (~80000 boundary mesh elements in the initial mesh between the taper and main fiber) due to meshing the surface and boundary in a single stage in the first step. I separate them out to get a coarser mesh in the bulk, and also make the resolution a bit coarser.

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