On Sat, 08 Dec 2001 23:53:11 Stephen Birkett wrote: >As Del says, you can do it experimentally, and this is the modal analysis >method (or equivalent). You basically drive a board (modulo all the >various limitations discussed here about loading vs not etc) and observe >the mode frequencies. The other way is to model the system itself >mathematically (e.g. FEM analysis, or more sophisticated techniques), To what sophisticated techniques are you referring? >obtain real parameters from experimental observation, and calculate the >predicted response of the board (requires sophisticated computer program, >not beer mats). This technique, apart from being more elegant than modal >analysis, allows the critical design-related factors, viz. a casual >relationship between board (and other) parameters and the response. I hate casual relationships between parameters and responses. I prefer them to be serious. >So you >can adjust parameters and see what the effect is on the response, without >having to make an experimental board etc. This you cannot do with modal >analysis. The modelling approach iss the sophisticated approach. [To some >extent modal analysis can be useful too, to calibrate your modelby >providing experimental data.] > >Stephen > The modeling approach is perhaps the sophisticated approach and certainly the cheap approach. In my experience, with a complicated structure, it's also not the highly accurate approach. It does work very well for studying design parameters, as you say. But in the end, if I needed a specific response I would still want to build a physical representation and do the modal analysis. I would then probably find it doesn't exactly match my model and would then tweak it (using the causal relationships from the model mentioned above). So a combination of the two would probably get you where you want to go, with most of the work being done with FEM. Phil F --- Phillip Ford Piano Service & Restoration 1777 Yosemite Ave - 215 San Francisco, CA 94124
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