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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