Re: Dyanamic analysis

From: <alwyn>
Date: Sat May 24 2003 - 14:17:00 EDT

I agree with Chris 1000%. I too have paid my dues and paid my time in learning. I get tired of people looking for cheap and free solutions instead of hiring competent engineers. We could do this, we have 25yrs experience in it and we're out of work.

I would say go ahead and mess it up, trouble is engineers get a bad rap and theres no money left to fix it, so everybody wants an easy quick fix then, after the mess is made.

EVERYBODY would do well to read your comments Chris.

Al

>I am looking to start the Dynamic analysis of piping system with
> centrifugal pump and another piping system with surge and wind loads. Can
> any one help me in giving the idea how to start off with initial
> assumptions and data.

   I don't know exactly what a surge load is, probably I know it by another    name. Wind loading is defined by the construction specification, which    you know by heart before you get started with any kind of analysis.

>To set the frequencies and which type of dynamic analysis
> suits whic applications etc.

   If you're talking about natural frequencies. ou don't 'set' them.    Frequencies are properties of the system and are calculated.

>group may find this question as very basic one, but expereinced ones
knowledge

> will help other one and that's how the groups objective is met.

   I'm going to risk sounding crabby, here, but I've been in the biz for    about 40 years and I figure I've paid my dues. Unless you've done some of    this or had some formal instruction in stress analysis, you probably    shouldn't be doing this kind of work, since it doesn't sound like you    know enough to begin, let alone determine if your analysis is correct.

   Dynamics is not kid stuff--it's non-intuitive and it's tricky and it's    difficult to validate. If you're depending on the software to do your    engineering for you and figure out if you have the right answer, you're    headed for big trouble. I've seen it a hundred times, not counting all    the times I've seen the symptoms on this list. Do some study, learn your    basic mechanics, and find someone who knows dynamics to provide you some    leadership. Read the stress analysis portion of the engineering    specification. Find several systems that have been subject to dynamics    analysis, and practice coding up the system on those, so you'll know what    answers to look for and what mistakes to avoid. aReadn the engineering    specification to learn what answers you need to provide. If you don't    understand the specification, you may be in over your head and the    answers you provide may not address the issues that need to be addressed.    That could cost your employer money or even lives.

   Let me quibble about one other thing. The 'group's objective' is    exchanging information between peers (Right, Paul?), not to provide free    basic education or engineering support. The analysis is your    responsibility. There's a lot of advice available here, but like all free    advice, it isn't going to subsitute for an understanding of engineering    first principles. Most of all it isn't going to help you keep your job or    your reputation if you screw up. Do your homework--if you have specific    questions, by all means put them to the list, but realize you need to    know a lot of things to eveluate the applicability of anything you read    here. And never forget that you're the guy in the barrel when something    doesn't work.

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

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[Non-text portions of this message have been removed] Received on Sat May 24 14:17:00 2003

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