Experiences from modeling very thin structures in COMSOL Multiphysics
Bergen COMSOL User Group Workshop April 10th 2013 Jan Kocbach
Note! This is a reduced version of the presentation without figures for the coil case
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Introduction
• Generally challenging to model thin structures in FE software
• Selected cases • Thin coil (RF module)
• Wellbore heat exchanger (Subsurface module)
• Thin elastic layers (Piezoelectric transducer)
• Comment on CAD models • Our approach usually to redraw model in COMSOL Multiphysics
• Should be possible with «Virtual operations» (not tested by us)
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• Advices: Sweeping the mesh, Virtual operations, Scaling the mesh
• http://www.comsol.com/support/knowledgebase/120/
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Case: Fields from thin coil (RF module)
• Thin coil in air excited by voltage
• First attempt • Change mesh parameters (resolution narrow regions, etc.)
• Limited success (meshing possible for somewhat thinner coil)
• Second attempt • Exclude coil from simulation domain, impedance boundary condition
• Still not possible to get mesh set up
• Third attempt • Convert coil to thin surface
• «Transition boundary condition» for losses
• Meshing possible for somewhat thinner coil, but now convergence problems in solution
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Case: Fields from thin coil (RF module)
• Fourth attempt • Change meshing algorithm
• Start meshing the surfaces that have problems (coil)
• Then the small domains sorrounding (make a tube/donut around the coil)
• Finally mesh the rest of the structure
• Meshing successful for thin coil – but convergence problem for solution
• Final solution • Start meshing the surfaces that have problems
• Small non-zero conductivity (sigma = 0 gives convergence problems)
• Avoid metal in model (subtract domains to avoid meshing inside metals)
• Use «Magnetic fields» physics interface (better convergence)
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Thin elastic layers
• http://www.comsol.com/blogs/structural-analysis-with-thin-elastic-layers/
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