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Using Bessel functions for a membrane

Posted Apr 12, 2022, 7:41 a.m. EDT Structural & Acoustics, Acoustics & Vibrations, Parameters, Variables, & Functions 2 Replies

Julio Rangel
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Hi there,

I am kind of new to Comsol, so far I have only done simulations on soft and rigid boundaries and basic normal velocity conditions, for acoustics. For a school project I am simulating the radiation of a drum; I know I have to apply a Bessel function of first order to the membrane and it must depend on the radius. Additionally, according to the theory, the argument of the function has to do with the ratio , where c is the square root of the ratio of membrane's tension over density and thickness.

Reading some Bessel functions' stuff in Matlab, and given that both softwares use the same function besselj(), I suppose I have to implement in a similar way. The problem is that I can not use a different syntax than only two natural numbers separated by a comma, as shown in the picture, besides I can not figure out whether it is expected to put the arguments mentioned straight on the same section.

What should by the right way to implement the bessel function for my case?

2 Replies Last Post Apr 14, 2022, 3:39 a.m. EDT
Jeff Hiller COMSOL Employee

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Posted: 3 years ago Apr 12, 2022, 8:50 a.m. EDT
Updated: 3 years ago Apr 12, 2022, 8:56 a.m. EDT

Hello Julio,

It's not clear to me what in your screenshot is the "[0, 0.25,.5,1,1.5]" - how that's related to the argument of the Bessel function you want to use and that you indicate should be related in some way to the radius and the ratio . But the syntax for the Bessel function of the first kind in COMSOL is documented in the Reference Manual, version 6.0, on page 291: besselj(n,z). Just plug in the n you want (apparently zero) and the z corresponding to the argument you need.

Best,

Jeff

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Jeff Hiller
Hello Julio, It's not clear to me what in your screenshot is the "[0, 0.25,.5,1,1.5]" - how that's related to the argument of the Bessel function you want to use and that you indicate should be related in some way to the radius and the ratio \omega_{mn}/c. But the syntax for the Bessel function of the first kind J_n(z) in COMSOL is documented in the Reference Manual, version 6.0, on page 291: besselj(n,z). Just plug in the n you want (apparently zero) and the z corresponding to the argument you need. Best, Jeff
Acculution ApS Certified Consultant
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Posted: 3 years ago Apr 14, 2022, 3:39 a.m. EDT

Looks like you are trying to apply several Bessel functions in one go using MATLAB notation, but that is not 1:1 with how to do it in COMSOL. You should detail more what you are trying to do; putting it one paper will help you collect your thoughts about the overall problem.

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René Christensen, PhD
Acculution ApS
www.acculution.com
info@acculution.com
Looks like you are trying to apply several Bessel functions in one go using MATLAB notation, but that is not 1:1 with how to do it in COMSOL. You should detail more what you are trying to do; putting it one paper will help you collect your thoughts about the overall problem.

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