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How is Dirichlet boundary conditions implemented in Comsol?
Posted 6 avr. 2017, 12:02 UTC−4 Acoustics & Vibrations Version 4.2a 2 Replies
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So I'm building a model with the Acoustics Module trying to model a piezoelectric disc, and when documenting the model the question of how the Dirichlet boundary conditions like voltage on either electrode or prescribed displacements is implemented came up.
The manual seems to be quite vague on this point, like is it using the method of Lagrange multipliers, or is it modifying the matrices directly to enforce the conditions, or something completely different?
So maybe someone here would know anything about it? =)
Thanks in advance,
Andreas Hagen
The manual seems to be quite vague on this point, like is it using the method of Lagrange multipliers, or is it modifying the matrices directly to enforce the conditions, or something completely different?
So maybe someone here would know anything about it? =)
Thanks in advance,
Andreas Hagen
2 Replies Last Post 7 avr. 2017, 09:22 UTC−4
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Posted:
8 years ago
Hi,
Most Dirichlet conditions (there are hundreds of them) are as a default implemented in an 'exact' (removing the equations) manner. This is what is called 'pointwise constraint' in our terminology.
In most cases you can choose a Lagrange multiplier approach instead. This is the 'Use weak constraints' check box in the settings for the individual constraint. This option is shown if you have 'Advanced Physics Options' on.
There are also a few cases (particularly in Multibody Dynamics) when a penalty implementation is available.
Finally, you can always inspect what is actually used in Equation View.
Regards,
Henrik
Most Dirichlet conditions (there are hundreds of them) are as a default implemented in an 'exact' (removing the equations) manner. This is what is called 'pointwise constraint' in our terminology.
In most cases you can choose a Lagrange multiplier approach instead. This is the 'Use weak constraints' check box in the settings for the individual constraint. This option is shown if you have 'Advanced Physics Options' on.
There are also a few cases (particularly in Multibody Dynamics) when a penalty implementation is available.
Finally, you can always inspect what is actually used in Equation View.
Regards,
Henrik
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Posted:
8 years ago
Thanks for the reply =)
So how I read the documentation for the pointwise constraint, it looks to use Lagrange multipliers implicitly, but instead of leaving them in the final matrix, it just eliminates them from the matrix straight away before solving.
Is that correct?
Cheers
Andreas Hagen
So how I read the documentation for the pointwise constraint, it looks to use Lagrange multipliers implicitly, but instead of leaving them in the final matrix, it just eliminates them from the matrix straight away before solving.
Is that correct?
Cheers
Andreas Hagen