How to model acoustic source points?

Posted 25 mar 2024, 14:15 GMT-4 Acoustics & Vibrations, Geometry, Modeling Workflow Version 6.0 1 Reply

Mohammad Shekofteh

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Hi there,

I've recently started learning COMSOL. I want to simulate sound propagation in a piping system in a 2D environment (or perhaps combine 1D with 3D later).

I have two questions:

I intend to work in the 2D area, dealing with lines and points in the geometry. I've discovered that I can assign a pipe shape and inner diameter to a line to represent my pipe. Additionally, in the materials section, I can specify the material of the pipe. Now, I want to know if there's a way to consider a fluid-filled pipe using this method. For instance, if my pipe is filled with oil, how can I assign my oil material to the inner section of the line?
I'm working with the Pipe Acoustics Transient module, and according to the COMSOL manual (Acoustics of a Pipe System with 3D Bend and Junction), they used a Volume Force as the starting point for wave propagation in the pipe system. However, they assigned this to a line rather than a point. In a simple scenario, I have a line representing my pipe filled with fluid, with a length of L, and I want to add an acoustic source point in the middle of the pipe. If everything is correct, sound propagation and pressure should reach each end of the pipe simultaneously.

Please assist me. I've spent several days searching, but I haven't been able to make any progress :/

Thanks.

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1 Reply Last Post 29 mar 2024, 09:13 GMT-4

Mark Cops COMSOL Employee

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Posted: 4 weeks ago

Hi Mohammad,

It sounds like you are working with the Pipe Acoustics physics. This is for modeling 1D wave propagation in long pipe systems, only considering the plane wave mode. The governing equations are formulated in terms of area averaged velocity and mean pressure throughout a pipe cross section. This can consider effects of both the fluid and the pipe. You can find and edit the settings for Fluid Properties (density and sound speed) and well and Pipe Properties (Pipe model, inner diameter, etc). If using oil, change the fluid properites to match the properties you have for oil.

You are right that there are limited interior boundary conditions available for this interface. You could consider still using the Volume Force with either a small line segment (much shorter than wavelength) to effectively act as a point source, or using a spatially dependent function in the expression for the volume source to limit where the load itself is actually applied. The second idea is used in this model (https://www.comsol.com/model/isotropic-anisotropic-sample-elastic-wave-propagation-78231). See Body Load 1 and also Analytic 1 (G_space).

-Mark

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