Interesting email corro with Roger Shawyer. There is much useful information here.



Quote ...Also no successful design used COMSOL without correction, as the software does not seem to cope with conditions close to cut-off.



Best regards

Roger

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Discordant dissonant comment about COMSOL Finite Element Analysis software "not seeming to cope with conditions close to cut-off" falsified, for example, by this peer-reviewed article (hat tip to Otto):where the authors of the peer reviewed article calculate how a particle in a rectangular waveguide can be pulled towards the light source or pushed away from the light source just by varying the frequency around the waveguide cutoff frequency. All of the fields and forces analytical calculations were validated using COMSOL Multiphysics Finite Element Analysis. The peer-reviewed literature contains numerous other reference of analysts successfully using COMSOL to analyze conditions below, near and above cut-off.COMSOL Finite Element Analysis is a very powerful tool with a huge number of modules available. COMSOL, as well as ANSYS, ABAQUS, ADINA, and other multiphysics packages are routinely used for such analysis at top companies, universities and research institutions (like CERN). Most large companies and research institutions have their own finite element packages as well.Just like any tool, what an analyst may achieve depends on the expertise and experience of the analyst and the COMSOL modules available, as well as their ability to write user-written subroutines (instead of just using a software package as a black box) .