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Simulation error using oil pipeline

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Hi,

I am beginner in comsol multiphysics. I would simulate wave propagation inside pipeline, but i get strange value as a result. i want to get transmission coefficient as a result.
my file is attached.
Any help please.

Thanks


4 Replies Last Post 2017年2月7日 GMT-5 05:12
Dave Greve Certified Consultant

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Posted: 7 years ago 2017年2月5日 GMT-5 13:36
Physically, a GHz wave will be very strongly attenuated in water. So you have nothing to calculate.

Another thing: you need to use a circular port, not rectangular.

DWGreve
DWGreve Consulting

Physically, a GHz wave will be very strongly attenuated in water. So you have nothing to calculate. Another thing: you need to use a circular port, not rectangular. DWGreve DWGreve Consulting

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Posted: 7 years ago 2017年2月5日 GMT-5 15:03
Thank you very much for your reply. when i used circular port i had an error. I want just to see the transmission loss.
Please, what do you mean by strongly attenuated. any ideas about value of insertion loss?

Thank you very much for your reply. when i used circular port i had an error. I want just to see the transmission loss. Please, what do you mean by strongly attenuated. any ideas about value of insertion loss?

Dave Greve Certified Consultant

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Posted: 7 years ago 2017年2月6日 GMT-5 14:22
> when i used circular port i had an error.

Comsol doesn't make it obvious how to do this. AFTER you select circular port, you need to right-click the port node and select Points > Circular port reference axis. THEN you can define the polarization direction of the waveguide mode- because, after all, any direction gives a valid waveguide mode for a circular waveguide.

By the way, there are interesting things that happen if you choose different reference axes on the input and output.

> what do you mean by strongly attenuated

Water is somewhat conductive. In the GHz range the skin depth in water is of the order of cm. (This is why your baked potato gets cooked on the inside). So a water-filled waveguide will have essentially no transmission if many cm in length.

Further, water (at least Comsol water) has a permittivity of 80, thus a rather short wavelength. So unless you have many elements per wavelength you are guaranteed to have an erroneous result.

Another issue, incidentally, is the skin depth of iron. This is far less than a pipe thickness. It is probably better to use the impedance boundary condition for the walls if you want to understand the attenuation due to wall loss.

DWGreve



> when i used circular port i had an error. Comsol doesn't make it obvious how to do this. AFTER you select circular port, you need to right-click the port node and select Points > Circular port reference axis. THEN you can define the polarization direction of the waveguide mode- because, after all, any direction gives a valid waveguide mode for a circular waveguide. By the way, there are interesting things that happen if you choose different reference axes on the input and output. > what do you mean by strongly attenuated Water is somewhat conductive. In the GHz range the skin depth in water is of the order of cm. (This is why your baked potato gets cooked on the inside). So a water-filled waveguide will have essentially no transmission if many cm in length. Further, water (at least Comsol water) has a permittivity of 80, thus a rather short wavelength. So unless you have many elements per wavelength you are guaranteed to have an erroneous result. Another issue, incidentally, is the skin depth of iron. This is far less than a pipe thickness. It is probably better to use the impedance boundary condition for the walls if you want to understand the attenuation due to wall loss. DWGreve

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Posted: 7 years ago 2017年2月7日 GMT-5 05:12
Thank you very much for your reply and explications, I will try all this options and recommendations.
Thank you very much for your reply and explications, I will try all this options and recommendations.

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