Note: This discussion is about an older version of the COMSOL Multiphysics® software. The information provided may be out of date.
Discussion Closed This discussion was created more than 6 months ago and has been closed. To start a new discussion with a link back to this one, click here.
Frequency Sweep
Posted 17 nov. 2014, 11:41 UTC−5 Acoustics & Vibrations Version 4.3 1 Reply
Please login with a confirmed email address before reporting spam
We have a combustion chamber (no flame yet). We identified the acoustic network in our actual(real) system by a loud-speaker, which is mounted underneath the chamber, and captured the response in 4 different points on the z-axis inside the chamber. Then we applied a frequency sweep in a frequency range of 70-300 Hz, and a fix amplitude at the speaker. finally, we got four frequency reponses, whichare the transfer functions between the loud-speaker and different microphones.
Willing to simulate exactly the same experiment in Comsol, we built the combustion chamber geometry As study, we used the Pressure Acoustic frequency domain (acpr). Right on the position of speaker membrane, we defined a Pressure boundary condition (to be assumed as inlet! or pressure manipulation point) and gave the P0 a fix amplitude (0.05 pa). At the positions of Microphones, we defined four Point Probes.
Then we executed the study and saw the frequency responce. It gives some of the modes in the right position, but not all of them.
But the problem is that exactly at the pressure point, we can only see 0.05 Pa and no Sinus signal, which is strange. However, in the position of Microphones, we see oscilations, which is correct.
The question is that we doubt if in the pressure point there should be also a harmonic signal! Otherwise, where is the whole pressure manipulation comming from, if the pressure in the Pressure node is fix?
Is the idea of using a pressure point as the speaker membrane wrong? How shall we define the pressure manipulation for the frequency sweep?
We can also, instead of 0.05 Pa in pressure node by using parametric sweep, apply a sinus signal (calculated by Matlab) as the value of boundary condition. But we are not sure if in this case, we would have two times sinus (one by initial value in the boundary condition and one imposed by frequency response of Comsol).
Willing to simulate exactly the same experiment in Comsol, we built the combustion chamber geometry As study, we used the Pressure Acoustic frequency domain (acpr). Right on the position of speaker membrane, we defined a Pressure boundary condition (to be assumed as inlet! or pressure manipulation point) and gave the P0 a fix amplitude (0.05 pa). At the positions of Microphones, we defined four Point Probes.
Then we executed the study and saw the frequency responce. It gives some of the modes in the right position, but not all of them.
But the problem is that exactly at the pressure point, we can only see 0.05 Pa and no Sinus signal, which is strange. However, in the position of Microphones, we see oscilations, which is correct.
The question is that we doubt if in the pressure point there should be also a harmonic signal! Otherwise, where is the whole pressure manipulation comming from, if the pressure in the Pressure node is fix?
Is the idea of using a pressure point as the speaker membrane wrong? How shall we define the pressure manipulation for the frequency sweep?
We can also, instead of 0.05 Pa in pressure node by using parametric sweep, apply a sinus signal (calculated by Matlab) as the value of boundary condition. But we are not sure if in this case, we would have two times sinus (one by initial value in the boundary condition and one imposed by frequency response of Comsol).
1 Reply Last Post 17 nov. 2014, 11:44 UTC−5
Please login with a confirmed email address before reporting spam
Posted:
1 decade ago
We can also, instead of 0.05 Pa in pressure node by using parametric sweep, apply a sinus signal (calculated by Matlab) as the value of boundary condition. But we are not sure if in this case, we would have two times sinus (one by initial value in the boundary condition and one imposed by frequency response of Comsol).