Question on acoustic / infinit element on abaqus

[rdpdo]

Hi,

I have some questions about simulating a Box of wood in air with abaqus. Reading the documentation I saw that this can be done using several techniques.


I must take care about the size of the elements. The 3D elements minimum size can be calculate using the formula

and using at least 6 node per wavelenght.

For the size of the accoustic elecments I use the formula

and I use element size of minimum 1/8 of the wavelenght.


1/. Enclose the box in a sphere of air. Box use 3D solid elements, air use Accoustic elements. For creating the coupling between thebox and the air sphere, I can use a TIE constraint. I must take care about the distance of the radius of the air sphere, wich is minimum 1/3 of the wavelenght.

I must also use aboundary contition SIMPEDANCE=NOREFLECTING at the surface of the air-sphere.


2./ I can use infinite elements by creating a air sphere with a little radius and and inifites elements on the surface of the air sphere. My questions are :
- Is the TIE constaint between my solid box and the air sphere with acoustic element is requier also in this case ?
- How can I calculate the minimum radius of the air spehere wich contain acoustic element in this case ?
- For using infinit elements, canyou explain me how to do this under CAE ? Do i must create a new part sphere just behind the air sphere (with a translation of fo example 0.000001) and apply the inifit element on this new part ? Or can I shell the surface of my air sphere wich contain already acoustic elements ? If yes, how ? (I'e tried to mesh a surface by declarating a surface but it seems impossible...)

3./ It seems that the infinites elements can be use directly on the surface of the box, with no air sphere at all. Is it true ?

Thanks you very much for your help. Regards.