Why Does My Axial Fan Wobble at Certain Frequencies?

[dabest1]

Hi,

We have an axial fan in the lab that apparently vibrates badly ("wobbles") at certain frequencies.

To find the resonance and the bad frequencies, I decided to do an ANSYS modal analysis.

I am still pretty new to it, and have a few questions.

1) Regardless of how many modes I pick, ANSYS picks certain frequencies. What is the significance of these frequencies?

2) I can't seem to input a rotational velocity into ANSYS. When I add a "Rotational Velocity" Modal, I try to input a 25 rad/s rotation but it does not go through...(I don't get the check mark to its left). So my question is, what is the frequency? Is that equivalent to rotation?

3) So I have just put a fixed point in the center of the fan, and run the analysis. I am getting different colors for the first 3 modes, but the shape seems intact. After mode 4, the entire shape gets ruptured...what does that mean? Let's say all the modes until 150hz had a smooth shape, and the next mode at 300hz is a ruptured shape. Does that mean that the "bad wobbly vibration" happens between 150hz and 300hz?

4) How do i find resonance frequency from these results?

Thanks!

 

[dabest1]

So I just connected a Static Structural module and was able to add a rotational velocity using that...why couldn't I do it within modal?