Style and Detail in Design Calculations? 1

[Amphoteric]

At work I get passed around to different bosses and even departments, and one point of contention is the "calculation record" - also called a design brief or design calculation. Datasheets and technical drawings have a really defined structure, but calc. records do not. It seems that everyone has their own opinions on how to do it right! How much information and explanation put down, how much to reference, and so forth.

Put down too little, and you're confusing. Put down too much, and you're wasting everyone's time.

Please discuss: What is your personal "style" or "philosophy" when it comes to writing design briefs?

I wrote some questions for consideration (you don't have to answer them, they're just thought-stimulator's):

1) Who is the target audience? Do you write as if you'll be hit by a train tomorrow, and new-hire-Tim has to pick up your calculation? Or do you write the bare minimum to save time for you, and the person checking your work?

2) How do you show the development of your work? Do you write equations symbolically, define and reference the terms, and show all the gory detail? Or do you write a quick blurb on what you're doing and program the equations into Excel?

3) If someone tells you a number, do you reference the person by name? Some people say that's offensive: that you should "Company ABC said..." instead of "Joe said..."

4) If something is a "rule of thumb" or a number "based on my experience" do you reference it?

5) If you are using third-party software (e.g. simulators, CFD tools, etc.) how do you do the brief? How do you keep track of the what/why of your inputs? How do you make sure your results are valid?

6) How is checking done at your office, and to what level of detail? Is it done properly or does it fall by the wayside?

7) How do you like to check work, your own or someone else's? Do you go over everything with a fine toothed comb, or do you eyeball the numbers, or do the calc a second way and see if the results match?


I realize that the answers all depend on the complexity/novelity/stage of the design cycle you're in.

Thanks in advance.

 

[csd72]

Conventional project - no comments, just basic calcs. If they cant follow them then they should not be reading my calculations.

Something that is very unusual will justify a lot more explanatory comments.

But the projects that I work on usually dont involve more than one person doing the calcs.

 

[KENAT]

I put pretty much every line of my calculations, even just re-aranging formula etc. I also make any skethes/diagrams easy to understand.

Most of the time I'll even draw the triangle if I'm doing some trig etc.

However, at least part of this is due to a learning disability I have, I can't usually skip lines in a calculation without risking losing track. Worked well in exams where most of the marks were for method not end result though!

KENAT, probably the least qualified checker you'll ever meet...

 

[rtmote]

Twoballcane, you are absolutely correct. I work in Oil and Gas and we are required to produce formal, standalone calculations for almost all structural elements of design. Unfortunately, many engineers do a piperack design as though it is the first one ever to be done, in the history of mankind......zzzzzzzz. As Shakespeare once said; A piperack is a piperack is a piperack.....

csd72, the project I work on involve hundreds of engineers all on the same project in their individual little cubicles, separated from the designers. All doing their own twists and then checking each others work with either a vengeance, or boredom.

I subscribe to Kenat's philosophy, draw it out with sketches, diagrams; make it easy to understand and spell out the simple stuff of loads, line by line. Basically, showing all the inputs to problem.

That cannot take three months right? I think engineers don't want to do this stuff, just leap into the output without diagrams and expect you to read their minds and still the designers are tapping their fingers asking, what do you want?

I believe the calculations should be an active part of the engineers tasks, documenting and starting real work. Analysis is not always mandatory and should only seek to confirm what you already know, not hold up the job!

Back to Amphoteric's opening comments, the design brief/scope should be explained, the key decisions, the design assumptions. I particularly do not like references to people, he said she said....Ugh! The engineer has to assume all responsibility for the design. Whatever who said what, is an internal matter guiding the engineer's judgment call. I have seen amazing calculations where the engineer has managed to ascribe every decision, no matter how small, to somebody (who didn't know they were held to account!) so that it is not the engineer's fault. It is a priceless example.

Wasn't there a time, calculations style/formats was a corporate issue? I, for one, in my field feel we are diverging so far from the aims that questions should be raised.

Robert Mote

http://www.motagg.com

 

[plasgears]

Don't abandon ballpark analysis, which gives a feel for order of magnitude. This could either be hand calculations or basic computer driven analysis. Of course, not everything can be executed by hand, but the suggestion is to get into the ballpark. This helps avoid surprises and errors in elaborate computer routines.

I often used the basic Lewis equation for gears before embarking on a detailed computer analysis. The better routines give graphic visualization of meshing gears, like PowerGear.