sahu
2010-02-27, 10:34
Hey,
I am currently working with a honeycomb structure produced by rapid prototyping and made of ABSplus. (armorphous thermoplastic: Acrylnitril-Butadien-Styrol)
I have done testing to determine the frequency response function and I have done a harmonic analysis in ANSYS using the mode superposition method.
The comparison of both results shows that the general shape of the magnitude is the same. However, the values for the resonant frequencies of the experiment are lower. For the first couple of resonances for example the experimental results are about 40 Hz lower than the ones from the Ansys analysis (126 Hz).
My question is whether the assumption of a linear system and modal damping (proportional damping) in the Ansys analysis could be the cause for the difference in the values of the resonances. I understand that a non-linear approach would be needed. Could the linear assumption make such a big difference? And would the resonances for the non-linear model be lower?
I have clamped my model to the shaker. I couldn’t fasten the nut very tightly because of the material, which I could have damaged if I did. Could it be possible that I added damping through that clamp? And could that also be a cause for the difference in the values for the resonant frequencies?
Thanks for your help,
Sandra
I am currently working with a honeycomb structure produced by rapid prototyping and made of ABSplus. (armorphous thermoplastic: Acrylnitril-Butadien-Styrol)
I have done testing to determine the frequency response function and I have done a harmonic analysis in ANSYS using the mode superposition method.
The comparison of both results shows that the general shape of the magnitude is the same. However, the values for the resonant frequencies of the experiment are lower. For the first couple of resonances for example the experimental results are about 40 Hz lower than the ones from the Ansys analysis (126 Hz).
My question is whether the assumption of a linear system and modal damping (proportional damping) in the Ansys analysis could be the cause for the difference in the values of the resonances. I understand that a non-linear approach would be needed. Could the linear assumption make such a big difference? And would the resonances for the non-linear model be lower?
I have clamped my model to the shaker. I couldn’t fasten the nut very tightly because of the material, which I could have damaged if I did. Could it be possible that I added damping through that clamp? And could that also be a cause for the difference in the values for the resonant frequencies?
Thanks for your help,
Sandra