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Negative Acoustic pressure values

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Old   June 1, 2023, 09:27
Default Negative Acoustic pressure values
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Hello.
I am doing an analysis of sound propagation from a solid disc when a periodic load is applied to it. i got the pressure values for different ferquencies with the Steady state Modal analysis but some of the pressure peaks are negative. What do these negative pressures mean? Are they vacuum pressure i.e. pressure below 1atm? Or are they pressure with just opposite direction? Should I consider these pressures as my sound level values in dB?
Here are the Graphs for reference>

Does the third graph mean damped?


My analysis is a steel disc in an air domain and I am plotting the acoustic pressure in the air domain duing the steady state modal analysis from different observation points. I am just using the POR values mentioned in the field output option. I will attach the model here to further clarify my simulation.
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Old   June 1, 2023, 12:33
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Waves have an amplitude and phase. Negative means it is out of phase.

And since d'Alembert's principle yields that you can decompose any wave into a superposition of a forward and backward moving wave, it is equivalent to a pressure wave going backwards but most ppl prefer the frame of motion going with the direction of propagation and not looking through a hypothetical mirror.


Interpretation depends on the application. Sound when it is heard is typically presented in dB but in many mechanical applications, you stick with the raw linear scale amplitudes.
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Old   June 1, 2023, 12:46
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Quote:
Originally Posted by Sim101 View Post
Hello.
I am doing an analysis of sound propagation from a solid disc when a periodic load is applied to it. i got the pressure values for different ferquencies with the Steady state Modal analysis but some of the pressure peaks are negative. What do these negative pressures mean? Are they vacuum pressure i.e. pressure below 1atm? Or are they pressure with just opposite direction? Should I consider these pressures as my sound level values in dB?
Here are the Graphs for reference>

Does the third graph mean damped?


My analysis is a steel disc in an air domain and I am plotting the acoustic pressure in the air domain duing the steady state modal analysis from different observation points. I am just using the POR values mentioned in the field output option. I will attach the model here to further clarify my simulation.



Well, I am used to accept the idea that pressure is always a positive scalar function, only the gradient of the pressure gives you a direction.
You can see on Leveque textbook several example of pressure wave propagations.
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Old   June 1, 2023, 18:24
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What is being plotted is most likely the modulus of the acoustic pressure vs frequency


The label of pressure on the axis is likely a user error. Abacus outputs |POR|
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Old   June 2, 2023, 09:57
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Originally Posted by LuckyTran View Post
What is being plotted is most likely the modulus of the acoustic pressure vs frequency


The label of pressure on the axis is likely a user error. Abacus outputs |POR|



Yes, it is POR. So, for my results should i only take the positive values? I am only concerned with sound that is heard.
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