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Why am I getting a messy signal FFT instead of a smooth one?

Submitted by r_1159 on

Hi

I am doing wave simulation on plates with various damages. Guided sinusoidal waves are generated and scattered throughout the plate. To compare the results I am getting FFt of displacement (frequency domain). The one without damage gives me a very smooth FFT while the ones with damage give me a messy FFT ( Please see the attached photo). Is it something to do with filtering or is any thing wrong with my results ?

 

Damages model

http://oi42.tinypic.com/zo6ty9.jpg



Undamaged model

http://oi41.tinypic.com/25uid8m.jpg



analysis duration is 6e-4 second but I get better shape in damaged model when I limit the analysis time to 2e-4. could be reflections from boundary ?

Cheers