Dynamic Analysis of a Laser assembly

[ollib]

We have to investigate several different designs of a laser assembly. In the system there is a laser mounted on a rig and pointing towards a target. Under field conditions the system is subjected to external "impact" loads. I'm writing this in "" because the project is in a very early stage and testing cannot supply any quantitative information about the impact loads. So location of the impact, and spectrum must be considered unknown for now. The direction of impacts can be considered normal to the structures external surfaces.
The design goal is to minimize the deviation of the laser beam from the target under external impact loads on the system. For now we have to compare one baseline to several new proposed structural concepts.
What we're planning to do is: Perform a dynamic response analysis on the structure.

1. We apply a broad spectrum load at several points on the external hull and calculate FRFs to the laser mount point and the target.

2. Look at the FRFs and identify resonances

3. Calculate maximum deviation of the laser beam in the target at resonace frequencies.

4. Examine mode shapes at resonance frequencies and apply structural modifications in order to alter shapes and reduce laser point deviation.

5. Check modificated structures

Now my question: Has anybody experience with problems like this which could be shared? Does the approach make sense? Any comments are welcome!

best regards! Oliver

 

[GBor]

Well, since you haven't received any response in a few days, here's my shot.

I'm not sure why you are examing response to a load that is unknown instead of performing a natural frequency analysis (modal) to determine what the natural frequencies might be. You could then perform a frequency response analysis making certain that you include the natural frequencies to see what the deviation of the beam would be with those forcing functions based on your natural frequencies.

This would provide you with information regarding whether or not you have any potential force operating at or around the natural frequency and, if you do, what the impact on the beam direction might be. You could still examine the mode shapes, but you wouldn't have to guess at the load spectrum.

I would think the loading from the natural frequency response analysis would have some analytical basis. If it turns out that all of your natural frequencies are well outside of any potential operating parameters, then you could go with some other forcing function as you suggest.

My 2 cents

Garland E. Borowski, PE
Borowski Engineering & Analytical Services, Inc.

http://www.borowskiengineering.com