I would like to obtain sound absorption coefficient of sound absorbing materials by using ANSYS. I have substituted the acoustic pressure from ANSYS into the transfer function equation as described by several journal papers but it doesn't work.
Hi
Let us first eliminate simple things - I am assuming that you use complex FRFs, i.e. real/imaginary numbers in your FRFs?
If the above checks out, then you should examine your Ansys model. I suggest you start with something well known and simple, an anechoic impedance boundary condition where you put the impedance rho*c, where rho is density and c i wave speed at one end of the tube and the source at the other tube end.
First, look at your computed wavefield. It should be that of a propagating wave, i.e. it should emamate from the source and have the wavelength lambda = c/f with constant pressure amplitude.
Next, use your equations and derive the absorption factor, which should be close to unity at all frequencies.
After the above, move on to model absorbers. The 3D simplest absorber model is to impose a complex wave speed in the absorber volume.
Hope this helps
Claes
Thanks Claes. I will try your suggestion first and then move on to more complicated model.
Yes, I used complex pressure values from ANSYS. However, I am not really sure at which 2 points the pressure values should be taken. The pressure values are then to be plugged in the transfer function equation to derive the absorption coefficient.
Hi
You can choose 'any' two positions. For a given spacing, there will be frequencies where you get singularities so I'd pick a 3-4 positions with different spacing and compute (combinations of) transfer functions for these.
Have fun
Claes
Sorry to bother you. I want to obtain the sound absorption coefficient of a material (MPP) from acoustic pressure in an impedance tube with ABAQUS instead of ANSYS. I applied a plane wave 1+0i, however, the imaginary part of the test pressure is consistently zero which is unreasonable. It will be appreciated if you could give me some advice.
Xueyu Bai and Muhd. Hafeez Zainulabidin
I am also solving a similar problem. Did you solve the problem? It would be great if you can share how you reached the solution.
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