GeoStar Post Dynamic Random Vibration

I'm currently 'trying', quite unsuccessfully, I will add, to use this feature. Has anyone any hints/tips to simplfy this process.
Basically I'm trying to caculate stress's on a cantilever beam(a simple model, fixed at one end, block mass on other)which will result from its own natural frequencies. There just seems so many variables!!!

 

[rob768]

Stop trying. In order to calculate stress you need a value of the exciting force causing the resonance, and the magnitude of damping. Calculating natural frequencies just gives you a mode shape, without any stress information at all. You can only use this model to extrapolate known or measured stress or displacements.

 

[JamboTron]

I possibly made my first post a bit simple.I am aware of what a basic frequency analysis does. This Geostar feature allows you to input an exciting force and damping qualities and uses the principle of mode superposition. There's just a whole load of other variable options which are making it complicated.

 

[rob768]

too true. Literature may help, and the best thing is to gain expereince and a feel for vaules such as damping. The magnitude of exciting forces may sometimes be estimated by analysis the most likely source. For instancel, if you estimate unbalance to be be a potential source, you can make an estimate on the actual unbalance by evaluting the unbalance class, and asume worst conditions within a certain class. For damping, anlyse the conditions. Is there no fluid damping and an all steel construction with no friction at bolt connections or other, then use low damping (for steel, average values are 0.5-2%). If there is damping, you'll have to make an estimate. And that is, indeed, the most difficult part of the analysis.

 

[JamboTron]

Thanks Rob768, trial and error, annoyingly, seems the way forward.