Source dependent on eigen frequency

Numerical methods and mathematical models of Elmer
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supreet
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Source dependent on eigen frequency

Post by supreet »

I am using the WaveSolver for performing harmonic analysis of a combustor.

I need to add a source that is dependent on the eigen frequency. Some tutorials use MATC expression and variables like time and space to add source functions. Does a similar variable for "omega" exist in the WaveSolver? How can this be done?

Thanks.
raback
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Re: Source dependent on eigen frequency

Post by raback »

Hi

When you add a source term in harmonic solution it will automatically be in the frequency that you use in your harmonic solution. In other terms, you cannot have a different frequency running your system than the one you use in your ansatz.

-Peter
supreet
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Re: Source dependent on eigen frequency

Post by supreet »

Hi Peter,

I have a source that goes as f = f(w), w being the eigen frequency that is being calculated.

Without this source, the calculated eigen frequencies are real. With the source included, I am expecting complex eigen frequencies indicating whether the modes will grow or damp.
Rich_B
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Re: Source dependent on eigen frequency

Post by Rich_B »

Hello,

If possible, post a small example with sif file, geometry files, and maybe some solver output, and you will get advice specific to your particular case.

Rich.
raback
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Re: Source dependent on eigen frequency

Post by raback »

Hi

The usual way to get complex eigenvalue is to introduce damping i.e. some terms that are proportional to the 1st time derivative. What is the cause of damping in your system?

-Peter
supreet
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Re: Source dependent on eigen frequency

Post by supreet »

Hi Peter,

The source is a flame in the combustor. The acoustic waves interact with the flame and the heat released has a harmonic variation, but with a phase lag. The response of the heat release depends on the frequency of the acoustic waves. The phase determines if the amplitude of the acoustic waves grow or decay.
supreet
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Re: Source dependent on eigen frequency

Post by supreet »

Hi Rich,

I am yet to write the sif for this case. Without the source, it is just a plane Helmholtz equation in harmonic form applied to an enclosure.
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