Acoustic analysis: configuration of absorber elements (CAABSF/PAABSF), excitation by a plane wave

Altair Forum User

Hi,

 

currently I am working on an acoustic analysis and I have some questions. I'd appreciate it if someone could answer them.

 

1) Absorber elements: I use CAABSF elements for absorption. How do I have to configurate the property PAABSF? The online help says the real part of the impedance should be equal to 'density multiplied with speed of sound' for each frequency. I set the imaginary part to zero. For the parameters S, A, B and K I didn't set any values. For 'RHOC' I entered the same value as for the real part of the impedance.

 

Is this correct? I don't want there to be any reflections, the elements should absorb everything. I didn't find any information for the imaginary part, S, A, B, K and RHOC.

 

2) For excitation I chose an acoustic source (ACSRCE). This is a sphere. Is there any possibility to define a plane wave (with an angle of choise) for excitation?

 

Pascal

Altair Forum User

Hi Pascal,

 

Imaginary part is acoustic reactance. So during impedence calculation imaginary module will be zero.

Altair Forum User said:

2) For excitation I chose an acoustic source (ACSRCE). This is a sphere. Is there any possibility to define a plane wave (with an angle of choise) for excitation?

I will check and update to you soon.

Altair Forum User

Hi Prakash,

 

thanks for the reply.

 

Altair Forum User said:

Imaginary part is acoustic reactance. So during impedence calculation imaginary module will be zero.

 

But is it correct to set reactance to zero if I want to create elements that absorb everything? My aim is to absorb everything from the acoustic source that crosses the absorber (no reflection, no transmission).

Altair Forum User

Hi @Kallli

Sorry for a late reply, After studying these are my comments/Understanding:

 

For setting non-reflecting boundary, on PAABSF card, you will have to define TZREID tabled1 in following way.

TZREID tabled1:

TABLED1, id, 0.0, (Rho(fluid)*C(fluid)), 3000.0, (Rho(fluid)*C(fluid)), ENDT

 

You need not set anything against RHOC field in PAABSF card…keep it default as 1.0.

 

Give the above a try and confirm the behavior from results.

 

So,yes, a value of zero in the reactance field in the TABLED1 card in the imaginary part of the impedance field in the PAABSF card will give full absorption.

ID no 10 in the PAABSF card refers to imaginary part which calls the TABLED1.

 

 

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Altair Forum User

Thanks, I'll try that.

 

I really appreciate you taking the time.

Samikhshak Gupta

Hi, I have a related doubt. How do we configure a sound reflecting boundary in hyperworks, I need to model a reflecting plane (floor) for my acoustic analysis as per the ISO-3745 standard.