Why ncode rms stress result different from Ansys Random rms result

[hayka]

Hi. I am using ansys ncode design life v 13 and doing vibration fatigue analysis. I modeled a simple beam with tip mass and firstly run a harmonic analysis with unit load that is 1 g. The material of the beam is Al 7075 T651 and I enter 1.6% damping ratio for the results between the 5-500 Hz. I also save the db file for post-processing the results. After harmonic analysis is finished I import the file.rst file directly into designlife and run a fatigue analysis for the 0.025 g^2/Hz 5-500 Hz white noise. I get the most critical node with 1 sigma rms value and stress psd. Then for the same mathematical model in ansys I run a random vibration analysis and get the 1 sigma rms value and stress psd for the same node. 1 sigma result are different from each other and when I compare the stress psd values at each frequency and especially peaks at the natural frequencies are very different from each other. The difference for peaks is not because of the damping ratio as I mentioned above I use the same mathematical model hence the same damping ratios.
Does anyone know why they are different?

 

[msquared48]

Wow! My first thought here is that is pretty mechanically specialized and technical. Are you sure you are in the correct forum here?

Have you tried this post in the Mechanical Engineering Other Topics forum yet? If not, you might get a better response there.

Just a thought...

Mike McCann
MMC Engineering

 

[hokie66]

Not speaking my language, either. Just a guess, but is this a university research project?