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Pressure doubling verification in COMSOL
Posted 06.04.2021, 19:34 GMT-4 Structural & Acoustics, Fluid & Heat, Acoustics & Vibrations Version 5.3 1 Reply
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I am making a simple model to verify the pressure field in an enclosed 2D recangular domain with hard wall boundary condition.
A plane wave with Amplitude Po is :
. If there is a a hard wall boundary on the right at distance L away, the field becomes 
I am building a rectangluar geometry in COMSOL, with hard wall boundary conditions on the top, bottom and right. The left is pressure boundary condition with amplitude of Po. The model is in the frequency domain at f = 900 kHz
The results shows a plane wave with amplitude Po instead of 2*Po. The medium is water with density 1000 kg/m^3 and c = 1500 m/s
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Hi Mohamed,
At a rigid surface, the reflection coefficient is 1. This means that the the reflected wave amplitude is equal to the incident wave amplitude. The total pressure amplitude is a sum of the reflected + incident waves, and therefore double right at the rigid surface.
You are defining a plane wave amplitude, Po, at one location as a boundary condition. Due to the standing wave, you will get a pressure field that is a function of frequency and distance. Pressure doubling does not mean the pressure will be 2Po, it means that the pressure at the rigid surface is double the incident pressure. You need to solve for what the incident pressure is at the rigid surface.
I would recommend starting with a 1D model and also rederiving the equation for 1D. If you have specific questions on a model, please upload the file. You might also look at using a background pressure field to better understand the incident vs. total pressure field.