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All, Thanks for the help. I should have given out more information on the original post. I would never thought it would cause a war of words between people on a forum. Last post again thanks all

Hi desertfox, The first link yes I have seen that link before as it appears to describe the surge frequency of the spring. The calculated surge frequency is 20 times higher than the natural frequency of the spring mass if they behave linearly SQRT(k/m). We are trying to keep this device away...

All, Thanks for the help. How can this be solved numerically? I guess my model is useless back to the drawing board

Tmoose, First mode is not a buckling or lateral frequency. It acts in the same direction as with no preload

Desertfox, I have looked at the surge frequency but that is not the first mode. The first mode is much lower than the surge frequency.

Drawoh, Yes that is it. The spring is always under precompression and is never at a free length. The spring load is suppose to keep the mass to the right just as your picture.

Electricpete, The spring has displacement as I said but I am interested in knowing the correlation between preload and natural frequency. This is why I left out some of the details because I was trying to see what is the correlation between the preload and the natural frequency before I...

All, 1. The spring is preloaded and has a mass attached 2. The spring is preloaded by about 25% and is always under preload. 3. The mass has more freedom to move in the positive direction but and a shorter stroke limit in the negative direction. Hopefully the attachment helps but I tried to...

Electricpete, I tried to make the problem simple to see if anyone would respond with a hand calculation relating preload with natural frequency. The design is a mass connected to a spring. The spring is compressed to an amount. All I am trying to figure is what is the natural frequency in...

Electricpete, A mass is connected and the spring is compressed at the amount you said fixed at both ends. If you know of a way to calculate the natural frequency I am interested.

All, I was looking for a hand calculation but is not simple to find. In my head I thought maybe someone here may have done a calculation on a spring to calculate a natural frequency if the spring had been compressed. I was just trying to figure out the relationship between preload amount and...

Tmoose, The mode is the preloaded end bouncing like that. I will have to take a look tomorrow.

FeX32, The difference between unloaded and loaded results in a factor close to 4. Loaded giving me a natural frequency ~4 times higher. Elements are linear. ivymike, I actually thought it would be close to the surge frequency but they were far apart. I have looked into that equation...

FeX32, The displacement is about 25% of the free length.

All, The easiest way to explain it would be a spring that is precompressed to fit within a cavity. I fix the spring by the the amount it is displaced and then I am trying to get the natural frequency of this system. I was looking for a hand calculation that gives me the natural frequency...

Hello, All thanks for the feedback what I am doing is forcing the compression by deflection in one direction. So I displace the spring and the displacement is fixed, then calculate the natural frequency. The only thing I can think of is maybe the deflection is causing it to behave non linear

Desertfox, I am aware of that equation you listed as I have been using it under non preloaded conditions to match pretty close to what the FEA model says. What I experience is when I add the preload the natural frequency goes up even though I didn't necessarily change the stiffness of the...

desertfox, Thanks I searched that link and I couldn't find anything with a constant preload. It does have all the scenarios for single degree of freedom with damping etc.

Hello, I hope I am asking this in the right location. I have a fairly simple question that I have not been able to determine. I want to know how to calculate the natural frequency of a spring mass system that undergoes a constant preload in the spring. This would be for a simple compression...