Re: New at Piping Design Central: Design Theory

>Dynamic Susceptibility Method for Piping Vibration, by SST Systems, Inc.
This is an interesting article. There seems to be a lot of confusion about what you get out of a modal analysis and how to use the results. Natural frequencies are easy to find but what's not so easy is using the results to figure stress. The short answer is that you can't figure stress without knowing what the loading is. The 'relative stress' you get with natural frequency extraction is meaningless unless you know the excitation. The SST article gives you a way to figure out what frequencies to watch out for which is sometimes all you might need. As the article says, it's not a way of determining Code compliance, but it can help you understand what you might be dealing with.

I'd like to follow up the methodology with COSMOS/M and I wonder if anyone knows the details (layout dimensions and pipe sizes) for that CAEPIPE exam. I'd like to do some dynamic FEA on the example to see how the susceptibilities track with calculated seismic stresses. If anyone knows thise details, I'd be grateful id you'd get in touch. I don't think there's any copyright issues, since I don't want anyone else's results or program documentation--just the example problem layout details.

Christopher Wright P.E.    |"They couldn't hit an elephant at
chrisw@skypoint.com        | this distance"   (last words of Gen.
___________________________| John Sedgwick, Spotsylvania 1864)