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On 12/30/2016 at 11:57 AM, Sourabh said:

Hi,

 

I have a query regarding an acoustic analysis using Optistruct.

 

I am doing 'Transmission loss' analysis of a duct system. For a start- i am trying with simple expansion chamber problem. I have defined acoustic source (ACSRCE) at inlet and non-reflecting boundary condition at inlet and outlet end of pipe (Using CAABSF element with PAABSF property entry of impedance equal to = “Rho*C”). In frequency response analysis, i have extracted input point (9001) and output point (9002) pressure values.

image6.jpg  image7.jpg

 

I am using Optistruct_14.0.220_windows solver. Following are the results for Transmission Loss (TL) – { TL = 20 * log10(Pin / Pout) }  -

image1.JPG

 

 I have also calculated transmission loss using analytical approach. Transmission loss in a simple expansion chamber is analytically calculated (worldly proven formula/graph) as shown – image2.jpg   image3.JPG

 

 

 

The transmission loss Vs Frequency graph from analytical approach is not matching with FEM solution. FEM solution is showing increasing values with extra trough at 144.0 Hz.

 

 

 

Does anybody have come across similar problem? Is anything wrong in model definition?

I heard of “Annular duct modes boundary condition” (used by software’s like LMS Virtual lab, etc). Are such boundary conditions are also available in Optistruct?

 

 

 

 

 

 

 

@Prakash Pagadala,

I tries converting the impact of ball into numerical values and assigned equivalent force on the plate, it generates some favorable results, which I shall confirm more.

If you can help me understand solution for the above quoted query, then maybe I can figure out a solution to my problem.
I need to understand assigning, ACSRCE, CAABSF and PAABSF

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Hi @Abhi05

There are few issues with the model. 

 

Please take the reference of the model I shared (use RANDSD, etc...) and try again, 

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@Prakash Pagadala,

 

The ball remaining stationery in your model has not changed but in my new model, I have changed a few things, however, there is one slight error that still exists.

I have shared it via FTP, could you please check?

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