# Natural Frequency Of Space Frame & Motorcycle Frame

1. Jul 2, 2009

### hotwheels123

Hi

How do you calculate the natural frequency and vibrational response of a space frame and what is its damping characteristic? What are all the aspects to take into considerations and how do you analyse failure due to vibration?

Thanx

2. Jul 22, 2009

### hotwheels123

Resonance and natural frequency

Does anybody know how to determine the frequency of a typical motorcycle engine. That frequency thats not supposed to coincide with the natural frequency of the motorcycle frame that will cause resonance.

How do you calculate and interpret these values? And how do you perform a model analysis on a space frame?

3. Jul 22, 2009

### Staff: Mentor

I would think you would need FEA or other simulation to try to predict such resonances. Either that or build them and measure them.

What is the context of your question? I'm not aware of resonance issues between motorcycle engines and frames (but they may exist).

4. Jul 22, 2009

### hotwheels123

Hi

Thanks.. I need to make sure the motorcycle frame im designing does not resonate due to the vibration of the engine. I'll be using ANSYS as an FEA tool and they do have a dynamic loading feature. Now what i need to know is how do you measure the engines load on the frame whch will clearly be a dynamic load. I assume it will be harmonic also. Am i making myself clear?

5. Jul 22, 2009

### Staff: Mentor

I would think you can get a good first approximation by measuring the frequencies of a working engine of the same configuration as your target engine (in-line 4, V-twin, V-4, etc.), and assuming some level of imbalance at those frequencies (to give you vibration of various force magnitudes. You can then use your ANSYS tool to see if the frame(s) have any natural resonances in those frequency ranges.

Do you have access to accelerometers? You could put them at the engine mounts on a similar bike's engine, and see what the spectra look like through the RPM range...

6. Jul 23, 2009

### FredGarvin

If you have ANSYS, then this is a no brainer to calcluate. Simply do a modal analysis. There are no BCs and no loading required for this kind of analysis.