Need an help in Modal Analysis

AI Thread Summary
The discussion centers on conducting a modal analysis of an audio system attached to a car's instrumental panel using ANSYS 13. The user reports extracting 12 modes, but the first six frequencies are zero, indicating a misunderstanding of the analysis setup. It is clarified that these zero frequencies correspond to the structure's rigid body motions, typical in free body scenarios. Suggestions are made to consider fixing the panel at connection points to obtain meaningful results. The importance of accounting for constraints in modal analysis is emphasized.
bhartish
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Need an urgent help in Modal Analysis

I am doing an modal analysis of audio system attached to an Instrumental panel in a car using ANSYS 13 version software. I have used SHELL281 element for meshing and Black Lanczos method to extract the modes. This shell element has six degrees of freedom. I Have extracted 12 modes but the first six frequencies I am getting zero value. I am not able to interpret the results. request anyone to guide .
 
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The first 6 frequencies will be zero if your structure is a free body. They conrrespond to the 6 rigid body motions of the structure (3 translations and 3 rotations).

It would probably be better to assume the panel is fixed rigidly at the points where it is connnected to the rest of the car.
 


Hi,
Why did you perform a free-free modal analysis? Why it is useful for? I mean, you should always have into account the constraints, shouldn't you?
 

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