Re: [PipingDesign] Fwd: Steam Stress Analysis

From: <Kevin>
Date: Mon Mar 24 2008 - 09:31:00 EDT

Nice way to correct me!

This seems to be a mistake on both company and the engineers part.

Companies need output quick, Engineers hardpressed for schedules, dont seem to get involved in depth to the problems. When I said I have not done a single stress model manually, I meant for the company. The terms of reference for all the projects that I have seen, ask for Caesar II or equivalent software for analysis. Why should I do manual calculations when my project engineer is shouting at my head for progress, structural engineer is yelling for support loads and layout group is asking if there is any change in the line routing.

Yes, if you model the system incorrectly, you will (THINK) that you have got the right solution and hence their is a need for training to understand the core of the analysis. But try not to reinvent the wheel each time.

>Engineers have been accomplishing great
>things without FEA for centuries.

Yes and many a times these great things have been overdesigned and were designed and constructed in those times when nobody gave a damn to schedule and project cost.

>Meaning that more mistakes can be be made and more broadly
>communicated than ever before possible.
Yes but when engineers did it by hand, you think they did not make ANY mistake?

Computers hardware and software are tools only. The main force and soul behind it is a good engineer. There is no denying to it.

But now let us come to the original problem, all I got from you is that there is nothing to help the post originator, he will have to start from freebody diagrams.

KG.

On Mar 23, 2008, at 9:38 AM, Kevin Green wrote:

> Although good at maths, strength of materials in university, I have
> not done a single stress model manually. Now a days it is not the
> practice. I only use Caesar II.

I've said this a hundred times and I'll be repeating as many more times as necessary to get people to understand. If you don't know how to do the work by hand, that is set up a free-body diagram for the problem, apply loads, calculate internal resisting loads and figure stresses, you should not be doing stress problems with Caesar or any other software. The thought processes required for a manual solution are exactly those required to use any analysis tool--the tool won't do your thinking for you. It won't tell you if the loads and boundary conditions are correct; that your material properties are applicable; that you've interpreted the results conservatively but not too conservatively or even that your solution is the only solution, let alone a solution that applies to the actual service. Without the ability to organize the problem, to think through what you intend to accomplish and to prove that results are valid and uniquely applicable to your problem, you're just one more loose cannon taking a WAG.

> And as Christopher wrote in his email, if you mess up with
> calculations, you will get somebody killed. So your company should
> invest in good software(Particularly Caesar II).
Your company should invest in trained people who understand the role of good software and who understand how to apply first principles of engineering to the application of such software.

> The benefit would be, if you model correctly, you will get correct
> solutions.

And if you model incorrectly, you will probably think you have a correct solution, even if you don't unless you can think critically in engineering terms about the problem you've solved..

> It is (of course every child knows) a fast method.
Meaning that more mistakes can be be made and more broadly communicated than ever before possible.

> You will not burn mid night oil for doing even small system and at
> the end of it all, you will not be sure if you did correctly or not.
And you can achieve precisely the same results with or without a computer

> I would like to know how my senior colleagues did the complex
> stress systems when computers were not around to help them.
Give some thought to this, since the results speak for themselves. The DC-3 Dakota, the Spitfire, the P-51 Mustang aircraft, the Golden Gate Bridge, the Taj Mahal, the Clipper ships, the Hagia Sophia… I could go on for a long time. Engineers have been accomplishing great things without FEA for centuries.

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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